Thread: Chip breakers ... not cap irons .. and what they really do!

I think (a bad start perhaps), that the key to understanding the function of the cap iron has to start with realising that the process of taking a clean shaving, as far as I can see, involves preventing the blade acting as a wedge and splitting fibres rather than cutting them.

The beam strength of the chip aside, fine mouth, high bed angle and cap iron deflecting chip upwards, all seem designed to create a bending moment in the shaving as close to the pointy end as possible.

...no?

Originally Posted by IanW

Well, this thread has ceratinly drawn some strong opinions from the crowd, and gone off at a few tangents, so perhaps a bit of summing-up is called for? As I see it, the original post shows that that simply moving a cap iron over some pretty small distances, all else being equal, can make a significant difference to both the appearance of the shavings, and the surface quality. As a (former?)believer in the cap-iron-as-stiffener-only theory, I find that an interesting result, at odds with my own views and experiences, and it begs some sort of explanation, whatever it may be (I certainbly don't have one at this stage).

I will have to trawl through the links to see if there are any plausible suggestions as to exactly what the cap-iron is doing at its 'sweet spot', but so far no-one has offered what I could accept as a full explantion in this thread, unles I missed it.

To me, it was demonstrated clearly that you can set too close (this is definitely my own experience, too, & obviously that of others), which to my reasoning, doesn't sem to fit with the chip-bending theory. Someone worked out (can't remember where I read it) that the average beam-strength of a shaving is so small, that the bend would have to be starting right at the cutting edge to have any effect, not 0.3 of a mm back from it, which is about 10-12 times the thickness of a fine shaving. So if bending of the fibres to break them at the blade contaact point is the explantion, either their calculations were wrong, or wood fibres have a much higher stiffness in micro sections than they have in thicker sections (which is quite possible, as many materials are 'stronger' in ultra-thin sections than thicker section strengths indicate).

As some other posters do, I rely on experience and guess-work when setting cap irons. I was taught as a lad to set at a 'fat 32nd', which is around 1mm, for general work, and a 'fine 32nd', which is perhaps .6-.7mm, for fine work. This seems to work for me for the majority of situations. I have never had much luck setting finer than about 0.5mm, and then only for very fine shavings. If I dial for a coarser cut, I am soon getting crinkly shavings that jam the thoat and work under the cap iron, which defeats the exercise utterly. Having highly polished cap-irons helps, but doesn't eliminate the problem, for me. I expend a good deal of effort in getting my cap-irons & blade backs mating as perfectly as I can, but admit they may not be absloute, so there is one area that could be improved.

I think the message from the 'experienced' set is that cap-iron settingss are important, but just one factor in a complex equation. Blade sharpness, cap-iron fit, general seaworthiness of the plane itself, and of course the wood being atacked, all make a big contribution to results. Not only that, but we all have different ideas of what will do "off-plane", based on our personal skill, equipment, and need to get the job done in a time that will pay the rent. Some strive to get a polishable surface with planes only, while others are happy to knock the rough off, and finish with scrapers, abrasives, or whatever is their weapon of choice. (And please don't get into the argument about which leaves the perfect surface in this thread - start another! )

If I were instructing a beginner in hand-plane use, I think I would still advise sticking with the settings I was given, as a good starting point, until the person became proficient with sharpening & general plane use. Once you are happy with your general abilities with the tool, if you are the inquisitive kind, start playing about with specific settings for specific purposes. Which is of course, where Derek is at........

Cheers,

As a (former?)believer in the cap-iron-as-stiffener-only theory,

Ian, that comment doesnt add up to me, i dont presume to know your thinking, but it looks to me that even if it was somewhat unconscious you must of had an idea that the cap iron contributed or you wouldn't have said the latter comment that you adjust the cap iron for finer shavings, if you only thought it was to stiffen the blade it wouldn't make much difference where you put it and not give it a second thought, the two comments seem at odds with each other

Dereks statement that he believes he is actually 're-inventing the wheel' because this information has been lost to all is outlandish in the extreme i would suggest

I will have to trawl through the links to see if there are any plausible suggestions as to exactly what the cap-iron is doing at its 'sweet spot', but so far no-one has offered what I could accept as a full explantion in this thread, unles I missed it.

