GRBL as cnc plasma?

Discussion about the arduino based g-code interpreter, grbl
tm america
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GRBL as cnc plasma?

Post by tm america » Thu Jul 03, 2014 9:56 pm

I am working on a machine that will be mostly used as a cnc mill but want to also run it as a cnc plasma cutter.The problems i am running into so far are.First the grbl seems to freeze up anytime it sees a p code which is used to set the dwell time that the torch is on before it starts to move the axis. This allows it to burn thru the metal before moving the torch.I'm wondering if there is another way i could pause the axis after torch on set a set amount of time?Second is trying to control torch height when the axis are moving to adjust for warping of the work piece..If i could figure out how to do it manually while the machine is running i would have something to tie the torch height controller into.But this is still a minor problem as i can just run a stand alone z axis with the torch height controller built in..So the main thing i need to figure out is how to pause the torch after turning it on without using a p code?

tm america
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Re: GRBL as cnc plasma?

Post by tm america » Thu Jul 03, 2014 9:59 pm

Oh also wondering if there is a way to switch the spindle enable for being a normally high to a normally low signal?Right now i had to use the n.c. side of the relay to get the torch to turn on with a m3 and off with a m5.But i dont like it this way As it turns the torch on anytime you reset the controller

cvoinescu
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Re: GRBL as cnc plasma?

Post by cvoinescu » Fri Jul 04, 2014 11:25 am

tm america wrote:h also wondering if there is a way to switch the spindle enable for being a normally high to a normally low signal?Right now i had to use the n.c. side of the relay to get the torch to turn on with a m3 and off with a m5.But i dont like it this way As it turns the torch on anytime you reset the controller
You'd have to recompile GRBL. Why not wire the relay so that it works that way? In most cases, it should be easy to do. What do you use for a relay, and how is it connected?
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

tm america
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Re: GRBL as cnc plasma?

Post by tm america » Fri Jul 04, 2014 2:51 pm

Ok after looking at things a little more i found my problem with the way the torch is triggering.. Looks like they sent me the wrong relay ?The one i got is a low level trigger. i was suppose to have a high level trigger relay..I'm gonna order a high-low level trigger relay so i can just switch the jumpers on the relay if needed..Still looking for a way to make it pause after the torch turns on to allow the torch to fully blow thru the metal?And also looking for a way to do a torch height controller with grbl?

WillAdams
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Re: GRBL as cnc plasma?

Post by WillAdams » Fri Jul 04, 2014 4:07 pm

tm america wrote:Still looking for a way to make it pause after the torch turns on to allow the torch to fully blow thru the metal?And also looking for a way to do a torch height controller with grbl?
Could you do a very small pair of Z-axis moves at an incredibly slow rate of movement?

I'd thought that dwell would be supported better though.
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tm america
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Re: GRBL as cnc plasma?

Post by tm america » Fri Jul 04, 2014 4:15 pm

I suppose you could do the small moves at a low feedrate..i imagine it would take a whole lot of playing with it to get the right amount of small moves to equal 400ms,or 500msmost of my pause times are 200ms. for thin stuff and up to 500ms. for thick stuff.with that i would be looking at a custom post processor.something that i could plug in a macro for the small z axis moves that would be triggered by the torch on-m3 ....That would free me up from having to manually change it in all my g code files..now for the hard part???/Torch height ??

cvoinescu
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Re: GRBL as cnc plasma?

Post by cvoinescu » Fri Jul 04, 2014 6:15 pm

The way I understand it, the height is critical only during ignition; it doesn't matter much after that, so people do things like this: https://www.youtube.com/watch?v=an5HYBQWTpg -- you can wire the "torch pressed down" switch as the Z limit, or, using GRBL 0.9e, as a touch probe.
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Nigel K Tolley
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Re: GRBL as cnc plasma?

Post by Nigel K Tolley » Fri Jul 04, 2014 11:39 pm

The major steps seem to be: get the torch to touch off, move afraction away, fire it up, then move it away a few mm. Then start cutting your part.

All modern plasma systems use feedback to control the current so that the distance isn't that critical once the arc has struck.

I'm planning to do a CNC plasma eShapeoko. Sadly I'm now broke again as a tax bill needs paid this month, so yet again it's not happening. :-(

Didn't realise there was an issue with pause commands. Seems really odd as it would literally be a single line of code in the interpreter for all pauses. Likely a really easy bug fix. Until that point, step the z up and down slowly.

tm america
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Re: GRBL as cnc plasma?

Post by tm america » Mon Jul 07, 2014 11:54 pm

Torch height is critical thru the entire cut process .Torch height affects the amount of dross and cut angle you get .it also is a huge contributor to the life of your consumables .If torch height is not just right you get horrible cut quality as well as ruining alot of pieces..at the minimum you need to be able to control it manually while the program is running..I run water tables on my machines and the metal will still warp a small amount from the heat but alot of times the surface tension of the metal will cause it to warp large amounts when it is cut.Plasma cutting is one of the toughest things to get right .You have to have just the right air pressure,amps,feedrate,torch height and cut strategy.all these along with super dry air proper grounding and a just the right accell rates ..All of this is needed to get accurate parts and have little to no dross and minimal cut angle ...There is alot more to it than there is to milling. milling is just about feed speed and feedrate coupled with the right bit and coolant for a given alloy .. but as long as you are close it will ussually come out ok.. plasma does not work like that .There is a very small window for getting good cuts..

cvoinescu
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Re: GRBL as cnc plasma?

Post by cvoinescu » Tue Jul 08, 2014 12:13 am

Well then, you'll need to build something to adjust the height, preferably automatically. How do the professional machines do it?

Are these guys right?
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

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