plasma table idea

[CwazyWabbit]

He is going to use an old pallet.

[simonr]

Its an idea taken from the internet - but it seems to work! It's a bit Smokey unless you wet the pallet first - and then risk the steel going rusty!

Si

[steve b]

On our commercial plasma the torch is on a plate that is held to the carriage assy magnetically so in the event of a torch/plate collision it just gets knocked out of its location points (3) and stops . The machine is an Esprit 260a HD - have a look at the www . The bed is a box frame and the plate rests on strips of 6mm sitting in a sub frame vertically about 50mm apart and with offset slots in the middle to put a shallow curve in each strip if you see what I mean?

cheers

Steveb

[simonr]

I figured, (for cheapness as much as anything) that if the torch carriage hits the frame, it will just stall the motors, and loose steps. Although this may ruin what you are cutting, it will not damage the machine.

Hopefully with torch height control, the torch will not hit the plate you are cutting - I may be wrong about that though!

Si

[robertspark]

the plastic groove bearings that are used on that carriage are :http://www.ebay.co.uk/itm/121255077715?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

When I was looking at designing and making one, I found that there are a range of V or U groove bearings available but its best to search for them on ebay.com, and they come in from china. There are larger rollers that are available from the US that tend to get used a lot on other CNC machines such as the MechMate, but the cost goes up, but they have a larger groove which is more suitable for running them on a box section corner.

The v or U groove bearings in the UK are sold as gate roller bearings (but they can be large) or patio door bearings or sash window bearings too.

The magnetic torch holder seems a good idea (there are a few clips on utube of other ideas that people have come up with).

neodymium magnets are cheap enough (thought about adding a few to sump plugs.... but someone beat me to the idea by a few years

(note the only problem with magnets and plasma cutters is the swarf / metal particulate blown about (especially without a water bath).

The adjustable angle torch holder on Simons drawing is a good idea as mine is square and will be cut and rewelded shortly to the correct angle.

Si, what software are you running with your mill? Mach3?

what g-code generator are use using (a solidworks addin?)

[Cynic-al]

Be interested to see how the pallet affects the cut

[robertspark]

Putting a 4th Axis on it interests me too for tube notching:

https://www.youtube.com/watch?v=7fK4qaf4maI

https://www.youtube.com/watch?v=3TeeW49Wiq8

maybe some useful software for someone here:

http://www.metalgeek.com/static/cope.pcgi

http://www.machsupport.com/forum/index.php/topic,16411.0.html

http://www.tyharness.co.uk/#100

they will allow you to generate sheet metal drawings that could then by g-coded to pattern cut

[simonr]

Si, what software are you running with your mill? Mach3?

what g-code generator are use using (a solidworks addin?)

I'm using Mach3 with Solidworks / Rhino V4. I have Visual Cam from MechSoft - which I bought after much deliberation. It's the only one that I found easy / intuitive to use.

Cynix-al - I tried cutting on top of a pallet and if you can live with the amount of wood-smoke generated, it didn't seem to affect the cut very much if at all. It cuts about 10mm in to the surface of the wood. It's not much different to cutting on a water bath.

This is todays version:

Using Box section on all four sides plus the bridge. Makes it more scaleable.

If any of you want a look at it in just about any CAD software, here is a link to the design as an IGS file (zipped)

[robertspark]

suggested points to consider:

1) metal flex in the carriage (carriage component) ... you've got a piece of plate which is bent to form the carriage U section, and there may be some flex between the v-groove bearings (less of an issue with the side plate component as the y axis will act as a brace.

2) what about considering reducing the component count (ie use as many of the same components in mirrored positions), I'm thinking the four corner pieces (end plate pulley and end plate motor components), if you slot all four components the same for the belt, then they are a mirrored component (hence can be batch made), you did the same with the z-follower component.

3) as item 2... the side plates could be mirrored, but they may get longer so they have belt slots both sides

4) suggest a weldment on the endplates and side plates so the RHS can be customer sourced and cut to length to reduce the shipping (you've obviously got this in hand, sorry not wanting to state the obvious [feel like an armchair critic]).

alternative... 10 x square milled blocks to fit inside the tubes, with a two bolts to mount it onto the end plates or side plates, and then two (or four) bolts to secure the RHS tube on with ... standard repeatable component.

