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Wobblycogs
04-11-2012, 01:25 AM
As per the good advice from a thread I posted a few days ago I've been digging around in the build logs for good ideas for my CNC build. I've set myself a pretty tight schedule for a first build I think as I would like to have the mechanical parts of the build done by the end of the year. I reckon with some late nights and early starts I stand a reasonable chance though.

I initially considered going for an MDF CNC machine (because it was cheap) but some excellent advice saw that idea consigned to the bin in no time flat. If I'm going to spend an age building a machine I might as well build it properly! I then considered a wooden sub-frame with the CNC being aluminium extrusion but that just seemed like a poor compromise so here we are with a frame designed in steel box section.

The X-axis rails and the bed are 80x40x4mm the legs are 50x50x4mm. The bracing around the bottom is 20x20x2mm. Overall, the X dimension is 1500mm the Y is 980mm (900mm leg to leg) and it stand 800mm tall. I believe this should give me a maximum possible cutting area of about 1400x800x200 which is a little more than I was initially aiming for.

7297
The frame will, initially at least, be bolted together possibly with epoxy on the X-axis rails (inspiration from here: My First Router, Built in Steel - CNCzone.com-The Largest Machinist Community on the net! (http://www.cnczone.com/forums/cnc_wood_router_project_log/30751-my_first_router_built_steel.html)). I would rather it was welded but I need to be able to dismantle the machine for moving in the future and I'm pretty sure I couldn't get it down the stairs in one piece :joyous:.

The current plan is to put the rails on the top of the X-Axis rail with the screw on the outside (there will be a screw on each side). To keep the length down I'm considering mounting the steppers on the bottom rail and using timings belts but I can't help feeling that's just complicating matters.

Looking at the design again I think I'll stick at least one vertical support from the bottom to top X-axis rail. Do you think this design needs any other bracing? My gut is telling me it could do with some diagonal bracing but I want to keep the weight down if I can so where would be best to put it? The big question I have though is regarding the straightness of steel box section. I've read quite a few posts that say it comes with a bit of a wobble on it, presumably I need to mount the rails onto something that is fairly straight and flat? How do I go about flattening out at least one side of the top X-axis rail?

Any comments about the frame or any of my other rambling ideas gratefully received :joyous:, cheers.

wilfy
04-11-2012, 01:36 AM
i can't wait to see what you come up with to get 800mm cutting area from a 980mm Y axis... i may just be copying your design if all works out well..

i have 654mm Y rails providing a cutting area of 381mm, so if you get your design up here and everyone says it's good i'll be doing whatever i can to reduce the size of my Y :D

good luck with the build i look forward to see the outcome

jonbabbz
04-11-2012, 10:34 AM
Looks familiar.....

Wobblycogs
04-11-2012, 11:30 AM
Now you mention it I remember seeing your build over the summer when I started seriously considering building a CNC. I liked the design so it probably stuck in my mind. Hope you don't mind a little creative borrowing :-).

Out of interest what size box section are you using under your X-axis rails? I'm guessing it must be 50x50 as I've just noticed that the rails over hang on the design I posted above. Did you find that the box section was straight enough for the rails without any flattening?

Wobblycogs
04-11-2012, 01:18 PM
Having realized that SBR20 rails are 45mm wide I scrapped the 80x40x4 box section in favour of 50x50x4. I've plugged the figures into the gantry stiffness calculator and if I understand it correctly I should be getting a maximum deflection of about 50um with a 30kg gantry (I assumed the maximum span was 750mm, it's actually more like 665mm) - I've not studied engineering though so I might be reading the spreadsheet completely incorrectly :-). Should I add another support to reduce the span further?

After seeing jon's (http://www.mycncuk.com/forums/router-build-logs/4764-jons-homemade-cnc.html) design I've reduced the number of bed supports and thinned them down a bit, they are now 50x25x3mm. I needed to reduce the weight a little as this is going to be installed on an upstairs floor which already has a fair bit of weight on it. My calculations indicate the frame weighs about 85kg so far but that doesn't include the multitude of fixings and brackets I'm going to need.

To keep down the mess I've added 2mm aluminium sheet on the sides and ends. I plan on making the ends hinged so that I can work on longer pieces if needed. The bed is sacrificial a sheet of ply or mdf.

The length of the X-axis has been reduced slightly to 1480mm with the rails being 1450mm. This is so that I can hopefully get all for long rails out of a single 6000mm piece of box section and save a little money. The reduced cutting length on X doesn't worry me as I was only aiming for 1220mm.

I'm pretty happy with this design as I think it's something I can achieve. Any comments are, as always, very welcome.


72987299

P.S. Thanks to jcb121 for the sketchup models.

jonbabbz
04-11-2012, 02:28 PM
Now you mention it I remember seeing your build over the summer when I started seriously considering building a CNC. I liked the design so it probably stuck in my mind. Hope you don't mind a little creative borrowing :-).Of course not, its in the public domain now. Just thought id seen it before when I saw it. lol.



Out of interest what size box section are you using under your X-axis rails? I'm guessing it must be 50x50 as I've just noticed that the rails over hang on the design I posted above. Did you find that the box section was straight enough for the rails without any flattening?60mm x 60mm x 4mm some welded some bolted as I have the same getting it upstairs issues as yourself. I didn't really have any issues at all regarding straightness. I just made a load of jigs for welding.

martin54
04-11-2012, 02:36 PM
Don't know where you will be buying your steel from but the standard length is 7.5 metres so might be best to work your figures on that rather than 6 mtrs. Think Jonathan will tell you that some diagonal bracing is needed but I don't have the experience to tell you what & where would be best.

Wobblycogs
04-11-2012, 02:51 PM
That's good to know. I've been working from the sizes I found at metals4u which seem to do 6m lengths max. I'd like to try and source the metal locally so hopefully I'll find a friendly place that will cut it down for me too. My comment about trying to get all four out of a single length is a bit moot now anyway as I realized that I wouldn't be able to hit my 1220mm cutting target on X, I've just finished stretching the frame up to 1800mm and adding an extra support column. It really brings home how important it is to design before building.

martin54
04-11-2012, 03:12 PM
Have a read of this from someone else's build, gives a bit of info about buying steel & should give you a better idea what you should be paying. Company you mentioned are probably ok if you want just a small length but are expensive if your buying full lengths, the 6 mtr limit will probably have something to do with maximum length they can get shipped. Most steel stockholders will only sell in full lengths but should be able to cut for you.

http://www.mycncuk.com/forums/router-build-logs/5090-my-baby-15-x-15-machine-4.html

njhussey
04-11-2012, 05:59 PM
That's good to know. I've been working from the sizes I found at metals4u which seem to do 6m lengths max. I'd like to try and source the metal locally so hopefully I'll find a friendly place that will cut it down for me too. My comment about trying to get all four out of a single length is a bit moot now anyway as I realized that I wouldn't be able to hit my 1220mm cutting target on X, I've just finished stretching the frame up to 1800mm and adding an extra support column. It really brings home how important it is to design before building.

If you struggle let me know. I'm only up the road from you in Hereford, the company that I work for builds grease, oil and water lubrication and cooling systems so we have a workshop that has a nice bandsaw for example! Let me know the lengths you need (and size) and I'll get a cost and will happily cut it up into the lengths you want?

My baseframe was cut (and welded) at work.

http://img.tapatalk.com/d/12/11/05/8eqy3yvu.jpg

Wobblycogs
04-11-2012, 06:11 PM
Wow, thanks for the really generous offer, I think I'll probably be taking you up on it one I figure out all the parts I need.

I had noticed that metals4u were expensive but I hadn't started comparing prices yet. I checked out metal superstores as someone recommended them, the total order cost was less than a third. The downside is that metal superstore essentially don't deliver, it is technically possible to get stuff delivered but their maximum weight is so low I'd need to place about a dozen orders!

Thanks again :joyous:

njhussey
04-11-2012, 06:19 PM
No problems mate...once you've set on a design PM me with the lengths etc and I'll go to our suppliers and get a price for the length(s) you need. I'll cut them up in my lunch hour(s) and let you know when I've cut them and you can pop over and pick them up.

Wobblycogs
04-11-2012, 09:44 PM
Ok, last update to the frame unless anyone can spot something really wrong.

