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View Full Version : Second CNC table build, here we go again....



Davek0974
26-06-2015, 11:13 AM
Hi all,
I am now starting my second table build, this time a bit bigger at 1250x1250mm cut area, I have also upgraded to a Hypertherm Powermax 45 cutter. My first table is now too small and cannot handle the speeds needed by the PM45.

I have just about decided to go with ballscrews all round, 16 or 20mm lead with anti-backlash nuts, motion is on HiWin 15mm rails and carriages with scrapers and wipers fitted.

Here's a couple of sketches of the gantry ends, just ideas at present but would seem to fit well..
http://www.mycncuk.com/attachment.php?attachmentid=15629&stc=1http://www.mycncuk.com/attachment.php?attachmentid=15630&stc=1

The main table will be 50x50x5mm box section steel, fully welded, the motion supports will be bolted on so I can shim them up and avoid welding warp etc.

The top rails or Y-axis will be above the bed so I can slide a bigger sheet in if wanted, this will also keep the tracks and screws above the pierce splatter.

Drive is with my existing Nema23 3.1Nm steppers, if that does not play nicely then I can upgrade easily to Nema23 servos.

I am aiming to get a speed range of 100mm to 9000mm/min so I can use the full range of the PM45 without messing around.

Feel free to offer any advice :)

m_c
26-06-2015, 12:04 PM
A plasma table has reappeared on my potential project list, and I do have a couple thoughts about mitigating dust.
.
I wonder if mounting the rails on the underside of the side frame would help dust from settling onto the rails, then have the screw mounted below the rails/gantry/carriage? On the inside edge you can then have a bit plate hanging straight down to stop dust coming of the cutting area, and arrange a couple brush strips on the outside to minimise dust blowing around and in.

Davek0974
26-06-2015, 02:42 PM
Yes, that could be a good idea, i'll sketch it up.

it would mean a small loss of Y travel or making the table a little bigger as the carriages will hit the support legs, no real issue there though.

Davek0974
26-06-2015, 03:00 PM
A bit like this?
http://www.mycncuk.com/attachment.php?attachmentid=15632&stc=1

Might be better, Not totally convinced though, the rail is now facing the pierce splatter zone.

Davek0974
27-06-2015, 12:15 AM
I have people advising I go with rack and pinion and I have people saying go with ballscrew - both with good reasons for and against.

How do i decide what method to go with???

Lee Roberts
27-06-2015, 12:23 AM
All the ones I've seen have been RP, share their thoughts with us, I would have thought ballscrews would be abit overkill given it's contact free cutting? I don't know but RP just seems like it would be a better fit, I guess it could get pricy if you got really good stuff but dose a plasma based machine need that kind of acuracy ?

.Me

m_c
27-06-2015, 12:32 AM
Just done a rough sketch of what I was thinking.
.
If you wanted to add support to the side rail, you could use a wider box section, and either move the rail nearer the edge and have the legs/supports mounted on the opposite edge, or use a double box section, with the rail on one and legs/support on the other.
.
Dust could be mostly eliminated by adding a couple brush strips, or suitable strips of metal with minimal gap either side of the rail to further reduce the ability of dust to settle onto rails.
.
And having just looked at my sketch and thought about how to protect the screw from dust, mounting it at the side of the rail so you only have one 'area' you need to minimise dust ingress might be an option.

m_c
27-06-2015, 12:41 AM
Regarding the R&P v Ballscrew, both have their pros and cons.
As Lee mentions, a plasma doesn't really need the accuracy of ballscrews, but the biggest drawback is coming up with a design to keep dust out, as I'm sure you're well aware, plasma dust is pretty abrasive and will quickly kill ballscrews.
However R&P on the other hand, provided it's designed well enough, will be relatively unaffected by dust, but you lose accuracy, and have the issue of dealing with wear, especially uneven wear which will be challenging to adjust out to minimise backlash while avoiding binding. Off course the solution to this could be simply changing the racks when worn, building in some form of spring loading of the R&P, or using anti-backlash pinions.
.
Both options have pros and cons, both will work, and both can be designed to have long service lifes. As with most things, it comes down to implementation.

Davek0974
27-06-2015, 09:54 AM
Hmm, thanks, I have doubts now, not good;)

I wanted accuracy for small part cutting in thinner materials, so high speed without wiggle on the torch.

Putting the screw and rail under the beam is ok but is filling the gap I wanted left clear for large sheet entry, likely only a few inches clearance left and the covers will be at risk of taking a battering from sheets.

I see machines like PlasmaCam (which I think have a good name?) running simple plate/skate runners but they do use servo drive, they seem to work ok. Other production builds like Torchmate and PrecisionPlasma use various other simple systems ranging from belt to R&P. All mostly with not much regard paid to keeping the muck off of transport parts.

But there again, none of them using ballscrew either!

I'm not sure where this project is going now, back to stage 1.

m_c
27-06-2015, 11:59 AM
Compromise.
Or just make a water table so you don't have to worry about dust :-)
.
If you do go for ballscrews, then you are going to have to ensure they're well protected, whereas R&P doesn't have to be. Yes you'll get backlash using R&P, but you need to remember that Plasma is not that accurate a method, so even 0.5mm of play isn't going to have much effect on most items.
.
Personally, I'd be designing the table so it sits above the side rails, that way the only thing in the way during loading would be the gantry. You then only have to handle dust from above, instead of spray back/dust coming up the way as well. You will still get some dust coming up the way, but hopefully a lot less.
.
Have you had a look at the swift-cut machines for some ideas?

Davek0974
27-06-2015, 12:25 PM
Thanks,
If i had the cash i would buy that 1250 table tomorrow! It is exactly where i want to be, has the full cut speed range I want, pity the pictures are not clearer ;)

I see that have R&P drive but use V-Rails all round, Can't seem to find that stuff?

I like the below-table idea too for the transport, places more stress on the gantry support but obviously works.

The motors are not much above what i have - they use 4Nm and I have 3.1Nm, both hybrid so thats a good sign.

Now, can i build that table with Linear rail or does anyone know where I can source the V-rails????

m_c
27-06-2015, 12:45 PM
Google has the answer - http://www.linearonline.co.uk/acatalog/Vee_Bearings.html

(although it did take a few attempts to find it!)

m_c
27-06-2015, 12:46 PM
Oh, and their youtube videos give a little bit more detail if you pause at the correct moment ;)

Davek0974
27-06-2015, 01:24 PM
Thats the stuff, thanks

Now i have even more options;)

Trouble is, what way to proceed???

Vee rails with R&P drive
Linear rails with R&P
Linear rails with ballscrews
Flat plate & skates with R&P
Other...

F1transportationserv
27-06-2015, 01:30 PM
Thats the stuff, thanks

Now i have even more options;)

Trouble is, what way to proceed???

Vee rails with R&P drive
Linear rails with R&P
Linear rails with ballscrews
Flat plate & skates with R&P
Other...

sorry about this but what are the advantages and disadvantages of these different types??

Davek0974
27-06-2015, 01:51 PM
Vee rails with R&P drive - seems to be pretty common, reasonably easy to build, precision depends on rail mounting, backlash in rack, adjustment of rollers
Linear rails with R&P - very accurate transport, precision depends on backlash again
Linear rails with ballscrews - highest precision, highest cost, hardest build
Flat plate & skates with R&P - a very common method, precision depends on quality of plate used and how its mounted, easy to replace, lowest cost, needs to be kept clean from grit etc

F1transportationserv
27-06-2015, 01:54 PM
Vee rails with R&P drive - seems to be pretty common, reasonably easy to build, precision depends on rail mounting, backlash in rack, adjustment of rollers
Linear rails with R&P - very accurate transport, precision depends on backlash again
Linear rails with ballscrews - highest precision, highest cost, hardest build
Flat plate & skates with R&P - a very common method, precision depends on quality of plate used and how its mounted, easy to replace, lowest cost, needs to be kept clean from grit etc

What is backlash?
And when you say highest cost re ballscrews how much are we talking??

