# Tight plane mouths and tearout



## yetloh (15 Dec 2009)

I posted as below well into another lengthy thread and Woodbloke suggested it could be the start of another meaty thread on its own, so here goes. 

Tight mouth plane mouths are often touted as being the solution to tear out, I don't believe it and, infinitely more importantly, neither does Karl Holtey. I have always thought this idea that the front of the mouth holds the fibres down so that the cutter can nip them off before they have a chance to lift is nonsense and the master agrees. In my opinion what matters is blade angle and sharpness. 

you might ask why then does Karl make his planes with such beautifully tight mouths? The answer is surely that this is a such a common misconception that most people regard a tight mouth as a sign of intrinsic quality and it is therefore a market requirement whether it is necessary or not. 

Any views anyone? 

Jim


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## Pekka Huhta (15 Dec 2009)

Well now, this is dead simple to test: take a plane with an adjustable mouth. Leave the mouth as wide as possible and try to plane a difficult grain with it. Repeat with the mouth as fine as you can. I don't know what's your planing technique, but for me tightening the mouth works. Along with the adjustment of the chipbreaker / cap iron it has a truly significant difference. 

Of course the tightness of the mouth is not the only and one parameter in planing. But neither are sharpness or blade angle. Mouth, cap iron, skew angle, speed of cut and many others are there, all the time, in every shaving. 

Some of those parameters or factors are more important to the cutting action than others. Many of them can be used for similar changes in the process: You can compensate one parameter by changing another. A good, close cap iron setting and a sharp iron can be used as a substitute for a big mouth. On the other hand if you have a gaping wide mouth and no cap iron, there's no such sharpness in existence that you could avoid all tearout in difficult woods. At least I can't. 

The mouths of the old wooden planes were in many cases big, ragged and under constant wear. That could be compensated by a cap iron, sharpening properly and adding a new mouth piece every once in a while. And they did a proper job as the carpenter knew what else he could change whan he could not change the width of the mouth. 


As said, tightness of the mouth is not the only parameter that solves all tearout. But neither are absolute sharpness or bed angle. They all act together; it would be silly to concentrate to just one or two of them. 

Pekka


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## Derek Cohen (Perth Oz) (15 Dec 2009)

Jim

Essentially, I agree with you. However it depends on the cutting angle.

On a common pitch smoother the size of the mouth does matter. Closing it up will reduce tearout. 

Once you get to a cutting angle of 60 degrees, the mouth size no longer plays a meaningful role. Terry Gordon (of HNT Gordon) has written on this.

Of course, on end grain the mouth size it quite irrelevant. 

Pekka, I don't find any benefit from a cap iron in reducing tearout. Research was done on this (in Japan several years ago) which demonstrated that you needed to have the capiron 0.5mm from the end of the blade to find any effect. 

Regards from Perth

Derek


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## Pekka Huhta (15 Dec 2009)

Derek Cohen (Perth said:


> Pekka, I don't find any benefit from a cap iron in reducing tearout. Research was done on this (in Japan several years ago) which demonstrated that you needed to have the capiron 0.5mm from the end of the blade to find any effect.



This could well be one of the places where one parameter is compensated with another. I've never owned a plane with a 60° bed, around our local woods there's no point. 

I won't argue about the benefits of cap irons reducing tearout. I know that for me it works, and setting of the cap iron is _for me_ the second most important factor in hand planing. And without bragging a lot I can say that I can do miracles with the right cap iron stetting on our local woods. It might be a less important factor with a high bed angle or hard woods, but for pine, spruce, birch and oak I'm very, very confident in saying that there is an effect. 


I'm asking a counter question: do you mean that it's just the same planing with an 1 mm wide mouth, chipbreaker set at 1,5 mm and then changing the mouth to 0,1-0,15 mm and setting the chipbreaker at 0,3 mm? For me there's a world between those settings, the difference between a ruff jack plane and a fine smoother. 


I think the only thing we can prove on this debate is that people get similarly good results by surprisingly different ways. For me it's just a positive thing to note.

