Moved from 55 to 45 Bronze #4

[Brian Holcombe]

No worries, I did not take offense. I apologize for my short reply, it is an interesting topic and certainly worthy of a more in depth study.

Unfortunately, It's a bit laborious to test without multiple planes similarly set and multiple chip breakers prepared for testing on them. So, for my purpose, I moved toward what I experienced to offer a wider range of successful calibrations.

[ian maybury]

There's little else to be done but to get on with it at times…

[Derek Cohen]

.... My thoughts are that the standard angle allows a wider tolerance for what will produce a good shaving, where the high pitch has a more narrow range and also generally requires a thinner shaving...

Brian, I do not view the high pitch requiring a thinner shaving. Instead, the thinner shaving is a product of the higher pitch. A pitch pitch is generally used on a smoother, where finish is all-important. A thinner shaving adds to the battle against tearout. Further, on a high angle BD plane, especially as the blade gets wider, so the planing requires more effort owing to increased resistance. Thinner shavings are easier.

Regards from Perth

Derek

[ian maybury]

To play with the numbers/mechanics of chip formation again. Through a mechanics of materials eye the thickness of the shaving/chip is a fundamental variable too. It's pretty clear we're in the business of bending it through a tight enough radius (which in difficult woods may need to be the tightest that can be achieved, or to just before failure) to create enough hold down effect - to minimise tear out.

When a beam is bent (in this case very approximately the chip) through a given radius, the level of stress is zero along the centreline - but increases to a maximum at the top and bottom surfaces. Compressive stress to the inside of the bend, tension to the outside. My memory is hazy, but the max stress increases very rapidly (for the same bend radius) as a 'beam' (chip) gets thicker. Much faster than if it was simply proportional - since there's a cube in the formula. i.e. 1 cubed = 1x1x1 = 1, but 2 cubed for example = 2x2x2 =8, 3 cubed = 3x3x3 = 27 and so on. So the stress probably increases in a progression similar to 1, 8, 27, 66, 125… with increasing chip thickness. (i'm open to correction on the maths, but the broad point will hold)

This basically means that as the thickness of the cut/a chip is progressively increased (even if only marginally) the resulting maximum stress the wood experiences with a given pitch/chipbreaker nose angle set up (bend radius) must skyrocket. i.e. as the depth of cut is increased the stress at which the wood fails (which will vary somewhat depending on species) must fairly quickly be reached. Given the cube rule very small depth of cut adjustments may have quite profound effects.

Once the chips start to break/ripple/fail then the chipbreaker (BD)/bevel (BU) will stop working as intended, and the hold down force will rapidly reduce - so the tearout will worsen.

Which in summary suggests that a given pitch/chipbreaker set up will (presuming no other limit is previously reached like e.g. the plane becoming too hard to push) likely have a maximum or limiting chip thickness beyond which chip failure will occur and it'll stop working...

[Winton Applegate]

This basically means that as the thickness of the cut/a chip is progressively increased . . . maximum stress the wood experiences with a given pitch/chipbreaker nose angle set up (bend radius) must skyrocket. i.e. as the depth of cut is increased the stress at which the wood fails (which will vary somewhat depending on species) must fairly quickly be reached. Given the cube rule very small depth of cut adjustments may have quite profound effects.

Nice description.
My views are antiquated taking into account the chip breaker research of late but
for really heavy cuts in the tearout prone wood talking mostly cross grain, even to some extent with the grant, I found the way to go was a scrub plane because it was narrow and since we are using a very heavily radiused blade the wide blade of a jack or #7 does not touch the wood so why do I need to haul all that iron back and forth across the plank for thousands of strokes ?

anyway
a scrub does not have a chip breaker !
And
with a bit of back bevel . . .

