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The first operation to make tuning knobs is shown. Six knobs are cut at a time to maintain wood grain continuity within the set. The knob holding fixture shown holds two of the preforms and cuts out two sets during operation #2. This fixture clamps each knob indepentantly.

Today's project is to finish the two seperate fixtures used to drill one end of the knobs and mill the other end of them....operations 3 & 4.

I thought I'd throw in a shot of my fret nipper too. This fixture holds the raw fret wire perfectly perpendicualr in order to "nip" a whole set of fret tangs on the cnc. The basic idea here is to create a set of frets that has the tang length of each fret established according to its particular slot. This allows the end of the tang to remain invisible and allows the maximum slot width to be used. It also creates a very flat, smooth surface on the bottom of the fret.

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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

Neat projects!
I'm interested to see if somebody starts making replacement knobs that keep the 'tensioning' setup intact for tuners like the Gotoh classicals.
I've seen some descriptions of (non-CNC) jigs which shape knobs and drill a hole (oversized), then glue the knob on to the square-section shaft. The Gotoh tuner knobs have a square, blind recess and then a smaller round hole for the fastening screw. Tightening the machine screw puts tension on a series of washers and bushings to take some 'slop' out of the mechanism. All this is defeated if you glue the knob on to the shaft, of course.
I don't know if other brand tuners work the same way?
I can't figure out how to (by hand) get that square recess done....

Cheers
John

Here's my idea. The outside pocket is milled out oversized and then filled with epoxy. After the epoxy has cured a second pocketing operation is performed to fit the shaft to the knob. This idea might also allow for additional shaping to produce geometry that meets the requirments of tensioned tuners (if I understand you correctly). You are right. I have no idea how this might be done reliably by hand. It's hard enough to mill the square pocket with tiny mills. I've had to order .02" cutters with special depth capability.

I will also try to just mill the post hole out and fit it directly to the shaft....do some strength tests to see if it will hold up over time. Lastly, if all else fails I can make aluminum inserts that will fit/glue into cavities in each knob. At that point though, I'll wonder how sane I still am.

_________________
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

Stuart-
I'll be watching!
I don't know how small square recesses are milled industrially - obviously those plastic knobs are just molded to shape.
Perhaps you need to get some sort of higher-tech ultrasonic water jet device or something?? (Not seriously...you've got lots of technology there already!)
If I could figure out a really reliable 'mold release' then probably epoxy in a round hole, around a square former- would do the trick for doing this sort of thing by hand. I've had some nasty surprises thinking that a film of oil would do the 'mold release' job.

Cheers
John

With the waverly tuners they have a 3/32 square shaft. I have been making 2 piece buttons, each with a 3/32 x 3/64 section milled out. I glue them up with a 3/32 square piece of teflon matching them. That is the only way I have been able to make the perfect match on those. The Gotoh steel string tuners have shafts that are not perfectly rectangular, they round slightly at the ends so a 1/8 end mill will create the right size pocket. I have been doing mine on a milling machine with a digital readout. I thought about CNC but for me it seemed easier doing it without, mostly due to indexing problems I wasn't experienced enough on the CNC to overcome.

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Burton
http://www.legeytinstruments.com
Brookline, MA.

Thanks, Burton.
One day I'll think about how to do that with a little router/Dremel jig.
Those plastic knobs don't look so bad, after all!

Cheers
John

Epoxy is pretty agressive so the right mold release is usually a polymer based release like...... http://www.axelplastics.com/products/xtend.php

We used Axel Extend fro many years releasing epoxy from aluminum molds...among many other brands that were all essentialy the same thing.....a cured, bonded release film that is really easy to work with. Still, I think it would be pretty difficult to mold around a straight pin and have it release. Usually, in this situation, a mold maker will build a very slight "draft" into the mold to create positive angles soley for the purpose of release.

I don't know what I was thinking about earlier. I ordered the .02" mills for fret slots. Getting confused in my old age. My idea for milling the tuning knob pockets is as depicted (with the fits exaggerated to show the idea). This will use a .0625" endmill for the pockets. This ought to hold with just wood but I'll find out one way or the other and have several backup plans just in case it doesn't.

_________________
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

The knobs are usually casted with a pin that creates the basic hole. Inside corners like this are usually "broached".....at least a set of Grovers I have are.

http://www.vwbroaching.com/broach_tooli ... h-material

I examined the inside of a Grover knob I have and see striations that indicate the hole was broached. It's also entirely possible that a hole could be molded along with the knob and the the pin inside the mold is net shape to the shaft (plus fit tolerances). This wouldn't be as accurate as broaching though.

