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

Originally Posted by ch!ppy

.......i am wondering why alternative explanations have to be explained away (i may not quite understand the question maybe), or eliminated, for it to be true that the cap iron is used to bend or break the shavings, as i said the high school texts by Walton lists the cap iron purpose as ". . .

Chips, you'll have to indulge me here - as I said, my training & lifelong experience have inclined me to be analytical and highly sceptical. Quoting an 'authority' is a good first step, but you ought to check where they got their info - was it from rigorous experiment, or are they quoting some older source without questioning where they, in turn, got their information? It was through this type of behaviour that physicians went on bleeding people to 'cure' them of diseases for two thousand years or more!

In the current discussion, the Japanese man & Derek have unquestionably demonstrated that you get a good result planing against the grain on some woods if you set up a cap-iron or chipbreaker just-so. The given explanation is that this is bending the shaving and breaking it, rather than allowing the crack formed by the cutting edge to propagate into the wood & form pits. This may well be the case. The problem I have comes from considering the relative dimensions of the shaving and the length of shaving that comes off the work before it contacts the cap-iron; then it will have to move a bit further before the bending moment transferred back to the cutting point is sufficient to exceed the modulus of rupture of the wood fibres. A shaving 1 thou thick or less is going to have a pretty high degree of elasticity, which is going to make it difficult to transfer the necessary force back to the cutting edge, so it's going to take a fair amount of bending to cause rupture. There may be enough beam strength in the shaving, as I said, materials take on different properties in ultra thin sections compared with larger sections, and the fact that the angle of the leading edge of the cap iron seems to be important supports the bending moment idea, so I may be talking a load of bollocks...

OTH, crack propagation could be enhanced by micro-chatter of the cutting edge, and corrrect dampening could be preventing this. Neither hypothesis has been eliminated yet.

You did ask....

I am not closed-minded about the chipbreakng theory - it may well be all or part of the explantion for the noticable improvement in performance, particularly under the specific conditions of the trials, but before I embrace it wholeheartedly, I would like to see a couple of points explained, principal amomg them being why it only works when the major turning point of the shaving is so far from the cutting edge (in relative terms), and not when it is closer, as intuition would suggest it should......

Cheers,

Hi Ian, i'm a sceptic too, but beyond that like proper research. My own non NATA accredited testing didn't give me any particular insight into what was actually happening but it did make me appreciate that there were other variables to control. Two that were immediately obvious:

1: If one is not very careful about pushing the plane perfectly parallel to the board then the results will be muddied because any slight skew obviously increases (edit, decreases ) the effective cutting angle.

2. Once a clean face has been established, there is a better mating of plane mouth with chip which (i hope we don't have to debate ) has a positive effect on the subsequent shaving. Ergo every test should start with a control face... out of a thicknesser or something? Or, as the Japanese did, you need to remove the plane mouth as a variable.

Overkill perhaps but if it's being treated as capital R research to define rules with which to supersede received wisdom then we must be (even more than Derek always is!) rigorous.

On a final note, these tolerances are minuscule! It was very hard to set my blade at these tenth of mm increments. I think for the results to be more than an academic curiosity an effect will have to be able to be communicated to the rest of us and achievable without the use of a micrometer.

Good luck Derek, I'm not trying to throw obstacles in your path

Cheers

There is no doubt that the chipbreaker works as experience has shown.
What exacty happens is not necessary knowledge for most woodworkers but is interesting to many.
I would make a couple of points:
Firstly, if you want to know what has happened the shaving is the thing to examine - has it broken, distorted, clean break etc.
Secondly a suggestion to Ian. If the chipbreaker is too close to the edge the shaving will be exceedingly short when it reaches the breaker and there may be a relatively greater component of the force pushing it back into the wood ending up with more of a splintered finish and/or short pieces clogging the the cutting edge. I'm not too keen on analogies but have been thinking of how much easier it is to manoeuvre and remove a long splinter than a short one. I always end up digging a hole in my finger for the short ones.
This all fades into insignificance now that science is suggesting that humidity has no effect on swing bowling. Nothing is sacred any more
Cheers,
Jim

Originally Posted by Berlin

If one is not very careful about pushing the plane perfectly parallel to the board then the results will be muddied because any slight skew obviously increases the effective cutting angle.

