Tangential control with Mach 3

[krumly]

I'm new to CNC, and am looking at building a "pizza wheel" fabric cutter.
You're basically looking at a standard 2.5 axis router type set-up and a rotary head to keep the pizza wheel cutter tangent to the curve (or in-line with the incremental straight line segment cuts, if you will). Z-axis control is dirt simple - basically a "pen up/pen down" operation like a pen plotter.

Gerry in the general control software forum thought Mach 3 could do tangential control if arcs were converted to line segments. Anyone have any experience with this? What if I wanted my tool head to contain both the rotary pizza wheel cutter as the primary tool , along with a retractable pen adjacent to it so I could switch over to cloth marking or plotting on the fly?

Thanks,

krumly

[ger21]

Mach should be able to do that, but, depending on how you want to swap tools, you'll probably need to write a macro or 2 to get it working for you.

[NC Cams]

We did a variation of the arc to segments conversion for our cam cutting program. We did this because we had a hard time getting the machine code to operate as a cam generator in one area and an arc cutting device in another even though it was supposed to do so quite readily. It didn't.

The trick is to convert the circle into hundreds of "flats" via point to point milling instead of circular interpolation. If you create enough "flats" (in our case, we run 1/4's or 1/8th degree segments.

Since the cams we're cutting are cut into 5" dia disks, this is sufficient integrals to eliminate the "flats" in the finished cam lobe. We have 1/10 to 1/12 degree capabilities but have never had to do it yet. For something as big as a pizza dish, you might need to go to even smaller segments than quarters or eighths.

THis method will readily convert a circle/arc or even something more complicated into something manageable for a device to CNC machine cut. It does work well for us and we tried several methods before we settled on it.

[krumly]

Thanks, nccams -

For fabric cutting I think the interpolation of circles as short segments is fine. My CAD program use NURBS and cubic splines as well, and outputs them to DXF as line segments to a designated chord height tolerance - way beyond what I'd be worried about when someone goes to sew the panels togehter, anyway.

What I'm specifically interested in is how you'd use Mach3 to have a 4'th axis (in this case the pizza wheel knife blade sitting directly over the designated XY coordinate) rotate to be in-line with the line move. I don't understand the program that well to figure how you'd set it up. I saw something about formulas in the demo in one of the toolbars. Is it possible to make the A position in any G01 line of code equal to the angle formed by the segment from the previous line G01 XY position to the currently designated G01 XY position in a line move? The trig conversion here would be trivial.

Thanks,

krumly

[ger21]

Mach3 does the tangential control automatically. There's a setting in there somewhere to set it up. I'll take a look when I get a chance.

[krumly]

Gerry -

You peaked my curiosity. I found a "tangential control" checkbox under the settings dialog (Alt 6) with two values to edit for "lift angle" and "lift z" below it. I also dug into the on-line documentaion and there is a brief mention of this feature for tangential knife control exactly as I'm looking for.

I'm not exactly sure what "lift angle" and "lift z refer to in this context, but I'll dig into it some more. Thanks,

krumly

[ger21]

See section 4-9 on page 39 of the Mach3 .pdf manual. It says the a axis can be configured for tangential control, but doesn't go into detail. It may be as simple as clicking the button you found. G1 moves only.


Edit. After a quick search on the Mach support group, apparently, you setup the A axis as a rotary axis, and activate tangential control on the settings page. I just tried it in simulation mode, and the A axis does rotate automatically, although I'm not sure it was set correctly (motor tuning)