Hi All,
I am building some chairs with tapered tenons on the legs. I live in Albuquerque and so more or less I work in a kiln (my garage). My thought is to build a small enclosure for the seat blanks and put a household humidifier in there for a few hours before drilling out all the mortises to get the relative humidity of the blanks higher than the legs.
Does this a) sound like a reasonable idea b) sound like a total waste of time and I should just wedge them in and call it good.
They are tapered so if the tenons shrink they would theoretically just go further into the chair and I recently built a chair that is purely mechanically joined with wedges and it is rock solid and it moved from Jersey to ABQ so maybe I am overthinking it.
Appreciate any feedback!
Replies
It will take more than a few hours to change the MC of a seat blank. I think you want the moisture to go to the center of the blank which will take days or weeks (depending on humidity and size). Weigh the blanks to see how much MC change you are getting. Humidifying might be worth doing if the wood is very dry (<5-6%). Otherwise, I'm guessing no.
Your question is difficult without actually knowing the MC of the blanks and tenons. Having the MC of each similar (within a few %) is important. Having them in the range of 7-10% is also important. This is the midrange of what they might be throughout the year. People in coastal areas can go a little higher.
One thing you could do (without a moisture meter) is to bring the pieces into your house, weigh them, let them sit (with air around them) a few days to a week and weigh again. They are below the equilibrium moisture content in your house if they gain weight. Repeat. They are close to the EMC in the house when the weight gain slows way down.
I have the opposite problem as you. The EMC is high in my mostly unheated shop in the winter. I take the wood into the house a week or more before I start a project for which MC change would be bad. I take it back into the house each night as I'm doing a project. I monitor it with a moisture meter as well.
After saying all that, I have to admit to building four Oregon maple kitchen stools with backs last summer and paid little attention to moisture. They had both tapered and wedged tenons. MC didn't seem all that important with no miters or long gluelines. In contrast, a few months ago I built a kitchen butterfly table with madrone (high shrinkage species) mitered edges and was very careful about keeping materials in the drier environment of the house.
Thank you for the thorough response! That makes sense with what you are saying re pieces with exposed glue lines vs tapered tenons. I think I will take your advice about moving the blanks into the house and weighing them - or maybe I should just get serious and buy a moisture meter at this point. Much appreciated!
The other way to go would be to super-dry your tenons prior to assembly. Curtis Buchanon's "Democratic Chair" videos have a section in there where he talks through it. I think it's a simple light bulb in a box setup. The net result is the same; lower MC for the tenons.
Of course he does not work in a kiln...
I think this will be the approach I take moving forward - I already cut my tenons, but I could super dry them as you suggest and then just give them one more shave in the tenon cutter. The result will be that they just protrude a bit further through the chair and I cut off a bit less of the leg at the end so no big deal. And in theory the MC of the tenons will still be lower than the chair even if it isn't a huge difference. I think that, combined with the wedges should make these pretty solid. Thanks for the feedback!
I've seen many (most?) chairmakers use a light bulb kiln to dry their tenons. I've never heard of someone humidifier their seats.
I'm in agreement with the above -- I think it will take a long time to raise the seat's moisture content.
So we’re fabricating 200 colonial style chairs per day from sugar maple in Canada, shop is heated in the winter so very dry and not air conditioned in the summer. Seat blanks are 1 1/4 inches thick, legs, stretchers and backrest spindles are turned on automatic lathes, backrests are steam bent and dried in a kiln. They all come together about a week after having brought the wood in the rough mill , sometimes the seat blanks comme pre-fabricated from a sub-contractor on a flat bed truck. 50 years later, regardless if they are in a home or unheated garage, they hold together perfectly going through seasonal changes with grace, my mom, 95, still sits everyday in her Roxton/Vilas rocking chair, only the varnish on the arm rests have worn away.