:drunk:Decisions, decisions!
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:drunk:Decisions, decisions!
My latest thought is to bolt down a 20mm aluminium plate to the top of the steel raised area (shown in photo). I will then use the machine to skim the surface flat. Then I will use the machine to drill a grid of holes which I can then tap (maybe the router could do this??) for holding jigs and fixtures.
A plate with holes in should work well. But I don't think the WC spindles have enough torque to tap directly? However, you can try thread milling using a special cutter (~£40), plus your CAM will need to be capable of a spiral cut with user parameters on the pitch:Quote:
Originally Posted by biketrialsdave
Forward to 12:23 to see thread being cut:
https://www.youtube.com/watch?v=a43S2y7Ccy8
Can't imagine that plate is flat enough to be useful and could cause you more trouble than it's worth.?Quote:
Originally Posted by biketrialsdave
Personaly I would just buy Machine tooling plate that is ground perfectly flat. Put your Profile etc directly on this and then shim out any error using the nice flat surface for reference. No need to skim flat. Then you can drill tap matrix of holes. Forget tapping with router type spindle no where near enough torque or control to do this unless thread milling. It's nothing of job to do with spiral flute tap in a Cordless drill.
Quote:
Originally Posted by JAZZCNC
Just to clarify...use the machine tooling plate as the bed? The problem I see is they are very expensive? Any links to something appropriate?
Cheers,
Dave
Try these people. I deal with Lincoln branch but believe they have place in WH that will give you a quote and you'll find the price of Machine tooling plate isn't that much more than normal plate. Being Cast plate it's much more stable and being ground it's obviously flat so is worth the extra IME.!Quote:
Originally Posted by biketrialsdave
http://www.ascmetals.com/
Here's Some I prepared earlier.!!
Attachment 16414
Thanks Jazz! Would I get away with 15mm?
I think I need to sit down and consider reducing the size of my machine. I don't envisage (famous last words) doing any large wood projects etc. A bed size of ~400mmx400mm would be more than big enough. Costs would be reduced across the board and I would have more room to manoeuvre around the machine in the shed! The biggest downside I see is that I already have THK linear rails I purchased a few years ago which would need cutting down. Seems a shame to cut them (also, I'm not sure how easy that would be!?).
Yes some times best to sit back and re-think before jumping in.
Ask your self what's the main purpose of the machine going to be.? Be realistic and honest with your self. If it's mostly wood then you don't need go to the trouble of expensive plate.
Your original design sat on nice flat stable surface will work ok for most woods, plastics etc. If it's aluminium then yes the strength and accurecy is needed so the costs rise.
Regards cutting rails then it's always something to avoid really purely on being a waste. The actual cutting is easy. All you need is angle grinder with 1mm thin cutting discs and you'll whiz thru them.
Been said many many times on forum with lots of examples and this is think towards Steel if you want cheap and strong. But slight warning here.!! IME trying to make something from the scrap bin work, like what you found, always ends in a compromise of some kind and in the grand scheme often doesn't save you much money long term so be weary of this appealing route.!! (That said Steel offcuts etc are ok just avoid structures for bases etc)
Agreed. I've always struggled with being a perfectionist and over-designing things!
While I have your very valuable attention, do I need to go with "Heavy" extrusion over "light"?
Booked tomorrow off work so hoping to spend some time on this now I've got some other projects out the way.
I've been looking at stepper drivers too. Think I'm going with the AM882/EM806. It looks like Aliexpress is the place to get them, just need to find a "reputable" seller... On the subject of buyign things, I can't seem to find the bloke in China who was the go to person for ballscrews etc? His eBay shop was something like "linearmotionbearings2008" ???
You could also try Fred at BST http://es.aliexpress.com/store/314742 email him direct for the best price
Chia website is http://stores.ebay.com/linearmotionbearings
Go with BST slightly better quality and great to deal with.
Thanks guys!
Quick question (I'll post an update later)....I'm going for HTD 5mm pitch pulleys (as suggested), what ratio should I start with for x and y axis? Also, I assume I want a larger diameter pulley for more teeth/belt contact as opposed to a smaller one?
If using typical router setup with 10mm pitch screws and steppers then you don't have a ratio so it's 1:1.Quote:
Originally Posted by biketrialsdave
Common pulley size is 20T. Don't go too small because there's not enough teeth engaged. Don't go too large because you increase screw inertia which affects acceleration and power required.
The main reason for using pulleys is to lessen resonance which affects steppers. The abilty to apply a ratio is just a bonus.
One advantage if usng say 10mm pitch is that you could apply 2:1 ratio and increase torque and resolution if ever required. Or go other way and apply ratio if you ever needed more speed but with 10mm pitch you won't anyway thats why 1:1 ratio is often used.
