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Sorry about the color on these photos...I was just trying make the idea clear here.

The basic idea, in the case of making a set neck guitar, is to get to the point of having the neck assembled and glued while holding to the cad model as closely as possible.

Considering that it is in the gluing process that several things can go wrong to throw the final intonation off on a guitar, I thought the best plan would be to use the same registration system when cutting the part as when gluing the finished parts together. This follows through to the gluing of the neck and body but none of that is depicted or discussed here.

This leads to the point where virtually EVERY cut made on the guitar is registered to an origin thus placing every feature to a pretty precise location.

The idea of using pins sideways occurred to me long ago, registering aluminum molds together with a system that can be easily cleaned after molding. A sideways pin also reduces the amount of vertical space required to precisely hold something on the xy plane. Additionally, there is never any binding of the part to the tool so it just pops off the tool after vacuum is removed, although it holds VERY precisely to the xy plane when vacuum is applied.

I do everything this way now.

Note: Steel pins are used when cutting parts and these nylon pins are used when gluing. They are super cheap.

Note also: Both tools are designed to accommodate all operations done to the object but I do a little extra step that you can't imagine by looking at the tool.

Op 1. The blank on the tool is faced to create the first flat plane. Then a set of those sideways grooves is cut. This promotes a better vacuum when beginning the first cuts of the part.

Consider this a precision blank. It's still a blank because it contains no feature of the part itself...but it DOES hold tightly and registers precisely to the tool. This is done to make certain the blank won't slip when cutting the profile in Op 2. Sometimes the blank is so bad to start with that I'll have to run a piece of masking tape around the full profile of the blank and the tool to help with registration and also to help with the vacuum seal. Once a flat plane is established with the registration slots the blank, all subsequent operations go very smoothly.

Op 2. The blank is flipped over and the back of the fretboard is cut. The outside profile (expanded .02"), the final gluing surface, and the final registration grooves are cut into the fretboard. These grooves are the ones you see in the pics.

Op 3. The fretboard surface is cut along with the grooves. The .02" expanded profile is left on.

Next comes the gluing which uses the same registration slots. The .02" expanded profile is left on the neck as well....to be removed along with the .02" left on the fretboard. This is removed is subsequent machining ops.

You can see the same approach occurring with the headstock facings.

When these necks are finished...every feature is pretty dang close to the cad model.

Another thing to note is that this allows the fretboard on and off the tool with such precision that detailed inlays can be produced even though numerous gluing steps are required. This is how I do my dots too.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Really interesting use of those registration pins. Something I'd never considered. Thanks for sharing.

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Allen R. McFarlen
Barron River Guitars & Ukuleles
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Cairns, Australia

Stuart,

That is a really cool method of registration. I kinda sorta remember seeing something along those lines before but I could be having false memories as well. A question for you though. I can see how if the slots were machined to an exact depth, you'd have a very nice and tight fit that located the part very firmly in the x-y plane. How much allowance to you give in terms of depth?

e.g. are you machining to exactly .0625 depth or are you machining a little deeper to allow for tolerances?

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Depends on the pins of course....but if they are spot on...the groove will be a split cylinder with a .0635 radius. So, a .001 radius larger than the pin.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Very cool, thanks for sharing. Would be especially helpful for things like headplates and FB's where there is not a lot of stock for a vertical pin. I use vertical acetal pins between my FB and neck, and the one time I cooked one off to remove it, discovered the pins became so soft they easily sliced with a spatula. Not sure that's a good thing if trying to heat treat a neck but I may have used more heat than needed. I'll have to look for nylon pins. Your decals look very difficult to make and are very well done.

I'll have to try this out one of these days. I have a little skepticism but not because of the methods, but because of the machines a lot of us use. There's clearly an accuracy discrepancy between an industrial quality metal working machine and a "home built" (but sturdy) machine trammed with string and dial indicators!

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Here's where I get the pins...

http://www.mcmaster.com/#standard-dowel-pins/=10olnl1

When you say "decals" I'm not certain you understand that these are all wooden inlays. Those round pucks, from outside to inside are Bloodwood, Bubinga, Ebony (dropshadow), and Holly.

