Use the SheetCam rotary POST it converts the linear moves into polar moves based on the diam of the tube.

(;-) TP

Sorry but because i'm not very experienced in gcode, can you be more specific and if possible give me an example of how can i cut for example a hole of diameter 50mm or a rectangle 30 x 30 mm on a tube of diameter 300mm.
What dxf parts do i have to import on sheetcam, i suppose the circle or rectangle but how do i define the 300mm tube?
Thanks in advance. 

Simple import the drawing of the holes as a dxf as you wouold cut it if it were on a flate plate. Then specify the tube diameter as the material thickness.

Apply the cutting function as you normally would then post the results using the rotary post.SC will then translate the XY into XA axis moves.

That works IF you are using a chuck with your 4th axis so the tube runs on the centerline. IF you are using the roller method then the process is different.

Hope that helps, (;-) TP

Actually I just found a problem with the rotary post. It may get the feed rates wrong. Does anyone know if the mach g-code interpreter has a parameter to tell it the diameter of the tube on a rotary axis? I see that OEM DRO 825 is the diameter but I can't find an equavalent parameter.

The problem is in MACH (;-) You have to use A axis radius correction. Turn it on in config then apply the radius on the settings page. Then maybe it will do the feeds correctly. ALSO your  A axis MUST be fast enought to be able to match the X/Y feeds speeds OR mach just slows down to the slowest component.

To use the 4th with plasma it MUST be settup as a very fast 4th.   (;-)

(;-) TP

What I am trying to do is supply Mach with the radius from the G-code instead of entering it in Mach every time.

The other alternative is to define the rotary axis as linear and then get the post processor to work out the feed rate for every line segment. The main disadvantage with this method is that Mach will probably run quite rough. It doesn't like running plasma with a feed rate on every line.

You can update the Radius through a Macro call from inside Gcode at the beginning of each program if you want. If you are using SheetCam you can also bring in the Radius from sheetcam via a Gcode variable you just have to mod the post a touch>LES is really good at that for users. ALso with the variable trick you need an update Macro to run from the macropump.

I am not sure WHY you need to constanatly mess with the feerate?? Once set correctly Mach does a good job of maintaining a constant velocity for plasma work. AT LEAST it does here.

(;-) TP

Another thought would be to set up the rotary as a linear drive and set the drive up so that one rev of the drive is equal to 10 inches then use scale on that axis to set the actual circuference of the tube to be cut.

(;-) TP

What I am trying to do is supply Mach with the radius from the G-code instead of entering it in Mach every time.

You can set it from G-code with a Macro:

M666 P1.2345

Pass the radius with the P word.
The Macro only needs one line:

SetOEMDRO(825, Param1 ())

Hope this helps
Al

You can set it from G-code with a Macro:

I was hoping to avoid that as it complicates things for my customers. I want to keep it as easy as possible for end users.

LES is really good at that for users.

Thanks. That's me

I am not sure WHY you need to constanatly mess with the feerate?? Once set correctly Mach does a good job of maintaining a constant velocity for plasma work.

If the rotary axis is set up as linear then the feed has to be scaled depending on the cut angle. For instance if cutting parallel to the tube then the feed is scaled 1:1. However if you are cutting perpendicular to the tube axis then you need to scale the feed rate to match the angular rate you need. Angles between these two  will have a feed rate that is between the two extremes.

Another thought would be to set up the rotary as a linear drive and set the drive up so that one rev of the drive is equal to 10 inches then use scale on that axis to set the actual circumference of the tube to be cut.

Now that is an idea. The question is, when you scale the axis does it also scale the feed rate?