Grinding a Scrub or Jack Plane Blade

There are two ways to grind a curve onto a blade. The first is just do it freehand at a grinder. Since the surface is going to be chewed up (although it can be chewed up neatly!), the blade shape is less critical. So just get as close a curve as you can. The grind angle is ideally around 30°.

The second method is the one I prefer since it produces a clean, smooth curve. Cut a piece of hardwood the same size as the blade. At the end of this piece, shape the curve you want to grind. The typical radius is 3" for the scrub and 8” for the jack.

  1. Use this as a guide to mark out the curve on the blade.

  2. Grind the curve SQUARE to the edge ….. NOT A BEVEL … yet. You will run the risk of over-heating the edge if you grind a sharp bevel.

  3. Now clamp the blade to the hardwood. This may now be used to guide the bevel angle.

What you are going to do is use the curve on the hardwood as a template for the blade. The curve runs up against the edge of the grinder rest, and the blade (bolted to the top) is extended until it contacts the grinder wheel at the 30° preferred angle. You then turn the blade against the wheel using the curve of the hardwood template as a guide.

A while back I upgraded the grinder to a belt sander and custom made a blade holder along the lines of a Tormek. The same principle remains for grinding. This machine is pictured below.



Once you have ground the curve (either fashion), it is necessary to hone the blade (sandpaper, waterstones, etc). It is not necessary to hone to as high a grit as other plane blades as you are not trying for a smooth finish. A 1200 waterstone is adequate, although I would prefer to go to at least 8000 myself since this makes a difference with hardwood.

Also, read article that deals with using the Lee Valley Honing Guide to hone a fine edge on a scrub plane blade (my upside down guide) —
Advanced Angles on the LV Honing Guide MK II.

Derek Cohen
Perth, Australia

July, 2006