Making The Acoustic Belly Bridge
Source: Guitar Bridge Repairs
Making The Acoustic Belly Bridge:
While simple and elegant, the acoustic belly bridge has a lot of engineering built into it. It was designed so as to eliminate any need for mechanical attachment with supplemental screws, or bolts, despite that fact that some guitar makers still felt the need to add them. The bridge all by itself has enough gluing surface to withstand all gages of strings with the exception of heavy gage strings, which you should never put on a guitar anyway.
The Construction Process:
I’m assuming you have your wood purchased, and your plans for the bridge in place. If not refer back to the article on selection of these items in Acoustic Guitar Belly Bridge.
Bridge Plans: Acoustic Guitar Belly Bridge Plans:
Start by sizing your bridge blank with the proper width, length, and your selected thickness, (usually between 3/8″ and 1/4″ is normal). Make sure the blank is perfectly square in all dimensions!
Now you can choose to make a bridge template from your bridge plans or simply use transfer paper and trace the bridge outline on the bridge blank. Another method is to use spray adhesive to attach the plan to the wood and cut the bridge outline with a straight edge and a sharp marking knife and free-hand cutting the curves.
Use a scratch awl to mark the bridge pin centers and also both ends of the saddle.
Let The Cutting Begin:
Next take the blank over to the band saw and rough-cut the bridge outline. I usually cut about .5 mm outside of the line and sand to the scratch line for accuracy.
Belt Sander Time:
I would recommend you install a Stationary Belt Sander Fence on your belt sander if you don’t already have one. Here is an article on how to make one: Stationary Belt Sander Fence. Carefully hold the blank tight against the fence and sand all edges to the scratched line. On the curved portions you will need to hang the blank over the curved sander wheel.
Sanding The Ramps.
The Bridge Ramps are perhaps one of the most difficult items to make right. To help with this, I have developed a jig to make this process simple and repeatable with great results every time. I will make these plans available at the Plan Shop. Here is the article explaining how to build this jig: Belly Bridge Ramp Sanding Jig.
If this is to be a one time only bridge making venture, there is no need to make the elaborate jig described above. You can simply and carefully hold the bridge on the curved portion of the idler pully to sand the ramps. Just take your time and don’t force things. Go slow and check your work often. It helps if you trace the scalloped lines of the bridge ramps where they join the top of the bridge near the 2 end bridge pins. This will act as your guide.
Sanding The Rear of the Bridge:
The Belly Bridge has a rolled down edge at the rear of the bridge – on the other side of the bridge pins. This is easily contoured by holding the bridge perpendicular to the belt on the stationary belt sander. Hold each side of the bridge and “roll” the bridge across the belt surface as it travels beneath the bridge. This arching action will create a very nice radius edge on the bridge backside.
Drilling The Bridge Pins:
Now take the bridge to the drill press. Select the proper drill diameter and set your drilling depth. Use a brad point drill as this type bit will very easily center itself on the hole you pressed in with the scratch awl. Place a sacrificial piece of wood beneath the bridge to eliminate tear-out. Carefully drill each of the holes. Be sure to go slow when you drill. This is not a speed contest.
Countersink The Pin Holes:
I find it a nice feature to countersink the bridge pins just a bit. This is easily done with a ball-shaped bit, which closely matches the bottom of the bridge pins. Be sure to use a depth stop on the drill press so all of the holes look exactly alike. If you like do a trial and error on a scrap piece of wood the first time.
Route The String Ramps:
The string ramps are important in that they help to extend string life and make tuning the guitar easier. I just chuck up a 1/16″ or so straight cut bit in the Dremel Rotary Tool and start with the tool vertical and carefully lay the router down toward the guitar nut to cut a curved ramp into the bridge. Another and easier method is to hold the router on a 45 and make each ramp cut. Then, come back and round them by just touching them up with the Dremel.
The Saddle:
The saddle is best left for later. I usually make the bridge, glue it in place, then check the exact scale length and make any necessary adjustments and cut the saddle slot after the bridge is glued in place. We will discuss that in another article.
Tags: acoustic guitar belly bridge, guitar bridge, how to make a belly bridge, how to make a guitar bridge
