My scratch-built plasma table

[ej4]

Fantastic build info. I've been browsing for a couple months here for ideas, and I have to say this is one of the simplest, cleanest designs I've seen yet. Very straightforward.

A couple simple questions, if I may -

...so I welded them in pairs. I took B-Line unistrut 4-hole splice places and 4-hole T's and welded them together, then welded them to the ends of the cross braces. After tacking them up and making sure both pairs of braces were the same length, I cut them apart.

Can you explain this a little further? I think I understand what you wrote, but I'm not seeing how this guarantees four equal braces.

Also, what are the specs on your linear rails? It's probably a common part, but I'm not finding the rail+truck sets on mcmaster or ebay; I must be looking in the wrong place...

Thanks-
Ed

[grahamcowan]

From my previous post: ...so I welded them in pairs. I took B-Line unistrut 4-hole splice places and 4-hole T's and welded them together, then welded them to the ends of the cross braces. After tacking them up and making sure both pairs of braces were the same length, I cut them apart.

Can you explain this a little further? I think I understand what you wrote, but I'm not seeing how this guarantees four equal braces.

What I did was for each pair of braces (one pair is the upper and lower brace of one end of the table) I took a 4-hole B-Line unistrut T and a 4-hole B-Line unistrut straight splice plate and welded them end-to-end. So I ended up with a bolt plate that had 3 holes across the top and 5 holes down the middle. I clamped it to my weld table and stood the braces up one at a time and tacked them to the new bolt plate.

Easily put, all I did was cut one hole from the 4-hole straight splice plate and weld it to the end of the 4-hole T. That way the new bolt plates that are on the end of the braces each have a bolt hole on opposite sides of the tubing.

After I tacked the braces to the new plates, I made sure that they were all exactly the same length from the outer edges of the plates to the same on the other end (when I say exactly, I mean as exact as a tape measure can muster) and then I finish welded them. Then I cut the plates apart to have 4 braces - 2 with a single bolt on opposite sides and 2 with a single bolt on three sides. The fourth picture in this post (My scratch-built plasma table) shows the final product. Maybe I got lucky in the assembly, who knows, but after I bolted them together on the table, they put the Y-axis rails within 1/32". Not bad for eyeballing.

Also, what are the specs on your linear rails? It's probably a common part, but I'm not finding the rail+truck sets on mcmaster or ebay; I must be looking in the wrong place...

My linear rails are metric. The blocks are about 2" x 2", and the rails are pretty much 55" long. I don't even think they have a part number or brand. Definitely not NHK. I searched and searched all over the place online and ended up on eBay -- these were the cheapest rails I could find (I just now searched eBay again and couldn't find them) so I pretty much designed my whole table around them. I tried emailing past auction winners to see if they got a good deal but I got no replies back, so I just went for it. They were $150 each, which included 2 blocks each. I had to scrounge to find 32 M6 screws to use in them, too.

McMaster is way too expensive to get rails from. They offer brand new, high-dollar rails that are excellent if you can afford them, but really aren't worth it. Keep searching eBay. It took me almost a month to find and decide on mine.

[ej4]

Thanks - I get it now.

-ed

[grahamcowan]

Quick update on my table.

Since I was having issues with my workflow (i.e. getting something from my head to the computer and then to the table) I decided that a Wacom USB graphics tablet would help out.

And indeed it did. I now will be using Inkscape (free!) with my 6x8 Wacom tablet, which is 100% supported by Ubuntu 6.06. It works right out of the box and I can pretty much draw or trace anything I want to. I kept the old assortment of converters, CAM programs, and gcode utilities just in case, but otherwise I'll be using the tablet.

Thought I'd share.

P.S. I did have to recompile GTK with --with-xinput=xfree to have GIMP and Inkscape be able to use the pressure sensitivity on the tablet.

[FPV_GTp]

Very nice build

cheers

[Industrial Dog]

Very nice build! I have completed a table with the same idea of making it a muti-use. It's not anywhere as neat as yours. I've got it running the router right now.

I'm working on the plasma portion of my build and I didn't see any noise filtering on your system. Did you install a choke on your torch trigger?

[grahamcowan]

Originally Posted by Industrial Dog Very nice build! I have completed a table with the same idea of making it a muti-use. It's not anywhere as neat as yours. I've got it running the router right now. I'm working on the plasma portion of my build and I didn't see any noise filtering on your system. Did you install a choke on your torch trigger?

What kind of noise filtering are you referring to?

My torch gets turned on only by shorting the trigger contacts together via relay on my PMDX mainboard.

[Industrial Dog]

I'm referring to ferrite clamp on or dough nut type beads that act as a resistor to RFI entering your system from the plasma start arc through your trigger switch wiring.

I was looking at using the same system of a relay to trigger my torch.

[grahamcowan]

Originally Posted by Industrial Dog I'm referring to ferrite clamp on or dough nut type beads that act as a resistor to RFI entering your system from the plasma start arc through your trigger switch wiring. I was looking at using the same system of a relay to trigger my torch.

Never really thought of it. On the other hand, I've not had a problem yet. If I do, I am sure I will research the RFI problem and look for solutions.

[rumblfmp]

Cool,

although I am not to sure how a plasma torch can be cool :-)
Love the way you documented this project with the photos and all, gives me some nice ideas for my next project.

Thanks,

Rob

[grahamcowan]

Thought I'd give an update.

I've built a ventilation system underneath my plasma table to draw off the smoke. Works pretty well. I have it vented to a louver in a window nearby. I am using a 12" blower from Northern Tool and it works VERY well.

Also, as a trial, I swapped out one of the drive rods. I had originally installed 1/2"-8 Acme threaded rods for the drive system. Eight revolutions = 1 inch. I bought a 1/2"-8 rod, but this new one has 8 starts. One revolution = 1 inch.

I can now achieve cutting speeds of 720ipm.