Wednesday, February 29, 2012

I'm through with tenons (and can't wait to make more)

Perhaps the most challenging aspect of the step stool project is the mortises that house the through-tenons. This is a part of the project where any sloppiness will result in big gaps on the outside of the case. Further complicating matters, I needed to transfer the location of the mortises from the tenons marked on the inside of each side. With no good straight reference surfaces to register against, there was no good way to transfer those marks around to the outside face with marking tools.

The real trick to good through tenons (or any through joinery like through dovetails or box joints) is starting with good square joints to mark from. In this case, that meant making dead straight and square tenons. But with tenons this wide and long, I couldn’t rely on my normal techniques to get the job done. Fortunately, I won a Bad Axe Toolworks tenon saw at this year’s Woodworking in America (I’ve been keeping this a big secret) and this big boy really came through for me in this episode.




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6 comments:

Tom Iovino said...

You mean you WON a Bad Axe saw at WIA 2011? Holy smokes.. where have I been?

Rob Bois said...

Don't blame yourself Tom. I really kept the whole thing under wraps. I limited myself to no more than 11 gloat tweets per day.

Anonymous said...

you won the saw !? I thought it was that guy they call Bowis ? ;)

Project looks great so far.

Runningwood

nielscosman said...

Wait, you won a bad axe saw, like for free??? :)

Unknown said...

1. Any thought to using a double tenon instead of a single tenon?
2. Are you worried there won't be enough room side to side to fit the wedges?

Rob Bois said...

With a cross grain joint like this, a double tenon would actually invite the step piece to split in half as the solid sides expand in the summer. One alternative would be a single tenon in the middle with two additional tenons on each side with oversized mortises and no glue. That would allow the outside tenons to move back and forth within the mortises. However, the groove I used to seat the step effectively serves the same purpose of allowing the step to expand and contract while still being fully supported. In fact, I just took the finished stool to a show, and noticed the fronts and backs of the steps are now proud of the sides by about 1/16" despite being sanded completely flush a month earlier.

As for the wedges, I haven't gotten to that part of the project yet but you can either trim your tenon sides a bit shy of the full mortise width, or you can taper the outside of the mortise to create a very strong mechanical joint when the wedges flair the end of the tenon out. But you are correct, in one way or another you need to allow room for the wedges, otherwise you will not be creating a mechanical joint, but just a "friction" joint.