Plasma cutter question

[James E]

I have to notch a couple of pieces of steel tomorrow evening (Tuesday the 2nd) and have rented a plasma cutter from the local Sunbelt Rentals place. The cuts I have to make are small, it's under an old pickup and they don't have to be neat or pretty. The metal thickness is about 3mm and is within the rating of the cutter I'm renting.

I've never used a plasma cutter before and wanted to know if there are any tips and techniques anybody can give me before I crank this thing up for the first time. I don't want to set my garage or myself on fire.

I have some scrap that I can practice with.

 

[Cryptic1911]

It's gonna shoot sparks and globs of metal like a mofo in whatever direction that tip is pointing, so be aware of what is behind it, so have a hose on standby

 

[78Bird]

yep.

I <3 me a plasma, but they aren't the neatest or safest things ever.

make sure there's no piles of anything flammable where sparks can smoulder and catch later.

I'd cut a couple pieces of scrap to get a feel for it before you go under there.

 

[Notch1988]

I've found with mine that it needs a very good ground so be sure to get it onto bare metal. As well, I wear my welding helmet when cutting, I find it much brighter than oxy/acetylene cutting and cutting goggles aren't enough.
I assume you know that you need an air source as well, whether the machine has it built in or you've got a compressor.

 

[Buckgnarly]

DO NOT TREAT THAT ARC LIKE AN OXY ACYTELENE FLAME!!! The onlt time I have gotten arc burn was stupidly looking closely at the plasma when doing some intricate cuts one night. Did not look long, but it was enough to have sore eyes for two days.

You can usually use the gun to block the arc, but still be careful.

Also make sure to know if it has a drag tip or "freehand" type tip. The drag will hold the tip off the workpiece, the other you have to do it by hand. I like both, but probably prefer the freehand once you get good at it.

 

[wnstwolf]

Your in trouble. Post back after your test run. At the end of the project you will want to buy one! Good luck be safe..

 

[Jagmandave]

Unless you just can't reach it, I use a grinder with a cutoff wheel anymore for almost any cuts I neet to make, it's quick, easy to control and leaves a nice clean edge. Plus too and also, I already have one!

Obviously, if you had a lot of cutting to do the PC is faster, but it sure leaves a lot of cleanup work to do after the cut. Good luck with your project.

Post up some pics when you can.

 

[Buckgnarly]

Unless you just can't reach it, I use a grinder with a cutoff wheel anymore for almost any cuts I neet to make, it's quick, easy to control and leaves a nice clean edge. Plus too and also, I already have one!

Obviously, if you had a lot of cutting to do the PC is faster, but it sure leaves a lot of cleanup work to do after the cut. Good luck with your project.

Post up some pics when you can.

If you are doing a lot of cleanup work after a plasma cut, you are either not doing it at the right speed or the machine settings are off. Done properly, they leave clean cuts but many people try to push the limits of thickness and machines.

 

[MoonRise]

+1 on making a good 'ground' connection.

Also, think safety!

For you, use proper PPE. Correct darkness of shield or welding helmet to protect your eyes. Helmet or shield to protect your face. Welding gloves to protect your hands/arms from molten steel.

For the work area, be aware of what is under or around or behind the area to be cut. Cause plasma will cut through pretty much anything conductive in the path of the plasma jet! And the spraying molten steel/slag can do a number on things around the area if said hot stuff splatters onto them (wires, plastic pieces, etc).

Watch out for fuel lines!!!!

Plasma is pretty fast. Watch out for where the 'tail end' of the plasma jet is going (hold the torch at an angle and the far end of the plasma jet may be angled into something on the far/back side of where you are cutting and may cut or gouge that as well).

Something to do with a jet of ~10k F air/plasma can get through things in a hurry.

Plan your cut and maybe do several 'dry-runs' with the machine off to check for torch and operator clearance and position and so forth. That's for when you are cutting in an 'awkward' position like under a vehicle, etc.

3mm is about 1/8 inch thick. RTFM for the proper/suggested machine parameters for cutting that thickness of metal.

Also, RTFM for hints or requirements on things such as torch stand-off distance. Some machine need you to keep a little bit of clearance between the torch tip and the workpiece, others (Hypertherm) you can just drag the torch tip when cutting at 'lower' power or with the 'smaller' machines (30 amp or so, which would be plenty of power to cut through 1/8 inch steel) or with shielded tips. So RTFM.

Plasma needs clean dry air, so rig up things properly. RTFM for the air-flow requirements of whatever plasma cutter you are using.

 

[A**holes Garage]

+1 on making a good 'ground' connection.

Also, think safety!

For you, use proper PPE. Correct darkness of shield or welding helmet to protect your eyes. Helmet or shield to protect your face. Welding gloves to protect your hands/arms from molten steel.

