Shield Holes Plugging

[Paint Chip]

Hi folks, looking for some guidance. I've just got my plasma table running and pretty low on the learning curve yet. I am running with the DTH off for the time being, but cutting pretty flat plate so it seems like that should not be too big an issue. I have the distance between touch offs set to 15 in. so it resets the Z home fairly regularly. The problem I am having is the holes on my shield seem to be plugging up with slag and then the cut quality goes to hell - I lose full penetration and have to stop the program. Is this an issue of air quality? Pressure? Running too close to the plate (switch Z compensation is off)?

My set up is:
Hypertherm PM85 with 45 amp nozzel/electrode, mech shield and mech torch
CandCNC Bladerunner DTHCII
Mach3 w Bladerunner custom screen
DTHC-HYT-TAP_SoftPierce+Marker-rev11D post processor
PPLLC Patriot 4X8 table
Cutting 1/4 in hot rolled plate

Dave

[urbnsr]

My guess is your pierce height might need checked. What height are you at during piercing? Can you post a small example of the code you are running?

[Paint Chip]

Its set to 0.15 - from the Hypertherm manual. I did stop it the program once and slid a piece of 1/8 in plate under the torch head - it had a couple thousands clearance left so it has to be close. Here's some code:

N0010 (Filename: ForgeAssemblySheetRevised2.tap)
N0020 (Post processor: DTHC-HYT-TAP_SoftPierce+Marker-rev11D.scpost)
N0030 (Date: 27/02/2017)
N0040 G20 (Units: Inches)
N0050 F1
N0060 G53 G90 G40
N0070 (Part: ForgeAssemblySheetRevised2)
N0080 (Operation: Outside Offset, Layer 1, T9: Plasma, 0.066 inch kerf)
N0090 (tool number: 9 Distance between Touch-offs: 15 Feedrate: 45)
N0100(Preset Volts: 137) (Preset AMPS: 45)
N0110 ( Air Pressure Preset: 75)
N0120 ( Soft Pierce : 60 percent )
N0130( Suggested Tip Size: 45 ) ( DTHC Delay: 2 sec )
N0140 ( Min Cut Length for DTHC ON : 1 units )
N0150 S900 (Global DTHC ON/OFF is ON )
N0160 M22
N0170 S10 (Turn off DTHC at the beginning)
N0180 M22
N0190 S3137 (Preset Volts set to 137 Volts)
N0200 M22
N0210 S445
N0220 M22
N0230 S875
N0240 M22
N0250 S520 (DTHC Delay set to 2 Seconds)
N0260 M22
N0270 S711 (DTHCIV tuning set to level 1)
N0280 M22
N0290 M00
N0300(Paused: Check the DTHC Settings Hit RUN to continue)
N0310 G00 Z1.500
N0320 X21.701 Y0.099
N0330 M900 (Check for Z active)
N0340 G28.1 Z0.75 (Start Touch-Off )
N0350 G92 Z0.0
N0360 G00 Z0.039 (Switch Offset Lift)
N0370 G92 Z0.0
N0380 G00 Z0.150
N0390 M03
N0400 G04 P0.6
N0410 G01 Z0.060 F150.0
N0420 F90.0
N0430 S20 (DTHC is on)
N0440 X22.203 Y1.562 F45.0
N0450 X22.521 Y2.491
N0460 S10 (DTHC OFF)
N0470 X22.548 Y2.568
N0480 X22.704 Y3.026
N0490 M05
N0500 S10 (DTHC is off)
N0510 G04 P0.5
N0520 G00 Z1.500
N0530 X19.632 Y0.026
N0540 Z0.150
N0550 Z0.150
N0560 M03
N0570 G04 P0.6
N0580 G01 Z0.060 F150.0
N0590 F90.0
N0600 S20 (DTHC is on)
N0610 G03 X19.794 Y0.105 I0.042 J0.121 F27.0
N0620 G01 X19.858 Y0.291
N0630 S20 (DTHCON)
N0640 X22.389 Y7.672 F45.0
N0650 X22.453 Y7.858 F27.0
N0660 G02 X22.484 Y7.881 I0.031 J-0.011
N0670 G01 X22.681
N0680 S20 (DTHCON)
N0690 X27.950 Y7.887 F45.0
N0700 X28.147 Y7.888 F27.0
N0710 G02 X28.178 Y7.865 I0.000 J-0.033
N0720 G01 X28.243 Y7.679
N0730 S20 (DTHCON)
N0740 X30.792 Y0.305 F45.0
N0750 X30.857 Y0.119 F27.0
N0760 G02 X30.826 Y0.075 I-0.031 J-0.011
N0770 G01 X30.629 Y0.074

[acourtjester]

I see 2 things your air pressure is set for 75 PSI that may be low. and line 410 you have the F set to 150 I have mine set for F60.
have you actually checked the pierce height before the torch fires. just change line 390 to M00 for a test and see where it is then.

