"Planecraft - Hand Planing By Modern Methods", seems to be a book that was instigated by Record as a way of promoting their tools. The first edition was 1934 and the edition I've got was published in 1950.
It holds a number of useful clues about the question of laminated Record irons. All the photographs and illustrations in the book (which presumably date back to the 1934 first printing?) show bench plane irons with straight edges and angular corners to the tapering top section.
I'll give some quotes from the book and you can make up your own mind regarding their significance,
"Steel facings on iron backs are now standard practise, but it is not easy to discover when this welded or composite cutter was first introduced."
"Within living memory...the purchase of a satisfactory plane iron was largely a matter of luck. It might be too hard or too soft; it might hold its edge or it might not."
The book talks about the history of the Crucible Process, and then says, "The effect of this was that the slag, or rich iron silicate which was present, mechanically mixed with the steel, could be freed readily. The removal of this cinder greatly improves the steel. The process was costly then, and it remains costly today, but the quality of the steel is so incomparably better than the cheaper-produced Bessemer open-hearth steel of later introduction, that Record plane cutters are always made from best crucible cast steel"
The book then goes on to talk about Record's research, "the main lines of the research were devoted to careful analysis and accurate heat treatment, the ultimate result being the well-known and proved Tungsten steel cutter, fitted to all Record Planes. This forms the latest and most far-reaching development of the plane up to the present time...The reader will naturally ask 'Why is this Tungsten steel better than ordinary steel?'. There are two reasons which stand out most clearly. The first is that Tungsten has the property of uniting with the Carbon in the steel and forming Tungsten Carbide. Tungsten Carbide is the main constituent of all high speed cutting materials....It is therefore logical that a plane iron containing the correct amount of Tungsten is harder and more resistant to wear, and will take a keener cutting edge, and hold it for a longer period than would ordinary steel...Secondly, the correct and proper introduction of Tungsten is greatly beneficial in steel for plane irons as it prevents grain growth in the steel. This means that in the fully hardened cutter the steel is of very small grain size, which is immediately obvious when a blade is fractured. Because the steel is more resistant to shock, and therefore the keen edge will suffer less damage when cutting than any other steel."
"Thus, by using skilled engineering, not only is the bevel of the cutter correctly ground, but a uniform thickness and parallelism are attained in every blade (a factor which has so much to do with the efficiency of the whole assembly), and the elimination of looseness and chatter when the plane is in service."
"Finally, every Record Tungsten Steel Cutting Iron is tested on a Hardness Testing Machine".
"Planecraft" is a smashing book, I've never really read it before, I wish I had. It also gives very clear instructions for setting the cap iron distance,
-For rough work, 1/32" to 1/16" from edge
-For finishing work, 1/64" from edge
-For hard woods with irregular grain, as close as you can get it to the cutting edge
Bit of a digression from the thread, but I've recently read similar instructions in the three volume Charles Hayward collection from Lost Art Press.
So I'm puzzled why I've never really been aware of the full implications of the closely set cap iron until DW publicised it on this forum? It's not like I'm a newcomer to furniture making, I'm from a woodworking family, I went to a school that took woodworking seriously, I trained in cabinet making and antique restoration under Bruce Luckhurst in the early 80's, and I trained again at the Barnsley Workshop. So it's not like I gathered my woodworking knowledge from a few Youtube videos, yet my thinking was that a cap iron should be set in the range 0.5-1.5mm from a cutting edge and the way to deal with tear out was a high pitched iron, a back bevel, or by scraping/sanding.
How is it that such an effective technique completely passed me by?
Maybe it's because I bought into the David Charlesworth ruler trick pretty early on after he first wrote about it? And while this doesn't actually preclude a closely set cap iron psychologically it tends to bias you way from it? Incidentally, I find I'm turning away from the ruler trick for all but the worst problem plane irons. For a Bailey style thin iron with a high spot on the non bevel side that made flattening off a problem I'd now use the Paul Sellers hammer trick to fix it, and for a premium thick iron I'd just return the iron to the manufacturer as defective.