Masking bridge location

[Mike Conner]

Building my first flat top instrument, a dreadnought with Englemann front and walnut back and sides. Going really well so far and getting ready for finish prep.

My archtops have floating bridges so this will be my first glued on bridge. My thought is to create a mask to protect the bridge location from finish (Endurovar waterborne gloss) and have raw spruce to glue down the Macassar ebony bridge. Any recommendations on materials for the mask and adhesive? My thought so far is some smooth finished thin cardboard and lightly applied 3M contact adhesive.

I expect that some delicate scraping will still be needed once the mask is removed.

[Barry Daniels]

No contact adhesive, please. And cardboard is too thick. Use either masking tape or frisket. Make the mask slightly smaller than the bridge because the edges get a little extra build and will need to be scraped and cleaned up.

[Mike Conner]

... Use either masking tape or frisket. Make the mask slightly smaller than the bridge because the edges get a little extra build and will need to be scraped and cleaned up.

Thanks Barry,
Any tips on how to trace the bridge outline on to the masking tape? I was thinking of sticking to some plastic to trace the bridge and cut out the outline (very slightly smaller than the bridge footprint), then peeling from the plastic to transfer to the spruce.

I hadn't heard of frisket before. That might be just the thing.
//mike

[Peter Wilcox]

I use masking tape (blue painter's because it peels up without residue) stuck down to the top covering the bridge footprint. Then measure and mark two lateral corners of the bridge, hold the bridge down and trace around it with pencil. Using straightedge and #11 scalpel (freehand the curves), cut all around just inside the line slightly smaller than the bridge. Then peel away the outside tape and there's the mask.
After spraying, score all around the mask and peel it off, and as Barry says scrape any buildup at the edges.

I'm sure there are better ways to do it, but that's my method.

[Mike Conner]

Thanks, Peter.
Your method is the most "direct". I guess the critical part is to have a really light touch while cutting the tape to avoid slicing into the spruce top.

[Barry Daniels]

Yes. Practice cutting the tape on scrap to get the right touch.

[Bryan Bear]

I do similar to above with some differences that bear explaining.

I use French polish and have not really had any significant' buildup of the edge. Endouro-var is probably different in that regard. I tape off the bridge location with blue masking tape, clamp the bridge down and carefully score the tape around the bridge (being careful not to cut the spruce). Then I have the actual footprint masked. I French polish right over that and can peel the tape away when I am done. I scrape a very small ledge around the perimeter of the bridge. This ledge is not deep and is less than half a mm wide. It is just enough to ensure that the edge of the bridge will not get hung up on any ledge that the FP may have left preventing full wood to wood glue surface.

[Freeman Keller]

For what it is worth, I do not mask the bridge foot print before finishing. I just finish the whole top with lacquer. After finishing I tape the bridge on the top and do the final neck setting to the bridge and make sure it is absolutely correctly positioned. Some people scribe around the bridge, I prefer to use masking tape. Remove the finish with chemical stripper and chisels, put a tiny relief around the edge to allow for the small ridge of finish and glue it on.

I know that Taylor masks their tops before finishing but I worry that the bridge might move when I do the final setting.

ps - I don't know about Endurovar but KTM-9 will come off with chemical stripper. You should test first obviously.

[Tom Owen]

I position the bridge on the unfinished top drill thru 2 bridge pin holes, and then mask with tape. I put tape down on a piece of glass lay the bridge on it and cut around the bridge with a sharp knife. Carefully peel the tape off the glass then on to the top. Taylor uses 2 1/8" nylon locating pins, I use bridge pins to make sure the bridge stays put during gluing. Using a vacuum clamp, as I do, reduces any chance of the bridge moving during gluing.

[Mike Conner]

...I position the bridge on the unfinished top drill thru 2 bridge pin holes, and then mask with tape.

Tom,
I have the polyethylene locating pins from StewMac, and my plan is to locate the bridge and drill for the locating pins. I will be clamping with bolts through some of the bridge pin holes and clamps through the soundhole. Thanks for sharing your process.

[Alan Carruth]

The varnish I use is pretty hard stuff, and can be difficult to remove. It helps a lot to have a clean surface to start from, with only tape adhesive residue to worry about. I mask the top under size, as close as I dare to the final bridge outline. Once the neck is on and I know exactly where it will go I locate the bridge and drill the outer two pin holes into the top with a 3-16" drill. The bridge holes then get reamed to taper, and some plastic pins are used to fix the bridge on the top so that I can scribe the outline. I find it helps to tape off the ends a little under the bridge on top of the finish; the tape gives an exact reading of where the bridge ends ad makes it easier to stop before I remove finish beyond the outline. I know that sort of thing doesn't happen to you...

[Barry Daniels]

I have switched to leaving about 1/32" of finish under the bride perimeter and then routing a corresponding ledge on the bottom edges of the bridge. This slight overlap leaves a much cleaner transition and also provides a bit of location help during glue up.

[Freeman Keller]

I'm like Barry, I leave a very small bit of finish under the edge of the bridge. I also made some UHMW cauls for the inside - you want something that glue will not stick to if you plan to drill any pin holes first (I do lots of repairs so there are always pin holes). You want something that glue will not stick to - its embarrassing to glue your caul to your bridge plate.....