Pekka


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## Paul Chapman (15 Dec 2009)

Except when using heavily cambered or toothed blades, I always adjust the mouth of my planes so that there is just enough room for the shavings to get through - and that applies whether I'm planing long grain or end grain. I think in the past people didn't tend to alter the mouth setting on planes because Bailey-style frogs predominated and changing the mouth setting was such a palava. However, with Bedrock frogs or most bevel-up planes with an adjustable front, it's so easy to change the setting.

However, it's important not to have the cap iron set too close with a tight mouth or you will get shavings jammed. I always set mine a fair bit back.

In my experience planes work far better with a tight mouth.

Cheers :wink: 

Paul


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## Mr Ed (15 Dec 2009)

My current setup of 3 main planes are all bevel up with adjustable mouths. With this it is easy to close the mouth up tight, so because everyone says you should, I do. That said, through experimentation recently I am increasingly thinking that higher blade angles are the key to combatting tear out. The tight mouth is no trouble to do on adjustable planes, but wether it actually makes any difference I can't say for sure, whereas the high angle definitely does make a difference.

Ed


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## Paul Chapman (15 Dec 2009)

yetloh":3jbxwsfw said:


> Tight mouth plane mouths are often touted as being the solution to tear out



The ultimate solution, of course, is the scraper plane - which is all about the angle of the blade rather than the mouth. But I still feel that, in general, planes work better with tight mouths.

Cheers :wink: 

Paul


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## woodbloke (15 Dec 2009)

EdSutton":2acz0gzw said:


> My current setup of 3 main planes are all bevel up with adjustable mouths. With this it is easy to close the mouth up tight, so because everyone says you should, I do. That said, through experimentation recently I am increasingly thinking that higher blade angles are the key to combatting tear out. The tight mouth is no trouble to do on adjustable planes, but wether it actually makes any difference I can't say for sure, whereas the high angle definitely does make a difference.
> 
> Ed


I'm the same as Ed here...with BU configuration it's so easy to close up the mouth to practically zero (that's provided you can ensure the blade is square :wink My planes are all set at a 50deg effective pitch but a 60deg ep may well not require such a tight mouth. I can certainly plane some of Waka's birds eye maple without any problem with a BU smoother and a very tight mouth - Rob


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## xy mosian (15 Dec 2009)

Paul Chapman":1zas4p4v said:


> The ultimate solution, of course, is the scraper plane - which is all about the angle of the blade rather than the mouth. But I still feel that, in general, planes work better with tight mouths.
> 
> Cheers :wink:
> 
> Paul



Would that be a scraper blade with or without burr? Surely with a burr the scraper has a low angle again.


xy


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## Paul Chapman (15 Dec 2009)

xy mosian":ccd113aw said:


> Paul Chapman":ccd113aw said:
> 
> 
> > The ultimate solution, of course, is the scraper plane - which is all about the angle of the blade rather than the mouth. But I still feel that, in general, planes work better with tight mouths.
> ...



Scraper planes can be made to work well with or without a burr. With a burr it's not really the same as a low-angle plane because the shaving is turned up at a very steep angle as soon as the burr cuts it, which is why a scraper plane produces no tear out.

Cheers :wink: 

Paul


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## Alf (15 Dec 2009)

Paul Chapman":127woo31 said:


> With a burr it's not really the same as a low-angle plane because the shaving is turned up at a very steep angle as soon as the burr cuts it, which is why a scraper plane produces no tear out.


At which point it becomes a low angle with a cap iron? Kinda? (I'm horribly rusty on the theory stuff; forgotten most of it.)

Reckon I'm with Pekka on this one; there are so many possible variables, and that's just in the material we work with. I simply don't believe that those who went before us acquired these ideas that a tight mouth or a cap iron were good things if there wasn't something in it for _someone_ somewhere along the line that gave them that notion in the first place. Whether x or y is of beneft in our own situations is for us to find out. Much of the (frustrating) charm of using planes is finding out what works best, and the fact it can change from timber to timber keeps it interesting.

Having said which, has anyone tried to see if it's possible to use a two-piece cap iron without the toe piece in place - to see just what the results are without a cap iron in a regular Bailey/Bedrock style plane? It's something I've wondered about for a while but never got round to trying it.