Davek0974
27-06-2015, 02:03 PM
Backlash is the slop or lost motion you can get with rack and pinion drive, normally gears are run with a small clearance between the teeth, when used in motion control you take all the clearance out by spring-loading the pinion against the rack so there is no clearance at all, this works well until the pinion or rack wears and backlash comes back. This will cause steps in the cut finish where the direction changes or circles to come out not quite round etc, basically its a bad thing.

Ballscrews can have anti-backlash nuts fitted which are two nuts with tension between them.

Cost for a 1.4m 20mm screw with end bearings and nut in the UK is about 350-400, length is also limited.

m_c
27-06-2015, 02:39 PM
You do realise you can get anti-backlash gears?
Essentailly two gears mounted together and spring loaded out of alignment. You could do something similar using two gears mounted apart with a spring loaded belt between them, however you have to remember high acceleration forces could overcome the anti-backlash spring and allow backlash to develop briefly until the forces reduce again.
Then you don't get prefect motion with a straight cut rack, as you get a slight notchyness as each tooth engages/disengages with a resultant increase/ (there is a proper term for this, but it's essentially what makes straight cut gearboxes so noisy), but for a plasma cutter it's not really an issue. If you're really concerned, you could use a helical rack, but I wouldn't worry about it.

Davek0974
27-06-2015, 03:09 PM
Thanks, i have read of some innovative ideas re backlash removal.

Without sounding rude to anyone here, I have just had a reply from a very well respected heavy-duty expert in plasma cutting process and machinery via email, his examples of work are what i would like to see and are well known.

Due to my budget constraints, it is felt that I should be looking at V-Rails and rack and pinion, or, ground, flat plate and skates with rack and pinion for my build.

This makes a lot of sense and is in line with 90% of the commercial production built machines available - no point in re-inventing the wheel.

I will price up and sketch out a v-rail build.

There is another option for drive - open-ended toothed belt with an omega loop drive - this is simply a length of timing belt stretched tightly from front to back with the motor on the gantry and the belt wrapped in a loop over the sprocket. It is supposed to be a very good system as long as steel corded belt is used and it's pulled tight.

My existing build uses a belt but its looped which doubles the stretch possibility and its too small at only 10mm wide, also due to the poor design at the shafts, i cannot stretch it very tightly.

Its too easy to forget things like a budget at times :(

Need to get back on track now I think ;)

Davek0974
27-06-2015, 04:01 PM
In summary -

1 - Go for the belt option again this time, but get it right! I think belts, designed properly would outlast a rack, easy to replace too.
2 - Using Linear rails is a possibility, pretty much same cost as V-rail but easier.
3 - This time I will go for two motors on the Y-axis, this will remove having a long cross-shaft in the gantry and the resulting torque twist it suffers, at a risk of racking the gantry, but plenty of builds have two slaved motors and work ok.
4 - Keep the rails above the table, with a gap under for sliding in bigger sheets. Having the rails up high means a low gantry - good for stability etc
5 - Stick with the motors/drives I have, they are Nema23 size so easy to upgrade to Nema23 servos later on if needed.

m_c
27-06-2015, 06:56 PM
Out of your list, personally I'd say go for two servos now for the twinned axis, rather than buying an extra stepper/drive.
Servos are what is going to make the biggest difference in achieving higher speeds while still maintaining accuracy.

Davek0974
27-06-2015, 07:05 PM
Hmm, would be an idea but i already have the spare motor and drive :)

I bought an extra last time round.

Davek0974
28-06-2015, 04:21 PM
Torque and RPM...


Is it best to use a small drive pinion on the rack with higher motor rpm or larger pinion with lower motor rpm??


A 20t pinion will move 62.83mm/rev and at 3:1 reduction I will need 429.73 motor rpm for 9000mm/min travel.


A 32t pinion will move 100.53mm/rev and at 3:1 reduction I will need 301.58 motor rpm for the same speed.


I am fairly certain a larger pinion meshes better than a smaller one, but what size would be best considering my 3.1Nm motors.


My existing table is belt drive but works out at 100mm/rev travel and 300 motor rpm for 9000mm/min speed. When i did my high speed test it was running at 450 motor rpm so I know they can reach at least that.


I have a heavier gantry on the bigger machine, but also twice the motor power as i'm using two slaved motors.


Any views guys?

m_c
28-06-2015, 11:58 PM
Smaller will give you better acceleration, and bigger higher speed.
If you know what torque you'll have, and the weight of your gantry, then you can work out your (theoretical) max acceleration. As I'm sure you'll be aware, there's no use having a high top speed if you don't have the acceleration to make use of it.

Davek0974
29-06-2015, 10:56 AM
I'm now looking at direct drive, a 17t pinion will give me 53.39mm of travel so I will need 168rpm to reach my top speed of 9000mm/min.

The gantry will weigh at a guesstimate 30kg and will have two 3.1Nm motors, direct driving it.

This might work better as it keeps the motor rpm way down in the high torque area.

Any chance you could illustrate the maths needed for the acceleration estimates???

Robin Hewitt
29-06-2015, 12:01 PM
I'm now looking at direct drive, a 17t pinion will give me 53.39mm of travel so I will need 168rpm to reach my top speed of 9000mm/min.

The gantry will weigh at a guesstimate 30kg and will have two 3.1Nm motors, direct driving it.

This might work better as it keeps the motor rpm way down in the high torque area.

Any chance you could illustrate the maths needed for the acceleration estimates???

2pi/.05339 gives you a 117.68 advantage over a 1m pulley

So 2 x 3.1 x 117.68 = 730N

So a 30kg gantry will accelerate at 730/30 = 24 m/s/s about 2.4G on a good day with a following wind.

Assuming I haven't totally cocked up, someone should check this :subdued:

Davek0974
29-06-2015, 12:44 PM
Thanks, if that is indeed correct then I have slightly more acceleration than needed, even allowing lavishly for other losses:)

I have read that plasma cutting only needs around 0.2 to 0.5G for quality so it does sound encouraging.

Robin Hewitt
29-06-2015, 01:44 PM
So what is the bending force on your gantry from accelerating the Z axis components?
Suppose that is 3kg of motor, slide, torch, screws and stuff. Wild over estimate.
We know that 1kg force will accelerate 1kg mass at 1G because that is what happens when you drop it.
So to accelerate 3Kg mass at 0.5G requires a force of 1.5kgf
Why do you need 30kg of gantry to withstand 1.5kg in X and Y?
Perhaps it is the 3kg in Z you are worrying about?
Perhaps you should take a few gantry length bars, support them at either end, put a weight in the middle and see how far they actually bend.
Maybe 30kg is not necessary after all?
Maybe 30kg is only there to accelerate the 27kg it contributes all by itself?

Davek0974
29-06-2015, 02:32 PM
Ideally, it needs a structure that resists torsion moments - this is where my current machine fails - the gantry is a length of 44x44 structural aluminium which is ok in the beam but poor in tension as the centre box is only 18mmx18mm.

The torch and axis are not balanced and when accelerating it twists one way and the opposite on decelerating - causing ripples in the cuts.

What is ideal is a simple, light structure that ca withstand torsion or twist as well as support 3-4kg in the centre.

What that is, I have no idea, most machines just use box section because it's there I guess.

It needs a thick enough wall section to take 5-6mm screws firmly so I guess 5-6mm thick.

Without getting a structural engineer on the job, what stock item would be best suited here?