For the work area, be aware of what is under or around or behind the area to be cut. Cause plasma will cut through pretty much anything conductive in the path of the plasma jet! And the spraying molten steel/slag can do a number on things around the area if said hot stuff splatters onto them (wires, plastic pieces, etc).

Watch out for fuel lines!!!!

Plasma is pretty fast. Watch out for where the 'tail end' of the plasma jet is going (hold the torch at an angle and the far end of the plasma jet may be angled into something on the far/back side of where you are cutting and may cut or gouge that as well).

Something to do with a jet of ~10k F air/plasma can get through things in a hurry.

Plan your cut and maybe do several 'dry-runs' with the machine off to check for torch and operator clearance and position and so forth. That's for when you are cutting in an 'awkward' position like under a vehicle, etc.

3mm is about 1/8 inch thick. RTFM for the proper/suggested machine parameters for cutting that thickness of metal.

Also, RTFM for hints or requirements on things such as torch stand-off distance. Some machine need you to keep a little bit of clearance between the torch tip and the workpiece, others (Hypertherm) you can just drag the torch tip when cutting at 'lower' power or with the 'smaller' machines (30 amp or so, which would be plenty of power to cut through 1/8 inch steel) or with shielded tips. So RTFM.

Plasma needs clean dry air, so rig up things properly. RTFM for the air-flow requirements of whatever plasma cutter you are using.

Agree, good info.


http://weldingweb.com/index.php

 

[BigGMC]

Do not begin cutting while suffering from a hiccup attack....... lol




Seriously tho, they are a very efficient cutter (providing the machine is operating correctly and within its limitations), any jerking motion you make will be reflected in your cut.
Previous replys covered things well, thats all I got to add.

 

[ddawg16]

Your in trouble. Post back after your test run. At the end of the project you will want to buy one! Good luck be safe..

x2^^^^

 

[purplezr2]

Unless you just can't reach it, I use a grinder with a cutoff wheel anymore for almost any cuts I neet to make, it's quick, easy to control and leaves a nice clean edge. Plus too and also, I already have one!

Obviously, if you had a lot of cutting to do the PC is faster, but it sure leaves a lot of cleanup work to do after the cut. Good luck with your project.

Post up some pics when you can.

Mine will cut 1 inch smooth enough that it take about 5 secs with a grinder to knock the slag off. On thin stuff(1/8 or 1/4) I can knock the little bit of slag off by hand almost.

 

[James E]

Great info. Keep it coming. I'm renting one because if I do it right, the two cuts I need to make will take about two minutes, versus just plain impossible with a cutting wheel.

I'm notching a frame crossmember for clearance. I'm taking out just enough metal that a grinder would not be feasible and the bends on the part and the lack of space make even a small cutting wheel near impossible to use. To use a cutting wheel, I'd be taking off more material than I need or want to just because of the direction I'd have to come from.

Plus, it just gives me a reason to use a cool tool I've never used before. Now it looks like my biggest problem is that the truck is up on a lift, it's not driveable at the moment and my garage floor is Racedeck. I've got to come up with something to cover the floor up with. I'll also have to do some cleaning tonight as the truck is an old beater and the entire bottom end is filthy with oil and grease. That's a fire waiting to happen.

 

[MoonRise]

... and my garage floor is Racedeck. I've got to come up with something to cover the floor up with. I'll also have to do some cleaning tonight as the truck is an old beater and the entire bottom end is filthy with oil and grease. That's a fire waiting to happen.

Yeah, compressed air + 10,000F + fuel (grease/oil/etc) = InstaFire

For the garage floor, again a 'Yeah'. Protect it. I'd lean towards a few sheets of cement board (Durock, Wonderboard, etc) and covered with a welding blanket (which will scorch if big enough slag or molten metal drips/falls onto it, hence the non-combustable hard boards underneath.)

Or spread a layer of clean dry sand underneath where you will be working. Doesn't burn and keeps molten falling stuff from bouncing and 'skittling' over to other areas. Sweep/blow/vac up when done.

And you are aware that notching a cross-member will weaken it? Plain 'strength' as well as 'stiffness' and fatigue life?

 

[wnstwolf]

James if possible tack a guide to the outline of what your cutting to run the edge of the torch against. If your notching and you want it to be somewhat neat this will aid in kepping things on line. Of course your under the truck so easier said than done..

 

[James E]

And you are aware that notching a cross-member will weaken it? Plain 'strength' as well as 'stiffness' and fatigue life?

I am aware and was hesitant to say what I was doing lest the thread turn into dire predictions of the truck folding up on me like a wallet.

