I am going to be building a number of new production machines in the next year or two for the company I work for. We have played around with buying a cnc plasma instead of machining or paying to laser the nuge number of parts that will be needed for these machines. The thickest material we would most likely work with is 5/8" steel. Am I going to get a lot of taper on the cut if I go with plasma? How hard is it to use an oxy/acet. torch with cnc? I will be sending the first projects parts out for bid at our local laser shops this next week. Thanks for the help.

Trent

Hi Trent,

The profiling work I've had done by laser is fantastic. If you want an accurate profile, I'd say go with laser cutting.

Plasma, I'd say is less accurate, so it should cost less. It may not be as dependable for vertical cuts because there is a mechanical aspect to plasma cutting: a perfect shaped hole in the cutting tip is required for an accurate jet. How long this tip stays in perfect condition is something to wonder about.

Oxyacetylene I'd reserve for the heavy cutting that laser cannot handle. Again, there is a mechanical aspect of how good the cutting tip is. There is also a much wider heat affected zone than with laser or plasma. The kerf width of oxyacetylene is considerable, too, and making a vertical cut is almost a crap shoot, because just the silliest little abnormality can throw the direction of the cutting jet off. Although you certainly can use cnc to guide any torch, you probably would not get the cutting accuracy on oxyacetylene that you'd associate with cnc cutting.

over 3/8 with most plasma cutters you will get some skew on the cut, especially if the tip and insert have some time on them, it's just the nature of the critter.. A higher capacity [say 3/4 to 1" rated] will have less 'sensitivity' to these type of problems..
Usually over 1/2" an Oxy / Actelylene cutter will do a 'straighter' job..
Laser is very clean, very close to water jet cutting,
plasma in the middle,
and gas ax will require the highest amount of cleanup,
basically inverse to the cutting equipment cost..go figure..
again, depending on the size and tolerances for YOUR needs, this may not be a factor.. especially if most cut edges are eventually going to be weld joints..

enjoy..

Not as bad as you may think to use oxy/acetylene.
http://www.cnczone.com/gallery/showphoto.php/photo/723/sort/1/cat/500/page/1
And
http://www.cnczone.com/gallery/showphoto.php/photo/724/sort/1/cat/500/page/1
I use 00 tip up to 1/4" with a kerf of .050", 0 tip to 1/2" with a .060" kerf and #1 tip to 3/4" with a .070" kerf. I can get things set-up (with a little practice on scrap) so that there is nearly no slag clean-up. Easily as good as plasma, with no beveling. It is easy to keep the tip clean in a machine, no user error. Using the machine has improved my hand torching, it doesn't make mistakes. If you are cutting steel, gas has incontrovertable advantages to consider. No bevel and even my cheesy hand torch has a max capacity of 5" listed in the manual. The accuracy is only limited by your machine, a torch cuts a perfect kerf. Look at the inside points in the M. I can hold a few thousanths with my machine (providing the plate doesn't move, a problem with plasma as well, I tack the sheet down around the edges and in the middle to stop lift and shift). Plate heating is a factor, I can cut a hole around 1" dia. Much smaller and you'll start to get molten metal. With planning, I can cut 1/4" strips. Just not 2 right next to each other with no lag time. I'm cutting out parts for a big R/C car from 1/8" right now, small and detailed. I can easily cut 3/4" plate with a tip change.
My machine, made on the cheap.
http://www.cnczone.com/forums/showthread.php?t=6923
MIKE