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icuker
07-26-2010, 05:14 PM
I bought an old solid wood unlabeled uke (maybe an old Harmony?). It has cracks etc and a belly bulge and the bridge wasn't seated fully on the top. I took the back off to fix cracks with cleats and popped the bridge off.

Good news is that cleating and putting a bridge plate in helped to level the bellying. Now my 1st question is about the bridge. Do I measure the distance between the front of the nut to the top of the 12th fret and to the front of the saddle to set the bridge? Or do I measure from the very top of the nut...saddle? I know I'm talking microscopic differences here, but I wanted the intonation as well as it can be.

Also, there is wear on both nut and saddle (it's a glued into the bridge or possibly all carved out of one peice so that it is not seperable) plus I would like to avoid making new nut and saddle, if possible, for the first try.

Second question is this: There is a bit of potato chipping of the back side probably when I glued and clamped the cleats, and i was wondering if when I glued the back on again, will it want to pull apart or will the glue hold well enough?

Thanks in advance!
Rus

camface
07-26-2010, 08:56 PM
Generally it is suggested to take the measurement from the front of the nut to the 12th fret, then that same distance + about 1/8th of an inch to the saddle.

Making a new nut and saddle isn't all that difficult, and can be done quite cheap. I'm confused as to how the bridge is carved out of one piece? Pictures?

Are you working outside or somewhere where there is rapid change in humidity and temperature? That is usually the cause of the warping. Let it sit inside for a day or two and it should return to normal. If you were to glue it on now, it would probably want to shift more. It is best to do all the work in similar temp/humidity, especially gluing. Good luck!

Allen
07-26-2010, 11:47 PM
Edge of nut next to fret board to center of 12th fret. Then double this distance to give you the distance from the edge of the nut (fret board side) to bridge. As for compensation, it depends on so many factors. Scale length, action, string type that you are going to have to take your best guess.

One method is to get your scale length, number of frets and go to Stewart MacDonals fret calculator (http://www.stewmac.com/FretCalculator) and get the compensation factor from their calculations.

Another way when using a bone saddle is to shape the top of the saddle so it's rounded over on back and front. Giving you one single high contact point at approximately in the middle of the saddle. Then measure off your scale lenght to the front edge of the saddle. This will compensate the scale length by 1/2 the thickness of your saddle. Gets you pretty darn close form most people, and a lot closer than many store bought ukes ever are.

Moore Bettah Ukuleles
07-27-2010, 07:57 AM
My compensation for the strings I use and .090" action above the 12th fret:
Tenor = 2mm
Concert= 3mm
Soprano = 3.5mm

icuker
07-28-2010, 01:22 AM
Thanks for the replies.

I guess I'm still foggy over the compensation calculation. Now that the belly is flatter, I might check my string height/action with the bridge just clamped into place and if that seems good, I'll glue. If then I have an intonation problem, then I'll need to understand compensation better? Am I getting the gist of the conversation? Feel free to let me know if I'm thinking about this all wrong. With the calculations Chuck gave, I'm not sure what those numbers mean.

Also, you were right, I was gluing up the uke in my garage, it has been hot and humid, so that probably helped created the potato chipping of the back. I moved it to inside the A/C house, and will glue it up in a few days and hope for the best.

Philstix
07-28-2010, 07:18 AM
Compensation accounts for the increased tension on the string caused by moving it down to the fret. If the fret moved to the string no compensation would be needed. Thus Chuck''s numbers reflect how much compensation is needed with a string height of .09 inches at the twelfth fret (top of the fret to the bottom of the string) using the particular strings he uses. If the action were higher it would need more compensation. If the strings were stiffer it would take more compensation. Shorter scales needs more compensation since the lengthening of the string and thus increased tension by moving it to the fret is proportionally greater. As it is, if your string heights are near to Chuck's dimensions his compensation numbers will work.