New Machine Build- 4x4 machine

[tmbg]

I guess it's time to start a project log thread for my table... I started it over a year ago!

It's a 4x4 steel table, made from 2x4x3/16" steel tube for the frame and 2x2x3/16" steel legs. The slat surface area is 50" square, and the frame is 54" outside dimensions. There's a piece of 16ga sheet welded to the bottom to create a 4" deep water table, and slat holders for 3x1/8" slats.

I built the table itself over a year ago and bought my plasma cutter, but I got stalled out looking for linear rail to use on it and other projects got in the way. I finally bought some rail on ebay and got the project moving again.

The gantry is made of 2x4x1/8" aluminum tube with 1/4" aluminum sideplates, welded. It runs on THK SSR25 rail. They're probably overkill, but they were the easiest thing I could get in the length I needed. The rails are 1360mm (around 53.75"), and my gantry carriages are around 7.5" wide, giving me 46" of travel. My target was 48", but I would rather have two trucks per rail for stability than get that extra 2" of travel.

I'm driving both sides of the gantry using 20dp-20pa rack and pinion. The racks are welded to the frame, teeth down. I'm using hobbycnc motors that I bought for a mini-mill I built a while back, they're rated 205oz-in unipolar, and I think something like 275oz-in bipolar parallel. Right now I'm using the hobbycnc controller to drive them, but I have a G540 on order. I was going to order different motors for this table, but I am now thinking that these motors, being 2.2mH, are about ideally matched to the G540, and will have plenty of torque. Any bigger and I'm just losing speed. I'm driving the pinions through a 3:1 belt reduction of my own design, giving me very close to an inch of travel per stepper rev. I was easily able to get 600ipm rapids and 200in/s^2 accel in my first gantry tests last night. The gantry isn't fully loaded yet, but I'm also only using a 24V power supply right now. I'm optimistic about my speeds.

For the plasma cutter, I purchased the ubiquitous PowerMax 45. Everything I'd read about it here suggested it was the ideal machine for a small cnc table, and while I've only been using it handheld for the last year, I absolutely love it. It's a great machine, and was a good investment.

I'll post some more pictures later, but here's last night's video:

YouTube- Cnc plasma

[Lawrence_0485]

Hi nice looking machine you got there. From the video it looks like your gantry is lagging on the far side of the table. As you know that will pull out of square and make your parts unsquare too. Like i said thats just what it looks like in the video.

[tmbg]

Yeah, im not sure whats going on there. The far side is slaved to the near side via mach3, and I don't know if the lag is in the software, the driver, or what. I have a g540 coming, and I hope that it will solve my issues.

[Lawrence_0485]

ya i couldn't help you there. I run two monster 10'x22' plasma tables at work and not real knowlegeable on the electronics side of it yet. I just know the physical mechanics of it. Anyways hope you figure it out. hey here is an idea, It looks like its lagging in both directions and catching up when the gantry comes to a stop. If you are able to up the voltage, could you give that side an extra volt or two to make it run a little faster. Just an idea tho

[mcArch]

Is your gantry aluminum or steel?
That lag in the youtube video is quite odd!
-Mike

[tmbg]

It's aluminum. My original design called for steel, but I decided saving weight in the gantry would allow me to run smaller motors and maintain high transit speeds and accel. The tube that I originally bought for the gantry is 3/16" 2x4 steel tube. The aluminum part is 1/8" 2x4 6063. It weighs less by a factor of four!

[tmbg]

It's been awhile, but my machine made its first cuts today! Got my CandCNC LC-THC up and running, and it was super easy and works great!

There's no water in the water table yet, this was one of the first test cuts:

YouTube- video-2010-08-28-01-17-40

[millman52]

I'm assuming you got the gantry lag out. What was causing it?

[tmbg]

could have been either my mach settings or my drivers, I'm not really sure. I never tested it again in that setup, now I've got the G540 running them and everything's fine.

Now I'm thinking that I need to add a second parallel rail to the gantry for the X axis; the car runs on one rail, and at high cut speeds, there's a lot of movement in the torch head.

[tmbg]

[multiplex]

turbo flange i see