How Do I Mark String Spaces on a New Wooden Archtop Bridge?

Kojo27 · #1 03-22-2011, 04:17 PM

Hey-hey......

This might belong in a luthier's forum, but I don't belong to one... so - help?

I just bought a new compensated rosewood bridge for an acoustic archtop. Problem is, I have to determine exactly where each string is to cross over the bridge (or "saddle") -- and cut a teeny-tiny groove for it to stay in. This maintains proper string spacing, obviously.

I hope you guys know what I'm trying to explain here - I've been sweatin' this one, trying to avoid a trip to the (super-expensive) shop. Let me re-phrase it:

The overall span of the strings, sixth to first, is 2 1/8". So how do I arrive at the measurements for making the six grooves for the six strings to lie in? This is "precision work" -- if I mis-measure, or make any error in the spacing and sawing, I'll end up with an extra groove on the saddle top -- the wrong one, and the right one. And really, only maybe, and hopefully the right one!

HELP! This seems so easy, and probably is, but I'm blocked. I half suspect I'll end up arranging the A, D, G, & B strings within a 2 1/8" space, with the two E's at each side, by "eye-balling" them, using no math at all.

All comments, suggestions appreciated.

Kojo

Dad3353 · #2 03-22-2011, 05:45 PM

Quote:

Originally Posted by Kojo27

...All comments, suggestions appreciated...

Good evening, Kojo...
I'm no luthier, but, if it helps, with my calculator I divide 2.125 by 5 (5 spaces between 6 strings...) and get me 0.425 as equidistant spacing for the grooves. The total string spread is then 2 1/8 from the centre of top E to the centre of low E.

Hope this helps...

billkath · #3 03-22-2011, 06:15 PM

I'm no luthier either, but- if you followed Dad's advice-wouldn't the bottom (bass) 4 strings "feel" closer together, due to string thickness? I believe that you have to compensate for that by offsetting the distances to allow for the thickness of the strings. I think StewMacs have a string spacing guage designed especially for this, and it's very cheap.

GodinFan · #4 03-22-2011, 08:52 PM

Take the old bridge, tape it to the new one and mark the string locations. Worked for me.

monk · #5 03-23-2011, 12:12 AM

billkath is right. The thickness of each string has to be taken into account.

GodinFan's advice will get the job done. It doesn't take a very deep groove, just enough to keep the string in place.

Kojo27 · #6 03-23-2011, 05:44 AM

Thanks guys -- good advice here.

GodinFan -- I might have to do it this way, using the old bridge as a model, but the whole reason I'm changing the bridge is that our local repair guy (who's also the village idiot) has cut so many grooves in the old bridge, trying to get the spacings right, that it's a heck of a job just finding which grooves the strings belong in when I'm changing strings.

I just had this thought: I could take off one string, mark the right groove with white-out (or whatever) and continue with the other strings and grooves, and THEN copy the new one from the "marked" one. I'll have to trust that Villiage Idiot's last attempt is accurate, of course. It feels pretty good -- in the ballpark -- but I haven't looked closely. This is a really cool R-18 Martin from 1940. Has a great 20's jazz sound. So I want to get it right -

pingu · #7 03-23-2011, 06:00 AM

20 bucks
STEWMAC.COM : String Spacing Rule

billkath · #8 03-23-2011, 06:02 AM

STEWMAC.COM : String Spacing Rule

brad4d8 · #9 03-23-2011, 06:46 AM

Maybe I'm optimistic here, but I recently noticed a couple grooves in some string areas on my Artist Award and it seems that if I just let the strings run "naturally" from the tailpiece over the bridge, they find the right spot. If I replace or work on the saddle, I would rely on this to find the right spots. FWIW, they do seem to be spaced appropriately with this method, at least to my eyes and hands.
Brad

Kojo27 · #10 04-17-2011, 11:19 PM

This is how I finally did it:

I cranked the action WAY up on the Martin R-18 and put the new bridge (top) in line with the old one; then, using White-Out, marked each side of the string as it passed over the new bridge/saddle. I removed the new bridge and used old strings as "rope saws" to saw back and forth between the White-Out marks, and this made tiny resting places, sized just right for each of the six strings. For the treble strings I just nicked the wood with a knife.

Voila! Perfect. So there's yet another way. Thanks for all the input. Without it, I never would have come around to this idea.

(BTW: This guitar is 71 years old and looks it. Not pretty, but plays and sounds soooo nice. Now with compensated saddle/bridge.)