Robin Hewitt
29-06-2015, 03:34 PM
When I started making one I got a piece of 4"x4"x10g aluminium box and made the gantry as the long axis. Across the front I bolted a linear rail, using the bolt from behind kind so the dust could not get inside the block via the bolt holes. I used 4 1/2" bolts and spacers so I could bolt everything from behind without crushing the box. I cut the box ends dead square. I inserted 1/2" square plates with 8mm steel nut inserts dead centre from either end. The gantry end plates had 4" x 4" recesses and an 8mm bolt hole. When I tightened that sucker up it became incredibly rigid. The gantry end plates got double round linear blocks running on 30mm round linear rails which held the assembly in place simply by being bloody heavy. I liked my design but it all went horribly wrong because the 5mm pulleys were such a crap fit on the 5mm belt. I lost heart.

Robin Hewitt
29-06-2015, 03:49 PM
I tried to add a picture but failed miserably...

The message you have entered is too short. Please lengthen your message to at least 10 characters.

http://www.mycncuk.com/attachment.php?attachmentid=15642&stc=1

Davek0974
29-06-2015, 04:45 PM
That looks ok, the 5mm belt is very light, more suited to 3d printers i think.

What happened in the end??

JAZZCNC
29-06-2015, 05:56 PM
Dave I'd stick with belt drive on Linear bearings and just protect it good. V-pulleys are a pain in the arse on routers and with Plasma dust etc I'd think they would be a just has big a mare.

Belt with give you best of all worlds. Higher resolution, Higher efficiency, less maintenance, Smoother action. R&P is ok and works but more to building it to do properly and it becomes expensive. Belts will be cheaper and easier to replace if damaged.!

If was using a Ballscrew (which I probably wouldn't) I'd put it down the middle and run it thru a tube tunnel with slit in bottom. I'd use profiled linear bearings on underside like you have shown.!

Davek0974
29-06-2015, 07:54 PM
Thanks, I have opted to try a direct drive version now, linear guides, rack and pinion with 15T pinion.

Part of the issue I have now is caused by the belts so I don't want to add that back into the mix.

I have also got some larger motors coming - 4Nm with DSP drivers and a higher voltage PSU, that all means i can build more of the new table before removing bits from the old one.

Ballscrews are out for the present.

If the direct drive fails then an easy upgrade to belt reduction boxes is made. Rack and pinion seems to be the industry standard, a few are direct drive, we will see what happens I think.

The gantry is looking like 50x75x3mm steel, with a strengthening strip inside where the rail and rack screws on.

Aluminium was looked at, and is lighter, but stiffness suffers as a result and I want it rigid this time ;)

Davek0974
29-06-2015, 10:20 PM
Frame bracing???

First frame idea, overall size is around 1500mm x 1500mm x 1000mm to bed level.

Should i be looking at bracing or gussets anywhere???

http://www.mycncuk.com/attachment.php?attachmentid=15647&stc=1

Robin Hewitt
30-06-2015, 01:26 AM
Aluminium was looked at, and is lighter, but stiffness suffers as a result and I want it rigid this time ;)

Aluminium has the huge advantage that it is usually quite straight. Steel box section can be quite horrendously bent, as far as CNC building goes, but still well within tolerance. Even slightly bent can make it hard to align a rack. I agree with Jazz, belt for a plasma cutter.

Davek0974
30-06-2015, 08:12 AM
I find the thinner wall box to be pretty straight usually, especially down in the 2-3mm section.

I have belts on my existing table and they cause issues, not solely down to the belts but as 90+% of commercial builds use rack, I am going that way first this time.

JAZZCNC
30-06-2015, 08:23 AM
Part of the issue I have now is caused by the belts so I don't want to add that back into the mix.

Very much doubt the Belts caused the issue.!! Belts are super accurate and very close to ballscrews for efficeincy so if you had any issues they probably came from how it was designed or put together rather than the belts.

One thing I do know is that an old mate of mine builds Plasma Machines and his first test machine used Direct drive R&P and didn't work very well. Low resolution and low efficeincy needing large motors, think it used 8Nm or 12Nm Nema34.?
Anyway it was crap.! So then went to sprung loaded into rack with 3:1 ratio using timing belts with Nema 34 motors. This worked but he couldn't reach high feeds as the ratio and slower spinning motors worked against him. He was also having issues with R&P binding etc at higher feeds.

Last machine I seen was using gearbox's and what looked like Nema23 motors.!

Davek0974
30-06-2015, 09:11 AM
Reality check time...


How do you decide what table is the right one?


I know the 2'x2' i have now is too small, it works ok for most of my jobs but i can only cut with the plate square on the bed so no quick twisting it to get another cut out etc.


I can physically fit the 4'x4' (1250x1250) into my shop, thats ok.


I cannot lift a sheet of steel that size, have little possibility of lifting gear etc. as its only a double garage. A sheet of 3mm which is my most popular is about 36kg so only just about ok but the other one i use a fair bit of is 4mm and would be 50kg, no way i can lift that.


Would it be better to go 3'x3' instead?


Cost difference in build is minimal, but what makes sense - having the real estate and not using it or saving floor space etc??

Davek0974
30-06-2015, 04:28 PM
View from front looking at current gantry design.

http://www.mycncuk.com/attachment.php?attachmentid=15648&stc=1

This is for the open-bed style table with the longer gantry arms. The linear guides can be easily covered from the top.

The gantry beam will pass through the side support plates and be welded up and gusseted inside with some nicely cut parts, the outer face of the vertical supports can be strengthened with a couple of ribs to resist side-sway.

Mounting the support rails is harder on the open bed style though, I was going to bolt them on but this style really wants a box frame at bed level.

Robin Hewitt
30-06-2015, 05:01 PM
Every action has an equal and opposite reaction. If you apply 300N accelerating force to the cutting head, the gantry will push sideways with 300N.

Davek0974
30-06-2015, 06:01 PM
Yes I can remember that from school ;)

But those 300N can be countered by applying gusset plates and ribs where needed, most tend to throw a slab of alu at it but that might not be totally needed i think.

Robin Hewitt
01-07-2015, 01:10 AM
Or you could move the rails up closer to the gantry they support. The gantry only needs to be 2" above the bed, doesn't it?

Davek0974
01-07-2015, 07:24 AM
In theory yes but my Z-axis needs a bit of clearance as its a pretty heavy built unit. I am trunk not to lift the rails - that was design idea one, but it means you do not have a clear open bed - you have rails either side which makes loading harder especially if juggling a bigger sheet on your own.

My high-rail option is sketched out earlier, it had no risers at all on the gantry - the beam was right down on the carriages.
http://www.mycncuk.com/attachment.php?attachmentid=15649&stc=1

Davek0974
01-07-2015, 09:46 AM
Or you could move the rails up closer to the gantry they support. The gantry only needs to be 2" above the bed, doesn't it?

To add scale to my poor sketches, the bottom of the gantry beam is 140mm above the bed surface, not too bad??

Davek0974
01-07-2015, 04:58 PM
Ok, stuff is on order.

The final result is 50x50x2 for the gantry beam and frame legs, 50x80x2 for the motion support/bed frame.

The final capacity is going to be the half sheet 1250x1250 / 4'x4' size.

Direct drive rack and pinion with a view to change to belt reduction drive or even ballscrews later on.

JAZZCNC
02-07-2015, 09:02 AM
Good man thats what like to see no messing around.:thumsup:

Davek0974
02-07-2015, 10:02 PM
Good man thats what like to see no messing around.:thumsup:

Oh I can mess around, to a point, then I just dive in and go for it.

http://www.mycncuk.com/attachment.php?attachmentid=15652&stc=1
The top box is the gantry beam, 50x50, the motor sits down the bottom on a plate that swivels on the point shown. It will be spring loaded but restricted so it cannot jump out of the rack and chew it up.

A couple of 75mm gusset plates under the beam on the inside and a rib or two on the outside should stiffen things up a fair bit.

