[Fiero Addiction]

lamicron,
The belts are close enough to zero backlash that it can be considered zero for this kind of application. I also have no drive reduction, so there is no extra backlash from that. I haven't had to replace or re-tension any belts yet, so I am very satisfied.

510rob,
The Esab PCM-875 is rated to cut 7/8" steel according to the manual that came with it, but I'm betting 5/8" is a more realistic limit. The heaviest matarial I've cut is .4" mild steel and if I have everything set up right it does a nice job with very little taper, but more often I get more taper than I like. I'm still figuring out the best settings as far as cut speed and height. I have to run it quite a bit slower than the recommended cut speeds in the manual. I think the kerf is wider than most, it runs about .9". It uses high frequency pilot arc starting, which hasn't been a problem for me. I got the unit on Ebay for $1200, brand new with warrany.
The Thermal Dynamics 35C is discontinued, but it's the same as the Drag-Gun Plus that they still sell. It's a small 35 amp portable unit with a built-in compressor. I still have it around for manual cutting jobs. It's rated for 1/2" steel, but I found 3/8" was a more reasonable limit, and even that was too much most of the time. The TD torch seems to work a lot better than the Esab, finer kerf, cleaner cuts, better consumables life, but a lot of that probably has to do with the lower output current. If I never had to cut anything over .25" I may have stuck with the 35C. The high frequency start on this unit did give me some trouble too, and it was never intended for mechanized cutting.

[hugoglez7210]

I recently bought some machine called a mega-plotter the owner toldme that it works good, so I tough I coul do some modificacions and use it as a plasma table, he gave a box with step motor driver alredy plug to a the step motor it turns on but I'm stuck with the driver for the computer he gave me the drivers on a flopy disk he said those are from ability systems, but the flopys are just blank. can you help me what kain of drives i can use

[radioactive]

Nice job on the build it looks like it turned out great...

I would like to build one almost identical to yours. Do you mind sharing where I could find most of the material other than the steel? vee rails, steppers, belts, pulleys, etc.?

Also did you have any pieces plasma cut for you that you possibly still have the drawing for? Like the side plates for the gantry portion...

Is the table opening 4'x4' or slightly larger? I wasn't sure if I should make the opening exactly 4x4 or if it needs to be slightly larger to prevent the torch from cutting above the edge of the table...

Thanks!

[Fiero Addiction]

McMaster Carr - fasteners, open end belt, V rails, adjustable feet
Stock Drive Products - pulleys, belt clamps
Modern Linear - V rollers (size 2)
VX Bearings - skate bearings

I have the X and Y carriage plates drawn in CAD. I'll upload them.

My table inside area is 56" x 60". I don't know what the actual cutting capacity is, the torch cannot quite travel all the way to the edges except on the far end of the X axis where it could go over. Notice how the X rails extend beyond the ends of the table to increase the travel.

I had an occasional problem with the belts running off the edge of the double 608 bearings that are used for idlers. I replaced some of them with back to back flanged 608 bearings to form a sort of pulley.

Jon

[Fiero Addiction]

I just wanted to add a few notes for anyone who is considering using the drawings I posted. The gantry end plate is sized to use #2 V rollers in the top holes and 608 bearings on the slotted lower holes to hold the gantry down on the rails. The rails are #2 V rail bolted to 1x1 steel tubing.

The Y carriage plate uses #2 V rollers top and bottom. The top ones are fixed and the bottom ones are adjustable via eccentric bushings. The dimensions are to fit #2 V rail bolted to 4" tall tubing.

Jon

[kermit582]

hi I was just wondering if you are driving the table from both sides or just one side on the x axis

[Fiero Addiction]

Both sides are driven; two motors, two drivers for the X axis.

[kermit582]

I was wondering if anyone has ever tryed a belt drive on a 4x8 table? would it work? or is that to far of travel for a belt drive

[matttargett4]

kermit,

ive just finished my 10 x 5 table, belt drive works great i wouldnt do it different if i did it again, i have a 12Nm nema 34 each side, 2:1 reduction onto a 14 tooth 1/2 inch pitch belt, ds 10m /min no sweat, great acceloration, no backlash, brilliant repeatablility, i found it to be much cheaper than the rack ad pinion option.