because i dont think you can say to a certainty what the 'sweet spot' is, there are too many variables to proclaim that a certain measurement is perfect, the specie of wood, the grain, the depth of cut etc, i get a piece of timber and run my hand over and take a shaving to get the feel of it. if someone handed me a strange plane i may have trouble finding the spot or rather taking 'the perfect' shaving in short time, i need to get the feel of the plane, the blade..i wouldnt know where to begin to in describing Dereks examples from a remote place, not enough info, i would do better if i was standing along side him (assuming i didnt knock him over the head first with the plane for insulting carpenters or what he thinks they do or dont know and stating it as fact!). standing along side i can feel the timber, i can feel the blade, from a remote place i cant tell how keen an edge he has, some blades wont take the 'ultimate' edge (and this is more or less what he trying to achieve or tell everyone what it is, the ultimate setting), good quality O1 takes a finer edge than air dried steel imo, some of the sweetheart blades do well, old cast blades and laminated blades, newer (post -war)blades found in bailey type planes will only sharpen to a certain degree ,not saying they are useless but they have some limitations, as does A1 to a lesser degree but its still there. from here i dont know how well derek has honed his blades, i'm not confident they are the best that can be done (no offence but i use different methods to him), good enough for most things, perhaps, but i would look there to find small improvements. how well is the mouth fettled, you can close up the mouth even more when using small distances for the cap iron, if the mouth is smooth and at an angle, it may well be something as simple as that why his plane is clogging. when you start to fettle the mouth and plane for perfection then one may want to keep it just for fine work as opposed to a bailey type plane being quite versatile, or perhaps use a dedicated infill plane for smoothing.

setting the cap iron to around what you mentioned is as good as any place for someone to start using a plane (and for a long time later, relying more on the mouth spacing or depth of cut to achieve a smooth finish, (few people would want to mucking around changing a cap iron within .1 of mm!), even more than that can be ok for some work depending on the nature of the wood, from there tweaking can be done if the results arnt what you wish. imo, if i can manage to put into words correctly, the cap iron bends the shavings and when set close breaks it over a tad, bending it over somewhat, the cap iron angle tends to push down on the broken edge of the shaving holding it (the fibres) in place at the wood surface, (which would other wise show up as tearing) while the blade continues to move forward and cut, there may well be at a micro level if you see it, that the fibres are lifted a fraction while planing but because of the nature of wood in many instances it returns to its former place and leaves a smooth surface, if not it shows up as tearing or rougher surface, more or less the same effect can be achieved by having a close mouth setting (perhaps more easily with a good infill plane), the mouth obviously holds the fibres down while cutting

The pictures of the Brese plane suggested to me that we have not clarified the difference between high- and low cutting angles. I suspect that the Brese plane has a 50- or likely 55 degree bed. It is a single iron plane, that is, it does not use a chip breaker.

There are two questions: firstly, why is the shaving slightly crinkly (in spite of the fact that it takes amazing shavings), and secondly, how does it do so without a chip breaker? I shall get to these in a roundabout manner.

Part of the missing information concerns the reason for all the research into the chip breaker in the first place.

The Japanese research was conducted with supersmoothers in mind. These are planing machines. The experiment utilised a blade with a 30 degree bevel in a bevel down configuration, approximating a bed of 40 degrees. The central aim was to examine the effect a chip breaker had on planing, but in the background is the understanding that the best surface comes from the lowest possible cutting angle. That is, all timber types aside, a low cutting angle should slice the fibres more cleanly than a high cutting angle (the extreme example being a scraper), which instead pulls at the fibres.

We know that a high cutting angle prevents the fibres splitting off early, and we know that a closed mouth can support the fibres in a similar manner. However, the Kato research was conducted without a mouth, and these effects are not part of their results.

Simply put (yes, please Derek!), the chip breaker bends the shaving in such as way that it is not permitted to tear out. If the leading edge of the chip breaker is too far from the edge, then it cannot provide this support. However the angle of the leading edge is also important here, in the same way as the cutting angle is on a high angle plane. The Kato experiment used a leading edge of 80 degrees. 50 degrees did not perform as well. The higher leading edge angle (on the low set blade) was effective in bending the shaving in a manner similar to a high angle blade.

Berlin wrote

I think (a bad start perhaps), that the key to understanding the function of the cap iron has to start with realising that the process of taking a clean shaving, as far as I can see, involves preventing the blade acting as a wedge and splitting fibres rather than cutting them.