Motors, controllers and rack arrived today :)

Davek0974
04-07-2015, 05:45 PM
Steel came Friday, nice and straight and after a few stress tests (me standing in the middle of a 7m long beam) I realised just how rigid this stuff is http://www.practicalmachinist.com/smile.gif

Construction question:

I was thinking of welding on some 100x50x10mm pads under each corner of the motion frame and similar to the top of each leg, then bolting the two parts (welded motion frame/bed and welded leg assembly) together, just to give the opportunity to shim out any variation in leg length etc. Good idea, bad or not worth it???

Next, the bed/motion frame - should I attempt to weld it up as one piece, or weld closing plates flush into the ends of the cross-members, drill/tap and then bolt together?? If yes then how to weld the closer plates in - only way i can think is to heavily bevel the plates then insert and fill bevel with weld tying into the tube sides??? Plates would be 46x76x10mm.

http://www.mycncuk.com/attachment.php?attachmentid=15664&stc=1

Davek0974
11-07-2015, 07:14 PM
Got the metal cut today...
http://www.mycncuk.com/attachment.php?attachmentid=15690&stc=1
Ends squared up and deburred, also cut,drilled and tapped the mount plates for the motion frame and the insert plates for the cross-beams. All ready for a welding session now. http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif

I'm fitting castors and screw-down feet so I can move it about and level it up when assembled.

While I'm gathering info, extraction....

On my little table I built an air-box that sits along the front of the table between the now unused water tray and the slats...
http://www.plasmaspider.com/download/file.php?id=36632&t=1 (http://www.plasmaspider.com/download/file.php?id=36632&mode=view)

In the front i cut a slot with an area bigger than the pipe cross-section and also slightly tapered towards the middle in an effort to even out the air flow. It works well as long as the unused parts of the table are covered - i get no muck in the shop at all.

It's connected to this radial blower...
http://www.plasmaspider.com/download/file.php?id=36631&t=1 (http://www.plasmaspider.com/download/file.php?id=36631&mode=view)


I know I can get more out of it by dumping the corrugated pipe and fitting solid duct but it's not going to do a table with an area four times as big.

I don't have any spare power capacity so simply sticking a big-ass blower in there won't do it, need to get smart here. I could maybe run two of these blowers, they are pretty cheap to buy and with external motors they are immune to metallic hot muck.

I had thought about a zoned system - a four zone would work ok with the same blower. Question is, how would I do it???

Any smart ideas on extract??

Don't want water - its only half as effective and makes the machinery in the shop rust.

Davek0974
12-07-2015, 07:06 PM
Welded the end plates into the cross-beams...
http://www.plasmaspider.com/download/file.php?id=36647&t=1 (http://www.plasmaspider.com/download/file.php?id=36647&mode=view)


The leg joint plates onto the main beams...
http://www.plasmaspider.com/download/file.php?id=36648&t=1 (http://www.plasmaspider.com/download/file.php?id=36648&mode=view)


And the foot plates onto the legs...
http://www.plasmaspider.com/download/file.php?id=36649&t=1 (http://www.plasmaspider.com/download/file.php?id=36649&mode=view)


Fairly confident in the welds, did a quick destruction test on scrap first, nice and hot concentrating on the thicker parts and washing into the 2mm tube. Joints are ground flush now. Casters will be added soon, to the side of the feet, the feet can be screwed down to lift it off the wheels.

Davek0974
18-07-2015, 11:44 AM
Got two welded side frames - standing side by side, there is no visible warp, I'm pretty chuffed with that as it was a concern. I levelled the frames between the bench and sawhorse using a spirit level http://www.plasmaspider.com/images/smilies/icon_e_wink.gif wedged them up, shimmed the bolting points between frame and top beams then tacked the outer and inner faces, seam welded the lower and upper faces fully, then seam welded the outer face, inner face is left tacked as there is a cross-bream to go in.
http://www.plasmaspider.com/download/file.php?id=36759&t=1 (http://www.plasmaspider.com/download/file.php?id=36759&mode=view)



Its a bit bigger than my existing one http://www.plasmaspider.com/images/smilies/icon_eek.gif http://www.plasmaspider.com/images/smilies/icon_eek.gif Looks good though.
http://www.plasmaspider.com/download/file.php?id=36760&t=1 (http://www.plasmaspider.com/download/file.php?id=36760&mode=view)


Upon assembly i realised i could not weld in the lower cross-beams as planned, I'm not really up to vertical mig yet, cannot get it on the bench, and the underside welds could not be done at all. Answer - make some more bolt fitments out of 10x50mm bar, weld them on and bolt the lower cross-beams in, this will make disassembly easy too.

Robin Hewitt
18-07-2015, 12:05 PM
Good welding, you deserve to succeed :thumsup:

D.C.
19-07-2015, 12:01 AM
how to weld the closer plates in - only way i can think is to heavily bevel the plates then insert and fill bevel with weld tying into the tube sides?

If you are trying to weld thin steel and thick steel together you need to run the weld pool down the thick piece of metal and then quickly move across to the thin metal, back to the thick metal, down a bit across just enough, back again to the thick piece, down again etc etc

If you try running a bead equally down the joint, the thin metal will blow out or the thick metal will not get proper penetration.

A CNC machine is never going to generate enough force to cause a properly formed weld to fail, it will probably never get above 1% of the failure point. But if you decide to do nice 'stack of pennies' welds that would make an instructor happy you will be introducing a lot of heat into your frame that will cause stress and distortion over time.

Clamp it, tac it, clean it, back weld an inch at a time and drink lots tea so the heat doesn't build up.

This is an awesome video for demonstrating welding heat distortion, well worth 10 minutes.



http://www.youtube.com/watch?v=0pf-qQDslhU

Davek0974
19-07-2015, 09:31 AM
Amazing, thanks.

Is it the same for Mig though which is a lot faster, I guess it would be???
I would love to be able to Tig like that ;)

Davek0974
19-07-2015, 09:35 AM
If you are trying to weld thin steel and thick steel together you need to run the weld pool down the thick piece of metal and then quickly move across to the thin metal, back to the thick metal, down a bit across just enough, back again to the thick piece, down again etc etc



Exactly how i do it, always bias towards the thicker part and set power for the upper end of the thinner part.

I had to cut a 10mm plate off the end of a 50x50x2mm tube yesterday as i welded it on 90deg out :thumbdown: and i was impressed with the penetration i was getting, took some cutting to split the joint.

Davek0974
19-07-2015, 07:55 PM
Had a quick mess about with the Tig, i was semi impressed but seems a lot hotter, probably moving too slow?
http://www.plasmaspider.com/download/file.php?id=36791&t=1 (http://www.plasmaspider.com/download/file.php?id=36791&mode=view)

I'll stick with the Mig http://www.plasmaspider.com/images/smilies/icon_e_smile.gif


Got the lower cross-beams fitted, then after a few tests it seems that a good way to fix my spacer/support strip was to use good ole pop-rivets, worked nicely. Also managed to get one of the racks fitted.
http://www.plasmaspider.com/download/file.php?id=36792&t=1 (http://www.plasmaspider.com/download/file.php?id=36792&mode=view)

Davek0974
22-07-2015, 08:06 PM
Ok, linear rail came today http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif

Using a taught line to check my beams, I have a slight bow in both sides, as you look at the table they would bow towards each other at the centre, the amount is about 1 to 1.5mm on each side so thats pretty bad and would give me a 3mm variation from centre of motion to either end.

Question is - how best to tackle this????

Clive S
22-07-2015, 09:02 PM
Ok, linear rail came today http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif

Using a taught line to check my beams, I have a slight bow in both sides, as you look at the table they would bow towards each other at the centre, the amount is about 1 to 1.5mm on each side so thats pretty bad and would give me a 3mm variation from centre of motion to either end.

Question is - how best to tackle this????


