QTPlasmaC with fourth axis - rotary

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07 Jun 2023 20:56 #273116 by mariusl
So the consensus is that we can do it with QTPlasmaC using Sheetcam. I just need to understand how we deal with the fourth axis in QTPlasmac.

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Marius


www.bluearccnc.com

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07 Jun 2023 21:10 #273118 by snowgoer540

I have a license for the rotary plugin of Sheetcam. I could do a sample if you tell what you want to look at?



I was just curious what that particular table running mach3 required to get there. There’s a few ways, I’m sure.

I don’t think anyone’s done a 4th with qtplasmac that I know of, from a GUI standpoint it should be able to handle it, but I’m sure it’s not tested.

From a PlasmaC component standpoint, it would be all THC driven. But there’s the option to keep Z movements if that’s the CAM option chosen, currently that wouldn’t support THC, but with a bunch of extra work it might be possible to do both?

I go back to wondering how other tables do this successfully.

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07 Jun 2023 21:11 #273119 by snowgoer540
I should add that I recently saw some JD^2 promo videos and it did not look like they used THC. The cuts also looked like hot garbage at the corners of the tubing, IMO.

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08 Jun 2023 07:06 #273140 by mariusl

I have a license for the rotary plugin of Sheetcam. I could do a sample if you tell what you want to look at?


I was just curious what that particular table running mach3 required to get there. There’s a few ways, I’m sure.


I go back to wondering how other tables do this successfully.

That machine makes use of the plugin in Sheetcam. I don't think the THC is used or required at all for tube cutting.
I take it if we switch the THC off in PlasmaC we could do it.

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Marius


www.bluearccnc.com

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08 Jun 2023 10:58 #273158 by rodw
My understanding is that Sheetcam runs a wrapped rotary. In other words, the X or Y axis is wrapped around the tube. So it's not really a C axis. You You could achieve this manually by changing the ini file stepscale based on the diameter of the tube and the steps per revolution.
To produce a wrapped rotary job without Sheetcam it's super simple in any CAD system that supports sheetmetal.
Just design your tubular part and then do an extruded cut 0.01mm wide for the full length of the tube. Then flatten your part!
Voila, an unwrapped rotary.

Round tube cutters do not need a THC (or even a Z axis under CNC control) because the torch only needs to be set at a fixed height.
Square and rectangular tube rely on the THC to lift the torch as it rotates. It would not be terribly difficult to calculate the circumference of a square tube with a radius on the corner to treat it as a wrapped rotary. Then bonus marks if you can calculate the rotary feed rate to account for the corners! 

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08 Jun 2023 11:17 - 08 Jun 2023 11:18 #273161 by LesNewell
While SheetCam does rely on an unwrapped drawing of the tube it internally wraps that drawing around the tube geometry to generate the code and calculate the rotary angle based on diameter. For square/rectangular it calculates the Z height depending on the tube angle. Relying on THC to handle square tube does not work very well. When cutting on the flats of the tube SheetCam uses X,Y moves.
It also has your bonus points for calculating the feed rates for the combined X,Y,Z,A moves. For small corner radius tubes the machine needs to move very fast to maintain the surface feed. You can see that in the video Marius linked. I generally recommend designing the rotary axis to handle at least 200RPM and X,Y axes at least 10m/min (400IPM).

Does anyone know how QTPlasmaC handles referencing when keep-z-motion = 1?
Last edit: 08 Jun 2023 11:18 by LesNewell.
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08 Jun 2023 11:21 - 08 Jun 2023 11:26 #273162 by mariusl
All you say is correct Rob. It is how Sheetcam does it. If you watch that video the guy explains it in some detail how to determine the square tube circumference and the steps. Only thing is that Sheetcam actually use the Z axis on square tubes so far I understand it.

Sorry I didn't see Les answered above

Regards
Marius


www.bluearccnc.com

Last edit: 08 Jun 2023 11:26 by mariusl.
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08 Jun 2023 11:28 #273164 by rodw
Well we now have it from the horses mouth. Thanks Les!

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08 Jun 2023 15:39 #273182 by tommylight
Round tube = no THC and no 4th axis, must have float switch or ohmic, makes work much smoother.
Square tube = some types/sizes would be just fine wrapping the total of all lengths (yes lengths :) ), without radius's, but most will not be comfortable work doe to extinguished arcs and/or torch hitting material.

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08 Jun 2023 16:03 #273187 by mariusl
The torch will not hit if the Z axis is driven by Gcode like the Sheetcam plugin does.

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Marius


www.bluearccnc.com

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