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routing the finish under the bridge on a newly built guitar
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Author:  jack [ Wed Jun 24, 2015 6:51 pm ]
Post subject:  routing the finish under the bridge on a newly built guitar
Hoping to find out some information about routing away the finish under the bridge on a newly built guitar . Are there any suggestions from those who have done this? maybe a youtube or some tutorial?
Many thanks, jack
Author:  Josh H [ Wed Jun 24, 2015 8:45 pm ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
Hi Jack,

Here is a quick run down of what I do.

1) I locate the bridge and drill bolt holes through the "A" and "B" string holes. I then bolt the bridge in place and take measurements one last time to ensure it is where I want it.
2) I trace around the bridge with a fine needle, just scoring the surface of the finish right next to the bridge. As long as you don't slip with the needle you will never see this line.
3) I remove the bridge. Then I take a razor blade and cut through the finish just inside the line that I scored with the needle.
4) I put a layer of green painters tape on the top around the bridge, making sure the tape lays perfectly flat.
5) I take a laminate trimmer (ridged is what I use for this) with a ⅛" spiral bit. I set the depth so that it just removes the finish and skims the wood. I start in one of the bolt holes and work my way out to the line where I cut through the finish with the razor blade. Clean up router marks with a little sandpaper

At this point you should have freshly cleaned top wood to glue your bridge to. You will also have a very thin ledge of finish between the needle line and the razor blade line.

6) The final step is to scrape or rout a small ledge into the underside of the bridge so that the bridge sits down on the the freshly cleaned wood surface, rather than sitting on the finish ledge left between the needle line and the razor line. Hesh posted a video that showed a great jig they came up with for doing this.

7) Glue the bridge in place
Author:  jack [ Wed Jun 24, 2015 9:00 pm ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
Excellent directions Josh.... Many thanks, Jack
Author:  Greg Maxwell [ Thu Jun 25, 2015 7:38 am ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
I use a very similar process:

1. Place low tack sign makers tape over bridge area
2. Locate bridge using dowels in the two E holes (don't glue in the dowels, friction fit)
3. With bridge clamped, use sharp pencil tip to mark edge of bridge all around
4. Remove bridge and mark a fine line 3/64" inside of bridge footprint line
5. Using a straight edge and a new #11 x-acto blade, score the lacquer under the 3/64th line (carefully freehand the curved area)
6. Remove the tape from the bridge footprint area
7. Using a Foredom with flexible shaft and a StewMac base, route off lacquer up to the scored line
8. Mount base upside down in a vice and freehand route a 1/16" ledge around bridge bottom border (test scrap for perfect depth)
9. Remove tape and glue on bridge using hot hide glue, use dowels to index for fast location

I've tried many methods, this one is by far the best for me.
Author:  jack [ Thu Jun 25, 2015 8:20 am ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
Many thanks Greg for your detailed reply, jack
Author:  Bill Higgs [ Thu Jun 25, 2015 8:32 am ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
What about the fretboard extension? Do you guys do the same?
Author:  Josh H [ Thu Jun 25, 2015 5:28 pm ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
Bill Higgs wrote:
What about the fretboard extension? Do you guys do the same?


I just tape off the area under the frerboard extension. I don't tape off the bridge area (like Greg does). I don't bother routing a ledge into the underside of the FB extension. It is not a high stress joint the same as the bridge, and it will come apart easier if the neck needs to be removed.

I use Fishglue for the bridge and FB extension.
Author:  Greg Maxwell [ Thu Jun 25, 2015 8:14 pm ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
I use a vacuum jig to route off the lacquer under the FB tongue, and like Josh I don't route a ledge. You could easily use the same process that I outlined for the bridge area to remove the lacquer under the tongue if you prefer.

