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View Full Version : How do you prepare the soundboard for gluing on the bridge



Vespa Bob
06-20-2016, 01:57 PM
One of the trickiest tasks for me in instrument building is the attachment of the bridge. First, there's the there's the measuring to be done, a task requiring absolute precision in every direction, secondly, one needs the correct clamps for the job, then comes the part that causes me the most grief - creating a clean, bare wood patch upon which the bridge will be glued. There are two, possibly three ways I know of to accomplish this, one is to mask off the bridge area before spraying and the other is to spray the entire top first, then after the lacquer has dried, scrape it down to bare wood on the bridge area. The third method, although I've never heard of anyone doing it this way, is to glue the bridge on first and mask it off before spraying on the finish. I have tried the first two methods and prefer the first as I find it easier than trying to scrape off the dried lacquer. Both these methods however, leave a ridge, or step at the edge, the lacquer standing proud of the bare wood, even if only a minimal amount of coats are applied. It is beyond my capabilities to create an exact fit where the bridge would drop in perfectly without some imperfection showing up once it's glued. What I have done is to scrape out the area a shade smaller than the bridge footprint, then chamfer the edge of the bridge to allow for the "step". This works somewhat, but I am yet to produce a perfect bridge to top joint.
I would love to here how this task is carried out by those who are more experienced than me.

Bob

Moore Bettah Ukuleles
06-20-2016, 05:48 PM
I rout mine. Tape it off, mark it and rout 1/16" within the line. I use a Dremel in a StewMac base with a 1/8" carbide spiral bit. Fast, easy and perfect. I don't bother chamfering the edge. Never had a problem with Titebond.

Vespa Bob
06-20-2016, 06:59 PM
Thanks for the prompt reply, Chuck, I like the idea of routing routing the area, especially since I have the Stewmac base! I assume the routing is done freehand?

Bob

sequoia
06-20-2016, 08:27 PM
Actually I don't find this step hard at all. Simple. Before finishing, lay down tape at the approximate bridge position. Position bridge exactly on tape with compensation. Pencil around bridge. Cut 1/16 inside of pencil line and remove surrounding tape leaving strip. Finish top as desired...Later... Remove tape strip. Lay down wide strip of tape double thickness over general area. Lay down bridge and remeasure out. Draw lines against bridge and cut tape out with an exacto knife. Your trough will now line up with your original measurement plus a 1/16 inch inside border. Apply glue to bridge and drop in slot. Clamp. Squeeze out goes onto tape. Carefully remove tape and viola! a perfect glued on bridge with no seam against finish and yet securely glued to bare wood. Simpler to do than it sounds. No routing necessary.

Beau Hannam Ukuleles
06-21-2016, 04:17 AM
I rout mine. Tape it off, mark it and rout 1/16" within the line. I use a Dremel in a StewMac base with a 1/8" carbide spiral bit. Fast, easy and perfect. I don't bother chamfering the edge. Never had a problem with Titebond.

When I first heard this method years ago I thought it was crazy- but now that is how I do it. The router is very stable and easy to control. I do the whole footprint but that isn't for the faint of heart as you can ruin a finish with one slip of the scalpel.

resoman
06-21-2016, 04:52 AM
When I first read Chuck's description of his method of taking off the lacquer I figured it was not for the faint of heart. I finally sucked it up and tried it and it's really the way to go. Pretty scarey the first time but so clean and fast and I leave the dremel set up all the time. I tried this with a dremel base and the base just wasn't stable enough and wouldn't hold depth well. I tried it on a placebo top first :rolleyes:

Moore Bettah Ukuleles
06-21-2016, 06:22 AM
The photos show the process. Sorry, they're out of order.

Allen
06-21-2016, 09:44 AM
Scalpel around the outside of the bridge to score the lacquer. Then I mask carefully to that line. After that I scrape the finish off. Pretty quick and easy to do.

Vespa Bob
06-21-2016, 12:27 PM
Once again, I appreciate the help and advice given here, You guys are truly great at sharing your knowledge! It would seem that the apply finish first, then scrape or rout it off afterwards is the most popular way to go. I must admit I never liked scraping the area, but I'll certainly try routing it, since I have had some success with inlay routing. Allen, would you mind telling what tool you use to scrape the finish off? I've used exacto knives, small chisels and homemade scrapers, but I always end up with an uneven surface.

Bob

Allen
06-21-2016, 09:10 PM
I score the outside with a medical scalpel. Don't know the blade number, but it's ridiculously sharp so it doesn't take any pressure at all.

I've tried scrapers for this but found that a straight industrial single sided razor blade works best. The type that has a folded over bit of metal on the blunt side. I break them in 1/2 so the length is more suited to the tiny footprint of my bridges. I do have a full length one for the large area.

I also have an exacto knife that I use to get into tight corners and edges.

Vespa Bob
06-22-2016, 04:06 AM
Thanks for the reply, Allen. You're obviously more adept than I am as I tend to dig trenches when scraping!:)

Bob