On a final note, these tolerances are minuscule! It was very hard to set my blade at these tenth of mm increments. I think for the results to be more than an academic curiosity an effect will have to be able to be communicated to the rest of us and achievable without the use of a micrometer.


Cheers

Hell, I really was keeping out of this but you've made two points I'd like to comment on.
The experienced woodworker is constantly changing his/her angle of attack to suit the wood and, as you say, changing the cutting angle. There is probably far more feedback to the skilled craftsman than is generally recognised. It does make it difficult to link practice with theory.
Setting the chipbreaker to small tolerances isn't as difficult as it sounds when it's described in tenths of a millimetre.
In the days of imperial measurement when the map was red you were told to start with about a sixteenth gap. (1.6mm roughly) It's fairly easy to roughly half that and if necessary half it again and you have a sixty-fourth (0.4mm) A bit more, a bit less and see what works the best.
Cheers,
Jim

Jim, don't forget, we aren't talking about what's perceptible but exact, repeatable settings for test purposes. The tolerance between .8 and .4 ...OK even .4 and.2 but between .1 and .2!?. Man that is getting SMALL and if that's the critical range it's a tough ask for me at least.

Cheers

Some time in the distant future...

"yeah, my old man always said to set the cap iron at a fat 280 microns for Tassie oak..'

Originally Posted by Berlin

Some time in the distant future...

"yeah, my old man always said to set the cap iron at a fat 280 microns for Tassie oak..'

rofl

Originally Posted by Berlin

Jim, don't forget, we aren't talking about what's perceptible but exact, repeatable settings for test purposes. The tolerance between .8 and .4 ...OK even .4 and.2 but between .1 and .2!?. Man that is getting SMALL and if that's the critical range it's a tough ask for me at least.

Cheers

Exactly so. That's why it's so difficult to relate testing to what actually is done - not what happens but what is done on the bench. It always seems to be a balancing act between mouth (of plane lol), chipbreaker, depth of cut and angle of plane to direction of movement. Then you'll see blokes going in a circular type movement in places. Add pressure on the plane and things get really complicated in theory.
I often think of something I read about the human brain how it's able to process information so rapidly that it allows the hand to catch a ball which is following quite a complex curve. if you had to work out the maths first no-one would ever be caught out.
Cheers,
Jim

Are you saying Phil Tuffnel was a mathematician?

Originally Posted by Berlin

Are you saying Phil Tuffnel was a mathematician?

idiot savant perhaps.

:u:u

(just jokes if you're reading Phil!)

The tests as they stand lack any sort of scientific rigour. There are too many variables to be able to deconvolute the results and assign specific reasons for the change in performance. As some have pointed out, there is still no reason that the result couldn't be assigned to any number of other factors. Heavens, it's far too early to be drawing conclusions and then embarking on tests on Australian timber.
I would advise that the test should be carried out on "standardised" timber, if that is even possible. For example choose a timber that is notoriously straight grained and then rive it and choose the staightest subset from that. Plane it flat on the jointer so you have a sample that is as close to straight grained as possible. Then plane it on the jointer at some defined angle to the grain al la a tapered table leg. Then you have a bit of wood with a standard angle of the grain that can be reproduced if need be. This eliminates variables as much as possible as you plane through the wood or have to use subsequent pieces.

I would use a bedrock style plane so the frog can be easily adjusted. I would set the plane up for tests with and without the cap iron in place (you could either use a greatly cut down cap iron so you have lateral and depth adjustment or no cap iron and some cork under the lever cap to prevent movement - cut down cap iron would be best.) Adjust the mouth to be identical in all cases. Use a thin original iron and a thick modern blade. Compare the results of planing without the cap iron(or short cap iron) using thin and thick blades. This should better isolate if it is due to greater rigidity of the blade. If it's due to vibration, the thicker modern blade should perform better. If it's better again with the cap iron (in an optimised position) on the thin blade it doesn't tell you much, but if it's yet better again with the cap iron on the thick blade, it may indicate that both effects are at play(chipbreaker involvement and cap iron tension).

