Few planes cause as much confusion for today's woodworkers as the try plane. Depending upon who you talk to, what part of the world they are from or what text you are reading, this plane may be called the try plane, truing plane, long plane or jointer plane. In addition, some folks will recommend these planes be honed with a slight camber while others will insist on a straight edge. So why all the confusion? In my opinion, the confusion began from the naming conventions used by the manufacturers of the metal bench planes when they first appeared on the market.
I'm going to pick on Stanley for a minute only because they are the most common. Stanley identified their line of bench planes by number, #1 through #8. They also named these planes so that users at the time would be familiar with their intended use. The problem is, that Stanley based their naming of the planes only on a particular plane's length. Over time, the true meaning of what made a fore plane a fore plane and what made a try plane a try plane got lost. This is a common example of what can happen when people in a marketing position with little real knowledge of a subject are allowed to make decisions related to that subject.
I discussed Stanley's #5 and #6, and their shortcomings, in my blog on the fore plane. This time I'm going to pick on the #7 and #8. Stanley called their #7 (22") a try plane and their #8 (24") a jointer plane. They based these names on the relative length of the plane. In all fairness, the #7 does make a very good try plane and the #8 does make a good jointer, when they are set up correctly. This is where the confusion begins.
Peter Nicholson, in his 1845 text The Mechanic's Companion states that the purpose of the try plane is to "reduce the ridges made by the jack plane, and to straighten the stuff: for this purpose it is both longer and broader, the edge of the iron is less convex, and set with less projection...." On the other hand, the jointer "is principally for planing straight edges, and the edges of boards, so as to make them join together; this operation is called shooting, and the edge itself is said to be shot."
This makes things a little more clear in the distinction between the try plane and jointer. Nicholson does give lengths for these planes as well, but as with most measurements of the period, these are generalizations and not rule. A try plane and jointer plane could potentially be the same length. The true difference in these planes is in their purpose and therefore their setup.
As the try plane is for trying (or truing) surfaces after the jack (or fore) plane, it's iron is cambered, though less than the fore plane, so that it does not leave plane tracks on the surface, which is wider than the plane. The jointer on the other hand, while resembling the try plane in appearance and length, is actually a joinery plane, not a surfacing plane. It's purpose it to straighten board edges and especially to "make them join together" in an edge joint, hence the phrase "jointing the edge." With this in mind it makes more sense for a jointer to have a straight iron like other joinery or fitting planes (e.g. rabbet planes), not a cambered iron like the surfacing planes (fore/jack, try and smooth), because the iron of the jointer is wider than the surface being planed.
Now don't confuse jointing the edge with trying the edge. If an edge needs to be squared to a true 90 degrees (for example, the front of a case which will have a face frame applied), a trying plane actually makes this process easier. The plane can be shifted side to side to take a tapered shaving, with the thicker part of the shaving being taken from the higher edge. However, when making a joint between two boards, one wants a flat edge for gluing. This is the purpose of the jointer plane.
Jointed edges need not be a perfect 90 degrees if the two boards are match planed. When match planing, the money (show) faces of the two boards to be joined are placed together and the mating edges are planed at the same time. When planed together, the boards can be opened like a book and the angles of the edges will be complimentary to each other, resulting in a flat panel, no perfect 90 degree edges necessary. If you don't believe me, draw it out for yourself and see how it works (I may make match planing a future blog). A cambered iron cannot make this joint as well as a straight iron.
Hopefully, this clears up some of the confusion surrounding the try plane. You can see now that a #7 and #8 both can actually make very nice try planes or jointers. It all comes down to how you set up the iron.
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