Powermax 85 vs 105 for cutting 3/4" mild steel

[RhinoGuy]

Hi everyone. I am currently running a Powermax 85 on a piranha plasma table. The table has THC and I am using Hypertherms ProNest software. I am fairly new to plasma cutting and cant seem to get 3/4" plate to cut correctly. The holes always end up tapered or out of round on one side and the edges of the plate are sometimes not straight. I am thinking about changing the power source out to a Powermax 105 to see if it will help any. Any thoughts on that? I am just wondering if using the 85 at its maximum is causing me to have cut quality problems.

Great community you have here by the way. I have spent quite a bit of time reading through post.

[jimcolt]

Air plasma produces a certain amount of taper, and the taper is increased as hole diameter gets smaller. There are some rules of thumb and best practices that can minimize the taper. The Powermax85 does an excellent job on 3/4", however that is its maximum recommended rating. You could step up to the 105, which only gives you an extra 1/8" in pierce capacity, but higher duty cycle and faster cut speeds......keep in mind that the 105 needs 3 phase power. If you can provide pics of issues with your parts that you are having...maybe we could offer some advice on technique that will help out.

[RhinoGuy]

Thanks for the response. Ill try to find some parts and get a picture. I have noticed that the larger the hole is, the better it looks. Should I be able to cut a decent 7/8" hole in 3/4" plate? Or is that asking too much?

[SegoMan DeSigns]

That should work, just give it a long lead in. If the hole needs to be precise I undercut then clean out with a drill bit.

[djreiswig]

I cut 3/4" with a Powermax 65, so you shouldn't have any trouble with an 85.

[RhinoGuy]

This is on 3/4 plate. The top side looks pretty good, but the bottom side doesnt turn out well. It looks like the software starts the hole pretty close to the middle of the cut.

[djreiswig]

Try slowing down your feedrate. I did some holes in 3/8" and was surprised by the difference slowing down made. Do some test cuts with different speeds. But make sure you turn off your THC or it will dive when you slow down. I think I went down as far as 25%.

[motoguy]

Someone mentioned cutting holes at ~30% of standard cut speed. I had always cut at 50%. I tried 30%, and was amazed at how much better the holes turned out. I now cut all my holes (in thicker material) at 33%, and I may even try your suggestion of 25%.

Yes, be sure to disable your THC on that cut, though!

Also, the arc will "lag" quite a bit on thicker material. May want to add more overcut to help clean up the end of the cut.

[RhinoGuy]

I'll try slowing it down and disabling THC. I have tried slowing down the speed but I didn't know that THC needed to be disabled. Is there a certain thickness that always needs to have THC disable?

[djreiswig]

It's not the thickness, it when you slow down the metal melts away more and causes the voltage to go up since the gap gets larger so the THC will try to lower the z to adjust.

[motoguy]

Yup. At any given thickness, slowing your cut will increase your voltage, which will cause the THC to think it's too high, which will crash the torch into the metal. So, if you slow down from your book specs, disable THC or you'll crash your torch.

[TJS]

Newbie here. So where do you turn off the THC in the tool settings for an inside offset run like the holes. Screen shot would help.
Thanks. Running Command CNC update 1.1 and hub 1.8
T.J.

[Rodw]

I'm not a user of it but CandCNC has gcode commands to turn the THC on and off. Most likely a M67 or M68 command.
So you would normally use a cutting rule in sheetcam. This is a two part process. Create code snippets for THCon and THCOff that contain the correct gcode command per your docs and then in your profile cutting process, there is an option to insert a series of cutting rules.
So you may have a rule something like "On small shapes and holes < 35mm, reduce speed to 33% and turn off THC at beginning of cut and Turn on THC at the end of cut".

There are a number of examples on this forum. User SeanP has posted several examples.