I've extended the X-axis rails to 1800mm which will mean a serious re-arrangement in the workshop, an extra support has also been included to up the stiffness. Bracing, in the form of 50x5mm plate, has been added to help prevent the frame from distorting. I think the bracing could be better but it should help once it's bolted down tight. The only other change is to move the long stretcher (at least that's what it would be called in woodwork) to the inside of the leg as I think it looks better that way. The weight comes in a at around 100kg which I can live with - I just won't invite anyone into the workshop :-)

73057304

Jonathan
05-11-2012, 12:33 AM
That looks much better than the initial design. Your steel sheets will help a lot to do the job of the diagonal bracing pieces, but they could cause problems with resonance since it's a large unsupported thin area, but that should be easy to solve by adding some thin strips to them should it be needed.

Are you not having the height of the bed adjustable? It's a pretty big advantage in terms of rigidity, although I doubt it will be moved much...

1800mm for the X-axis is a tricky size for the ballscrews. The cheapest option is just to use RM1610, but due to the critical speed you'll be limited to about 6m/min using the standard bearing blocks and assuming the screw arrives without any bend. To go any faster, without rotating the nut, is going to require a larger diameter screw (e.g RM2510) or larger pitch (e.g RM2020), which gets expensive as you would most likely need Nema 34 motors.

Wobblycogs
05-11-2012, 11:11 AM
Before I rush off and redesign the frame again I'd best ask a few questions :-).

What is the maximum length length I could reasonably use RM1610 up to and still get a good feed rate? I see people talking about 7 and 8m/min as the top speed they run their machine at so 6m/min doesn't seem so bad. I suspect though that 6m/min on this length is like getting 100mph out of a Nissan Micra - possible, but not advisable.

Lets say for a moment that I find a few more pennies down the back of the sofa and I can afford RM2510 screws and Nema 34 steppers. Would I then have to beef up all the electronics as well? The 34's seem to be about four times the price of 23's (on Zapp) if that's also the case with the electronics I think it puts it out of reach. Could I use 23's on Y and Z or would they have to be 34's as well?

Am I right in thinking that the problem with the screw having a bend is a reduction in the critical speed? If I understand correctly the critical speed is the point at which the screw starts whipping around, yes?

Yes, the bed will be fixed for rigidity. On another thread someone suggested that for machining aluminium I'd be best off raising the piece up on a stand to reduce the Z-axis extension which seems like a simpler solution than trying to make the bed move up. I want to work aluminium but I don't see myself machining large pieces so a stand is a pragmatic solution.

The side sheets were there mainly to prevent chips flying everywhere but I'll add some additional brackets to the design so they act as bracing.

Cheers.

WandrinAndy
05-11-2012, 12:00 PM
What is the maximum length length I could reasonably use RM1610 up to and still get a good feed rate? I see people talking about 7 and 8m/min as the top speed they run their machine at so 6m/min doesn't seem so bad. I suspect though that 6m/min on this length is like getting 100mph out of a Nissan Micra - possible, but not advisable.

In response to a query of mine Jonathan suggested that 6m/min is quite a reasonable speed and that the calculation of the critical speeds was quite conservative. Also seen JazzCNC often recommend that a machine is operated well within it's theoretical technical limits.


Am I right in thinking that the problem with the screw having a bend is a reduction in the critical speed?

I would guess that a bent screw would be unhealthy... It might also cause resonance, premature wear of the ballscrew assembly, and possibly binding?


If I understand correctly the critical speed is the point at which the screw starts whipping around, yes?

Yep, I think that's correct.

Just a quick Q Wobbly.... Am I right in thinking that you've extended your overall length 1500 -> 1800 in order to get a working length of 1220... It is possible to get working 1220 within an overall length of 1500?

Wobblycogs
05-11-2012, 12:34 PM
I think it's possible to get a 1220 working length out of 1500, I'm not sure my design will be good enough to do it though. My reasoning went something like this: 1500 - 1220 = 280. That means that I can have a maximum of 280mm from the back of the Y-axis bearing to the centre of the spindle assuming there is nothing else blocking the movement and the front Y bearing is not ahead of the spindle centre line. That's certainly achievable but... with this frame design the legs will, I think, limit my maximum X travel to 100mm less than the rail length which would mean the gantry would have to be no more 180mm and that feels too narrow to me. To be fair I could probably manage it with 1600mm on X but I figured if I'm going to make it larger I might as well make it comfortably large :-)

WandrinAndy
05-11-2012, 12:44 PM
Ah, the legs.... I missed those... And with the extra length you could space the bearings further apart for improved rigidity... So size does matter! ;-)

Wobblycogs
05-11-2012, 01:08 PM
So size does matter! ;-)

Yep, and as with everything bigger is better :-)

I'm having a love hate relationship with the legs where they are.

The two upsides that I can see are that I can have a more rigid gantry without losing X travel that wouldn't have been lost anyway and it gives me a 50mm recess each side that I can move the Z-axis into. I'm hoping that will allow me to achieve 800mm of workable length on the Y axis but I'll be happy with 700. The downside of course is that the machine has to be that bit longer in X. The longer X is though the small the loss is as a percentage of the total length - yet another reason bigger is better :-)

Jonathan
05-11-2012, 01:35 PM
You should be able to fit the gantry into 280mm, maybe 300mm, quite easily, especially if you let the Z-axis stick out at the front. On my machine the X-axis bearings are 300mm from end to end, which is adequate. It's certainly good to increase that if you can, but not absolutely necessary. The same is true for getting the centre of mass to lie precisely between the bearings on X.
7310
You can make a sufficiently strong Z-axis 160mm, maybe 150mm, wide so the frame doesn't need to be wider than the Y-travel plus 160mm. Again, if you want to make the Z-axis wider and space the bearings out more that's a good idea to get better rigidity.

Nema 23(/24) motors will be fine for the Y and Z axes. For X, try using irving's spreadsheet:
http://www.mycncuk.com/forums/faqs-problems-solutions/1524-what-size-stepper-motor-do-i-need.html

njhussey
05-11-2012, 02:34 PM
Wobbly.....steel prices for you

50 x 50 x 4mm box - 23.77 Each (7.6mtrs)

50 x 25 x 3 box - 13.25 Each (7.6mtrs)

50 x 5 flat - 6.99 Each (6.4mtrs)

VAT will (unfortunately) be on top of these prices. Anyway, once you've finished tweaking your design let me know and I'll firm up the prices :D

Wobblycogs
05-11-2012, 03:00 PM
Thanks Neil, I never thought I'd say it but compared to what I thought I was going to have to pay at Metals4U VAT doesn't seem like such a hardship!

As an aside, I was talking to the wife about the build over the weekend and it occurred to me that box section steel is actually about the same price as wood. 7.6m of PAR pine would set you back about 19 if bought in 2.1m lengths and considerably more if you could source it as a single length.

njhussey
05-11-2012, 03:21 PM
Thanks Neil, I never thought I'd say it but compared to what I thought I was going to have to pay at Metals4U VAT doesn't seem like such a hardship!

Damn...should have put a markup on it lol ;)

Wobblycogs
06-11-2012, 11:40 AM
Ok, so I stayed up to the wee small hours trying to figure out what size ballscrew and stepper I should be using on the X-axis but there's some things I don't think I'm understanding. I'd like this machine to be able to cut aluminium so my calculations are based around this. My thinking is that if it can cut aluminium then wood shouldn't be a problem (hope that's right).

In the post describing the motor calculation it says that for cutting aluminium a speed of 1800mm/min or better is desirable but the best I can achieve, even with the largest Nema 34 motor, seems to be about 1600mm/min. In this post (http://www.mycncuk.com/forums/material-finishing-tips-techniques/4610-routing-aluminium-help.html#post31244) though Jazz talks about cutting at around 700mm/min which is well within the realms of possibility. What speed should I enter for Max linear speed (B22) when cutting?

From trial and error I've found two setups that appear to work
7313Nema 24 (Zapp, SY57STH76) + RM1610

7314Nema 34 (Zapp, SY85STH80) + RM2510

I wasn't sure exactly what Screw Fixing (B19) meant so I left it as supported-supported. Would bearing blocks be considered fixed though?

