Radiusing a cap-iron?

[D_W]

I will pose one other question to the folks radiusing cap irons - how many 175 year-old wooden planes do you find that had the cap iron carefully cambered?

I have never seen one. It's likely that those planes were used by people who well knew how to use them efficiently. When there is no historical basis for something, it should cause new users to stop in their tracks.

 

[D_W]

If there is an ideal spacing from tip of blade to capiron and you like to use a cambered blade why would you not want a cambered capiron to match the blade? I use a 5 1/2 plane for most work and it has a nice wide blade. I don't set it to cut it's whole width but just a part of it at a time. I then adjust the angle using the lever from time to time to use another part of the blade as one part dulls. Having an even spacing from capiron to tip of blade seems entirely logical and don't why I have not tried it before.

When the iron gets dull, you sharpen it. once you have some experience as a user, it takes two minutes and does not consume much of the iron.

Using an iron in heavy work that is set far to the left or right is undesirable, it will easily negate the difference between sharpening a little bit more. It's undesirable with edge jointing, too, since the cut will be biased to the side that hangs more off of a board.

Aside from that, I doubt any reasonable left or right set would have a different enough projection for a user to notice. It is an act of creating potential real problems when you're trying to solve hyptohetical ones.

 

[Beau]

If there is an ideal spacing from tip of blade to capiron and you like to use a cambered blade why would you not want a cambered capiron to match the blade? I use a 5 1/2 plane for most work and it has a nice wide blade. I don't set it to cut it's whole width but just a part of it at a time. I then adjust the angle using the lever from time to time to use another part of the blade as one part dulls. Having an even spacing from capiron to tip of blade seems entirely logical and don't why I have not tried it before.

When the iron gets dull, you sharpen it. once you have some experience as a user, it takes two minutes and does not consume much of the iron.

Using an iron in heavy work that is set far to the left or right is undesirable, it will easily negate the difference between sharpening a little bit more. It's undesirable with edge jointing, too, since the cut will be biased to the side that hangs more off of a board.

Aside from that, I doubt any reasonable left or right set would have a different enough projection for a user to notice. It is an act of creating potential real problems when you're trying to solve hyptohetical ones.

You clearly have a bee in your bonnet about cambered irons so I will leave it there but I have worked this way since my training some 25 years ago and not found it "undesirable". Not advocating it as the only way to work but have found it works for me.

 

[D_W]

Cambered cap irons, not cambered irons.

All of my bench planes have some amount of camber, even the jointer I use for match planing.

What we're talking about here cambering the cap iron doesn't have a terminal effect, just no practical effect and no historical basis.

If there is a plane that you use where you have some camber and the close cap iron set is being used to limit tearout, even if you prefer to rotate an iron left or right, it still won't make a difference to camber a cap iron - you can't get far enough left or right to have any impact. But you can certainly take the cap iron out of play later if you want to use the iron with less camber than is currently on it. I'm sure there is more than one reason that nobody did it on older planes.

 

[David C]

There is too much imprecision here. Camber is a variable feast.

I have used a tuned up 5 1/2 to finish plane for many years. This is not "Historically correct" but so what? It was the only bench plane I had which worked properly, and my components were carefully machined. How many have used the old trick of a back bevel (on the machine planer) for dense interlocked timbers?

As it happens I have slightly cambered my c/b , to approximately match the camber on the blades, for many years. I make no great claims for this simple modification, but it stops the corners overhanging the blade when using an ultra close setting, (as per Kato Kawai).

There has been absolutely no downside to this modification.

David Charlesworth

 

[memzey]

I'm with D_W on this. It seems to make perfect sense that the iron should match the profile of the plane sole for the whole mechanism to work as intended. Further more, heavily cambered irons (such as I have on a rank set No.5) are essentially meant to ease the process of rapid stock removal and not produce a fine finish. The cap iron effect is reduced in these setups but comes into its own when smoothing and jointing where a flat iron with rounded corners or a very slight camber is used. I'd bet a well known expert like DC above could get a rounded cap iron to work but for what benefit I don't know and as for the rest of us mere mortals, leave well enough alone I think. The risk is you'll render the cap iron unusable and the potential benefit is it won't be any worse than before. I don't like those odds and I'm not someone averse to taking a risk or two!

 

[custard]

How many have used the old trick of a back bevel (on the machine planer) for dense interlocked timbers?

