Sheetcam circle problem

[jeremy_smitty]

I converted a laser engraver into a cnc plasma. I am currently having issues, on and off, with cutting circles.

Lets say I have three circles to cut on a plate. It will cut the first one perfectly. It will pierce the next circle, and move to the edge of the circle, and stop cutting the remaining portion of the circle. It will then go to the next circle, and complete it 100%.

I have eliminated it being the design program, by using the shape design program inside of sheetcam. It still does the exact same thing.

The weird thing is sometimes it will complete all three circles, depending on the time of day.

Any ideas on how to resolve this? I have ensured the ground clamp is grounded well, on a clean piece of steel. I am starting to think that there is a problem with the post processor programming. That being said, sometimes it works just fine.

[adbuch]

Check to make sure you have sufficient air pressure to the torch. You may be running out of air and the compressor is catching up while it is doing the "non-cut" for the second piece.

David

[jeremy_smitty]

I don’t believe air pressure is the problem, as I have 13 cfm available. The table is only capable of cutting an area of 15”x15”. Ill check again tonight.

[adbuch]

I don’t believe air pressure is the problem, as I have 13 cfm available. The table is only capable of cutting an area of 15”x15”. Ill check again tonight.

Best to install an inline air pressure gauge directly at the gas port entrance on your cutter. Make sure you have your air pressure set to the recommended value for your particular plasma cutter. Then keep an eye on the gauge and when it stops cutting, check to make sure it has not changed. For example - for my 45xp and 85 I have it set to 100 psi while air is flowing thru the torch, and it remains constant the entire time it is cutting.

David

[weldguy]

I am with these guys on the air pressure as at least the first thing to check. It's more common than you thing even with large compressors. As David mentioned a gauge on the back of your plasma cutter where the air comes in is the way to monitor pressure and be sure it doesn't drop below 90-100 during cutting.

What plasma cutter are you using?

[jeremy_smitty]

I am running a razorweld 45.

I was monitoring it last night, and the gauge on the machine (which is built into the front of it), stayed at 80-90 psi consistently. I am going to pickup another air regulator today, which I can monitor at the back of the machine. Obvoiusly this will effect rge air flow due to more constriction.

Right now i have one at the beginning of my air piping.”, about 20 feet down line. This goes to a 50 foot air hose, which connects to an incandesiccent filter mounted on the back of the machine. I believe there is another water separator on the inside of the machine.

[weldguy]

Ok, the Razorweld 45 wants to be operated at 75psi so you want to dial it down from you 80-90psi to 75 based on the gauge on the front of the machine. On the air inlet you want to be sure your feeding it a solid 100psi all the time and a gauge on the air inlet will help you to determine you have that covered.

[jeremy_smitty]

The gauge on the front of the machine should have the needle at 75 psi, when the plasma trigger is depressed, correct?

[weldguy]

The gauge on the front of the machine should have the needle at 75 psi, when the plasma trigger is depressed, correct?

It does not state that in the manual I don't think.

[BTA Plasma]

Post your code.

[tcaudle]

Any ideas on how to resolve this? I have ensured the ground clamp is grounded well, on a clean piece of steel. I am starting to think that there is a problem with the post processor programming. That being said, sometimes it works just fine.

Whn you lose arc its from one of two things: either the torch is off or the arc can't be maintained due to lack of current flow.

Couple of things that might help"

1. There is NO Ground Clamp on a Plasma Cutter. Its the WORKCLAMP. It supposed to be tied tot thee WORK. Simply clipping it to the table or a close by ground is not the best way to get consistent cuts. The current PATH between the electrode in the torch and the Workclamp has to be extremely low resistance . Just like if jumper cables don't make really good contact on BOTH ends of each cable they don't work well. SO your Workclamp needs to be attached to the WORK (metal you are cutting). As slag builds up on your slats the "connection" between your table and the metal gets worse. Even rust can increase resistance . Cutting at 45 Amps you don't have a lot of margin to get full penetration.

2. Consistent air of the correct pressure and flow (there is a difference) is essential . It typically will not STOP an arc but bad air makes really MESSY cuts)

3. The THC can cause loss of arc by raising too far . That should be obvious if you are watching (with your reaming good eye).

the action of plasma cutting is to form an arc from current flow across a gap. Once the air ionizes and lets the arc punch though the arc should continue until its either terminated (torch turned off) or the path of conduction is too high resistance to keep the air ionized. In short if ALL of the current is not flowing across that small junction AT the point of cutting, it can go out,

Lots of things to watch and it all happens fast. If you have any indicators to show if the torch signals staying on the entire time would help.

Stay with it and you will discover the gremlins then you get to deal with other stuff!

Keep on Cuttin!

[weldguy]

Great read, thanks Tom