Chair Joinery Questions

[Bob Jones]

I've been reading about chair building recently. In green woodworking, it seems common to oversize the tenons a little, dry them for a while, and drive tenons in to the mortises for a strong joint with no glue (being mindful of the grain orientation). How is it that this does not split the mortised leg immediately?

Tapered tenons - These seem to be used only for the joint that connects the leg to the plank seat of a windsor chair. Would you ever use tapered tenons to connect the legs of a "post and rung" type chair? Why or why not? What if you wedged them?

Reason for asking? I think tapered tenons look like a good idea that could be easy to execute with the LV tools, but I'm thinking there is a reason I don't see more of them connecting chair legs. The Rorkee chairs by CS has me wondering why that is not more common.

FYI - I've been reading Mike Abbott's book on chair building. It is a great step-by-step tutorial with nice pictures. It does have me wanting to try some "greeen woodworking", but I'm finishing up some cabinet work first.

thanks for any help!
Bob

[Jim Koepke]

Would you ever use tapered tenons to connect the legs of a "post and rung" type chair? Why or why not? What if you wedged them?

I think they would likely fall apart over time.

I think with the green wood joinery there is some flexibility in wood before it is dry. In one video the workers were cutting the mortises with shell bits so they could make a hole that is bigger inside than the entry of the bit. The tenons were more like a knob. Once they were put together and things started to dry (shrink), the parts were held together tightly.

jtk

[Mike Holbrook]

Amazon is "out of stock" for Mike Abbott's newer version of his book on chair building. They were also "out of stock" on John Kassay's " The Book of American Windsor Furniture: Styles and Technologies"... Apparently interest in green woodworking and chair making is on the increase. There is an interesting video on YouTube, The Final Squeeze by Abbott which shows a class in which he is squeezing green wood joints together using a big clamp. I don't see any glue being used. If all the parts are "green/wet" maybe the various parts all shrink together? As we know it all moves some. I think I am ok providing the link to the video below, more are available at Mike's site, living-wood.co.uk.

https://www.youtube.com/watch?v=JsvRJIquuXE

[Sean Hughto]

I've built several stools and benches, but only one chair so far. So I've got a bit of real world experience making these joints, but would by no means claim to be an expert. My experience is that its easy to split a seat with either tapered tenons or in wedging them. Now I haven't made anything from green wood that is still wet (as opposed to air dried stock), so maybe that is different. I've found that with a lathe And good drill bits, making well fitting cylindrical m&ts is not hard. Modern glues and wedging make for a very strong joint. Learning to make good fitting wedges and to drive them only until seated takes some practice though. Fwiw

[Mike Holbrook]

I am putting together a chair kit, as I wanted to try a bowback, side chair, windsor for the back problems I have and I don't have the tools together to make one yet. The instructions say to simply split the chair spindle ends and place wedges & glue in them to hold the spindles in the seat and bowed back. Splitting the dried wood on those thin spindles makes me nervous. I am thinking about drilling a small hole at the depth I need and sawing down to it with a very narrow backsaw or bowsaw blade.

[Bob Glenn]

A couple thoughts;

Wedged spindles ( in windsor chairs)......If you wedge a spindle into a seat (called a fox wedge sometimes) cut the spindle rather than split it. I don't however see any reason to fox wedge a spindle, since there is little if any tension pulling on the spindle. You can and should wedge the spindle where it goes through the bow. I usually start a split with a chisel after the assembly, then insert a wedge glued on one face only. Be sure the split is perpendicular to the grain in the bow.

Tapered tenons...... a tapered chair leg tenon can split a seat if driven in too hard. When wedging, as above, be sure to drive the wedge perpendicular to the grain to prevent splitting the seat. Tapered tenons work well when in the vertical but I don't think they would work well horizonally, since the torquing forces side to side would work to loosen the joint.

Peter Galbert and others have successfully made windsor chairs with only wedged m/t joints, no glue. The key to success is in good design and well fit joints.

Instead of making your tenon over sized then drying them and driving them into the mortise, it is easier to cut the tenon over size, dry it in a kiln, then size it to fit mortise. The small amount of moisture differential between the two pieces will equalize and lock the joint together.

I wouldn't use green wood to make your seat, then put a dry tapered tenon leg in the mortise. I think you would have a split seat a year or so down the road.

Good luck with your chair.

[Bob Jones]

Thanks for all the good info!

[Steve Baumgartner]

Much good info from Bob Glenn. I took some of Mike Dunbar's courses and have made about a dozen Windsors, and his guidance agrees. The most important aspect of wedging a tenon is to make sure the wedge is perpendicular to the grain in the mortise part. That way the wedging force is along the grain, which won't split, not across the grain, which will. This applies equally to spindles going through back bows and to legs going into seats. You'd be amazed how easy it is to split a 2" seat blank!

With years of moisture cycling, tenons will inevitably become compression set and then loosen. That is, when they expand in high humidity they in effect crush themselves inside the mortise. Then when they dry out, they are a bit smaller in size than originally. It helps some if you orient the grain of a leg stretcher so that the tangential grain is parallel to the long grain of the leg. That way the expansion and contraction take place mostly across the width, which is also the direction that the leg will give a bit. The long grain of the leg will yield very little, and makes the compression set worse.

Compression set is the reason for using tapered tenons where the legs meet the seat. On those joints, the weight of the sitter presses the joint back together and keeps it tight. Of course, the price paid is that the tenons eventually protrude above the top of the seat. And, there is no point tapering the tenon unless it goes all the way through, since when it bottoms out the self-tightening action is defeated.

One way to keep leg stretcher joints from coming apart is to intentionally pre-stress them by making them a bit longer than the exact measurement between the legs. That way when weight on the chair tries to push the legs apart it is just reducing the pre-stress, not actually getting to tension that can pull the spreader's tenon out of the leg.

Steve