Sash Weight pocket cutting

I've just been having a conversation on a forum about the best way to cut out the pockets for the weights. A specialist chisel was mentioned but most folks make saw cut. I ground down an old chisel and did a quick test.

Here's the result..

I'll try a slightly thinner blade and witha bit of practice it will be real time saver.

The problem I originally had can be seen here http://slidingsash.blogspot.com/2008/11/big-mistake.html