Use roller chain to move gantry.

[Beetman05]

Thank everybody on this form it has giving me a lot of ideas and information on how to build a 4'x4' cnc plasma table. I am a farmer and this will be one of my winter projects my idea is to use #40 roller chain on each side to move the gantry use sprockets on each end with spring tension to confiscate for any wear which I think will be very little, on my combine chains run 5000 to 8000 ipm with very short chain length get 200 to 300 hrs before replacing chain compared to 300 ipm on cnc. Some use belting which would be smother but do not see any other benefits. Reason I like chain idea is cost, have chain on hand brought at auction cheap many years ago and www.surpluscenter.com has sprockets very reasonable. Anybody use roller chain or think this is a bad idea.

Garry

[Verfur]

I think one big concern would be all the dust, slag chips and ect. collecting on the chain lube. I think if I were to try it I would clean the chain with WD40 and use some chain wax. Check with the local motorcycle shops on the chain wax. the reson is the wax drys and is not sticky pluss aids in lubrication and rust. Plus you have more clearance in the chain and sprocket and always have slack in the chain which may make holding a tolerance an issuse.

Have you thought about useing the chain like a rack and pinion? Like weld the chain down and run a sprocket on a geared down stepper motor or two. It might work
if you run two chains side by side slightly stagared so as the teeth on two defrent sprockets would keep any backlash out. Hum, maybe worth a try like you said the cost is right.

John

[Beetman05]

My thinking was to keep chain dry no lubes on it that is how my combine is run when I combine a crop like soybeans sometimes you are working in a cloud of dust all day very harsh condition for chain, lube on chain would make dust and dirt stick to it, so they stay dry and run 25 times faster then cnc table would, also was going to put turnbuckle and spring in the chain length to maintain very tight tension max working load is 810# for 40 chain could make very tight.

Garry

[2muchstuff]

The chain idea is a good one but not the best for accuracy. Accuracy costs money, the more money - the more accurate. If you tightened up the chain to even 750 lbs on each chain, that would be 1500 lbs pull across your table. Is your table capable of that kind of pull, what about warping the table if the pull on each chain is different. Your springs would have to be die springs to get that amount of tension in a small package. You need to keep so many teeth in contact with the chain to avoid jump. To get the required number of teeth in contact you will need idler sprockets on either side of your driven one to help wrap the chain around. With the high chain tension on the idlers/ driven sprockets that will put a lot of tension on the bearings, shafts and mounting plate. More tension= more friction= slower speeds which leads to bigger motors to overcome the slow speed. I don't want to be the bearer of bad news.

[Beetman05]

Better to have bad news now in the planning stage then after a project is completed. My 810# was what the chain was capable of I would think it would require considerably less then that to maintain no slack in the chain for a 4' table. I thank you for the input even if it isn't what I wanted to hear. I still like the idea hopeful somebody will comment that has tried it.

Garry

[Verfur]

as to the Idea of the rack and pinion the chain would be supported on the back side by a heavy metal rail with full contact under the table and would only need enough tension to pull it strait. It would have to lift the hole gatntry to slip a tooth and if it were driven on both sides it could not be lifted. Just like a regular rack and pinion.
I do think you may still need two chains side by side on each driven side with the teeth staggared to remove slack. The drive would be two stagarred sprockets on the same output shaft. I now that it would not be as acurate as ball screws or even a geared rack and pinion but after all it is going to be a plasma table.

its Just a thought. I am sure there are many down sides but the up side is the cost.

John

[Verfur]

Beetman05,

If I may ask, what are you going to use for guide ways? Have you seen Ynebbs router with angle iron guides realy cool. I think I am going to try the angle iron idea with a 4' * 2' router for my self. I no it is not extreamly acurate but this is just for model aircraft work.

[ynneb]

I have always liked the idea of chain too. I eneded up using timing belts.
I have seen pictures of machines using chains b4.
Since you are using it for a plasma torch the thing to bear in mind is that plasma does not have high accuracy, therfore anything more accurate than chain would be overkill anyway.

I say go for it. Especially since others have done it b4 too. When I find the picture i will posts it in this thread.

[Verfur]

ynneb,

Do you recall how they dealt with the backlash or if they just did not worry about it?

P.S. how strait will you angle iron guided router cut?

John

[ynneb]

Do you recall how they dealt with the backlash or if they just did not worry about it? P.S. how strait will you angle iron guided router cut

I am just wondering what backlash you were expecting from tensioned chain around the gog ?

Very straight for my needs, I guess for an engineer who wanted to make machine parts that had to fit into each other it wouldnt be considered straight. That been said, I do all sorts of timber work and the pieces line up, and fit into each other well.

[Beetman05]

I was going to use skateboard bearing on 1/2"x 4" cold roll flat for my guide similar to the torchmate cnc table make some eccentric bolts for the adjustment reason like the idea is cost and easy to make brought bearings on ebay for 48 cents each and cold roll has tight tolerance. When I get some time I will experiment with some chain stretched 4' between two sprockets to see how much tension is needed and how much backlash I will get before the final design. John that is not a bad idea using chain as a rack, chain would not be moving so element tension and wear.

Garry

[Weldtutor]

Hi Beetman
These photos show a CNC plasma table (not mine) with chain drive that the builder has done some quite fine cutting with. Don't give up on the chaindrive idea. Cable drive might be worth your consideration as well. The rails are also flat bar, similar to what you are planning to use.
Weldtutor