You can always use the epoxy method that is quite often used on here.

Davek0974
22-07-2015, 09:14 PM
I had thought of that but seems a possible method may be to fit the rails as-is and then fit a stretcher bar under the slats to force the beams out a little, 3mm should be easy.

Could even use the middle slat support possibly, not got that far yet though.

Davek0974
25-07-2015, 07:54 PM
Got the Y axis motion fitted and the gantry supports tacked up.

http://www.plasmaspider.com/download/file.php?id=36922&t=1 (http://www.plasmaspider.com/download/file.php?id=36922&mode=view)

http://www.plasmaspider.com/download/file.php?id=36923&t=1 (http://www.plasmaspider.com/download/file.php?id=36923&mode=view)


Even without the beam fitted the side supports are very rigid, most encouraging.

Davek0974
26-07-2015, 03:07 PM
Got the gantry supports welded up - very little distortion which was great, impressed myself with that one http://www.plasmaspider.com/images/smilies/icon_e_wink.gif

One thing I can now say is, that gantry beam is damn rigid, i put a dial indicator between the gantry and side beam and it's practically a solid object http://www.plasmaspider.com/images/smilies/icon_eek.gif http://www.plasmaspider.com/images/smilies/icon_eek.gif

http://www.plasmaspider.com/download/file.php?id=36926&t=1 (http://www.plasmaspider.com/download/file.php?id=36926&mode=view)


http://www.plasmaspider.com/download/file.php?id=36927&t=1 (http://www.plasmaspider.com/download/file.php?id=36927&mode=view)


http://www.plasmaspider.com/download/file.php?id=36928&t=1 (http://www.plasmaspider.com/download/file.php?id=36928&mode=view)


Also got the X axis and THC mount welded up, came out nicely.

One question - I had to move the x motor rearwards, placing the rack on the back face of the beam - no biggy but, I had forgotten the rack bolts go across the rack face so are now screwing into nothing. Should i fit some short support angles like 10x20x4mm 100mm long and welded to the beam, and then mount the rack to them????

Or something better???

njhussey
27-07-2015, 10:25 AM
One question - I had to move the x motor rearwards, placing the rack on the back face of the beam - no biggy but, I had forgotten the rack bolts go across the rack face so are now screwing into nothing. Should i fit some short support angles like 10x20x4mm 100mm long and welded to the beam, and then mount the rack to them????

Or something better???

Looking good Dave, I presume that you mean Z axis motor not X? I'm not sure how much force the stepper will exert on the rack but I would think a long piece of angle tacked on to the back beam would be ok to mount the rack, just have to be careful that you don't distort the beam welding it but you seem to have done a good job of not distorting things so far :applouse:

Davek0974
27-07-2015, 11:44 AM
No definitely X-axis, the Z-axis is mounted on the THC unit, X-axis on the carriage.

I have opted to try the 3M VHB double sided tape for this - no distortion and easy to fit, seems to be getting good remarks on other builds.

njhussey
27-07-2015, 12:07 PM
Hah...i meant Y axis not Z but I guess you call it the X....confuses me everytime!!!!

Davek0974
27-07-2015, 12:55 PM
Ha :)

Depends on the table i guess, my one is x=left/right, y=front/back, z=torch

Davek0974
27-07-2015, 08:55 PM
Reclaiming some motion distance....


After building the base frame and motion, I decided to build a new floating head using Hiwin and a single carriage - pretty much a standard design. However, this moved my torch 30mm closer to the front of the table than I had planned which left very little over-travel on a full 1250mm sheet - not good.

The first pic is a cross-section of the average torch mount with the Hiwin at the bottom and the circle being the torch clamp.

http://www.plasmaspider.com/download/file.php?id=36943&t=1 (http://www.plasmaspider.com/download/file.php?id=36943&mode=view)


Now, as I am using wide/stable Hiwin rail, could this idea work?? It regains a valuable 30mm of spare travel on the Y axis.

http://www.plasmaspider.com/download/file.php?id=36944&t=1 (http://www.plasmaspider.com/download/file.php?id=36944&mode=view)

Davek0974
28-07-2015, 04:33 PM
Here we go, down to 27mm distance now, thats a little less than my existing unit http://www.plasmaspider.com/images/smilies/icon_e_smile.gif

http://www.plasmaspider.com/download/file.php?id=36960&t=1 (http://www.plasmaspider.com/download/file.php?id=36960&mode=view)


The side effect is that to get the torch back on centre, I have to shift the Hiwin carriage to the left a fair bit, luckily this will be over the machine side beams and will not affect anything at all - perfect http://www.plasmaspider.com/images/smilies/icon_e_smile.gif

njhussey
28-07-2015, 05:55 PM
That should be fine Dave I would have thought, it's not carrying any weight and ther are no forces acting on it after all. For complete ease of maintenance could you not turn the torch mount through 90 (gap facing the front) and use one of the fixing bolts (now coming in from the right and tightening into tapped holes in the 5mm steel plate) to tighten the clamp? I'm not sure from the drawing if there's ease of access to get to the torch mount?

Davek0974
28-07-2015, 07:35 PM
Yes, but then there would be a risk of losing the torch alignment when the torch clamp is released to remove the torch. Hopefully with the clamp mounted firmly from the base, it will stay fixed once aligned.

Davek0974
30-07-2015, 08:22 PM
Got the floating head mount fitted to the Z-axis, probably work better when i fit a means to stop the carriage and torch falling off the bottom http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif

http://www.plasmaspider.com/download/file.php?id=36980&t=1 (http://www.plasmaspider.com/download/file.php?id=36980&mode=view)

njhussey
31-07-2015, 10:35 AM
Dave, I'm probably being a bit thick....but how are you moving your Z axis up and down? From what I can see you've got your Z stepper mounted on the profile behind the fixed Z front plate? Is there something on the bolttom of your Z front plate that connects to the stepper behind the plate?

Davek0974
31-07-2015, 10:40 AM
No, the round object sticking out of the top is the coupling for the stepper, it's just not fitted yet :)

It means i can move the z up and down by hand easily.

Inside its a standard screw type affair.

njhussey
31-07-2015, 10:49 AM
No, the round object sticking out of the top is the coupling for the stepper, it's just not fitted yet :)

It means i can move the z up and down by hand easily.

Inside its a standard screw type affair.

OK I'm still being thick :stupid:....but I'm still not seeing how you're connecting your stepper/screw to the front of the Z axis, your torch holder?


http://www.plasmaspider.com/download/file.php?id=36960&t=1 (http://www.plasmaspider.com/download/file.php?id=36960&mode=view)

That's the front of your Z, how's that connected to your stepper/screw or whatever??

Davek0974
31-07-2015, 11:09 AM
Ok, looking at the diagram you quoted, the long 5mm slab at the base is the large flat vertical plate shown in my picture :)

The Hiwin rail/block in diagram is shown on the bottom left of my picture - the block is not fitted yet.

njhussey
31-07-2015, 11:29 AM
I get that Dave, but not how the block and torch mount connect to the stepper?

Davek0974
31-07-2015, 11:35 AM
Ah, right.

Behind the plate lies one of these -
http://www.ebay.co.uk/itm/NEMA23-75mm-Z-Axis-CHROME-Proxxon-CNC-Kit-/311406367336?pt=LH_DefaultDomain_3&hash=item4881441268

Its a standard Z-axis unit, screw drive, 2mm pitch, 75mm travel - the motor sits on top and drives the screw direct, the middle block is fixed to the gantry carriage and the upper/lower blocks move with the motor/screw.

Works well.

njhussey
31-07-2015, 11:48 AM
Ah ok, so why do you need the rail and block on the plate that's moving up and down? Fine adjustment? Surely mounting the torch holder on the bottom of the plate will be enough?

