29 September 2010

Woodworking course - 4

We finished our lap joints,  T-lap and end lap and tried out a slip joint

After that we made a first try to make a machined haunched tenon joint
Lay out:  We work with fifth for the haunch height and the depth of the mortise,  where the tenon is made a tenth short to allow some room for glue.  The tenon gets over one third of the thickness of the wood.  In this case 10mm for 25mm thickness (3/8" and 1" ).
This is different from for example Rodale's Illustrated Cabinetmaking where a tenon goes probably half the stile width and uses half the thickness. It allows for 1/16" clearance.  The shoulder gets 1/3 to 1/4 of the tenon thickness  and a cosmetic shoulder 1/8".  The difference can be due to the machines used,  with a horizontal mortiser it is easier to go deep and once you go deep you need more thickness to support the sides.  And I guess that the ideal tenon becomes narrower in depth giving a good section at the shoulder without cutting the whole stile away.
Maybe deep tenons are more appropriate for flat frames like doors and windows,  where stiffness is important and half deep tenons for furniture where a tenon is mostly limited to half the depth.

First the horizontal mortiser

And then the tenon machine.  To see this machine working I have to refer to Roy Underhill as he shows a more advanced version of a tenon machine on his shows episode Old woodworking machines.

To finish the tenon saw to cut the haunch and probably a rasp or a chisel to round the tenon.