How perfectly flat are biscuit joined panels?

Page 1 of 3  
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 tips?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I
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.
Joe C.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
HI Toller, 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 boards. Dave
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dave W wrote:

results for

biscuits get

planed
adjacent
Ditto. Mill your stock to be even thickness and edges as square as possible. I see gluing up panels as a process of successive approximation. The biscuits keep 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 clamping.
hex -30-
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Toller,
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 each board.
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 of board |-------- | --------------------------| | | < 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.
Bob S.

I
any
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Howzzat? They certainly do add strength to the joint. It will now break outboard of the biscuits rather than outboard of the glue.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
George,
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 anyway?
Bob S.

like
all
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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 biscuits.
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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

like
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 line.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"toller" wrote in message

I
any
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.
--
www.e-woodshop.net
Last update: 11/06/04
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
My first question is how are you measuring the offset?
UA100
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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 start with
How are you clamping and how are you attempting to keep the surfaces FLUSH during the glue up??
John

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.
--

-Mike-
snipped-for-privacy@alltel.net
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I guess I am either not holding it level, or the S2S isn't flat. I will face joint some wood and test it out. Thanks
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"toller"wrote in message

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 dimension.
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.
--
www.e-woodshop.net
Last update: 11/06/04
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

is
jointer,
you're
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?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"George" wrote in message

flat
will
every
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 do:
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 foolish.
--
www.e-woodshop.net
Last update: 11/06/04
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

you
there
step
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 advice.
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 proper conclusion.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"George" wrote in message

man
And you're telling him to blame his tools instead of FIRST checking to see that his stock is not the problem?
... you're looking awfully foolish, George.
--
www.e-woodshop.net
Last update: 11/06/04
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

is
jointer,
you're
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?
--

-Mike-
snipped-for-privacy@alltel.net
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.