YHK - yet another hacker news clone

How to make a CNC plasma cutter with high-frequency start

13 points edward 3 days ago 4 comments

Xunxi 1 hour ago | parent

Nice build. There's been a lot of momentum in the desktop wire EDM community too, with projects like picoEDM, Gedm, openEDM, and baxEDM. Precision is the usual weakness of plasma cutting, but I suppose it makes up for that in speed. Have you tried tuning for kerf width or taper, or is that more trouble than it's worth at this scale?

CamperBob2 47 minutes ago | parent

Potentially easier solution for the USB problem: measure your cables with a DMM until you find one with good end-to-end shield continuity. A large proportion of USB cables have no effective common-mode protection (to say nothing of EMI shielding) because one end or both ends is ungrounded.

Animats 2 minutes ago | parent

Tying the grounds of multiple devices together over USB cables is likely to create a ground loop. Grounding is supposed to be a tree, rooted at the stake in the ground out by the electric meter. If you don't have that, every loop becomes an antenna. That's why braids are usually grounded only at one end.

This matters when you have something as RF noisy as a plasma cutter nearby.

If you have a scope, you can start looking at signals to see where there's RF hash. Then you can try putting ferrite inductors around various power and data cables to see if it helps. Often it does.

There are USB opto isolator cables.

I'd really like to see a big red switch on that setup to turn everything off. If somebody like a first responder ever needs to shut that thing off, it's not at all obvious which plug to pull first.

(I used to use the rather antiquated plasma cutter at the original TechShop. It never started properly. Plasma cutters start by creating an arc between electrode and the nearby nozzle. That makes some plasma, which is then blown out to the workpiece. Once there's plasma from electrode to workpiece, the nozzle is cut out of circuit. The one at TechShop had a consumable copper electrode and a consumable copper nozzle cap. The electrode is supposed to get all the wear, because the nozzle cap is only involved when the arc starts. TechShop's machine often failed to cut the nozzle cap out of circuit, and it consumed nozzle caps faster than electrodes. TechShop sold nozzle caps.)

convolvatron 20 minutes ago | parent

slag, cut taper, leadins and warping affecting surface level are all constant annoyances with plasma. I find it a lot easier to just send jobs to a waterjet shop nearby.

my friend did a lot of bulk plasma cutting, and his solution was to build a tumbler filled with abrasive and dish soap, and after a day or so the edges would be smooth and rounded. but that's certainly not a replacement for machined parts.