Large Shoulder Plane - The Joiner's Friend
The large shoulder plane is not an essential when first starting out, but as your experience grows and projects become more varied this tool becomes very helpful indeed. In woodworking terms the shoulder plane seems a recent development. I'd speculate its only been in serious use for about 175 years. It has one very specific task, to refine the shoulders of tenons. It can be used for other tasks but if you mistake it for a rebate plane you'll be very disappointed. Sticking a rebate is best suited to something like a Record 078, wooden filister plane or basic wooden rebate plane. However a rebate can be refined with a shoulder plane, it's just not designed to do that.
In the photo above you can see how the plane sits on the length of the tenon, using the tenon as a reference surface. The plane is then introduced to the shoulder, this is the upstanding section of the joint. Fine cuts are then taken to get an accurate fit. Being honest, a shoulder plane should be avoided if at all possible, joints should be cut right first time. For most work this is always possible. However when work has large shoulders, typically found on stairs or doors with diminished styles and is also of a customised nature, sometimes a joints needs a little extra help.