(which I hate to use but is worth it on scrubbing bubbinga (which I found the chip breaker useless and in the way for (hence the "!" )(thick chips clogging throat against that awful bulbous thing)

. . . I got really nice results (pretty easy to push (compared to any other set up) and markedly less tearout).
So for heavy cuts
after the battle of the battles
the winner take all
battle of the best

When the dust cleared
there was one duo left standing

Scrub and his side kick 15 Degree Back Bevel Man
Shazam !

So I suppose that is why I still don't get too excited about chip breakers. I go from Scrub Man to BU Jack to BU smooth and kind of forget to look at the others.

What with disassembling to sliding the frog back and forth . . . bother . . .

[ian maybury]

Sorry Winton, i missed your comment here. I'm a bit short of in depth practical experience in this space, and have just been working through a thought experiment to figure out some possibilities.

Combining the above and another discussion though. (a) It's likely that a chip breaker equipped plane will as above reach a depth of cut limit beyond which the chips will start to fail, and problems set in. i.e. chip breakers probably are at their best on lighter cuts close to smoothing. (b) The angle of the nose of the chipbreaker has to matter. If it was e.g. 90 deg then it'd just stop the chip dead. If the same as the pitch of the plane then it'd likely just continue bending the chip in a constant radius.

It does seem that appropriately bevelled BU plane irons work very well too. Maybe a very closely set chip breaker behaves much as a BU iron with a bevel angle very similar to that of that of the nose of the breaker. Your results with steepened bevels and/or back bevels seem to bear that out...

PS I set up my LV scrub for the first time a couple of months ago (at the end of the sharpening binge) - it's quite incredible the ease with which they peel off really thick chips. from the pine i tested it on anyway...

[Steve Voigt]

I'm a bit short of in depth practical experience in this space, and have just been working through a thought experiment to figure out some possibilities.

Combining the above and another discussion though. (a) It's likely that a chip breaker equipped plane will as above reach a depth of cut limit beyond which the chips will start to fail, and problems set in. i.e. chip breakers probably are at their best on lighter cuts close to smoothing. (b) The angle of the nose of the chipbreaker has to matter. If it was e.g. 90 deg then it'd just stop the chip dead. If the same as the pitch of the plane then it'd likely just continue bending the chip in a constant radius.

On (a), it is definitely not correct that "chip breakers are at their best on lighter cuts close to smoothing." Really, the whole point of using a chipbreaker over other methods of tearout prevention is that you can take comparatively heavier cuts. With a high angle plane on really nasty grain, you are going to be reduced to taking sub-thou or 1 thou shavings to finish, while the chipbreaker will let you finish in the 2-4 thou range, meaning you're done in a half to a quarter of the time.

You are right that any method of tearout reduction will have a depth limit. But practically speaking, with a chipbreaker on an iron that has the very small amount of camber appropriate for smoothing or trying, you will reach a physical limit (the plane becomes unpleasant to push) before you reach the point at which tearout is no longer eliminated. You can take cuts up to about 10 thou with such a setup, which is about as much as anyone would want to push for any length of time, and then back it off to finish.

On (b), there is a wealth of information on this subject. See the Kato/Kawai video, Dave Weaver's article "setting a cap iron" on Wood Central, or some of the studies Kees has posted on his blog. In short, steep angles up to 80°, which is what Kato/Kawai used, can work, but they reduce the usable range of chipbreaker setting rather drastically; in other words, you go from "no chipbreaker effect" to "plane's too hard to push" in the space of a few thou.

Probably the best advice for the angle of the chipbreaker was given 180 years ago by Holtzapffel, who wrote that the chipbreaker should present a "nearly perpendicular wall for the ascent of the shavings." Since he was speaking of a plane bedded around 45°, he's just telling you to bevel the nose of your chipbreaker at around 45°. It's that simple, and the angle is not very critical.

I read your comments about the cube rule in the other post. It's interesting, but really doesn't have much bearing on actual work. I don't know why; probably because the actual range of shaving thickness is too small when we are trying or smoothing.

