Help Luthiers! Define "chalk fitting" bridge feet.

[baldy McBalders]

Hello all,
Three months into entering the exciting and somewhat harrowing world of DB, I am still trying to get the feet of my bridge to sit as perfectly as possible on the table, and I saw during my perusing of forum postings the concept of "chalk fitting"; as opposed to essentially back-figuring what this process entailed, I thought I'd ask directly how to go about doing this. As always, thanks for the help in advance!

[baldy McBalders]

Ah poop; Sorry for not posting in setup and repair. Thanks.

[kurt ratering]

in a nut shell...to chalk fit something you first apply a light coating of chalk to what you want to fit to. then place the item you want to fit (bridge, patch, etc.) where it needs to go on top of the chalk. now wiggle it side to side just a hair, flip it over and have a look. the points of contact will be highlighted by the chalk, remove these spots with a knife or scraper untill it is tightly and evenly speckeled with chalk. i use a china marker or grease pencil to fit bridges. its easier to see and isnt as hard as a piece of chalk so its less likely to damage the varnish and wipes off with a little mineral spirits. hope this helps

[baldy McBalders]

Perfect explanation! Many thanks!

[360guy]

carbon paper is what I use. Make sure you're rubbing the bridge at the correct angle ----don't tip it forward or back. You'll find that 50% surface contact is about the best you'll get sometimes. You did your best. Keep moving.

[GerardSamija]

The pictures and method shown in this page - http://www.luthier.ca/tutorials/brid...e_fitting.html - show a 'cello bridge being re-fitted at the feet. But at least a portion of this lesson can be applied to fitting a bass bridge. I have not made a similar jig to the one I use for sizes violin to 'cello, as a bass bridge is large enough that rubbing across the belly works well if done carefully. The smaller bridges tip a bit too easily. Even a bass bridge rocks all over the place if one is not careful (or perhaps if the hands are small, or weak, or both). I don't use chalk nor grease pencil, but have no problem with the pencil being used. Just never remember to try that... and fitting the way I do works well, always resulting in 90% or better contact. This becomes more difficult when a belly is old and much-damaged, but that just translates into spending a longer time doing the job and using smaller movements, nibbling off smaller amounts of wood, to get the fit just right.

It cannot be over-emphasized just how important to sound is the proper fitting of the bridge to the belly. Same for the fit between the top end of the soundpost and the belly. Most soundposts show small shiny areas along one edge when taken out. That's just wrong. The post should make such even contact that the whole top is slightly shiny from the final movement in fitting and the pressure against the top once strung to pitch. This can only be achieved if the post is fitted with a slight, very slight, bias in contact, the part furthest from the bridge being the most snug, the part closest having a tiny gap - about a paper-thickness, more or less depending on the relative stiffness of the belly, the tension of the strings used, angle of the strings over the bridge, distance between post and bridge, all thrown together using intuition to get it just right. Trial and error gets this nailed down such that when brought to pitch the pressure is perfectly even across the whole soundpost top, minimizing danger of soundpost cracks in the belly (edge contact makes for a 'stress riser' in the highly split-prone spruce), and of course helping in optimum sound production as do all elements of setup when properly finished.