Cannot maintain Pierce Height

[sundrop45]

Cannot maintain pierce height on PC

This issue began as a occasional problem, would be cutting with no issues and during a on-going cut it would raise to pierce then dive into material staying there and frying my nozzle and some times electrode. Now it's a constant and expensive frustration!

I'm following the manufacturing "Height Control Set Up" and have talked with the techs there on a number of occasions and its now down to a expensive guessing game. When I attempt to adjust the pierce height to .100 no matter if I increases or decrease the Z Shift in increments of .01-.02 the torch ultimately goes into the material during adjustment procedure and/or dry run & actual cut.

The Z Axis carriage is free and clean as are the bearings. Replaced the Z Axis motor as suggested by PC with no change in the problem.

Although a older machine it has been used very little and now that I'm retired I've been drumming up work to recoup my purchase expense with orders on the books that I can not deliver. Help would be greatly appreciated!

Plasma Cam Model DHC 4x4 table software 3.11.

Hypertherm Powermax 600
Electrode 120574
Nozzle 220330
Swirl ring 220332
Deflector 120303
Using Hypertherm suggested factory settings.

[jimcolt]

First, you are not using the best consumable set to get good cut quality, good consumable life and best performance from your Plasmacam's height control. The shielded consumables last longer, cut with better edge angularity, and are shielded from double arcing to the material. The parts you are using are unshielded consumables that re there primarily for 3 dimensional cutting applications that need the torch to get into tighter areas....but simply don't perform as well.


You need to open up your operators manual to the mechanized cut chart for the shielded 40 amp consumables:

cut chart.jpg

Then, instead of the standard retaining cap you need the ohmic cap......which has the means to connect to Plasmacam's ohmic contact wire....this allows the height control to auto calibrate at the beginning of each cut cycle:

Powermaxmech consumables.png

Shown as the lower retaining cap under the shielded consumables, part number 120964 must be used. Plug the ohmic wire from the Plasmacam machine into the tab on the cap and it allows the Plasmacam height control to sense the plate surface before each cut. Under the height control tab in the software you need to chose "ohmic or sense material before cut" (depending on the software level you have). The ohmic cap and the shield (120827) then electrically finds the material surface and auto calibrates the height control, it will then rise to the proper pierce height.

You also need to set the pierce height, which typically will be about .120", set the "time to pierce" (per cut chart), the cut speed and set the cut height (.060"), and you should be good.

A great group to join is the www.plasmacam.com owners community. You need your plasmacam serial number when you sign up....there are thousands of Plasmacam owners on that forum that are more than willing to help troubleshoot all other owners issues.

Jim Colt Hypertherm

[sundrop45]

Thank you for the advice Jim. Surprisingly with my many conversations with Plasma Cam I've covered the type consumables and have been asked yet no one has suggested this before. I'm not aware of a "omhic" wire on my machine so will have to investigate where this wire is located. As luck would have it I just ordered a pack of 5 each nozzle and electrode of the fine cut so will have to reorder your suggested setup.

Thanks, Don

[sundrop45]

Well Jim looks like that's not the problem after all I have a DHC not a DHC 2 according to a previous post my machine doesn't have the omhic wire.

I've been chaceing my tail on a issue I've had from day one because I haven't had the time to stay on it. Now that I have the time, folks at Plasam Cam are going to get tired of talking to me we are going to figure this out.

[jimcolt]

The DHC does not have the ohmic capability, but you should still use the shielded consumables.....they will not fail when the torch touches the material like the exposed nozzle that you are using will. You will have to properly use the z axis calibration process that is well covered in the Plasmacam owners community forum.....in a written procedure.

The diving usually indicates that the z offset is no set correctly or that you did not propely zero the z axis, so the height control is trying to correct the height by indexing the torch closer to (and hitting) the material. It relies on operator input top operate correctly....the newer DHC2 with ohmic sensing solves the zeroing setup issues.