Probably "thought experiments," though interesting, are not very useful unless they are tested at the workbench. We can come up with models all day long, but if they don't work in practice, it's time to get a new model. That not to say that there's anything wrong with theorizing though. I'd encourage you to test some of your hypotheses with a plane and some wood, and see what you come up with.

[Bob Jones]

I love all of the analysis that people put into these topics. I get a kick out of people thinking that 45 deg and O1 steel is just not good enough for 90%+ of the time. Yall keep studying, I'll do my best to use what I figure has worked well for something like 200 years

spoken in in ignorance of course

[ian maybury]

Meant in the nicest possible way Bob (and i agree that theory only gets you so far/we're only playing with ideas here and may be miles off), but i guess these topics come up because people keep on (for whatever reason) running into problems. Not all of the time - probably because there's lots of woods that are not particularly prone to tear out, and which make a planing friendly flexible and not too brittle chip that's not set-up sensitive. It's only when you push the envelope that the fine detail starts to really matter, and at that point it helps to have some mental models on which to base some trial adjustments. (which may not work out of course, but intelligent engagement probably beats random guessing or getting hung up on the 'they' say this works so it must work - it must be me/i must be doing something else wrong kick).

I can't argue with proven practice and/or experiment Steve, I'm far from up to speed on the work done in the field, and may have overshot a little with the 'at their best' comment - but it depends on what meaning is drawn from it. As above problems don't arise all of the time, or i.e. the rule of thumb stuff works very well for most woods. Another phrasing might be that in those situations a chip breaker (on top of the chip breaking/turning/downforce generating effect of the blade pitch) is less important, and/or the setting doesn't matter that much.

Another angle is that the maths suggest that thick chips/shavings generate much more downforce for a given set-up/bend radius, and may only require a lower pitch/lower breaker angle/more retracted breaker. Maybe even no breaker, in that the pitch angle will act much like the bevel face on a BU set up anyway. (think of the scrub - it has no breaker, but that doesn't mean it doesn't generate any downforce since it has pitch - only that the set up is optimised for a very thick chip)

The maths basically only predicts that the stress in the chip/shaving must rapidly increase as it it increases in thickness, and that for a given breaker set up/bend radius it will likely with increasing thickness eventually fail. This will in theory still happen (?) in planing friendly woods too - but it seems likely that in practice other issues like the plane becoming too hard to push intrude before chip failure starts.

Which brings us back to difficult and tear out prone woods. This is where chip breakers and getting the set up right matter most ( are at their best?), and it does seem that in this situation that thinner shavings/cuts reduce the tendency to tear out and maximise their effectiveness. Which doesn't mean that you can't or won't need to take thicker cuts prior to finishing, and that getting the (likely different if it's to be optimum) breaker set up right for those cuts won't matter just as much - but it seems likely to be at the expense of some increased tendency to tear out, and at risk of finding that a setting that works beautifully for thin finishing cuts is too aggressive in this case...

Don't mind my shooting my mouth off - as before it's just play and for all i know i'm potentially miles off base here...

[Kees Heiden]

Here you can read about varying pitch, chipbreaker settings and cutting depth on difficult wood: http://planetuning.infillplane.com/h...s_van_der.html

[ian maybury]

Thanks for that Kees. I'd seen but not properly read your post before, but hadn't seen Steve Elliott's stuff. I took a fairly quick read through the papers. It's great to see the work getting done. Luckily too the the experimental results seem to tie in fairly well with what might be expected. There's a few specifics that caught my eye (pardon if i've misread/got the wrong end of the stick anywhere) This is getting a bit exotic, so feel free to take it off line or park in the event that it's likely to bore others:

1. It seems actually that the chip is already starting to fail by type 1 or 'normal' shavings. I'd thought that perhaps it might not have happened until steeper/closer pitch and chip breaker setting were reached. (i was guessing that the type 0 shaving described might be 'normal') I guess that the factor that means it's OK is that the type 1 chip doesn't at this stage fail completely - so that despite its onset the tear out reducing downforce produced is actually increased/maximised.