What I don't understand though is why changing from a 1610 ballscrew to a 2510 nearly triples the total torque but doubling the mass of the gantry to 70kg makes only a small difference (in fact in the scenario with 24's is still ok with a super heavy gantry but the 34's are out of the safe range).

Am I doing something wrong here? The smaller motors and ballscrew seems to be a much better choice which feels totally counter intuitive to me.

Cheers

Jonathan
06-11-2012, 12:12 PM
The common bearing blocks are somewhere between supported-supported and fixed-supported since the bearings are not sufficiently spaced to truly count as supported:
Fixed-end, supported-end, free-end are ball-screw support conditions you need to understand in order to design the best actuator system for your equipment (http://motionsystemdesign.com/linear-motion/importance-ballscrew-end-fixity-0894/)

You need to increase the motor voltage - 70-75V is common for Nema 23/24 motors and Nema 34 motors will work on the same, but can be operated from mains voltage with expensive drivers, which shouldn't be necessary here.

The reason the increasing the ballscrew diameter from 16mm to 25mm makes such a large difference is because the moment of inertia of the ballscrew is proportional to the radius to the power 4, so you need (25/16)^4=5.96 times more torque to accelerate it at a given rate. The gantry is driven via a huge mechanical advantage, and increasing it's mass only increases the inertia proportional to the mass (no power), so it doesn't make such a big difference.

Wobblycogs
06-11-2012, 03:30 PM
Very interesting article, thanks. I'll leave it set to Supported-Supported to be on the safe side.

Should "Set Phase Current" be the rated current of the stepper? I'm sure that's going to be the winner of stupid question of the month :-).

I couldn't help feeling I was drowning in a sea of numbers comparing the various options so I put together a little table (hopefully others might find this useful as a starting point). I threw in a single calculation for a shorter X-Axis as well just to see how much of an effect that had.


#
Ballscrew
Length
mm

Stepper
Nema
Supplier
Price
Max Speed
mm/min

Limiting Factor


1
1610
1800
60BYG301B
23
CNC4YOU
25.99
3500
Critical Speed


2
1610
1600
60BYG301B
23
CNC4YOU
25.99
4500
Critical Speed


3
1610
1800
60BYGH401-03
23
CNC4YOU
38.99
3500
Critical Speed


4
2510
1800
60BYGH401-03
23
CNC4YOU
38.99
1900
Torque


5
2510
1800
86HS115-4208
34
CNC4YOU
79.99
4000
Torque


6
1610
1800
SY57STH76-3008B
23
Zapp
26.40
2750
Torque


7
2510
1800
SY85STH65-5904B
34
Zapp
51.79
1500
Torque


8
2510
1800
SY85STH80-5504B
34
Zapp
75.60
2100
Torque


9
2510
1800
SY85STH156-6204B
34
Zapp
108.17
2100
Torque



Assuptions
Voltage set to 70V for all steppers
Phase current set to rated current of stepper
2510 screws have a minor diameter of 19mm
1610 screws have a minor diameter of 12mm
Speed is set for cutting
Fixing is Supported-Supported (I'll be using Chai fixings)
Gantry weight of 35Kg

Looking at the table I think my best bet if I want to go for 1800mm on X is row 5 which gives me 4000mm/min when cutting (and 7000mm/min in rapids). Row 1 looks like a good cheaper option though with only slightly reduced speed but rapids would be the same as cutting.

So, to all those who know a lot more about this than I do, what would you do? Please feel free to tell me I'm massively over-spec'ing / that I should build a smaller machine / suggest other parts etc.

Cheers

JAZZCNC
06-11-2012, 05:29 PM
My advice is only build this length if you truely need it because over 1500mm your in funny territory. 16mm is too close for whip and vibration etc and has you've seen 25mm takes you to another level regards motors/drives/PSU and for no gain really.

Your Max speeds are a bit off mark thou and provided you use decent voltage you will easily get more than 4000mm/min cutting speeds. Don't get caught up in the critical speed figures has they are wide margin and in practice you can get much higher speeds provided the power is there.

I run twin 1500mm 20mm 5mm pitch geared 1:2 with 75v and 6NM 34's and can easily cut at 7mtr/min and rapid @ 11-12mtr/min. Going by the specs for a 5mm pitch screw then they are probably spinning close to twice the critical speed and have been doing for years without any trouble.
Now I'm not saying to do this has 10mm pitch is clearly better and less hassle. When I built my machine 10mm wasn't available from Chai or china and far too expensive in UK so this was my only option, But today thats not the case so go for 10mm.

Regards cutting Ali @ 1800mm/min then thats not realistic for DIY machine at any decent DOC(Really it should be removed from the sheet has it's misleading.!!) and would need a very very strong machine with a very powerful spindle. I rarely cut Ali much above 1200mm/min and 95%+ of time it's below 1K.

I you must have the length then IMO go for the 25mm/34 combo has it will give the least hassle and yes while in theory it won't quite reach the speeds 16mm Dia would allow it will still easily full-fill your needs.

Wobblycogs
06-11-2012, 06:00 PM
Thanks Jazz that's spot on what I needed and really helpful, I think I'm just starting to see how the multitude of factors play off against each other.

I suspect the speeds in that table are a bit low because I went for supported-supported and was quite conservative with the limit.

I'll have to get the calculator out and see what the financial damage is if I stick at 1800 on X :-). Whether I build it 1500 or 1800 I've got to get a load of stuff out of the workshop so I'm tempted to stay with 1800. I've also got a project in mind that would need more than I think I could reasonably do on 1500 (lol, two bad excuses)

I realized today that my frame design makes mounting the screw bearings really awkward so it might be back to the drawing board for that. My aim of getting the mechanical side of things done by the end of the year is looking wildly optimistic already :redface:

Jonathan
06-11-2012, 06:29 PM
I think I'm just starting to see how the multitude of factors play off against each other.

Which is precisely why I linked you to the spreadsheet instead of just telling you the answer :joyous:, but it seems that's what you're after so...


So, to all those who know a lot more about this than I do, what would you do?

I'd use RM1610 and rotate the ballnut instead of the screw. From using the spreadsheet it should be now be obvious why it is such a big advantage to not rotate the screw.
The X-axis on my machine is 1700mm travel, with RM2510-2094mm ballscrews and rotating nuts. The highest it seems reliable at with 3Nm motors is 12m/min (so about the same as Jazz's but with substantially smaller motors), although it will intermittently run at 15m/min still with no signs of vibration/whipping problems. Tenson here has RM1610-1500mm and rotating nuts, so you may wish to ask him how it is performing as that should be a good indicator of the feedrate that configuration would get with 1800mm.

If sticking to a conventional setup it's not so clear cut. RM2510 and Nema34 is probably the safer option, but your table suggests there's a significant chance that the RM1610 and 3Nm motors would outperform it quite significantly you could go for the latter as it is the cheapest option and if whipping is a problem change to a rotating nut at a later date and keep the same motors/drivers.

JAZZCNC
06-11-2012, 07:13 PM
The highest it seems reliable at with 3Nm motors is 12m/min (so about the same as Jazz's but with substantially smaller motors),

Not much difference really because I have single motor turning 2 screws and you have 2 motors, plus 34's are stronger and will hold more torque higher up the curve.!!

Don't see the point of going to all the expense and trouble of implementing a rotating nut design and all it's complexity's when the standard setup will still allow everything he needs anyway.? The extra expense of components and having someone (Namely You) machine the rotating nut assembly cancels out extra cost of 34's etc for what is affectively wasted speed has he'll never cut at those speeds and Rapids are only usefull in quite limited circumstances.!

If speed is required then yes I'd take the rotating nut assembly route has it clearly will allow higher feeds but if cutting below 7mtr/min which most materials are then why go to all the trouble.??

wilfy
06-11-2012, 07:51 PM
Wobbly.....steel prices for you

50 x 50 x 4mm box - 23.77 Each (7.6mtrs)

50 x 25 x 3 box - 13.25 Each (7.6mtrs)

50 x 5 flat - 6.99 Each (6.4mtrs)

VAT will (unfortunately) be on top of these prices. Anyway, once you've finished tweaking your design let me know and I'll firm up the prices :D

where the frig did u get them prices?

