Building an adjustable bridge

[AaronVW]

I have been looking for threads on building my own bridges and have mostly run into folks building the one piece maple bridges. I made one of the one piece maple bridges for my first mandolin build which is a two point with all kinds of non-traditional woods. #2 is an f5 and I just had to build an adjustable ebony bridge. If it is any help to others out there I have decided to document my process of building the bridge and will post the photos and progress here. If anyone has any tips or techniques that you use, please feel free to post here. Questions are also encouraged! I'm starting out with a steel string guitar bridge blank, wheels and posts from Bill James and will be using a drill press, bandsaw and Dermel w/ router base. Here is a "before" picture.

[Mike Conner]

Aaron,
Looking forward to seeing how you approach this. I have a section in my build journal on building a bridge in my Journal here

http://www.mandolincafe.com/forum/sh...rnal-Completed

I'm very curious about alternative ways of building bridges without needing shaper jigs, etc. I found my dremel a bit under powered for milling the heavier cuts in ebony and ended up using a trim router and a plywood jig. Thanks for making the effort to share your experience! //mike

[bmac]

My first comment is perhaps premature... But why use all that expensive equipment on a bridge which could be built with very simple hand tools.and no electric equipment whatsoever. You have listed perhaps a thousand dollars worth of tools to build a ten dollar bridge.

[Geoff B]

BMAC, I doubt he bought all those tools and supplies just to make one bridge...
Aaron, no advice, I seem to use a slightly different process each time I do it--which goes for fixed and adjustable. The most critical things to me are the contact with the top, the slight tilt toward the tailpiece and making sure the spacings work for you (overall and within each course) or whoever will be playing it.
I haven't done enough with density or mass to comment, but there are people who have and probably have good advice there too.

I agree that I haven't seen many threads on adjustable bridges, I think your intention of adding that to the cafe could add some value for future lookers...

[AaronVW]

Bart,
Why use all that "expensive equipment?" Well, because I already have all of those tools and don't feel that I need to forego their use simply because it could be done another way. I am, however, interested in your methods and would love to see some of your work. I have seen some builders make their bridges using fancy jigs and router tables, others who use CNC. They use what they have, I use what I have. I would love to see someone post some pictures of their Swiss Army bridge!

Geoff, I look forward to getting to see some of your instruments. I'm sure my methods will vary as I make more and/or acquire new tools. I intend this project to show A way, not THE way to build a bridge.

[Bill Snyder]

I think this is dandy. I am just curious what the Dremel w/router base is going to be used for.

[AaronVW]

Well it took me longer than I expected to get started on this one. Here is the progress so far...
I started with a steel string guitar bridge blank and printed out a diagram of a bridge that can be found here: http://www.lutherie.net/mandolin.bridge.schematic1.gif

The first thing I did was to drill the holes. 7/64 followed by 1/8 at a lesser depth. This way the threads on the pins will bite into the base but the top of the bridge will be able to move freely as the wheels are adjusted. Using a drill press makes it easy to keep both pins perfectly parallel and centered through the bridge:



Next I cut out the pieces like so:



I then set up a spindle sander on the drill press to shape the pieces like so:



And here are the pieces after rough shaping and sanding. I also used my belt/disc sander to touch up the sides and to bring the overall thickness of the bridge top down to where I wanted it:



I built a simple jig to hold the top to rout the compensation. I liked the smooth look of the bridges made by a few builders who are using CNC. I have had good functional results using a saw and chisel but was never really happy with the harsh look of the resulting compensation slots. This is what I came up with - The jig is simply two pieces of 1x2 with bolts holding them together. The bolts are tightened and the jig holds the bridge top in place and creates a flat plane to set the dremel router base on. I used a dental lab bur but Dremel makes one just like it for about $3 :



This is what the top looked like right after cutting:



Then I sanded everything lightly and rubbed it a bit with steel wool. After fitting the bridge to my mando and doing a set-up, I will radius the top according to where the string notches are set and the whole thing will get a good polish.

[Mike Conner]

Aaron,
Interesting design - I like the way you approached the compensation. I imagine that the Dremel did fine with light cuts.

Did you thread the holes in the base for the posts, or did you just let them cut their own way into the ebony?

[AaronVW]

Mike,
I did not tap threads for the holes in the base, although it would have been better if I had. I cracked one base by screwing the post in too far but that may have happened even if I had tapped it. I just don't have a tap for that thread size yet. Maybe I should go spend $15 at Harbor Freight and get one! The Dremel did work well for light cuts and overall I am happy with the results. I'll post a photo once I get it all strung up.

[Mike Conner]

Aaron,
I bought the inexpensive Harbor Freight metric tap and die set just to get the 4 x 0.7 mm tap (and handle) that matches the bridge posts. It was less than $20, and buying the tap alone from the usual suppliers like MSC or Graingers was way too expensive for this casual use. The posts went in like butter. I was as concerned about snapping the brass posts as I was splitting the wood.