2. It broadly bears out the thought that thicker shavings will quickly lead to type 2 chip failure or chip breakages, and that the effectiveness of breakers decreases in this situation - with the result that tear out worsens. Presumably as a result of the downforce being reduced or rendered intermittent by chip breakage(s).

3. It confirms that chip breaker settings are not critical on a wood like pine - that it's with more difficult wood that the 'fun' starts, and that the wood type and depth of cut are major variables in themselves.

4. The number of variables involved is scary. Not so obvious when talking, but it becomes a much more difficult matter entirely upon switching to actual testing and trying to design practical experiments to cover the bases - you end up having to test the set ups that look most relevant, or are easily set up using stock tools.

Some thoughts:

It'd be interesting to trial combinations of chip breaker angle, pitch and breaker distance - there's perhaps some gains to be had depending on how the chip is handled. I doubt they flow tight against the surfaces as shown in some of the drawings - more likely that they curl through a radius and only touch the surfaces at tangent points. Depending on how these variables (available on a BD plane) are set it could be run through a more or less constant radius, or start tight and then loosen, or start loose and then tighten. They may not matter, in that a simple single angle BU iron does pretty well, but who knows? It'd make sense to test simple pitch angles as on a BU plane too.

I'm unsure as to the mechanism of chip (partial) failure assigned to type 2. The term 'shear failure' is used, but that to my mind would suggest a lengthwise delamination of layers within the wood. This could be what happens if wood is weak in this direction (as implied by the ease with which it splits along the grain - true shear failure would be a bit like bending a stack of veneer strips that have not been bonded together/it wouldn't be very stiff/the layers would slide on each other), but it might also be failing as a result of it's being 'over bent' as in the case of an overstressed beam where the tensile and compressive stresses induced in the outermost fibres become too much. The latter seems for example the most likely the cause of type 2 failure, but if delamination was happening then it would surely prevent this?

Perhaps there might be some value in thinking of modelling (in mechanics of materials terms) what's going on inside the chip for differing set ups. The reaction of the chip is the source of the downforce that prevents tear out, and a better undertsanding of how the chip might fail (maybe it already exists?) might be helpful to predict optimum set ups. i.e. that maximise downforce by dealying chip failure, but minimise undesirable forces.

The other thought that strikes me is that Steve seemed to get his best result on rosewood (in terms of tearout control) using what in effect was just a very steeply pitched iron. This might be related to your finding that the force to push the plane forward, and the force required to hold it down is higher with a BU format blade at a steep bevel angle. As in if a BD/breaker equipped iron delivers reduced forces in these directions, then that suggests that the downforce being applied to the chip may be reduced, and that tearout will likely be worse. i.e. the situation is essentially one where the forces applied to the plane by the user are resisted by the reaction of the chip. (and the supporting surface) Whatever is going on there has to be a force balance.

If in this scenario the tear out reduction seen with a BD/breaker equipped plane is actually better or even just as good, then the question becomes what magical it is that's going on to achieve this AND reduce Fc and Fn - since on the face of it the requirement for a force balance suggests there may not be as much down force being applied to the chip.

Mouth opening is another fundamental variable. It's got it's limits (as in it can't be narrower than the depth of cut), but predicting how it interacts with pitch/breaker/set back adjustments seems likely to get complicated. It's presumably best to be tight enough to stop the chip tearing out of the surface, but maybe (?) not so tight as to bend it tighter than the subsequent pitch/set back/breaker combo….

Anyway - just IDLY speculating since i'm definitely not the guy doing the work...

[Kees Heiden]

That's a long post Ian

And I don't have many answers I'm afraid. Like you wrote, there are a lot of variables and testing things like these gives only a very limited range of conclusions. Hopefully the real world value of these conclusions make the experiment worthwhile.