Cheers, Alf


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## Paul Chapman (15 Dec 2009)

Alf":1t2yzgtr said:


> Having said which, has anyone tried to see if it's possible to use a two-piece cap iron without the toe piece in place - to see just what the results are without a cap iron in a regular Bailey/Bedrock style plane? It's something I've wondered about for a while but never got round to trying it.



I've not tried that, Alf. However, I've standardised on a tight mouth with the cap iron set back a bit, so that the cap iron is not doing much in terms of the shaving, rather than a wide mouth and a close-set cap iron. I think you have to go with one or the other because a tight mouth and a close-set cap iron results in jammed-up shavings.

Cheers :wink: 

Paul


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## xy mosian (15 Dec 2009)

Thanks Paul. I've not thought much about this lot before. Just get it working. Must learn more theory. Keep it up gang!  

xy


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## David C (15 Dec 2009)

If a plane with a tight mouth and a close set chipbreaker chokes, it is because the front edge of the chipbreaker/backiron is not properly prepared.

No major manufacturer that I know of sells perfectly prepared chipbreakers.

David Charlesworth


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## woodbloke (15 Dec 2009)

David C":pq39idct said:


> If a plane with a tight mouth and a close set chipbreaker chokes, it is because the front edge of the chipbreaker/backiron is not properly prepared.
> 
> No major manufacturer that I know of sells perfectly prepared chipbreakers.
> 
> David Charlesworth


When I used BD planes a lot with a chipbreaker, it was always honed at about 45deg (iIrc) in the Eclipse guide and the underside meeting the blade was also honed. The front edge of the mouth was also relieved a tad so I never used to experience choking. 
With BU planes it doesn't happen anyway :wink: and if it does it's very easy to clear with a pointy stick or a Phillyplane brush - Rob


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## David C (16 Dec 2009)

Rob,

Thank you for explaining those details, it was too late for me last night.

I should perhaps also add that this applies for fine shavings. For heavy shavings the edge of the C/B should be moved back a bit, the old books usually say about a sixteenth of an inch 1.5 mm.

We no longer relieve the front edge of the throat here, (we used to when I wrote book 1). If the C/B edge is accurate there is no need, and the use of a honing guide is much more certain than the method shown in book 1.

Once one increases the effective pitch of a plane iron to the point where Type 1 shavings turn into Type 2 shavings, (Bruce Hoadley and Leonard Lee) the size of mouth certainly becomes unimportant. It plays no part in the surface finish and could be 1/2 an inch wide.

I am inclined to agree with Paul that a tight mouth, (and close set C/B) does improve regular pitched planes, but this is more difficult to prove.

Derek,
I thought that Japanese research said something more like 4 thousandth's of an inch? 0.5mm is easy to achieve, and I reckon to be able to set as close as 0.2 to 0.3mm.

best wishes,
David Charlesworth

PS Block planes on end grain seem much nicer with a tight mouth.


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## Derek Cohen (Perth Oz) (16 Dec 2009)

> Derek,
> I thought that Japanese research said something more like 4 thousandth's of an inch? 0.5mm is easy to achieve, and I reckon to be able to set as close as 0.2 to 0.3mm.



Hi David

The actual figure was 0.3mm from the edge.

http://planetuning.infillplane.com/html/chipbreaker_study.html

Regards from Perth

Derek


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## David C (16 Dec 2009)

Derek,

Thank you very much.

David


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## yetloh (16 Dec 2009)

I remain unconvinced that the tightness of the mouth is material in avoiding tearout. The only planes I have with adjustable mouths are low angle block planes and I haven't done a side by side test with different mouth openings; might try that when I can get some time in the workshop. There was certainly a noticeable difference between 55deg and 60deg on some difficult wood I was working a few months ago. 

As for chip breakers, I think the name is a misnomer - In most cases, they would be more accurately described as blade stiffeners. My experience with planes without them suggests that they have no significant effect on the ability of shavings to successfully escape through the throat. 