Same with Z axis keep 1:1 ratio but use a 5mm pitch screw for better resolution/torque.
Just the information I was after, all makes perfect sense. I can't thank you enough. Will have to send you something your way when I'm done!
Don't be daft it's what we do and why we are here to help each other.!. . . . just post pics and vids. .Quote:
Originally Posted by biketrialsdave
Still tons of work to go but a few pics of the latest design... I went back and reduced the overall size fairly substantially as I realised I didn't need it. I'm a lot happier with the general direction now.
Attachment 16570Attachment 16571Attachment 16572
Coming together but . . .
the spindle hangs a long way out in front of the gantry - what's happening with the Z axis? Can you show a side view of the Z axis ? Is it profile rails on Z - looks like they are very close together and possible you are not pocketing the ballscrew etc. therefore giving large overhang.
Stiffness drops off significantly as you move out from the gantry so worth getting it more compact if possible.
Dave drop that Linear stage for the Z axis it's massive weak spot on machine.
I'd also look to beef those plates holding motors etc but other than those 2 things it's coming together nice. .:applause:
Edit: didn't see Rout's post same thing really.
One other thing regards the Drop bracket on the Y axis at rear it needs more support from a brace.
I know what you're saying, that is a concern of mine. At the moment I'm using a thk kr33 assembly as I bought it a while back. However, I am planning to use the excess thk linear rail that I'll have left in the future. Perhaps I should design that in now...
No perhaps about it Dave needs to be done. The Z axis is KEY area don't matter how well built rest of machine if Z is shite or weak.!!Quote:
Originally Posted by biketrialsdave
OK, I'll get onto that tomorrow! I assume 2 linear rails with the ballscrew in-between them sitting in a slot to reduce the overall depth? I'm using THK HSR15 carriages for the other axis, I assume these will be OK for the Z too?Quote:
Originally Posted by JAZZCNC
The drop brackets on the rear are 5mm steel at the moment. I can increase this and also add some kind of right angle bracket perhaps.
Lee - How do I delete a reply I made ?
Even if you don't really need them for strength, this is one place where "20" rails and carriages can be useful to give just a bit more clearance between Z plates for the ballscrew and nut. If you have to buy them and don't have something in stock already, this might be something to consider.Quote:
Originally Posted by biketrialsdave
Yes more than enough regards forces etc but has pointed out by neale 20mm can work better regards spacing etc. Personally I use 20mm on all axis for simplicity and hardly any difference in price.Quote:
Originally Posted by biketrialsdave
Yes you need more bracing to stop deflection. 5mm steel isn't really upto to it without being braced.Quote:
Originally Posted by biketrialsdave
I have 15mm rails on Z and they work ok but they use M3 bolts on the rail and carriages which look very small compared to M5 on the 20mm rails on my Y axis. When cutting I can feel vibration across them especially the top ones and for this type of machine I would go with 20mm on Z.
Thanks for all the feedback guys. I think I'll go with Hiwin 20mm for the Z axis. What would be the "minimum" recommended centre distance between the two rails? I want to keep this as small as possible to maximise the effective Y axis length but without compromising rigidity. At the moment my whole Z axis assembly is 130mm wide..
Well generally I always suggest 250mm minimum, obviously this harder to achieve on smaller machine with smaller z assembles...Quote:
Originally Posted by biketrialsdave
.Me
My Z axis plate is 147mm wide and the Z rail centres are only 115mm apart. I did this to maximise Y travel and placed my Y axis bearings pretty much back-to-back.
This works fine for me, but it can give you more stability and less likely to rack if the Y bearings are spread further apart, but you are trading Y travel. If you do spread the Y axis bearings out further, closer to Lee's figure, then I don't think you need to follow suit with the Z rails and can keep them fairly compact.
Attachment 16583
Attachment 16584
Attachment 16585
Your machine looks great, thanks for all the advice.
I've increased the plate width to 170mm now. The z rail centres are 118mm apart at the moment. Do you think the carriages need to be separated more in the z axis? (They are 119mm centres) I'm trying to reduce this length as much as possible in order to reduce the total height of the z axis plate (if that makes sense.
Also, is it worthwhile pocketing the carriages slightly like I've done elsewhere?
Attachment 16587
My rear plates are between 180-200 wide which I find is good balance between strength and space saving for a small machine. On larger machine I will try to make wide has possible to get most ridgidty. Carriage separation I make wide has possible and take the bearings to the edges of plates. Vertical Separation is roughly half the rails length.