When you want to look what happens inside the wood I think you should use a video camera with a lot of magnification. The videos from Kato are a start. i think they have about 200 times magnification. They are a bit over exposed so hard to see what really happens.

Indeed thicker chips means more tearout danger. The reason is simple, a thicker chip increases the vertical force lifting up the fibres. This is equally true for planes with higher pitch and planes with capirons. The virtue of the plane with the chipbreaker is that the moment this tearout happens seems to be reached more gradually. Even when tearout starts to happen it doesn't seem so bad until it really runs out of hand of course. The plane with high pitch seems to react more binarry, good behaviour and then suddenly deep tearout with a slightly thikcer chip.

Regarding those forces. The plane with a high pitch prevents tearout with a different mechanism then the plane with the chipbreaker. The high pitch only reduced the vertical force, it doesn't pull up on the fibres as badly. The chipbreaker really supports the fiber. Different mechanisms means different forces. The plane with the higher pitch "plows" through the wood (we call this a scraping action) while the plane with the chipbreaker still cuts at 45 degrees. This is not a black and white situation of course, but a scale of varying degree.

[ian maybury]

Pardon the length. Bit of a habit of mine. It's very hard to get a clear understanding of what others mean in this sort of situation anyway. Seems to me Kees though that work and thought like this is very worthwhile - in that it equips us with a mind model to apply in making adjustments in response to problems. Which must increase the chances of suceessfully resolving them.

'The plane with a high pitch prevents tearout with a different mechanism then the plane with the chipbreaker.' This is where my inclination would be to focus - to try to understand exactly what's going on in the chip to predict the various forces in both situations. My engineering/design mentality means that I'm immediately drawn to treating the chip and the dynamics of chip flow as an (albeit dynamic) structural problem. Point being that the chip is the source of most of the reaction forces that we act to oppose in holding down, and pushing the plane forward - and in doing so we apply the downforce that prevents tear out.

High speed film (video these days?) is one way of looking at what's physically going on. Modelling is another. I'm not quite sure how - finite element analysis is a fairly commonly available capability in many CAD packages these days, but i'm not sure if they could model what is in essence a dynamic or chip flow situation. There's CFD capability about too, but i don't know if it's applicable as it's normally applied to fluid flows. There's some small/boutique providers of specialised services like these about, and it might not necessarily that expensive to do, but it'd require a pretty in depth understanding of the physical properties of various woods too...

My one caution about the distinctions being made between BU and BD planes is this. Not sure if i have it right, but if the layout of a BD iron with chipbreaker means that it's pulled more down to work/requires less hold down force of the operator (which on the face of it seems a good thing) that may have a downside. In that the hold down effect presumably comes from the iron 'hooking under' the chip - which will in effect increase the tendency for it to tear out. It could be that most of the hold down force on BD comes from impact with the chip breaker - which might (?) mean that it's mostly the push forward (Fc)/compression that acts to push the chip down.

Which is what I meant in the point about force balance - if downforce is to be applied to the chip as its cut to prevent tearout it has to come from somewhere. We're unlikely to bottom this stuff now, so maybe best to park it...

[Kees Heiden]

Yes I have to park it now, because I'm leaving for a couple of days.

[Winton Applegate]

Mouth opening is another fundamental variable. It's got it's limits (as in it can't be narrower than the depth of cut), but predicting how it interacts with pitch/breaker/set back adjustments seems likely to get complicated. It's presumably best to be tight enough to stop the chip tearing out of the surface, but maybe (?) not so tight as to bend it tighter than the subsequent pitch/set back/breaker combo….

I suppose it has all been put to rest that the 45° bedded bevel down can do it all with some attention to quality of chip breaker and setting.

I will say, about the throat opening for a bevel UP, that I found throat opening to be almost irrelevant once the correct bevel was found. I could have the throat open an eighth of an inch and still have no tear out where before that the shallower, by say 8 or 10°, angle was tearing out and I could take the throat right up to where it choked and was still getting tear out.