Official Luthiers Forum!

I'd be interested in knowing how much vibration there is in the bits themselves even with "perfect routers and collets". We are routing hard wood that isn't perfectly homogeneous. When routing inlay sockets with small bits or even rosettes you can feel the vibration when the wood density changes. Steel and even carbide have some flex.

When I'm slotting bridges I use 1/4 shank bits with smaller dia cutting sections to help control flex at least in the shank of the bit.

I'm not really too concerned with perfection to the thou, as long as I can't see or feel any slop in the fit. How many thou of space does it take to have a saddle you can remove w/o Visegrips?

I wonder if plastigage for checking bearing clearance on a crankshaft is soft enough to squish between a saddle and bridge slot bottom?

Then when the top flexes with string tension, does the bridge bend and what does it do the the fit of the saddle bottom.

There is a limit to precision in woodwork. I try not to chase what I can't see but I've sure been known to try!

_________________
Brian R, Wood Mechanic
N8ZED

Brian I agree with all that posted but wanted to add one thing.

In this specific application it's not a rosette, it's not inlay of a logo and it's not a fret position marker. It is defining the exact scale length of the instrument. Just 0.003" of error begins to change how the instrument will play, in tune, everywhere on the neck. With this said it can have an impact on how well the instrument sounds and plays in tune.

This is why Dave pulled out all the stops and took over ten years to develop his saddle mill sourcing dozens of sample parts for suitability and precision. He had it on the drawing board before I met him.

I'm chuckling here remembering the post I made about the builder on the west coast who sold a guitar with the bridge 1/4" off in location and the thing sounded like ****. It has been flipped perhaps more than half a dozen times and we had it grace our shop to set it up as well as possible so its current owner can dump it too.

Before anyone goes there sure the bridge could be removed, neck too and the top refinished with the bridge in the right location. No one who had owned it wanted to invest that much in the thing it was a great disappointment to them so they flipped it.

He used a very expensive and rare wood (back and sides) wasting it and this guitar even with the bridge 1/4 inch off in location was his 125th instrument..... It had sold for over $10K.....

Anyway for me saddle location is when I pull out all the stops and get as detailed as I know how to.

Agree totally Hesh. Inlay/rosette routing was simply an example where precision routing is slow enough when done by hand that you can see, feel and hear bit flex vibrations. My point being it's there to contend with.

Neck and bridge geometry deserve the utmost attention and a lot of fussing too.

And I love your jig! Some day I'll post a pic of my ultimate banjo jig built on a 1/2" aluminum plate (true story).

_________________
Brian R, Wood Mechanic
N8ZED

I'd love to see the jig and 1/2 aluminum plate is great for stability. Dave's prototypes for the mill were approaching that I think.

I have managed to cut a perfect slot routing full depth with 1/8" bit on a 1/4" shank. I would rather take it in passes, but I take the win.

I have not been able to nail the slot with multiple passes- the bit always moves laterally, a very tiny bit, when moving the bit deeper, even with a plunge router. Not ideal for bits, but perfect for these slots.

_________________
Measure Twice,

Karl Borum

If you want to take passes, use a smaller diameter bit (e.g. 7/64") so you leave some wood on each wall for the finish pass. Either do each wall individually with the small bit (use shims between your fence and the router base), or change to 1/8" bit and do a single pass where it's taking a light cut on both walls and the bottom at the same time. But it's probably unnecessary effort if you're getting good enough results doing it in one shot.