micro bevels a no no on bevel up low angle planes (LV LAJ) and BU low angle block planes. hmm
Hi,
The more I read the more confusing things become.
I decided to buy a copy of David Charlesworth DVD, Hand tool tecniques Part 1: Plane Shapening. His sharpening method uses the “Ruler Trick”. From what I have read online and here at the forum some people advise against using the Ruler Trick when honing low angle block planes or low angle Bevel up bench planes. Others have said that the ruler trick actually makes sharpening more difficult in the long run. In Ron Hock’s book, The Perfect Edge, he writes… “12 degree bed angle is about miniumum for clearance behind the edge and any back bevel would reduce that eliminating the necessary relief”. So do I have this right.. You don’t put a micro bevel on a low angle bevel up block plane or any other BU low angle plane?
What is the prefered method then for sharpening low angle bevel up planes? Do you just resharpen (hone) the primary bevel? omitting the micro bevel (secondary bevel)?
Do the LN and LV plane blades need their backs flattened before being put to use? David Charlesworth advocates flattening the backs of all new plane blades. The back he says should be polished as well as the bevel of the blade to insure a razor sharp cutting edge. You want to remove the manufacturer’s machine marks. According to him the intersections of 2 polished surfaces (edges) will give you a blade that is capable of shaving the hairs off your arm..
wanda
Replies
Wanda,
Both surfaces that make up an edge experience dulling wear in use. I feel you should initially get the backs of the irons to agree with the honing stones you're using. That's why flat stones are important, flat is the only really easily repeatable condition you can create. I strongly feel that anyone who experiences a sharper edge using the ruler trick simply isn't taking care of the dulling wear on the flat face when they hone.
As to the back bevel on bevel-up planes, Ron Hock has it right as far as he goes. The clearance angle on 12º bedded bevel-up planes is very minimal and a back bevel only makes the situation worse by further reducing the clearance. A lot of things influence the amount of clearance necessary. How sharp the iron is, the bevel angle (more acute angles require more clearance), the type of wood and the depth of cut are just some of the things involved. If you want to minimize the effect of limited clearance use a 25º bevel angle, keep the iron sharp and take very light cuts.
The ruler tricks you...
I have to say I agree with Larry that "I strongly feel that anyone who experiences a sharper edge using the ruler trick simply isn't taking care of the dulling wear on the flat face when they hone."
In my experience the ruler trick is counter-productive in the long run, even if there is a short term benefit. I began using the ruler trick on an African Mahogany coffee table after seeing Lie-Nielsen's Deneb Pulchaski use it in a demo on Youtube. At the time I did not have a high-angle frog for my #4 and was experiencing MAJOR tearout despite having a very sharp blade and solid setup - I was aware that a slight back bevel would increase my angle of attack on the wood fibers, hopefully solving my tearout problem - which it definitely helped.
In the end I was left with a blade that I couldn't lap as effectively as the others because of that back bevel and I ran into trouble maintaining the same bevel consistently through sharpenings (also made it harder to detect the "burr" on the back). It got me out of trouble on that project, but given the amount of work it took to re-grind the bevel off the back of that blade I should have stuck with my scrapers or went for the HA frog (which I purchased later anyway).
Now as far as your comment "So do I have this right.. You don't put a micro bevel on a low angle bevel up block plane or any other BU low angle plane?" I would disagree. I would not use a back bevel on a BU plane, but I use micro-bevels on all my edged tools for the reason that they significantly reduce sharpening time and extend tool life.
My method for sharpening, bevel up or down, starts with grinding a primary bevel (usually 25 deg.) on the grinding wheel, sharpening a small secondary bevel to 4k grit (25-30 deg.), then honing my final micro-bevel to 8k a few degrees above that. I do everything freehand so I rely on that primary grind as a guide for my other bevels.
ALL blades (LN, LV, IBC, Pinnacle, etc.) should be lapped and honed before use, IMO.
-Ian
HI Ian,
Last night I found an article online/utube video.. where the man was sharpening a plane iron on plate glass.. that's fine and dandy but he was putting a bevel on both the back (flat side) and the bevel side of the blade. creating a small micro bevel by lifting up the honing jig on small wooden shims. Then he would move onto the next finer grit. Again lifting up the jig using a slightly thicker wooden shim sharpening the bevel side and then the face of the blade... He used 3 grit sizes in total. I've never seen a plane blade sharpened like that. All this talk about back wear and front wear... oh my!