[kermit582]

do you have any pics or a build log onhere?

[matttargett4]

kermit,

icant say that i do no, im just in the finishing stages so will post pictures when all is tidied up if you like, is a simple system really, on my x axis the belt is fixed at both ends in a clamp, the gantry uses two nylon rollers to tension the belt and wrap it around the drive pinion, i ve tried to sketch it in paint underneath, the rollers are 75mm apart horizontally and vertically, ive just put a groove in the outside of the roller to help the belt run in the middle, only 3.5mm deep to encourage it to the middle, appears to do its job. any more questionsgive me a shout

matt

[bamwa]

hello, i'm curious as to what you mean by a groove. Why not use a washer on each side of the roller. Can you post a pic? Thank you in advance.

[matttargett4]

hi,

all it ive done is turned down the central 30mm of the roller by 7mm dia with a 45 degree slope on each side to try to make the elt self centre, the profile should be in the attatchment below, excuse the paint drawing, its all i had o hand.

ill probably get shot down for ths big time, but form what i hav learnt from this forum and through a very small amount of practical experience compared to some members i think the most important thing in designing / building your own machine is to not be frightened to have a go at what you think might work and see what happens, particularly with the general mechanical engineering stuff like this, i tried a flat roller, it worked ok but i thought it could be better so i changed it, why did i put a 3.5mm groove in the roller, because it looked kinda right, and it does pretty well what i want it to, maybe it would be better if it were deeper i dont know, my main piece of advice would be keep you design pretty simple, complication causes failure in my experience aftr that give it a go and enjoy it since it is after all a hobby for most of us.

Here endeth the gospel according to me! dont be afraid to ask if you want to know something else, quite cool to think somone else is interested in my messing about!

[Torchhead]

You may find instead of a "groove" in the idler pulleys that a "Crown" works better if you run them against the flat side of the belt. Something to do with a belt under tension moving to the high spot but I can't give you the engineering justification because I am just an old beat-up EE (:0

TOM CAUDLE
www.CandCNC.com

[Richard Honey]

I agree with your crown idea Tom.

As a kid on a farm in Western Australia we had a lot of machinery and equipment driven with flat belts. Invariably the pulleys were not flat but had a slight crown.

The flat belts ran true even with significant misalignment of the drive and driven pulleys. In many cases we simply drove our old International W30 tractor up to the machine, looped the flat belt over the two pulleys and reversed the tractor to tension the belt. No high tech alignment there.

As far as I can work out the belt creeps towards the part of the pulley with the biggest diameter' and as the crown of the pulley is the giggest diameter; that where it tries to stay.

If we imagine a flat belt running on a tapered pulley; the belt will only be making proper contact with the bigger part of the taper. If there is sullicient belt slackness, the belt will automatically climb up the taper until it runs right off the high side of the pulley.

A pulley with a crown is similar to a pulley with two tapers; hence once the belt climbs to the top of the taper it will stay there, because to go further would be to start to go down the other taper and belts don't like doing that.

So there we have it. A beautiful union of flat belt drive, steam engine technology married with computerised digital control and drive technolgy.

A marriage made in heaven!

[Degrom]

Hi there..

Great design!!! Do you have any pictures of some of the cuts you have made and what was the thinnest sheet metal you have cut with it?

Thanks for sharing your design with us.
Bert.

I used belts for a couple reasons. They are easy to tension and virtually backlash-free, no need for the spring-loaded pinion to keep gears in tight mesh. Belts don't wear (much) and don't require lubrication. If a belt gets damaged, it's cheap and easy to replace. They were about half the price of rack, at least from the suppliers I was dealing with. The 3/8" belts are a little small for the X axis, I can visibly see some belt stretch when accelerating or decelerating at high rates. I would go 1/2" or 3/4" if I did it again.

