3/8'' stainless cut not finishing

[_Ogre]

i cut 3/8'' stainless for the first time today. the cut edge is nice, dang near perfect, but the last 1/8'' is not cutting. these are a few test washers: 1.5'' od and .44'' id hole

top: cut all the way around, .1'' lead in/out, 38ipm, 131v, 65 amps, .15 pierce ht. no dross, the .44 hole dropped out but that's not always the case


bottom: not cut all the way, minimal dross


i've tried speeds from 38 to 45 ipm. have not varied the volts or amps.
i believe i'm having a similar problem to what jhart is having in this thread http://plasmaspider.com/viewtopic.php?f=4&t=12343

we needed 2 flanges to do a build in the morning so i cut them both. this is the bottom. 38ipm, 65a, 131v, .1 lead in, no lead out and a .1 delay at the end of cut. not sure mach3 can slow at the end of the cut as suggested by jim colt in the thread posted. small holes still connected.



any other suggestions to try?

[rikduk]

I"ve had the same issue with thick stainless.
Are you using sheetcam?
If you are using the latest versions with cutting rules, you can slow, lets say to 75%, 0.187 before end of cut.
I think you said in another post you are using stable sheetcam, but you should try the latest versions.
Pretty much bug free (I've had no problem)
But the cutting rules are just awesome.
Heres a link for a video: http://www.youtube.com/watch?v=_gsNhcWF2lE

[BTA Plasma]

Post your g code. It doesnt look like your .1 lead in/out is long enough and your pierce delay is too quick.

[jimcolt]

Stainless as it gets thicker....causes the plasma arc to trail at an angle between 15 and 30 degrees. Think of the bottom of the arc as cutting a bit behind the top of the arc. On many machines there is a plasma off delay that can be programmed at the end of the cut. This type of delay stops the motion for your hole where you want the cut to stop, but keeps the plasma running for a time duration (maybe a few tenths of a second), allowing the bottom of the cut to catch up to the top. Too much delay and you will get a large divot.

You can also experiment with slowing down a littl bit at a time until the slug drops. Too slow and you will get dross.

Another method is to program an overburn, essentially staying on the radius of the hole about .150" to .200" past the lead in kerf, allowing the trailing bottom of the arc to finish the cut.

Last, but not least.....if more power is available (like the 85 amp process), try that.

Steel does not have this problem as it has an exothermic reaction created by the oxygen content of air....this keeps the arc burning in a straighter manner. Stainless does not oxidize easily, so is a strictly thermal (melting) process.


Jim Colt Hypertherm

[BTA Plasma]

It is called pause at the end of cut when you setup a tool for stainless in sheetcam.

[_Ogre]

i looked at the video link that rikduk posted, all those codes that bta preloaded in sheetcam make sense now. i was going to ask what those were for eventually

i'll have to look at those codes and rules when i get back to the shop monday. not sure if my version supports all those rules features for slowing down before a turn. if so that will fix a lot a problems i'm having for speed at sharp angles too.

as stated i did a .1s pause at the end of the cut with no leadout. i cut the 2 flanges they need for this morning but need to cut some more later. i'll experiment more on the pause and slower speed until i see some divots or dross start to form.

the 65 amp consumable pierced fast even in 3/8 stainless, i did notice a curl in the plasma stream on the finished edge. as jim says ss is different than mild steel. i cut 3/8 mild with a clean drop out on the holes and the part.

money was not an issue when we bought the pm65, didn't want to overbuy with the pm85. am i regretting my thought process...

[jimcolt]

I would use either 65 amps or even 45 amps for the best quality on 3/8" stainless. Lower power produces squarer edges. For 3/8" stainless once you get the programming figured out to make drop cuts...there really is no need for 85 amps. I only suggest it because brute force (more power) will make drop cuts easier than less power, although the cuts generally won't be as nice.

Jim Colt