smooth plasma cuts

[worntorn]

I'm getting some amazingly smooth manual cuts from my PU 205. I was initially having trouble moving the torch across the work smoothly and the cuts can only be as smooth as the feed is.
I removed the little spring steel standoff that comes on the 60 amp torch (the Chinese style torch with zap strap switch) and started using a .25 thick aluminium straight edge to guide the torch. This way the torch cup sits up on top of the straight edge and the tip rides against the .25 tall vertical edge.

So the aluminium piece is both straight edge and standoff.

This method maintains a tiny constant distance between the tip and the work, something a bit less than 1/16". This is a lot closer than the factory standoff. The close gap seems to produce a smoother faster cut with less dross.

Also, for some reason all the drag and catching that was happening when using the factory standoff is gone and the torch slides along smoothly on the straight edge with minimal effort. The small gap between the tip and the work seems to be ideal, the cuts can be made very fast and the finish is near perfect, just as good as those I made using the milling machine feed.

I'll post some photos when I get a battery in the camera.

[worntorn]

Here's the photos

[Rbeckett]

Yup, dats a sweet edge. closer is better aint it. Looks like minimal prep for fit up and welding into place from there.

[worntorn]

Just like you said it would be, less dross and smoother cut. Thanks for the tip:)

[Zman0690]

can we get a pic of your setup now?

[worntorn]

It's just that piece of aluminium laying under the plate in the first pic. I suppose you could also use a piece of 1/4" x 2" or 3" mild steel or stainless. The torch does seem to slide nicely on the aluminium tho.

I'll see if I can video a cut happening.

the difference in cut quality between this using this simple flat bar as standoff and straightedge vs using the factory wire standoff and a straight edge is considerable.

[Zman0690]

yeah anything would be good as I'm not quite sure I'm following as I'm probably over thinking your setup.

[worntorn]

yeah, I'm sure you are overthinking it, not much to it. Remove the little standoff ring and store it away, tho I doubt you will ever use it again.
You can see how the 1/4" thick straight edge lays in the corner formed by the cup & tip.
The tip ends up being elevated off the work ever so slightly.

Here is a little video clip of a cut. It was a bit tricky to hold and focus the camera in one hand while cutting with the other, but I think you will get the idea. I hoped the video would show how smooth the cut is, but it doesn't really. The cut is almost as smooth as the pictures at the start of this thread. That cut was done the same way except two hands on the torch, little smoother torch movement.
http://www.youtube.com/watch?v=N9HSkft-0xw

[Zman0690]

perfect, that third pic is exactly what I was looking for and I was WAY over thinking your setup. I'm going to have to go try this out now. I really appreciate it.

Z

[jakeru]

Wow, that's awesome. Do you find it a problem that the metal straight edge conducts electricity? I've heard its not good to touch the tip to the work (including the straightedge?) because it can cause an arc "short circuit" inside the torch, which can damage the consumable parts (which aren't really supposed to arc directly to each other, except at the start). Do you find that to be the case at all? I was thinking though maybe the metal straightedge could just be taped (on either the top or the bottom or both) to make it not conduct.

I am using a Super200P; it doesn't have the same cutting head as yours, no "standoff", and the tip and consumables are a copper like material. I think it may be a 40amp cutting head. The machine OTOH, is supposed to be capable of putting out 50 cutting amps.

Also can I ask what amperage settings you recommend using various thickness metals... is there a chart available somewhere. For example, I am working on some .065" (16 gauge) aluminum sheet; what cutting current would you recommend I use for it?

Thanks in advance for your help!

[worntorn]

No problem so far using the aluminium straight edge, but I haven't used it all that much, perhaps 20 or 30 cuts about one foot long each on average.
For the 1/8" mild steel cuts I played with the amperage some and settled on 22 amps as best.

I have not been able to make a nice cut in aluminium yet. The aluminium cuts are smoother when done fast, but still a bit rough. My friend Murray who has a Hypertherm 30 has the same problem when cutting aluminium. I'm thinking that is just the way aluminium turns out when plasma cut.

I'm sure there are plasma cutting charts somewhere, however if they are anything like the Miller or Lincoln weld calculators, they won't be of much use.
For example, my Miller tig calculator says to tig .065 SS at 70 amps for a fillet weld. I find that 38 amps is all I need and 70 amps just fries the metal and tends to burn through.

[lugweld]

Aluminum cuts always look sloppy and considerable cleaning and prep must be done before welding them together. Aluminum just is a different creature and doesn't contain carbon.