Davek0974
31-07-2015, 12:56 PM
Ah ok, so why do you need the rail and block on the plate that's moving up and down? Fine adjustment? Surely mounting the torch holder on the bottom of the plate will be enough?

The second rail/block you mention is the floating head, it only moves a few mm, just enough to trip a switch as the torch probes the metal surface before cutting.

You can't do initial height sensing without one.

njhussey
31-07-2015, 12:58 PM
Ahhh...ok I get it now:stupid:....said I was being thick!! I know v little about plasma cutters....and it shows!!

Davek0974
01-08-2015, 05:22 PM
Little bit slower now, onto the small fiddly bits....

Got the Axis hard-stops and beam end-covers designed, cut and fitted..
http://www.plasmaspider.com/download/file.php?id=37020&t=1 (http://www.plasmaspider.com/download/file.php?id=37020&mode=view)


Fitted the floating head, torch mount and probe/limit switches...
http://www.plasmaspider.com/download/file.php?id=37017&t=1 (http://www.plasmaspider.com/download/file.php?id=37017&mode=view)


The front Y & A axis limit/home switches...
http://www.plasmaspider.com/download/file.php?id=37018&t=1 (http://www.plasmaspider.com/download/file.php?id=37018&mode=view)


And the Y far-end limit switch...
http://www.plasmaspider.com/download/file.php?id=37019&t=1 (http://www.plasmaspider.com/download/file.php?id=37019&mode=view)


Started work on fitting the cable chain to the X axis now. http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif

njhussey
01-08-2015, 05:24 PM
Looking good, it's the little bits that seem to take the most time....

Lee Roberts
02-08-2015, 02:46 PM
Looking sweet Dave, nice bit of metal work there!

Davek0974
02-08-2015, 04:53 PM
Thanks,

another slow day today, had a few orders to make then fitted the cable tracks and trunking and started planning out the bed support frame.

Davek0974
06-08-2015, 06:51 PM
had a couple of hours today, fitted the last of the limit switches and started on the slat support frame.

I thought a seperate frame would be best to avoid putting any heat into the side frames and make replacement easy.

50 40 x 5mm angle fitted into bed opening and a strip fitted to its bottom edge to support the slats vertically.
http://www.plasmaspider.com/download/file.php?id=37140&t=1 (http://www.plasmaspider.com/download/file.php?id=37140&mode=view)


Quite disappointingly when i did the heavy tacks to secure the bottom return strips, the angle warped and is now 4mm high in the middle http://www.plasmaspider.com/images/smilies/icon_redface.gif

Not good, not sure what to do about it - ignore it and let the THC tackle it, maybe slit the angles vertically in two or three places, press it flat and weld up or something else.

I didn't think angle that heavy would warp!

Apart from that it s all going to plan http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif

Davek0974
08-08-2015, 05:45 PM
Slat bed fitted at last, total PITA http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif

http://www.plasmaspider.com/download/file.php?id=37169&t=1 (http://www.plasmaspider.com/download/file.php?id=37169&mode=view)


Not 100% happy with it as the 50x3mm strip i ordered is a range of anything between 48x3 and 52x3 !
Will be changing it some time soon i think.

I also fixed the warped slat rails very nicely -
http://www.plasmaspider.com/download/file.php?id=37170&t=1 (http://www.plasmaspider.com/download/file.php?id=37170&mode=view)


A quick slice with a 2mm disc and weld-up, now it sits perfectly flat on the side beams http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif

The vertical weld was also my first vertical-up weld as i'm normally a bench top welder, didn't come out too bad i thought http://www.plasmaspider.com/images/smilies/icon_e_smile.gif

Stripped it all for paint now, hopefully the weather will be good tomorrow.

Davek0974
09-08-2015, 05:34 PM
Feeling a bit blue today...

Gantry...
http://www.plasmaspider.com/download/file.php?id=37188&t=1 (http://www.plasmaspider.com/download/file.php?id=37188&mode=view)


Main frame...
http://www.plasmaspider.com/download/file.php?id=37189&t=1 (http://www.plasmaspider.com/download/file.php?id=37189&mode=view)


Had to repaint the side beams as i forgot to fit the dust shields for the HiWin rails, probably not too important as the blocks have hard scrapers and extra seals fitted on all ends http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif

Now to start rebuilding and final fitting.

Davek0974
10-08-2015, 09:32 PM
Extract tray / chamber arrived today...
http://www.plasmaspider.com/download/file.php?id=37206&t=1 (http://www.plasmaspider.com/download/file.php?id=37206&mode=view)


Quality is excellent, glad i outsourced this part http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif

njhussey
11-08-2015, 09:19 AM
Looking good Dave, coming together nicely!

Davek0974
14-08-2015, 10:14 PM
Coming back together now...

http://www.plasmaspider.com/download/file.php?id=37301&t=1 (http://www.plasmaspider.com/download/file.php?id=37301&mode=view)


http://www.plasmaspider.com/download/file.php?id=37302&t=1 (http://www.plasmaspider.com/download/file.php?id=37302&mode=view)


http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif

Davek0974
16-08-2015, 05:37 PM
Z axis wiring...
http://www.plasmaspider.com/download/file.php?id=37320&t=1 (http://www.plasmaspider.com/download/file.php?id=37320&mode=view)


Table wired up...
http://www.plasmaspider.com/download/file.php?id=37321&t=1 (http://www.plasmaspider.com/download/file.php?id=37321&mode=view)


The timer on the bottom rail is an off-delay of about 20 seconds for my downdraught fan, every cut start and stop triggers the Aux BOB relay and the delay holds the fan on between positioning cycles etc. At the end of the last cut it runs on for the full delay to clear any remaining fumes.

Preliminary panel wiring...
http://www.plasmaspider.com/download/file.php?id=37322&t=1 (http://www.plasmaspider.com/download/file.php?id=37322&mode=view)


I've got an old BOB laying around and spare PC which i've installed a basic Mach3 setup on, hopefully be able to get the lot tied together this week for motion testing.

Davek0974
22-08-2015, 06:51 PM
IT Lives http://www.plasmaspider.com/images/smilies/icon_e_smile.gif

Achieved first motion today, got it lashed up to an old BOB and very poor PC (way below Mach3 specs) and it seems happy, a short video...

https://youtu.be/n34DDnw8org

It was running this file...
http://www.plasmaspider.com/download/file.php?id=37396&t=1 (http://www.plasmaspider.com/download/file.php?id=37396&mode=view)


Which was the simplest file my mediocre G-Code skills could manually type http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif

Have played with motor tuning and it will go way beyond requirements so pegged it back at my 9000/mm/min target. Acceleration seemed very willing to perform but I'm not sure if the PC is hampering it there or not, its only a 500mhz CPU and Mach is supposed to need 1Ghz or more.

Still, it runs and runs VERY well indeed, smooth, fast and gives me the impression it will work nicely with the torch on.

I have tried to make it lose steps - pushing the Mach "Stop" button when running at 9000mm/min give a very abrupt stop indeed but no lost steps, can't get much more severe than that i think.

Next i need to do some book-speed tests with real cut files and verify the home position after each cut, not even sure its worth doing a pen test - it just seems happy and gives me confidence.

The final step is the tricky one - I need to strip the BOB, THC and plasma from my running table, dismantle that to move it out of the way, move the new machine into position, level it and fit the last parts to it. Then install the extract system, bed frame and slats and start test-cutting. Sounds easy but I know for a fact that as soon as i decommission the running table, jobs will come in!!! The only safe way I think is to put up the "closed" sign for a few days and get it done - we are away in a weeks time for a week so i might just extend the holiday closure period a bit to give me some slack.

Good day today http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif

njhussey
22-08-2015, 07:52 PM
Looking good...good to see your machine come to life!!! I'm itching to get back on mine and finish it now I've seen yours working...