I wonder if the ruler trick is meant to be used with a honing guide to insure repeatability. I Don't hollow grind my blades. I use a course 220 grit Norton waterstone. I also use the LV Mark 11 honing guide which makes putting a microbevel on a plane iron easy. I have tired free honing on my cheaper Stanely chisels but I used the Mark 11 when I sharpened my LN chisels.
All my blades have a primary bevel of 25 degrees. If you are using your low angle block plane for trimming endgrain Should you hone a 30 degree secondary bevel on the 1000 grit stone and finish up with a 2 degree micro bevel on the 8000 polishing stone.
How about a #4 bench plane... What's the ideal pitch? 55 degrees? if working with hardwoods (oak, maple?)
wanda
Glass works too...
Wanda,
Some folks like to use a piece of plate glass as a substrate for wet/dry sandpaper or diamond compound instead of using traditional water/oil stones or a diamond plate - the Scary Sharp system runs along these lines I think. I used a glass plate to lap the bottom of my planes for a while but switched to using the iron top on my TS for that task (bigger working area).
"I wonder if the ruler trick is meant to be used with a honing guide to insure repeatability." - Your honing guide (LV MK2) has settings specifically for setting a back bevel independant of the ruler trick. The ruler itself is meant to be the shim providing a slight elevation across the width of the stone, resulting in only the area of the blade directly behind the edge to contact the stone. Again, I prefer not to use this method because once you have invested the time to properly lap a blade you should only have to revisit that process momentarily during sharpening, not spend hours on it (like you probably did the first time you lapped it). I find that it can be a pain to keep the ruler stuck to the stone on some grits, and it can be hard to get consistant results - I would rather just flatten the whole back completely and not worry about it.
Larry also made reference to the fact that you will have adhesive and abrasive wear on both polished surfaces (your bevel and the lapped back), which is another reason to treat the whole back and not use the ruler trick IMO.
I Don't hollow grind my blades. I use a course 220 grit Norton waterstone. - and thats perfectly fine if that works well for you. However, there are some good reasons to consider a hollow grind, the biggest probably being speed. It only takes me about 5 minutes to regrind my primary bevel on my 6" grinding wheel, much faster than when done by hand. The second reason is the hollow grind itself - by removing most of the material from the midddle of the bevel the amount of metal I need to remove to get my edge back is greatly reduced, again resulting in faster sharpening. Also, when sharpening freehand i find it is easier to feel the bevel position on the stone with a hollow grind - only two points of contact as opposed to a flat bevel that has the potential to round over and yield poor results.
If you are using your low angle block plane for trimming endgrain Should you hone a 30 degree secondary bevel on the 1000 grit stone and finish up with a 2 degree micro bevel on the 8000 polishing stone. Thats pretty close to my setup... I would drop the angle of your secondary a bit if you were doing a lot of end-grain work though. I would advise against skipping grits as well - higher grits are meant to polish, not grind away tons of metal. Stay with each until you feel the wire edge, lap the back then move on.
Keep in mind that the type of steel used in your blade will determine what angle works best as far as edge retention and performance - generally O1 steel holds up better at lower angles than A2 which performs best at 30 deg. or better. Thats not to say they cannot be sharpened however you want and work, but you may find yourself returning to the sharpening stones more often.
How about a #4 bench plane... What's the ideal pitch? 55 degrees? if working with hardwoods (oak, maple?) Thats a hell of a question.... and "it depends" is the only answer I can give. Among other things it depends on the types of wood you normally use, and not all hardwoods are equal either. Different frog angles, or blade bed angles, are called Common, York, and Middle pitch: "Common Pitch" refers to the normal 45 deg. bed on most BD planes, "York Pitch" is a 50 deg. bed angle, and "Middle Pitch" is 55 deg. Generally speaking the higher the bed angle, the better the performance in gnarly grain at the expense of the force required to push the plane (it increases substantially the higher you go).
I won't pretend to be an expert (definitely not) and I'm not going to go into the different chip classifications produced at different cutting angles. I have a 45 and 50 deg. frog for my #4 and I have worked everything from Pine to Wenge with few problems. I use common mostly because I use a lot of softwoods and softer hardwoods, but the York is good to have for when I run into bad news. Take the time to try different setups and get familiar with your tools - that experience will tell you what to do when you run into trouble.
-Ian
Is a 8000 stone really necessary and does it make a difference?
