plasma cutter won't make clean cut?

[dwneumann]

I recently purchased a used Miller Spectrum 300 plasma cutter (manfuacture year 2000). It is clean and well maintained and everything works properly but it won't make a clean cut in material anywhere near its rated thickness of 5/16". Even in 1/8" mild steel, the plasma will not penetrate the full thickness of the material unless I turn the output to its maximum (27 amps) and use a really slow cutting speed (perhaps 4-6 ipm). But if I do that the plasma will penetrate through the full 1/8" thickness but there is so much dross on the sides and bottom of the cut that it looks like a sever cut not a clean straight cut. I've tried both with and without standoff, and I am keeping the torch perpendicular to the work (I'm sure I'm not gouge cutting).

This is a switchable 110v/220v machine, and I have it running on a 220v / 30amp curcuit (yes I checked the internal switch to make sure it's switched for 220v input). I put in a new electrode & drag tip, and checked that the airflow is not blocked. I'm supplying it with clean dry shop air through a 3/8" hose with an inline water separator. There has never been an inline oiler anywhere in the air supply, and there is no sign of sputtering or any other sign of contaminated air. I have the machine set to 60 psi as recommended in the manual, and the compressor is supplying more than enough air to keep a constant 60psi reading at the gauge on the machine.

Do I have to increase the air pressure when I cut thicker material? The manual says nothing about that even though there is a pressure adjustment knob on the machine. It seems to me that there is enough heat to create all that dross but not enough oomph to penetrate the material.

It must be something I'm doing wrong, but what?
Thanks for your guidance...
Dean (novice plasma user)

[migmaniac70]

Everything i was going to suggest to you, you already have coverd, I am truely at a loss for any ideas.
Except for getting a volt/amp meter and take some readings to see if your getting the juice.

[Scott V]

How long is your arc Length? Just to make sure you are getting full output. Seems like 27 amps should be around 1/2 inch plus anyway. I know the brand new Miller machines it's at least (27 amps) 3/4 because it will cut that on 120 volts. If you have a good 120 volt circuit.

How much air is coming out your tip? Do you think you have something blocking the air line or regulator in your machine. You need flow as well as pressure.


Hook it up with no filters and do a test run. It's hard to tell if there is not enough flow.

Esab has a Plasma Flow Measuring Kit for checking that. Never heard of anyone buying one though. I had problems with this unit the other day. Not enough flow and the arc would not turn on.

[GaryM]

hmm almost sounds like you dont have the ground hooked up.

Just and idea!

Gary

[fun4now]

ground ?

i dont know about your unit but mine shuts off after a cuple seconds if i got no ground. but the starter ark is lighter than the running ark so it is werth checking.
i would check all the wires. its used and you never know.

are the plug wires hooked up right ? is the ground wire broken inside the rubber casing, may have been stretched and broke inside the wire insulating giving you a pore ground.

as said above you coverd most all the usual problems only thing left is check all the wires, in power and out.if all looks good you might take it in to a shop for a checkup and service.

is the presher gage reading 60psi wile you are cutting ?

[dorn]

How much dross should there be on the back side after cutting. When I cut with my Powermax 380 there is a fair amount on the back side to clean up with a grinder. Most of the stufff I cut is out of 16ga. crs. Can sombody post a pic of what the back side should look like after cutting? I will take a pic of one of my cuts and maybe you guys could tell me if it looks normall. Thanks Don

[Scott V]

How much dross should there be on the back side after cutting. When I cut with my Powermax 380 there is a fair amount on the back side to clean up with a grinder. Most of the stufff I cut is out of 16ga. crs. Can sombody post a pic of what the back side should look like after cutting? I will take a pic of one of my cuts and maybe you guys could tell me if it looks normall. Thanks Don

16 gauge there should hardly be any is you have you speed set right.
Are you pulling or pushing the torch? Try pulling it toward you,(smoother) for the best quality cut.

I have a Thermal 38 xl that I can run a few test cuts today.
I did notice I was getting some dross on my cnc table with at 30 amps when making pretty tight cuts.( cutmaster 101) I think it's hard for the table to move that fast in the very confined areas.

[fun4now]

i'll try some 16gage

i'll go out and cut some also. if you are getting enough to need a grinder i would say somthing isent right. probly speed like Scott V mentioned or not enough air.
i'll post some pic's later for ya.

[Scott V]

http://archive.metalformingmagazine.com/1998/05/plasma/plasma.htm

Read this.

[dwneumann]

source of trouble found

thanks for all the responses fellas.
Based on your guidance I went out and double checked everything on my setup and I found that there is absolutely no difference in cut quality between a cut made with the ground clamp connected to the work and a cut made with the ground clamp disconnected (yes I had clean metal where I connected the ground). So there must be a ground fault somewhere in the machine. I checked the connection at the clamp and checked the ground wire as far as I could (I opened up the machine and followed the ground wire all the way into the wiring bundle). I saw no faults, so I guess I'll have to take it in for servicing.
Thanks for suggesting grounding as the problem. That seems to be it.
Dean

[GaryM]

Hope its not a big problem with the ground.

Good Luck


Gary

[Scott V]

Here is one a couple of pic's notice the dross on one side and not on the other. Also on one there is dross at the start and not all the way down. That was cause by different cut speeds. These are all drag cuts with a old nozzle.

[dorn]

Scott, Thanks for the pics. Mine looks nothing like that. I was just out in the shop and made a few cuts. They were horrible on the back. I tried more/less air and amps nothing helped. I took the cover off and checked the connections all look good. Ground is good. I will post a pic tommorrow. Thanks for the help

[fun4now]

check your consumables

if you are cutting without a ground it will burn up your consumables fast.

sorry my pic's look like pooo pooo. i gess ill have to figure out how to get this camera to take real closeup's, as there was almost no slag i kept trying to get closer to get what was there to show. so all i got was blurry gess i need a photo class

luckily Scott V knows how to work his camera. nice shots got any tips

hopefuly your ground lead just got stretched and it will be a cheep fix to change it out.

[dorn]

Not the best picture. But I think you can see what I am talking about.