Hi,

I plan to draw bore an M&T joint but I'd like the exposed peg to be
square. The piece is maple and the peg is ebony. AFAICT, I've got two
options:

1. I can round 90% of a square peg or I can
2. Use a dowel and cap the hole with a square end.

Number two seems like the easier solution (I don't have access to a
lathe), but I'm not sure how well the ebony will take the glue. If I
go that route, how deep should I square the hole to accommodate the
ebony cap? (I'll use an oak dowel in scenario 2.)

Any thoughts?

Jeff

3. Use a square hole and peg. Not necessarily an easier solution unless
you've got a square mortiser.

Jeff wrote:
Hi,

I plan to draw bore an M&T joint but I'd like the exposed peg to be
square. The piece is maple and the peg is ebony. AFAICT, I've got two
options:

1. I can round 90% of a square peg or I can
2. Use a dowel and cap the hole with a square end.

Number two seems like the easier solution (I don't have access to a
lathe), but I'm not sure how well the ebony will take the glue. If I
go that route, how deep should I square the hole to accommodate the
ebony cap? (I'll use an oak dowel in scenario 2.)

Any thoughts?

Jeff

On Jun 5, 1:27 pm, Russ wrote:
3. Use a square hole and peg. Not necessarily an easier solution unless
you've got a square mortiser.


I have drill press mortising bits but we don't get along very well.
If I botch this operation I lose about eight hours of work. When the
stakes are high, I trust my chisel over those things.

On Tue, 05 Jun 2007 10:17:49 -0700, Jeff wrote:

Any thoughts?

Buy this month's FWW. Big article on pegged tenons, drawboring and
chamfered tops.

My technique (from FWW over the years) is to saw square stock, then to
round half of it with a dowel plate. I then drive this in with a light
hammer, using a small wrench on the square to stop it rotating.
Chamfering is done in situ, using a special chamfering chisel. This is
just an old chisel about 1" wide, cut off at about 40° to make a massive
skew and fitted with a short handle. You use it with an upward
almost-levering action.

My chamfered pegs are almost always black, either African Blackwood, bog
oak, or if I'm desperate, ebonised oak or maple.

I've also made them in the past (especially small ones) by planing the
tops with a block plane and shooting block before inserting.


My flush pegs are round, made of assorted scrapwood (usually bamboo
chopsticks, but also hornbeam, fruitwood or whatever I'm using) sized on
a dowel plate.

Number two seems like the easier solution (I don't have access to a
lathe), but I'm not sure how well the ebony will take the glue.

I thought the point of draw-boring M&Ts was that they're held together
mechanically, so glue isn't as critical. If you're concerned, you
could sand the ebony's glue surface with a very coarse grit and use
epoxy.
I think I'd consider either using a round dowel with a separate plug,
or just using a square peg in a square hole. As long as it's cut
accurately, you shouldn't need glue at all, especially if the hole and
peg are tapered a bit.
And I'll second the recommendation to look at the recent issue of Fine
Woodworking - even looking through it at your local library or
bookstore should get the basics across.
Good luck,
Andy

On 5 Jun, 23:10, Andy wrote:

I thought the point of draw-boring M&Ts was that they're held together
mechanically, so glue isn't as critical.

No, they're more like putting a nut onto a bolt. It's the sides of
the bolt that take the load, the nut is just there to make sure the
bolt stays in the correct position to keep working.

A mortice and tenon shouldn't need to be glued. It's strong in shear
because of the tenon and it's rigid against racking because of the
shoulders of the tenon. It shouldn't be loaded in tension at all.

Of course for smaller work (furniture) rather than architectural
framing, these rules aren't always followed. Tenons are tensioned and
especially racked against (chairs!). They may also be cut less than
tight, so glue's needed for gap-filling too. In principle though, it's
still basically not a glued joint (they precede useful glues by
centuries). Their strongest aspect is shear sideways against the
tenon, which glue just doesn't help with. Racking can't be glued well,
because the shoulders are end-grain and so would be a weak glue joint.
The only real change glue makes is to make them resist tension, or to
resist racking by gluing the sides of the tenon.

This is why small tenons fail on chair legs - the large racking forces
are coupled into the tenon and overload the narrow neck. For framing
carpentry, a tenon should never fail, even though the forces are far
greater. The forces in that sort of structure might break a beam if
over-loaded, but agood design shouldn't fail at its tenons first.

Pegged tenons shouldn't be loaded in tension either. That peg isn't
strong, compared with the tenon in general. If framing breaks pegs,
then it's badly designed (or more usually, badly cut) and the peg was
taking a force that the tenon ought to have taken instead. In small
furniture peg break-out is a real problem (short-grain weaknesses) and
is usually caused by putting tension into an M&T joint. If you are
going to abuse this joint with tension, it needs to be glued as well.
You've now made a joint that contradicts centuries of joinery practice
and it will break when the glue fails in time. Traditional joinery
(dovetails etc.) is designed to start rattling loose after the glue
fails, but not to fall apart or to break.

On Jun 5, 6:10 pm, Andy wrote:
Number two seems like the easier solution (I don't have access to a
lathe), but I'm not sure how well the ebony will take the glue.

I thought the point of draw-boring M&Ts was that they're held together
mechanically, so glue isn't as critical. If you're concerned, you
could sand the ebony's glue surface with a very coarse grit and use
epoxy.

Glue is only a concern if I cap the dowel with a square plug of
ebony. I'm not sure how ebony will take to the glue. The dowel beneath
it will be fine as it will be held firmly in place by tension from the
tenon. The plug is a concern.

I think I'd consider either using a round dowel with a separate plug,
or just using a square peg in a square hole. As long as it's cut
accurately, you shouldn't need glue at all, especially if the hole and
peg are tapered a bit.

I think I'm going to try the suggestion above in which a square peg is
partially rounded to fit the hole with a doweling plate.
Unfortunately, I don't own a doweling plate. I ordered one last night.


And I'll second the recommendation to look at the recent issue of Fine
Woodworking - even looking through it at your local library or
bookstore should get the basics across.

I picked it up last night. Good stuff. Thanks.

On 6 Jun, 13:12, Jeff wrote:

Unfortunately, I don't own a doweling plate.

Handy things to have, and easy to make yourself. Good little exercise
in metalworking too: You make it very simply from soem O-1 gauge
plate, then harden it on the kitchen stove.

You can read about how to make one in my upcoming book 8-)