How I make small mitre planes, part 8: The Bridge

The bridge, which traps the wedge, is made and brazed into place.

installed bridge

The bridge has been brazed into place, checking the fit with a feeler gauge

First
Add flourishes (a cupids bow in this case) to the bridge and polish. Brazing will tarnish that but it is a lot easier to clean up than to shape in situ.
Decorate parts of the shell that will interfere with the bridge before the bridge is added, in this case, a cupids bow on the front plate.

I use a wedge angle; it locks with hand pressure but the angle isn’t so low that it takes miles to lock.
I like the entry to be at least 1/2” thick and the front edge of bridge 1/8” (or more but not less) back from mouth (measured horizontally). The bridge itself is 3/4″ to 7/8″ long, depending on the positioning and eye appeal. I cut it long, decorate and trim as needed.

The leading edge setback is necessary when opening the mouth, it can be more but not less. It is close to the mouth so the wedge presses the front of the blade, where it matters the most.

bridge clamped for brazingPositioning
Transfer the alignment marks from the sole to the inside of the shell (visible in the photo). I like to keep the top of the bridge just a bit below the top of the shell so filing, polishing, etc the shell doesn’t effect the bridge. That will also largely determines the position of the bridge.
Don’t clamp too tightly, the sides will get a bit soft when brazing and the camp can dent the sides, especially if they are brass. I use wide steel pads (as clamp pads) for brass sides.
If the bridge is a tiny bit oversize, you won’t need to clamp it.

Bridge brazedSilver braze from the underside of the bridge (ie don’t add any filler to the topside); the silver runs everywhere and you only want the barest fillet on top where it is visible (says me who has a hard time achieving that). Use files and sand paper to remove the blobs (making sure the bottom of the bridge remains flat!); gun bluing will tarnish the silver so that it sorta blends (compare the leading photo of the shell/sole join with that of the finished plane).
If you do a nice braze job, the metal wedge will fit perfectly – the 0.0015″ feeler gauge (in the leading photo) can’t find any gaps.

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