Torch height issue

[midislandcutting]

Hi there, we're new to CNC plasma cutting and are having some inconsistent cut height issues, primarily when the torch is setting initial cut height. We have been cutting with little to no issues for the last few weeks but recently this has become a consistent problem.

The problem randomly will happen during the course of a cut file, sometimes on the first cut, other times after multiple perfect cuts. The torch will travel to the start point and then proceed to do one of the following... (a) lower until ohmic sensing, retract to pierce height, fire torch, - does not plunge- , start x y movement. causing partial cut similar to gouging... (b) lowers and stops nowhere near material (2 or 3 inches above material), retracts, fires, plunges and starts movement well above material. causing no cut... (c) lowers torch too far, causing torch to make contact with material and then push itself against material, lifting gantry slightly, retract for pierce height, fire, plunge and make contact with material, start movement. Causing torch head to drag on material, or physically drag material with torch movement.
After these issues happen, the displayed height of the torch in mach 3 does not match the physical height of the torch.
I have paused the operation in mach 3, re-set operation to start at the flawed start point, re-set torch height manually, and then had mixed results on it cutting properly or not.

To me it seems that there is some issue with the ohmic tip and it is not detecting or detecting a false point at which is sets the material height. But that does not explain why it sometimes does not plunge after torch fire.

I've also had this issue happen, re-made the cut file from scratch in sheetcam and then had no issues cutting the new file. tho this may just be coincidence, it has crossed my mind that sheetcam is producing flawed cut files during the postprocess???

We purchase the system second hand and don't have a lot of specs or info really to go off of. The table itself is some sort of home built system I'm assuming as I can find no info on the name thats on it (Aximech), we're using a Hypertherm 65 cutter with 45amp fine cut ohmic tip, Sheet Cam and Mach 3. Both sheet cam and mach 3 seem to be older versions. The table does have a THC unit but we have been cutting without THC turned on in mach 3, I had turned it on at one point before any of these other issues but it then seems to consistently cut to low and drag the tip on the material. I have since found out how to adjust that and will be attempting to adjust it once the other issue is resolved.

Any advice or insight into where to start the troubleshooting process would be much appreciated.
Thanks in advance!

[acourtjester]

What type of drive is used for the Z axis?? you may have a slippage in the Z drive assembly. I would check the setscrew in the coupling of the motor and drive assembly. Do you check the ohmic sensor operations manually to be sure it is working coincidentally, it should show in the diagnostic page as digitize. I move the Z up and down watching the digitize box on that page to see if it goes on and off.

[WyoGreen]

It's usually a good idea to have a mechanical backup switch to the ohmic sensing, as sometimes dirt, paint, rust, etc will cause the ohmic to fail to sense. You don't say if this is a water table, but if it is, sometimes water in the nozzle will also cause ohmic sensing to fail (sensing too soon).
These things may be causing some of your problems.
Steve

[midislandcutting]

This is basically our z axis drive set up


I have not checked any functions as related to the computer as i currently have a limited knowledge of the systems, tho when manually adjusting the torch height, i can hear what seems to be a relay or switch activating and de activating as i make or break the ohmic sensing connection, which to me says that function should be registering at least when i'm doing it manually.

The table is not a water table. Its set up to be a downdraft but we do not currently have a ventilation fan hooked up.

[acourtjester]

Ok with the relay clicking sound I would assume there is an ohmic sensor module attached but may not be connected to the controller or the correct input pin so the software and see it. What needs to done is ID-ing the controller electronics and looking for the Ohmic sensor module, so some tracing of the wiring and where they are connected. Could you take close up pictures of you controller's components, no need for the drivers or power supplies. Or any brand names on the circuit board in the controller.

[weldguy]

I'm with AC, check all your electrical connections to be sure they are clean and secure. If it worked before then its safe to assume all connections are in the proper locations just may be loose or dirty. Once you have confirmed all connections are clean and rock solid test functions without plasma on to eliminate an electrical noise issue also and post back.

[john78]

Definitely check all your connection.

Need a bit more info if anyone can successfully help you. What motion control is Mach3 using? What THC do you have?

Maybe post up some pictures of your setup and also like to see the g-code. Material thickness and amp settings on the Hypertherm might help to.
You also said the torch position does not match height on the DRO. What is the info on the torch lifter. TPI and motor steps per inch. Lot more info that is needed to sort this out.

There is an axis calibration under the settings page if you are using a standard mach3 screenset. You can command the z axis to move a specific amount and measure the movement. Then enter the actual movement and mach3 will adjust the steps per inch.

[midislandcutting]

Thanks all for the input, i did clean some stuff up yesterday after work and will be checking more of the electrical connections when i have a chance, i will try and get some pictures and more info for you all.

[midislandcutting]

So I change out the connector at the ohmic sensor as it wasn't in the greatest shape and cleaned up the nozzle, changed the consumables for good measure as well.
I also blew out the electrical boxes as they were quite dirty with fine metal particles/ dust. But all the wiring connections seem to be secure.
I honestly don't know much about cnc set ups or anything about this machine other than the limited knowledge that was shown to us about how to cut the designs my wife is making.
The material we are usually cutting is 14 gauge hot rolled steel, and the hypertherm is set to 45 amps. we have set the cutting tool in sheetcam as per the hepertherm manual for the shielded 45 amp fine cut consumables we are using.
The torch position usually matches the height in mach 3, and i can zero it and it will track normally when moved manually, i just noticed that when I do randomly encounter one of these errors, after, the displayed height no longer matches the physical height. As in mach 3 is re- zeroing when it thinks its sensing the material but in fact is not.
I have no idea of any info about the torch lifter or motor steps/inch or TPI...

