Help with Theta X direction

I have an older CNC fabric cutter (carlsondesign.com) that I'm wanting to upgrade with new motors, controls and software (LinuxCNC or similar). I can figure the standard XY side of the controls however this uses an air solenoid to move the head up and down (speed controlled by needle valves and dwell settings) as well as a pen. "Z" actually steers the cutter head in the direction it needs to roll the cutter. For the cutter, think of a pizza wheel cutter. It uses a 28mm round razor blade that has to track in the direction it's headed (for it's X/Y position) and then lift up, turn and drop back down for corners or angles that exceed its steering limit.

Looking for info pointing me in the right direction for where to start searching this type of controls. Right now I don't even know where to start searching.

Thanks for the help!

Some clarification on my question:

This is basically a drag knife (however uses a round blade). If you go to either carlsondesign.com or autometrix.com you will see these machines.

The 28mm razor blade just rolls along (sort of like a pizza cutter does). The Z axis steers the blade in the direction of the XY motion. On the Autometrix machine the blade holder is fixed and not allowed to swivel which is better than the carlson system that allows it to swivel. We've bad both machines. I kept the old carlson machine and am just trying to upgrade it.

Thanks!

What program do you use to generate the gcode? Can you attach an example please.

Badger - I use a program from Autometrix called PatternSmith to do the nesting. However the design work is done in AutoCAD LT and output at a DXF. I have both draw lines and cut lines defined by a layer/color as to which is which.

Below is the output code that goes to the cutter. However it is obvious this is not Gcode..... This is for a 12" x 12" box with just a cut layer.

#Plot
` NewTable
0 penup
1 penup
` Panel 1
0 penup
1 Cutter_Select
` Polyline
1 penup
flush_plot
80000 set_feedrate
12001 1 acut
flush_plot
1 pendown
35000 set_feedrate
12001 12001 acut
1 12001 acut
1 1 acut
12001 1 acut
1 penup
flush_plot
1 penup
flush_plot
80000 set_feedrate
#EndTable

So it looks like you have two problems.
1. The proprietary file format used by the plotter
2. Calculating the cutting tangent.

Does your nesting software allow output of different file formats or does it just output for Carlson Design?

The path of least resistance would be to convert to a Gcode workflow. One easy way to do this would be to use Sheetcam to do your DXF file nesting. Its Postprocessor is easy to modify and would allow custom code to be output on an Arc and calculate the radius plus on pen up and pen down. But I suspect sheetcam won't be as nice to use as what you are accustomed to. It might be possible to convert your current file format to gcode so you can use your existing nesting software.

I know PCW on the other forum posted on indicated that this had been done before by calculating the tangent of XY to orient the knife. I'm not sure how this was done as whilst it is possible for a component to know when its cutting an arc, it does not know the arc radius so some trickery is required. There is an experimental branch called state tags that I think would provide this information but its pretty old.

A user recently said they parsed a gcode file to find arcs before it was cut so let me find that post.

Found it!
forum.linuxcnc.org/10-advanced-configura...f-an-arc-its-cutting

And I found a forum post from the owner of sheetcam where he said that Sheetcam included a post processor for a tangential cutter.
forum.sheetcam.com/viewtopic.php?t=3687

Controllong your machine from gcode would be pretty easy. You could use the motion.spindle-is-on pin to fire the solenoid to lower the knife or you could use one of the M62/M63 or M64/M65 to toggle a digital output. You could also send an analog value back to LinuxCNC with M67/M68 to set the angle but this is not as good as being able to calculate the tangent in real time.

I use an extension gcodetools in the drawing program Inkscape to generate gcode for my rugmaking machine. Gcodetools has a tangent knife function including lifts, which I don't use, but I do use it to rotate my tool in the direction of travel. There is some old support on cnc-club.ru in the "english" forum but it has been active for a while.

andypugh wrote:

rodw wrote:

Found it!
forum.linuxcnc.org/10-advanced-configura...f-an-arc-its-cutting

I think that might be the wrong link?

Yeh I think so but now with your help it is now relevant as it shows how to calculate the heading (Tangential direction) to orient the knife. (And even the arc radius if thats required...)