Sizing Key Mortises (was inconsistent rail pins)

[William R. Monroe]

Hi Terry, List,

I use the Spurlock mortise sizing cauls every time.  I'm happy with the 
results, but I have always questioned how they function.  To my 
(oversimplified - at times) brain, I've always felt that pushing these cauls 
into nice moist keys and then letting them dry was missing something. 
Specifically, I would think that this would work well to size a moist key, 
but that the caul would size the key mortise while wet, form fitting the 
moist fibers.  Then, as the key dries, shrinkage would happen.  I would 
further speculate that the more moist the keys, the looser the end result 
would be.

Perhaps I'm missing the boat, here, and the end result is less for the 
"exact" size of the caul, but for a consistent size on all the mortises, 
very close to the caul size, which is then made up for with different 
bushing cloth thicknesses.

Thoughts?

Regards,
William R. Monroe


> Assuming the keys are spruce or basswood or some other similar wood, you'd 
> be surprised at how much the key mortises can swell. Get things good and 
> wet > in there and with the Spurlock mortise sizing cauls I think you will 
> have very consistent results. I'm just guessing, but I would keep the old 
> bushings wet at least overnight to make sure the surrounding wood will 
> swell a little bit. Maybe you need to do a few hours on a wide mortise and 
> see how long it takes to loose the couple thou extra width - that's 
> assuming the mortises are irregular - perhaps they are not.
>
> Terry Farrell