I'm thinking about wicking in some thin superglue to lock the posts in the base, but I'm really not sure they're moving in the base when I adjust since my saddle has blind holes.

The plastic type "steel wool" from Lowes worked great for buffing and polishing the ebony. Got a decent satin sheen - wasn't trying for a shiny surface.

[AaronVW]

Installed:

[Marty Jacobson]

Well done!

[Mike Conner]

Really good! I like the way the compensation notches blend into each other instead of sharp transitions.

Where did you get the posts and thumbwheels? I used the standard ones from LMI, and I have the ones from StewMac and they look the same. Are the ones you used a smaller size, more appropriate for mandolin?

//mike

[Bernie Daniel]

Very impressive work. Great thread and useful too!

[AaronVW]

I used the posts and thumbwheels from Bill James at Axinc.net. They are just right for mandolin, better than the ones I got from LMII before.

[Mike Conner]

Great site! Definately going to look at them for the future builds! Thanks!

[Pete Jenner]

Nicely done.

[belbein]

You guys all have my undying respect. I've been trying to salvage three partial bridges: I have just the bases, and have been trying to build saddles. And I've made every mistake that can be made: drilling the holes last; sanding on the belt sander; cutting the compensation slots with a dremel freehand; etc etc etc. And after weeks of work: not a single saddle. A lot of sawdust, though. And lots of creative new permutations of Anglo Saxon imprecations. But not one saddle. Which makes me wonder why (other than the Shake and Bake feeling of completion ["and I did it mahSELF!"]) anyone builds their own bridges.

[AaronVW]

Ha! I can see how you would feel that way. And I would say that building an instrument is full of opportunities for frustration and error. I just figured that I wasn't going to build an entire mandolin and then let someone else make my bridge! That's pretty much why I made my own strap too.....

[Mike Conner]

... Which makes me wonder why (other than the Shake and Bake feeling of completion ["and I did it mahSELF!"]) anyone builds their own bridges.

For my GOM build there are three reasons:

1) bridges, or just saddles, with the proper string spacing and compensation are not commercially available (maybe from custom order from Cumberland?)

2) I wanted to use a bone saddle insert for both tone and more setup options

3) what Aaron said!

//mike

[David Houchens]

And just having fun trying different kinds of wood.

[Darryl Wolfe]

Nice work Aaron

I've been doing this for many years. I pretty much started out as you have done. The one thing I found is that you can make a couple or so in this manner, but....for consistency and clean repeatability of the finish and look, you must jig up. I do reproductions, so it is imperative in that field that I get the "look" of the mass produced bridges from the 20's complete with microscopic machine marks from the cutter blade.

Here are a few photos from the other day. On one photo you can see my bridge template laying on the table (4th pic). This is used on my table router with a pattern bit. The bridge blank inserts into it and indexes off one of the drilled post holes via a pin.

It another photo you can see rough carved bridges as they come out of the template (last pic).

Some things I have not mechanized such as radiusing the bottom. A curved form on my table belt sander with 50 grit paper does this nicely, but is messy (1st pic).

I do the inset on top for the saddle with a little jig on my band saw (3rd pic).



However. My key to doing this is all of the initial work. I cut and dimension all of my stock to exact dimensions to the thousanth. I cut long strips for multiple tops and bases from the rough hunk of ebony. I then dimension exactly in the thickness planer. I then have jigs to cut each piece exactly to length. I have multiple jigs that allow the drilling of the saddles and bases to be done by virtue of the stock being accurate. This includes the saddle cutouts for the wheels and all of the drilling of the "first hole" in the pieces. I drill the second hole the exact distance from the "first hole" by virtue of a swing post stud on my drill press. Put the "first hole" on the post and swing it under the drill bit and drill.

I hope this helps you.

Keep up the good work.

I'm having trouble uploading the files...will edit the post

[AaronVW]

Thanks, Darryl! That gives me some good ideas. I think that in the future I will make some jigs in order to keep thing consistent.

[David Houchens]

Darryl, very nice looking work. Most of my work is done with jigs on a milling machine. I always want to do big batches. That's one way of it paying off for me. But it seems I'm always behind and only do two at a time. I'll catch up one day. I'd like to think so anyhow.

[Marty Jacobson]

Just thought I'd show off my new bridge... it has a beam which extends down into the base, which makes it nice and stiff, as well as keeping the saddle axially indexed to the base. The beam can be ebony or maple, depending on how light you want it to be. I was trying to solve saddle sagging and saddle rocking issues in one design. We'll see how they hold up. So far, so good. I've got a few in the field for a month or so.