The beam strength of the chip aside, fine mouth, high bed angle and cap iron deflecting chip upwards, all seem designed to create a bending moment in the shaving as close to the pointy end as possible.

...no?

Exactly.

More later.

Regards from Perth

Derek

I really hope the irony of a group of intelligent adults scratching their heads over the mechanics of a hand tool on an internet forum isn't lost on anyone.

(... sent from hand held communicator via space telegraph to global letter box...)

Chippy, let's deal with some of the points you raise.

Firstly, the factor of blade sharpness is irrelevant. You will just have to trust me that the blades are sharp (honed to 13000 grit, by the way) .

It is also not about the steel composition, which may impact on durability of edge and, again, sharpness. I've used blades here that range from O1 and A2 to M4 and PM-VII. This is again irrelevant to the situation.

The other issue to dispose of, before we get to the important discussion, is the apparent need for absolute precision in finding the sweet spot. Refer to my earlier comments. I think that you misunderstand the purpose of my study - the various settings were to demonstrate that the chip breaker can have a significant effect on the performance of a double iron plane. By extension, one can also infer that some BD single iron planes may be at a disadvantage in not having this feature (look at the improved performance with the LN plane. More in a while).

I argue that I am indeed reinventing the wheel, insofar that much of this information has been around for centuries, but seemingly ignored or misunderstood by most in modern times. I include myself in the latter group.

Let me emphasise that the aim of my post is to improve the performance of out handplane work. Understanding what is involved is integral to this.

A little background is relevant at this point. This topic has been aired on a few forums in the USA, as well as one in the UK. Discussed by some, but no one else has gone out and tested different conditions. The different conditions include different wood types and different angles of attack. How is the sweet spot affected by these? The woods typically used in furniture in the States are medium hard (at most) by our Oz standards. Their woods, again on average, are far less complex in terms of grain direction. By-and-large it is quite possible to get by with a Stanley #4 smoother. In terms of performance, per se, I have stated that all the LNs, LV, Cliftons, etc are overkill - their performance benefits are unlikely to be recognised on the mild timbers they use (this statement does not take into account the pleasure of using these planes, nor the fact that they are easier to use by virtue of better construction. These factors alone are sufficient reason to own them, if you desire and can afford them).

My thoughts ran to how a #4 plus chip breaker would go on Jarrah. This was part of my first 3 experiments. It became apparent to me that the chip breaker indeed had a sweet spot, and that it did not work across the board. Specifically, it failed to smooth hard, interlocked grain on the Jarrah better than the high angled planes in the comparison. Bottom line: One size does not fit all. There is a place for high cutting angles in smoothers.

Next question: if the original aim of the study was to achieve the finest possible finish with a handplane, which suggested the use of a common angle (45 degree) cutting angle, what can we expect from a high angle plane? Is this automatically going to result in a matt, obscured surface? The latter is the claim from the anti-high angle brigade.

If my experience over the years, supported by the evidence of this present study, is to be believed, then it is evident that it is horses for courses: with hard, interlocked grain, the superior surface finish came off high cutting angles. However - and this is very important - a slightly lower cutting angle plus the chip breaker effect led to a better finish than a higher cutting angle alone.

OK, I will pause there for others to read and respond.

Regards from Perth

Derek

Originally Posted by Berlin

I really hope the irony of a group of intelligent adults scratching their heads over the mechanics of a hand tool on an internet forum isn't lost on anyone.

(... sent from hand held communicator via space telegraph to global letter box...)

The cap irony?

Just did some tests with my Ulmias. Same blade and cap iron switched between a jack-ish plane with a 45 degree bed and a smoother at 50. I used a gap gauge and digital calliper to set the cap iron at .15, .22, .3, .5 and backed way off 3 mm or so. The iron is 3.6mm thick. I only had one off cut of tassie oak which is, unfortunately for the test, knot free with dead straight grain.

Any way: in the jack
.15 - just gummed up, was very fiddley to set and tore up the surface.
.22 ditto
.3 - creepy straight shavings. Weird. V Good surface.
.5 -gently curling and occasionally straight shavings. Good surface.
3.0 - curly shavings, moderate surface with a little tear out in one spot.

Smoother
.15 - as above
.22 - could only manage very fine shavings surface good to very good.
.3 - not as straight as the shavings fro the jack but an impeccable surface.
.5 ditto... yep, just as good a surface
3.0 - normal curly shaving, good surface still no tear out.