WandrinAndy
06-11-2012, 07:56 PM
I reckon it's inside trading wilfy. Lol

njhussey
06-11-2012, 08:01 PM
It's through work and we buy quite a lot of steel so I guess get half decent prices...hadn't really thought about it ;)

wilfy
06-11-2012, 08:10 PM
argh i need to find a local supplier for my steel... i really need to get a length of 50x25 for less than 25

Jonathan
06-11-2012, 09:03 PM
If speed is required then yes I'd take the rotating nut assembly route has it clearly will allow higher feeds but if cutting below 7mtr/min which most materials are then why go to all the trouble.??

I agree - clearly the only reason to do it is if it works out cheaper or if you especially need the higher speed and (perhaps more importantly) acceleration. Personally I would do it even if the cost is slightly greater since the factor of safety will be much greater, so you will have a more stable system. Perhaps ask Chai for the price separately for two RM1610-1800mm and RM2510-1800mm so we can compare the relative cost more precisely?

Wobblycogs
06-11-2012, 10:47 PM
Funnily enough I asked Chai that exact question yesterday but he didn't include prices in his reply, just the drawings I asked for. I suspect something got lost in translation so I've tried again.

In the spreadsheet is the screw length the total length including the machined ends or just the portion between the bearings? If it's just the threaded portion between the bearings then I may be able to get away with 1600mm which puts me (just) into RM1610 + 23's category by the looks of it.

What I'm thinking is if I place the nut towards the front of the gantry and keep the rails at 1800mm then the gantry is free to move beyond the end of the ballscrew - yep, that's clear as mud so there's a couple of pictures attached showing what I mean. I've not seen any builds like this so I'm guessing it must be a bad idea but it looks like a simple way to keep the length of the ballscrew sensible and not lose any cutting length.


73207321

Wobblycogs
07-11-2012, 10:43 AM
So I've got some prices from Chai for the different bearing sizes:

2 * RM1610 @ 1800mm with 2 ballnuts = $130 Air shipping $76 Total $206 (128)
2 * RM2510 @ 1800mm with 2 ballnuts = $142 Air shipping $97 Total $239 (149)

Total price works out like this:

2510+34 Setup
Ballscrews: 149
Steppers (86HS115-4208): 160
Drivers (CW-8060): 126
Total: 435

1610+24 Setup
Ballscrews: 128
Steppers (60BYGH401-03): 78
Drivers (CW-5045): 87
Total: 293

Difference: 142 extra for larger screws.

However, from what I've read and what's been said here I'd be better off driving the steppers in the 1610 example on 70V which would mean using the CW-8060 drivers. That reduces the difference to 103. Note: I've not researched the best drivers, I just picked the ones CNC4YOU had.

JAZZCNC
07-11-2012, 11:26 AM
Me I'd be spending 100 extra safe in the knowledge you won't have any issues with whip or resonance. Match it to drives linked below and you'll have a very stable system capable of decent cutting speeds.

These Digital drives are the ones you want they knock the spots off those cheap CW-8060 analogue drives which can't compare in performance.
Leadshine AM882 Digital Stepper Drive 80VDC 0.1A - 8.2A With Protection Function | eBay (http://www.ebay.co.uk/itm/Leadshine-AM882-Digital-Stepper-Drive-80VDC-0-1A-8-2A-With-Protection-Function-/300737954780?pt=LH_DefaultDomain_0&hash=item46056103dc)

If you really want the best in performance and accuracy from a stepper/drive combo and can run to it then these are the ultimate.
Leadshine 300W 3-phase Hybrid Servo Drives Set HBS86H Drive + 86HS40-EC Motor | eBay (http://www.ebay.co.uk/itm/Leadshine-300W-3-phase-Hybrid-Servo-Drives-Set-HBS86H-Drive-86HS40-EC-Motor-/300806661044?pt=LH_DefaultDomain_0&hash=item46097963b4)

Jonathan
07-11-2012, 11:28 AM
You can get good drivers which are much cheaper (36.20) than those, for instance:
Cheap CNC! Wantai 4 PCS Stepper Motor Driver DQ860MA 80V 7.8A 256micro CNC Router Mill Cut Engraving Grind Foam Embroidery-in Motor Driver from Industry & Business on Aliexpress.com (http://www.aliexpress.com/item/Cheap-CNC-Wantai-4-PCS-Stepper-Motor-Driver-DQ860MA-80V-7-8A-256micro-CNC-Router-Mill/679049120.html)

You may get customs fees, but even if it's the full 20% it's still nowhere near the price of buying in England. I've bought quite a few of them and can confirm that they are good drivers. Since they are 80V you could use the same ones for both size motors, so this makes the price difference just the difference between ballscrews and steppers, which going by your numbers is 103.

The Nema 34 motors especially would benefit from better drivers, particularly higher voltage ones. Some more options, not nesscarily the cheapest, just the first I found:
New Leadshine AM882 Drive 80VDC 0.1A - 8.2 | eBay (http://www.ebay.co.uk/itm/New-Leadshine-AM882-Drive-80VDC-0-1A-8-2-/270837356589?pt=LH_DefaultDomain_0&hash=item3f0f2a182d)
2MA2278 CNC Stepper Driver For Nema34,Nema42,Nema51 Stepper Motors 7.8A 110/220V | eBay (http://www.ebay.co.uk/itm/2MA2278-CNC-Stepper-Driver-For-Nema34-Nema42-Nema51-Stepper-Motors-7-8A-110-220V-/180994296477?pt=LH_DefaultDomain_0&hash=item2a2419ca9d)

If I had to use Nema 34 motors then I would use the 220V drivers since the high voltage will significantly increase the torque you get from the Nema 34 motors in the higher speed region, but they do cost almost 3 times as much as the first drivers I linked to...

Jonathan
07-11-2012, 12:20 PM
Hmm, just read the beginning of this thread again. You're after 1220mm travel on the X-axis but we're discussing buying 1800mm ballscrews, so did you suddenly decide to increase the travel?

300mm is a good width for the gantry, so to get 1220mm travel you could easily use 1550mm(ish) ballscrews. If you're slightly more imaginative with positioning the bearing mounts then you only need the travel plus the length of the ballnut and end-machining, which for RM1610 is 57mm for the ballnut and 76mm for the end machining (including 10mm extra for the pulley). That makes the required length 1220+57+76=1353mm. Call it 1400mm just to 'be safe' and suddenly the motor and ballscrew choice becomes a lot easier as the critical speed is much greater...

On my machine the rails are 2000mm with 2094mm ballscrews and 1700mm travel. The new rails I got are 2200mm, but I'm keeping the travel the same and using the extra 200mm to increase the bearing spacing (among other things!) and using the same ballscrews. This is a similar situation since the frame and rails will be a fair bit longer than the ballscrews.

If you're after more travel then you could get about 1650mm travel with the 1800mm ballscrews.

Wobblycogs
07-11-2012, 12:35 PM
Yes, I decided to increase the travel. I went and re-measured the workshop and I came to the conclusion that I had to rip out a length of workbench and cupboards if I was going to reasonably fit the CNC in there. I figured I might as well use up all the space I'd created so upped the length to 1800mm (poor excuse I know). Since then I've thought up a couple of projects that would use the extra bit of length. I'd like to get a bearing spacing of at least 250mm on the gantry so I'm guessing a bit over 1600 for the workable length of X.

Jonathan
07-11-2012, 12:43 PM
Ok fair enough, if you want 1600mm travel then the discussion is valid :)

Option 3 is to find out how much RM2010 ballscrews cost:
Aliexpress.com : Buy Anti Backlash Ballscrews RM 2010 L1000mm*2pcs with 2pcs SFU2010 ballnut for CNC Machine from Reliable Ball screw suppliers on BST AUTOMATION (http://www.aliexpress.com/store/product/Anti-Backlash-Ballscrews-RM-2010-L1000mm-2pcs-with-2pcs-SFU2010-ballnut-for-CNC-Machine/314742_519166820.html)

If you wait for the seller to be online or just send them a message I'm sure they'll give you a price for RM2010-1800mm (or whatever). They also have RM1616 and RM2020, which would also be good since then the critical speed is no longer an issue (you can gain back the resolution via the pulleys):

http://www.aliexpress.com/store/314742/search?SearchText=high+lead

Wobblycogs
07-11-2012, 04:44 PM
Right then, after much dithering I've decided to go with the 2510 screws and some nema 34's. I've not picked the motors and drivers yet but looking at what's been recommended I can clearly get something that will work in a 34 package so it's time to press on with the design :-)

Since I'm using 50mm box for the frame I can't directly mount the screw bearing block onto the frame. I'm hoping to get around that by mounting the bearing block and motor on a plate (green) which then bolts onto the frame. The picture below shows the business end of the screw but there's a similar plate at the other end as well. Good idea / bad idea?

