DIY Plasma Table- Auto Z with Ohmic - help needed

[Plasma629]

Hello all,

I have a 4x4 cnc router table which i retrofitted into a plasma table by:
-I removed the spindle and attached a hypertherm 45xp machine torch
-Hooked up THC (THC3T-02)
-Got sheetcam
-Using Mach 4 with ESS

currently my sheet cam PP is set to output only X and Y, NO Z movements...with m3/m5 and torch on/off.
I am able to jog down manually to the sheet and set z zero and start gcode, after the torch fires my THC starts doing its job and moves the Z axis up/down depending on the metal curve. I cut very thin 24-26G on 30 amps low speed so the sheet it never fully flat.

The first cut is always great but my issue arises when i have a part which is not one long cut and involves many holes and cuts far apart, sometime my THC will move the torch up but when it jogs to the next location to fire it is too hign and does not know till it already fires and the THC needs to try to bring it down again, by this point the part is ruined.

I have read many forums on OHMIC touch off and wanted to get some feedback on my thought before i go buy material, i am hoping to achieve the below:

when M3 is triggered to fire torch i would like the machine to jog down to sheet and set Z 0 and jog back up to pierce height then fire torch, I want this to happen every time M3 is triggered.

Is this the best way to get my table up and working or would you suggest another approach?

PS: i do not understand macros at all, if someone can help me write a M3 macro which will do the above i will be forever be in your debt.

Also hypertherm has a ohmic retainer (part 220953) if i buy this is this all I would need to be able to do the auto Z 0 or will I need additional hardware? another option is the CandCNC feather touch off kit for $85.

Regards,
plasma629

[machinedude]

i looked at that THC a little bit and seen something on here with someone having issues with their z axis with that brand. i'm not sure if the two are the same model but below is what this member ended up fining out. i passed over that brand just for the simple fact of the lack of documentation online to look over.

******PROBLEM SOLVED. I finally got a reply from ROBOT3T. The solution to my THC3T-02 z axis problem was that it won't work if the z-axis step/dir setting in Mach3 is set to "active high". Seems like that would be an important thing to include in the instructions. Anyway, I changed it to active low and now can control my z properly. Of course it changed the direction that the z homed and moved, but was able to fix that by changing direction other direction settings in Mach3. Now I can finish hooking up the plasma and get back to cutting metal.*********

i don't know if this will help or not just something i came across here and figured i would point out since it was still fresh in my memory still

[Plasma629]

i looked at that THC a little bit and seen something on here with someone having issues with their z axis with that brand. i'm not sure if the two are the same model but below is what this member ended up fining out. i passed over that brand just for the simple fact of the lack of documentation online to look over.

******PROBLEM SOLVED. I finally got a reply from ROBOT3T. The solution to my THC3T-02 z axis problem was that it won't work if the z-axis step/dir setting in Mach3 is set to "active high". Seems like that would be an important thing to include in the instructions. Anyway, I changed it to active low and now can control my z properly. Of course it changed the direction that the z homed and moved, but was able to fix that by changing direction other direction settings in Mach3. Now I can finish hooking up the plasma and get back to cutting metal.*********

i don't know if this will help or not just something i came across here and figured i would point out since it was still fresh in my memory still

Thanks for the find but I have already got the Thc3t-02 working to my liking.

I should probably clarify i need help hooking up a OHMIC sensor to my hypertherm 45xp and have my M3 or any other macro do a touch off to 0 Z axis before each fire of the plasma torch.
Hypertherm sells a OHMIC cap but i cannot find instructions on how to hook it up or if I need additional wires/connectors?
Or is going the CandCNC feather ohmic unit a better option?

Also need help writing that macro i mentioned earlier

[djreiswig]

You should be able to find a post processor that will give you touchoffs.
For the ohmic, you will need more than just the cap. You need some sort of isolated power supply so you don't fry your controller with the plasma voltage.
Some have used a water switch unit. You should be able to find info on the forum.
I think you could probably get the feathertouch to work. If you post more info on your controller it would help.

[machinedude]

if i remember right if you go to the actual web site for that controller they might have have the Ohmic stuff needed. the wire on the torch is only one aspect of Ohmic sensing. this picture from neuron breaks it down with their system i would imagine the THC and ethernet and break out board tie everything to the software. i've only scratched the surface of the controller side of things so i'm not much help there

[machinedude]

one other note is you can get into a post processor and change how it spits out the code if need be as well. just another possibility to customize for your set up and needs.sometimes a post only gets you close and you have to make some minor tweaks so you don't have to edit it afterwords. food for thought

[Plasma629]

I dont think buying a Neuron THC is a option for me.

The THC controller I am using is a THC3T-02
(https://drive.google.com/file/d/1I95619 ... 32xKL/view)

I think I need the touch off to be configured in Mach 4 via a Macro?

I have the below motion controller/BOB:
(https://www.automationtechnologiesinc.c ... -breakout/)

I am using the ESS smoothstepper

Regards
Plasma629

[machinedude]

i knew i seen they had Parts of the Ohmic IHC. this picture might offer some clues as to how they fit it into their system? i did not see anything as far as hooks up go for this feature for the THC you have. looks pretty basic from what i skimmed through. they have another unit that is stand alone but i can't find any manuals on there site to look through?

