Suggestions for DIY Plasma Tube Cutter - University Capstone Project

I am part of a student engineering team and we are working on designing a CNC Plasma Tube Cutting machine that will cope thin-walled chromoly tubing, and also mark the tubes with bend lines/guides so that they can be bent afterwards in our tube bender. We have a couple of ideas that we are looking at incorporating to reduce the total size and cost of the machine (as it will only be used for ~2 months a year, and have to be stored in our small space the rest of the time). We are hoping that you fine folk can help point us in the right direction. As this is on a student budget, you can probably imagine that we are trying to be frugal where possible. We are hoping to keep the whole project under $3k + the cost of the plasma cutter.

1. Active Torch Height Control: Is this necessary? We will only ever be cutting 1.00" OD and 1.25" OD tubing. If we can design it so the cutter sit's at one of these two preset heights, is the height control strictly necessary? To my understanding it is mostly needed on thin flat sheet because the heat distortion can warp the workpiece towards/away from the cutter. Because we will be cutting tubes, I think that the circular structure will prevent the cut edge from deflecting too much. Is it required for other reasons?
2. Manually moving the tube between feature locations to reduce machine size: Most tube lengths we are cutting are about 2-6 feet long. This means a "traditional" cnc tube cutter would cut one end of the tube, travel 6 feet, and cut the other end of the tube. The features cut and engraved on the tubing really only require 2-3" of axial tube movement. Is there a sensible way we could design the machine to only need 2-3" of travel? I don't know what this would look like in the g-code/programming side, but we are envisioning the following for our machine:
   - Machine cuts first tube end
   - Tube is manually repositioned to next feature location
   - Machine cuts/engraves next feature
   - Reposition tube to next feature etc.
   I'm sure this can be done, but I'm not knowledgeable enough about g-code programming at the moment to know if this will be hard to implement or not. We want to make the machine user-friendly, so ultimately I'd like to have one g-code program to cut all the features for each tube, but for it to pause/resume for each tube repositioning at the click of the button or something.
3. Recommendations for a budget friendly computer controllable plasma torch? The hypertherm powermax 45 is on our wish list, but it is quite costly. We will only ever be cutting 0.035"-0.065" thick chromoly and mild steel, so it really does not need to be a high-power machine.

Thanks so much for your help in advance! I have really enjoyed perusing some of the active DIY projects on this site, and I hope to post my project as we get into it!

To do plasma on a budget, start with Linixcnc
PlasmaC User Guide
You probably can get away without a THC if all its cutting is round tube. But it will only cost another $69 to add it.
I don't think it would add much cost to extend the range of travel beyond 2-3" and even to go a full tube length if you have a think about options.

Hey Rod, Thanks for the input! I don't think any of my members have any experience with Linux, so that might a pretty big hurdle to get over. Would you still consider this a valuable route considering this? The entry price is very appealing though!

As for the range of the machine, I agree making it a bit longer would not add much cost. 2-3" was used as an example to emphasize the idea, but we will still likely try to make it as small as possible unless we can come up with another way to store it.

This forum may not have much experience with Linux but this forum does https://forum.linuxcnc.org/
I was thinking you might be able to use a couple of round tubes with sleds resting on bearings and a belt drive to move the torch back and forth. You could remove the tubes for storage and make them as long or as short as you liked.

Don't move the cutting head along the tube, move the workpiece tube along. That's the standard way to commercial tube processing machines to work.

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Originally Posted by pippin88

Don't move the cutting head along the tube, move the workpiece tube along. That's the standard way to commercial tube processing machines to work.

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On the few hobby level builds I've seen, a bunch of them move the cutter. The main advantage I can see to moving the cutting head is that the inertia is constant. Is there an advantage to moving the workpiece instead?

Quote:

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Originally Posted by Xyphota

On the few hobby level builds I've seen, a bunch of them move the cutter. The main advantage I can see to moving the cutting head is that the inertia is constant. Is there an advantage to moving the workpiece instead?

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Yes, I had a bit of a think about this before posting. It would be much easier to move the cutter than the material which has to be held in a rotating chuck. But you could do it either way.