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Why Do Biscuits Hold

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Forum topic by mcase posted 1383 days ago 1330 views 0 times favorited 20 replies Add to Favorites Watch
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mcase

438 posts in 1730 days


1383 days ago

According to all woodworking wisdom, tenons set with their faces across end grain should fail. About five years ago I built a red oak platform bed with a hutch. The hutch (essentially a bookcase) has four 1×8” uprights and the top is attached exclusively with biscuits with their faces contacting only end grain in the top. Well they didn’t fail. In fact, I can’t get them to come apart. I wanted to turn this King size bed into a Queen. I thought I could salvage the hutch. I thought a few good bashes with a heavy mallet would free the end grain attachments on the top. All I received was a shock up my my arm and not the slightest gap or give on the joinery. Traditional tenons do fail in this configuration, but the biscuits held.
All thoughts welcome.
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20 replies so far

View rance's profile

rance

4125 posts in 1761 days


#1 posted 1383 days ago

1) They expand when you glue them, giving them a tighter fit.
2) The grain is crossways, not longways, for strength reasons.

To get tennons to fit like your biscuits, try loose tennons. Cut them a tad thicker than you need, soak them in water, then squeeze the hell out of them, or at least the water. Leave them in the clamp for days until they COMPLETELY dry. Lastly, after you take them out of the clamps, cut them to final thickness. Then when you add glue and insert in the joint, they’ll expand to TIGHTLY fill the joint. HTH.

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

#2 posted 1383 days ago

Well, I have serious reservations about the idea that biscuits “hold”.
They don’t qualify in my book as tenons and I fail to see that they offer any strength to a joint. I stopped using my plate joiner long ago.
I’m having trouble picturing this case as you describe it, but if it has one-by uprights there is a very good chance that it is the glue that’s doing such a good job.
What glue did you do? I find Titebond III has quite good hold and on side grain joints I never use anything in the joint but good glue.

ddwwb

-- Will trade wife's yarn for tools.

View Rick  Dennington's profile

Rick Dennington

3272 posts in 1795 days


#3 posted 1383 days ago

mcase: I have a tendency to agree with Don Butler on the biscuits, and the holding power they are suppose to be good for. I used them more for aligning the boards in a glue-up, but seems like everytime I did a glue-up, I had mis-alignment problems, as opposed to board-to board glue-ups. I spent more time planeing,
sanding, scraping, etc. to get a flat panel. So I quit using them for that purpose, and haven’t used my plate jointer in several months. No matter how flat and true the wood was, it happened nearly everytime….I wasn’t relying on the biscuits for strength so much as for alignment.I’ve used Titebond II and III for all my work, and found it sufficent for holding power….No more biscuits for me….And if I have a big glue-up with a lot of joints,
dados, etc., I use the Titebond Extend to gain that extra several minutes for glue set…. Works for me…

Edit: I will agree on the fact that biscuits do hold to a certain degree once they swell up and expand in the wood, but you have a very small window there to work with them…..


-- " I started with nothing, and I've still got most of it left".......

View Lee Barker's profile

Lee Barker

2163 posts in 1451 days


#4 posted 1383 days ago

I think mcases’ original post is describing biscuits whose slot is cut at right angles to the grain direction in the receiver. That would be an endgrain glue joint, not acceptable in traditional thinking. But they do hold that way, and I think it is more mechanical than chemical but still a combination of the two.

I do not use biscuits in a situation where there is shear, as in chair skirt to back leg. But they are useful to have in the arsenal and I think it is a mistake to dismiss them totally.

Regarding problems using biscuits in alignment for edge gluing, I submit that’s a problem that is most likely laid to the machine. Technique is a factor as well, but to expect the kind of precision you want in that situation from a poorly designed and/or sloppily built machine may be a mistake. We have all discovered that there is a reason good equipment costs more than not so good equipment, and reality dictates that we make our own decisions all along that continuum.

-- "...in his brain, which is as dry as the remainder biscuit after a voyage, he hath strange places cramm'd with observation, the which he vents in mangled forms." --Shakespeare, "As You Like It"

View Rick  Dennington's profile

Rick Dennington

3272 posts in 1795 days


#5 posted 1383 days ago

Lee: I beg to differ on two points you made: The jointer that I use is a DeWalt DW682, and it is not a cheap jointer, and as far as I know, there is nothing wrong with it..When I used it, I always double-checked to make sure everything was right before starting..Set at 90 Degrees, 45, etc., everything locked like it needs to be…So the machine is not the problem. It does eveything it is supposed to do, with clean cuts, also. I used it long enough to discount technique (I believe for myself), but yes…I do agree that a cheap-made machine will not give you good results in what you are after, or wanting it to do….DeWalt p.j. are not cheap, and I consider them a high quality tool….Maybe I had too much coffee the days I was using it…...or not enough..lol.

-- " I started with nothing, and I've still got most of it left".......

View Lee Barker's profile

Lee Barker

2163 posts in 1451 days


#6 posted 1383 days ago

Well put, Rick, and I certainly agree about the DW. I had one as a second, and wish I hadn’t sold it. And I also am in tune with your comments about technique—I don’t question that.

So what’s the variable that made your boards misalign? Any ideas?

I use a Lamello Top 20 (cost me $908 at the time—an unforgettable, stomach acid squirting kind of price tag) and while I can’t say that joints are perfect, they’re as close as you’ll get in woodworking. Picking it up does not involve any kind of compromise thoughts in my head.

That said, I don’t use it for aligning boards for glueup—it just seems like extra work and time with nothing improved over walking the boards together and whacking with the mallet where the misbehavior occurs. And there’s certainly no reason to seek extra glue surface in a joint like that.

