Clearance angle/back bevel

[Winton Applegate]

Though the books say to finish a marathon one must have a dambed good reason and keep it in the for front of your mind.
It's complicated.

Since Mike hasn’t got back yet
I can blather on for a while until then . . .

even tho the cutting angle is the same , it is not wise to put BB on it?

Well yes that is what I said, partly because I am so irrationally militant against all this obsession with violating a simple flat surface on the back of the blade for no practical gain except well, I won’t get into the ruler mine field tho I do enjoy the whole hopeless last stand thing of the lone machine gunner battling away against impossible odds as his gun begins to seize and the last belt of ammo is fed in . . .
. . . all the while the blasted two way is muttering on some rot about the war being over . . .

I suppose it is the case only with the 12° BU but mostly it is because the BD planes have started it all all this need with varying the underside face of the blade, which is the bevel, and really it isn’t all that necessary.
. . . back bevel the hell out of your 20° bedded bevel ups if you must but I don't see why.

(something happans to dynamics jyst after cut-on trailing side of edge under the plane)

yes wood fibers are flexible, more so than say . . . machining steel would be, and then especially when the blade begins to wear some; the wood fiber flex pushes the blade some what up out of the cut
I used to TRY to compensate for this by advancing the blade slightly and pushing down harder.

Now speaking strictly from my learning curve which was exclusively on purple heart and bubbinga , before moving on to walnut and the more friendly woods,
for the former two woods not enough clearance and advancing the blade like that and pushing down harder were HUGE MISTAKES.
Enough clearance (at least 12° minus some wear bevel and sharpening (changing to a fresh blade from the stack of blades) were KEY to producing a flat surface on the wood.
WAY MORE SO THAN USING A LONG JOINTER PLANE.

If I waited and tried the above dodges, advancing blade and pushing harder, I wound up with a convex surface on the wood because the beginning of the cut was deeper than the middle of the cut and IT SEEMED but doesn’t make sense that the end of the cut also was deeper. Using a properly sharp blade there was no problem with convexitude dude.

and the "back pressure" (Soupnig up block plane article) becomes too great, forcing the blade up out of the wood?? Skidding results?

No
not really
back pressure is more along the lines of resistance to forward progress/taking a heavy cut compared with having too much back pressure to take that heavy cut.

Perhaps Kees can correct me, because I am about to be wrong here, but the force causing the blade to rise up out of the wood is called “N” factor or in any case not the same as the back pressure force.

Back pressure would be the force that bends the blade down into the wood deeper.

The force resulting from not enough clearance and the blade getting dull, at least in part, causing the compressed wood fibers to now over come the geometry of the blade and reject it out of the cut would be the force roughly opposite to the back pressure.

Master.... Is this the only downside/significance of clearance angle?

There is the heating effect on the blade. Probably not significant in most cases. With the purple heart, at least some of the planks, I would get a build up on the blade of the “resins” in that particular type of wood. It may have been less if the blades didn’t get as hot from having less clearance and being dull and forced to cut anyway.

Now that is splitting some serious BS though.

Finally, and for me this is the crux :
BACK BEVELING THE FLAT SURFACE OF THE BLADE IS A PAIN IN THE JIG
it is far easier to flatten the back and leave it alone with the occasional polish while working the wire edge.
Back beveling ACCURATELY, meaning not rounding the silly thing, is a useless bother for a bevel up and not all that important, but at least mildly useful, for the bevel down but just as tedious . . .
well . . .
nearly as tedious because it is ok to round it on the bevel down because we are not talking clearance any more but EFFECTIVE cutting angle ( the clearance is on the opposite (bevel side) of the blade next to the wood.

The next to the wood modification would be on the bevel side of the blade and even though it is on the wood side of the blade would be called a secondary bevel.
The back bevel on the bevel down blade would be on the flat face on the NON wood side of the blade and simply because it was being done to the flat face of the blade would be called a back bevel. (being done to as in molested or interfered with)

As a result of trying to type those last few paragraphs I may, now, be completely insane from typing all that and be in need of some serious vacation time.
The big snow storm is coming in now and work has called and said stay home so . . .
. . . by the grace of Bob . . . that vacation time has arrived.

I may not respond again now for a while, if ever, . . .
if there is a fire or world calamity that I need to know about I can be found laying on my side on the carpet, staring blankly and unblinkingly, drooling and slowly gasping for air like a beached fish.
thank you for your questions . . .
Wheeewu

[Brian Holcombe]

Suffice to say I agree with Winton. I like to keep the back flat, I avoid things like the ruler trick.

[David Ragan]

In all sincerity-thanks guys👍😀
i read all the above a few times- and will do so again after the effects of the painmeds wear off from my knee surgery
in spite of appearances, i at times like things to be simple