The plate is currently drawn at 100x300x5mm as it was going to be steel but I'm now thinking aluminium would be better as it would be easier to work (I want to provide some vertical adjustment holes for example). Will 5mm aluminium be strong enough?

The motor housing is drawn in 20mm aluminium which looks far thicker than I need but I have very little experience to go by. Would 16mm or even 12mm be strong enough? I'm going to drill and tap the edges to join the pieces together so it can't be too narrow :-). Ideally I'd like to use the same thickness plate for parts on the gantry and Z-axis so that I can just buy one large piece of plate which, fingers crossed, will be cheaper.

Finally, what grade of aluminium should I go for? The motor housing and probably a few other bits will need to be milled out; I've got decent variable speed router so I was going to give it a go with that (taking very light cuts and with a template). I seem to remember someone saying they were using C250 but it looks like 6082 is easier to machine from what I've read.

Cheers :biggrin:

7322

D.C.
07-11-2012, 05:10 PM
If you are thinking of getting some of the leadshine drives in the next couple of months:

http://www.mycncuk.com/forums/marketplace-discussion/5289-leadshine-digital-drives-bulk-purchase.html:whistle: (http://www.mycncuk.com/forums/marketplace-discussion/5289-leadshine-digital-drives-bulk-purchase.html)

Jonathan
08-11-2012, 04:45 PM
I contacted the supplier I linked to in my previous post to find their prices for the RM2010 ballscrews. He replied promptly with the following:


For:
RM 2010 -L1800mm*2pcs with 2pcs SFU2010 ballnut with end machining
Best price for you is USD360.00,include the freight by Fedex/
For:
RM 2010 -L1500mm*2pcs with 2pcs SFU2010 ballnut with end machining
Best price for you is USD325.00.


Clearly that's $121 (76) more than the RM2510 from Chai, but with 2010 you could still use the 3Nm steppers and drivers and get better acceleration than with the 2510 ballscrews. The 5mm difference in diameter may not seem like much, but remember the torque required to accelerate a cylinder is proportional to the radius to the power 4, so 20mm needs only around 41% of the torque that 2510 requires.
The reason none of us mentioned RM2010 earlier was because Chai doesn't stock them and they are very expensive from England, but these prices change that even though they are a bit more expensive.


Since I'm using 50mm box for the frame I can't directly mount the screw bearing block onto the frame. I'm hoping to get around that by mounting the bearing block and motor on a plate (green) which then bolts onto the frame. The picture below shows the business end of the screw but there's a similar plate at the other end as well. Good idea / bad idea?


Good plan as it makes it easier to align everything since you can have adjustment via slotted holes in the plate.



I'm now thinking aluminium would be better as it would be easier to work (I want to provide some vertical adjustment holes for example). Will 5mm aluminium be strong enough?


No I don't think so, I'd say 10mm based on what looks about right!



The motor housing is drawn in 20mm aluminium which looks far thicker than I need but I have very little experience to go by. Would 16mm or even 12mm be strong enough? I'm going to drill and tap the edges to join the pieces together so it can't be too narrow :-). Ideally I'd like to use the same thickness plate for parts on the gantry and Z-axis so that I can just buy one large piece of plate which, fingers crossed, will be cheaper.


20mm is excessive, but as you say it's sometimes best to keep things the same thickness to make it more efficient when you buy the material. Have you put a pocket in the mount for the motor to rest in? It will make it easier to align the pulleys since you'll have more of the shaft extending through the aluminium, e.g:

7345

6082 aluminium is readily available and cuts easily, so that's fine.

Wobblycogs
08-11-2012, 06:37 PM
Cheers, I was reading Iwant1 (http://www.mycncuk.com/forums/router-build-logs/4755-ive-built-machine-100-different-times-my-head.html)'s build thread yesterday realized I was trying to rush this project and that something was going to go wrong if I didn't slow down, do a bit more homework and spend longer on the design. I really wanted to get this done in the time I have off but it looks like that was more than a little optimistic, perhaps it will be ready for the end of next year :-)

As I've now got a lot more time I'll seriously consider using the 2010's instead. Over all I think the cost is going to be about the same but better acceleration would be nice to have. I have to admit I hadn't realized how big the 34 motors were until I imported one into the model. It's a chunky bit of kit compared to the 23 package.

Based on your advice in another thread I've moved the screw up to be level with the rail as well as increased the plate to 10mm.
7346
The motor housing has been dropped to 15mm plate. It already has a cut out to allow better shaft protrusion but I've realized I'll need to slot the cut out and mounting holes to provide tensioning capability.
7347

I think the frame design is pretty sound so I'll aim to get that built over Christmas (I've got to build something or I'll go stir crazy) and then work on the rest of the design in parallel.

Wobblycogs
17-11-2012, 08:36 PM
I've done a lot of reading of build logs in the last week and a fair bit of tinkering in sketchup to (hopefully) improve the design. I thought it was about time to do an update and to find out if I'm going in even vaguely the right direction.

First off we have the gantry connection to the rails and x-screws. I noticed a lot of people were advised to make this connection stronger so hopefully this will be strong enough.
740474057406
The block that attaches to the ball nut is a 50mm lump of aluminium. The green bolts are M8x90 and go most of the way through. The blue bolts are M6x30 and screw in to the block between 15 and 20mm. After seeing someone else's build I've gone for a two plate gantry design as I think it'll be simpler in the long run. There will be slotted screws holding the two plates together so fingers crossed I should be able to get the screw and gantry connections aligned. I'm not keen on the three M6 bolts close together on the top plate but I think they've got to stay. They are there to counter any torque applied by the green bolts and face plate if things aren't 100% square.

I've slightly redesigned the bed to make it simpler to build and to move the legs to be directly under the x-rail. It's shown bolted together but I've decided to weld at least some of the joints so that I get it done this century.

Now here's where I'm going a little off-piste with the gantry I think. I read the recent thread discussing gantry designs and liked the L shaped solution made from 45x90 extrusion. I also liked the C shaped designs so I thought why not try and combine the best of both worlds and use some 90x90 heavy extrusion (this is now in the sketchup library if anyone else wants it). I'm guessing this will give me both vertical and horizontal strength and the extra bit of mass should help damp any vibrations a bit.

I'm currently pondering running the y-rails along the front of the gantry rather than top and bottom as most people do. Although this will cause the Z-axis to stick out about 50mm more than the top and bottom rail design it will also allow me to maximize my y-cutting distance and have a slightly wider y-bearing spacing. The gantry side plate will be braced front and back and reduced in size to only what is required as the design progresses.

74077408

One thing that is starting to concern me a little is cutting all this aluminium. I have a good selection of wood working tools but not much in the way of metal working tools. Do you think it would be possible to hand route 20mm aluminium? From what I've read slower bit rotation is better, the slowest my router will go is 10,000rpm which seems to be slower than most so I think I'm in with a shot but some advice would be much appreciated. Cheers :-)

Wobblycogs
19-11-2012, 12:16 PM
I've managed to get over my stupidly large gantry design by totalling up the cost of the aluminium plate and extrusion and nearly passing out. My new version 5 design uses KJN 45x90 profile like a lot of builds I see around these parts. What I'm struggling with now though is how to mount the SBR20 to the extrusion.
7414
In the image above I've centred the rail but it doesn't matter where I put it the rail lines up really poorly with the extrusion. Has anyone managed to find a good solution to this? I'm so tempted to just give up and use profiled rails but the extra cost is off putting to say the least.

A couple more shots of the current gantry design, comments welcome.
74157416
The gantry over hangs the back axis bearing a little so that I have space to mount the stepper. The over hanging weight is fairly minimal so I think it should be ok. The stepper will be slotted so that it can move up and down to tension the belt.

I went with the taller C-shaped gantry design because I want a good separation between my Z-axis bearings. The Z travel is about 300mm (more than I was aiming for) and I'm hoping that extra bit of height in the C-shape will help stiffen things up a bit.