Davek0974
22-08-2015, 08:46 PM
It certainly was a relief, especially when i managed to get Mach3 to auto-square the gantry for me when its homed :)

Davek0974
28-08-2015, 04:38 PM
Made the replacement wall panel today, fitted the extract fan to it...

http://www.plasmaspider.com/download/file.php?id=37476&t=1 (http://www.plasmaspider.com/download/file.php?id=37476&mode=view)


This should replace one of the slabs in the garage wall directly, hopefully be able to undo the two bolts, pull the slab inwards and replace with this one.

The fan is connected to the table via a short length of 12" flexi ducting. Its controlled from my G-code, have altered the post processor to put the on/off codes where i want them.

I'm off for a weeks holiday now, plan is to move the table into position as soon as i return http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif

Lee Roberts
30-08-2015, 01:26 PM
Looks great Dave well done so far :).

.Me

D.C.
03-09-2015, 04:53 PM
Made the replacement wall panel today, fitted the extract fan to it...
This should replace one of the slabs in the garage wall directly,

Is the fan for dust removal or heat removal?
If you try venting electronics outside you will end up killing your electronics with condensation, which would be bad. :(
You can mount a closed loop radiator externally for heat removal, but air is a no-no.

Davek0974
03-09-2015, 05:02 PM
Nah that fan is the table bed downdraught fan - needs to vent outside, intake air will be through the open door. Will be cold in winter but no other way to vent that much air.

Davek0974
06-09-2015, 06:46 PM
Back from a way too short holiday http://www.plasmaspider.com/images/smilies/icon_e_sad.gif Stripped the workshop out and moved the new table into final position...

http://www.plasmaspider.com/download/file.php?id=37627&t=1 (http://www.plasmaspider.com/download/file.php?id=37627&mode=view)


http://www.plasmaspider.com/download/file.php?id=37628&t=1 (http://www.plasmaspider.com/download/file.php?id=37628&mode=view)


The extract fan panel fitted perfectly, but shifting that volume of air turns out to be damn noisy, i can probably expect trouble from the neighbours i think, will have to be careful when i choose to do my cutting http://www.plasmaspider.com/images/smilies/icon_cry.gif

Finishing off the panel now, fitting the BOB boards and wiring them in, then i need to build something to hold the monitor and keyboard etc, some sort of workstation.

Then i have to puttee workshop back together again http://www.plasmaspider.com/images/smilies/icon_e_sad.gif

Davek0974
10-09-2015, 07:05 PM
Panel finished...
http://www.plasmaspider.com/download/file.php?id=37681&t=1 (http://www.plasmaspider.com/download/file.php?id=37681&mode=view)


Mesh below the slats...
http://www.plasmaspider.com/download/file.php?id=37682&t=1 (http://www.plasmaspider.com/download/file.php?id=37682&mode=view)


Bit busy up that end of the shop http://www.plasmaspider.com/images/smilies/icon_e_wink.gif
http://www.plasmaspider.com/download/file.php?id=37684&t=1 (http://www.plasmaspider.com/download/file.php?id=37684&mode=view)


Stuck the monitor on the wall, seemed a good place, still working on the keyboard and mouse/trackball, might be a slide-out under the front of the table. I couldn't fit the PC into the main cabinet - not enough space http://www.plasmaspider.com/images/smilies/icon_e_sad.gif
http://www.plasmaspider.com/download/file.php?id=37683&t=1 (http://www.plasmaspider.com/download/file.php?id=37683&mode=view)


One odd thing I noticed when motion testing with the proper PC, the X & Z axis worked perfectly but the Y & A needed the "step active low" setting reversing in ports & pins? They sounded very rough and notchy when set the same as the other axes.

This seemed odd as all drives are the same, wired the same and connected to the same BOB????

Any ideas why I need to run two axes reversed signal level???

JAZZCNC
10-09-2015, 07:33 PM
Any ideas why I need to run two axes reversed signal level???

If all wired same and the drive doesn't have an active edge Dip switch then probably because setup different in the drive software. Some drives will provide a Dip and most Digital drives you can access thru software.

If none of the above then could just have been set different at the factory,?

Dragonfly
10-09-2015, 08:04 PM
"Active Low" means the drivers are wired with common +5V and step pulse inputs wired to the minus terminals, right?

Davek0974
10-09-2015, 08:07 PM
"Active Low" means the drivers are wired with common +5V and step pulse inputs wired to the minus terminals, right?


Yes, all wired common +ve

Davek0974
10-09-2015, 08:09 PM
If all wired same and the drive doesn't have an active edge Dip switch then probably because setup different in the drive software. Some drives will provide a Dip and most Digital drives you can access thru software.

If none of the above then could just have been set different at the factory,?

But these were tested with a different BOB when i was building the table and all settings were the same????

One difference is that the test PC was underpowered and only ran at 25khz, the work PC runs at 45khz, step and dir pulse length is 2us on both PC's

JAZZCNC
10-09-2015, 08:33 PM
But these were tested with a different BOB when i was building the table and all settings were the same????

One difference is that the test PC was underpowered and only ran at 25khz, the work PC runs at 45khz, step and dir pulse length is 2us on both PC's

Don't know then. Maybe the new BOB does some filtering and signal boosting depending on the PP voltage.? If your on the edge with say 3V PP then the BOB could be boosting and inverting the signal just on that line.??? . . . .Strange beasts these CNC machines.!!!!

Davek0974
10-09-2015, 08:46 PM
Hmm, interesting

Just thought of another difference, the CandCNC MP3000 DTHC uses three parallel cables - one from the pc to the controller and then one to the motor drive BOB and another to the I/O BOB, these last two are new, shorter cables.

Might be worth swapping the old long cables back in???

Dragonfly
10-09-2015, 09:48 PM
Don't think cable length is the cause. Anyway I see only one BOB on the photo and presumed you use Mach3.
Actually did you test all drivers set to "active low"? As far as I understand you have Y and A coupled as master and slave. Wrong polarity might make them "rough" as they need to move in sync while the others may also need low trigger but do not show rough movement because they are single. ??Hmm.

Davek0974
10-09-2015, 09:53 PM
The mp3000 has two BOB's one for motor control and one for inputs and outputs, yes i am running mach3

All drives were running active low on the test pc, Y and A are slaved in mach and each on their own output.

Davek0974
11-09-2015, 12:15 PM
CandCNC advised me to up the pulse width to 5us and that seems to have sorted it out, all drives now running the same way.

JAZZCNC
11-09-2015, 01:56 PM
CandCNC advised me to up the pulse width to 5us and that seems to have sorted it out, all drives now running the same way.

So you were just on the wrong side of the pulse edge then. Could only really be this or the BOB inverting signals really.! Changing the pulse width doesn't always work thou unfortunately so you've been fortunate.!

Davek0974
11-09-2015, 02:19 PM
Yes its an oddity i think,

A Mach guru has just pointed out that the BOB has opto isolated outputs and the drives have opto isolated inputs so i am driving an opto with an opto, he seemed to feel that was not a good idea generally.

JAZZCNC
11-09-2015, 03:29 PM
Yes its an oddity i think,

A Mach guru has just pointed out that the BOB has opto isolated outputs and the drives have opto isolated inputs so i am driving an opto with an opto, he seemed to feel that was not a good idea generally.

Nah not at all it's common as muck with Just about every BOB worth it's salt having opto's has will any decent drives and there'll be few machines that don't run with both.!

Unfortuantlly it's more a sign of poor drive or BOB with slow opto's.!!

cropwell
11-09-2015, 03:57 PM
If every bit and bob and driver has opto isolation why not cut out the middle man and have a fibre optic connection ? I'll bet there are some machines with bespoke electronics that do it.

