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How do you use a finger joint bit?

3730 Views 5 Replies 6 Participants Last post by  malb
Hello everyone, this is my first post here. I am working on a small living room project that involves joining one foot sections of poplar to make a long piece of trim that I will use as a baseboard. I decided to go with the Rockler finger joint bit 1-3/8" Dia x 1-1/2" H x 1/2" shank part number #22617. I made lots of test cuts out of scrap pieces from the same boards I will be using but never got both routed pieces to come together flush. they were always offset. The method I used was to mark the center point of the piece I was routing and aligning one of the bit blades to that center line, then creating my cut. then I repeated the same step for the second piece and finally turned one board over to bring them together. If anyone here could give me some better instructions as to how to solve this problem, I would appreciate it. this particular bit does not come with any instructions and I've already tried just about every video I can find online.
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This video is based on a different make, but the set up will be the same.
There are several other you tube videos, have a look.

There is also a lot of confusion about the names of these joints. "finger joint" should be used for the tapered to a point cutters that fix end to end.
Box joint is a square cutter designed primarily for making corner joints. Never assume the person your talking to understands the difference, always make the point, square, or tapered when ordering or asking for help..
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I’d say that you have a much better luck cutting the box joints with a very simple straight bit and a very simple jig. Save yourself the money and the frustration.

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It will be much easier to simply make a 45 degree cut widthwise not lengthwise on each piece and glue the two together. If done carefully the joint will be almost impossible to see.
Seeing how you own the bit and having issues with making it work I'd suggest calling Rockler and asking for their advice. They may well have a video that explains the proper setup and use of that bit. Better yet if they have a local store I'd go there in person if possible. Personally I haven't used a finger joint bit ...yet, but there is usually a certain setup that will ensure a proper fit, even with making box joints.
The standard approach for these bits is to have all components the exact same thickness, straight and flat with square ends. One side of the joint is cut face up, the matching part is cut face down. Centering of the bit in the material is then not as critical as it otherwise might be as the finished forms should automatically self align.

Obvious things:

If the materials are not exactly the same thickness, no amount of juggling the centre point of the board to the mid point of the bit profile will help, there has to be some misalignment on at least one surface of the joined product.

If the materials are not straight and flat, you cannot guarantee that variations in the surface will not affect the passage of the material past the bit, causing random errors in the finished profile that cause mismatching when joined.

If the ends are not cut perfectly square (or at perfectly complimentary angles if you wish), components will not be straight when joined, and will assume a snaking pattern in one or two dimensions when assembled.
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