Jim


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## woodbloke (16 Dec 2009)

yetloh":926xdj1f said:


> I remain unconvinced that the tightness of the mouth is material in avoiding tearout. The only planes I have with adjustable mouths are low angle block planes and I haven't done a side by side test with different mouth openings; might try that when I can get some time in the workshop. There was certainly a noticeable difference between 55deg and 60deg on some difficult wood I was working a few months ago.
> 
> As for chip breakers, I think the name is a misnomer - In most cases, they would be more accurately described as blade stiffeners. My experience with planes without them suggests that they have no significant effect on the ability of shavings to successfully escape through the throat.
> 
> Jim


I think here it's a case of 'whatever works for you.' Philly makes many of his BD smoothers with a high angle of around about 60deg ep and they work exceptionaly well with a single iron cutter..._but_, they also have a very tight mouth _and_ are made from 6mm thick tool steel (I know...I have a Phillyblade) I've made one or two planes in a similar way and have found the same thing. 
'Chipbreakers' so called do effectively stiffen the leading edge of the blade and prevent chatter but they also help the shaving to curl and break - Rob


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## Philly (16 Dec 2009)

Jim 
I've had conversations with Karl on the "tight mouth" subject - he feels the "super-tight" mouths which a lot of custom plane makers incorporate in their planes are un-necessary. 
I think it's pretty easy to demonstrate that a tight is superior to a wide mouth when planing difficult timbers, but its only one of many factors that go toward making a good plane (and especially a smoother, which is what we're really talking about here.) A well supported iron, secure and even clamping pressure, flat sole and also a pleasant amount of mass all contribute to a good cut. And when we add high effective pitch into the equation we end up with a plane that has no excuse for not performing well. Time to learn to sharpen...... :lol: 

As for the "back iron", as the chipbreaker used to be called. Larry Williams believes they were introduced as a cost saving exercise - he has some interesting info on this on his website. I believe back irons do two things - they apply pressure to the iron at the cutting edge, supporting and maybe "pre-tensioning" it. I also believe they act in a small way as a heat-sink, emulating the way a thicker iron would absorb heat - we've all used card scrapers and got burnt thumbs. Imagine how much friction occurs at the cutting edge? Just a theory, but hopefully it will get you thinking.

Hope this helps,
Philly


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## yetloh (16 Dec 2009)

I'm sure Larry Williams is right. A thin blade and a cheap steal chipbreaker must be less costly than a properly thick high quality blade.

I certainly agree that there are many factors at work in avoiding tearout but I do think mouth width is probably one of the less significant if indeed it is a factor.

Jim


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## David C (17 Dec 2009)

Derek's link is very interesting and shows that chipbreakers can be set up to have a very significant effect on tearout.

I believe Stanley's propaganda for the thin blades was also that they could be sharpened much more quickly on a stone, perhaps even without recourse to a grinder?

David Charlesworth


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## bugbear (17 Dec 2009)

yetloh":1brg3bjg said:


> I remain unconvinced that the tightness of the mouth is material in avoiding tearout. The only planes I have with adjustable mouths are low angle block planes and I haven't done a side by side test with different mouth openings; might try that when I can get some time in the workshop. There was certainly a noticeable difference between 55deg and 60deg on some difficult wood I was working a few months ago.



The fact that EP has a strong effect on tear out has no bearing on wether or not mouth size also has an effect.

Ditto cap-irons.

Clearly (?) in a plane configuration with a wide mouth where no tear out is occurring (perhaps due to high EP or close cap-iron) making the mouth tighter will have no effect (until it's so tight it clogs, of course).

BugBear


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## woodbloke (17 Dec 2009)

I think it would be an interesting exercise for someone (not me  ) to do a few planing tests with a No4 (and/or similar BU configuration) with different settings on the chipbreaker/mouth on something nasty...and report back. Pics of course would have to be mandatory.
The 'Wood from Hell' would be a good candidate 8-[ :lol: - Rob


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## David C (17 Dec 2009)

Rob,

What is your definition of the wood from hell?

Interlocked Santos Rosewood, Lignum Vitae, Tasmanian Blackwood and Satinwood come to mind.

More accessible, Yew?

David


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## Harbo (17 Dec 2009)

Perhaps that could be done at the Axminster event?