I get a shiny finish on figured hard Maple with cross grain, using 1500 paper on a granite plate. With this difficult grain, I use a LV plane, main bevel 30, with two micro bevels about 1 1/2 degrees each and a back bevel of 15 degrees. The mouth adjustment is about 0.006"
I use to use water stones, but keeping them perfectly flat, to give a true blade surface within a couple of thousands was too much work.
The 1500 paper with a LV jig is fast enough making the grinder not necessary to maintain the main bevel.
Thats really up to you and your own standards, but I'm willing to bet you would see a significant difference. I hone up to 8000 and I can literally see my reflection in the surface of a piece of Red Oak I planed last night.
As far as keeping them flat, its not a problem as long as you are disciplined and use a system. The cutting speed more than makes up for it IMO.
-Ian
Back bevel a non-issue IMO
Hi Wanda-
I've used BU planes (LN #62, LN Low angle block planes, LN low angle #7) with and without back bevels on the blades. I have never been able to tell the difference in use.
Best regards.
mj
Hi Wanda
There are so many opinions on sharpening. Here is another.
Keep in mind that we are discussing BU planes.
For years I avoided the Ruler Trick on BU blades. Now I use it each time I prepare a blade. This is not, as David Charlesworth originally intended when he published this strategy, to ensure that the back of the blade is flat, or a short-cut to honing the back of the blade. It is, instead, insurance against the incursion of a wear bevel. Larry likes to tell us about this, and so make chip in.
When planing all blades wear on both sides of the bevel. With BD planes one hones or grinds away this "wear". On the bevel up blade it cannot simply be ground away as it lies behind the bevel. Grinding back here increases the relief angle, to which you referred.
Now the good news is (a) the Ruler Trick removes 2/3 of one degree, so does not affect the relief at all. Let me repeat that - not at all. And (b), this micro backbevel is just where the wear bevel forms, and so makes this threat go away.
To be objective, I work with abrasive hardwoods all the time and have done so for many years. I use both BU and BD planes equally. At the high cutting angles I need for this wood BU smoothers are easier to use. The are certainly easier to push through the wood at these angles than BD planes with the same high cutting angles. On the other hand I much prefer the ease of honing a BD plane (as I freehand blades by choice and BU planes demand the use of a honing guide). At these high angles (e.g. 50 degree microbevel), the working edges do not last too long anyway. A BD edge at 30 degrees would likely last longer. So at the end of the day it is a decision made as to what you need - the longevity of a BD plane versus the capability of a BU plane.
Regards from Perth
Derek
"...Now the good news is (a)
"...Now the good news is (a) the Ruler Trick removes 2/3 of one degree, so does not affect the relief at all. Let me repeat that - not at all. And (b), this micro backbevel is just where the wear bevel forms, and so makes this threat go away...."
I guess it's possible that, when I wasn't looking, someone standardized the thickness of all the rulers in the World and made it impossible to set the edge of an iron anything other than a specific distance from a ruler when doing the ruler trick. I suppose that's how one can come up with such a specific angle. Even so, 2/3 of a degree is 5.5% of an inadequate 12º clearance angle in 12º bedded bevel-up planes. If one has something that's not as much as needed, I don't see how reducing what you have by 5.5% is going to do anything positive.
The reality is that both the wear bevel and the back bevel are forms of dubbing, one caused by wear and the other intentionally created. In use, the bigger a wear bevel gets the faster it grows. If the dubbing caused by the ruler trick made the threat go away, a wear bevel wouldn't have the growth pattern it has.
Why do I bother to answer this? Only because your reply obscurs a helpful tip, Larry.
Make it easy for the OP. She is a relative beginner. We both know what I have suggested works, and works well, no matter how picky you want to get with irrelevant details.
Regards from Perth
Derek
Insight?
Hi Derek,
"The are certainly easier to push through the wood at these angles than BD planes with the same high cutting angles."
My only BU planes are block planes, so I have no means of evaluating the difference. I am quite curious as what do you think accounts for such difference. The geometry is the same for BU and BD planes within a small (say 1/32") distance of the cutting edge. So, the source of the difference is likely to stem from something else - I can only think (as I have no measurements available) of the tote of BU planes being at a greater distance from the cutting edge than with BD planes. That would translate into a lower (and more efficient) angle of the applied force. But can you think of some other factors?
Best wishes,
Metod
Hi Metod
There are two factors that I can think of. I must emphasise that these are just my thoughts - I am not a mechanical engineer.