WandrinAndy
19-11-2012, 02:08 PM
What I'm struggling with now though is how to mount the SBR20 to the extrusion. In the image above I've centred the rail but it doesn't matter where I put it the rail lines up really poorly with the extrusion. Has anyone managed to find a good solution to this?
I followed a similar thought process Wobbly... I've seen folk suggest bolting thick flat bar to the extrusion and then in turn attaching the SBR20 to the flat bar, but IMO that partly negates one of the main benefits of using extrusion... relative ease of assembly.
Also just a quick caveat that the SketchUp 45x90 component... certainly if you are using one of mine, sorry... may not necessarily be accurate enough for this kind of accurate line-up exercise.


I'm so tempted to just give up and use profiled rails but the extra cost is off putting to say the least.
Agree, the costs are horrendous. Although it looks like Zapp is now also offering, in addition to the Hiwin range, a value for money range of linear precision profile stuff.... LSK or summat, that I think is about 25% cheaper than Hiwin?

I'm finding that there are sooooo many tradeoffs in any DIY CNC design.... That it's worthwhile setting aside plenty more time than initially anticipated :-)

Wobblycogs
19-11-2012, 02:29 PM
I followed a similar thought process Wobbly... I've seen folk suggest bolting thick flat bar to the extrusion and then in turn attaching the SBR20 to the flat bar, but IMO that partly negates one of the main benefits of using extrusion... relative ease of assembly.
Also just a quick caveat that the SketchUp 45x90 component... certainly if you are using one of mine, sorry... may not necessarily be accurate enough for this kind of accurate line-up exercise.

Attaching a plate or bar to the extrusion was all I'd come up with as well so at least I'm thinking along the same lines as others. I agree though it seems to defeat the purpose of using extrusion. I'm using the MacTavish 45x90 (http://sketchup.google.com/3dwarehouse/details?mid=3487e06306f0e10f22f2986410a0140&prevstart=0) component. It seems to be right but I'll double check it.

I'm seriously tempted to swap out the extrusion for some box section aluminium with a good thick wall. I can't help feeling that three pieces of box arranged as I currently have the extrusion would be equally strong. I'd almost certainly then fill the middle one with kiln dried sand to damp vibrations. The problem then moves to joining the box section to the gantry sides but that feels like a fairly easy problem - I feel version 6 coming on...

I was looking at the Zapp rails yesterday. The rails aren't to bad price wise it's the carriages that are the killers. I'm trying to convince myself that I'm only even going to build one CNC so I might as well do it right the first time but I just know I'll end up building another :-)


I've found that there are sooooo many tradeoffs in any DIY CNC design.... That it's worthwhile setting aside plenty more time than you initially anticipated ;-)
Never a truer word spoken.

WandrinAndy
19-11-2012, 02:57 PM
I'm seriously tempted to swap out the extrusion for some box section aluminium with a good thick wall. I can't help feeling that three pieces of box arranged as I currently have the extrusion would be equally strong. I'd almost certainly then fill the middle one with kiln dried sand to damp vibrations. The problem then moves to joining the box section to the gantry sides but that feels like a fairly easy problem - I feel version 6 coming on...

Then again.... if going for box section, why not go directly to Steel for it's greater rigidity ?

Btw, for me it all started about four months ago.... I was simply sitting thinking that it would be quite nice to be able to see the cut taking place on the router table, like one can see when making hand held router cuts.... And I started thinking "upside-down" router tables, and then there was simply no turning back...

That one single thought started my downfall ;-)

Wobblycogs
19-11-2012, 03:15 PM
Funny you should say that as I was just looking at steel prices. I'm favouring aluminium because it's flatter and I may at some point move over to profiled rails. I saw a discussion on self levelling epoxy earlier today which I've put to one side for later (got to get some work done today), that could be a solution.


Btw, for me it all started about four months ago....

Oh you should think yourself lucky I reckon it start about 12 years ago for me. I've just kept putting it off and putting it off till I have a good workshop etc etc. I've still not got a good workshop space but I'm going to do it anyway. I have to admit though that I respect you for giving it a go in the space you have available, that's what I call real dedication.

njhussey
19-11-2012, 04:29 PM
Some bits turned up today...... :glee:

7418

asbo
19-11-2012, 04:33 PM
I haven't tried this but I've been thinking about it. The supported rail (at least the stuff I got from chai) has a series of machine screws(red) that bolt the rail to the support from below. Maybe these could be replaced with slight longer ones(blue) and bolt through the extrusion, support and into the rail.
7419

Wobblycogs
19-11-2012, 05:00 PM
Oooh steel, the build begins today :yahoo:. I'm hoping that's not all mine, I've already got more angle brackets than I know what to do with! Good to see it supporting it's own weight on what it probably about a 3m over hang though, I think this frame might just be strong enough :-). Cheers for to the update.

That's a cunning idea with the bolts asbo (and I like the drawing). Some careful planning would be required to get the bolts in as well as a long socket wrench and some careful hole cutting on the opposite side of the extrusion where it looks fairly weak already.

njhussey
19-11-2012, 05:07 PM
Oooh steel, the build begins today :yahoo:. I'm hoping that's not all mine, I've already got more angle brackets than I know what to do with! Good to see it supporting it's own weight on what it probably about a 3m over hang though, I think this frame might just be strong enough :-). Cheers for to the update.

No yours is only the bundle on the left, in fact there are 2 lengths missing (20x20) which should be here tomorrow.

Will start the cutting tomorrow morning :)

Jonathan
19-11-2012, 06:56 PM
Now here's where I'm going a little off-piste with the gantry


It's very similar to this one:



One thing that is starting to concern me a little is cutting all this aluminium. I have a good selection of wood working tools but not much in the way of metal working tools. Do you think it would be possible to hand route 20mm aluminium? From what I've read slower bit rotation is better, the slowest my router will go is 10,000rpm which seems to be slower than most so I think I'm in with a shot but some advice would be much appreciated. Cheers :-)


You could try using a carbide cutter, since 6mm is good at 13000rpm and 8mm is good at 9700rpm. Probably best to try 6mm as there's then more margin for error on the feedrate.



Has anyone managed to find a good solution to this?


Yeah...don't use extrusion, or add a 10mm plate. The plate is a good idea anyway to reduce local deformation (spread the load).



I'm so tempted to just give up and use profiled rails but the extra cost is off putting to say the least.


Linear guides are much stronger than round rails and just generally better - you wouldn't regret it. However I'm confident that with your current design you could cut aluminium quite well, so it's not a necessity.



Then again.... if going for box section, why not go directly to Steel for it's greater rigidity ?


Problem is the accuracy of steel box section compared to aluminium box, or extrusion. If just using round rails you'll probably get away with it, but it would be hard to mount linear guides on steel box section without entertaining self levelling epoxy.
(Oh just noticed Wobbly said that in the next post!)



Good to see it supporting it's own weight on what it probably about a 3m over hang though, I think this frame might just be strong enough :-)


It doesn't really tell you anything. With a CNC machine we're not worried about the material failing/passing it's elastic limit, we're instead concerned about making sure it doesn't deflect by a few tens of micrometers. In the image that will probably be bending at least a milimeter.

njhussey
19-11-2012, 07:04 PM
It doesn't really tell you anything. With a CNC machine we're not worried about the material failing/passing it's elastic limit, we're instead concerned about making sure it doesn't deflect by a few tens of micrometers. In the image that will probably be bending at least a milimeter.

I didn't stop to measure as it was raining ;)

njhussey
20-11-2012, 09:34 AM
Been busy this morning...

7426

Wobblycogs
01-12-2012, 04:01 PM
Last weekend, in the pouring rain, I collected the steel for the base from Neil who very kindly sourced it for me and cut it all to length.
7490
It was all covered in a good coating of oil which has been doing it's best to get every where this week so I turned it in to a somewhat cleaner pile of steel by rubbing it down with a degreaser.
7491
After spending an hour or so cleaning it I decided to get a couple of rust spots off with a wire wheel which is when I discovered that I'd actually only managed to get a light surface layer of oil off, there's a much heavier oil still on the steel. My question therefore is this: how clean do I need to get the steel in order to paint it?
7492
The image above shows a very clean piece at the bottom and a pieces that have just been degreased above. I'm sure the bottom piece is clean enough for paint but are the other pieces? If I've got to get all the oil off what is the quickest method as wire wheeling it all will take ages.