[sphurley]

He has soft pierce turned on, so the F150 is really F90 on Z. The problem is 60% is a lot for soft pierce, and he doesn't mention if he really has RS485 plug on the PM85. Set soft pierce to 0 (turns it off.). Can you tell if you are plugging at the pierce or further down the cut? Since you have DTHC off how flat is your plate across the cutting area? With torch off, run it around and measure the distance from the torch to the plate.
And as Jester stated I don't run 150ipm on Z myself. You want to make sure you see sparks coming from under the plate (you have pierced thru) before the torch drops to cutting height.

[jimcolt]

Do not use a soft pierce, be 100% sure the pierce height and pierce delay times are correct. The holes plugging the shield are only from piercing too close or with inadequate pierce delay.

-Pierce height.....slightly higher is ok. If lower you will cause damage as soon as the first pierce.
-Pierce delay is designed as a timer to keep the x and y from moving...and the z at pierce height until the arc has full penetrated the material. One incorrect pierce delay (too short) will start damaging the shield. The times in the Hypertherm manual assume no soft start (let the plasma cutter pierce the way Hypertherm engineering designed it to pierce!), and they assume that the timing cycle starts the moment the plasma detects current flow on the work cable. Some CNC systems and software start timing at a different point....so you would then need to experiment with times that will work. Longer is better, too long will cause the arc to extinguish on thin materials (arc blowout).

The shield on my Powermax85 in my home shop is 3 to 4 years old. it cuts like new.

Jim Colt Hypertherm

[Paint Chip]

Ok, thanks for the feedback. I do have the RS485 plug but I'll set the soft pierce to zero (assume that is done in Sheetcam). The 1/4 in plate I'm cutting is pretty flat - but my supporting slats might be uneven (using 12"Y x 48"X pieces - maybe I should swap orientation). I'll retest the pierce height with feeler gauges. Am I better off setting the distance between touch-offs to zero? I'll reduce the Z down speed to 60. I have some scrap from the last pieces I cut so I'll run some test pierce and moves to see if the plasma cuts through before it moves. I can also run around the next plate with the torch off and check the pierce height and the cut height. Maybe I should also move up to a 65A nozzel since 1/4 in. is the upper limit of a 45A nozzel. I'll post what I find.

Dave

[acourtjester]

I have PM65 and cut 1/4" most of the time and have never used a 65 nozzle, thing set as the book say, 45 nozzle is great.

[motoguy]

I cut 1/2" with 45A, when I want the best finish and angularity. As Jim always says, "the lowest amperage possible for a given material will result in the best cut edge and angularity". Speed being the trade off. On 1/2" steel, the 45A process is only like 18ipm...

[Paint Chip]

Ok, thanks. Good info to know. I thought maybe I forgot to change the pierce delay after cutting some 1/8" but I checked and it is set at 0.6 sec, which is by the book. I'll have to check the actual pierce and cut heights before I run the next stuff and I guess I'll replace the shield/nozzle/electrode, just to eliminate those variables. I have also turned the soft pierce off and slowed the Z speed to 60. Hopefully, one or all of these in combo solves my issue.

[sphurley]

You do have the RS485 HyT option so here is the problem you have.
At 60% soft pierce, you lower the Z rate during pierce to cut height, but because you have RS485 on your Hypertherm, you also lower the 45amps to 27amps during this soft pierce. That is great on consumables BUT, you must compensate for it in pierce delay as you are not piercing at the book 0.6sec for 45amps. So you are driving the torch into molten metal. I too learned this the old school way, $$$.
As I said I do use soft pierce and it can help consumable life if done right but one wrong move and $$$ consumables.

[sphurley]

PS, I don't think SP worked right in 11D post looking at your G-code.

[urbnsr]

OK - I think you should look at your actual pierce delay time.

I see 0.6 second delay, but when does that timer start? If there is any extra delay (mechanical or otherwise) from the time the software issues the torch on code and when the torch is actually on, you would not be getting the full pierce delay.

