M4 particle steel plane iron shavings
Phil Smith
>In an earlier post I put up pictures of 3V plane irons that Bruce Norton and I made for Wiley Horne and Steve Elliott.
During production of those plane irons we also made 4 CPM M4 plane irons to test the feasability of using and even more abrasion resistant steel for plane irons. We made 2 plane irons for No.5 plane and 2 for a No. 4 1/2 plane.
One of the questions to be ansewered was could we effectively sharpen the very hard and wear resistant tool steels. These tools were hardened and then tempered 4 times to give a final Rc hardness of 63 to 64. The goal was to produce an iron with a balance of both hardness and toughness. The back of the iron was lapped with diamond powder on cast iron plates. Use the sequence of 30; 15; 3.0 and 1.0 micron paste on cast iron. The edge was rough ground with a 7 inch 46 grit very soft pink wheel on a 3600 rpm grinder followed by finish grinding with a 100 grit wheel to give a wire edge. The edge was honed with 3 micron followed by 1 micron diamond paste to produce a razor edge. ANSEWER TO QUESTION NO 1. YES YOU CAN SHARPEN THESE TOOL STEELS TO A RAZOR EDGE in a short time.
Below is a picture of shaving taken with a Clifton no. 5 plane on red oak. The small shaving laying on the plane in the middle of the picture is a paper thin maple shaving I took setting up the blade in the plane.