Some good news though. I've tested a couple of the long rail pieces of steel with a reference straight edge and they are fairly close to straight <0.5mm in 600mm.

Cheers :-D

wilfy
01-12-2012, 11:35 PM
i'd find of source of TFR (traffic film remover) this is the stuff they put on at the car wash to remove tar ect off your car.. i used it to degrease an engine bay that had a cracked sump leak all over it before painting and it worked wonders, very little need for any elbow grease

JAZZCNC
02-12-2012, 12:13 AM
i'd find of source of TFR (traffic film remover) this is the stuff they put on at the car wash to remove tar ect off your car.. i used it to degrease an engine bay that had a cracked sump leak all over it before painting and it worked wonders, very little need for any elbow grease

I manufacture TFR it's just a strong Alkaline detergent and won't touch Tar. For that you need petroleum based product, Kerosene works good for Tar.
Any strong washing up liquid washed with hot water will work. Good TFR is pretty much strong washing up liquid(detergent) with foaming and rinsing agents to help with streaking, cheap ones are very caustic based and dull paint.
If you do go in search of TFR try a truck wash because truck wash is very strong being strongly laced with caustic soda to aid cleaning.

njhussey
02-12-2012, 12:26 AM
At work it's welded up and sent to the painters who shot blast it and then paint it. Only thing I can think of that will get the oil off is thinners as that's what I believe the automotive painters use.

Wobblycogs
08-12-2012, 02:28 PM
After trying every solvent and cleaner I could get my hands on I gave up and attacked it with a flap wheel and wire wheel. I'd only used a grinder once before to chase out a couple of electrical sockets and it was so messy I never tried again. I can't believe how much I've been missing out though, everything is going to get a good grinding from now on :-)

The angle brackets were probably the worst and they were awkward because as were small. Here's a before and after shot.
75327533
So after a few hours with the grinder I'd turned a pile of oily steel into a pile of clean steel ready for the next step.
7534
From reading around on welding forms it seems the next step is to pickle with phosphoric acid rust remover and then undercoat. Does this sound right? I want to get an undercoat on before starting construction as I think this build will take a while and I don't want all this work being undone. If I decide to get a welder it should be fairly easy to wire wheel off the undercoat in a few places. Any recommendations for undercoat? I was just going to pop down Halfords and get some car spray undercoat.

Jonathan
08-12-2012, 02:33 PM
That's far too shiny ;)

Powder coating is surprisingly cheap and saves you all the effort. I wouldn't be surprised if you can find a local company who would powder coat the finished frame for 30-40.

njhussey
08-12-2012, 02:54 PM
I've just twigged what you were trying to remove...it's the protective layer that stops it from rusting too badly if you're going to leave it anywhere for a while :( my frame has been sat in a damp garage for nearly 2 years and only has a small bit of surface rust in a few places, and nothing a quick tickle with the grinder and flap disc won't sort before painting ;)

7535

As Jonathan says powder coating is good but only on the finished frame as you can't touch it up like you can sprayed paint.

Halfords primer would be ok, though for the amount of steel you have it will cost an arm and a leg!!!

If you get stuck I have a friendly local (to me) painter who could probably do it quite cheaply. Or there is one place near Mitcheldean I think we have started to use at work for painting.

Wobblycogs
08-12-2012, 03:10 PM
Hmm, power coating sounds good idea but transport could be a problem for the finished frame. I suppose if I drilled and tapped all the holes first I could get the pieces coated individually.

I'd come to the conclusion that it must be a protective coating of some kind. It was a messy job getting it off but I'm pretty sure the paint finish will be better without it and there was some rust that needed removing anyway. I think next time I'll try just spraying over the top of it first.

Time to starting googling for spray primer I think.

njhussey
08-12-2012, 04:00 PM
Try your local motor factors, they might do bigger cans and probably be cheaper too!

r0bsk1
08-12-2012, 04:23 PM
Use an enamel paint. It doesnt need a primer. I use it to restore motorbike wheels and the finish is ace!

martin54
08-12-2012, 07:03 PM
Use an enamel paint. It doesnt need a primer. I use it to restore motorbike wheels and the finish is ace!

Not strictly speaking true problem is that you run the risk of the steel rusting under the enamel so although the finish looks good just now over time you may start to see blisters appear. To be honest I would probably look at buying a brush on primer rather than spray cans, your going to waste a lot of paint the size & shape these are. Brush on undercoat with a decent brush will be just as quick & will leave a suitable finish for what ever top coat you decide on. You can still buy it at a local motor factors or auto paint suppliers.

JAZZCNC
08-12-2012, 07:07 PM
Martins right what you want is etching primer with synthetic brush on coach paint available from any motor paint factors. . . Lasts for years and easily applied.!

martin54
08-12-2012, 07:12 PM
Jazz I joined the Royal Navy as a stoker, I know all about painting stuff lol

Wobblycogs
16-12-2012, 02:20 PM
Thought it was time to put in an update as a little bit of progress has been made.

Thanks for the advice about painting metal. In the end I went with CombiColor in bright yellow:
7650
It's great stuff, goes on smoothly with very little odour and the coverage is pretty good considering the colour. That lot you see there was covered using <100ml of paint. It needs another coat but the 2 litre tin I've got should be more than enough to do the whole frame. Also, I think it's bright enough even for me I can practically see the frame in the dark :-)

Not having worked in metal before I thought it wise to perhaps have a go at drilling and tapping for brackets before launching into the frame construction properly and lets just say I'm really glad I did. I won't bore you with all the gory details but here's a shot of attempts 1 and 4.
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On attempt 1 I chose a dopey hole pattern, the back holes are too close to the corner of the angle and all the holes are too close to the edge for my liking. At this point I didn't have a vice for the pillar drill, transfer punches or centre drills and I ended up having to make the holes in the bracket 8mm in order to get my M6 bolts in and there was no play in the bracket.

By attempt 4 I'd watched a couple of YouTube videos and had a drill vice, centre drills and transfer punches. The holes in the bracket are 7mm and after fitting the bolts I get about 1mm play in both directions (as you would expect). Phew, I was worried for a while that I couldn't achieve the accuracy needed.

As a final trial run I've drilled some new holes in the angle at 6mm and transferred those to the box section and the bolts go in fine. I reckon I can't be more than 0.1mm out now and probably quite a bit less.

I've got a couple of questions though...

In my design I've used M8 bolts to hold the brackets on as per this build (http://www.cnczone.com/forums/cnc_wood_router_project_log/30751-my_first_router_built_steel.html). I did a bit of experimenting with my steel though and I think M6 is a better choice. The box section I'm bolting to here has a 3mm wall and while an M8 bolt will hold the M6 feels much better as the pieces is bolted up. In terms of strength I think the M6 is more than enough, I've used my test piece as a pogo stick to see how strong it was to no ill effect. I wouldn't mind hearing the thoughts of anyone with more steel working experience though.

The other question is regarding the holes in the angle brackets, what size would you drill them? Assuming I use M6 bolts if I drill them at 7mm then I've got a little bit of play to adjust things if the alignment of the frame isn't perfect. Does this sound like a good or bad idea? There's a little voice telling me that I'll end up with a wobbly frame that I can never get properly aligned.

Cheers and Merry Christmas :-)

wilfy
16-12-2012, 04:08 PM
to quote jazz from a pm he sent me...

Tip use M5 bolts @100mm centres has the finer pitch means they have more thread engaged and small centres mean lots of support.

JAZZCNC
16-12-2012, 04:58 PM
Thanks for the advice about painting metal. In the end I went with CombiColor in bright yellow:
7650
It's great stuff, goes on smoothly with very little odour and the coverage is pretty good considering the colour. That lot you see there was covered using <100ml of paint. It needs another coat but the 2 litre tin I've got should be more than enough to do the whole frame. Also, I think it's bright enough even for me I can practically see the frame in the dark :-)

Sure I've seen that paint on an episode of "Only fools and horse's" the one where they painted the Chinese restaurant. . Lol

wilfy
16-12-2012, 06:15 PM
one thing i wanna know whilst people are talking powdercoat and paint... is it better to paint/powdercoat the surface you are going to mount the rails on or leave them bare metal?

