Powermax 65 and 3/8" brass FAIL!!!!!

[762frmafr]

So I tried my hand at cutting 3/8" brass today. FAIL! Machine settings were as follows. .083" KERF. 32ipm speed. 1 second pierce delay. .18 pierce height. .06 cut height. Powermax 65 set to 65 amps. Mach 3 set to 139 volts. THC off. I came up with these setting after performing 4 line tests. The line tests pierced and cut all the way through and looked like they would be ok.

This is the same files cut in 1/4" mild steel. As you can see, it is not the file.

These are some pictures of the same file cut in the 3/8" brass. What is weird to me, is that the top, where the torch is, looks pretty decent, and is also why i did not stop cutting after the first one. The bottom and sides is where the trouble starts.

Top:

Bottom:

Sides:

[762frmafr]

No one has any insight as to what may have gone wrong? Jim Colt maybe?

[BTA Plasma]

Speed way to fast

[jimcolt]

There are a few thousand different grades of brass. Each has different characteristics....with heat transfer a big issue. You will have the same issues with copper. As BTA suggests...the speed is likely way too fast. Make sure you are piercing at a much higher height (probably about .024") and cutting at .06" (using the machine torch shielded parts). Cut real slow, you will need to compensate for a wider kerf, and if you do not have enough pierce height or pierce delay time you will damage the nozzle orifice on the first pierce.

Steel cuts using the thermal (melting) property of the plasma as well as the exothermic (oxidizing) effect of the 20% 0xygen content in air. Brass, copper, aluminum, stainless do not oxidize easily (that's why we use these materials for certain finished products), so the cutting process is strictly a melting process. Materials with high heat transfer (most brass alloys, copper) suck the heat away from the melting process with great efficiency.....so you need to cut very slowly.

Thin brass and copper actually cut fairly well, anything over about 3/16" is not so good!

Jim Colt Hypertherm

[762frmafr]

Speed way to fast

The inside holes were cut at half speed. So 17ipm. And they still look like shit. Are you saying I need to go slower than that?

[BTA Plasma]

Try 10-12ipm on the holes and 15ipm on the outer geometry but before you do that make a couple of test squares to ensure the corners are flowing correctly in the corners. 65 amps on 3/8 brass is pushing the lower limits of amperage. Some materials do not follow the 60% cut speed for holes as do others. Some need a tighter gap (between holes and strait line geometry) and everything must be cut slower. Jim can attest that brass does not cut like steel.

[jimcolt]

The 60% rule on holes is for steel....only. Since there are so many grades of brass and bronze you need to experiment as I outlined in my previous post. You may not find an acceptable cut, and the best way to cut this material may be with machining or waterjet.

Jim Colt Hypertherm