Routing the Finish for Bridge Placement

I get a lot of questions about this so I took the time this morning to snap some photos and share my procedure. If I could do a video I would but I'll leave that to my friends across the pond as that is still over my head and too time consuming. The procedure is not as scary as it sounds. Of course if you've built any number of instruments you know that there are 1000 opportunities to screw things up and this is certainly one of those times. Do a couple of practice runs on some lacquered scrap first before attempting to do this on one of your precious ukes.

The top is masked (with GREEN tape for lacquer) and the bridge is indexed in the usual fashion, outlined with a sharp pencil and cut 1/16" on in inside perimeter with an X-Acto knife. The mask is removed and the routing begins with a cut just shallow enough to remove the lacquer and nothing else. I use an 1/8" carbide bit in a Stew Mac Dremel base. (You'll notice that I've put blue tape on the bottom of the base and I also paint the top of the base flat black to eliminate glare. Not necessary really but a good thing to do anyway.) You'll also notice Aaron Oya's patented dust deflection device attached to the carbide bit.

I've probably done 500 ukes this way and I find it very fast and easy. I timed myself on this one and it took 40 seconds for the lacquer removal on this uke. And it leaves a nice clean flat surface to accept the bridge.

I guess I can't attach more than a few photos at a time so here's the rest.

****Sorry, the pics seem to be out of order. This is why I don't even attempt to post a video!

the "dust deflection device" is super brilliant!

no guide? just freehand cutting? does the bit want to grab and pull on you?

I use a similar process. What is the purpose of the blue tape on the bottom of the Dremel base?

You kind of described this before without photos so I gave it a try. Scared the livin daylights outa me. But, it was with a laminate trimmer and it was really awkward so I'll give it another try with the Dremel as I just hate the scraping even tho I've got it down pretty good and fast.
Thank you!

mzuch said:

I use a similar process. What is the purpose of the blue tape on the bottom of the Dremel base?

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That's a good question! There used to be a reason for me covering the Dremel base with tape but I've been doing it for so many years I've forgotten what that reason is. haha. You can skip that part.

resoman said:

You kind of described this before without photos so I gave it a try. Scared the livin daylights outa me. But, it was with a laminate trimmer and it was really awkward so I'll give it another try with the Dremel as I just hate the scraping even tho I've got it down pretty good and fast.
Thank you!

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Yeah, I would never try this with anything but a small bit in a Dremel base. BTW, the finish is so thin that the bit doesn't even notice the lacquer, it just cuts right through it. I've never found the need to use a guide of any sort as it is very controllable. I also use the same technique for removing lacquer from the body when attaching my necks.

Great stuff Chuck. Saw this at the Collings factory back in 1994 - scared the living daylights out of me then! You are a brave man. I mask off using parcel tape and make sure to sand hard the bridge area when flatting between spray days. Masking tape is too thick for this.

Question? Do you put a radius in the front? If so, how does this method work? Does it produce a flat surface or do you follow the camber of the front?

Pete Howlett said:

Great stuff Chuck. Saw this at the Collings factory back in 1994 - scared the living daylights out of me then! You are a brave man. I mask off using parcel tape and make sure to sand hard the bridge area when flatting between spray days. Masking tape is too thick for this.

Question? Do you put a radius in the front? If so, how does this method work? Does it produce a flat surface or do you follow the camber of the front?

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My top radius is about 25'. The router base follows it nicely.

That looks like an upgraded and modified flag. Now I need to adjust. Thanks for that one, looks good.

I have been leery of leaving any lacquer under the bridge at all because I worry about adhesion problems. I figure that whatever the thickness of the lacquer is must be filled with glue between the bridge and the top. I had a bridge pop off once and now I remove all of the lacquer all the way to the outline of the bridge and haven't had a problem since. Do you put the radius on the bottom of the bridge too?

dustartist said:

I have been leery of leaving any lacquer under the bridge at all because I worry about adhesion problems. I figure that whatever the thickness of the lacquer is must be filled with glue between the bridge and the top. I had a bridge pop off once and now I remove all of the lacquer all the way to the outline of the bridge and haven't had a problem since. Do you put the radius on the bottom of the bridge too?

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I've never had a bridge come off. Ever. Make sure you use enough glue. Since the bridge also acts as a brace it is certainly radiussed to match the radius in the top.

Thanks for posting this Chuck.

I guess this question applies no matter how one cuts the lacquer, but, assuming that the radius sanded into the underside of the bridge (?) matches the radius formed into the top, so that they both fit well and the bridge radius reinforces the top radius, and the lacquer is 6mil thick or close and the lacquer is cut 1/16" in from the footprint, it seems like that leaves a thick glue joint? Does this rely on the flexibility of the top to get better contact towards the center of the bridge?

I have only done this twice, and used the router method, but I cut the lacquer a little tighter than 1/16" to the bridge footprint, more like 0.4mm. Then in feeling how the bridge fits the indent in the lacquer, just barely touching the contacting underside corners of the bridge so that they allow the underside of the bridge to contact the top wood, and not to be supported by the lacquer at the edges of the bridge, a very slight beveling but not so much that it leaves a gap when it is sitting in position. When it is fully fitted, the bridge fits in and is 'keyed' into the routed off indent., it does not shift. This is what I have used to locate the bridge before taping it down and vacuum pressing the bridge while gluing. Both bridges fit absolutely tight where the lacquer ends and the bridge starts. There is no gap, just a tight fit, and the bridge contacts the top wood in a dry fit, making a tight glue joint.

Is a 6 mil ( the thickness of the lacquer) glue joint too thick? How does that work?

It looks like those two holes are for locating the bridge during glue up? I like that idea..

Here is the router tool that I use. It is set deep from some 'hogging out' I was doing the other day. I made the base from acrylic. The grinder is a small pneumatic 60,000 rpm unit. It is quiet and smooth. When cutting the lacquer, it needs no guide, and does not pull in any direction. Even when cutting deeper for inlay, it does not really pull, freehand is enough.

The 2 little threaded holes in the router base are where it mounts to the Stew Mac rosette cutter base compass thingy.

I know one builder that bevels the edges of his bridges for a tighter fit. That's a viable option but I've never seen the reason to bother doing that. My lacquer is about .005" thick when cured fro a couple of weeks but i do extra sanding on the lower bout probably knocking another mil or so off the finish thickness. I use three C clamps when attaching the bridge and use quite a bit of pressure. I figure the top draws into the bridge somewhat, also reducing the space in between the two. So the gap may be closer to .002 mils. This still may be more than what some people are comfortable with but this is an instance where practical experience trumps theory as I've used this method on several hundred ukes and I've never had a bridge failure. That's proof enough for me that it works.

This process is not nearly as scary as when I used to use a little scraper. I inevitably would have to respray a couple when the scraper would cut through the masking tape and scratch the clear(where the bridge doesn't sit). This is a much much better way.

Out of curiosity, why not leave the finish on and use epoxy?

Thanks for sharing your method, Chuck. Now I see another excuse/reason for buying Stewmac's precision router base!

Bob