Wobblycogs
17-12-2012, 10:34 AM
You nailed the colour in one Jazz, l knew I'd seen it somewhere before :-)

I'll give the M5 bolts a try. I have to admit I'm using M6 because that's what I've got to hand and it looked ok. I'm guessing the advice was originally for mounting rails.

I'm going to paint the steel before mounting the rail. A paint layer is quite thin and should be fairly uniform. I'd guess the errors in the steel swamp any additional errors the paint might cause.

martin54
17-12-2012, 10:54 AM
Probably to late now but if you have a lot of bits to join together & making a lot of brackets then you are best off making yourself a little jig to ensure all the holes are marked in the same place on each bracket & each length of framing.

Wobblycogs
17-12-2012, 11:21 AM
Not to late and exactly what I am planning on doing, at least for the brackets. I'm going to clamp the drill vice to the table and then clamp in a stop so that, for example, the top left hole in every bracket is in exactly the same position. Then I'll move the vice and drill all the bottom left holes etc etc. I'll always reference off the same side of the bracket so I should end up with all of them exactly the same.

For the framing I'll certainly batch them up and mark them together, I'll have a think about how I might make a hole transfer jig though as that could really speed the process up.

martin54
17-12-2012, 11:43 AM
It's not just a case of speeding up the process, yes it will do this but more importantly if you ensure all the holes are in the correct place it makes squaring the whole frame up much easier & having a square frame is essential. Once you have made the brackets you could probably use one of the brackets as a jig for the framing.

njhussey
17-12-2012, 11:47 AM
What I do when I've got something like that to do is like Martin said make a template and I can use that to mark the brackets and also the mating piece of steel. I drill 3mm holes at the position I want them and then I've got a 3mm centre punch (old snapped off drill bit ground down and sharpened) that I punch the marks with. That way I can get both sets of holes matching, as long as I clamp it in the right place of course :)

njhussey
17-12-2012, 11:58 AM
I'm going to chop up the remaining angle for you this week, do you want any more angle brackets cutting whilst I'm at it? ;-)

Wobblycogs
17-12-2012, 12:24 PM
Worry not :-). I'm using the brackets as a jig in the way you describe, I even splashed out and bought myself some transfer punches to help.

Neil, I'm going to be bold and say I don't need any more brackets. If I do manage to screw it up I'd probably need a whole new set anyway. My attempt to cut a bracket by hand for testing makes me even more grateful than I was before for your help, I damn near broke sweat :-).

martin54
17-12-2012, 01:43 PM
Worry not :-). I'm using the brackets as a jig in the way you describe, I even splashed out and bought myself some transfer punches to help.

Neil, I'm going to be bold and say I don't need any more brackets. If I do manage to screw it up I'd probably need a whole new set anyway. My attempt to cut a bracket by hand for testing makes me even more grateful than I was before for your help, I damn near broke sweat :-).

Sounds like your in need of a bit of exercise lol, get the old treadmill out & go for a jog.
Shouldn't be a problem cutting something like that as long as you are doing it correctly, don't buy cheap hacksaw blades as they are useless for anything harder than cheese, I mean process cheese, cheddar would blunt them to quickly.
Don't try & force the blade to cut the material, let the saw do the work & you will be surprised just how easy it is with a little practice. I've got power saws for just about everything from wall mounted panel saw to cordless jig saw but still like to get a hand saw out from time to time just to keep my hand in for those occasions when a power saw is not an option.

Wobblycogs
17-12-2012, 02:26 PM
lol, exercise. I don't have time for all the things I want to do let alone doing things I don't want to do :-). The blade I've got in there at the moment is cheap and nasty and I used it for cutting some stainless steel last year so it's a complete toothless wonder. I ended up using the jigsaw which gave a surprisingly good cut even if it was a bit tricky on the corner.

Right, time to get on and actually build something...

Wobblycogs
02-01-2013, 06:19 PM
Quick update to say that I've started making the frame and so far so good. As I said to the wife, nothing that scrapping it and starting again couldn't fix anyway :-).

Joking aside I'm actually fairly pleased with my first real foray into the world of metal work. There have been a couple of minor hiccups but nothing that I can't fairly easily work around, the most serious problem has been breaking a centre drill in a hole I had planned on tapping. Unfortunately for me I tried to drill it out which caused the drill to wander as it bounced off the broken end of the centre drill effectively ruining the hole forever. 'Tis not a big problem though as there are three other bolts holding that side of the bracket on and it was only a bed bar anyway.

I made this jig for drilling the brackets which came in really useful:
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The studs are pieces of 7mm shank from an old drill bit. I slipped the bracket over the two studs to ensure it was perfectly aligned for the other two holes. I now have 26 brackets with identical hole patterns.

So far I've put together the bed and part of one of the sides. I'm going to try and get a leg or two fitted tonight.
78417842
I'm completely fed up with drilling an tapping holes :-). There's 112 tapped holes in the bed alone which is less than half what the machine will have when complete. I'm also going to have to add some more bracing to hold the frame square I think. The bed as shown is stiff enough that I can't noticeably cause deflection by hand but individual members are easy to move so I think it needs more. A few bits of angled bracing should stiffen it up tremendously though I think and give me an easy way to make sure it's perfectly square. I've got a ton of angle section left so I might use that rather than get more steel.

njhussey
02-01-2013, 06:26 PM
Welding would have been so much quicker but after seeing where it's going to go I fully understand why it has to be to be dismantled!!

martin54
02-01-2013, 06:30 PM
The bit that broke in the hole would be hardened so you wouldn't have been able to drill it out with a normal bit anyway, best way I have found if that happens & you don't have access to specialist equipment is.... If you can drill a small hole on the other side in the same place, take a bit of care when you get close to the end of the drill bit or you could end up with another broken bit on the other side lol.
Once you have drilled a hole use a bit of hardened rod to try I tap the bit back out. Does work if you are careful but a bit of mucking about is required so if the hole is not that important then normally best just to drill another one lol.

martin54
02-01-2013, 06:34 PM
Welding would have been so much quicker but after seeing where it's going to go I fully understand why it has to be to be dismantled!!

Yer so can I but couldn't you have used a combination of welding & bolting rather than bolt everything??
Just think of this as a prototype & once complete you can start producing flat pack cnc machines lol

Wobblycogs
02-01-2013, 06:52 PM
In the future (possibly a couple of years in the future) at least some of this frame will be welded. I'll probably weld it into three sections - 2 sides and the bed. That will reduce it to just 20 or 30 bolts rather than the hundreds it current is. I've not got anywhere to store the welding equipment at the moment and I wanted to get going so bolting seemed like the least worst option. I suppose I could have got it welded for me or hired equipment etc but I quite like this approach as I'm learning about metalwork as I go.

Shortly after breaking the first centre drill and then wrecking the hole I broke another one (rushing) but I learnt from my first mistake. I grabbed a knackered old spade bit which has a hardened steel point and just drove the broken off tip of the drill clean through the steel. It had broken off most of the way through so it was fairly easy to just force it the rest of the way. That left me with the counter sink intact so it was easy to follow up with the main drill. I'll try drilling down next to it if I break one shallow though.

JAZZCNC
02-01-2013, 06:52 PM
I'm completely fed up with drilling an tapping holes :-). There's 112 tapped holes in the bed alone which is less than half what the machine will have when complete.

Drilling and tapping lots of holes is the most Mind numbing exercise known to man and there isn't a curse or swear word that does justice to the feeling of snapping a Tap in hole 99 out of 100. . :dejection: . . . . . . Great incentive to learn to weld. .Lol

Unless it going down a Rabbit hole surely it could have been made modular from welded parts.?

Wobblycogs
02-01-2013, 07:38 PM
So far I've not snapped at tap and touch wood when I do it'll happen on something easy to replace.

I could certainly have welded some of it but I sat down with pen and paper and worked out the additional cost of equipment plus where I'd store the kit afterwards (especially the shield gas tank) and the difficultly with getting the frame up and down the stairs and then crossing my fingers waiting for dry days to do some welding etc etc - I decided to just get cracking with bolting it together. With any luck LOML will get a new job in the next couple of months and we can get cracking with building an extension that includes a garage / workshop, at that point I'll get a MIG welder I think as I've got a few projects I'd like to do.