I'll agree as one of the items often not quoted with the test results is the
type of stress that's applied. With dowels, the weakest direction is when
they're pulled directly out of the joint, as opposed to breaking. OTOH, moving
from smooth dowels to ridged dowels to ringed dowels makes a big difference,
yet most tests only say "dowels" and no more.
No one else seems to have mentioned...
If you're edge joining and using the dowel/biscuit for alignment, the
strength of the joint isn't in either.
If you're talking about using them in places where otherwise would be
something like a M&T, it's an indeterminate question as posed since any
comparison will depend quite largely on the size/number of the
dowel(s)/biscuits and the loading orientation.
I think you have opened a can of worms...lol
I do own a PC biscuit jointer ..and I do use it....
BUT to be very honest I tend to use dowels much more....as they
(Dowel) just seem to "fit" the work I do ...
Not going to comment on the strenght issue... both work well enough
for what I do...
Brands....? I settled on the PC.. BIt only after extensive thought
Start with a concept of load.
A biscuit installed parallel to the load has the shear strength of the glue
that holds it. A dowel - loose tenon - has far greater shear strength. A
biscuit installed perpendicular to the load has much greater strength, but
is still only 1/8" thick, vs. 3/8 or 1/2.
Then think withdrawal. Here the initial nod also goes to the dowel for as
long as the glue remains sound. Unfortunately, it's a cross-grain
situation, and the dowel will work loose of the glue with humidity cycles.
The biscuit suffers much less, and so over the long run will be better.
Now return to a real M/T and notice that it's also a great shear joint, but
cross-grained, and subject to the same, if lesser problems than its round
cousin. We pin the tenon, and there's a new shear kid in town. We have to
shear the pin to withdraw the joint. This is made extremely difficult by
the registry of the shoulder of the tenon with the face of the mortise.
Do you have some data for this? I'm sure you could calc the shear strength
of a hardwood dowel.
But where is your data showing that the glue has less shear strength? And is
it really the shear of the glue or the shear of the biscuit itself which is
at issue? I think I saw some photos of destructive testing of biscuit joints
out there. I seem to recall that they did not fail at the biscuit. Loose
tenons are a different story.
And is much wider. The cross section of the typical biscuit is much larger
than the cross section of the dowel.
A #20 biscuit has a cross sectional area of 0.35 sq in. You would need a
dowel 2/3 inches in diameter to match that cross section.
Not easy to use that size of dowel in 4/4 stock. :-) This is why the loose
tenon was invented.
I suggest you calculate the surface area before you make this conclusion.
I'm not going to do the math for you though. It looks like it is close.
Do more math: The dowel has the same cross-section throughout the
penetration into both pieces of wood, and the biscuit cross-section
lessens away from the joint. And, with today's glues the joint will
be the last to go. That makes the dowels the winners. Also there is
no comparison with strength of materials; a solid hardwood dowel wins
hands down over pressed paper.
We can theorise all we want until there is solid scientific
[experimental results] evidence one way or another to back up "common
sense". The point is that if you drop a ton weight on it, it won't
matter either way, and barring that, either is "strong enough", and
the important factor is ease and accuracy of assembly and cost, not
1) shear happens at the joint. that is the measure that matters for
shear. other modes of failure vary, but the section at the joint is
the relevant one for most of them.
2)biscuits are made from beech, not paper. most dowels are made from
birch. anybody with hard data about those species? I'm betting beech
has better strength than birch....
ease of use favors biscuits, unless you're talking about using big
dollar multi-spindle dowelling machines. strength data goes either
way, depending who you're talking to...
Sorry J - I wasn't asking what the cross section was. Typed out my reply in
too much of a hurry. I was headed down the strength of materials road. Was
it George or you that just posted the home brewed trials the other day?
That proved to be a very interesting observation.
My remarks were general observations on the nature of the three joints. The
ad hominem remarks made it clear that J is a convinced individual -
convinced that he's correct. I elected not to play.
Now, once again, you have the two loads to consider, and the information I
gave is accurate. Further, you have to consider the instantaneous blow -
the one which eliminates biscuits oriented along the line of load as
shear is a direct function of section. a dowel with a given section is
much thicker than a biscuit of the same section, so it weakens the
board it's in more. dowel joints often fail by blowing out the wood
surrounding the dowel rather than breaking the dowel itself.
On Thu, 03 Mar 2005 17:57:23 -0700, email@example.com wrote:
Ahh, I've been waiting to see if anybody raised that rather practical point!
I've also seen whole dowels pulled out of a joint, but I've never seen a
biscuit do so, as it breaks instead. Part of this may be the dowel having a
weaker glue joint, due to the relatively large amount of end grain. Once it
starts to fail, it either pulls out of the joint, or acts as a lever to blow
out the side of the wood.
Now, has anybody compared the difference between dowels, from smooth to ridged
to ringed? I've heard said that a ringed dowel is far stronger, but haven't
tried it or seen any data. Similarly, we now have the Miller dowel system as
I've ALWAYS used dowels and a doweling jig.. (30+ years)
and, I've always hated them but saw them as a necessary evil of some types of
Since getting the dewalt/craftsman b-joiner last year, I've put away my dowel
stuff in a deep, dark corner somewhere... IMO, biscuits make the dowel old
fashioned (not always a bad thing) and hard to align..
I seemed that no matter how precise I thought I was, (dowel jig, drill press,
etc.), some joints were just a bit off.. no problem with a biscuit, but hell
with a dowel..
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