New experiments

[Kees Heiden]

When you think about it. There are two sides to the normal force. It is the shaving pushing down from above and the convex wear bevel pushing from below. The first is best measured with a sharp blade. The second develops when the plane is used.

I have measured the pressure from the shaving. At 45 degrees this was decidedly negative. I think this tells something about the way the blade cuts. In this setting the edge cuts the shaving, and the shaving is pushed away. This is close to a pure cutting action. At 60 degrees (in the setting I tested, 0.05 mm cutting depth, a few degrees with the grain) the normal force is almost zero. That means that there is only a horizontal force on the edge. The blade pushes the wood forwards, not upwards. I think that this means that the wood is failing in compression.

Now of course it is not black and white like that. I think you always have a combination of cutting and compressing, just differing combinations.

[Warren Mickley]

Ta David - that reduces it to practicality. Setting up and testing a scrub plane for the first time a few nights ago demonstrated from the other end how chip breakers can only operate up to a certain depth of cut anyway. It's amazing how they glide through the wood at a scary depths - while requiring (relatively speaking) pretty minimal force. Adding a chip breaker would likely get interesting/stop it dead….

The term scrub plane is relatively recent. Stanley tools used it as a corruption of the German schrupp hobel. In the English and American traditions a jack plane has been used for rough work. Even the Pennsylvania Dutch used jack planes. Double iron jack planes have been in use since the 18th century.

[ian maybury]

You're way ahead of me on the history Warren, and on practicalities. My surmise (which could be wrong) was just that it was the absence of a chip breaker/cap iron that led to what felt like the low force required to push the scrub. They are however relatively narrow and with the heavy camber maybe don't cut over as much area as might seem to be the case.

Against that I guess there's no reason not to push the cap iron right back if using a jack plane as a scrub if that helps….

[David Weaver]

I think the point about the scrub is that it's a bit of a novelty - in my opinion it sells well because it's on the far extreme of the setups and people get enamored with it on a test board. It's not as nice to use to thickness a board, in my opinion, as a rank set (larger footprint) jack plane, and I don't like it any better for adjusting the width of a board. My rank set jack is radius 4" or so, so take that with a grain of salt. It's wider than a scrub plane, which makes it a bit nicer to use in my opinion.

In terms of setting a cap iron, on the really cambered irons, there's not a whole lot to do - you try to plane downhill or across the grain if you have to. It's the next step of work where you really gain with a cap iron, especially in terms of not having to push a plane that thumps is way through the board as it's bouncing in and out of the cut, and not moving past a marked line to eliminate unexpected tearout. I still keep a cap iron down close to the edge on a jack, but close is a relative term - there could be an eighth of iron sticking below it and if you ever actually get a chip an eigth thick in a medium hardwood, you get the man award!

[Sean Hughto]

I think the point about the scrub is that it's a bit of a novelty - in my opinion it sells well because it's on the far extreme of the setups and people get enamored with it on a test board. It's not as nice to use to thickness a board, in my opinion, as a rank set (larger footprint) jack plane, and I don't like it any better for adjusting the width of a board. My rank set jack is radius 4" or so, so take that with a grain of salt. It's wider than a scrub plane, which makes it a bit nicer to use in my opinion.

jack is to smooth as scrub is to jack

jack will get you there, but in twice the time and effort, just like a smooth plane might get a jack's work done

I find efficiency more fun.

[David Weaver]

jack is to smooth as scrub is to jack

jack will get you there, but in twice the time and effort, just like a smooth plane might get a jack's work done

I find efficiency more fun.

That last bit is my line!

A rank set jack should get you there in the same amount of time, and maybe a bit faster if it's wooden.

I never measured the radius on my planes until someone mentioned numbers a few months ago. My stuff is set more rank than the numbers other people gave. It may be that someone who sets their planes with fairly flat radius would have more of a place for them than me.

I do like a converted continental smooth plane better than a real scrub, though. That makes for a true two-handed plane.

[Sean Hughto]

Yeah, the radius issue may be the key. I have some well cambered try and jack set ups, but nothing even vaguely approaching the fingernail that is the scrub blade.

[Warren Mickley]

jack is to smooth as scrub is to jack

jack will get you there, but in twice the time and effort, just like a smooth plane might get a jack's work done

I find efficiency more fun.

Sounds like your jack plane doesn't work very well. A lot of guys have thought that with all their education they knew more than 18th century woodworkers.

[ian maybury]

Guess i'm in the space that bought a scrub because having to make some calls without the benefit of experience (i've used planes since childhood, but in effect as a general purpose do everything sort of tool sharpened straight across) the ability to rip off a lot of material on stuff that's too wide or twisted for the jointer sounded useful. (still think it is)

That a jack could be set up to do a similar job didn't even cross my mind - my instinctive response would have been that there was no way it would be practical set one up to take such a heavy cut. Which is probably true - until your 4in radius camber (which presumably doesn't project across the full width of the mouth) and the extra momentum kicks in.

The surprise for me was just that the scrub has proved to cut so deep with such ease. I'd expected a wrestling match.....

[Sean Hughto]

A few things, Warren:
1. I completely suck and no one should listen to me.
2. I never said anything about 18th century wood workers or, heaven forbid, that I knew better than any of them. I claim no education whatsoever in woodworking. I ain't on no high horse, you?
3. I grow tired of writing " in my experience" or "when I am working in my shop" but please assume all such qualifiers when reading any of my posts.
4. I try to only write from direct experience - not conjecture or theory or what I read somewhere. You can call my experience crap, and that's fine, but were back to my first point.
5. Given my general crappitude, they will have to pry my scrub from my cold dead hands.

i always find it odd how people on forums are offended when others do things differently from them or prefer different tools than the ones they prefer. It's as though in making a different choice I am disrespecting them. I'm not. I'll always tell people the straight dope about what I see in my shop and what works for me. It's likely that they will have to try things themselves and figure out what is best for them.

[David Weaver]

Sean, do you want to borrow my school picture?

Here's my jack plane, for reference of what I'm talking about. In my true piggish history, I had both the LN and LV scrubs at different times, you know, looking for true happiness and stuff. I landed on this because I got enamored with the mujingfang continental smoothers (they are great, but they are high speed steel and don't love washitas).

I got this on ebay, it's some german brand with 4 letters that I can't remember, and it has a pugeot freres iron (which is half the reason I wanted to try it, I'm assuming that's french and the french had a pretty good grasp on carbon steel, even though they seem to like it a bit soft.). It may look beat...because it is. I can tolerate that as long as it's beat price.

So, anyway, I can make hay with this plane a bit faster than I could with the "real scrubs". The iron is a freehanders dream. It grinds fast and easy, it raises a wire edge easy, it lets it go easily and it's tough and doesn't chip.

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[ian maybury]

To be fair we're all caught in our own thought and experience bubble - it's just the way it is. Even the very experienced. It's always hard to cross reference between bubbles, and equally there's no best or worst where reality is concerned. (Zen mind = beginner's mind and all that) The bit that matters I think Sean is that we each do our best to speak from our own experience - no more, no less. We never truly pull it off...

Wonder if there's room for a pre-distressed option in the veritas' new custom line of planes? No doubt there's a market...

[Warren Mickley]

My apologies, Sean. I did not understand the tone of your post. Thanks to David for efforts to help.