CNC routing plywood panels that might not be perfectly aligned on the table

[ryanjg11]

This is probably a pretty basic CNC question, but I currently have a 4x8-foot gantry style CNC router with an MDF vacuum table. I don't have any other hold-downs, unless you include double-stick tape with CA glue (which actually has never failed me).

I have some rectangular cabinet panels that I have already cut, but decided I need to trim 1/32 off all sides. That's an easy adjustment in Fusion360 CAM (I just use the material to leave, radial, -0.03125).

But, I have already removed this panel from the table, and I'll never be able to place it back onto the table perfectly aligned to either the X or Y axis.

In the past, I've placed a 1/4" router bit and my Wireless MPG to jog it so that it's JUST rubbing against the nearest X side wall, then jogged it down for another X side wall measurement on the far end of the panel, and adjusted so once again, the bit is just rubbing. Then, I bring the bit up, set X=0, then MDI G54 +0.125 to center the 1/4" bit and zero it one more time for my final X=0 position.

That could work, and will be accurate enough for what I'm doing, but I'm wondering if there is a way I could do this AFTER I have glued the panel to the table using the double-stick tape and CA glue hack? Once it's placed, it won't be perfectly aligned to the X axis.

I know CNC12 has some probing options, but it seems more for actual probes than the manual technique I mentioned above.

Am I trying to define a new coordinate system here?

Or would it just be easier to take the measurements at both points of X, and bake that rotation into the Fusion file in CAM?

[cnckeith]

you can use either the manual technique or any combination of probes. touch probes or touch plates. and use Coordinate System Rotation to rotate the machine to match the pc of plywood you laid down on the table. F1 Set Part Zeros, F5 CSR

[Ken Rychlik]

I would fix those parts on the table saw in my shop faster than I could set up for that operation. If you need to do that type of stuff a lot, you could attach two strips at 90 degree angles. Trim them with the machine, and then bump your part to the fence you just made.

[RogDC]

I would try the Method Keith suggests first.

If that doesn't work for you, drill some holes in your MDF table for wood dowels, 3 should be sufficient to align, two on one side ( Y axis), one on the other ( Y Axis), use your vacuum table or glue and tape to hold down, remove the dowels before trimming the perimeter.

If you're worried about air leaks on the dowel holes after use, glue them in the MDF and flush trim to the table.

[ryanjg11]

Thanks all. I hadn't realized I could use my Avid style touch-off plate to do this (Keith's last image).

I'm guessing I'll need to jog the bit to be close to touching the plate, low enough to touch the inner walls of the probe.

And hitting cycle start will get it to slowly move along X+ until it touches?

Will the result be a new coordinate system? If so, anything I need to do in CAM to make sure this coordinate system is used?

[ryanjg11]

I would fix those parts on the table saw in my shop faster than I could set up for that operation. If you need to do that type of stuff a lot, you could attach two strips at 90 degree angles. Trim them with the machine, and then bump your part to the fence you just made.

Agree the table saw could be a quick answer, but even with my zero clearance insert and a clean crosscut blade, I can't get as good a surface finish as a compression spiral router bit. Edges need to be crisp as I'll be veneering some solid wood edging to it.

[Sword]

Use a new sharp saw blade, raise it just high enough to score the bottom, then raise it up to make a full cut second pass.

[ShawnM]

Use a new sharp saw blade, raise it just high enough to score the bottom, then raise it up to make a full cut second pass.

Yup, this is how it's done for razor sharp edges.