_________________
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

Stuart, and Burton-
Thanks!
It's a 'good day' when I learn something new!

Cheers
John

Stuart,
I understand operation #1 but am confused on op #2. Are your buttons convex shaped on the surface where your fingers would be placed while rotating the tuner knob? Does the aluminum cavity have a concave bottom to match a [possible] convex shape on the button?

Do you rip the excess stock from op#1 off the back side of the button with a table saw or is this milled off in op #2?

Do you hold the button in op #2 with screw force only or will you use the screw combined with vacuum as well? It looks like there is a tool path around the bottom of the button shape cavity for an O-ring?

I too have struggled with the idea of machining a flat inside of the button hole. Like Burton, I had thought about machining the buttons in halves then glue them up after words. This method made the most sense to me but it also added more steps to the process plus you would have to deal with a glue line and that mess. There really doesn't seem to be an easy way to make wood buttons so casting them makes more sense in a production process. Guess that is why Gotoh provides us with "Ebonized" buttons.

Thanks for sharing your methods with us.

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tim...
http://www.mcknightguitars.com

I have made wooden buttons by first machining the "finger" portion off of a stock metal button down to it's "core".
Then use the core by gluing it (CA) into a predrilled hole in wooden blank.
The downside is sacrificing a set of buttons but they may have ended up being tossed anyway.
This was then mounted in the lathe using a mandrel upon which the blank was held while machining.
Don't remember now how I did the convex faces but believe it was on CNC. Need to take a look at the tooling to remember.
Nelson

I'm going to hit the local hobby store one day soon. I recall that they had some small square-section tubing that might be useful for this sort of project.
You'd need to temporarily plug one end of the square tube to prevent glue getting in there, I suppose.

Cheers
John

The buttons are convex and the tool cavities are concave.

You might be a little confused because the first pics contained examples of a slightly different design with little raised edges. The latest pic shows the final design, which is a simplified version. I like the first design but it got to looking a little too "gothic" or "medieval" compared to the rest of the design. The simplified design removes the "medieval" aspects and now the knobs set into the overall design a little better.



During op #2 the buttons are separated from each other, excess material is removed, and the final surfacing and 3D edge chamfer is done. At the end of this op the button is finished...except for the two remaining operations having to do with the hole.



Screw force only. The channel you see must be cut lower than the curved surface because one could not actually create a SHARP inside edge on that cavity because of the geometry.....so that edge has to be removed.....hope that made sense.

The screws push steel pins which push the white, delrin pins shown in the pic.

Also, I produced two tools of each type so I can load one tool while the other is cutting. At the rate I'm going I expect I'll be able to make twenty full sets in two days.



I thought of doing that too but after all is said and done, I think my way will actually be less time consuming....maybe....if I don't have to create the epoxy cavities and add another operation. At the very least, once I'm done ALL the operations except the first are done on the cnc in groups of 12 so perhaps there will be a good economy of scale. Furthermore, I've developed the toolpaths more to guarantee the final result than to be productive.

I like the Gotoh stuff but I want my tuning knobs to match the inlays on the rest of the guitar.....bloodwood....purple heart.....wenge....whatever. It looks sweet when I lay it all out on the table. I want this to be art when it's done

_________________
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 was making resin inserts which were glued into holes in the wooden buttons. The inserts had the proper 'rounded rectangle' shape on the inside of them with a round outside. I really don't trust the wood, mounted to a metal shaft, to last forever without cracking or falling off and I don't like the idea of gluing them on, so it seemed like the logical way.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Bob-
That (resin inserts) certainly sounds like a good plan- you could sell those by the dozen if the price was right!

Cheers
John

What resin are you guys using that would be harder than say ebony? Is it a metal reinforced resin?

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tim...
http://www.mcknightguitars.com

Bob--I'm trying to understand the difference between gluing the wooden buttons to a resin vs a metal insert. I used notches in the metal to ensure a "mechanical" bond. I would think that the metal would be much more durable than resin where it's keyed to the tuner shaft. I must be missing something.
Nelson

To tell the truth, I doubt it would be worth the time making a new mould. When I did a group offer on wooden buttons, in twelve different styles and at less than the wholesale LMII price, I didn't get enough orders to even dent the setup cost. Now I only develop new products for industry or if someone else is paying for the dev time. I'll make you 100 sets if you think you can move them, though!