[Plasma629]

Seems like I need to get the hypertherm ohmic consumables and a ohmoc "unit" such as the candcnc feather touch unit.
http://www.candcnc.net/images/Manuals/H ... s-REL6.pdf

Now my question is will the candcnc unit be compatible with my motion comtroller/table setup?

[Rodw]

There is a simple ohmic sensing circuit as part of the official linuxcnc documents I wrote. It should be able to be used with any hardware and any controller.
http://linuxcnc.org/docs/devel/html/pla ... rimer.html
For protection, we use an output pin to say we are probing so the circuit is disconnected at all times unless probing and an input pin which is turned on when the torch shield touches the material.

There is a much more sophisticated version that I have just got going that is specific to Linuxcnc and Mesa hardware which I outlined in my last post on my build thread here on the forum

viewtopic.php?f=103&t=22826&start=125#p173948

This version developed with Mesa's support uses a power supply with isolation rating for 500 volts and a Mesa THCAD-5 isolated voltage to frequency A-D board which is also able to withstand over voltage of 500 volts indefinitely. The THCAD is so sensitive, we can see the voltage go from 0 to 24 volts over 0.04mm of travel as the torch shield touches the material. A LinuxCNC software component allows us to set both an on threshold (which I think a reasonable default is around 18-22 volts) and an off threshold (say between 1-5 volts). This give us really good switch hysteresis to prevent false triggers.

I've been working on getting this fully documented and incorporated into the official Linuxcnc Plasmac config
http://linuxcnc.org/docs/devel/html/pla ... guide.html

I'll publish the THCAD circuit on my build thread here shortly.

[machinedude]

There is a simple ohmic sensing circuit as part of the official linuxcnc documents I wrote. It should be able to be used with any hardware and any controller.
http://linuxcnc.org/docs/devel/html/pla ... rimer.html
For protection, we use an output pin to say we are probing so the circuit is disconnected at all times unless probing and an input pin which is turned on when the torch shield touches the material.

There is a much more sophisticated version that I have just got going that is specific to Linuxcnc and Mesa hardware which I outlined in my last post on my build thread here on the forum

viewtopic.php?f=103&t=22826&start=125#p173948

This version developed with Mesa's support uses a power supply with isolation rating for 500 volts and a Mesa THCAD-5 isolated voltage to frequency A-D board which is also able to withstand over voltage of 500 volts indefinitely. The THCAD is so sensitive, we can see the voltage go from 0 to 24 volts over 0.04mm of travel as the torch shield touches the material. A LinuxCNC software component allows us to set both an on threshold (which I think a reasonable default is around 18-22 volts) and an off threshold (say between 1-5 volts). This give us really good switch hysteresis to prevent false triggers.

I've been working on getting this fully documented and incorporated into the official Linuxcnc Plasmac config
http://linuxcnc.org/docs/devel/html/pla ... guide.html

I'll publish the THCAD circuit on my build thread here shortly.

when i look at this operating system and what is being done with it i am impressed with it. the over all cost is extremely reasonable well no doubt. i just wish i was more computer savoy and could get the operating system to load on a computer:) you guys need linuxus for dummies i wish it was more plug and play.

[Rodw]

i wish it was more plug and play.

Well it is, you just need to ask for help on the Linuxcnc forum. PLasmac is the most plug and play of any of the Linuxcnc Machines.

I did add a brief dummies guide on my build thread a little while ago.

Basically you just download an ISO image, burn it to a USB stick with win32diskimager and you get Linuxcnc and Linux installed in one hit. The only catch is that Linuxcnc is in the middle of upgrading to a new distribution version (from 2.7 to 2.8) so once you get it up and running, there is an additional step to upgrade but that is documented.

Its my plan to develop a reference build of a Linuxcnc plasma controller.

[Plasma629]

There is a simple ohmic sensing circuit as part of the official linuxcnc documents I wrote. It should be able to be used with any hardware and any controller.
http://linuxcnc.org/docs/devel/html/pla ... rimer.html
For protection, we use an output pin to say we are probing so the circuit is disconnected at all times unless probing and an input pin which is turned on when the torch shield touches the material.

There is a much more sophisticated version that I have just got going that is specific to Linuxcnc and Mesa hardware which I outlined in my last post on my build thread here on the forum

viewtopic.php?f=103&t=22826&start=125#p173948

This version developed with Mesa's support uses a power supply with isolation rating for 500 volts and a Mesa THCAD-5 isolated voltage to frequency A-D board which is also able to withstand over voltage of 500 volts indefinitely. The THCAD is so sensitive, we can see the voltage go from 0 to 24 volts over 0.04mm of travel as the torch shield touches the material. A LinuxCNC software component allows us to set both an on threshold (which I think a reasonable default is around 18-22 volts) and an off threshold (say between 1-5 volts). This give us really good switch hysteresis to prevent false triggers.

