My little CNC plasma table (no pun intended)

[rugludallur]

First off any advise given is greatly appreciated.

I have a fairly good metal workshop and I am looking to add a CNC table to the setup. Mostly this will be used for plasma cutting but it might do the occasional woodworking job.

I am looking to cut 6m x 2m plates (20ft x 6.6ft) so the cuttable area will be slightly larger.

Most of the plates are thin but the my plasma cutter has a 1" capacity and a machine torch.

Currently I am looking at a pair of 2000 oz stepper motors, one for x and one for y with z set manually.

Given the dimensions a rack and pinion setup is almost required, I am looking at building a drive shaft into the gantry and having racks on both sides for smoother operation.

Any recommendations for RACK/GEAR types/models?
Any recommendations for reduction gears ?
Any recommendations for Drive (controller card)?
Any foreseeable problems with software for these dimensions ?

Yours faithfully

Jarl Stefansson
www.rugludallur.com

[Evodyne]

Jarl,

Hello! I just went through a nice build log by Moondog. He built a nice, big machine. His machine did use servos, but with different reduction and the right motor sizing steppers would work just as well. What was interesting was that he used a belt drive vs. rack and pinion. Seems simple and rugged. Precise? You be the judge-visit his site and see the boat kits he produces with he machine. The build log is here. His web site is CapeBoatWorks.

Ynneb has also put together a larger machine. Again, servos. I'm not sure if it is rack and pinion or belt driven. He has a web site here , but I think he is still getting it up and going. See his machine in the DIY CNC Machines section, here.

Other than suggesting these links, I'm afraid I can't be of much more help. Good luck!

Sincerely,

Lance

[Apples]

Jarl,

Here is my machine.

Started to build my plasma table.

Apples

[rugludallur]

Great looking machine Apples, there are a couple of questions that I have if you have the time.

Apples:
1. How dit the "no gear" strategy pay off ?
2. How are the gecko drives functioning?
3. Are your current steppers undersized/oversized so that you notice ?

General:
Does anyone here have any clue as to why the geckodrive website is down?
Anyone have experience with USB gecko products ?

Evodyne:
It's a small world, Moondog is building boats designed by the same boat designer my sailboat is designed by (Dudley Dix)

Jarl

[Apples]

rugludallur,

Apples:
1. How dit the "no gear" strategy pay off ?
2. How are the gecko drives functioning?
3. Are your current steppers undersized/oversized so that you notice ?


1. It is fast without the reduction. I have only driven it 4-5 times will test more this weekend. Might have to gear it down yet.

2. Gecko drive SCREAM !!!!!! they are brilliant, simply put. BUY THEM.

3. The gantry weighs about 50kg, have you seen the video. It is getting thrown about pretty quick. They motors seem very good.

Good luck

Peter

[Torchhead]

Resist the urge to do a direct drive rack and pinion or belt drive. While you will have breath taking rapids (something like the earth's escape velocity) your resolution and noise level will be less than impressive. 2000 oz/in.....wow your machine could double as a car crusher (just kidding). With a light gantry and no cutting forces 200 oz-in geared down at 3:1 are plenty for rapids up to 300 or 400 IPM. If you need higher rapids I would recommend looking at servos. I'm sure you have read all the points of steppers vs servos but the major one a lot of people miss is that you are always (in the design process) trading speed for torque. A servo spins and has increased effective torque at 2500 to 4500 RPM depending on the motor. The gear ratios are closer to 6:1 for that speed so using 100 oz-in servos with the reduction gives you the effective torque of a 600 oz-in directly coupled.

Consider using a dual drive on the gantry (you can get by with even smaller motors on each side).

The size of the table only comes into play if it impacts the weight of the gantry. The motors will run down a 30ft slide and easily as a 6ft provided the frictional forces stay constant. Bigger (longer) tables don't need bigger motors unless you want faster rapids (like 1000 IPM) to get to the other end quickly. Even then they won't be 10 times bigger than a normal machine

Tom C
(designer of the THC300)

[rugludallur]

Hi Tom,

Thanks for your advice, the only reason I had those 2000oz monsters in mind was that I had the option to buy them cheap. I had pretty much made up my mind to have one stepper on each side of the gantry and to slave/master them in software. Do you know a good place to buy Gears, I have looked at a couple of places but none look that good.

Yours

Jarl