So, a mixed bag. I could generate the straight shavings but they didn't correspond with my best surface. Maybe I should have tried.28 and .33. Mind you, .3mm is less than a fingernail thickness (mine anyway) and finding a species specific sweet spot tenths, hundredths of a mil apart is, if I'm honest, pretty anal and probably not something I'll get hung up on.

I'm sure there is a sweet spot though if one is inclined to find it.

Cheers

Originally Posted by ball peen

the cap irony?

:u

Originally Posted by Ball Peen

The cap irony?

Plane and simple....


As an aside Derek, do you think that clambering the cap / chip breaker-irony doodad becomes relevant?

I imagine that it doesn't hold too much importance - because on a jointer you don't need toas the blade is square, and at the other extreme, say a cambered Jack your shavings are coarse anyhow. On a smoother with a very subtle camber, how much difference is there in the set of the cap from the blade at the centre and at the edges anyhow?

Thanks,

Nick

Originally Posted by ch!ppy

Ian, that comment doesnt add up to me, i dont presume to know your thinking, but it looks to me that even if it was somewhat unconscious you must of had an idea that the cap iron contributed or you wouldn't have said the latter comment that you adjust the cap iron for finer shavings, if you only thought it was to stiffen the blade it wouldn't make much difference where you put it and not give it a second thought, the two comments seem at odds with each other

Fair comment, Chips, however, there are two reasons why I hope my thinking isn't totally illogical..

First, I'm usually not one to try fixing what ain't broke. What my old woodwork teaacher told me back then, has always worked, so I've stuck more or less with it & not had too many problems.

Secondly, it's not altogether at odds with the cap iron as dampener theory. Each blade/cap iron combo is going to have a number of variables such as the point at which the blade cantilevers off the frog, the amount of blade actually cantilevered (determined mostly by the blade thickness & sharpening angle, though frogs also vary in how far they extend down to or into the sole material). These variables will create a different resonant frequency for each situation, and in order to keep this in check to maximum efficiency, you will need to search for the best spot at which to apply pressure to the top surface of the blade.
However, as you point out, within a fraction of a mm of the 'perfect' spot probably does just as well for all practical purposes, so my settings of plus & minus are possibly within that range.

When I said I was an adherent of the dampening-only effect of cap irons, I was exaggerating a little - I do retain an open mind about nything I don't fully understand. A large slice of my life was spent in research, and one thing it did teach me is that things are rarely as simple as we would like. I'm ready to be convinced that there is more to cap-irons than dampening, when hit over the head with irrefutable evidence, but I want to see some of the possible alternative explantions eliminated, 'cos I'm such a sceptical old carmgeon.......

Cheers,

Originally Posted by nick_b00

Plane and simple....


As an aside Derek, do you think that clambering the cap / chip breaker-irony doodad becomes relevant?

I imagine that it doesn't hold too much importance - because on a jointer you don't need toas the blade is square, and at the other extreme, say a cambered Jack your shavings are coarse anyhow. On a smoother with a very subtle camber, how much difference is there in the set of the cap from the blade at the centre and at the edges anyhow?

Thanks,

Nick

Hi Nick

I place a camber on most of my planes. I do have a jointer that has a straight blade, which is used for match planing. I have a straight blade in the planes used on a shooting board. Otherwise they all have a camber of differing amounts.

Sometimes a jointer can be a smoother insofar as if the surface off the jointer is good enough, why bother to use a smoother as well? I would not deliberately take fine shavings with a jointer when starting out, but my final runs could be with the chip breaker moved forward.

The chip breaker on the #604 in the experiment was given the same camber as I would usually give the blade. This was to maintain even pressure and distance across the blade. The chip breaker on the LN#3 was not cambered, and this did not appear to make a difference (e.g. clogging) when planing.

Positioning the chip breaker is different for the various planes, with the "coarse" planes being pulled back to allow thicker shavings to flow as the surface quality is of lesser importance.

What I did note with an non-cambered chip breaker, when used on a cambered blade, was that the closer-to-edge side of the blade were much more vulnerable to causing clogging than the centre section, where the chip breaker was that little bit further back.

Regards from Perth

Derek

You can tell a good thread by the way it gets on to four pages and people are still spitting chips.
Cheers,
Jim

And to cap it all we're still smiling ...

Regards from Perth

Derek (who is now expecting a plague of puns, or an array or alliterations )

Or just some plane speaking.