Accurately locating a routing fixture to modify parts

[kjoiner]

Hello,

It's been a while since I've used a fixture on my Stinger 23. In this case, I need to modify a PVC extrusion. Currently, the extrusion has 5 sets of mounting holes that I want to cut into keyholes. The extrusion is 68 inches long so it's too long to modify in one shot. I plan on making a fixture that I will 3D print. The fixture will align one set of holes and I'll run a toolpath to make they keyhole. I will then slide the extrusion along and align the next set of holes etc. I need to be able to accurately locate the fixture so my zero in V Carve and the zero on the physical fixture match. Since I'm designing the fixture, I have total control over any features I want. One thought is to put a 1/4" hole in the fixture and then put a 1/4" cutter shank in the collet. I'll use the shank to position the fixture similar to how I would do it on a manual milling machine. My question regards setting the zero in V Carve Pro. It has options for 4 corners, a center, and an offset. If I put a 1/4" hole let's say an inch in from the corner of the fixture, how do I set the zero in V Carve?

Attached is a screen shot of the fixture. The small radii of the keyholes are the remnants of the original holes that are cut into keyholes. The large countersunk holes are for threaded brass inserts that will be used to clamp the extrusion while cutting.

Thanks!

Kyle

[jjwdawg]

If this is a one-time job, I think I'd just place a sacrificial piece of MDF or plywood on the table, and create your fixture by routing a slot and/or pin holes in it - probably much faster than waiting on a 3d print. Then you wouldn't have to align the fixture to the router, since it would already be in place. Create your part toolpaths in the same file as your fixture ops, and just leave your router's zero in the "Router Home" position (or wherever else you want).

If it needs to be repeatable to reuse in the future, I'd basically do the same thing, but design the fixture to be located on the router's bed in a repeatable way - probably flushed up against two edges of the router bed.

Finally, to answer your actual question :-) ... I would leave V-Carve's zero in the lower-left (or wherever you're accustomed to having it), and use the G92 command in WinCNC to set your pin location. e.g.: If the pin is at (5,10) in V-Carve, then align the spindle to the pin location on your router, and enter "G92 X5 Y10"

[kjoiner]

I think I figured out a happy medium. I set my zero point in V Carve to the center. I then imported my fixture and placed its locating hole at the center in V Carve. When I run the part, I'll just move the spindle so it's centered over one of my T tracks and then lower it with a locator pin in the collet (shank from a broken off 1/8 cutter from previous adventures) and align the fixture with that. I can then clamp the fixture in place.

3D printing the fixture will allow me to use it in the future if the concept works and I can hand off the process to someone else.

[Jim Becker]

If you have a fixed position that the fixture mounts to on your machine, be sure to record the fixture specific x-y zero position in WinCNC so you can repeatedly return to that spot and "set" x-y zero for the work you will do on the fixture. By default, you can record up to ten absolutely positions in memory and that can be extended with a modification to the WinCNC.INI file to accommodate pretty much as many remembered absolute positions as you might need.