This week’s blog from Rob Stoakley
Some time ago, one of the comments arising from the blog entry, ‘A Royal Spanner’, requested the idea of discussing the various steels used for tool blades and the appropriate grinding and honing angles for each.
I make the assumption that many readers will be familiar with this sort of stuff, but there might be relative newcomers to woodwork to whom this article is pertinent.
Going right back to basics, a look at a plane or chisel blade will reveal two bevels: a large ground bevel and a smaller honed or ‘micro’ bevel. It’s the honed bevel which is of concern as this is the bit that actually comes into contact with the wood.
Back in the days of yore, there was only one type of metal commonly available and to simplify the metallurgy (and I’m not a metallurgist!) it was a high carbon, oil quenched steel, referred to as O1, where ‘O’ stands for oil. Over decades of practical experience, it was found that the best grinding angle was 25° with a honed bevel of 30° and these angles are still recommended for everyday use with this type of steel.
Enter Lie-Nielsen into the fray, who in the last few years introduced their A2 steel, which is a much tougher material and consequently can be more difficult to hone. The grinding angle for this steel remains the same as for O1, e.g. 25°. However, due to the metallurgical make up, it is not recommended to hone it at 30° as the edge will crumble. Instead, it should be honed slightly higher at between 33° and 35° where the edge is more robust and not quite so friable.
The latest steel to hit the woodworker’s bench is Veritas® PM-VII, which I believe stands for ‘Particle Matrix, Version 11’. Now this is an immensely complex area to talk about within the brief context of an Blog, but I recommend you to read about it on the Veritas website.
I use this steel in all my Veritas® planes and I’ve found it to be really excellent. Briefly, it holds an edge far longer than A2, but is as easy to hone as O1. I’ve stuck to the tried and tested grinding and honing angles (though slightly higher for a low angle plane) for this stuff and it still works very well with a much higher honed bevel, but this can only be done with low angle planes.
O1 steel – grind at 25° and hone at 30°
A2 steel – grind at 25° and hone at 33-35°
PM-V11 – grind at 25° and hone at 33° for low-angle planes; grind at 25° and hone at 30° for ordinary Bailey planes.
I hope this has gone some way to explain the different grinding and honing angles for the various types of steel, but if you’re still befuddled, please don’t hesitate to leave a comment and I’ll attempt to clarify.