Hello
This is my first post ever to a woodworking site, so let me know if I should post this elsewhere, or missed a similar question in the archives! Thanks!
I’m getting near the finish line in constructing a copy of Lon Schleining’s “essential workbench”, which is my first “real” woodworking project after years of home remodeling and building a workshop. So far, I’m very pleased with the results and have learned quite a bit.
I’ve constructed the bench top and aprons (and inner jaw of the twin-screw end vise) of hard maple, but thought that a contrasting wood for the outer vise jaws might be a nice touch. I was thinking of using cherry since I have a bit of it on hand. Using Hoadley’s data tables, it seems that hard maple has more than twice the resistance to compression perpendicular to the grain than does cherry, and so would be a much better choice. However, is that true in practice? Would cherry work for most common vise applications or not?
Alternatively, I thought that I could make the outer vise jaw from an inner 3/4″-1″ thick piece of hard maple face glued to an outer 1.5-2″ thick piece of cherry. This is where my understanding of wood movement breaks down and I would appreciate an expert’s expertise. I know that the maple and cherry have different amounts of radial and tangential movement, and my only source is again Hoadley’s book. That book indicates a ratio of tangential to radial shrinkage for maple to be 2.1 and cherry to be 1.9. However, these values are of course shrinkage values from green to dry wood. My wood currently has a moisture content of about 6 percent, and thus, as the midwest summer approaches, I expect some changes, but not of the magnitude suggested by the Hoadley tables. Thus, my second question is will face gluing a hard maple inner board to a cherry outer board lead to problems in the vise jaw down the road? Your comments, clarifications, and suggestions are greatly appreciated.
Regards
rokdok
Replies
Rokdok,
Welcome to Fine Woodworking.com
To answer your first, basic question, cherry will probably work fine for the vise jaws. Cherry isn't as hard as maple, but unless you really crank down very hard on the vises you aren't likely to need the extra strength that maple would supply. Normally you wouldn't ever tighten the vise all that hard because if you are creating enough pressure to damage the jaw face, you would also be damaging the workpiece. In fact some woodworkers prefer a softer jaw material, such as pine, because it has a bit more "grab", will conform to slightly irregular stock, and won't dig into the workpiece. If you go this route, attach the soft face with recessed screws so it can be replaced if it gets chewed up.
If there were to be a problem with using cherry, it would be with the dog holes in the vise jaws, since the pressure is concentrated on a much smaller area. If you are only using the dogs to hold a workpiece for planing or carving the pressure needed to hold the piece isn't that great and the cherry should be adequate.
If you are planning to use the dogs to clamp up glue joints, which I would recommend against for several reasons, then you should probably use maple for the jaws since the pressure required for gluing will be higher.
Tangential to radial shrinkage normally isn't used to determine whether two different species of wood are compatible in a glue up. The T/R ratio only gives a rough sense of the tendency of a piece of wood to distort with changes in moisture.
A glue joint between two pieces of wood is much more directly affected by the grain orientation of the two pieces and their actual shrinkage across the width of the joint as their moisture contents change. A glue joint between a radial surface on one board and a flatsawn surface on the other will have far different, and considerably greater, stresses than two radial or flatsawn surfaces glued face to face for instance.
No matter what the grain orientation, gluing two thick pieces of wood together usually creates a glue line with a lot of stresses on it as the pieces shift with moisture changes. If you want to face the cherry jaws with maple, the better approach would be to glue a thin piece of maple, about 1/4" thick, to a thick block of cherry. With this set up the maple is flexible enough to follow the movements of the cherry block and the glue line will probably hold up well.
The most stable joint would result from gluing two quarter sawn faces together, if you are gluing two flatsawn faces together then the rings should be oriented in the same direction to limit stresses on the glue line.
Hope this is clear and helpful.
John White
Edited 4/21/2006 10:40 am ET by JohnWW
Edited 4/21/2006 2:37 pm ET by JohnWW
Thank you, John, for your answer to my questions. I've often wondered about the T/R values, and you've cleared up some misconceptions on my part that I hope will help me to be a better woodworker in the future. Thanks again for your thoughtful and informative response.Best wishes.Rokdok
Edited 4/21/2006 5:58 pm ET by rokdok
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