Why do pairs of sash planes appear identical?
This question comes up all the time. It is one of those things that will become obvious when you use them. Sash planes were almost always sold in matched pairs. The planes appear identical except that the #2 will often have a steeper pitch on the iron. The #1 is set rank and works the stock to near the finished profile and the #2 is set fine to finish the job. If you only had one plane, you would literally take three times as long, always setting the blade back and forth, and the wedge would be worn out in no time.