David Charlesworth

I do that, but only because I read about it in one of your books! I didn't realise it was an "old trick", I've worked in several furniture making workshops but never seen it used anywhere else, even though it works amazingly well.

 

[David C]

We used it a lot here.

I am sure I read about as an old time machinists technique.

Its parallel is the tiny back bevel on a bench plane.

Glad you enjoyed it.

David

 

[custard]

We used it a lot here.

I am sure I read about as an old time machinists technique.

Its parallel is the tiny back bevel on a bench plane.

Glad you enjoyed it.

David

I suspect you're being modest again and that you thought it up in the first place!

 

[D_W]

There is too much imprecision here. Camber is a variable feast.

I have used a tuned up 5 1/2 to finish plane for many years. This is not "Historically correct" but so what? It was the only bench plane I had which worked properly, and my components were carefully machined. How many have used the old trick of a back bevel (on the machine planer) for dense interlocked timbers?

As it happens I have slightly cambered my c/b , to approximately match the camber on the blades, for many years. I make no great claims for this simple modification, but it stops the corners overhanging the blade when using an ultra close setting, (as per Kato Kawai).

There has been absolutely no downside to this modification.

David Charlesworth

David, you'll need to describe why the cap iron overhanging part of the iron that isn't outside of the plane is a problem in the first place. You cannot push a plane where any part of the cap iron protrudes from the sole, and thus any part of the cap iron that sits past the corners of an iron will never be in the cut. Only parts of the iron that are appreciably below the cap iron set will have a chance of ever touching wood.

There are a lot of things that we don't do when they're pointless. We don't sharpen the end of the iron that doesn't touch the wood, we don't put a third handle on the plane for a hand that we don't have, and thus we do not camber cap irons unless we are the types of folks who would do something like the prior two. It serves no purpose, but it certainly makes a modification that you can't take back.

As far as historically correct, I would imagine that a competent user of double iron planes from 200 years ago would make someone with new "premium" planes look pretty bad in a demonstration of skills. They likely knew more about getting a large volume of quality work out of the planes than any of us will. If there was a point to cambering the cap iron, at least some of them would have done it.

 

[ED65]

What seems to be getting missed here is that the far left and right of the iron should never be deep enough in the work such that you'd modify the cap iron...

Perhaps expanding on this a bit will help a few who might be thinking of trying it out.

If you're using a plane with a heavy camber on the iron you are by definition using it for roughing work or scrub planing, so the cap iron doesn't need to be anywhere near to the edge because you shouldn't be worrying about tearout, period. If for whatever reason you need to set the cap iron close enough that its corners would slightly overlap the corners of the cutting iron (don't do this unless you have no choice due to some oddball situation with your plane) this doesn't matter because they will always be safely inside the throat. Because you're not Popeye. And if you don't have forearms like Popeye you're not taking shavings >2mm thick in the centre.

If you're using a plane with a light camber on the iron the corners of the cap iron are never in the cut because the shaving thickness will be correspondingly thin, in line with what the plane is set up to do. With a straight cap iron mated to a cambered cutting iron the spacing is only critical at the centre where the shaving is thickest, since the protection from tearout improves out from the centre as the edge gets closer and closer to the cap iron's leading edge. So for the corners of the cap iron to project past the sole you'd have to be taking a shaving that's thick enough in the centre that it exceeds the setting of the cap iron. Put in your own measurements on that according to how you commonly set your cap iron for tearout protection and you'll see why it's not going to happen in practice.

 

[Beau]

Cambered cap irons, not cambered irons.

Covered that in my earlier post. If the blade is a cambered it's logical the capiron should also be to keep the same spacing from tip of blade to capiron across the width of the blade.

 

[D_W]

Cambered cap irons, not cambered irons.

Covered that in my earlier post. If the blade is a cambered it's logical the capiron should also be to keep the same spacing from tip of blade to capiron across the width of the blade.

It's not logical unless you disregard what the shaving thickness will be at various parts of the iron. You will never have a full thickness shaving on the outside quarters of the iron.

 

[D_W]

What seems to be getting missed here is that the far left and right of the iron should never be deep enough in the work such that you'd modify the cap iron...

Perhaps expanding on this a bit will help a few who might be thinking of trying it out.