Davek0974
11-09-2015, 05:28 PM
If every bit and bob and driver has opto isolation why not cut out the middle man and have a fibre optic connection ? I'll bet there are some machines with bespoke electronics that do it.

Probably purely a cost issue, this stuff is not really found on the high-end machines, I have no doubt those ones would have fibre where needed.

:)

Davek0974
11-09-2015, 06:06 PM
Ok, we have action http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif

Mixed bag of results, sort of exciting and disappointing all at the same time.

The good parts...
It works, speed is no issue,
The ripple effect in my cuts has disappeared,
It does not shake and wobble all over the place,

The bad parts...
The voltage is still way off of book specs, no change,
Can't get a clean cut on aluminium yet,
Need to work on divots,

Here we go...
Pierce & Cut heights are all as per book and this was checked several times by stopping mid cut and measuring the gap.

35mm washer, 45A 107v, 4000mm/min. Nasty divot as no cut rules yet just perpendicular lead in and no lead out.
http://www.plasmaspider.com/download/file.php?id=37708&t=1 (http://www.plasmaspider.com/download/file.php?id=37708&mode=view)


Add a 2mm overburn and turn torch off 2mm before end - divots now pretty good.
http://www.plasmaspider.com/download/file.php?id=37709&t=1 (http://www.plasmaspider.com/download/file.php?id=37709&mode=view)


Same speed, acceleration as listed, small shape again - 35mm sq. Same 2mm overburn etc but divot is terrible again????? There is a marked improvement between the 1st and 2nd cuts but little change between 2nd and 3rd so i set the acceleration at 1500mm/s/s. I can improve the internal corners a bit by setting Mach to stop CV on angles > 89 degrees but don't know if that is a good idea or not??/
http://www.plasmaspider.com/download/file.php?id=37710&t=1 (http://www.plasmaspider.com/download/file.php?id=37710&mode=view)


3mm aluminium - 6400mm/min 45A 106v, lots of top dross, tried slower but made little difference. Had better cuts on old machine http://www.plasmaspider.com/images/smilies/icon_e_sad.gif
http://www.plasmaspider.com/download/file.php?id=37711&t=1 (http://www.plasmaspider.com/download/file.php?id=37711&mode=view)


1.2mm stainless is not too bad, 7900mm/min 45A or 4800mm/min 30A 109v

10mm steel, 0.9s delay, 117v, 500mm/min 45A.

Had one nozzle blow out completely, was getting poor cuts and found the orifice practically missing, no idea how that happened at all, as i'm testing I have been very careful of wrong pierce heights etc.

So, as i said, a mixed bag really. The divots are concerning, I need to get that bit nailed as well as the aluminium.

If anyone wants to chime in with some useful settings, please do. Is there a group test file that those with some spare minutes could cut for comparison???

Davek0974
12-09-2015, 01:31 PM
Swing-out keyboard, seems to work ok...
http://www.plasmaspider.com/download/file.php?id=37745&t=1 (http://www.plasmaspider.com/download/file.php?id=37745&mode=view)


http://www.plasmaspider.com/download/file.php?id=37744&t=1 (http://www.plasmaspider.com/download/file.php?id=37744&mode=view)


Big success, thanks to a member on another forum for his settings on the 3mmAluminium...
http://www.plasmaspider.com/download/file.php?id=37749&t=1 (http://www.plasmaspider.com/download/file.php?id=37749&mode=view)

Pretty clean I think.
http://www.plasmaspider.com/download/file.php?id=37750&t=1 (http://www.plasmaspider.com/download/file.php?id=37750&mode=view)


1.2mm Stainless, not too impressed yet, might have to get some 30A consumables and try that out, not sure I can cut my stuff unless I can get this better.
http://www.plasmaspider.com/download/file.php?id=37747&t=1 (http://www.plasmaspider.com/download/file.php?id=37747&mode=view)

http://www.plasmaspider.com/download/file.php?id=37748&t=1 (http://www.plasmaspider.com/download/file.php?id=37748&mode=view)


Now, the last major issue - that damn unequal bevel, here is a bit of 3mm steel with a 3mm slot, these parts need to slot together. You can see one side is good the other is bad, this aligns with the Y axis.
http://www.plasmaspider.com/download/file.php?id=37751&t=1 (http://www.plasmaspider.com/download/file.php?id=37751&mode=view)


Heres some more, 3mm again, placed on table as in picture. I have marked the angled edges.
http://www.plasmaspider.com/download/file.php?id=37746&t=1 (http://www.plasmaspider.com/download/file.php?id=37746&mode=view)


Now, I could fudge this by leaning the torch over to compensate but that is a bodge and will only ever get me two bevelled edges. So, what can do this, the consumables are new and today I have checked the condition of them between every cut after yesterdays blow-out. Overall the cut quality is impressive - the new machine is smooth and this is reflected in the cuts but this problem migrated from the old machine so must be torch related?????

Also, I can improve internal corners by switching "Stop CV on Angles >89" on in mach3 settings BUT this then gives me a jerk at the start of every arc and radius cut, I think this can be seen in one of the pictures above. So I can't run that setting as a default and as very few jobs are fully square, its practically pointless. Can Exact-Stop be triggered from Sheetcam??? Is it really this difficult?? What do you guys do for sharp internals???

SO many settings and tweaks, doing my head in. I think I can crack the divot problem, a lead-out plus torch off before end of cut seems to be reasonable but I can tune this over time.

This bevel issue is bad though I think.

Davek0974
13-09-2015, 02:34 PM
Yesterdays little fun test... http://www.plasmaspider.com/images/smilies/icon_lol.gif
http://www.plasmaspider.com/download/file.php?id=37786&t=1 (http://www.plasmaspider.com/download/file.php?id=37786&mode=view)


3mm Stainless, 108v, 45A, 3800mm/min, pretty clean...
The bottom 4 lines are on the new table, the top mess is the result i had on the old table which made me build the new one!!!
http://www.plasmaspider.com/download/file.php?id=37787&t=1 (http://www.plasmaspider.com/download/file.php?id=37787&mode=view)


Test shape, old m/c vs new m/c...
I know the slot is buggered - this was because i used the test file for mild steel and forgot to tweak the settings on the slot part first http://www.plasmaspider.com/images/smilies/icon_redface.gif
http://www.plasmaspider.com/download/file.php?id=37788&t=1 (http://www.plasmaspider.com/download/file.php?id=37788&mode=view)

You can at least see the waste in the slot, that a 3mm slot and the waste is about 1mm.
http://www.plasmaspider.com/download/file.php?id=37790&t=1 (http://www.plasmaspider.com/download/file.php?id=37790&mode=view)


So, not too bad today, also been messing with divots, internal holes. Tried a 5mm overburn with the torch off 1mm before the end, so the end of the cut is 6mm from torch off and you can still see a mark. Will keep messing with that one but at least she's up and running again. http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif

I have twisted the torch mount to correct the odd bevel or at least balance it out, I'm leaving the torch at the current angle - it's working so until i find a reason, i'll live with it
I

Davek0974
17-09-2015, 07:40 PM
30A consumables arrived today, gave them a spin on 1.2mm 304 stainless and got excellent results http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif http://www.plasmaspider.com/images/smilies/icon_e_biggrin.gif As good as the finecuts on the 30XP were at least.

Both pics as they came off the table...

Top...
http://www.plasmaspider.com/download/file.php?id=37883&t=1 (http://www.plasmaspider.com/download/file.php?id=37883&mode=view)


Bottom...
http://www.plasmaspider.com/download/file.php?id=37884&t=1 (http://www.plasmaspider.com/download/file.php?id=37884&mode=view)


Voltage was low as normal it seems, 76v instead of book 98v but speed was bang on at 4000mm/min, pierce height 2.5mm, cut height 0.5mm. Still need to dial the THC in as its a bit unstable on thin stuff but at least it works and the table is now producing paying work.