The crossmember has some folds in it and the amount of metal I'm taking out is minimal and along the edge. I'll be taking no more than a strip of about two inches by a quarter inch. I had considered welding on a metal gusset along the cuts to reinforce it (perhaps even welding back the strips I remove), but I'll probably wait and see how the cuts turn out before I start thinking about welding metal back in.

The durock and sand ideas are great, by the way.

I will have a buddy over who wants to watch the cutting. He'll be my spotter so that if I set my hair on fire he can shut me down.

 

[wilcolater]

All good suggestions,I like the one about hiccups, I use a plasma to notch steel joists and rafters and clamping on a guide works great, freehand cutting to a line you will end up with a cut that looks like a electrocardiograph. A fire watch is also a good idea and more fun.

 

[AndyA]

I've used damp towels to protect stuff before. Keeping a bucket full of water and towels is a good idea for smothering anything that catches. A fire extinguisher is good also.

I don't know what size plasma you're renting. If the metal is thin I have to move quickly to keep the proper cutting speed. Practice on scrap material of similar thickness. Try turning down the current. See if the rental place has fine-cut tips. If it's a smaller unit, then it'll probably be ok.

Make sure you have new consumables in the torch. Worn consumables will make sloppy cuts.

Dry air is important. Wet air will ruin the consumables (You may not care. Treat it like a rental!)

Where you point... it will cut! Don't be afraid to stop mid cut and reevaluate what you're cutting. Similar advise to the old saying "measure twice, cut once"

Use a scribe for layout lines. The shiny scribed line seems to show up better than other markings when you have the hood down and the arc struck. Soapstone seems to disappear on me whenever I start cutting.

The cutting is done with an arc. Same sort of thing as welding. It will burn your eyes. I'd use a #5 or darker shade welding lens. A quality lens of any shade will provide protection, but you may be seeing spots afterwards if the shade is too light. If you have trouble seeing with the darker shade, light up the area with some good worklights.

Try not to breathe the fumes. The plasma will vaporize some of the metal. If there's any paint, grease, or other nastiness, it will also be vaporized. A strong fan won't hurt anything (unlike some welding processes). Adding a P100 respirator is a better idea. Supplied air is an even better idea. (I'd be ok just using the fan if it's doing a good enough job)

Watch what's behind your cut. The plasma is going to blow out molten metal. If thin material is very close you may blow a hole in it. In the best case you'll probably have to wire brush anything behind the cut to clean off the junk. A piece of scrap metal laid behind the cut may save the trouble.

 

[darkk]

Plasma cutters can and will give you a very nasty *sunburn* if your skin is not protected well. Make sure you use dark enough lenses and wear full face protection and be sure to be careful of the blow back if there is something solid directly behind the cut area. Especially if it is flammable. Back in the day, wearing contact lenses while cutting was not recommended.

 

[Capstone]

When I read the OP, I thought to myself.. "Are you trying to cut something from below, with a PLASMA?!" I just got finished with my first major welding project and I agree with all the posts, mostly from experience...

* I got "sunburned"
* I had a loose connection on my plug for the compressor and it stop running while useing the plasma and burned out the plastic air disperser
* I used the so called "plasma shades" at first and my vision had a white spot for the rest of the day
* I had a glob of molten metal almost land on my foot

Its a "cool tool" but definitely respect the power needed to blow through metal in mere seconds.

 

[James E]

Great info and alot I hadn't thought about.

I'm under the truck but beside what I'm cutting so I'm definitely not going to get dripped on. Nothing directly behind what I'm cutting so I have room to put some kind of a backstop for spray.

I'll try using my welding helmet. I hadn't even thought about the bright arc when I came up with this idea. I'll also wear full, heavy clothing. Wet towels and a bucket will be there and a fire extinguisher, too.

The one they gave me is a Miller Spectrum 375. It's really small. No instructions, no tips no nothing, so I'm glad I posted here first. I'm going online this afternoon to see if I can find the instructions.

 

[MoonRise]

The manual for the Spectrum375 can be found at the Miller website.

http://www.millerwelds.com

Just have to cross-check what torch it has, as Miller lists 'different' manuals depending on what torch the machine has.

Neat and capable machines that can run on either 120V or 240V input power.

Also, if you think the Spectrum375 is small, check or look up the Spectrum375 X-Treme. 49-55 lbs (without or with the torch and cabling) for the 'full-size' Spectrum375 versus just 18 lbs (including torch and cabling) for the Spectrum375 X-Treme.

Also, for some more info about plasma cutters and safety and plasma cutting in general, check out the Hypertherm website. (the Miller Spectrum375 X-Treme and the Hypertherm PowerMax30 are 'cousins').

http://www.hypertherm.com

and

http://hypertherm.com/en-us/Training_and_education/Intro_to_plasma/

Remember I mentioned the PPE??

