Biscuit joinery alignment - Woodworking Talk - Woodworkers Forum
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post #1 of 6 Old 12-31-2016, 10:22 AM Thread Starter
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Biscuit joinery alignment

I have been having a problem with the results from my BJ for a few years now and it's time to put it before you good folks to see if I can resolve the issue. When doing edge trim for shelves(usually between 3/4 and 1 inch thick), I typically biscuit join them. I use a DeWalt biscuit joiner. I cut the biscuit slots on mating pieces referencing the same edge of the wood(top or bottom). In addition, I typically create a flat surface from a piece of plywood on my bench to further eliminate any reference error from the joiner. In addition I clamp down the piece that I am cutting the slot in to prevent any space between the flat stock surface and the piece that I am cutting the slot in.

Inevitably, the pieces do not line up perfectly. There is always a lip that needs to be sanded or planed off. Given the fact of how careful I am to use all of the same (top or bottom) surfaces to reference the fence on the BJ, I still don't get a perfect joint.

Any ideas on how to eliminate this PITA situation ?

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post #2 of 6 Old 12-31-2016, 11:15 AM
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I have the same joiner and never had problems. First I make sure the fence is 90 decrees to the joiner. If the stock I am joining is thinner than the joiner's base I clamp it to a workbench so it overhangs the workbench. I reference from the top down. When I cut the slot I hold down the fence tightly against the stock and let the motor get up to speed and slowly plunge.
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post #3 of 6 Old 12-31-2016, 11:42 AM
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Biscuit jointers are not designed to give you a perfect joint. The biscuit is made of pressed particle so when the wet glue gets into the cavity with the biscuit, it will swell and tighten in the cavity.

Its' never hot or cold in New Hampshire... its' always seasonal.
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post #4 of 6 Old 12-31-2016, 11:43 AM
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I use it off the bench ....

Instead of using the fence, I use the base plate. It's "contrary" to the instruction manual. BUT some experienced woodworkers also use this method. Here's a thread I started here a while back:

You have a much larger surface to reference using the bottom of the jointer's base than the fence. Naturally, being an experienced woodworker I did NOT read the instructions, just winged it. Seems like it was OK after all.

The video of the "wrong" method ...

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 12-31-2016 at 12:00 PM.
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post #5 of 6 Old 12-31-2016, 11:47 AM
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My BJ is a Porter Cable. After glueing up, I can usually get everything flat using nothing more than a scraper.
The biscuits will still allow some up and down movement during the glue-up. It's important to keep your boards absolutely flat against the bar on the barclamps. Tap with a rubber hammer if necessary to get a smooth alignment during glue-up.

If you don't have time to do it right the first time, when will you have time to do it over?
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post #6 of 6 Old 01-02-2017, 03:05 PM Thread Starter
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Biscuit joinery alignment problem

Woodnthings - the pic of your set up; i.e. the dewalt BJ, the sheet stock as a base and clamping down the work piece is exactly the way I'm doing it with exactly the same BJ. On shelf trim which is typically only 3/4 to 1 inch thick, I don't typically reference off the top of the piece, mostly because the surface area of the top is not sufficient to stabilize the biscuit joiner. The way you have it pictured is far more stable to getting a good parallel biscuit slot into the piece.

I must be screwing something up between the two surfaces for them not to be aligned. Theoretically, referencing from the same surface on both pieces the alignment should be perfect.

Thanks for the tips to all. At least I know that the procedure I'm using is correct; it's just me that's messing it up.

BTW, I was able to correct the problem with a flush trim bit and running the piece through on my router table. So the project came out well.

Happy New Year to all.
Stay safe in the shop.

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