Regards the pockets then it depends on the material your using.? If your using Ground cast plate then no because it defeats the object of the plate being ground. If just rolled Plate then yes it needs to be machined because it's often not flat.
If using Ground plate and you want registers for the bearings then Mill some Aluminium blocks or dowels into the plate inline with the edge but slightly overhanging the bearing side then secure with loctite.
Then Machine away the overhanging part to give your reference edge but set cutting tool flush with ground surface so not cut away. In practice it's actually much quicker than buying rolled plate and machining away pockets and more accurate.
Personally I tell people not to bother unless they are sure the whole machine is accurate from base upwards because they make adjustment much harder and in flexible.
In an idle world then yes you'd have them but the reality is that building in your Man cave then in-accurecy is sure fire going to be there so any thing to help adjust error out is welcome.
Also in DIY setting then it's unlikely you'll be chasing Um accurecy and neither will you be stripping it down every other week. So provided you take care when setting up and use good quality fasteners, tighten them up properly and use retainer then you'll not have any troubles and chasing away error will be so much easier.
One potential Gotcha I spotted on your drawing. The holes in the Top and bottom plate which fasten them to the rear plate may interfear with the bolts on the Gantry bearings.? Easy done so check it.!
Some progress. Am I going in the right direction? My only concern is I've had to mill a channel to allow the BF12 mount to not interfere with the plate holding the motor. Where the slot is the thickness of the plate is down to 10mm. However, its quite a narrow channel...
Attachment 16588Attachment 16589Attachment 16590
Split the difference by machining both sides like this.
Attachment 16591
I've been busy all this week so not had time to work on this. However, I've sneakily booked Monday off so I can get some more time on it! Instead of constantly asking questions, I've tried to think of all the main concerns I have at the moment. I would be very greatful if anyone can answer a few!
1. I need to work out how I am going to attach the extrusion (bed) to the aluminium tooling plate. I think I have two options: a) Either drill the tooling plate and insert bolts from the underside which screw into t-nuts in the extrusion. b) Or use aluminium corner brackets on the inside of the extrusion?
2. I think I need to assess how I am connecting the extruded pieces to eachother (for the bed frame). The X axis extrusion is actually comprised of a 45x45 piece and a 45x90 piece ontop of eachother. Unfortunately I cant seem to find a single 45x135 piece? At the moment they are only attached together by the steel end plates. Do I also need some internal corner brackets? I was also wondering if to add some plates bolted to the side of the 2 extrusion pieces?
3. How should I re-inforce the steel end plates? Would it be a case of simply increasing the plate thickness from 5mm? The end plates don't hold the ballscrew bearing houses (these are attached to the extrusion). The plates at the back of the machine do, however, hold the stepper motors.
4. Is it possible/recommended to add a vaccum to the z axis for swarf? Is this only to be used for wood? I am also going to add brackets for a coolant hose.
5. I need to consider draining the coolant. Could this simply be a hole cut into the tooling plate with a pipe which goes through the table beneath into a bucket? My only concern is I don't have a "fall" for the water.
Hopefully those all make sense!
Thanks again,
Dave
#1 Drill the Plate and screw from under side.
#2 Drill thru the upper extrusion and bolt into lower T-slots. Can add some Blocks into the slots to stop them sliding.
#3 If just bracing then 5mm steel will be just about ok, But personally I'd use 9.5(3/8")mm Aluminium so don't have hassle of painting etc plus steel on ali is not good mix.
#4 Can do it but it's difficult and not very effective unless high vacuum. Much better with Blown air and minimal Mist to clear/Lube chips.
#5 Simple holes at one end and angle the machine on bench using feet.
Hmm I may have to re-consider the steel then. The cost of getting all this aluminium machined is going to be a bit eye watering!
On a side note, what would you recommend as the minimum internal fillet radius? Or should I leave internal corners as right angles and assume it will be filleted to whatever when machined?
Not much progress with the machine at the moment... I've gone off on a tangent with designing an Ethernet motion controller for Mach 3 (don't ask how that happened!)
On a side note, I also have a job request up for yet another project I'm currently working on: http://www.mycncuk.com/threads/9328-...Parts-Required
Well the time has finally come... I THINK I'm finally finished! :eagerness:
I've decided to keep the steel end plates. I can get them cut for free (which is a big plus) and I'll paint them to help prevent bi-metallic corrosion.
Attachment 16920Attachment 16921Attachment 16922Attachment 16923
Looking good now.
The X axis stepper motors have the adjustment slots horizontal - will this actually give you much belt length adjustment? Any reason the slots cannot be vertical?
Good spot! I just checked and only have 3mm of belt length adjustment... I'll make the slots vertical!Quote:
Originally Posted by routercnc