Tight plane mouths and tearout

[Philly]

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

 

[yetloh]

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

 

[David C]

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

 

[bugbear]

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

 

[woodbloke]

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

 

[David C]

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

 

[Harbo]

Perhaps that could be done at the Axminster event?

Rod

 

[Philly]

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

 

[woodbloke]

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

 

[woodbloke]

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

 

[David C]

Could well be Indian Laurel.

I will look forward to having a go.

David Charlesworth

 

[woodbloke]

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

 

[Modernist]

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.

 

[Modernist]

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.

 

[woodbloke]

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

 

[Derek Cohen (Perth Oz)]

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

 

[woodbloke]

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

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

 

[Alf]

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.

 

[Derek Cohen (Perth Oz)]

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

 

[jonbikebod]

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.