Rod


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## Philly (17 Dec 2009)

One other thought on size of the mouth - I set up my planes so the mouth is wide enough for the thickest shaving I expect the plane to take. So a Jack has a wider mouth than a Jointer, etc....
Hope this helps,
Philly


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## woodbloke (17 Dec 2009)

Harbo":gk1ivuk7 said:


> Perhaps that could be done at the Axminster event?
> 
> Rod


I'll bring a lump along to the Rycotewood event...will post some pics later on this evening - Rob


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## woodbloke (17 Dec 2009)

Herewith a pic of the 'Wood from Hell': 







which defied all efforts to plane to a decent finish at a Bash a couple of years ago, the pic shows a scraped finish from PaulC's new LV scraper. It wa finally tamed by DenebP at the first West Dean event with a razor sharp, LN low angle jack with a very tight mouth...but it took some doing :shock: 
I think it's Indian Laurel (not sure though) Those who attempted to master it at the Bash will attest to it's complete and utter cussedness :twisted: :twisted: :twisted: to plane - Rob


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## David C (17 Dec 2009)

Could well be Indian Laurel.

I will look forward to having a go.

David Charlesworth


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## woodbloke (18 Dec 2009)

David C":1apo41up said:


> Could well be Indian Laurel.
> 
> I will look forward to having a go.
> 
> David Charlesworth


David - you'll be very welcome...I'll see if I can choose a 'nice' :evil: bit for you :lol: - Rob


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## Modernist (25 Dec 2009)

A very interesting thread. - Just a few thoughts.

Re heat - When planing Am Cherry the sole of my LN 4 1/2 (without lubricant) becomes too hot to touch. Initially I dismissed the thought of this altering the temper however on reflection I'm not so sure. This would be more of a problem on a thin blade plane.

It's fairly clear that at EP of 55-60 deg + the mouth width becomes irrelevant however at low angles the reverse is true. This also raises the issue of the smoothness of the front edge of the mouth. A rough edge produces a variable mouth at fine settings which has to be a bad thing.

The front mouth edge/cap iron setting is also important for avoiding jamming. A prepared front edge and fine mouth will allow the cap iron to be set closest without jamming. Having said that it is vital to allow room for the shaving to escape (by moving the cap iron back).

It may be that the two approaches of fine mouth/cap back or close cap/wider mouth both work for different reasons but I'm not sure which circumstances would favour either. I'm not wholly convinced about the role of the cap in any case as the shaving is formed and away from the edge before it acts.

The older I get the more conmvinced I become as to the virtues of BU planes. Even my steep pitch is now achieved by a 45 deg hone on a LN LA Jack. Issues of blade support, mouth adjustment, lack of chip breaker and ease of use seem overwhelming. There is also no chance of edge breakdown on A2 which is important as the honing angle is >30 deg.


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## Modernist (25 Dec 2009)

Having said all that I was reading the Alan Peters article in F & C today and noticed he was using a wooden Jack. I have had a very little used 1940's vintage Marples Jack in a box for 20 years and dug it out for a play. It may need a skim off the sole but I was very impressed with the ease of use and will tune it up properly and add it to the arsenal.


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## woodbloke (26 Dec 2009)

Modernist":3bbaqyot said:


> Having said all that I was reading the Alan Peters article in F & C today and noticed he was using a wooden Jack. I have had a very little used 1940's vintage Marples Jack in a box for 20 years and dug it out for a play. It may need a skim off the sole but I was very impressed with the ease of use and will tune it up properly and add it to the arsenal.


A wooden jack is indispensable IMO in any 'shop. I've just bought another decent one (see a recent Blog entry) which I intend to turn into a curved sole plane (aka Peters) for shaping a concave wooden seat - Rob


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## Derek Cohen (Perth Oz) (26 Dec 2009)

There is nothing like a wooden jack. I have one that I built that is 15" long with a monster, cambered D2 blade. 

However, what does one call a jack-like looking plane that at 12 1/2" is really too long to term a smoother and too short to be a jack? I'm not sure if I posted this before, but it works so well that it has become my favourite plane ...

http://www.inthewoodshop.com/Commentary ... ntein.html

Not a jack but not a smoother ... a sort of jack-smoother 

Regards from Perth

Derek


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## woodbloke (26 Dec 2009)

Derek Cohen (Perth said:


> There is nothing like a wooden jack. I have one that I built that is 15" long with a monster, cambered D2 blade.
> 
> However, what does one call a jack-like looking plane that at 12 1/2" is really too long to term a smoother and too short to be a jack? I'm not sure if I posted this before, but it works so well that it has become my favourite plane ...
> 
> ...


Planes of that style Derek were usually called 'Technical Jacks' and were intended for use in schools, hence the shortened stock...I think though they were a tad longer than the one in your linky - Rob


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## Alf (26 Dec 2009)

I would take an unsubstantiated wild guess that someone fancied/required a much lighter jack for some reason, Derek. So made it a couple of inches shorter and went with the sunken handle/razee/technical jack design. Might have been to reduce weight/size of a travelling kit, might have been because it needed to be used in an awkward place. Dunno; s'very purty though. 

I'm another one in the wooden jack camp - for real jack plane work with a serious camber on the blade, verging on being a scrub. A technical pattern as well, as it happens. Some musings on it here. iirc Charles Hayward was a big advocate of them; a wooden jack was always the listed in his books and articles on what tools to have.

Cheers, Alf

ETA 'cos Rob sneaked in with a post while I was typing: I have a strong feeling that the shipwright folks often went in for the technical style too, hence the 'razee' description - a term adopted from the practice of reducing the number of decks on a ship.


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## Derek Cohen (Perth Oz) (26 Dec 2009)

Alf wrote,


> for real jack plane work with a serious camber on the blade, verging on being a scrub.



Totally agree. 

Now this is where I do my impersonation of Paul Hogan ... "you think that is a jack .....?"  






15 1/2" long in Mesquite with a 5/16" thick 2" wide D2 blade, 8" radius ...






This plane powers through anything!






"...... this is a jack plane!"  

Best wishes for Christmas and be safe over the New Year festivities

Regards from Perth

Derek


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## jonbikebod (28 Dec 2009)

It is worth bearing in mind that it wasn’t Stanley or Bailey who started using or invented the cap iron. All of the traditional English and Scottish wooden and infill bevel down planes use one. These also use heavy irons so I am inclined to think the cap iron does have merit and this seems to be confirmed in the research in Derek’s link. Karl Holtey isn’t convinced but he is increasingly making bevel up planes which is a different and simpler arrangement as only the EP and mouth play a role. I had never previously thought of the cap iron as a heat sink but I am not sure how relevant this is so long as the steel doesn’t get hot enough burn the wood or loose it’s temper – not things that I have ever had a problem with.
Jon.


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## Crooked Tree (28 Dec 2009)

My tuppence worth:

I have a Stanley SB4 (a present, now used for rough work since I bought a 1960s Record No.5) which is bevel down and does not even have a chip breaker. I have always been surprised at how well it works, despite the comments in the old books. It seems to perform OK in pine and oak. although I guess that it might struggle in something more exotic. The blade is slightly cambered by default - I think thath the oil stone may need flattening!


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## martin99 (28 Dec 2009)

jonbikebod":3oyy20d9 said:


> It is worth bearing in mind that it wasn’t Stanley or Bailey who started using or invented the cap iron. All of the traditional English and Scottish wooden and infill bevel down planes use one. These also use heavy irons so I am inclined to think the cap iron does have merit and this seems to be confirmed in the research in Derek’s link. Karl Holtey isn’t convinced but he is increasingly making bevel up planes which is a different and simpler arrangement as only the EP and mouth play a role. I had never previously thought of the cap iron as a heat sink but I am not sure how relevant this is so long as the steel doesn’t get hot enough burn the wood or loose it’s temper – not things that I have ever had a problem with.
> Jon.


Quoting Mr G from the dark side: 
"Some doubt about the function of the cap iron.
i've come to the conclusion that the cap iron has just one essential function, which is to transfer pressure from the wedge (in a woody) or the lever cap (in a steel plane) to as near to the edge as possible. For obvious reasons IMHO."
I think I agree with that.


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## woodbloke (28 Dec 2009)

martin99":2o6i0341 said:


> jonbikebod":2o6i0341 said:
> 
> 
> > It is worth bearing in mind that it wasn’t Stanley or Bailey who started using or invented the cap iron. All of the traditional English and Scottish wooden and infill bevel down planes use one. These also use heavy irons so I am inclined to think the cap iron does have merit and this seems to be confirmed in the research in Derek’s link. Karl Holtey isn’t convinced but he is increasingly making bevel up planes which is a different and simpler arrangement as only the EP and mouth play a role. I had never previously thought of the cap iron as a heat sink but I am not sure how relevant this is so long as the steel doesn’t get hot enough burn the wood or loose it’s temper – not things that I have ever had a problem with.
> ...


The reason is to support the edge in a BD plane and to prevent 'chatter' whilst in a BU plane the edge is supported by the bed, hence the chipbreaker isn't needed...not that it could be fitted anyway. 

As for agreeing with Mr. Grimm...I need another wee dramm - Rob


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## David C (29 Dec 2009)

Referring back to Brian's post, I don't know where this idea that you can't have a tight mouth and a close set cap iron/chipbreaker comes from.

It is perfectly possible to have both in a 45 degree bed plane. If one draws a crossection of the throat this should be clear.

Shaving traps or choking only happen when something is not prepared correctly. Usually the front edge of the CB, or perhaps the front edge of the throat.
Best wishes,
David Charlesworth


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## Steve Elliott (29 Dec 2009)

I agree with David C that it's possible to have both a closely-set chipbreaker and a fine mouth without causing problems with shavings getting clogged.

In most cases it's not necessary to set the chipbreaker extremely close. Using a sharp blade and taking thin shavings are my first choices for dealing with tear-out. A higher effective pitch is helpful when planing difficult hardwoods but a high EP will leave a cloudy-looking surface on some softwoods. A fine mouth and a pitch of 45 degrees or so is more likely to leave a good surface on softwood.

As for a fine mouth, one advantage that hasn't been mentioned is that a fine mouth makes it easier to judge blade projection. If I'm setting a blade to take a shaving .001" thick or less it's easier to feel the blade projection or to sight down the front of the plane to see it if the mouth dimension is small.


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## Derek Cohen (Perth Oz) (30 Dec 2009)

Steve Elliott":31wmok4k said:


> ... A fine mouth and a pitch of 45 degrees or so is more likely to leave a good surface on softwood.
> 
> As for a fine mouth, one advantage that hasn't been mentioned is that a fine mouth makes it easier to judge blade projection. If I'm setting a blade to take a shaving .001" thick or less it's easier to feel the blade projection or to sight down the front of the plane to see it if the mouth dimension is small.



Absolutely, Steve.

As we all know, softwoods generally do not like to be scraped and are left with a fuzzy surface. As the cutting angle of a smoother approaches that of a scraper, this effect is progressive. I have, however, achieved good surface finishes with a very sharp 60 degree cutting angles on both BU and BD planes .... and no chip breakers  

Setting the blade projection is probably the only real reason for a fine mouth on a shoulder plane (used for this purpose) since endgrain does not tear out. 

Regards from Perth

Derek


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## Modernist (30 Dec 2009)

David C":2k392gnq said:


> Referring back to Brian's post, I don't know where this idea that you can't have a tight mouth and a close set cap iron/chipbreaker comes from.
> 
> It is perfectly possible to have both in a 45 degree bed plane. If one draws a crossection of the throat this should be clear.
> 
> ...



I agree but you made an earlier comment which confused me



> We no longer relieve the front edge of the throat here, (we used to when I wrote book 1). If the C/B edge is accurate there is no need, and the use of a honing guide is much more certain than the method shown in book 1.



I think that refining, rather than perhaps "relieving" is beneficial in ensuring a clear passage for the shaving in the area of the cap iron (depending on the quality of the plane). I am still not sure what you mean in the quote above.


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## David C (30 Dec 2009)

Yes, sorry, clear as mud.....

In the distant past when first book of articles was written we used to file and polish the front edge of the throat, at 15 degrees forward angle.

Over time I developed a better way of preparing the front edge of cap/chipbreakers, using a honing guide to ensure that they are never steeper than 45 degrees. So we no longer slope the front edge of throat, but do continue to lightly file if necessary and polish.

I can now set as fine a mouth as desired, even down to 4 thou", and the CB as close as possible for fine work in highly figured timbers, with no risk of choking.

The cap setting is more difficult to quantify, but I think I can get to between 8 or 12 thou".


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