I have been using my DHC2 for 9 years.....occasionally it drags on the material....when it does I go back and look at my settings and it is always my mistake. When set correctly the height control is flawless on my machine. I was just cutting some 3/16" steel treadplate a few minutes ago with the diamonds up....you can see the height control correcting the torch height over every bump!

Jim Colt Hypertherm

[PlasmaMac]

In addition to cutting with the correct consumables, make sure that your machine is also connected to a copper ground rod (in addition to the ground clamp with your cutter). and ensuring that the arc voltage shift setting is set correct (usually in between 1.00 - .67 with Hypertherm cutters on an older DHC machine, this can may vary depending on the situation though).

If your grate slates are gunked up, sometimes it is better to connect the ground clamp for your plaz directly to an edge of the the material that your cutting instead of the grates.

Hope this helps out somewhat.

JAG

[yeomansjon]

In addition to cutting with the correct consumables, make sure that your machine is also connected to a copper ground rod (in addition to the ground clamp with your cutter). and ensuring that the arc voltage shift setting is set correct (usually in between 1.00 - .67 with Hypertherm cutters on an older DHC machine, this can may vary depending on the situation though).

If your grate slates are gunked up, sometimes it is better to connect the ground clamp for your plaz directly to an edge of the the material that your cutting instead of the grates.

Hope this helps out somewhat.

JAG

I just started having Z-Axis issues again and came across this comment. What do you mean by "make sure that your machine is also connected to a copper ground rod (in addition to the ground clamp with your cutter)."? I have my ground clamp from my Hypertherm clamped to the grates and will try connecting it direct to the plate since my grates are pretty hairy, but what is this second copper connection? Are you talking about an earth ground or a ground that connects to the plasmacam controller?

[PlasmaMac]

Yes, an Earth ground definitely helps. You wouldn't connect it to the controller, but rather to the under-section of your grate slates (usually towards the back of the machine). This can help all kinds of issues having to do with height control...ect. There is a really great set of instruction that explains exactly what to do on it on the set up portion of the plasmacam video manual if you get a chance to take a look.

Good luck, Brother and have a good weekend!

JAG

[tcaudle]

I know that everyone calls the WorkClamp a "Ground clamp"....its not. It has positive voltage in relation to the electrode. It is not referenced to a ground unless you cause it be by clipping to a grounded object. Image a car battery sitting on a wood top bench. There is a neg terminal and a positive. If you touch them to each other they spark and huge current flows. if you touch either one to a ground (or anything else) nothing happens.
If you measure from that connection (even earth ground) to the other battery terminal you will read the battery voltage REFERENCED to what it is connected to .

Because the signal out of a plasma is not pure DC it has noise on it....both connections. That positive side (Workcalmp) noise is just as bad as the Neg electrode side and clipping it to a piece of materiel that is not grounded inducts that noise into the material and anything else it touches or has contact with. BIg ole antenna.

[yeomansjon]

Yes, an Earth ground definitely helps. You wouldn't connect it to the controller, but rather to the under-section of your grate slates (usually towards the back of the machine). This can help all kinds of issues having to do with height control...ect. There is a really great set of instruction that explains exactly what to do on it on the set up portion of the plasmacam video manual if you get a chance to take a look.

Good luck, Brother and have a good weekend!

JAG

Ok Thanks PlasmaMac, I did some checking and I am finding that my earth ground isn't the best so that may be my whole problem. I will fix that this week. I do have the procedure for setting the Z-shift, and then the Arc Voltage Shift and sometimes that works, sometimes it doesn't. It's always been very intermittent. That may be from this ground potential issue where i'm not getting consistent arc voltage readings. Sometimes if I want to move the torch height up, I adjust by .01 and the torch moves up the correct amount, but then if I want to go more, i'll go another increment, and then torch may crash into the table, go all the way up, whatever. Seems to follow chaos theory. I'm definitely thinking I have a ground issue now that I have been looking at what you said about the different in the potential at the work clamp vs. earth ground vs. table ground.. Thanks for your help!

[PlasmaMac]

No problem and any time, Brother!

JAG