[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.

[Alnico]

Thanks guys - I was thinking more about this since last night, and yea, the second idea of the jig fitting corners of the table seems better.

I guess what I could do is...

1. get a piece of "furniture plywood" which I would cut to fit to set on the "table" of the machine and fit within all 4 corners. (Its unlikely I'd find a continous piece of hardwood that size - but furniture plywood is pretty stout)

2. Set that big plywood piece on the table and cut jig dowel pts, using the CNC itself, which match the dimensions of the guitar body or neck. (write a special file for that, borrowing pts from the guitar body file)

That way, when I place the wood piece on the CNC table, it (hopefully) will always be in the same place everytime, and the pts can be referenced on the machine (IE: 0,0 is at x inches and y inches of the table).

Might that work?

[luthier]

Can you build two home switches ( lever micro switches from radio shack)into the corner to stop the machine when the x and y get to that point?
Marty

[Stepper Monkey]

I just use a pistol laser sight mounted above the spindle and shooting through it,as I have a spindle open in the middle the same as the lathe spindles do. A drawbar spindle would also work for this. That way when no bit is present my exact zero is projected as a red dot on the workpiece.
If you don't have a hollow spindle, just offset it somewhere off the front or side of the spindle and know the distance of the offset. You don't really even need to know that and it still works for an arbitrary reference point.

Otherwise go old school and just use an edge finder. If I understand you fixture correctly, you don't even need to zero off of the part you are making, you can zero off of part of the machine itself, right?

[turmite]

Hi Alnico,

I don't think anyone really caught your description of the neck. It is a one piece neck and therefore will not have a fretboard attached later. If I were doing a Tele neck I would rough bandsaw the wood and leave four tabs, two per side that would end up both as my index pin locators as well as my means of holding the part to the table. This will require building a fixture to machine the fretboard side but nothing complicated. If you have a dxf of the neck post it and I will attach the tabs as well as draw your fixture for you.

Attached is a Mezzaluna Bass I am doing and you can see what I mean by the index pins.

You will notice three 1/2" holes with points (x's) in the center of the holes. I think those are magenta in color but am not sure. You will also see a series of teal colored x's at various locations around the outside of the body profile. Those are screw hole locations.. The three 1/2" holes are index locations. I can go anywhere on my table and find the absolute starting position of that drawing my picking the center of the index hole I used to start my program from. There are several ways to do this but I happen to use G92 due to a quirk in my system that requires I be able to run my program from anywhere on the table and do it quickly.

Using this setup I can drill three new holes mirrored from the originals and machine the back of the body just as accurately as I do the front.

Mike

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?

[Alnico]

If I understand you fixture correctly, you don't even need to zero off of the part you are making, you can zero off of part of the machine itself, right?


Yes, I'm trying to avoid using any system of lining up pts visually, such as using a laser. Hopefully with the jig in place (which is butted up against all 4 corners of the table) I can tell the machine to (summarizing) "go to the center of the table... then up 12 inches from the bottom... now make that pt 0,0." ..and that 0,0 will be coordinated with the other dowel pts I drilled into the jig. (which line up with the dowel pts on the flipped-over part)




The three 1/2" holes are index locations. I can go anywhere on my table and find the absolute starting position of that drawing by picking the center of the index hole I used to start my program from. There are several ways to do this but I happen to use G92

Thanks - it's the "several ways to do this" that have me intrigued. I'm just trying to avoid lining points up visually... is that what you meant by "picking the center of the index hole" or can the machine find that itself?

(I was reading up on G92 just now)

[turmite]

Hi Alnico,

I probably didn't explain my process in depth enough.

I use Mach2/3 as my controller, if that helps any.

In my cad drawing that I posted you will see that the guitar is basically sitting on x0y0. I simply did that for my original drawing. When I wrote cammed the code for it I move the drawing so that one of those 1/2" holes in the x in it was located at x0y0. I then cammed a short program to drill those three 1/2" holes on my table, or it could have be a scraficial board, or even a fixture. For me it was my table. I visually located where I wanted the holes to be and jogged the machine to the position. This x/y position was recorded and then I ran the hole drilling program. I inserted three 1/2" pins in those holes that protruded out of the table about 1/2". My blank already had those three holes in it from the original machining process so all I had to do is slip the blank over the three pins, use the predrilled screw holes to hold it down to the table. Now remember I told you I had recorded the x/y position? I can now home my machine, move to that x/y cordinate and be sitting at the correct position each time I need to change bits or whatever.

Let me ask you a question. Do you have home limits, or reference switches on your machine? If so, this system will work.........well actually, even if you don't have switches it will work, but will take a little more set up for referencing the machine.

Mike

[GuitarEng]

Unless you can cut everything from one position on your jig, you should never "eyeball" the location.

What you are thinking sounds good, just make sure that you have a good way to locate your jig on your table. I have a K2 and I used a couple of the screw holes for the t-slot sections. I never shift these sections, hence, they give me a pretty consistent locating method.

FYI, I use MDF for my jigs as it is very resistant to changes in humidity & temp. Just make sure if you decided to use MDF that you get rid of all the dust, it can be carcinogenic.

I use a lot of standard sized dowels for locating parts. They are cheap and easy and offer decent accuracy for most wooden parts.

[rlrhett]

There seems to be two homing functions going on here, and I'm getting confused about which we are talking about.

1) You want the piece to be located on the table exactly the same time after time (and to flip the piece over).

2) You need to home the tip of the router in Mach 3 relative to the table in three axis (x,y,z).

I get that using a jig drilled or clamped to the table will make certain that your piece is the same relative to the table, but how are you proposing to "home" the spindle relative to the jig/table/workpiece?

Will you jog the spindle to a mark on the jig/table/workpiece and eyeball it?

Can you, or will you, rely on limit switches in the corner of the table? If so, will you change the coordinate system in your CAD/CAM program to reflect the table's limit switches? What if your bit is not exactly the same height time after time, will home switches give you an accurate "z" home?