Flipping a piece and finding zero point

[Alnico]

First post, Hello! Consider for the sake of discussion a one-piece Tele style neck, working from a 3D CAD.

From what I've read, you would place the rough-cut wood piece on the "table" under the router, and it would start from 0,0,0 to cut the outter shape of the neck, shape the radius of the fingerboard, and then cut the fret slots. It would require changing bits, but the wood piece stays in the same place the whole time.

(What is used to hold the piece in place? I've read where some luthiers use double-sided tape? Or are jigs/braces more common?)

After the top side of the neck is done, its time to flip it over and have the router shape the back of the neck and route a channel for the truss rod (it would later get a "skunk stripe" to fill over the rod)

My main question is, after flipping the piece over, how do you place the back of the neck so that the dimensions work from a zero starting point? Is it mainly a matter of good eyeballing? Or following lines drawn as guides? Or braces/jigs?

The first (top) side is easy - but how do you line up the otherside after flipping it over?

[ger21]

Since it will have a radiused fretboard, some type of fixture would probably be necessary to hold it in place.

A better way to go about it would be to do the back side first, without the fretboard attached. Do the fretboard as a seperate piece, and attach last.

[HuFlungDung]

If you can plan ahead for fixturing, add enough stock allowance to drill a couple of dowel holes in the first machining position. Suppose you were to add some extra length or width to permit this.

Then machine a subplate (or another board) with two dowels to mate with the fixturing holes in the part. Set up this subplate and locate the reference point over one of the dowels. Usually, you might place the two dowels on a line parallel to one machine axis, to facilitate setup of the fixture.

Then, flip the part over in cadcam and relocate your X0Y0 over the one dowel. Post new code from that location.

A final step will be some sort of procedure to cut away the excess material containing the dowel locators. You might do this with a saw, on a project like yours. Or, you might reclamp the part where it sits and write a couple of short programs to cut the excess material off the ends of the part.

[Alnico]

Thanks guys - another example might be a Strat body. If I start w the wood on one side and cut out the outline, then the pickups and tremolo holes, and the forearm contour. At some point I have to flip it over to have the machine route out the things on the backside: the rest of the tremolo hole and spring cavity, as well as the body contour.

(HuFlung's suggestion about an extra piece makes sense)

[GuitarEng]

you always have to locate your part. In some cases, you can just double stick a board to the table and go for it...letting the machine trim away all the fat. In others, you need to use dowels, jigs, or stops to locate a part.

Cutting stuff is easy, figuring out how to hold it down is sometimes the harder part!

[mar999]

Hi heres what i do i make table cutouts for both sides of the body(with location holes X_Y) and place the body in the cutouts wit 4 small pieces of carpet tape, the cutout is about 3/8 deep for the body

[mar999]

heres the pic
http://www.cnczone.com/forums/attach...0&d=1175456168

[mar999]

the small pieces of tape are about 1 inch long hold it firm and the cutout fits the body like a glove about 002 all the way around

[mar999]

as for the neck i use what Ger21 said a neck jig with two location holes for datum line

[Alnico]

If you guys don't mind, I'd like to bring this back up. I got sidetracked in the past weeks, but since then I've come up with an idea which makes it even more important to locate the zero point on the reverse side.

I've got a pretty good idea of what I want to do to actually hold the flipped piece in place, and it's not too far off from what HuFlung mentions above... mainly a subplate which lines the body up with dowels.

But this doesn't neccesarily find me the zero point... HuFlung and GuitarEng say "relocate/locate" the X,Y. But it still feels like "eyeballing" to me. I've got 2 possible ideas:

1. Have 2 holes in the subplate - one in the center near the bottom which is the size of the bit. And another hole in the center near the top. With the motor not running is it possible to manually lower the bit into the hole at the bottom, and clamp the subplate to that spot.. then repeat with the other hole near the top.

2. Or create a subplate* which is big enough to butt into a corner (X and Y), and will always fit into that position when placed that way. The dowels will always be in the same spot when that subplate is placed there.

(*the subplate is actually milled in the place where it will be used)

Would either one of these work? The point is to eliminate "eyeballing".

[ger21]

I'd use #2.

[rlrhett]

Anilco,

I think I understand what you are talking about. A jig to hold your part that has 90deg corners you can fit into a fixed corner. Still don't see how that helps you to home/zero your machine to the same place.

Perhaps when you implement this you could post some pictures. You know, a picture is worth a thousand words.