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:
I can round 90% of a square peg or I can
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.)
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.
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.
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
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.
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'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.
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-)
HomeOwnersHub website 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.