The first is that the totes on the Veritas BU planes are more vertical. The Bailey pattern totes angle further forward and add weight over the mouth, which increases resistance.
The second factor is that BU planes have a low centre of effort. Pushing through this requires less force than the higher centre of effort Bailey pattern planes.
Regards from Perth
Derek
Insightful
Hi Derek,
Thank you for sharing your insights.
"the totes on the Veritas BU planes are more vertical" - this part makes much sense to me. I am not so sure (and that,s my thought <g>) about the role that the center of mass plays. My thinking (what else without different plane designs at hand) is that the cutting force originates along the cutting edge, and the friction force along the sole and parallel to it. Both have to be counteracted by the woodworker. How significant is the role of the center of mass to these two (I am sure there must be some), I wish I knew more about.
Indeed, a mechanical engineer (or anybody else with a good grasp of force diagrams) would be welcome to share.
Best wishes,
Metod
"...The second factor is that
"...The second factor is that BU planes have a low centre of effort. Pushing through this requires less force than the higher centre of effort Bailey pattern planes...."
Can you explain "centre of effort" and how it applies to planes. All I can find that might be relevant applies to sail boat and sail design. Unless it's something involving the Center of Effort winery. In which case you may have had a little too much?
I'm not an engineer, just an amateur wood scientist.
I would have to ask you to explain "center of effort" because, like Larry, that is something I am unfamiliar with.
I cannot see how planes with equivalent cutting geometry will require different amounts of force to push unless one has significantly more mass than the other. The ergonomics of the handles might change the location on the force a user applies to the tool but it should not change the amount of force required to move the tool as long as the geometry is the same - I have serious doubts that the Bailey pattern tote adds any perceptable resistance BD vs. BU. I have both types of plane and in my experience any difference in "pushing force" can easily be explained by a slightly duller or sharper iron in either tool.
As far as the ruler trick establishing a 2/3 deg. back bevel... I disagree. Even being extroardinarily careful and methodical with my setup, there are too many variables at work for me to claim such a tolerance (not saying that others couldn't, just unrealistic). Invariably the iron would drift, shift, wobble, or the ruler would move altering the intended angle. In my experience, after the initial time investment of lapping the back flat has been spent, subsequent lapping is a brief task on a maintained blade so I see no reason to resort to the ruler trick. The reason I used it in the past was to tame unruly grain and even then I wished I had opted for a HA frog instead.
-Ian
"Centre of Effort" is indeed
"Centre of Effort" is indeed a term used in sailing and it is the best I can come up with at this time to explain in technical terms what I directly experience.
Keep in mind that I am not a mechanical engineer. While I did study a little of this before I moved into psychology, that was 40 years ago and I have no technical references to use now. Hopefully others can help here.
So where does C of E comes from? I windsurfed very seriously for about 30 years, competing on both the local national circuit and in a few international competitions. At this level I needed to understand the design of the equipment and how to tune it. C of E refers to the centre of forces produced by the wind on the sails when sailing across the wind. One has to find a balance between the forces of the wind that similtaneously drive you forward and sideways. These forces may be tuned by the shape of the sail - bag the sail out and you move the forces up and back. Flatten the sail and you move the forces down. Forces that are at the top of a sail (high centre of effort) will unbalance it, and forces that are low (low centre of effort) will be more stable.
Like a suma wrestler, a low centre of effort/gravity creates greater stability.
Several months ago I approached a friend of mine, a professor of physics at one of the local universities, to compute the forces from the angles taken from a typical BD Bailey pattern plane versus those from a typical Veritas BU plane. The conditions were to hold the cutting angles and blade widths the same. His replay was quick:
I don't see the need for any maths, if everything is held constant (including the tote and hand angle) then there should be no difference.
Forward angled totes will naturally lead to the operator applying more downward force increasing the friction between the bottom of the plane and the wood leaving less forward force.
I don't know about "vertical" totes on the Vertias stuff
I just measured my Lee Valley BU totes - tricky because they are curved but I get for the;
BU Smoother : 71º
BU Jointer i: 74º
The good old stanley #4 is 61º
Assuming the operator applies a force F to the tote at right angles to the tote.
Relative to F, the "forward force" to "downward force" ratio for a 60º tote is 1.73
For a 70º tote its 2.75
ie a ~60% difference
Of course The operator does not alway apply force to the tote at right angles to the tote especially as the operators arm moves thru some sort of arc and angle during the planing action.
