Hi
I've put together a dual router table designed to quickly cut alternating width box joints. The design was inspired by a Cosman video some time last spring. It does what I ask of it very well...but not perfectly. Before I say more, here's the setup:
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The backside of the fences have an inlaid t-track holding bolts through the sled, allowing me to slide the fence laterally to set the gap between the cutter and index pin. I set the gap on each side to the cutter diameter of the opposite side. The routers are currently set up with 1/2" and 3/16" bits, both spiral upcut whiteside.
So the issue, on both sides (both routers), the start of the cut is 0.002-0.004 wider than the exit of the cut. Put another way, the sides of the inside of the notch are not parallel. This happens to a greater degree with the 3/16" side than the 1/2". This occurs regardless of cut depth. As low as a .05 cut depth will produce non-parallel inside walls. The pictures below display this:
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Here are a few things I've addressed while trying to sort this out:
The index pins are rock solid and not flexing. They interface the workpiece squarely.
The sled has virtually no play.
The bits are sharp and true.
The routers are solidly mounted and square to the table (note the tape shims...miserable process). The MDF being compressed by the bolts has been saturated in thin CA glue.
There's a lot to be said about router & collet runout, but I don't think those would cause my issue.
The fences and table are flat, and square to each other.
Router speed seems to have something to do with it, worsening with some speeds vs others, but I haven't found a magic rpm that eliminates it. The cut in the pictures above appears very clean and is basically tear-out free.
Anyone have an idea of what's going on? Am I asking too much from this setup? Generally, this is an issue that I can live with, as the glue swells the joints enough to fill the gaps, but they have caused some grief on a few occasions.