I've been working on getting this fully documented and incorporated into the official Linuxcnc Plasmac config
http://linuxcnc.org/docs/devel/html/pla ... guide.html

I'll publish the THCAD circuit on my build thread here shortly.

Appreciate your reply and your write up is great! but for the price the candcnc feather touch comes more or so all in one unit and at 85 hard to beat, would i be able to connect this to my controller?

feather touch manual: http://candcnc.net/images/Manuals/Hooku ... s-REL6.pdf
Controller: https://www.automationtechnologiesinc.c ... -breakout/

[Rodw]

I can't comment on the Feathertouch as I have no experience.
I do have a Robot3T unit but I never used it.

For Linuxcnc users, the THCAD-5 is only USD $69 and you need one 390k scaling resistor which will set you back 5c or so.

[djreiswig]

If I recall, the orange and orange/white wire connect when the tip & plate touch. There is a limits circuit which can be used with a switch as a backup for the ohmic. If it misses you will want the switch to keep from breaking something. The limits circuit just goes through the unit, it isn't connected to the ohmic portion so you could run a different backup circuit.
All you should need is a free input to set as probe and use g31 in your post.

[Plasma629]

If I recall, the orange and orange/white wire connect when the tip & plate touch. There is a limits circuit which can be used with a switch as a backup for the ohmic. If it misses you will want the switch to keep from breaking something. The limits circuit just goes through the unit, it isn't connected to the ohmic portion so you could run a different backup circuit.
All you should need is a free input to set as probe and use g31 in your post.

Hmm what do you mean the orange/white and orange connect? Here is a picture of my control BOB:

I have 3 wires from the feather touch... Green(Limits), Orange/White(Common), & Orange(Z-home)....i do have input signal port P12 open but dont know which wire to put there and what to do with the other 2 wires?

Thanks for all the help everyone!
Regards,
Plasma629

[djreiswig]

Exactly what I said. When the tip & plate wires touch the orange & orange/white connect. So if you hook one to common and the other to your input, that circuit will close when the ohmic senses.
One of the z home terminals is hooked to the orange common wire and the other z home terminal is hooked to the green wire. If you hook a switch on your z that activates if the ohmic misses between the two z switch terminals you can use it as a safety. Typically it's wired as an e-stop. You would use a n/c switch that will break your e-stop circuit to keep from crashing your torch when the ohmic misses.
This is all from memory, so no guarantees.

[Plasma629]

Exactly what I said. When the tip & plate wires touch the orange & orange/white connect. So if you hook one to common and the other to your input, that circuit will close when the ohmic senses.
One of the z home terminals is hooked to the orange common wire and the other z home terminal is hooked to the green wire. If you hook a switch on your z that activates if the ohmic misses between the two z switch terminals you can use it as a safety. Typically it's wired as an e-stop. You would use a n/c switch that will break your e-stop circuit to keep from crashing your torch when the ohmic misses.
This is all from memory, so no guarantees.

Thanks!! I got the probe function to work!!

I tried using many different postprocessors in sheet cam but none are working to my needs....I would like a g31 probe function before each M3 firing of the plasma torch, here is how im envisioning it:

-Machine jogs to x,y location
-startrs G31 & sets Z 0
- Goes back up to set pierce height
-M3 torch fire / wait pierce delay
- Come down to cut height and start cutting.
-M5 torch off end of cut
-Z axis move to save Z movement height (before moving to area of next pierce.

The above should repeat for each cut in the gcode...is there a post which can do this currently? or can you help me write it?

Much appreciated!

Plasma629

[djreiswig]

What post are you using? It shouldn't be too hard to add a probing function.

[Rodw]

In some of the CandCNC posts, there is a variable (I think you have to edit the post file) that enables an external touchoff so an external file is loaded.


You would have an external touchoff.ngc file that looked something like this at the most basic level but could be extended to include error checking etc.

WARNING: Metric

Code: Select all

o<touchoff> sub
(#1 pierce height, #2 pierce delay, #3 cut height)
F500
;g0 z15
G38.2 Z-15 (Probe to find the surface)
F50
G38.5 Z20
G0 Z[#5063 + 0.4] (Move to Probe Trip point + switch hysteresis)
G92 Z0 (Set Z zero)
G0 Z#1
M3 S1
M64 P1 (turn on torch )
M66 P0 L1 Q5 (Wait for Arc OK from Torch)
G4 P#2 (Pause for pierce delay)
G0 Z#3 (goto cut height)
o<touchoff> endsub
M2

Note that Linuxcnc has much more sophisticated probing than Mach3 so this probes towards the surface with G38.2 and then probes away from the material at a slower speed with G38.5. Then it adds 0.4mm for switch hysterisis and sets Z0 with a G92.

You probably have to modify this to use it without changing the onPenDown method in your POST. Or modify how its called.

HAve fun!

[djreiswig]

He's using Mach4, so the post will be different.

[Rodw]

He's using Mach4, so the post will be different.

Oops, I got confused with another post about CommandCNC

[raumindustries]

Its my plan to develop a reference build of a Linuxcnc plasma controller.

I'd like to help with that.