 

[James E]

Great links. It's an X-treme, by the way. Not sure what torch it came with.

I'm trying to think of what metal stuff I need to cut up just for fun. I've got some scrap that I need to take to the dump--maybe I'll chop it up into little pieces first.

 

[James E]

I cut the piece tonight. I wound up removing the crossmember as it wasn't as difficult as I originally thought it would be. After tripping the breaker three or four times, I figured out the settings and got to cutting.

I think I need a plasma cutter.

 

[wnstwolf]

I warned you.. ;-)

 

[Capstone]

I cut the piece tonight. I wound up removing the crossmember as it wasn't as difficult as I originally thought it would be. After tripping the breaker three or four times, I figured out the settings and got to cutting.

I think I need a plasma cutter.

... and a 50amp circuit home-run to your garage to make sure you never pop the circuit mid-stream again.

 

[MoonRise]

I cut the piece tonight. I wound up removing the crossmember as it wasn't as difficult as I originally thought it would be. After tripping the breaker three or four times, I figured out the settings and got to cutting.

I think I need a plasma cutter.

Hmmm, "tripping the breaker" sounds like you probably had it on 120V power off of a standard 15 amp wall outlet.

There is a scale on the power output knob with settings (amps output) for both 120V input power (20 amp output is the 'max' when running on a 15 amp circuit breaker) and 120V-20 amp/240V input power (max the machine out if you want to on those input power settings).

Plasma is pretty fast and 'easy', within the machine's limits.

Post pics. We love pics. But you knew that, didn't you?

 

[fiveoboy01]

I've used a plasma cutter extensively in the past and the advice given is spot on, I just want to stress safety and eye protection. The sunburn thing is no lie... but if you're only doing a tiny section you may not have to worry about that too much.

Have fun, you just might want to buy one after you're done

 

[James E]

Capstone and Moonrise, you're both right about the circuit. I have higher-rated circuits in the garage but since I moved the cutting outside, I could either use the outside receptacle (15 amp) or use a very long drop cord.

Since I've run big-drawing items on that 15 amp circuit without tripping it, I started with the power output knob at the high end of the 120 range and just moved it down until the breaker stopped tripping. It wound up midway in the 15 amp range on knob. That cutter must really draw some current.

I really want one now, but at $1,500 for one, I could rent this one 31 more times before I break even. I'm 43 and this is the first time I've rented one--plus the rental store is right around the corner. I'm going to go on the assumption that I probably don't need one (not that that's mattered to me before) so I think I'll hold off.

 

[Imcrazy]

Since when has "needing" one been a pre-condition to pulling the trigger and getting one.

At least that is what I tell my wife.

 

[Crusty Nut]

Just buy the rental unit. You know it works, you like it, and it is probably half price. I use the hell out of my plasma and just like a lift or anything else awesome, everyone says "well I never needed one until now, but now I can't live without it"

 

[ddawg16]

I cut the piece tonight. I wound up removing the crossmember as it wasn't as difficult as I originally thought it would be. After tripping the breaker three or four times, I figured out the settings and got to cutting.

I think I need a plasma cutter.

Tried to warn you......you just don't listen.....do you?

 

[James E]

I listen. I just have a habit of ignoring what I don't want to hear--or so my wife tells me.

 

[stingry]

I listen. I just have a habit of ignoring what I don't want to hear--or so my wife tells me.

My wife calls this "selective hearing!"

Cheers
Steve

 

[MoonRise]

I really want one now, but at $1,500 for one, I could rent this one 31 more times before I break even. I'm 43 and this is the first time I've rented one--plus the rental store is right around the corner. I'm going to go on the assumption that I probably don't need one (not that that's mattered to me before) so I think I'll hold off.

$1500 for a 30-amp class plasma seems a bit on the high side.

Hypertherm PowerMax30 ('cousin' of the Miller 375 X-Treme) usually goes for around $1100-$1200 NIB, IIRC.

Plasma, I think Hypertherm first.

Plasma is awesome, isn't it?

Some electricity and some clean compressed air and you have a machine that can cut through metal really-really fast (within the limits of the machine). Steel, stainless steel, aluminum, copper, whatever. Hardened steel (like a Grade8 bolt) or soft plain low-carbon steel, it doesn't matter to the plasma cutter.

There, am I helping?

 

[AndyA]

$1500 should get you double the machine.
My cutmaster81 new was (iirc) $1400 and change. 60 amps. Rated for 7/8" cut, but I've cut 1" and it still looked good. I could probably get by with one rated at 1/2", but it's been nice to have the extra when you need it.