If you're using a plane with a heavy camber on the iron you are by definition using it for roughing work or scrub planing, so the cap iron doesn't need to be anywhere near to the edge because you shouldn't be worrying about tearout, period. If for whatever reason you need to set the cap iron close enough that its corners would slightly overlap the corners of the cutting iron (don't do this unless you have no choice due to some oddball situation with your plane) this doesn't matter because they will always be safely inside the throat. Because you're not Popeye. And if you don't have forearms like Popeye you're not taking shavings >2mm thick in the centre.

If you're using a plane with a light camber on the iron the corners of the cap iron are never in the cut because the shaving thickness will be correspondingly thin, in line with what the plane is set up to do. With a straight cap iron mated to a cambered cutting iron the spacing is only critical at the centre where the shaving is thickest, since the protection from tearout improves out from the centre as the edge gets closer and closer to the cap iron's leading edge. So for the corners of the cap iron to project past the sole you'd have to be taking a shaving that's thick enough in the centre that it exceeds the setting of the cap iron. Put in your own measurements on that according to how you commonly set your cap iron for tearout protection and you'll see why it's not going to happen in practice.

An excellent explanation. That leaves us only to challenge those suggesting your explanation is wrong to set up a plane, protrude the cap iron below the sole and take a comfortable shaving. Of course, your explanation is not wrong.

There is a square root of two in here somewhere for a common pitch plane, but we don't need to get too deeply into that.

There's also the issue that a shaving is thicker after planed than the removed wood thickness was, so if we're measuring shavings, we're overestimating just how much wood we're removing at each set. perhaps if we've set the cap iron at 4 thousandths and taken a 3 thousandths shaving, we're really only removing 2 thousandths of wood.

The real acid test, though is if you can leave the cap iron straight and actually find a need for improvement somewhere that would suggest it's appropriate to permanently modify some of your hardware. The answer is, of course, you can't.

 

[David C]

I am afraid the logic is incorrect.

I judge camber by the light showing at either edge when the blade is offered up to a straight block of industrial plastic.

For squaring edges with a 2 3/8" blade this gap might be 10 or 12 thou".

If the timber is particularly dense and prone to tearout, K&K suggest a C/B setting of around 4 thou".

This leads to the outer edges of the C/B being over the edge of the blade. Something that I am not happy with.

This is solved by slight camber on the C/B which has no ill effects.

It may not be necessary in some people's view, but it is easy to do and has no down side.

This is not some theoretical argument, I have done it for many years.

David Charlesworth

 

[DTR]

This is going off-topic, and I know I'm going to regret asking, but...

.......the blade is offered up to a straight block of industrial plastic.

As you undoubtedly have straight-edges, squares, rules etc of known virtue in your toolkit, why on earth do you need a block of industrial plastic? :?

 

[Bedrock]

I don't want to get into a fight here, and it may be I am not understanding all that is being said. However, if you are using a scrub plane for bulk removal/initial flattening, it is likely that there will be some tear-out. If this is as much as 0.5-1mm. deep, that is a further 0.5-1mm. that you will have to remove from the whole board for final finishing.

That being the case, why not seek to minimise tear-out in the first place?

As a general rule, I don't find the premise that as this was the way it was done 200 years ago, then it still remains the abiding principle. It is certainly part of the learning curve, but not an absolute. Maybe not the best comparison, but it wasn't so long ago that surgeons saw no need to sterilise their hands or instruments between operations. In consequence, most surgical patients died of post operative infections.

Thankfully, medical practise has moved on.

 

[David C]

Dave,

I don't want to offer up sharp edge to steel tools.

David

 

[D_W]

I don't want to get into a fight here, and it may be I am not understanding all that is being said. However, if you are using a scrub plane for bulk removal/initial flattening, it is likely that there will be some tear-out. If this is as much as 0.5-1mm. deep, that is a further 0.5-1mm. that you will have to remove from the whole board for final finishing.

That being the case, why not seek to minimise tear-out in the first place?

As a general rule, I don't find the premise that as this was the way it was done 200 years ago, then it still remains the abiding principle. It is certainly part of the learning curve, but not an absolute. Maybe not the best comparison, but it wasn't so long ago that surgeons saw no need to sterilise their hands or instruments between operations. In consequence, most surgical patients died of post operative infections.

Thankfully, medical practise has moved on.

