questions about splits during drawboring

 

I got a question from a reader recently that I thought it would be easiest to answer in a post. It concerns drawb0ring, and the position of the pin holes in the joint.

“When doing a drawbore joint with two pegs, (in case of leg to apron joint) do you think that it is necessary to offset the mortise holes to prevent possible split in the leg? In a case where the face of the leg where the mortise holes are to be done, you can see the annual ring running down the leg(rift or quarter sawn).  I would think that one would look at the actual grain in the leg and try to put the holes so they are not over the same  “annual ring”.

Have you seen some old furniture suffering from split mortise caused by drawboring?”

In English work (this includes New England) of the seventeenth century, there is no effort made to stagger the position of the pin holes in each mortise. In other words, they are just aligned off the edge of the mortised member and kept away from the top and bottom edges of the mortise – (this latter prevents splitting of the tenon’s edge).

boring stiles for pins

pins in radial face, joined stool

pins in tangential face, joined stool

 

The face of the stock you bore into also dictates the likelihood of splitting. The pins that enter the tangential face are bored in the radial plane (sounds complicated, but see the pictures above) Oak splits easiest in the radial plane, so sometimes you get splits in the tangential face. In my experience these happen during the boring, not during the pinning. One exception is if the tenoned rail is not tight up against the mortised stock, then you can get a split easily. So the rails need to be pulled up tight before driving the pins, this is one function of the draw-bore pins.

driving pins for joined stool

In stools, splits from pinning are rare, the stiles are so chunky that they are tough. In joined chests, the stiles are rectangular in cross-section, so the narrower dimension sometimes can split. The one in this photo is about 1 7/8″ x 3 1/2″.

small splits between two pins

chest stile

Here’s another that split in the same plane.

splits between pins

So that’s where I expect to see them, in the narrow side view of the stiles of chests, cupboards, etc. I think it would be very unusual to see them in the radial faces of any stock…

Keep in mind the action of the period tool that cuts these holes, it’s a reaming-type cutting tool, so easily capable of splitting.  Easy does it.

piercer bit

 

Some of these pictures have been around before, for more on drawboring, see

https://pfollansbee.wordpress.com/?s=drawboring

 (All of that aside, I have seen some [New World] Dutch work, work shows the pins for mortise-and-tenon joints positioned diagonally, presumably just for this reason – to lessen the chance of splitting the stock. Usually it’s the tenon that is at risk.)