To clarify, I tape off the bridge area after the lacquer finish has been wet sanded and buffed. The sign makers tape protects the finish while routing and provides a nice white surface to mark the bridge footprint prior to scoring with the x-acto. I used to use a vacuum jig to route the bridge area lacquer off, but found it just wasn't precise enough. I can easily route to within 1/64th of the footprint line using the Foredom, and the depth is much easier to get perfect than when using a router and a vacuum jig.
Author:  alan stassforth [ Thu Jun 25, 2015 9:37 pm ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
I've been placing, drilling and slotting for the strings before the back is on.
Then I use bridge pins for locating the bridge.
Nice to see that the pins and string ball ends are set up right this way.
Alan
Author:  Terence Kennedy [ Thu Jun 25, 2015 11:39 pm ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
I learned it at the Charles Fox course back in 2003. He used a StewMac base and a Dremel. He had a thin layer of felt on the bottom so he could push down and get another thousands of depth. I use gasket cork.

I pin the bridge with two 1/16" brads in the saddle slot, put low tack tape under the bridge and score lightly around the bridge with a #11 Xacto. Remove the tape and score 1/32 inside the tape.

I route a ledge in the bridge with a gadget similar to David Collins'

Finish off the area with small wood sanding blocks with adhesive backed paper for a flat surface.

You have to be sure you get all the sealer off. Sometmes it can look like you are down to wood and you are not. Also get the corners squared off so the wings fit tight.
Author:  bluescreek [ Fri Jun 26, 2015 5:47 am ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
https://www.youtube.com/watch?v=EJG5Frbu78c
at about 9:45 you will see how I rout the finish off
Author:  Hesh [ Fri Jun 26, 2015 6:54 am ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
Not to be a contrarian.... and having routed finish off under the bridge a number of times I prefer using hand tools..... (go figure....:)) and a very sharp chisel.

Why? I find that I have more control, way better view of the work, and less chance of a mishap such as something vibrating loose with either the SM base or the chuck.

There are other considerations in my case as well that need to be mentioned to understand why I prefer a very sharp chisel. For example as Terry mentioned we route a ledge around the bridge that is in the neighborhood of .005" or so inset from the bridge foot print. That's a pretty small margin for error meaning that great lighting, a steady hand..., and the uber sharp chisel are in my view easier to control with these tolerances.

Simply viewing your progress when routing is more difficult because of the base and the tendency of the rig to block light.

On the other hand the vast... majority.... of makers be it f*ctories or individual Luthiers often leave a good deal of finish under the bridge and if that's one's bag the router method is fast and does not need to all that accurate.

Conversely if you are keen to exploit all the gluing surface that you have available to you a chisel works better for me.

I'll also mention that this is something that we do very frequently. In the past four days we have had to clear and expand the bridge patch on three high-end instruments. I'm mentioning this for one reason and one reason only. We can do it either way, we have to do it frequently, but still we choose to use a sharp chisel and find it easier, more accurate, and I would even make the case that it can be quicker if the top is not a basket case and runout city.

Anyway either method works, be sure to freshly scrape both surfaces just prior to gluing the puppy on.

One last consideration as well. Cedar tops look great, sound wonderful, and can be a repair Luthiers nightmare.... Why? Because they tend to want to get a divorce from their bridge IME more often and faster than say spruce. And.... when the bridge lifts on a cedar top it almost always takes a nice chunk of the top with it.....

What's this got to do with routing the bridge patch? What we often see when a bridge lifts on a cedar top is if the maker scored the finish and went just a tad deeper than the finish the bridge will take this wood with it too when it lifts.

As such if your router is taking any wood and not just finish and it's a cedar top the chances are greater that when that bridge lifts, and it most likely will.... it will damage the top in the process to a greater degree. This is true for spruce as well but not to the degree of damage that we see with cedar.

With a very sharp chisel, some tunes playing and no clients interrupting me I find that I can leave the top as I intended it to be and get all of the finish that I want gone in very little time.

But again either method works.
Author:  bluescreek [ Fri Jun 26, 2015 7:47 am ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
I take it you didn't see my method Hesh I don't use a router I use my inlay base for the very reasons you mention , visibility .
Author:  kencierp [ Fri Jun 26, 2015 7:53 am ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
I am still using masking tape, has worked for me many years -- I do use a chisel as a scraper to remove any trace residue from the tape adhesive. I wondered about the cross grain scoring of the sound board when defining the bridge outline with a scalpel blade -- Cedar does peel easily even with no fractures.