-- "...in his brain, which is as dry as the remainder biscuit after a voyage, he hath strange places cramm'd with observation, the which he vents in mangled forms." --Shakespeare, "As You Like It"

View KayBee's profile

KayBee

999 posts in 1847 days


#7 posted 1383 days ago

I have the DeWalt and the same problem. It’s pretty common. If I recall, the blade/motor isn’t flat in the housing. Anyway. If you check both the tip of the blade at right and left on a flat surface, there’s a small difference. Very small, but it cuts the slot at an angle, not parallel to the fence. The difference isn’t big enough that things don’t go together, but it actually pulls the boards out of alignment. Slots are going in opposite directions. Haven’t figured out a good fix yet. Mostly don’t use biscuits much.

-- Karen - a little bit of stupid goes a long way

View Rick  Dennington's profile

Rick Dennington

3272 posts in 1795 days


#8 posted 1383 days ago

Lee: Thanks for your thoughts on the problem at hand…There most certainly was something there that kept the boards mis-aligned…not all the time ,but pretty much.I never could quite get a handle on it as to why. I do as you do and once bisquit jointed and glued, they went into my Bessey clamps, and loveingly tapped together and flat (or so I thought), and after 5-6 hrs., or overnight, they would be mis-aligned a very little…UUUHHHHMMMM…....just read KayBee’s post….That surely could be it…I’ve never noticed the slots being slightly angled, and didn’t know about the blade/motor problem…Sounds like she may hit the nail on the head.
I’m gonna cut a few and see if I can spot it…..Thanks again Lee and KayBee….Oh, and Lee….I had that same gut wrenching feeling when I too looked at the Lamello. $980 will buy a lot of coffee…..lol. I’d need a couple of pots if I bought one to settle my nerves…... lol..

-- " I started with nothing, and I've still got most of it left".......

View Lee Barker's profile

Lee Barker

2163 posts in 1451 days


#9 posted 1383 days ago

On we go, Rick. My first BJ was the ill conceived and worsely made Porter Cable, was it 555? There was no tracking at all on the fence, so you were on your own, trying to get it parallel to the blade (which wanted to duck back into the tool, duh). Impossible to do, period. That was the worst power tool I have ever purchased.

Reading your post, I thought it might be fun to find out what is acceptable error in a BJ. So I just took a piece of 1” MDF and cut four slots in it with my Lamello. I used the stock on-board fence, not the auxiliary one. I am surprised at the accuracy. I measured with a digital dial caliper, #20 cut, 6-7mm in from the end of the slot. Two of the four varied .001, one varied .0005, and one was dead on.

It’s further testimony to the quality of this tool to note that this is the one where you can raise or lower the blade with a knob on the top of the housing!

BTW, I am in no way connected with Lamello or Colonial Saw etc.

-- "...in his brain, which is as dry as the remainder biscuit after a voyage, he hath strange places cramm'd with observation, the which he vents in mangled forms." --Shakespeare, "As You Like It"

View mcase's profile

mcase

438 posts in 1730 days


#10 posted 1383 days ago

Lee,

“I think mcases’ original post is describing biscuits whose slot is cut at right angles to the grain direction in the receiver.”

Yes that is precisely the situation. I don’t use them where they are subject to leverage as in a chair, but in this static situation they seemed to hold up great after 6 year despite that the receiver piece (the top in this case) was joined with an all end grain glue surface. PS. I had that same original Porter cable which I replaced with the very respectable new Porter cable. Thanks for you input.

View CharlieM1958's profile

CharlieM1958

15663 posts in 2819 days


#11 posted 1383 days ago

Dual Lamellos? Sexy.

-- Charlie M. "Woodworking - patience = firewood"

View extremehobbiest's profile

extremehobbiest

42 posts in 1587 days


#12 posted 1383 days ago

Ahh – PC-555 reunion. Had one of those too and sold it. Replaced with the DW682 which refused to cut a slot parallel to the face of the wood. This experience has obviously been experienced by others. I would never describe the DW682 as a high quality tool with that major performance deficiency. I replaced it with the Lamello Classic C2 and all biscuit alignment problems went away.

View Cato's profile

Cato

641 posts in 1913 days


#13 posted 1383 days ago

I have the PC 557 I think is the model # and I too use it for indexing alignment.

It seems to work well for me in the panel glue ups I have done, but then again my efforts at fine woodworking are not that extensive, and maybe its a confidence thing mixed in as well, since glue ups can be stressful at times.

I guess I find it handy for the dry fit positioning to make sure that I am a go for glue up. I figured scraping glue off and light pass back thru the planer were part of the finishing process anyway.

I would be stoked to glue up a flat panel that only needed the glue scraped off!! Maybe one of these days in my dreams, but for now I still lean on the PC for a lot of joinery.

View supervato's profile

supervato

153 posts in 1530 days


#14 posted 1383 days ago

For the most part all i use them for is face frames. Really dont use them for anything else. Tell you the honest truth when used them in glue ups they really didnt help alignments very well. Now that i have my joining skills and planing skills where they need to be i dont use them. I have also heard they nhave really no structural increase in strength. Now i would say the glue you put in between the biscuits on the edge grain or on the biscuits is the strength your feeling. I guess wht im saying is they have thier place.

View a1Jim's profile

a1Jim

112000 posts in 2178 days


#15 posted 1383 days ago

Like all joinery there are places where biscuit joinery is fine and places where I think other joinery is far superior.
Sorry Rance but I don’t understand the idea of compressing a shop made loose tenon , I think it is completely unnecessary with today’s modern glues and may create a split in the wood rather than hold better.

-- http://artisticwoodstudio.com Custom furniture

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