Biscuit Joiner Problem

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I have a DeWalt Biscuit Joiner that I use to make boxes or cabinets. That is 2 sides and a top and bottom. The fence for the joiner is set at a height of 3/8" and is is down, or parallel to the blade. I am using 3/4" plywood. My method is to place the top and bottom pieces on a flat surface with their inside faces up. I have one end of a piece overhanging whatever surface the piece is on. The other end is clamped to the work surface. I then place the joiner wherever I have made a mark and position it so the fence is pressed against the end edge. The slot is then made into the inside face, parrallel to the end edge. The distance from the end edge is the same as the distance of the fence from the blade. I now lay the side pieces down with their outside faces up. I place the fence of the joiner on the outside face and hold it there. The joiner is pushed against the end edge of the side and the slot is cut. I then place the biscuits and glue and clamp the pieces together.
My problem is that when the glue is dry the top and bottom pieces overhang the side pieces by about 1/16". This happens at all 4 joints and has happened on several cases I have built.
Can anyone tell me what I am doing wrong? I use a router with a flush trim bit to correct things but I would like to avoid having to do that.
Thanks for any and all help.
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Kinda hard to tell from the description (got a headache, not your fault), but there is one rule you want to follow without fail: Mark your reference surfaces/faces (the ones you want to be flush to each other); and always make cuts from that "referenced" surface, face, edge.
If your tool is in good shape and the blade is not wobbling, it's pretty hard to not come out with flush surfaces providing you consistently cut ONLY from that "reference" surface/face.
Do things line up when you do a dry fit?
If your biscuits are too loose in the slot due to a dull or wobbly blade cutting an oversize slot, you may want to check your clamping technique.
In that case, these might help:
http://www.e-woodshop.net/Jigs.htm
Scroll down to "I-Beam Supports/Clamp Assists".
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Check the slots you've cut in the ends of the sides, and you'll find that they are about 1/32" closer to one face than to the other.

The procedure you describe should produce dead-on flush fits, regardless of the thickness of the stock or the setting of the joiner.
If your description of the procedure is accurate, then you're somehow reversing the side pieces inadvertently when you assemble the case.
I can think of two ways this could happen: a) you lose track of which faces are inside and which outside b) you inadvertently switch the left and right sides, and the front and back sides (which would have the same effect, putting an inside face outside).
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The problem id that you are not using 3/4" plywood. The 3/8" mark is not the center of the plywood sheet. It is, however, making the slots 3/8" from the edge of the side, thus the mis-match. It may be OK if you flip the top and bottom plywood over so that the 3/8" slots align. You can make fine adjustments until they do align. Meantime, measure the true thickness of the plywood.
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With all due respect, Ed, if he has described his procedure accurately, and is not inadvertently reversing the pieces before assembly, it won't make any difference whether the plywood is 3/4 of an inch or 3/4 of a mile thick, the slots will still be in the right place.
Tweaking the adjustment of the joiner until the slots are exactly centered is an unnecessary waste of time and wood: no matter what the thickness of the wood is, no matter what the distance from the reference edge is, the machine always cuts the slots at the same distance from the reference edge. If the reference edges line up, the slots will too. His problem is that his reference edges aren't aligned properly when he assembles the case.
Can't tell from here if he's inadvertently swapping inside/outside faces, or left/right and front/back pieces, but he's sure doing one or the other.
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You are correct that the distance does not matter if the pieces are oriented the same way, BUT, stuff happens. Getting the slot centered, while not a necessity, has the advantage of making the parts universal. While you say it is a waste of time and wood, if it solves his problem, it eliminates the extra trimming step he has now. . Either way works as long as you do the layout and mark the parts for the proper side to match.
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3/4" isn't made any more. Measure it! It isn't 3/4" anymore.
It is likely 11/16. Being 1/16 thin because it is metric or they are stealing 1/16 due to some tree hugger law or judgment.
Martin
Doug Miller wrote:

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RE: Subject
A 6" dial caliper is your friend these days.
Lew
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It doesn't matter whether it's a full 3/4" or 1/16" shy or whatever. If he's cutting slots at some fixed distance, whether it's 3/8", 5/16", or whatever, from some reference point on each of the mating pieces, and installing them with the reference points in the correct relationship to each other, everything will fit. His problem is that he's reversing the pieces somewhere, somehow, between the cut step and the fit step.
My guess is that the OP *thinks* he's cutting slots exactly in the center of what he *thinks* is true 3/4" plywood and therefore *thinks* the orientation of the reference surfaces doesn't matter.
It's true that if you really are cutting slots in the exact center of the plywood, then the orientation of the reference surfaces doesn't matter -- but that's not the optimal way to look at the problem. Things work much better if you realize that if you keep the reference surfaces oriented correctly, it doesn't matter if the slots are in the exact center of the plywood, or a little bit off-center, or a lot off -- the pieces will still line up.
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That's provided everything else is done properly. He might not be holding the joiner completely flush with the wood. There might be a burr on the joiner. The wood might not be cut perfectly straight. Hell, even the biscuits might be slightly undersize or otherwise flawed. There could be any number of reasons his cuts are not lining up properly. If everything else is as it should be, then Doug is correct.
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Well, yes, but those issues will cause misalignment regardless of what technique is used. My point is that instead of obsessing over getting the slot exactly centered in the workpiece, it's much simpler to just make sure the reference surfaces are in the proper orientation when the piece is assembled.
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assembled.
Sure, you're right. As far as alignment goes, it doesn't matter where the slot is really as long as the mating slot is lined up with it. Having them centred only adds to the strength of the join and has nothing to do with alignment.
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"Doug Miller"

Sheeesh, folks! Read the above and take it to heart ... if you want to give yourself every chance of success in this endeavor, in a world where things will go wrong if given a half a chance, there is NO better method ... PERIOD!
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Absolutely true. But no matter how well you mark them, they eventually will be put together the wrong way.
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Thus the inclusion of the phrase: "in a world where things will go wrong if given a half a chance, "
:)
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So Kim comes up to me this morning with a dowel that she located in "my" shop and wanted me to cut it "ABOUT" in half. She is waving that thing she brought over to show you and yours last night and wanted a dowel to put in the end of it. I had already forgotten "what she sewed" was for and figured she wanted to use the dowel to hang the piece on the wall. Soooo she says the dowel needs to be shorter than the width of the thing she made but almost to the ends. I laid the dowel on the thing she made and marked where the cut should be with her watching and agreeing with the location of where the cut should be.
I went out to the shop and cut the dowel and brought both pieces back in. As it turns out I had actually marked and cut the dowel "ABOUT" in half as she had requested.
When I handed the 2 dowels back to her she compares the lengths and says "they need to be the same length" !!!!!
GEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ!!!!!!!!!!!!!!!!!!!!!!!!!!
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"Leon" wrote

GEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ!!!!!!!!!!!!!!!!!!!!!!!!!!
Ah, yes ... the cry of frustrated testosterone being overwhelmed by the logic of estrogen. We know it well! :)
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"Swingman" wrote

That we do.
My favorite is the which restaurant do we eat at routine. I go, "Where do you want to eat honey?" She sez, "Oh, anywhere is fine with me." I go, 'OK, we will eat at the __________ ." She goes, NOOOOOOOOOOOOOOOOOO!!!!......., we can't eat there!!!!"
Feminine logic at its best.
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Being a card carrying coonass, I'll eat just about anything, so I just let her decide ... of course, and once the menu is presented, it has to be properly scrutinized for substitutions, and lengthy negotiations commenced with the wait staff, because there is obviously no way in hell you can just simply accept what is on the damn menu, eh?
There was a story in the news this morning about a hermit in the piney woods of East Texas. I've begun to understand the appeal ....
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Absolutely! I have learned through out the years that proper technique or method is EVERYTHING. I seldom measure anything on a project anymore except for the length and widths that have to be a particular measurement. The more things you can do with out a tape measure the less mistakes you will make.
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