We addressed this by inserting a wait for the ARC-OK signal in between the M03 and the pierce delay. And we're using a reed relay to fire the torch. Our start code (different system, but for example):

Code: Select all

 M03
 M66 P0 L3 Q5 (Wait for ARC-OK from torch)
 G04 P0.6

So the software fires the torch and then after the ARC-OK signal goes high, the pierce delay timer starts. The ARC-OK wait code might actually add to the pierce delay time, but I think it's better to have a little longer than shorter.

I would, at least, verify the pierce delay timing to make sure your getting the full time.

HTH
Paul

[Paint Chip]

Steve (sphurley) - I see what you are saying - I thought SP only applied to torch movements - didn't realize the % also applied to the cut amperage. The problem does seem to get worse with every pierce so that may be exactly what's going on. You mentioned you don't think SP worked right in 11D? For the time being I can run with soft pierce off, but is there a later version that I should be using? 11D appears to be the current version on the CandCNC website for download.

Paul (urbsnr) - I will watch to see if the pierce is complete before the torch starts moving with soft pierce off. I can see where waiting for an arc ok signal would be beneficial and it seems like the post processor should do it (and obviously, from the code mine does not), but do the pierce delay settings in the book already take into account some system delays? If so, then I might end up sitting at the pierce point too long. Maybe I'm just taking "by the book" to literal. I'm getting the feeling that each system is different enough that all the settings need to be tested to see if they actually work before using them.

I appreciate everyone's help - mistakes made while learning can be painful (at least to the wallet), but it certainly makes the motivation for lessons learned to sink in fast pretty high.

[urbnsr]

Dave, I believe the book specs are the amount of time the torch is actually burning metal. I, too, feel each system is different enough that the book specs cannot account for it. And you might not have the "system delay" that I am referring to, but it may not hurt to check. It is hard for me to see the correct delay, so I tested with the cutter off and just watched how long it took from torch-on signal until the Z axis lowered to cut height. That's when I noticed the pierce timing wasn't being followed as it should have been.

[acourtjester]

There seems to be 2 newer versions, 11J for the parallel port and 11M for the ether-cut.
check here for the J version about half way down the page. you may also look at the firmware updates too if you need it.

[Paint Chip]

Thanks for the tip Paul. That's something I can try looking for. Hope I don't get frustrated and stomp my bifocals to death though, lol.

[Paint Chip]

acourtjester - I'm afraid my system is a bit of a fossil - running 486 serial port computer with windows XP. From the CandCNC website it looks like 11j is for ether cut and requires upgrades I don't have. At some point, I may upgrade, but gotta go with what I have for now. Thanks for the response though.

[sphurley]

Tom shared 11M7 over on his forum.
https://www.candcnc.com/supportforum/vi ... 1660#p9450

[Paint Chip]

Well, after reading the posts associated with your link, it appears I might be able to use this newest version if I set the "options" in the pp correctly. Thanks for the tip. Does this version also apply the soft pierce % to the plasma current?

[Paint Chip]

I finally got a chance to run some test cuts and verify a few things. I checked the pierce height and cut height with feeler gauges and they both appear to be spot on. I imported CandCNCPlasma-rev11M7.scpost for the post processor and set the variables to the appropriate settings for what hardware I have. I set the soft pierce to 100%, which is off. I left the cut height, pierce height and pierce delay at the book settings. I slowed the plunge rate to 60 ipm. I then ran the test cut file, which was a series of 1 in. lines. The machine definitely pierced the material (1/4 in HR steel) before it started moving in the X direction. It was a bit harder to tell if it fully pierced before it started moving down to the cut height because it happens pretty fast, but I believe it did - the pierce through seemed to be the first thing to happen each time. The test cuts all looked pretty good. The pierce points had more dross splattered around them -I'm guessing because of the higher current, but the holes were nice and symmetrical after removing the dross and the last pierce was the same as the first. The shield holes are all open this time so it looks like the soft pierce set at 60% was too low and/or my pierce delay was too short for the lower current at that setting. Their is no dross splatter on the shield either.
I'm going to rerun the parts file I ran previously and see if it cuts without issue this time. I'll update this post with the results.

Update: The parts ran without issue and the nozzel holes are still all open - success!! The pierce does complete before it starts going down to cut height - it just completes, so the book setting appears to be pretty close to exactly what is needed with the plasma at 100% current.

Here's a picture of some of the parts I was cutting - the slot is only 3/16 wide so the pierce points show a little - but still very nice for 1/4" plate . Thanks to all for the help!

[sphurley]

Now work on lead in's and out's and you will be really happy.