I would want to see that the plane sole is checked that the three important points are coplanar. Since we are talking about fine shavings we want to eliminate variables such as sole runout that is close to or greater than the shaving thickness. Yes even 1thou. The blade must be held in exact and unchanging registration with the wood otherwise one could argue about those variables too. And so on it goes.

Does it really matter

Originally Posted by IanW

Chips, you'll have to indulge me here - as I said, my training & lifelong experience have inclined me to be analytical and highly sceptical.

no problems Ian, there all good questions and points you make, i'll just split up my comments, not to be a PITA but because it makes it easier for me to comment.
nothing wrong with being analytical and sceptical, i understand. i'll just add though that working with wood or timber is less about science and more about feel, sure science can give you a perspective, but imo when working with a natural product you can get too bogged down and intuition and feel is the best and quickest path to the best final result (probably sounds lame, one day i might get good at explaining myself)

Originally Posted by IanW

Quoting an 'authority' is a good first step, but you ought to check where they got their info - was it from rigorous experiment, or are they quoting some older source without questioning where they, in turn, got their information? It was through this type of behaviour that physicians went on bleeding people to 'cure' them of diseases for two thousand years or more!

sure, but there are some differences, bleeding ppl with a fleam didnt work, it might have taken the silly buggers yonks to notice but they did notice, whereas using a back iron, cap iron or chipbreaker or whatever you want to call it that has been successful for ..i dunno centuries...if it aint broke type thing

Originally Posted by IanW

In the current discussion, the Japanese man & Derek have unquestionably demonstrated that you get a good result planing against the grain on some woods if you set up a cap-iron or chipbreaker just-so.

i'll have to go back and have a look, it sounds like Derek has altered his posts from original (based on a couple of recent posts), links might be helpful for me to these studies and discussions, the other day i tried searching and only came up with derek commenting in a thread with barely half dozen posts in it (so not much of a discussion, there must be others somewhere i assume) and the position he took in that (which might have been an early on in his thoughts) is completely opposite to what he writes here (advocating the chipbreaker wasn't successful unless a huge 3mm back on a smoothing plane, actually he said the chipbreaker was more a hinderance than help) so i find it very confusing if not impossible to follow when the goal posts keep changing. never the less its not a new concept, no re-invention of the wheel per say and i guess the same logic should apply, when where these japanese studies done etc

Originally Posted by IanW

The given explanation is that this is bending the shaving and breaking it, rather than allowing the crack formed by the cutting edge to propagate into the wood & form pits. This may well be the case.

sounds like the explanation i gave earlier where the fibres have a certain amout of flex and return to the surface, too much 'crack' or lift and the surface can demonstrate tear or a rough finished surface and the points i made about 'ultimate' sharpness and blade metallurgy's is relevant to this, not to mention mouth postion. it sounds (might be wrong) like the Japanese study and derek are trying to remove the mouth from the equation which seems sensible on the face of it but in reality the mouth is there, so if you are looking at it analytically these cohorts need to be addressed, not ignored, they effect each other as a whole

Originally Posted by IanW

The problem I have comes from considering the relative dimensions of the shaving and the length of shaving that comes off the work before it contacts the cap-iron; then it will have to move a bit further before the bending moment transferred back to the cutting point is sufficient to exceed the modulus of rupture of the wood fibres. A shaving 1 thou thick or less is going to have a pretty high degree of elasticity, which is going to make it difficult to transfer the necessary force back to the cutting edge, so it's going to take a fair amount of bending to cause rupture. There may be enough beam strength in the shaving, as I said, materials take on different properties in ultra thin sections compared with larger sections, and the fact that the angle of the leading edge of the cap iron seems to be important supports the bending moment idea, so I may be talking a load of bollocks...

