View Full Version : Cut out a fabrication step, plasma cutting tip.

09-04-2007, 06:12 PM
I normally made a cardboard pattern, then cut out a main pattern from light sheet steel, sand the shaky hand wobbles off, then lay that pattern on the sheet and trace with the plasma torch. I have been doing it that way since the 80s when the plasma cutters came out. It was the fastest way to make something and reproduce it.

I have a sheet of mirror stainless, laid the cardboard pattern directly onto it, clamped it down with a clamp, and traced with the plasma cutter. I smelled something hot a time or two, but no black spots on the cardboard at all. I figure I saved about a hour or more and my steel sheet pattern.

Doing this, or cutting beside a ruler (looks like a saw cut), the radius of the plasma tip minus the cut swarf radius is the offset you set the pattern to.

I cut out a beautiful stainless oil tank, took most the morning designing it and cutting it out, hammer rolled the edge all the way around the horseshoe, then almost Fubar'ed the whole shebang while tigging it up.. My tig arc was wandering around on the stainless, no clue why, I sharpened the tip about three times, it was almost like lightning, never hitting the seam where I desired.

I quit before I throwed it into the woods out back. Perhaps I will gas weld it tomorrow, or throw it into the woods?

Bob Ford
09-04-2007, 06:31 PM
Be sure you ground both sides of the seam that you trying to weld. You are getting a eddie currant effect.


09-04-2007, 06:48 PM
Yes, sanded with a lap type sanding disc on a grinder, I ground my tungsten as normal on end..

Welder is a synchrowave 200, pedal about 50% running 120 amps on knob.

Never tried welding this mirror stainless before, it was originally motel bathroom mirrors. Beautiful metal. About 22 ga or thereabouts.

Bob Ford
09-04-2007, 06:57 PM

Not sanded or ground! Place your ground clamp on both sides of the weld or get as many ground connections as possible.


Bob Ford
09-04-2007, 06:59 PM
Your arc path is jumping around to get the best path to ground.

09-04-2007, 09:21 PM
You know of course you are right. My fab table, a one inch thick x 30" slab on legs has had paint sprayed on the top. My clamp was on the table, and the tank was stuck to the table when I quit. Meaning it was arcing.

Tired, near senile and blind I guess. I'm lucky my memory still works huh?

09-04-2007, 11:50 PM
Your lucky you still have friends here to tell you your faults. :)

And how to fix them.

09-05-2007, 12:21 AM
Hey David,glad your day went better than mine:D

Good tip on the cardboard,another method similar that I use is to make a plywood templet.The head on my cutter just happens to be 1" od,so I draw out what I want and then make it either a 1/2" bigger or smaller as need arises.I did about 300 3x7" oval perforations in some 8" C-purlins that way,it took longer to slide the jig down than it did to burn the ovals.

09-05-2007, 12:22 AM
Well wolfie what about this rash>????? HA.... Don't mind them lil flakes of skin, they'll crawl off.

Have you ever farted so loud it made a pitt bulldog run whimpering from the room?

Faults? It's a wonderful life... I got no complaints, had a good run. My family had a betting pool going that I'd not make it to 18, then 20... HA, good joke.. Done doubled that.

09-05-2007, 10:53 AM

What was the sheiding gas used?

What was the filler rod - hope it was a narrow strip of the parent metal?

Did you use a strip of copper backing at the gap? It helps for a better weld and traps some of the shielding gas so the weld is not contaminated?

Where are the pictures?


09-05-2007, 01:55 PM
Straight Argon, 316 1/32nd stainless rod, no copper in house, it gives off sickly fumes when molten. I have done back-welding with it on rusty old cars.

If you want pictures, come take them yourself. I am moving too fast these days.
Seriously David if you are traveling through, I got a extra driveway for your RV. I warn you thou, the chips are about a inch thick and need shoveling up. NOT a showplace museum for old tools. They get used hard.

Too puny today to make it to the shop. I push it too hard when wanting something completed. Does everything have to be a death roll project? My normal way of accomplishing a lot of things. Perhaps I need retraining?
I'm Dehydrated and I'll be back up later.

Frank hit it, I was tired, not paying good attention and a poor ground through the paint on the table top.

4:30 update.. I may have to walk away from this one.. Even thou I rolled beads into the bottom and top plates went around the perimeter and cross tacked it, it is warping up like a dead fish. I upped the gas to 17cfm, with a gas lens that blows the part with argon. I am doing better today, but still had to walk off once. It still has not hit the woods.. yet.

09-05-2007, 08:42 PM
Hey Dave. I have also had a resent experience with the thinish, mirror polished stainless and welding. That stuff is pricey too by the way.

I was making some heat deflectors for the hot rod exhaust.

That stuff warps up terribly with just a small amount of heat. I wonder if the polishing process induces some strain into the sheet and the heat just releases it.

I overcame the problem by making my joints supper tight so I could use as lil heat as possible and just fuse welded it with no filler.

Really small weld bead and fully welded.

Dunno how much control yer welder has but mine has an "Arc force" control. I usually leave it balanced in the center between "smooth" and "digging". I moved the control more towards digging to narrow the arc some and it helped tremendously.. JRouche

09-05-2007, 10:53 PM
David you probaly already checked it but if not you might check that stainless with a magnet as alot of the mirror finish stuff is type 430 Brite Annealed finish wich will be magnetic and not that corrosion resisting as it has almost zero nickle. 304 with a no 8 or 10 (mirror finish) is not very common for architectural things. It costs 5-8 times as much as the 430.

09-06-2007, 09:55 AM
I got about two inches of beautiful weld by fluttering the torch in and out to build a puddle. Where I got the arc and puddle stabilized it is pretty beads.

This material spot welds beautifully. Perhaps I should have started with spot welding my flanges I bent over to weld. That would have been better than tacking it up with the tig.

This has been a learning experience, not all good. I have about 8 or more hours lost now and it will hit the pile for sure.

09-06-2007, 10:09 AM
Well, SS is still getting good scrap price I think!!!!!!!!

Don't hurt yourself when you heave it into the scrap pile:eek: :D .

09-06-2007, 12:48 PM

Actually, to be honest, I got a excellent pattern with a few tack welds on it. Drag the plasma around it..

AND it's shiny..

Alistair Hosie
09-06-2007, 05:37 PM
and you'll see another 40 years too sonny boy:DAlistair