Toothing Planes - Part 2

I've done a bit of internet research about toothing planes.  They are (or were) used mainly for two separate tasks.  The first has to do with roughing up the surface of a substrate board that a veneer will be glued to.  A century or two ago when veneers were a lot thicker than they are now, the veneer was roughed up with the toothing plane also.  The tiny grooves left by the plane help keep the veneer from sliding around during the gluing process and they also give a place for excess glue to go.

Toothing planes were also used for surfacing gnarly-grained woods.  One can plane from any direction thanks to the iron's tooth profile and the high angle of attack - typically a 75°-90° bed angle.  Cleaning up the grooved surface that is left behind can be easily done with a smoothing plane or scraper.  One can also verify flatness of a board by planing diagonally in one direction and then the other direction.  The pattern of grooves can reveal where low spots are.

Some have mentioned that roughing up your workbench top with a toothing plane can make it hold work better.  Chris Schwarz said this works well, but Richard McGuire cautions that glue or oil can't be removed as easily.  Also, metal shavings (from saw sharpening, for example) can easily get trapped.  Those of us with little space and only one bench probably shouldn't do it.

With the help of my wife, who has a MUCH better camera and is a far better photographer, I got some better photos of the iron.  Not sure how these pics will transfer to Blogger because they have a much greater resolution than my usual pics, but here goes.

End-on view of bevel (below) and teeth.  Note the shape and angles.

Closer view of left side of iron with ruler.  The teeth are about 25 per inch.

Note that the teeth do not have a flat face on the iron's back surface.  This is very different from the current toothed irons produced by (for example) Lie-Nielsen  ( see photo here).  On their irons, each tooth has a flat because of the way the grooves are machined into the flat face.  It's like having lots of tiny chisels next to each other.

My iron has about 25 teeth per inch.  Toothing planes came with coarse, medium or fine toothed irons.  I read somewhere that coarse teeth were used on soft woods, medium teeth on hard woods and fine teeth on veneers.  Freddy Roman's October 2, 2015 blog entry shows an iron with approximately 40 teeth per inch.  I'm thinking mine is a "medium".  Freddy states "Usually a coarse blade is used for carcase work, medium blade for veneer, and fine blade for marquetry."

Based on info from Patrick Edwards' May 2, 2011 blog post and a July 11, 2008 post on a UK woodworking forum, it is likely that the old toothed irons were made using a striking chisel or punch.  The picture below is from the Nicholson File Company and shows how the grooves on a file (not a toothing iron) were typically made.  Notice the angle of presentation of the chisel to the iron.  It looks as if the chisel moves to the left as it dives deeper into the iron and this raises the tooth to the left.  Some sleuthing by people on the UK forum concluded that this was most probably the method used for toothing irons and so reveals the original shape of the teeth.  My iron's teeth look a lot like this.

Drawing of how a chisel was used to form the teeth of the iron.
Picture from "A Treatise on Files and Rasps", published by the Nicholson File Co., Providence, RI, 1878

Here's a top view of the teeth.  You can easily see that the teeth are not perfectly uniform in spacing.  Almost certainly these teeth were formed by hand rather than a machine.

Top view showing teeth not perfectly uniform

Same view but with white background

Regarding sharpening of the toothed iron, Patrick Edwards says that you should never touch the grooved side of the iron on a sharpening stone or it will "ruin it forever".  Freddy Roman mentions only sharpening the bevel.  Ed, from Anthony Hay's blog, says to very gently wipe the burr off the flat side.  Shannon Rogers says in a his #111 video blog entry that sharpening the toothed iron is "no different".  It was unclear what he meant, but I took it as "no different from sharpening any other iron", meaning flatten the back, grind and hone the bevel and remove the burr by swiping the back on the stone.  Maybe he was thinking of the new style toothed blades, but I don't think that would be a good idea for the older blades as it will alter the shape of the teeth.

One last thing about my iron.  It is cupped on the grooved side.  With a straightedge resting on the end of the iron, I can easily slide a corner of a piece of paper between them.

End-on view.  Iron is cupped - see the gap in the middle?

When I sharpen, I'll have to deal with this cup, but I can't flatten the back.  If I'm seeing this correctly in my mind, sharpening a cupped iron at about 30° will result in the middle of the edge (the 2" area in the above photo) being set back slightly and the sides (the 1" and 3" areas) would be more forward.  Since this iron is then bedded at about 80°, the middle of the blade might not contact the wood when the outsides are grooving it.  Not sure how to handle this, but I'm going to have to try to counter this cupping.  Maybe if I sharpen as if I was trying to put a slight camber on the iron (by pressing more heavily on the sides of the iron when sharpening) - but only enough to make the edge straight and not really put a camber on it.  I would love to hear others' thoughts on this.



Here's a bibliography (or is that blogography) of the referenced sites I got information from:

Ed (last name unknown) on Anthony Hay's blog:
https://anthonyhaycabinetmaker.wordpress.com/2011/01/29/the-toothing-plane-a-tool-of-our-time/

Freddy Roman: http://periodcraftsmen.blogspot.com/2015/10/the-toothing-plane.html

Swingleydev forum: http://swingleydev.com/ot/get/162189/thread/

W. Patrick Edwards: http://wpatrickedwards.blogspot.com/2011/05/more-toothing-plane-info.html

Shannon Rogers: http://www.renaissancewoodworker.com/toothing-planes-high-angle-and-low-angle/

Nicholson File Company: "A Treatise on Files and Rasps", published by the Nicholson File Co., Providence, RI, 1878.