I have done maybe 20 biscuit joined panels with a PC557. Typically over a
4' length, with 7 biscuits, there are a couple inches with a 1/16"
difference, and maybe a foot with a 1/32" difference. It takes a few
minutes with 80 grit to get them even. That is on the good side; the
backside can be much worse and take much longer to get even, if I bother. I
suppose the back would be better if I planed the wood, but unless it is
critical I just use the lumberyard's S2S, since no one will see it anyhow.
Is that typical, or should I be getting better results? If the latter, any
You should be getting -much- better results than 1/16th off, especially with
the spacing you're quoting and PC557. One common error is to use the fence
to register some boards (probably while stacked on top of each other) then
think you're using the fence on the last board but since it's sitting on the
benchtop, the base of the joiner is resting on the benchtop instead of the
fence resting on the board, throwing off the depth that the slot is cut.
If that's not the issue, how flat are your boards to start with and are you
using clamping cauls during glue ups? Even lumberyard S2S moves after
surfacing. Just a couple of things that I've found help. I've never had a
step of more than 1/64, easily sanded or planed away.
I have had much the same result with biscuits. Best panel results for
me have been with heavy cauls above and below the panel. The biscuits get
me close but the cauls pull everything into place. If the boards are planed
before joining, there should be only minute differences between adjacent
Ditto. Mill your stock to be even thickness and edges as square as
I see gluing up panels as a process of successive approximation. The
you converging toward a flat panel as you glue and assemble. The
certainly keep things
falling apart for multi-piece glue ups. Biscuits will not, IME
guarantee a flat panel
at the end of the day. I prefer cauls about every 18" along a glue up.
Biscuits are nice
but they are only an adjunct to good stock preparation and good
The biscuits (so the experts say) do not add any strength to a panel like
you're doing and are only used for alignment. Three biscuits should be all
you need. With the kind of offset you're experiencing, you're technique may
be off a little. I have the same model and if you are always referencing
from the working surface - then that surface should end up flat across the
joints (give or take a few thousandths).
But if you're getting a 1/16" difference - read the manual again and be sure
the plate of the PC is held flat to the working surface while you cut the
slot. The bottom of the PC should not be sliding or riding on anything. If
it is and as you say, you're using S2S then you're seeing the difference of
Below is an attempt at ASCII art to show how to raise the board using a
scrap board so the PC is not referencing to anything except the board your
cutting the slots in. The tilt-down plate of the PC is held firmly in=place
on top of the board. Now when you insert the biscuits in the slots - the
slots are all cut from the same reference point.
--------------------------| < PC Plate rests on top and held firmly
|-------- < Slot ~ 1/2 way referenced from top
| < Scrap board used to keep panel board
above workbench while cutting slot
There are certainly other methods you can use but I think this should show
why you are getting the offset.
You'll note that I qualified that statement. There have been several
articles in that past couple of years that when the various types of joints
were tested, biscuits did not significantly add any strength. As for your
statement - a long-grained, properly glued joint is stronger than the wood
itself and "should not" break along the glue line. So by adding biscuits
you're only moving the distance from the joint and biscuit where the wood
itself will fail. Besides, how much strength do you need in a panel glue-up
I don't think so. Using few biscuits over a length, the glue area is
much larger than the combined biscuit area which amounts to the
face-areas of the cuts being the "lost" area from both surfaces.
Otherwise, think of the two pieces being cemented with glue and no
Either way, the pieces are much stronger at the wood/glue surface than
wood/wood. The biscuits essentially act only as an alignment guide.
A Google will find other sources in agreement with this. The region
of the biscuit contact is very small over the length of most pieces
being joined this way. The glue over most of the non-bicuited length
is what is doing the job. Biscuits stop slipping and sliding in all
directions, and make gluing /clamping much easier than otherwise, an
they are used for alignment, that's all.
Think again. The biscuit is tougher to break across its random compressed
self than the wood along the grain just as the glue line is more difficult
to break than the wood.