As a side bar Mike Doolin uses CA right on top the finish!! Even with pin-less bridges -- how about that!

I think Mike is currently using UV cure polyester.

While the factories actually save time and material routing off the finish using a CNC a machine I wonder about the economy of effort as well as risk and reward for the small shop?
Author:  Greg Maxwell [ Fri Jun 26, 2015 8:45 am ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
Hesh, I completely agree about Cedar. I reglued two bridges this week on Cedar tops and as is typical, both took wood with them when they came loose. And there is always more risk of chipping lacquer on Cedar when cleaning off the excess that was left underneath, even when scored.

This thread shows that there is always more than one way to approach something. I've tried every method except pre-masking the bridge area, and using a mini inlay router has turned out to be the best method for me by far. For my hands and eyes, I'm better at it with this rig than with using a chisel. Of course great lighting is key and for me, an Optivisor. Using this method, I no longer stress as bridge gluing day arrives. But it was an evolution for sure!

Whatever the method, IMO it is very important to leave as little lacquer under the edge of the bridge as possible. I've tried scoring and chiseling to the exact footprint of the bridge, and while this method does result in good adhesion, I can always see traces of the edge and some rippling in the lacquer after glue-up. Ditto for sanding a tiny bevel on the edge of the bridge. Routing (or chiseling) the lacquer to within 1/32" of the footprint line and then routing a perfectly-sized ledge on the bridge makes a clean install that stays put... even on a 12 string. Every bridge I've ever had to reglue (both repairs as well as new builds) was due at least in part to poor contact at the edges due to 1/16" or more of lacquer underneath combined with no ledge. I've seen imports with as much as 3/16" underneath.
Author:  Terence Kennedy [ Fri Jun 26, 2015 9:44 am ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
Hesh wrote:
With a very sharp chisel, some tunes playing and no clients interrupting me I find that I can leave the top as I intended it to be and get all of the finish that I want gone in very little time.

But again either method works.


I actually use a chisel for part of it as well. I rout pretty close to the line and work up to it with a chisel. I also try to just get down to the sealer for the actual patch area with the router and finish that off with the sandpaper blocks and chisel. I try not to rout directly to bare wood if I can avoid it but in my hands the contour of the top usually results in some uneven areas that have to be smoothed out with scraping and sandpaper blocks.

I've been doing it for 10 years and still get a little nervous each time. It still takes me almost two hours to get everything ready for gluing. I think I have everything perfect and then look at it in a different light angle and see an area of color change indicating a little spot of sealer/shellac remaining.

My biggest problem starting out was not getting clean corners for the wings both on the top and on the bridge ledge. Had a couple of wings lift from poor contact.

I usually rout a trial ledge on a short piece of wood binding and slide it around the bridge patch area and make sure it clears everywhere and is the right width/overhang.
Author:  Hesh [ Fri Jun 26, 2015 11:18 am ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
Sorry John I did not see your video because my bench computer is a 10 year old MacBook and so slow these days.... it can't handle video.... :? :D For some reason the spell checker stopped working a few years ago too if you all have not notticed..... :) I plan on loading some flavor of Linux on it or pitching it out the window... I'll check out your video when I get home though and thanks for posting it.

Ken when I first heard of CA on finish for bridges it was back in 2007 and Rick Turner was also doing it that way. It's important to note though that both of these very fine Luthiers use cat poly finishes. Cat poly as in our very own Joe White and his superb finishes is the very toughest finish that I have ever worked with. Even chiselling it off you can immediately tell that the stuff is tough, sticks to the guitar like nothing else. As such this method works for these guys and they most certainly know what they are doing.

For repair pukes though like me we find the servicability of this practice to be lacking in so much as CA is not keen to release with anything beyond a hammer, hatchet, or claymore.....:) If the bridge ever lifts, and they usually will at some point the top damage may make this repair far more epensive and/or damage the cosmetics of the instrument as well. The jury is still out though and it could be that these bridges will stay put.

I still think that CA is evil....:) and never used it anywhere on my guitars except to keep my nuts on.... :? :) and these days we use it for fretting as well.