I have two tap files that i had different issues with... but it doesn't want to let me add them as an attachment, it says it's an invalid file.

here's some pictures of the set up.
Thanks again for any and all input!

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[john78]

That is a start. Looks like a Gecko G540 stepper drive. CandCNC low cost torch height control. I have the same height control. Board above the stepper drive is the plasma interface card. Has the voltage divider on it. I don't see the ohmic sensor anywhere. Can you find it and get a picture? Follow the ohmic wire from the torch. Also check all mechanical connections. Make sure there is no excessive play in the lifter and make sure motor coupler set screws are tight. Also noticed the THC says 38 volts. Is this what you are cutting at?

Change the file extension of the tap file to a zip file then upload it. Like I did below.

[midislandcutting]

Thanks for the info, I will follow the ohmic sensor wire today and see if i can figure out where exactly it goes. I will also check over the mechanical connections as suggested.
As for the THC saying 38 volts, that is how the machine came and I have not adjusted anything... as i said im still learning all about this.. I don't actually believe when we are cutting the THC is monitoring the material height and adjusting torch height. The torch usually just comes down, touches off, retracts, fires, plunges and then cuts at a given height... I think I just don't have it turned on in mach 3 tho.
here is a picture of our mach 3 set up exactly how we had it prior to hitting run.

IMG_0192.jpg

I'm going to try cutting another piece today and see how things go.

Also here is those Tap files. The cabin file the torch head did not sense the material and pushed gantry up slightly, when retracted and started cutting it dragged the torch head along the material. The job file the torch sensed material too high and ended up gouging off part of material but not actually cutting. On both of these operations the error occurred somewhat in the middle of the operation, after completing multiple good cuts, and then continued to cut fine after the one segment.

cabin.zip

job.zip

[acourtjester]

You may try getting a manual for that unit and seeing if there are things that need to be set for the THC to work. In Mach you need to have input pins set correctly for the signals to get to the software, Like a floating head switch ( a safety) the ohmic sensor and THC input signals.
http://www.candcnc.net/images/Manuals/L ... l_REV7.pdf

[midislandcutting]

I think the THC is set up to work as i turned in on in mach 3 once and it cut a lot closer to the material, i don't believe the voltage settings where set properly tho as it was cutting too close i think. Generally i have been cutting with it turned off in mach 3. My issue I don't think is to do with that, more that when the unit is finding the material at the start of a cut it is sometimes starting an inch or two above material or right down against it.

I Did cut a small sign today and did not have any issues with torch height arise, tho its hard to say if its fixed as it does this problem so randomly.

As requested I traced the ohmic wire back from the torch head into the control box.
The larger white wire is coming from the power source. The think black wire is the wire connected to the ohmic tip, it is connected to the inner wire of the larger white wire. The outer wire casing of the large white wire is connected to the brown wire. This brown wire is attached to a terminal as seen in picture. It also seems to have a diode or something bridging to the green wire/other terminal. That green wire is grounded to the cnc table frame. The Ohm measurement between the torch tip wire and the connector of the brown wire is around 2M Ohms. Tip wire to frame ground is 0 ohms. With table turned on, both torch tip wire and the brown wire connector have a Voltage of 46V. I'd assume it reads a Voltage drop difference when the tip grounds out on the material and thats how its determining when it makes contact with material?

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[john78]

acortjester, unfortunately the G540 only has 4 inputs. The THC will use three and it looks like the fouth input is used for the ohmic. He would have to add a BOB or change the G540 to something else if a float switch was added. This is the reason I changed my setup from a G540. No room to upgrade.

It sounds like something is wrong with the ohmic sense circuit like you suspect. You could go to the diagnostics screen and test the ohmic. Looks like it uses g28.1 for the ohmic. You can enter "G28.1 Z0" into the direct g-code input. This should cause the torch to move down until it touches the plate. The Z Home Indicator should light when it does. You can take the ohmic wire and touch the material and verify the ohmic works with the indicator. Also check the debounce settings in the general config. You might want to try and increase it. If you have alot of electrical noise Mach3 may pick that up as the switch closing. It may be at 25. Set it to 50-100 and test it.

[john78]

There is something else there for the ohmic. Wouldn't just be the relay. Found this on the forum. An example of how I think yours is wired. Might have something like the Kemo switch. If it is CandCNC equipment then it might have a feather touch ohmic somewhere.

[tcaudle]

Lets clearify some stuff. The THC does not sense the material while it s cutting. All i can do is read the ArC gap voltage and use it to adjust the height. I won't get real technical with how it does that but is based on the fact plasma cuts at constant current so the longer the arc, the more voltage it takes to keep the current constant. The voltage you set on the LCTHC is a "target" (what you want the voltage to be . YOu cannot "set" the voltage because the plasma sets the voltage What should it be if the torch is cutting at the right height (.063)?. Well the Hypertherms come with a manual that has cut charts that tell you what the arc gap voltage is on different materials and (this is important) at what feedrate. Typically in the 120 to 138 vol range. Its important you are actually reading the correct voltage. The LCTHC needs a THC Sensor in the plasma that divides the raw torch volts by about 7 and the LCTHC uses that and figures out that that means in terms of real volts and uses that and displays that number as well. it has a built in test function to make sure the internal electronics are working . Then its down to the voltage pickup card at the plasma .
It sounds like something is wrong in the voltage reading because NOTHING cuts at 38 volts . In fact about the lowest you would ever see is around 78 volts using Fine cut consumables . Normal types cut at much higher settings. In the end the LCTHC is a simple UP / DOWN jog conrol for MACH3 and its internal THC logic .

LCTHC-Manual_REV9.pdf

Here is a manual that can give you some operational info. The LCTHC was sold off and we could not release any info on it but the company never produced any and went out of business so i went back in some backups and found the manuals .