Forgetting a Step Leads to Challenging Situation

I'm finishing up the second of two shoe shelves and after I glued up the undercarriage, I realized I hadn't chopped the mortises for the buttons that would be used to attach the top.

There are supposed to be mortises in the inside faces of the upper rails

I recall reading once about a "drawer lock chisel" that can help you mortise in tight spaces.  But I don't have one, so it's time to improvise.

For the mortises in the short rails, there was enough space to fit a chisel and a hammer, but it was still not easy.  Prying out the waste with a chisel held at a low angle was tough - the long rails got in the way.

Chopping a slanted mortise

This was a job for some rarely used tools.  Normally for a 3/8" wide mortise, I use the 5/16" mortise chisel (the yellow handle in pic below).  But it's a very long chisel and length is not your friend in this situation.  Pictured with it are two 1/4" chisels - the blue-handled Irwin and a cheap (read: horrible) chisel that was part of my first ever set of chisels.  But there is an advantage to that cheap chisel, namely that it's relatively short (it can't hold and edge worth a damn, though).  I was able to use it to pry out waste, where other longer chisels couldn't fit.  I also pulled out the heavy metal hammer in the picture because of its smaller head than my wooden mallet.

An assortment of chisels and hammers

I also pulled out of a drawer a 1" Stanley chisel (garage sale find a few years ago) that was far shorter than other 1" chisels I have.  The 1" chisel is useful for paring the sidewalls of the 1 3/8" long mortises.  Being relatively short allowed this one to fit in these tight spots.

Very short blade on this 1" chisel

After completing five of the six mortises, I settled on a method that worked well.  I used the Irwin 1/4" chisel to chop an angled mortise (the final mortise width is 3/8").  I could then use the short 1" chisel to pare the side walls.  The short black-handled chisel was able to get into tight places to pry out waste wood.

Chopping an angled mortise in a long rail

The mortises came out fine.  But it took at least three times as long to chop these mortises in the assembled carcase than chopping them before glue-up.

A completed mortise in a short rail

We all forget to do some things, or to do them in the right order.  But when that happens, consider it a challenge.  How can I get the task done with the carcase in the way.  It forces you to think ... and maybe to use some forgotten tools deep in a drawer somewhere.