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  #1  
Old 11-07-2010, 01:37 PM
naccoachbob naccoachbob is offline
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Default Question about Masking a bridge before finishing or after

I posted this in the DIY section, but hope putting it here will give some good responses.
Since I'm using a nitrocellulose finish, I need to know what to do about the bridge.
I can put the neck on, situate the bridge correctly, and outline it to mask it off.
Some people finish a guitar, then scrape the wood under the bridge before gluing. I did that before, and it worked well.
Some mask the bridge first and then put on the finish.
With the product I'm using, which way is the best? I better decide now if the bridge needs masked, before putting on any other coats of finish.
Thanks for your help in advance,
Bob
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Old 11-07-2010, 01:51 PM
Rod True Rod True is offline
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Bob, are you saying you've glued the bridge onto the body? Or are you wanting to just mask off the top where the bridge goes with the bridge outline?
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Old 11-07-2010, 01:58 PM
Brackett Instruments Brackett Instruments is offline
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There's 2 problems with masking for a bridge. Regular masking tape is kinda thick. (.005" I think) This causes a buildup of thicker finish around the bridge. The other problem is, finishing will change the position of the neck slightly. This isn't a big deal, but could affect intonation.


I've masked the bridge area on my last several builds, but.......... I use frisket film to mask instead of tape. The film I use is only .001" thick.
I locate my bridge, but don't route the saddle slot until the guitar is finished, and the bridge is installed. This assures correct intonation.
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Old 11-07-2010, 03:00 PM
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Tim McKnight Tim McKnight is offline
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I rout the finish off after buffing. I have found this to be the most accurate method to locate the bridge and easiest method for me.
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Old 11-07-2010, 05:05 PM
dekutree64 dekutree64 is offline
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I mask the bridge, but not all the way to the edge. About 1/8" border between the masking tape and the actual bridge edge, to let the finish build up and then scrape that. That way I have plenty of guaranteed fresh wood, an easier scraping job, and no finish buildup
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Old 11-07-2010, 06:15 PM
Hodges_Guitars Hodges_Guitars is offline
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Quote:
Originally Posted by Tim McKnight View Post
I rout the finish off after buffing. I have found this to be the most accurate method to locate the bridge and easiest method for me.
+1 for this method
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Old 11-07-2010, 06:59 PM
naccoachbob naccoachbob is offline
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I have not mounted the bridge.
I was concerned with whether to mask its location, or to wait until all the finish was done, then scrape down to the wood in the bridge's location.
Last time I waited and scraped down. I was using Target's EMtech 6000, a water based finish.
This time I'm using nitrocellulose. Thinking that it might be a harder finish, and make sanding/scraping difficult, I considered masking ahead of time.
If I do mask, I'll make the mask about 1/16" smaller all around so that finish is slightly under the bridge. Don't think that will have an effect on the gluing.
Bob
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Old 11-07-2010, 07:04 PM
naccoachbob naccoachbob is offline
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Tim, and Hodges. Do you use a dremel for this routing?
How deep do you rout? I'm not expert at measuring finish depth.
Maybe just "inch it in", just go one pass after the other to get to bare wood?
I can see where the final setting of the neck could make the location change. Don't want to end up with bare wood showing, and try to match up finish just for a small spot.
thanks,
Bob
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Old 11-07-2010, 08:14 PM
Todd Stock Todd Stock is offline
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Use a laminate trimmer with a quality downcut spiral bit, good quality guide bushing, and a smooth, consistent thickness plywood template.
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Old 11-07-2010, 09:10 PM
Rod True Rod True is offline
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I've done all three methods, scraped, routed and masked.

I like the scraped least as it just takes to long, the routed method requires some nerve to do but the best way to get to depth is to touch the bit near the bridge pin holes, just sneak up on the wood and don't actually cut the wood.... Also mask around the bridge profile so you don't go outside of the bridge shape. If you can, do as Todd mentioned and make a template to route the bridge profile out with a template bit in the laminate trimmer. You'll still need to scrape or chisle at the corners though.
I like the masked because you can decide to leave a bit of finish under the bridge (or not in my case) and then scrape that little bit left to fit the bridge right. You have to be careful when cutting the finish at the perimeter of the tape. You don't want to slip and cut into the body area leaving a repair and you don't want to cut to deep (which can be a problem with the other methods too) and severe the fibres of the wood.

Regardless of the method you choose, it won't mater for the finish you're doing as it will respond pretty much like the EM6000. Again, I've used both Nitro and the EM6000, they both scrape fine and actually, the nitro routes just a bit cleaner than the acrylic...

