chopping mortises

mortise gauge layout
mortise gauge layout
Typically, seventeenth-century New England joinery uses mortises about 5/16″ wide, set in from the flat front face about the same thickness…so here I have set a mortise gauge to strike the width of the mortise.
chopping mortise w mallet
chopping mortise w mallet
The standard practice in my shop is to chop most of the mortise with a mallet and a 5/16″ mortise chisel. In something this size it’s not necessary to bore out the waste first, the green oak chops very easily. 
mortise chisel detail
mortise chisel detail
I align the chisel in such a way that the bevel is plumb, this helps knock the chip upward as the chisel is struck down. I alternate the chisel’s position, so I chop a V-shaped opening in the middle of the mortise’s length. Then I gradually widen this opening.
hand pressure for mortising
hand pressure for mortising

To finish off the ends of the mortises, I often use hand pressure. In this view, I’ve risen up onto the balls of my feet, and come down with my whole body to drive the chisel. Then I can pry the waste up from the bottom of the mortise.

 

The pictures here are the beginnings of a set I am doing to illustrate the making of a joined stool. There are many more steps to chopping mortises, but these few are the gist of it. The moisture content of the oak is important, usually it’s fairly wet inside when I chop these joints. The stock in the photos was planed wet from the log less than a month before…

joined stool
joined stool

3 thoughts on “chopping mortises

  1. Hi Peter,
    (Nice Heron photo above!)

    Not really related to this post. The picture of the mortise gauge made my mind wander. I got to wondering if there were “developed” scratch stocks in the 16th/17th centuries?

    I was scratching a bead on the bottom of some aprons for a stool I was making recently. Not a 17th century joined stool, but a much later and beloved stool that finally broke for the last time. I decided it has been in the family around 100 years and so I should make a new one to replace it for the next century.

    So when I saw the picture of the joined stool in this entry, it made me wonder.

    Take care, Mike

  2. Mike,
    yes, there were scratch stocks…but the trouble is, we don’t know what they were called, nor what they looked like. But there is evidence for the use of some scraper-type molding cutter, in the form of moldings that fade in & out over a very short distance. I will do a post on scratched moldings soon. I have some to do on a cupboard I’m starting now.

  3. I too mortise with the chisel’s bevel held vertically. I commence chopping at the far end of the mortise and work towards me. This seems awkward at first but the chips fly up, out and away from me. Using the same amount of force as I proceed, I chop to one depth all the way across the mortise. The result is another relatively flat surface to chop into. Chop and level to the next depth and so on. This avoids the mickey mouse hard to clean up triangles at each end of the mortise. Adjusting chopping force to the oak’s moisture content, you can then chop a whole bunch of mortises that have relatively flat bottoms without even checking their depth. Wood is wonderful!

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