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Cast iron honing plates for diamond paste

Diamond paste is the current buzz, partly because it is cheap and partly because it cuts any steel and does so faster than anything else around. My own interest began when I needed to prepare chisels and plane blades from some of the “supersteels”, CP3V and CP10V, D2, and M2 and M4. My Pro Shaptons were not suited for these steels, and were better reserved for 01 and A2.

Diamond paste is available from many sources, such as the water-based pastes from Tools for Working Wood

and the mineral oil-based pastes from Lee Valley

Smear a pea-sized blob around your substratum, and use this as the honing medium. Substratums may be hardwood, MDF, mild steel … but the best is cast iron.

The diamond bed themselves into the substratum, and then behave like a diamond plate. Recharge them ever now-and-then. The diamond paste in the above syringes should last a long time. I purchased a few tubes on Ebay some years ago, and it does not look like running out for some time yet.

Which grits? I am using three: 40 microns, 10 microns, and 0.5 microns.

I was looking around for a better substratum than hardwood, which I had used with moderate success for a few years, and really wanted cast iron plates. Buying suitable plates, which would need to be machined flat, appeared to be a costly option.

A few of us (Tom at Wood Central, one other) appear to have come up with the same idea at around the same time, so I can’t take all the credit for this. The idea is to cannibalise old, broken cast iron handplanes for their soles.

The plates I made all run about 6” in length and a little over 2” in width as I used smaller planes. I freehand sharpen so this size is ample for my needs. This may not work well for those using honing guides – in which case use larger plane bodies. If you do use a honing guide, I would recommend laying down a thin sheet of vinyl sheeting to safeguard the wheels and wheel bearings.

Building the honing plates

  1. I used a metal bandsaw to cut up the body, saving the area from the mouth to the rear.

  2. Build a simple box around the body.

  1. Once the glue has dried, raise the box on steel rules. This will enable the iron sole to drop through the bottom. The idea is to raise the cast iron plate a few mm above its wooden base.

  1. Now fill the interior of the base with car filler.

  1. Prepare a base/lid for the box.

.. and glue it on. Almost done.

  1. Add strips of 220 grit sandpaper for non-slip …

  1. To run in the lapping plate, add a few peas of diamond paste, even it out across the plate, and then use a blade to press the paste into the surface of the iron.

In the picture below I have flattened an old Witherby chisel on 40 micron diamond paste.

Below are three plates:

40 microns – 7 ½” x 2 ¼” (from a #5 ¼)

10 microns – 6” x 2 ¼” (from a #3)

0.5 microns – 6” x 2 ½” (from a #4)

Note that all the plates are stamped with the micron number – you do not want to contaminate a plate by adding the incorrect paste.

All the best with yours.

Regards from Perth


April 2011