your not really talking a load of bollocks, but if you dont mind me saying your missing some bits too, perhaps because your trying to be too analytical or scientific, one answer doesnt fit all, you would need different studies for each specie of wood and then you could re-do for true wood and heartwood and you could continue ad-nausium for different pieces of timber, it would drive you mad. your dealing with a natural (beautiful wonderous) product, that starts of as W O O D , milled to timber and then further shaped by us with tools. your not going to get, a one size (measurment) fits all, in all circumstances for the ultimate finish (each has to decide whether its worth the trouble to go to the extreme), feel the timber take a test cut is my advice, one size fits all for more or less a very good finish, but depth of cut, speed of pushing the plane, angle of pushing the plane-skew, specie of wood, grain, plane, blade etc etc all contribute, if you were to muck around using micro measurements (feeler gauges, micro metres etc) it might just take the fun out of it, i think it would for me

Originally Posted by IanW

OTH, crack propagation could be enhanced by micro-chatter of the cutting edge, and corrrect dampening could be preventing this. Neither hypothesis has been eliminated yet.

you dont get an argument from me about this, i have said that the cap iron contributes to tension at the cutting edge (particularly in a bailey type plane) and certainly part of its job, and this micro chatter (as you call it, seems like a good term, not purely academic either, if you consider the heat at the cutting edge, not that any measurement are needed but you can feel the heat on the blade when planing when you touch it cant you) is along the lines that i tried to express in another post.
crack propagation (as you say-another great term-is what i trying to relate in another post, could you be my editor haha) can be reduced and if this is an experiment then the cohorts should be eliminated or the results are tainted. my suggestion was that not all steel can be honed to 13000 grit, you might think its doing something but some steel just doesnt take that fine an edge, then there is issue with dubbing if done by certain methods, but i am not trying to turn this into a sharpening debate, its just that it is relevant if trying to say the difference in .1mm of CI (got sick of writing cap iron) makes a difference when other cohort effects havnt been addressed (ultra fine edge reduces crack/splintering propagation), then there is , and imo this more important (even though derek will hate it and prob p_ss everybody esle on the planet off), that the bevel be flat ground, not only that but if just one honed bevel, not a secondary bevel (i know too much work, bla bla but you did ask ). i am not saying everyone should change their methods, what works for them is fine but since we are talking ultra fine settings this makes the difference in the end result, you can plane difficult timbers at lower angles the cap iron can be set back a tad (so you get the longer fibres), the heat is dispersed more without hollow grinding, the strength of the cutting edge is increased, reducing that crack propagation (great term!)

Originally Posted by IanW

You did ask....

i dont mind, and i did longish answer

Originally Posted by IanW

I am not closed-minded about the chipbreakng theory - it may well be all or part of the explantion for the noticable improvement in performance, particularly under the specific conditions of the trials, but before I embrace it wholeheartedly, I would like to see a couple of points explained, principal amomg them being why it only works when the major turning point of the shaving is so far from the cutting edge (in relative terms), and not when it is closer, as intuition would suggest it should......

Cheers,

its a natural product with pores and fibres and such and has a moisture content, too close and they crush (clog up) and length (position of CI) can vary depending on a number of factors, depth of cut etc..for sure you can plane without a cap iron/chipbreaker assuming the blade is not too thin for the proposed task (cut depth and density of wood for example) and that the grain is behaving itself, not curling back etc, but thats in a perfect world and usually to plane without cap iron will require a higher angle...

with the way this is going i wouldnt be suprised if someone comes out with an cap iron and wheel attachment for chisels LOL

cheers
chippy

Originally Posted by ch!ppy

with the way this is going i wouldnt be suprised if someone comes out with an cap iron and wheel attachment for chisels LOL
cheers
chippy

Don't even mention it Chippy. If people can make combination rasps and chisels they'll do anything.
Cheers,
Jim