Study: Edge retention of plane iron with respect to steel type

1. Summary

This study aims to quantify edge retention of modern steel, in comparison with the older Stanley and Record steel types. The edge retention of PM-V11 steel, for instance, is three times larger than for Stanley steel. A-2 steel is somewhat worse than LeeValley's PM-V11, but by a smaller margin than expected. Record steel, nominally the "best crucible tungsten steel", is a clear winner over Stanley blades.

2. Introduction

There are many conversations online about which steel type is best for plane irons, based on theory and speculation. This empirical study aims to quantify edge retention under controlled conditions.

3. Hardware and protocol

Six different irons were tested with three different cutting depths. Each cut was done on the same piece of wood, with the grain, after sharpening the blade with the same technique. That technique has a 3 degree backbevel which make the plane as a 48 degree bed. Every chipbreaker (cap iron) was raised around 1/16" above the edge to avoid interfering with the cut.

4. Results

Every trial was done with a different cutting depth and method.

1st test	Depth of cut	0.002”
	Planing	normal
	End of test	when the blade begins to slide
2nd test	Depth of cut	0.0025”
	Planing	lot of pressure on the toe
	End of test	when the blade slide regularly
3rd test	Depth of cut	0.001”
	Planing	normal
	End of test	when the blade begins to slide

The first and third trials aimed to study the importance of cutting depth on blade wear. The second trial is the most that an iron can do if the user is willing to work harder and tolerate more sliding - like in a roughing operation.

Many A-2 irons, which are a very popular steel amongst woodworkers, were trialled. There are numerous steps involved in manufacturing an iron. The final result depends on all of them, and not just on the steel type.

For greater perspective, old blades in good condition were trialed alongside modern steels, such as the A-2 and the relatively new PM-V11 from LeeValley. Woodriver steel was also part of the test. The American supplier Woodcraft mentions that their steel is "high carbon steel", whereas in Canada, Rob Cosman says it's A-2 steel on his website.

The wood type used is yellow birch, with a Janka hardness of 1260. The 1-5/16" edge was planed for a length of 16".

The results are:

Blade supplier	Steel type	Plane used	# of cuts	# of cuts	# of cuts	Average	Included angle	Bevel angle
			1st test	2nd test	3rd test
Woodriver	High carbon steel	Woodriver no.4	135	160	145	147	48	35
Record	Tungsten steel	Record no.5	199	250	170	206	48	35
Stanley	?	Stanley no.5-1/4	120	174	118	137	48	35
LN	A-2	LN, 4-1/2	330	456	346	377	48	35
LV	A-2	Woodriver no.4	300	390	287	326	48	35
LV	PM-V11	Woodriver no.4	446	451	428	442	48	35

5. Discussion

Unsurprisingly, older steels are generally worse than the newer generation. Older steels (Record and Stanley) averaged 172 cuts, whereas modern planes (Woodriver, LN and LV) gave us 323 cuts - almost double. Excluding Woodriver, we get 382 cuts for modern steel.

It's also interesting to witness the large difference between Stanley and Record. One wonders why Stanley planes are sold at a premium compared to Record.

Although the Woodriver is very pleasant to use, the poor quality of its iron cannot be ignored.

A-2 steel, from LN et LV, are both good irons, with a slight edge (16%) to LN.

PM-V11 steel from LV gave us exceptionally good results in comparison with LV's A-2, and exceeded LN's A-2 by 19%.

Cutting depth for smoothing planes is usually closer to 0.001", as in trial #3. Under these conditions, PMV-11 steel had 24% edge retention advantage compared to LN's A-2 steel. There was an even bigger improvement compared with LV's A-2, with 49% extra cuts.

It might seem contradictory that the trial with the deepest cut (0.0025") gave us more cuts than the other trials. We suggest that when a thick shaving is cut off, the fibers are raised and torn rather than cut. This, along with the increased pressure on the toe, allows for a larger number of cuts.

6. Conclusion

Should we change all of our irons for PM-V11 or A-2? That's a tricky question - the answer depends on the woodworker's ability to sharpen. It does not confer much of an advantage for fast sharpeners, but those who take longer for this operation might enjoy the increased durability of these modern irons.

Finally, modern irons are thicker, which brings stabilility and decrease vibration to poorly-tuned planes, such as many of the older Stanleys.