Hi Derek - I can see that by slipping the block over a rail (for example), and rotating on the centre pin, that would show the centre of the rails width. How do you know where to place the shoulders (I'm working on a general 1/3, 1/3, 1/3 spacing)? :duno:
Mailman,
I havn't tried it, but I suppose, if you put a spacer behind one of the pins it would place a mark 1/3rd. of the way ffrom the edge, then do the same the other side, for me I use a mortise guage.
Derek.
If you make a new guide, and put a nail at 1/3 and 2/3 across the gap between the guide pins, that will mark out 1/3 and 2/3 on the wood for shoulders. It works with any fraction. I don't know if it's any more useful then a mortice gauge though...
The thirds rule is fine but I generally set the mortise for the nearest chisel width to a third rather then an exact third. Unless it looks wrong of course in which case your thirds divider could be useful. I still divide up using a steel rule set at an angle.
I'm a bit of a heathen when it comes to Thirds. It always looks too thin, especially on ex-1" stock. I always err on the fat side (no making up your own jokes, please). So for nominally 1" boards (which, if I'm lucky have finished at 21mm) I would use 5/16 or 8mm tenons.
A jig like this is fine for finding the centre of a piece (provided you don't want to get too close to the end), after that, you do with it as you please