Messages Archive

problems laying out, marking 135 degree dovetails *PIC*

Bill Tindall, E.Tn.
In laying out and marking 90 degree dovetails the flat end of the board provides a secure reference surface for scribing the base lines and saw lines of the dovetail. So far I have only encountered the insecurity of reference arrises for these tasks. To wit:

The first step in laying out a dovetail is to scribe the base lines for the base of the tail and pins. For an angled dovetail these base lines are measured from the end of a board that is beveled at the dovetail angle, in my case 45 degrees (or its complimentary angle 135 degrees).

The point on the end of the board is not a stable reference surface that one can freely drag a marking gauge across without crushing this point and thereby moving the reference. Geometry shows that for a 45 degree bevel on the end of the board, the base line will lay 1.41 times the thickness of the board below the tip of the board. (1.41 is the square root of 2). I have not figured out the most reliable way to mark this line.

Marking the other side of the board is also a problem. The marks for sawing can be done with a saddle gauge. This one my son-in-law made with his printer. The base line for this side of the board is located 1.41 times the board thickness below the arris on this side, or 1.41 times the board thickness, plus the board thickness from the board tip. Again, how to best locate this line?

My first successful 135 degree dovetail was mechanically sound, but it had gaps. I have been making joints and varying things to see what causes fitting problems. I have not found it straightforward to translate what I know about making convention dovetails to these ones. Particularly, it is more difficult with these compound angles to make corrections after sawing and chiseling or to make measurements that will predict the fit.

I have found that the base lines are critical. If they are off the tails might be tight but the joint won't close at the proper angle as shown in the picture.

More practice joints are scheduled for today....its raining, a lot, so no outside farm work.

© 1998 - 2017 by Ellis Walentine. All rights reserved.
No parts of this web site may be reproduced in any form or by
any means without the written permission of the publisher.