The Traditional Tools Group Inc.

Note: This is a classic reprint of an article from NEWS #030, August 1996.

A frequent question about moulding planes is “how do you sharpen the blades?”

What Not to Do.

  • The first step is to appraise the moulding plane.
  1.  
    1. If it is very old or rare it is best to leave it alone.
    2. If the stock is bowed or worm eaten it is best to leave it alone.
    3. If the iron is very heavily rust pitted it is usually beyond use.

What to Do.

  • The second step is to flatten the back of the iron.

If the rust is light this is achieved by rubbing on a coarse honing stone; oil stone, ceramic or diamond hone according to fancy.

If the rust has pitted the iron, the back can be ground flat.

Alternatively the iron can be annealed, filed flat and heat treated.

When the back is flat proceed through the sharpening steps.

  • The third step is to establish the shape of the iron.

The best technique is to work to witness marks.

First wedge the iron in the plane with some projection. Then mark the profile by either;

  1.  
    1. using a scriber, (colour blade with marking blue first), or
    2. running slip stones along the plane's sole until the iron is abraded level with the sole's contours. (use kero as a lubricant).
  • The forth step is to shape the grinding bevel. (about 25 degrees).

Grinding Flat Contours

Flat contours such as ogees and ovolos can be ground free hand on the edge of the high speed pedestal grinder. A skilled user can produce a perfect edge on this machine. The secret is to use correct type of wheel and maintain a sharp wheel surface. Few people master this machine so the technique for complex shapes is probably safer. (If you have a die grinder, and the skill to use it, this is the quickest tool for complex shapes.)

Grind within a millimetre of the witness mark.

Grinding Complex Contours.

Complex shapes are worked to within a millimetre of the witness marks by using round files and slip stones or diamond or ceramic sticks.

Complex contours include any moulding with a quirk. Beads are typical of these shapes. The trick is to avoid dead spots in the cutting action. To achieve this the profile must be sharpened with back relief.

The moulding plane iron is a composite of two materials; a soft body of wrought iron to which a strip of carbon steel has been laid or fire welded. This steel is about one millimetre thick and only this thin layer of steel is hardened. The bulk of the iron's thickness is soft and can be filed.

Honing Moulding Plane Irons

The hard thin edge must be abraded with slip stones or similar. Maintain a flat bevel of about 50 degrees and aim to just form a burr on the witness mark. Stone the back to remove the burr. This action may have to be repeated several times.

If the moulding plane is to cut well, the iron must be razor sharp and its profile must be parallel with the profile of the plane’s sole.

Replacing Moulding Plane Irons

  • Some old irons cannot be used.
  • Rare or very old irons should be left for the serious collector.  Such items should be left “as is”.
  • Some irons are simply worn out or damaged beyond repair. They may be heavily rusted or the steel may be cracked.
  • New irons are easily made from gauge plate (flat ground stock).
  • With luck old irons can be purchased at market sales.
  • To shape the cutting edge use the steps described above.

Patience is a virtue, with moulding irons it is also a necessity.