Bisquit Jointer vs Dowel Pro Jig

[Lew Hodgett]

Having spent a few years doing machine design in my youth, was taught to avoid depending on a weld or fasteners alone to carry the load.

As a result, joints were designed to put the material in compression and welds were designed to be in shear.

The same design concepts apply to wood and adhesives used in furniture/cabinet designs.

Glue joints are very strong when placed in shear.

Glue joints are not nearly as strong when placed in tensile loading.

Simple and straight forward, but sometimes we forget to apply the basics.

Lew

[J. Clarke]

Further, the statement that "the glue is stronger than the wood itself" applies to commonplace species of wood glued into face grain. Gluing some of the exotics is problematical, and gluing end grain is as well. Note that in the Fine Woodworking test the butt joint was the only one that failed in the glue line.

Then there's the issue of creep--keep PVA under constant load and it moves, slowly, if the design of the joint doesn't prevent it from doing so.

[Robatoy]

Also, one must do a proper M&T joint for it to have all this 'magic' strength. A poorly fitted, poorly proportioned M&T can be quite fragile.

[Jack Stein]

I don't think a stub tenon will support much weight w/o glue? Stub tenons are common in cabinet door construction.

I don't own a biscuit machine, don't plan on buying one. I'm still wondering if I should spend the cash on a decent rail and stile set for my shaper. Having said that though, it appears that a properly fitted biscuit joint is comparable to a properly fitted M&T joint. Reading Robotoys article:

noted that a guy that makes exterior doors and gates has found after 3

1/2 years of using plate joinery that he has had NO failures. That would indicate that while M&T may be stronger, plate joints are strong enough for most applications.

[Jack Stein]

OK, then the question would be, is a biscuit joint weaker to the point it makes a difference? It would seem to me that if the joints were failing, no one would be using the $700 biscuit joiner? I know they are not needed for strength in long grain joints such as the original poster was asking, but assume they must work for end gain joints or why would anyone spend $700 on a Festool Domino, or a $30 HF for that matter?

[dpb]

Jack Stein wrote: ...

They're fine for face frames, light panels, etc., etc., etc., ... Their main advantage and why they're used as much as are is quick and easy and accurate.

They won't/don't replace m&t for anything that has any actual load--heavy doors, chair rails, etc., ...

[Jack Stein]

I agree.

I hear this all the time, and always wonder what happens when the moisture in the glue evaporates and the swelling recedes? Ideally, I would want the tenon to be stable, and the mortise to shrink around the tenon, not the other way around. I guess the glue itself could remain keeping the swelling up, but still, any moisture will eventually evaporate, and swelling should recede, right?

In other words, if the swelling DOESN'T last more than 4 hours, should I call the doctor?

Really though, glue simply doesn't work well on end grain, ergo the reason for M&T, plate, pocket screws, dowels and so on are still in use today. Glue failures cause all joints (dependent on glue) to fail, so joining techniques haven't changed joint failure rates much, but glue has. (Not sure that came out right, but I'm in a hurry)

Pocket screws do not require glue at all, and watching the TV guys apply a pint of glue (clear white glue so you can't see it when it oozes out all over your wood until you stain it at which point the folly of your ways has GOT to bite you in the ass, but not enough to keep you off the tv) always gives me pause to chuckle.

[Jack Stein]

If you think a M&T joint will be working after the glue fails, you also have a big surprise coming.

[MikeWhy]

Biscuits are mechanically compressed and dried. They don't shrink back to their manufactured size even after redrying in a kiln. They need to be stored in closed containers to minimize swelling from the moisture in the air.

Simplest test: wet one with a sponge and see what happens at the end of 4 hours. Try baking it for those 4 hours, just to be sure. (I haven't tried it. Just passing on my understanding of biscuits.)

[Tom Watson]

When I glue up solid wood panels I pay a lot of attention to stock prep. Eliminate all cup, crook and bow on the jointer, or with a plane. Get everything to the same thickness by making a final pass through the planer or sander using the same setup for all the stock to be machined. Rip all the pieces with a blade that will give you a glue line edge.

I machine biscuit slots about two inches in from a line that coincides with what the finished ends will be and about every twelve inches throughout the length. I use one biscuit on the centerline for boards up to about 5/4 and a pair of biscuits set no less than 1/4 from the faces above that thickness.

Here is where I differ from what some guys do: In my opinion, and it is only an opinion but it is based on observation and experience; I don't count on the biscuits for strength, I think the glue line provides the strength. I use the biscuits to reduce the clamp time so that I can have a quicker turn around time on the glued up panels. I also don't count on the biscuits for alignment, except in a very rough sense. I use a Lamello biscuit joiner and Lamello biscuits, which I believe to be more consistent in their properties than others that I have tried - and I still can't count on perfect alignment. So, what I do is drive finish nails into one edge of each of the boards , more or less in the center of the edge of the board and more or less on the centerline between the biscuit slots. Then I nip the heads off, leaving about a heavy eighth inch standing proud of the board edge. When I carefully assemble the boards together during a later step the pins will keep the boards even along their faces as I apply clamping pressure. It doesn't take very much time and it works.

