Bridge problem

[viento]

My new 6-string acoustic bridge is finished.
I have its position too.

Normally I would stick a foil or thin tape underneath on the top,
mark the exact outline and with an exacto knife carefully
cut through this outline.
Then everything, except the marked bridge area on the foil is peeled off
and the top is ready for spraying.
When the lacquer has cured, the film gets peeled off and the bridge can be glued on.

Only: since the top is not spruce but of the relative softer red cedar wood,
I don't dare to cut the foil with an exacto knife.
This could create a "predetermined breaking point" on the top,
which could possibly rip when the strings are pulled.

Does anyone have an alternative idea that could solve this problem?

[Alan Carruth]

Use a sharp knife and be really careful not to go deep.

[viento]

Yes, I was really careful and succeeded.
Btw, the top wood is 3mm thick.

[redir]

One more suggestion, when you tape up the bridge foot print before finishing make the area of the tape slightly smaller then the actual foot print. Because when you go through the finishing process you will get a build up of finish that ramps up to the thickness of the edge of the tape and the eye can detect it.

I usually make it .1 inch or so smaller all round the foot print. This also allows you to correct any mistakes you may have made in positioning the bridge.

Once you are done with the finishing then tape up the area, locate the bridge and then with a very sharp knife mark it out. Then it's real simple to scrape the excess finish with a chisel.

Some guitar makers will actually make a rabbet cut to the depth of the thickness of your finish around the bridge bottom perimeter so that it rides over that excess finish ledge. If you choose to do that .1in is too big. So consider that.

I don't do that as I make bridges as small as possible and want the whole footprint glued down but it's a good technique.

[Alan Carruth]

I think it's a bad idea to clear away a smaller area of the finish than the actual bridge footprint. For one thing a thinner glue line is usually stronger; that gap is tending to weaken the joint around the edge in particular. Another issue is that the peeling stress on the glue line is highest along the back edge of the bridge. The stress level depends in part on how wide the glue surface is along the line of pull; as the width of the bridge is reduced the maximum stress along the back edge rises disproportionately. Reducing the width of the glue surface makes it more likely that the bridge will peel up.

Doing this makes gluing the bridge down easier, of course. You don't have to be quite as careful about how you scribe the line and clean off the finish, since little chips won't show. Also, it's easier to clean up excess glue from a finished surface. I can understand why people do it, I just don't think its a good idea.

[redir]

I may not have made my self clear enough but I make the foot print smaller for the purposes of finishing then I remove the finish under the full foot print and glue the bridge down.

In the past I would not use tape and then scrape the entire foot print away. Then I found that using tape sort of speeds up that process. But if the tape is the exact same size as the bridge footpring then you get finish build up at the edges. So if you make the tape slightly smaller that finish build up is now on the inside and then you simply remove that by scraping away.

This stuff is always difficult to explain

I never did like the idea of making a rabbet joint around the bridge either. I like to glue the entire bridge down.