Last edited by Rod True; 11-07-2010 at 09:18 PM.
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Old 11-08-2010, 09:16 AM
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Tim McKnight Tim McKnight is offline
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Here is my method:

- Lay down two layers of 2" wide blue masking tape, covering most of the lower bout top to protect its surface.
- Locate the bridge
- Drill the outer E/e holes
- Insert pins through E/e holes to secure bridge position
- Scribe around perimeter of bridge using a surgeons scalpel, cutting through the tape and finish. Do this very lightly in a couple of passes then you can feel when you are into the wood.
- Remove the bridge
- Remove the tape below the bridge
- Rout finish off using a 1/8" down cut carbide spiral bit in a Dremel
- I start at one hole and sneak up on the wood so as not to cut into the wood BUT just remove the finish
- Work from the center outward towards the perimeter
- As you approach the perimeter tape/scribed line you can see the finish "curl" as you sneak up on the scribe line. This is the line that you do not want to cross!
- Sand the entire area with 180 grit
- Its all done free hand with a pair of magnifier goggles. This has worked well for me and I can prep for a bridge in about 10 minutes.
- Remove all the masking tape
- Attach the bridge with HHG and let it set over night before removing the clamps. BTW, you only want to use LIGHT clamping pressure or else you can deform the top and starve the joint of glue.
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Last edited by Tim McKnight; 11-08-2010 at 12:16 PM.
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Old 11-08-2010, 10:57 AM
cpabolting cpabolting is offline
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Quote:
Originally Posted by Tim McKnight View Post
Here is my method:

- Lay down two layers of 2" wide blue masking tape, covering most of the lower bout top surface.
- Locate the bridge
- Drill the outer E/e holes
- Insert pins through E/e holes to secure bridge position
- Scribe around perimeter of bridge using a surgeons scalpel, cutting through the tape and finish. Do this very lightly in a couple of passes then you can feel when you are into the wood.
- Remove the bridge
- Remove the tape below the bridge
- Rout finish off using a 1/8" down cut carbide spiral bit in a Dremel
- I start at one hole and sneak up on the wood so as not to cut into the wood BUT just remove the finish
- Work from the center outward towards the perimeter
- As you approach the perimeter tape/scribed line you can see the finish "curl" as you sneak up on the scribe line. This is the line that you do not want to cross!
- Sand the entire area with 180 grit
- Its all done free hand with a pair of magnifier goggles. This has worked well for me and I can prep for a bridge in about 10 minutes.
- Remove all the masking tape
- Attach the bridge with HHG and let it set over night before removing the clamps. BTW, you only want to use LIGHT clamping pressure or else you can deform the top and starve the joint of glue.
Love the support and help you give each other!
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  #13  
Old 11-08-2010, 12:19 PM
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Tim McKnight Tim McKnight is offline
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I should issue a warning [if] you you use masking tape on a fresh nitro finish. Don't leave the tape on for more than about 20 - 30 minutes or you could damage the finish. Nitro, especially fresh nitro, is susceptible to interactive softening from adhesives, solvents, plastics and rubber compounds.
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  #14  
Old 11-08-2010, 01:57 PM
cpabolting cpabolting is offline
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The whole pricess of removing finish for a bridge looks like it needs to be perfect in the execution.....kind of like a Brazilian waxing LOL
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A brand new duet I wrote with my daughter:
https://youtu.be/u0hRB7fYaZU

Olson Brazilian Dread #1325
Olson Brazilian SJ #1350
Olson Tiger Myrtle Dread #1355
Olson Brazilian Jumbo #1351
Olson 12-string Jumbo (one of only a few)
Martin D-42 Johnny Cash #51/200 (only 80 made)
And a few others

Quite a few limited edition and rare Martins
-----------------

http://www.kekomusic.com

Last edited by rlouie; 11-08-2010 at 02:12 PM. Reason: inappropriate
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  #15  
Old 11-08-2010, 03:00 PM
Todd Stock Todd Stock is offline
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I make a template out of 1/4" birch ply which fits the bridge outline exactly. Once the bridge is positioned using a centerline finder and Saddlematic, I mark the forward edge and the ends of the wings with lacquer-safe green tape or delicate surfaces blue tape. I position the template on the top using the tape as a guide (even with forward edge of cutout and end of wings), clamp, then set depth using .003 shim stock (AKA notebook paper). I use a 3/8" bushing with a 1/4" downcut spiral bit to clean off the lacquer leaving a 1/16" lip around the edge. After sanding the bottom of the bridge to the top radius, I use a convex radiused router base plate to cut a matching rabbet in the edge of the bridge.
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