Medical practice and hand tool woodworking aren't similar, though. Hand tool woodworking has gone backwards in the last 200 years. Actually, if you look at items 400 years old, there really hasn't been much progress. Things like the double iron are an economic development. You can do all of the work without a double iron, that was demonstrated fairly well. It's just easier and cheaper to do it if hand labor is a thing, or tool purchases are a thing.

I agree that we want to minimize tearout. I don't use a scrub plane because it removes a similar volume of wood compared to a well-set jack plane, but leaves a much worse surface. I don't think most woodworkers who worked by hand 200 years ago had anything equivalent to a scrub. I agree that on subsequent steps, minimization is desirable. A little tearout is OK in the steps, but it should be something that is removed in the regular course of work with the next step (the try plane should remove the jack plane's tearout without additional work beyond flattening or working to a mark, and what little tearout the try plane might leave, the smoother should remove just in the course of preparing a final surface). All of this is done in practice with a set cap iron, usually with the jack set off and directional planing employed - and set closer with each subsequent plane. A straight cap.

Short story about medical practice. My grandmother grew up in a house in Gettysburg, it was used as a civil war hospital. The upper floor still has blood stains in the floors, or did until a tenant refinished them. The house came with pictures, and one of them was a pile of limbs behind the house, with.......................pigs in the background eating them. Thank goodness for medical progress.

Unfortunately, I think we know a lot less about planing (though we have more close up pictures available) than someone who was results-based 200 years ago. It's likely that most workers would've been able to tell you what worked best, even if they couldn't explain why. We go in reverse order now.

 

[D_W]

I am afraid the logic is incorrect.

I judge camber by the light showing at either edge when the blade is offered up to a straight block of industrial plastic.

For squaring edges with a 2 3/8" blade this gap might be 10 or 12 thou".

If the timber is particularly dense and prone to tearout, K&K suggest a C/B setting of around 4 thou".

This leads to the outer edges of the C/B being over the edge of the blade. Something that I am not happy with.

This is solved by slight camber on the C/B which has no ill effects.

It may not be necessary in some people's view, but it is easy to do and has no down side.

This is not some theoretical argument, I have done it for many years.

David Charlesworth

David, you're still in the weeds. I don't debate you can work with the setup that you're using. You seem to be convinced that you've solved a problem and that my logic is lacking, but you have less depth in this subject and you don't realize it.

I figured when you brought this up that you were referring to a cosmetic issue (and you are - the fact that the cap iron goes past the edge of the iron is of no consequence in actual use, and you haven't yet figured that out). At some point you will.

As far as the downside goes, if you've taken a hundredth off of the cap iron at the edges, the plane has lost the ability to control tearout on a straight ground blade without gaining any additional capability on a cambered iron.

One other aside, and that is that Kato and Kawai never prescribed 4 thousandth for any hand tools. The professors who did the work were very specific that the testing shown in the video (and the related paper) is to support development of machine planers (like the super surfacer). They wrote a separate paper that was intended to help people set the cap iron on a hand plane and it says no more than to suggest that examination of the quality of the shaving (when it begins to straighten) and the resulting surface are key for setting a cap iron properly. In practical use, there is never or nearly never a time that a cap iron on a hand plane should be set to 4 thousandths of an inch.

If you ever were to try to do that, you'd never get the part of the iron that you've cambered in the cut, anyway. The plane would become too difficult to push and not stay in the cut before you got to a shaving thickness equal to the cap iron set (you'd be only 1/3rd or 1/4th of the way to the parts you've doctored ever even seeing the cut). But beyond that yet, unless the mouth on your plane is large and the wear sloping away, you can't even get the cap iron down to the level of the sole, let alone beyond. It can only come within a few thousandths of an inch of striking distance.

As far as practical, I've been using the cap iron to reduce tearout since before there was any cap iron videos from K&K. When the video came out, I figured there'd be people who would take it too literally and believe they could or should set a cap iron equal to shaving thickness. I was in contact with Bill Tindall before the university who owned the videos ever even made them available - they were effectively locked away because they didn't want them to be available in the public domain. I was goaded by warren mickley, that's the reason I learned to use the cap iron, and goaded by the realization that people knew more about using planes 200 years go when they had to do it to eat. I rode the wave of "small improvements" before that for a while, including in making my own infill planes, only to find out I should've been paying more attention to how people did things when they had to be good at them to survive. I don't refer to theory, I refer to practice. Some things in practice are superior to others. In this case, you're on the wrong side of it, but the consequences are small, you're lucky.