So far as design:

The resin could be a polyester, a polyurethane, or an epoxy depending on formulation.

The resin will hold its shape if left to its own devices, so it won't shrink and crack or expand and loosen. It is perfectly shaped to the shaft which removes the ability of the shaft to put any sort of load on the walls by trying to move in its recess. Since the resin does have some conformity, it might be able to move with the wood slightly without separating or breaking. Woods that might not be able to hold their shape due to lack of hardness or excessive movement can be used with resin inserts. It also means that you need only machine a hole into the wooden part of the button.

If using chunky wooden buttons, none of these things should ever be a big issue other than having to glue on the buttons to avoid them possibly falling off and the issue of a perfect fit to a shaft (which can also be fixed with application of adhesives). I wanted a solution so that wood buttons as delicate as any metal buttons could be fashioned, while maintaining a perfect interference fit over time, and such that they needn't be glued on (there's something chintzy about gluing anything to a piece of metal).

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

well....the mechanical properties to look at when trying to determine the applicable stress within the stress field of a tuning knob are probably, cross-grain tensile strength and edge compression on wood vs. plain old tensile strength and plain old compression strength on epoxy. This is difficult because I can't find anything on ebony. I DID find good mechanical properties on maple though.

On maple the cross-grain tensile is about 650 psi. and the compression is about 3000 psi. I expect ebony to be a lot more on both counts but I would guess it wouldn't be double.

West Systems epoxies are "neat" resins with no fillers. They are also "toughened" which you want to look for that when picking out epoxy for this kind application. Tensile strength is about 6000 psi and compression is up to 11,000 psi. They have many kinds of epoxy and these are generic numbers but you can see it's MUCH stronger than ebony is likely to be. The issue isn't just strength though. Geometry also plays a major role. The issue here is how thick the wall is between the machine post the wood of the tuning knob. The thinner the epoxy wall the less those impressive mechanical properties of epoxy will come into play.

If we know ebony (with no epoxy) will hold onto the post when it is machined properly, then the use of epoxy will only make the structure stronger. This won't necessarily be the case with woods that are softer than ebony though. That's why I expect to be filling a cavities in the maple and bloodwood knobs with epoxy and why I'm making the walls of the cavity as large as possible.

_________________
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

Another factor in the durability equation is the location of the greatest stress.
That is of course at the center of the shaft and diminishing outward.
Nelson

Do you plan to machine some dummy tuner posts from something like Teflon and then glue the button to the post. After the resin cures, remove the button from the Teflon post? Or is there a better process?

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tim...
http://www.mcknightguitars.com

The point of greatest stress will be a point load where the white arrows are when turning the knob clockwise. This is a compressive load and will be applied directly opposed to the compressive properties of the epoxy....which is very high....so that aspect is optimal provided that there is enough epoxy opposed to the load and only a little bit of this load transfers through the epoxy into the wood below.

That point load will also apply a sort of tensile/shear load where the black arrows are. If that corner where the black arrows point is a sharp corner then that load will be concentrated (the wood grain runs laterally) RIGHT AT that corner point. Making a wooden/epoxy hole in the exact net shape of the post would actually concentrate both the compressive AND the tensile/shear loads together and force them at or very near this corner.

As it is designed, with rounded corners, the compressive load applies in one place and the the tensile/shear load is spread across a much larger area away from the compressive load. This geometry should optimize the load bearing ability of the tuning knob/post assembly by taking into account the loads and forcing them against the known properties of the materials and away from each other.

But all this analysis doesn't guarantee anything It's just a quest to hopefully optimize things.

_________________
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

That question was probably for Bob.

I'm going first try to just machine a receiving cavity into the wood for the post and see how that goes...wood on metal.

Then I plan to machine out a MUCH larger cavity, fill it with epoxy, then machine out a receiving cavity for the post - as depicted above.

_________________
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

Probably for you, actually, since I don't make the inserts in place

I use a multi-part mold for the inserts to ease removal, much like an injection mold.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Thought I'd toss up a photo of these knobs completed. Once they get a good cleaning and a few coats of Tru-oil they really look nice.....but this is the basic idea.

The top set is just milled to fit the post. I'm finding this to be more than adequate from a durability standpoint but I haven't enough experience to really count on this. We'll see.

_________________
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