5) the z-axis ((z-follower components) do they need additional bearings.... the only reason why I ask is when the y axis travels there may be the tendency for the z axis to rock given its not supported in that plane.

6) the bit that I'm noticing on mine with a timing belt is tension.... and belt sag... I thought about using a short high tension spring to keep the belt tight.

Looks very good though.

[simonr]

Thanks Robert.

1) All the parts are made from 3mm mild steel. Flex may be an issue, but based on a test on another part 100mm long folded channel out of 3mm, you have to put a fair bit of force in to get it to flex. I'll try it and see if there is a problem.

2) A lot of the components are repeated, or the folds mirrored. Here is the BOM:

ITEM PART QTY.

1 X-Motor Mount 1

2 Pulley Support 3

3 Side Plate 1

4 Belt Clamp 6

5 Y Motor Bracket 1

6 Side Plate Mirror 1

7 Y Pulley Bracket 1

8 Carriage 1

9 Z Motor Mount 1

10 Z-Post 1

11 Z-Follower 2

12 Z Nut Keeper 1

13 Z-Axis Plate 1

14 Z Top Cap 1

15 End Plate Motor 2

16 End Plate Pulley 2

17 End Plate Keeper 4

In this, mirrored parts are shown separately - I've found it confuses the laser cutters if some parts can be folded either way, you end up with a random mix!

4) I'd tried to avoid any welding. While someone who can plasma cut, can probably weld too, it's probably better avoided. All the lengths of RHS fit in to 'sockets' so the table will try to resist twisting. Since they are (fairly) rigidly located, I didn't think they would need welding. If I produce a kit, I will offer the option of sourcing the RHS yourself or offer cut lengths suitable for some different cut areas.

5) May be an issue. It depends how well the V pulleys locate on the RHS - and I don't know the answer to that yet.

6) This method is used on a number of 'Rep-Rap' type machines - though I guess they use shorter runs of belt. I've made the belt width 15mm but I still agree it may be a problem. If it is, I have a plan to add an idler pulley on a sprung arm on each run of belt - which ought to help.

Don't [feel like an armchair critic] - I really appreciate any feedback!

I've sent this design off for a quote from the laser cutters to make 1 and 10 sets - Fingers crossed!

Si

[robertspark]

belt: http://www.ebay.com/itm/HTD-5M-Timing-Belt-5m-W-15mm-for-CNC-Robotics-etc-/161430687584?pt=LH_DefaultDomain_0&hash=item259604cf60

I went with 20mm on mine, only because I was concerned with the twist on long runs (if I decided to make them 2.5m long), and also the way they are driven from the carriages. ...the torque or belt speed should never be a problem

... I also have an intention to try to put a milling head on it for a try for wood / aluminium to see what happens.... http://www.ebay.co.uk/sch/i.html?_odkw=spares+or+repair&_from=R40%7CR40&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR11.TRC1.A0.H0.Xspindle+inverter&_nkw=spindle+inverter&_sacat=0

[requires a better z-axis though]

[simonr]

There's a video of someone using one, obviosly intended as a Plasma table with something like that but milling foam. He then uses the foam as a base for glass fibre to make funky shaped car panels!

Granted, Land Rovers don't really have 'funky' panels - but it looked cool none the less!

I'm doubtful that a plasma table would have the rigidity for milling - but it's worth a go! Worst case, you can use the spindle motor as the start of another project!

Si

[simonr]

This is an idea I like:

https://www.youtube.com/watch?v=vRCiOow5zRc

You could pretty much just suspend the sheet you are cutting from one edge.

Si

[robertspark]

yup I had seen that vertical table some time ago, the only concerns I had were:

1) what happens when / if a piece of material drops / warps slightly (too much heat + too slow a travel speed setting) and then drops

2) It seems braced for cantilever operation if you look at the side rails, hence didn't think my setup would work very well as it would have the tendency to maybe lean downwards with more load on the bottom bearings, thought about trying mine lear vertical (70 degrees say) so that the load is near perpendicular with the bearings (not so much of a twisting force) and when things were cut they were more likley to stay put and not fall forward onto the carriage.

seen this idea for a bit of belt tension (don't want too much or it will load the bearings in the stepper motor):

[simonr]

That's a very clever way of tensioning the belt! Let me know if you find some suitable springs!