I was a little concerned about direct driving the belts when I was building the machine, most of the info you read on this forum will tell you that you need further reduction, but for plasma cutting you really don't. My resolution is more than good enough for plasma cutting, and it has plenty of torque to move the heavy gantry and torch around. I can put a pen in the torch holder and draw shapes on paper with no visible steps.

[Torchhead]

I was a little concerned about direct driving the belts when I was building the machine, most of the info you read on this forum will tell you that you need further reduction, but for plasma cutting you really don't. My resolution is more than good enough for plasma cutting, and it has plenty of torque to move the heavy gantry and torch around. I can put a pen in the torch holder and draw shapes on paper with no visible steps.

If you are not concerned with the low resolution, low torque, and inaccuracy of direct drive then a little belt flex should not be of concern. You can never get more accuracy than you have resolution (smallest distance the tool travels with one step). If you are cutting out rough brackets for welding were you can have 1/16 margin, then build a machine to meet those standards. Since plasma is not "precision" cutting, it negates some of the need for accuracy, but remember that all the errors are cumulative. So if your table accuracy is only .030 then add the flame inaccuracy to that (maybe .020) and you are at .050 Plenty good for stuff that gets welded together. For other types of cutting (like decorative with fine cut) it limits you ability to do detailed cuts.

TOM CAUDLE
www.CandCNC.com
Totally Modular CNC Electronics.

[Fiero Addiction]

Prior to building this machine I was paying to have parts cut for me, and I later found out that they were cut on a Torchmate by a member of this forum. I can say that the same parts cut on my machine look just as good as those that were cut on the Torchmate. It did take me a long time to figure out what settings work best, and I don't use the machine that often so I'm still learning every time I use it. I did make a lot of scrap metal and waste a lot of consumables in the beginning. It was very frustrating at times, but it was well worth it.

Santa brought me a new camera for Christmas, I'll have to try cutting some artistic type stuff and post a few pictures. I normally make parts that are not extremely dimensionally critical. Automotive engine mounts and such, 10ga to .375" steel. It might be fun to try something different.

Jon

[Degrom]

Hi There,

I agree that Plasma is not accurate compare to a CNC mills or laser cutters. But I keep on asking do I really need that accuracy from a budget machine. This kind of table opens up a lot of opportunities to get your foot in the door...

I am not form the US so even the cheapest machine, if I have to import it will cost almost double the price its worth when it gets here.(Making this DIY machine worth a lot more if you really think about it..

Best regards,
Bert.

If you are not concerned with the low resolution, low torque, and inaccuracy of direct drive then a little belt flex should not be of concern. You can never get more accuracy than you have resolution (smallest distance the tool travels with one step). If you are cutting out rough brackets for welding were you can have 1/16 margin, then build a machine to meet those standards. Since plasma is not "precision" cutting, it negates some of the need for accuracy, but remember that all the errors are cumulative. So if your table accuracy is only .030 then add the flame inaccuracy to that (maybe .020) and you are at .050 Plenty good for stuff that gets welded together. For other types of cutting (like decorative with fine cut) it limits you ability to do detailed cuts.

TOM CAUDLE
www.CandCNC.com
Totally Modular CNC Electronics.

[Degrom]

Thanks Jon,

Pictures would be much appreciated. I would like to build a machine that would be able to cut proper straight line and circle cuts out of 2mm(0.07") sheet metal. If it can do more detailed cuts it would be a bonus to me.

I know thicker material will not be a problem...

Thanks again.
Bert.

Prior to building this machine I was paying to have parts cut for me, and I later found out that they were cut on a Torchmate by a member of this forum. I can say that the same parts cut on my machine look just as good as those that were cut on the Torchmate. It did take me a long time to figure out what settings work best, and I don't use the machine that often so I'm still learning every time I use it. I did make a lot of scrap metal and waste a lot of consumables in the beginning. It was very frustrating at times, but it was well worth it.

Santa brought me a new camera for Christmas, I'll have to try cutting some artistic type stuff and post a few pictures. I normally make parts that are not extremely dimensionally critical. Automotive engine mounts and such, 10ga to .375" steel. It might be fun to try something different.

Jon