So, though it's acknowledged as a difference which is really pretty
meaningless, it does is move the fracture zone a bit further from the glue
IME, the problem lies not with your biscuits, nor your plate jointer, but
the fact that you're using them with the wrong purpose in mind for the type
of stock you are using.
The key to good face and edge "alignment" of wood panels is in stock
selection and stock preparation. Biscuits, used properly in your example
above, only assist you in maintaining the alignment you achieved with the
first two parameters.
Without a jointer and planer, or practiced use of planes made for the same
purpose, you may not be able to get any better results with dimensioned
lumber than what you are experiencing.
A flat work surface is also of great benefit.
Remember, you are cutting the biscuit slots usually referenced to the
FACE of the board, and unless you are jointing the face of the board,
wood from the lumber yard is not really all that flat and straight to
How are you clamping and how are you attempting to keep the surfaces
FLUSH during the glue up??
Huh??? It's flat enough for bisquit work unless the stuff has 2" waves over
a 6' span. The bisquit jointer rides on the face and the edge of the boards
in an area about 4". Everything is relative to the top of the board, along
the bisquited edge. Not withstanding really warped material, flat from the
lumber yard or home center is flat enough for what he's doing. There's
something else wrong. Look - he claims a 1/32 to 1/16" error over 4 feet.
Either he's picking out some really bad - and I mean really bad wood, or
he's not holding his plate jointer properly when he's making the cuts. Or
rushing his cuts in some other way. Even if the lumber is warped - again
assuming an edge that at least appears to be straight and perpendicular to
the face, he should be cutting slots the exact same distance from the face
of each board in each location. He's not. That sounds more like he's doing
something wrong than bad lumber... at least to me.
Despite the "advice" thus far, you will never know what the real problem is
until you start out with stock that is milled flat, and to the same
Your goal is stock that matches perfectly when laid side by side on a flat
surface, If it does, then it is doubtful your application of biscuits will
throw it out of alignment.
If they do, then you can go from there, troubleshooting your plate jointer,
biscuits and technique..
Until then, don't believe a damn thing you read to the contrary until you're
sure your stock is properly prepared and dimensioned.
Aw, c'mon. As long as you reference the same face with a reasonable tool
and technique you match them - period, end of sentence. Proof of that every
time you join pieces at right angles. Same as unequal thickness, isn't it?
Aw, c'mon yourself ... or is it that you just want to argue this morning?
You know my point about starting with properly prepared stock is valid
probably better than most, if you do indeed teach woodworking as you say you
Once again, stock selection and preparation are the two MOST important
factors in a successful "flat" glue-up like the OP is talking about.
Start there, then solve any problems that remain ... (my contention is there
will likely be NONE in this case, but if there is you will surely be a step
ahead by being able to rule out twisted, warped, curved, bowed stock)
Now go ahead and continue to try and argue against those three points, and
their order, all you want, but you'll be wasting your time and looking
I agree I'm wasting time trying to get you to think, however, there is a man
with a problem who needs some help, which you're not addressing.
The only way you'll find the answer to the problem is by elimination, and I
don't mean the crap you're putting out, I mean by eliminating possibilities.
Thus, knowing that pieces of unequal thickness, if referenced and assembled
on the same faces will be flat eliminates unequal stock thickness as a
cause. Thus it's likely he's got bad equipment or technique which is
causing him to bore off square to the edge or ream the slots. That being
the case, he can get perfectly prepared stock and ruin it again with your
You can reach as far as you care to into your alimentary canal for further
straw men, but until you address the proper issue, you'll not arrive at a
And certainly don't do this experiment... Don't cut biscuit slots into a 2x4
and into a 1x3 and then try to join them together with the biscuits. Some
would not want you to see that the top edges should line up nicely even
though those two pieces of wood are different dimensions. Think about it -
how does your plate joiner index the wood?
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