Si

[robertspark]

thought about giving these a go: http://www.ebay.co.uk/itm/120838685452

they are a bit wide at 30mm, but thought it may not matter much.

need to form a bend, but thought there may be enough of a tail to form the crossover the belt

... edit -> found this company too ... too many choices haven't got a clue!

http://www.assocspring.co.uk/p/17/torsion_springs-music_wire/?PAGE_ID=1&INDEX-order=0&min_2=1.6&max_2=4&min_3=0&max_3=30&min_4=5&max_4=5&update=#startcontent

[Cynic-al]

Load on the motor bearing isn't something I'd thought about a lot before however all the 'commercial' machines I've used tend to be like this, I'd always assumed it was to get the right 'gearing' but I guess it also takes the working load off the motor. This machine has a shaft running to the other side with another belt & carriage to keep everything driving square but the machines that have independent motors either side use the same setup. It does introduce an extra area of play though.

The loops at the end of the belt are made by doubling the belt over so the teeth mesh, theres then a staple shaped metal plate over the belt to clamp it together and a bit of heat shrink to tidy it up. The peg that it's on is eccentric so that you can tighten the belt. Pretty standard I guess but pretty easy to do at home too

[simonr]

Got quotes back from the laser cutters.

1 set - £380

10 sets - £200

50 sets - £150

I'm going to get one set made and see whether it flies. It could potentially make for a pretty cheap build - Perhaps under £600 including everything apart from PC, Plasma Cutter and Software.

Si

[elbekko]

That is very cheap!

[simonr]

Bear in mind, that's just for the laser cut & folded parts. You still need to add 6m or so of 50mm box section (£30 ish) a load of V pulleys (£100) Stepper motors (£30 each), belt (£30), nuts & bolts (£20) and stepper drivers (£20 each) - so the kit will cost an additional £340 to complete.

Still, even as a one-off, £700 isn't bad for a plasma table! If I could make 50, the price drops to £500 all in which is quite appealing!

Si

[CwazyWabbit]

For a table you just have to put together 700 quid is dirt cheap

[robertspark]

thanks for the pic Cynic-al, I suspect the reason why they do it that way commercially is the brearings get less load + the gearing (sprocket / pulley arrangement) gives improved torque from a smaller motor which brings savings in smaller motor load, smaller driver, smaller power supply, and longevity is improved.

Anyone else frequenting the forum with a x-y cutting table (plasma, arc, wood etc) able to post pictures?

Si, the plasma would also bring savings if you used the cnc controller for multiple equipment (not many in a home shop run everything at once, or have the space too), hence the scale of cost is then reduced too, especially if you've got a mill and or lathe too in need of converting.

[mick the digger!]

I'd have a interest in a kit, please keep me informed.

[simonr]

I've just ordered almost everything else required from a mixture of cnc4you and eBay for a grand total of £307.31

57BYGH56-401A NEMA 23 Stepper Motor 12.6Kgcm 1.8Degre 4Leads 56mm for CN £24 1Pcs BR Series CNC Motor Shaft Coupler 8x12mm Flexible Coupling D25mm L30mm £3.91

Aluminum synchronous round Industrial synchronous belt pulley DIY robot 3M/5M x4 = £21.96 3 Axis CNC Router DIY Kit 5 Axis Breakout Board TB6600HG Stepper Motor Driver 5A £72.10

HTD 5M Timing Belt 5m (W=15mm) for CNC Robotics etc.. x 2 = £56.74

V Groove Pulleys x 14 = £63.50 (they gave me 10% off)

From cnc4you:

Nema23 Stepper Motor 3.1Nm x 2 = £65.09

I opted for bigger steppers than Robert for the X & Y axis becase too big is better than too small and there was only £3 each cost difference.

The additional bits to order are:

50mm x 50mm x 1.5 wall Box section x 6m

M6 Studding x 6m

8mm Silver Steel bar (to connect the drive pulleys) x 2m

I doubt that will come to more than £40 if I order through Parkers or IS&G so about £350 plus the laser cut bits.

If it all works OK, I'll do some kind of group buy on 10 sets, plus possibly the box section if we can agree on a size. I think the most useful generally would probably be 2' x 4' cut area (1/4 sheet).

Hope it works now!

Si

[bishbosh]

Don't know if you have considered this, but the rolling tolerance on box section for twist is 2mm per m and 1% (min 0.5mm) on external dimensions.

Not sure if that is going to be problem for the level of accuracy you need?

Data taken from Tata's Blue Book.