I almost always use cauls top and bottom - this provides my final check for flatness of the glue up - but the pins help avoid all the beating and hollering that too often goes on at this point.

As always,

YMMV

Regards,

Tom Watson

[Luigi Zanasi]

replies dedicated to woodworking, including a relatively reasoned debate on the merit of various joints.

Thanks,

Luigi

[Tom Watson]

Do you know why I am convinced that Bruno Hauptmann did not kidnap the Lindbergh baby? Because he, when shown the crudely made ladder that was allegedly used to gain access to the child's room, stated that it could not be possible that he had made that ladder, "Because I am a carpenter!"

Why do I use mortise and tenon joinery, and why do I take great care with the proportions, machining and gluing? Because, "I am a cabinetmaker!"

Next case.

Regards,

Tom Watson

[Luigi Zanasi]

How do you get the pins to go into the spot that creates perfect alignment? The slightest pressure up or down could create an extremely shallow "V", resulting into slightly misaligned boards. I don't know if I'm explaining myself properly, but if you don't clamp with exact even pressure, you might get misaligned boars. I.e. What do you mean by "carefully assemble the boards together".

I would think that the pins might create some beating and hollering rather than avoiding it. Sorry, I don't get it???

I am also happy to note that after a gazillion years of people saying that they use biscuits "for alignment" in panel glue ups, that everybody is fessing up that they actually cause a slight misalignment. So it's not only me or my biscuit joiner or my biscuits. :-)

Luigi

[Tom Watson]

I have the boards resting flat on the bottom cauls and I push them together, one at a time. It doesn't seem to be a problem in practice. I find that most misalignment problems show up when you try to clamp the panel assembly up. The way that I do this is to put both the top and bottom cauls in place and apply moderate pressure with the clamps that go on the cauls, with the intent of keeping the panel flat.. Then I apply the side clamping pressure. What I see too many guys do is apply the side pressure before the cauls are engaged in keeping stuff planar. Then, if they don't use pins, the joint lines creep and they have so much clamping pressure applied that the caul clamps have a hard time making up the difference. That's when most of the beating and hollering occurs.

Well, it's true in a general sense. It is a lot easier to align a face frame to a carcase using biscuits than it is to just slap on some glue and try to clamp it up. Of course, you still need the judicious application of force to get things into final alignment. That's why I own a three pound dead blow. My goal is to get panels or assemblies like the face frame to carcase to line up good enough that a few scrapes with a cabinet scraper is all that is needed.

Regards,

Tom Watson

[SBH]

Being new to the craft, can you explain how this is done?

Thank you

[Lew Hodgett]

What part of a router bit doing it's job (cutting wood) do you need explained?

Lew

[Lee Michaels]

"Lew Hodgett" wrote

The router bit goes round and round, round and round, round and round.

[Robatoy]

I think you 'll be able to find an explanation when you do a Google search. (Don't tell anybody, but the natives get a little cranky sometimes....) =3D0)

[Luigi Zanasi]

Agreed, that's why I use cauls & gave up on biscuits. & it works most of the time, some time with a judicious application of the rubber mallet in may case.

But I do see your nail/pins also having a use in preventing the slick wet glued boards from slipping lengthwise.

Thanks Tom.

Luigi

[Andrew Barss]

:> > "Sonny" wrote: :>

:> >> How much better (and faster) is using bisquits, for keeping boards :> >> aligned, than is using dowels?  I don't have a bisquit jointer, but I :> >> do have the dowel jig.  I'm considering getting the bisquit jointer. :>

:> > You don't need to buy a busquit joiner if you have a router. :>

:> > A 5/32" slot cutter and a 5/32 straight bit and you you're covered for #20 :> > biscuits. :>

:> > Lew :>

:> Being new to the craft, can you explain how this is done? :>

:> Thank you

: I think you 'll be able to find an explanation when you do a Google : search. (Don't tell anybody, but the natives get a little cranky : sometimes....) : =0)

Good suggestion, but the basics for the original poster are:

The advantage of a dedicated biscuit joiner are that you can put slots into the edge of a piece of wood or plywood (there is a fence that pivots down; fence is placed against the wide part of the board, and the spring-mounted joiner is pushed into the wood, cuting a slot), and the face of a piece of wood, by clamping a fence (i.e. another piece of wood) across the board, retracting the joiner's fence, and placing the joiner up against the board.

You can do the same operations, but not quite as comfortably, with a plunge router (assuming you have one). For edge jointing, you use a bit that has a narrow, wide cutter (like an upside down T, with the upright part the shaft of the router bit), which cuts into the wood's edge.

For slots in the middle of a board, you plunge a straight bit into the wood and move the router along a fence so it's the right length.

Personally, I'd use a biscuit joiner if I have more than a few of these slots to cut.

-- Andy Barss