The precise registration on and off the tool face facilitates the making of these. It would be pretty hard to do another way. They go on and off the vacuum fixture five times to make these. The headstock facing go on and off three times.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Most of the time though....it isn't the accuracy I'd miss...but a tool changer. The routers typically have about ten times looser of a repeatability spec but most of the time they are still tight enough to do this kind of thing. Without a tool changer though, I'd get pretty frustrated I think.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

I'm also using the McMaster delrin 1/8" pins, vertical application.

3d decal = inlay. Very intricate. Really excellent work !

Super cool idea I most certainly will try. Related question, when profiling the part held in place on an aluminum jig how do you cut through without cutting into the jig? Do you leave an onion skin and cut the part free of the matrix later or something else?


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Depends on the part....but in the case of the headstock facings I'll cut down to .05" above the tool surface and then take that off on the subsequent operation with a ball mill and a chamfer cut.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

I think it's probably what you're used to. I've never had a tool changer so I don't miss it too much. That and I have a really cool tool change macro that automatically measures the new tool length. So long as I'm nearby when a certain tool needs to be changed, it's actually a bit faster than many of the ATCs I've seen.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Stewart if you don't mind sharing what gasket material are you using and where are you buying it?

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I have enough of this to last the rest of my life....so I didn't inventory this item....so I'm not 100% on this...but maybe 90%.

It's EPDM foam cord that I probably got from McMaster-Carr.

http://www.mcmaster.com/#epdm-foam/=10ozw0t

Note that EPDM can be processed into dense rubber or foam....for this type of tooling you want "foam" cord for this kind of application.

When I get out to the shop today I'll see if there is any identifying info on the spool and get back to you.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Bobc ... ya ....that's the stuff.

I use 1/8th diameter most of the time. I'll use the 1/4" stuff when there's lots of room to work with.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Pretty much any rubber or gasket supplier will have the foam cord, I ended up getting a bunch from a local place a few hundred feet away. I ended up standardizing in the middle of Stuart's range: I use 3/16" round cord for everything.

I also like that indexing method, Stuart, that sort of accuracy and the ability to make all your stuff from aluminum are the great perks of working with metal cutting machinery. I've used a similar system of sideways pins for some of our fixtures, though I wish I'd thought of it back when I was still doing guitar stuff! All kinds of pulling and prying could have been prevented...

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I've done this same technique many times with dense urethane foam tooling as well...works just as well on that stuff too...though it's better when the density gets heavier. I've used it on density as low as 45lbs...and up to 75. Both work...75 will last longer.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

thanks Stuart, very inspiring to us non-engineer types like me. I made some pickguards the other day. The cutter only went down to a few thousands from where they were taped to the spoilboard. In my case the cutter was a 120 degree v. So consequently I had a LOT of hand work to fix it. In my case it was easier to finish is off by hand than go back to the CAM and try to fix it. So bravo for getting your methods worked out.

I strive to get there myself...

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Ken

I admit there is a lot I'm not understanding about the use of this jigs. When do you put the registration slots into the neck, for example? I get that an electric neck doesn't have the problem of a 4 inch heel, but I don't understand when you would ever have the neck blank facing up? What kind of blank to you start with, and how do you register THAT blank to accurately put the pin slots in? How do you tilt your blank up to have the head stock coplanar with the x-y plane?

I have similar questions regarding the fingerboard, but let's start with that. Maybe it'll all become clear if I understand how you are getting the first registration slots into the blanks to start.

Thanks!

I'm afraid any clear answer to that is going to require a serious amount of pictures, writing, and discourse, rlrhett.

Suffice it to say that I cut the back of the neck first and then flip it over to register it into a precision jig. From there I am able to cut a flat plane into the front of the neck and cut those registration slots.

The trick to keep in mind is that when making the fist cut...you can cut any feature you want to make the part register into the tool for the next cut.

For instance, on the first cut I drill holes in the gluing tongue that only serve to register and affix the neck into the next fixture.

The headstock gets registered onto a plate made with little half spherical risers where the tuner will go. When the back of the neck is cut I put little half spherical dimples in the back of the headstock. They mate to the next tooling plate. In this way I have cut registration features into the wood on the first op that register into two different tooling fixtures for the subsequent operations.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic