Machine taking off too soon
I've been away from my machine for a bit and just got back onto it tonight to cut out some project ideas I've been working on recently. I think this is something easy, but I've just been away too long and have forgotten a lot of the settings. Anyway, the problem is that my machine isn't giving the torch enough time to fire up and create a good arc. It will take off before the arc is complete and will leave me with a part that has some uncut spots on it.
Take a look at this video to see for yourself.
[nomedia="http://www.youtube.com/watch?v=PJ7tvH8fEcE"]YouTube - Jeep Comanche Hitch Sideplate Plasma Cut[/nomedia]
Any thoughts?
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You need to look in your plasma system manual under machine cutting parameters and look up the recommended pierce delay time for the materials, thickness and power level you are cutting at. The pierce delay time then must be set in your machine setup parameters. This time allows for the plasma to fully penetrate the plate and stabilize before movement occurs.
Jim Colt Hypertherm
Thanks Jim. I use sheetcam to create my G-code and I've saved a variety of different profiles for different thickness metals. this particular piece was 12Ga. mild steel. The closet to that thickness in my plasma metal is 0.135" which is what I used. I don't recall the pierce time off the top of my head, but I had it set to exactly what the manual states (I want to say around 0.6 to 0.9 seconds).
i don't know what your plasma system is (make, model) or the power level you are running at....so I cannot offer much on the line of advice! From the video it appears there is no pierce delay at all.
Jim
Thermal Dynamics Cutmaster 52. I agree, it's almost like there is no delay at all. I'm going to brush up on my G-Code and verify that SheetCam is adding a delay.
A portion of my G-Code:
N0310 M03
N0320 G04 P0.4
Looks like I'm only giving the torch 0.4 seconds of dwell time before it takes off. I'll look into increasing this time as it seems my machine is a little slow at producing an arc, especially on the initial fire. It seems to get better as it relights at various spots on the part down the line.
I don't use any delay time at all on 12 ga. using 40 amps, pierce at .150 and cut at.08.
I'd agree that I shouldn't need much, if any, delay for 12Ga., but it's not the thickness of the metal that is holding me up. When Mach3 gives my plasma the call to run and you hear the relay click, it takes a while for the arc to actually come on. By the time I get a good arc, my machine has already moved about a quarter of an inch. The first pierce is always the worst and then it gradually gets better over time.
If you're running Mach you might also want to verify in the settings window that your machine is set for time units of seconds. The other option is milliseconds, which makes .4 basically nothing. I had this issue when I first got my machine running - couldn't find the setting at first in Mach to get the units all jiving...
Thank you for the suggestion - I will look into that.
My 'G04 Dwell in ms' box is unchecked.
I also have a CM52, Are you using a doughnut current transformer for your "OK to move signal" or the Thermaldyne CNC wire harness? I had issues with the current transformer that was installed in mine, it all went away when I bought the $40.00 wire hareness and hooked it up.Originally Posted by TerraWombat
Maybe the start cartridge in the torch head is goobered up. Or the small filter inside the case is possibly getting plugged and not giving enough air flow to blow the start cartridge back quickly enough.
Just Some Thoughts
Mike
Thanks for the suggestions. I will take a hard look at the air supply to the unit and make sure everything is clean.
I am using the Thermal Dynamics automation interface kit 9-8311 to pick up my 'Ok to move signal.'
I didn't get a chance to inspect the air supply and check my filters last night, but I did need to do an emergency run of a couple of parts I needed. Instead, I "cheated" and increased the pierce dwell time to 1 second (up from 0.4 second). I had 12 identical parts nested - the first pierce took the longest and, as a result, the first part had a 1/8" tab because the machine took off too soon. Parts 2 - 12 cut fine, although the pierce delay became too long and burned through a portion of the piece. Could have avoided that by using a small lead-in, though.
Again, I'll check the air supply and filters. If I can't figure it out, I think I'll just manually fire the torch off before doing batches of parts to get that initial long-pierce out of the way! I desperately need to upgrade my air compressor and install an in-line dryer of sorts, too. I wonder if moisture is a cause for the initial long pierce time?
That Cutmaster has a 4 year warranty, Maybe you should take it in and get it checked. I had mine in for a intermitent cut problem and they replaced the complete unit for no charge! I seem to remember them talking about a air solenoid problem, maybe that is a issue.
I use one of the Ford inline filters with a toilet paper type cartridge. It works great and lasts quite a long time.
I agree firing the torch manually a few times before cutting is a quick cure.
FYI, I hope you didn't spend $300.00 on the interface kit, unless you have to have divided volts for your torch height controls. The $40.00 wire harness(#9-9385) plugs right into the PCB board and gives "ok to move" and torch "on/off" signals. Raw voltages are taken from pins on the board.
Good Luck
Mike
Yea, I was 'conned' into buying the CNC automation interface kit by a local sales rep that said I would absolutely need it for my application. I foolishly bought it without doing the proper research as I was both frustrated and anxious to get my "turn-key" CNC plasma machine up and running. Fortunately, I didn't spend anywhere near $300 for it, but it still was $175 from a guy on e-bay. I don't need divided voltage for my THC control and have a pair of wires going directly to the plasma unit to pick up that signal. So, all in all, a waste of money, but water under the bridge at this point. Every once in a while, you get burned - that was my burn
I've seen the toilet paper filter method on an air compressor forum and thought it was pretty slick. I really ought to look into that. If I can't figure out the problem on my own, I'll see about getting my unit serviced.
Thanks again for the info!
A long delay the first time you turn a plasma cutter on is how they are supposed to work. Most of them have a long initial delay to purge the lines, etc before they will turn the arc on. Then they have a postflow time where the air continues to flow x seconds after turning the arc off to cool the consumables. Most machines instantly relight the arc if the air is still flowing, but then resort to the long delay if the post flow has stopped. Sounds to me like you have an issue with the "arc ok" signal or settings in your controls rather than something worng with the machine.
I have a complete THC setup to finish installing on my machine, but right now I'm using it without an "arc ok" signal. To deal with the long initial delay I first zero the gantry, then back it off 0,0 about 1/4" and do a manual torch on peirce. Once that pierce is complete i hit manual torch off and then immediately hit cycle start. That way I simply have to enter a normal peirce delay everywhere in the program.
Thanks for the information. I should clarify that any time I've had the problem with the initial delay being too long it has been when the plasma machine was just turned on and the compressed air was just hooked up to it (because I was using the air line for something else in the shop).
As far as my 'arc ok' signal goes - as far as I know, it's wired correctly to the machine. My THC has an external box with an 'arc ok' light as well. When the torch first turns on and arc comes on, the volts (also a digital display on the THC box) jump to around 105-110V and the 'arc ok' light illuminates.
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