Tutorial - Fitting Bridges

[Hesh1956]

Here is a very simple and fast way to fit your bridge to the dome of your guitar top prior to gluing the bridge on the guitar.

Step one is to get set-up to sand the bridge on the actual guitar top. I use 120 grit sand paper to start and will switch to 240 once the heavy lifting has been done by the 120 grit.

Locate where your bridge will be located and use two small pieces of tape on the sides of the guitar to provide you with a visual reference for sanding. If your top joint is not visible also use tape to designate a center line for sanding. The objective here is to sand the bridge, as much as possible, in the exact same location on the guitar top that it will live when glued in place.

The latex gloves I find are a huge help in not letting the finish sanded bridge slip out of my hands while sanding. And the pencil eraser is placed under the neck block to help keep the guitar from moving while sanding.



Next I mark up the bottom of the bridge with a white pencil so that I can see when every area of the bridge bottom has been sanded. When all the marks are gone the bridge has been properly fitted to the top - that is the goal.



Here we see the progress with sanding the bridge. Still a ways to go.



When all of the marks have been sanded off I switched to 240 grit (not shown....I forgot to photograph it.....) and drew new marks and repeated the process until the marks were gone. This "second pass" with 240 grit goes very quickly.

Additionally I noted the RH in the shop (46%) and when gluing the bridge I will be sure to match the RH conditions since the dome of the top will change with RH changes.

Also be sure to be careful with masking tape on the guitar top. you don't want to lift any grain while removing the tape. I remove the tape at 45 degrees to the grain.

Thanks for looking!

[Lillian]

So, when is your book do out? You should only have a couple of sections left to write. Can I place an advance order?

[Serge]

Great tips there brother Hesh, thanks!

Serge

[Lillian]

Oh, just in case it didn't come through, I was serious about the book. I own or have repeatedly read all but the two that just came out and I have not seen one that is as clear and concise as your tutorials. Your photos are fantastic as well.

I guess I could just start gathering and editing all of your tutorials myself and I probably will. But I did want to tell you what I think about your work and how much I appreciate the time and effort you put into doing this just to share with us.

[Rod True]

Great Tutorial there Hesh, as usual.

I agree with Lillian, you could write a book on building a guitar you know. You really do have a way to keep things simple for folks.

Thanks

[Hesh1956]

Thanks folks! I think that I like taking photos and writing up what I am doing because I am lazy and anything that takes me away from say sanding...... is a good thing.....

[Alain]

Fantastic ideas, as usual man! I've learned a few things, again... This just goes to show how fantastic and necessary these forums are.

Just a little addition. I noticed you used the lower tack tape, but if you're stuck and have just the stickier stuff, you can always heat it up with a hair dryer before removing it. The heat will help soften the adhesive and the chance of any tear out is greatly reduced. Still, always remove at a 45% angle. Better safe than sorry.

[BillyT]

Great Heshtorial Bud! It's great seeing somebody else do it! It makes it so clear.

Technically, you really don't have to do the sanding in the bridge position, considering it's a radius, you could sand it...... anywhere......like..... a brace! ..........

[Bob Connor]

Yer nothing but a shit stirrer Billy

[BillyT]

Er.....! I have one question Hesh Buddy! Why is the bridge showing sanding witness at the outside ears? Shouldn't it be on the inside first?

There must be a heck of a warp in the bridge! Ight?

[BillyT]

Yer nothing but a shit stirrer Billy

Actually, I'm a lot more than that! But it just gets worse! ....Fecal agitation is just the little chocolate jimmie's on a great big sh_t sundae!

[Arnt]

Thanks for the tutorial, Hesh!

Er.....! I have one question Hesh Buddy! Why is the bridge showing sanding witness at the outside ears? Shouldn't it be on the inside first?

There must be a heck of a warp in the bridge! Ight?

I'm guessing those bridges come from John Watkins with a radius already milled into their bottoms, and this sanding is only done to fit them to the actual curvature of the guitar's dome which is this case is less than what was on the bridge, hence the sanding marks under the bridge's wings.

I shape the bottoms on my bridges with a "jig" made from a short length of 2x4" that has a 25' curvature along its edge with a strip of 80 grit sand belt glued on. I clamp it in a vise and sand until the bridge has sanding marks all over its bottom, and then clean those up with a scraper immediately before gluing the bridge to the guitar. It usually fits the guitar quite well, and what little pressure it may take to make the surfaces mate will help the top maintain its 25' dome. Not that I think this is all that important; the radius of the top's dome will vary with changes in the humidity later on anyways.

This (Hesh'es) method of fitting bridges is quite common for fitting arch top bridges, where the bridge is held in a fixture to stand up straight while it is being sanded. I almost ruined freshly lacquered a mandolin top finish with some debris from the sand paper which found it's way between the sand paper sheet and the mandolin top, so I'm a bit cautious about this method... I realize that Hesh does the sanding before the instrument is finished, but still that memory lingers...

[Hesh1956]

Billy very astute observation for such an old guy to make

And Arnt is exactly correct. My bridges come from John Watkins with a 25' radius on them. Although the top was built to a 25' radius too things change and you can never be sure exactly what you will end up with. I brace very light which methinks makes some of the dome go away. Also, even though the bridge plate is sanded in the dish too everything may change a bit when it is all glued together into a system.

So as Arnt indicated the wings hit first here and the middle last. This means that my dome, at least in the bridge plate area, is not 25'.

[Dennis Leahy]

Good tutorial, Hesh.

Since my bridge started out flat on the bottom, I did a step prior to your tutorial to get the general radius:

I took a piece of MDF and sanded it in my radius dish. That gave me a convex 25' radius block. I then put sandpaper on that block, and that was used to get the initial shape. Seemed like less chance for damaging the top, and then used the top for a final sanding to the *real* top radius. I too found the radius of the dish and the actual top to be different.

Hmmm... Maybe considering that the bridge is really just a stiff brace, maybe just maybe I should be sanding it only to the dish's radius, and then gluing it onto the top. Perhaps that will pull the top closer to its intended arch, rather than allowing the top to flatten out, just because it wants to? What do you folks think?

Dennis

[BillyT]

The process, that some use, of bending the brace and cutting a straight cut, that when released, renders a radius also applies when one glues the brace to the top.

The natural flat plane of the soundboard is going to bend the spruce somewhat back to the soundboards preglued shape.

To get a true radius one would have to overbend such as is done in tool and die with steel. There are actually formula's for it, depending on the size and densities, as I am sure there is for specific woods.

Of course, when one glues the top to the spherical sanded side the sphere returns back to a more true to intended specification, but I'm sure there's still a reflex. This would explain why there's a contact at the outside of the bridge first considering Johns 25' rad.

This brings up a question, do you radius the bridge plate before you glue to the inside of the soundboard?