Bridge Pin Pattern Lay-Out and Drilling

Take 1 sample note in each section, measure from front speaking length  termination point to front of bridge, then front of bridge to back termination point of speaking length. Enter to computer program to calculate down-bearing. 

Load the board/press down bridge with go bars to replicate downward pressure from strings. Raise up plate a little so it is not sitting flat on the soundboard. Make sure the bridge is still low enough for the ideal down bearing. 

Raise all bottom of perimeter bolts (WNG bolts are used here) so they are all just touching bottom of plate. The sensor in first picture will move its needle if the bolts are turned a hair too high. Rout down bridge at sample notes to achieve the ideal down-bearing. After bridge height is set at sample notes, plane down the hole bridge to match the samples. Sometimes the wood chips while being processed, repair accordingly. 

Lay the old bridge pin patterns on new bridges and mark where the original holes were as a reference. Mark all holes on uni-cords (bass string, 1 string per note) and bi-cords (bass string, 2 strings per note) but only center lines on tri-cords (steel wire, 3 strings per note).

Run straight lines from tuning pins (at V-bar section) or agraffes to hitch pins, mark string track without alternations, mark with a different colored pencil.

With the two references, even out the spacing of strings on bridge. Mark width between front and back bridge pins according to the original pattern.

Pick punches according to the original bridge cap, punch mark for bridge pin holes. The jigs here are custom made for the shop.

Before drilling bridge pin holes, make sure the size of pins and drill bits are planned and accurate. The drilling jig is set at 17 degrees with bubble level taped on for accuracy. It is better to drill at a mid speed. Too fast will cause the thin bits to burn and break.

When drilling, pay attention to the holes that may run into each other. Tilt the drill to avoid this. After drilling, sand off marks on bridge with sanding blocks from 150 grid to 400 grid. Now the bridge is ready to be painted with graphite and notched.

Note, also work order and method, from boss for the two days. The second note indicates... that he's pretty tired by the end of day. Fortunate to work at this little shop. It's been 6.5 years ^ ^.