Hand Tools

Subject:
Re: Cap iron setback and shaving thickness

david weaver
Hi John - that's exactly right. The iron has the curvature you're talking about, but there's no real functional reason for the cap iron to also have it unless the sole profile is the same radius as the iron.

I'm making the case here that we don't plane with the cap iron projecting through the sole of the plane (doing so results in enormous pressure required to move a plane, and a substandard "furry" surface as Patrick found out).

If the cap iron is not below the surface of the plane, then there is no functional reason to radius the cap itself unless there is an off chance that someone really had a desire to adjust the blade laterally and cut with only one side of the plane. I really don't see a reason for something like that and have never done it.

In short, the projection of the blade past the cap iron is dependent on shaving thickness. As the projection is around 1 or so, we find exponentially increasing pressure required and a surface that show defect from the shaving being smashed ahead of the iron because it can't travel over the surface of the cap iron smoothly without being crushed into the wood. As the projection gets close to 2x the shaving thickness, the cap iron begins to lose its effectiveness.

So, if we radius a cap iron to match the iron itself (in my opinion, we always want the radius on the iron, as you describe), the center of the iron is going to be in the 1-2x range in terms of distance from the cap iron (I have never measured these, so I can't say for sure what the exact numbers are). As we travel to the edge of the iron, the shavings will thin and they will become too far away from the cap iron for the cap itself to be effective in reducing tearout. They may be so thin that it doesn't matter, because they don't have the strength to lift (which is why I said that the difference may be immaterial, and in that case, it's no more harmful than just being a waste of time _unless_ the extra room at the corners allows a plane with a defect to continue feeding rather than addressing the defect).

There is detail not provided by Nicholson, but in that detail is the reason that he's radiusing the iron. If it has anything to do with reducing tearout, it doesn't have merit. If it has to do with ease of feeding, maybe it does. When I make wooden planes, the last troubles are usually at the edges (and I leave my irons square for that part, because it makes the most trouble there), and I have to do some wear adjustment or cap iron adjustment (thinning the bend slightly right behind the point of contact) to eliminate those edge problems. Relieving the cap iron at those corners may also do that, but I'd rather adjust the plane. If I have a feed problem again over time (which hasn't occurred with any of the planes I've made), then I can go back and adjust the plane based on the fact that I've had to learn with varying cap iron geometries.

That learning about the wear vs. the front bit of the cap iron is why I made the comment that i probably know more about this specific aspect than Nicholson did, unless somewhere in the text is a discussion of him making a bunch of planes and experimenting with different things.

The conclusion of all of that as far as I've come up with is that the best design for the cap iron is to match it to the sole of a plane. I can come up with all kinds of little straw scenarios that can poke holes in it, but each is suboptimal in the grand scheme of using planes (for example, laterally adjusting an iron a significant amount - i'd rather keep the iron cutting in the middle of a plane and noticed that the better older planes really didn't have much initial lateral adjustment, so that is out).

Messages In This Thread

Cap iron setback and shaving thickness
Re: Cap iron setback and shaving thickness
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Redoing the test
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If you're a beginner...
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Re: And a quote....
Re: Radius of cambered blade - some #'s *LINK*
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Contrariness
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Kato and Kawai
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Remarkable restraint
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Re: Cap iron setback and shaving thickness
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Not really lighting it up
Correction
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This seems pointless
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Maguire
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The Virtue
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"Planecraft"
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My apologies
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The big difference
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Jupiter Cakes
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No tear stained defense needed..
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Set-back distance and measurebation
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swingley thread
Blackburn
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Andrew Hunter
Japanese planes
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Cap iron sharpening
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Re:cap iron sharpness and maintenance
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Pictures *PIC*
Cap iron sharpness
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Cut depth, species, and wear
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Simple concept, easy 'splanation
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Tried this again today
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Double Iron vs. Thick Iron
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Double Iron vs. Thick Iron
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Re: Cap iron setback and shaving thickness
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planing
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Consumables vs skilled labor
Actually, you've fed right into..
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Re: Cap iron setback and shaving thickness
I knew *PIC*
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By the way, Mark..
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