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To address the end wedge……..if you want to miter the purflings at the end wedge, it is easier to cut and install the wedge after the plates are attached and the binding/purfling channels have been cut. This way you don’t have to cut the wedge section of the channels by hand.

Cal

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A good point, I've been doing it the hard way.

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Steve Smith
"Music is what feelings sound like"

I have not found a good solution to the back binding depth difference either. Maybe Jay is on to something and the oracle lies within the donut.

How are all the factories doing it??

Colin, I know that curvature is there at the ascending/descending areas, but I have never noticed it to be a problem that needed a fix. However when I did a wedge body it was a BIG problem. I could not find a good solution for the channel and ended up beveling the inside edge of the binding almost all the way across. It actually turned out good though. The binding was the exact depth of the chanel. It had a 1" difference between the bass and treble sides. Ps. I like your idea for The binding sized scraper!

Pat

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Pat

I don't use a donut, but rather little tapered wedges glued to the router base. The idea is to get the point that the router rests on as close the the actual cutting bit as possible. The flat edge of those donuts look around 1/4" wide, also with extra space between the bit and the donut, so morecspace than needed...

Glad to know I’m not the only one. My fix would be this… although it’s beyond me.

The router rides vertically up and down, but it also needs a hinge that allows

it to move vertically at the cutter. In other words… instead of rolling up and down a simple track it needs to be able to tilt at that joint.


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A tilt would not solve anything because you would lose control of the other dimension. Whatever rig you use is a compromise due to the complex geometry of the guitar's back and sides.

I also use a tiny foot very near the cutter instead of a doughnut and I find that the resulting ledge is fairly consistent.

A kid from my town that took the two year Red Wing MN Vo-Tec lutherie course and spent time in my shop worked in the binding department at Santa Cruz for two years,

They had a fixed router like the Elevate design that they used for the binding channels and then switched to a tower for the purfling.

Maybe experienced Elevate users could chime in.

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I have an older Elevate binding jig that I use now instead of my LMI type tower jig. The portion of the doughnut that rests on the top or back is not large, certainly less than 1/4". I have no trouble with my binding and purfling cuts. It is important to control your side geometry - I use a mold, I use inside spreaders and clamp the head and tail blocks. For my next guitar I'm going to use screws for the head and tail block as I think it's a better solution since I have to pull the clamps when I glue on the top and back.

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Steve Smith
"Music is what feelings sound like"

I’ve tried most of the tower jigs and sold this guy to Brandon. John Hall has said many times that the angle of the top or back doesn’t matter—what matters is having the sides perpendicular to the table. I’d always check with a square and work with the cradle until everything lined up right.

This thread’s getting pretty technical, so I may have missed whether or not someone already mentioned that.


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Yep, this is the same idea behind the method for setting up to rout the binding channels I described in a post above. I use measurements from the edge of the top to the benchtop to get the sides perpendicular to the benchtop and, once I have the body adjusted in the cradle, I run a square around the body as a double check to verify that the sides are perpendicular.

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It seems to me that the Elevate/Larrivee/Martin style jig is the most likely to give really consistent results regardless of back oddities. But, I've never gotten comfortable using one--the guitar body is so light that I have a hard time keeping it on the back "critical" point of the jig. That's just me. I've stuck with tower type jigs, but keeping the doughnut as small and narrow as possible. This has worked fine for me, and between working horizontally instead of vertically and with the extra weight, I go into routing bindings with more confidence.

I wish I could get used to the Elevate style jig--I do think it's the superior approach, but somehow it robs me of confidence at a critical time in building, so for me it's out.

Dave

In terms of actual data - versus conjecture - with regard to the error generated by binding jigs which reference depth of cut off the surface of the plate, the attached table gives the magnitude of that error for guide bushing offsets from the cutting edge in 0.060' increments from 0.060" to 0.240" where the resultant error is the difference between the error at the location where the local included angle formed by the bound edge and side is at maximum and at minimum.

For those wishing to follow the trig:

Vertical Depth Error = Horizontal Distance from Cutting Edge * Tangent of Local Top Angle



An example of the magnitude of depth error for a 12 fret-to-body dreadnaught with a maximum angle of 7 degrees and a minimum angle of 2 degrees and a bushing offset of 0.240" would be:

Magnitude of Error = Depth Error at Max Angle - Depth Error at Minimum Angle

Magnitude of Error = 0.029" - 0.008" = 0.021" or ~ 1/64"

So the smaller the horizontal offset between cutting edge and where the guide bushing/donut guides on the top, the smaller the difference in binding channel depth seen on the perimeter of the guitar body.

Finally, the width of the binding contributes some depth error as well, as the top of the binding is usually leveled relative to the local slope of the plate; however, that error for practical binding thicknesses (0.040"-0.090") is usually going to be small compared to errors generated by the offset in the guide surface of the bushing/donut using the StewMac and LMII bits (which have a 0.080" difference in diameter).

Taking a 0.060" thick binding into account, the error gets a bit larger by about 0.005":

Magnitude of Error (incl Binding) = (Depth Error at Cutting Edge for Max Angle + Depth Error at Outer Surface of Binding for Max Angle) - (Depth Error at Cutting Edge for Min Angle + Depth Error at Outer Surface of Binding for Min Angle)

Magnitude of Error = (0.029" + 0.007") - (0.008"+ 0.002") = 0.026" or ~ 3/128"

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I can't quite follow the math, but that sounds about right. I've noticed 20 thouish variation on a typical guitar.

Remember though, it's the same error no matter how tall the binding. I didn't notice it much when I was using quarter inch (8%), but notice it much more with shorter. (.150-14%)

Woodie, are you saying that thinner binding would increase the error?

Pat

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Pat

I used thickness as that seems to be the usual term of reference in catalogs and general usage in my training, with the common term for how short or tall the binding is being height, and length for the running length of the stock. I also agree that while the binding and side purfling height does not contribute to the error described in my posts, a taller binding treatment will tend to do a better job of camouflaging channel depth errors.

Also worth noting that the purfling channels may have very similar depth errors, but unless the height of the purfling material is within the error range, it is not an issue.

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For the times they are a changin'

- Bob Dylan