[Peepers]

I sure need some input on this problem.
Any Ideas?

I built my plasma table about a year ago and have been very luck to have had no real problems until last week. I cut art stuff from 16 ga steel.
My setup consist of Mach 3, SheetCam, THC300, and a Hypertherm Powermax 1000. I cut 16 ga steel using Finecut consumables at 250 IPM, .13 pierce height, .065 cut height, around 32 amps and 85 psi air pressure. My tip voltage is around 48 volts but is only good for my reference as the THC meter is not calibrated correctly.
These settings are the result of a lot of testing and have produced very clean
and slag/dross free cuts.
I know the manual says .08 cut height and 150 IPM at 40 amps but I found I got much cleaner cuts at my own settings.

The problem I have now occurred after I cut 10 or 12 nested pieces which cut perfectly. I loaded another file of nested parts all from the same post processor setup. I indexed to my start point on same sheet of steel and started the process. The torch has no problem piercing and the cut starts. Randomly the arc will bounce up form the steel and not cut this may happen for an inch or two or it may five or six and then continue to cut fine for a while and then do the same thing not cutting through.
It does not matter whether the THC is on or off or if it is a straight cut or a curve. I have tried slowing down cut speed, increasing current, changed consumables, just about everything I can think of and nothing has worked.
I have not been able to figure out if it is the plasma cutter or what.
Any ideas or suggestions will be appreciated.

[Torchhead]

Randomly the arc will bounce up form the steel and not cut this may happen for an inch or two or it may five or six and then continue to cut fine for a while and then do the same thing not cutting through.

Sounds like you are losing current flow through the machine. I would check my workclamp cable at both ends. Make sure you clamp to the work and not the table. With Fine Cut you are working at much lower currents and gap volts.

In one circumstance we found that the workclamp connection inside the plasma was loose and had built up corrosion (insulator) so current flow was unpredictable.

Since it happens with no THC and with the same cut file (?) and is not a total arc failure then the only thing that is missing is sufficient current flow in the cut to maintain penetration. That can come from an excessive cut gap but I assume the THC300 is tracking when it's turned on.

Make sure your THC300 has the "Fine Cut" switch because the base target volts won't go below about 85 or 90 volts (true tip volts). You meter being out of cal makes it difficult to see what the real voltage is. All the cal does is set the meter scaling (not the THC internal voltage).

TOM Caudle
www.CandCNC.com
Totally Modular CNC Electronics
3rd Generation Digital Torch Height Control

[Edwardo]

I have had the same thing happen once in awhile, nest a 4x8 sheet of 16ga and in a certain areas of the sheet it skips and doesnt cut through, not all in the same direction of cutting either but usually in the same area of the sheet, im wondering if its not in the steel it self being harder in patches on a sheet.

EDD

[Peepers]

Thanks for the help.
I will check out the work clamp leads at both ends today.
I am pretty sure that it is not a result of excessive torch gap. I usually cut at .065 and the THC does seem to track well.
I do have the Fine Cut switch on. I am going to try to recalibrate the THC 300 today also.
This is a problem that has just appeared after doing around 150 pieces trouble free.
I too have wondered if it was an inconsistency in the steel.
Thanks again for your input.

[Torchhead]

Aw come on guys! It's more likely to be earth wobble than changes in the density or hardness of steel! So after 150 pieces the steel density is varying enough to cause loss of penetration?

Comparably speaking, cutting with plasma is like blowing holes in a wall with a bazooka! It's vaporizing metal with a 25,000 deg flame and blowing it out with 70 PSI air (about 200 PSI at the nozzle hole). Plasma cuts hardened steel as good as mild steel. It can cut from 24ga up to about 10ga with the same gap and current settings. The cuts will be ragged but you will get penetration!

Just FWI, I cut 16Ga with Fine Cut tips at .040 or less gap and a 79V gap voltage. Feedrates are about 10% less than the user manual suggests for Fine Cut. You need to use the unshielded consumables for fine cut. I get almost laser quality cuts on 16ga.

Clock is cut from 16Ga hot rolled (mill scale). 18" diameter and finished in copper-flame with clear powder-coat.

TOM Caudle
www.CandCNC.com

[Edwardo]

When it happened to me i was cutting 150 small peices out of 1 sheet, 1/2 way through the run is when it happened, finished off the run with no probs, but all the skips were in 1 area, regardless it hasnt happened since unless i have my speed to high. I've been trying cold rolled lately and it goes ok, even had a go at aluminum and really like working with it also, unfortunatly people confuse Wall Art with Wall Mart and balk at the prices.

EDD

[Peepers]

Much thanks to you both for your responses.
The problem seems to be resolved.
I did some test cuts on some small pieces and all turned out great. After I got my confidence back I cut a very detailed piece 36"x30" with 197 pierces and had no problems at all. There were a lot of holes 1/4" or smaller and them cut at 125 ipm and did have a bit of slag, but not a problem to clean up. The larger area of the piece was cut at 250 ipm and was very clean and slag free.
Unfortunately I can not say exactly what the cause was.
I took your advice Tom and checked the workclamp connections. I tightened every screw and nut connection inside the Powermax 1000, all were at least a half to quarter turn loose. I measured resistance from steel with workclamp attached back to connection inside Powermax 1000 and had about .2 ohms. I recalibrated the THC300 meter, still question accuracy after going through the alignment procedure. Now I read 70 volts at 35 amps when cutting 16ga at .065 cut height and 250 ipm.
I am still puzzled as to what happened and a bit concerned that the problem will return.
Your right Edd some people just don't get the difference.
Thanks Again.

[jimcolt]

Peepers,

The most common cause for issues where the cut loses pentration mid cut....yet the arc remains on....is gas flow (air flow with an air plasma torch). A slight decrease in flow at the torch will give the same indication as turning the power (Amperage) down dramatically. Flow disruptions could be caused by:

1. Moisture in the air. Are you using a suitable air dryer?
2. Particulate in the air causing a blockage in the system.
3. Momentary pressure drop (pinched off air hose....compressor not maintaining pressure)
4. Loose fitting somewhere between the air inlet and the plasma torch.
5. Loose torch retaining cap....bad o-ring (the one that seals the retaining cap to the torch body).

These could be part of your issue.

Jim Colt

[Peepers]

Thanks Jim
I have a 60 gallon air compressor and 3 filters in line plus the one on the Powermax 1000.
I still see some moisture in the last filter. I have ordered one of the Motorguard filters to replace the last 2 in the line. I really need an air dryer. I am also going to replace and lubricate the O-ring, it does look to be a bit flattened.
Thanks for your input it is greatly appreciated.

[Edwardo]

Air issues makes sense for my set up at the time, i remember now i was having probs with the psi switch plus alot of moisture in the air!! But i still like earth wobble, i'll use that for alot of things.... Thnx Jim and Tom

EDD

[Mike 1948]

Thanks Jim
I have a 60 gallon air compressor and 3 filters in line plus the one on the Powermax 1000.
I still see some moisture in the last filter. I have ordered one of the Motorguard filters to replace the last 2 in the line. I really need an air dryer. I am also going to replace and lubricate the O-ring, it does look to be a bit flattened.
Thanks for your input it is greatly appreciated.

Here the most value priced air dryer I've seen and bought. Works great!
http://www.harborfreight.com/cpi/cta...emnumber=40211

Good Luck
Mike