Greg we need to get together and then post a pic of us with our genuine Dan E. Optivisors.... :) You made a great point that I have never really noticed prior but now that you mention it I have noticed it but it never registered. Finish does see to not stick as well to cedar... Maybe that's why it's used to repel insects....:)

Hey Terry - bridge wings are one of the hardest parts to get down and have them stay down IME as well. I can also appreciate the multiple looks and discovering things that we did not see prior - that's my world as well these days. I've been called Blind Mellon Luthier more than once ya know....:)

I thought of one more reason why I just go for the hand made Link Van Cleave chisels for clearing bridge patches.

You guys work on new stuff that often or always has a predictable, gentle dome that's uniform and constant. In the repair world worn pin holes, loose braces, time, RH, abuse, poor design all combine in time to make the guitar top not very uniform.... We may see creases upward from a worn bridge plate and using a router that registers, or the base registers off more uniform or not areas of the top can mean that we are routing off wood and digging a hole of sorts.

Again I think using a router base is fine but I do prefer a chisel because in my world things are usually far from perfect.
Author:  bluescreek [ Fri Jun 26, 2015 1:15 pm ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
I am with you on CA hesh. The more I do this the less I use it. I also like to get good clean wood to wood contact. Through the year I have cleared the bridge footprint with
Scrapers
Sanding
Remover ( 1 time and never again )
inlay router
I agree that once you find a technique that works for you , no need to do it any other way.

I use the bosche and lomb optivisor
Author:  dzsmith [ Fri Jun 26, 2015 8:20 pm ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
Glad to see you back on here, Hesh!
I never had the chance to thank you for improving my fretting skills.
Thannnnnkkkkkkksssssss!
Author:  Mike OMelia [ Sun Jun 28, 2015 2:43 pm ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
Would some of you please post pics of your bridge ledge cutting jigs? I recall one I tried based on a colt router and a clamped guide. Did not work well for me.
Author:  DennisK [ Sun Jun 28, 2015 7:17 pm ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
...
Author:  Terence Kennedy [ Sun Jun 28, 2015 9:14 pm ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
I used the StewMac Dremel router base with a radiused plate attached to mimic the top radius. I used their edge guide with a wood post so you can bring the bit right up into the guide post.

Image
Author:  Mike OMelia [ Sun Jun 28, 2015 10:28 pm ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
Im not sure if you are showing the efficacy of your ledge cutting jig. I do See some cuts. And they look like the ones I got. And that is to say, not very effective. I had to do a lot hand work to get it right. Seems to me part of the problem is trying to achieve an even cut at 3-5 mils around the periphery. Another part of the problem is proving it's terribly important. Seems to me I could just rough sand the edge and achieve the same effect. I get the mechanics side of the argument. I'm struggling here guys...

Note: the finish itself is soft. So is the top wood. Stuff is going to give under pressure. I use the LMI bridge clamp. That thing is one genius device. I can't believe for a minute I'm not getting a good bond. I sand the periphery of the bridge. And feather sand the periphery of the finish. Is this approach going to lead to failures?
Author:  Greg Maxwell [ Sun Jun 28, 2015 11:02 pm ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
Mike, I clamp my Stew Mac base upside down in a vice and use a 1/8" carbide inlay bit to route the ledge freehand. I cover half the width of the bit with the edge of the bridge, making a 1/16" wide ledge. When combined with a 3/64" lacquer border under the bridge, I have 1/64" margin of space. It may sound crude or risky to cut the ledge freehand but it works great for me. Is it necessary? I've never had a bridge prepared this way lift. Every loose bridge I've ever repaired has had a lacquer border underneath that prevented full edge contact.

As I mentioned above, I've tried the sanding/beveling of the edge of the bridge technique and while it can improve getting full glue contact, you can see it. The routed ledge is invisible if done correctly and you get 100% bridge to top contact.
Author:  Mike OMelia [ Sun Jun 28, 2015 11:09 pm ]
Post subject:  Re: routing the finish under the bridge on a newly built gui
Thank you. I see what you mean. I can see where free handing it would greatly simplify the process.
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