First of all note that a more upright tote creates less resistance than a more forward orientated tote.
There is more to it than this, however. My professor friend has no experience with sails and sailing but he recognises that the actions involved are not simply linear, and do involve some interaction.
My logic says that forces applied on the horizontal, in line with direction of movement (the plane moving forward), require less effort than forces that are applied off the direction of movement. In other words, a plane with a low bed (low centre of gravity) being pushed forward using a tote that directs forced forward (and through the plane), will encounter less resistance than a plane where the centre of effort is high and the forces are directed down and into the plane.
Someone can no doubt do a better job at explaining this, but this is how I think of the differences in forces between BU and BD planes. If am wrong I learn something. If I am right I learn something.
Regards from Perth
Derek
When is a tote not a tote
See photo. Pretty much ignore the arrow (that was for another discussion ).
The force comes into the plane roughly along the axis of the forearm.
Note the forearm is off center of the palm of the hand toward the pinky and more importantly toward the sole of the plane.
Same for BU or BD. Tilt the tote up or down the force is still down about two inches above the pinky or so. tilting the tote forward just makes one need to grip it so ones hand doesn't travel up the tote. I find the straighter more vertical totes of the Veritas planes to be more comfortable and produce less hand strain than the elegantly curved tote of my LN bevel up. I finally learned to not grip it hard when planing but to relax my hand and press low on the tote and only grip when lifting the plane off the work.
The photo is of an #3 that I couldn't use because my wrist kept banging the edge of the planks so I was even lower on the tote than the first photo shows. Best I could do and still take the photo.
Flip the blade over, stand it up on end or throw it out the window, it makes no change in the tote and the distance from the forearm axis to the sole of the plane.
The sail is the tote not the blade.
PS: on reflection if I were a carpenter and attempting to plane something I was kneeling on on the floor I would prefer a forward tilted tote; a vertical tote would be problematic because I would tend to apply force high on a vertical tote as if it were a knob. Other than that why a forward leaning tote ?
Ahoy, ye lubbers!
Dereks patter about center of effort (he has a sail plane?) sounds a little like the term "vector" that we used in high school physics. All this jabbering about tote angles (ain't luff grand?), and resistance (towing a sea anchor) seems to me to be ignoring one thing. (It does keep the discussion simple while allowing one to sound learned.)
You guys only use ONE hand when planing? I use both hands (mainmast and jib boom), and if the wood is hard, or the iron is less than perfectly sharp, I am pressing DOWN (adding ballast) with my forward hand. Reckon that increases the felt resistance? Course, the candle stub I rub over the sole from time to time helps with that (scraping the barnacles). Oh, crap! Another variable!
BTW Roc, I think you hit the ball out of the park with your observation that a dubbed edge on a low angle bevel up iron will skate along (like a hydrofoil) and take only a very fine shaving if any at all.
Yo, ho, ho, avast me hearties, etc,
Ray
bemused ? ( well . . . actually . . . amused )
This old thing again . . .
Comes back to this . . . a "bevel" that is rounded by all this trickery is rounded. Even though the edge shaves arm hair or what have you if the clearance angle is small to start with, as Larry says correctly over and over by the way, then rounding it is going to effectively put some of the of the 2/3 °, or what ever it is, "bevel" down on the wood surface which will prevent the edge from sinking into the wood very far.
What's that mean ?
. . .
It means the bevel up plane is riding down the wood face on the rulered back bevel like a ski. Sure if you are lucky it takes off some wood.
[ Rulered. Look at that . . . I just invented a new term. It may even replace the common word " screwed ". Dude, you're sooo rulered. Ha ha ha ]
Now take the bevel down plane.
There is way more clearance, unless one has misguidedly ground it to a wide sharpening angle, and with luck less rounding because we, that is to say YOU not me , are not tricking the "bevel" by using a ruler to help round the "bevel".
A true back bevel, not that anyone would ever want one on the blade of a bevel up plane, sharpened with a jig would be a flat facet not a roundy thing.
So
for two reasons, at least, the bevel down blade can sink down into the wood and take all the cut and more that the former bevel up blade could have if it too had had adequate clearance and a truly flat faced backBEVEL rather than the rounded "bevel".
DEEPER CUT MORE RESISTANCE. Deeper cut takes more horse power. THE ROUNDING AND LOW CLEARANCE ANGLE LIMITS THE DEPTH OF CUT.
And as i have banged the proverbial table over and over . . .
( he said frothing at the mouth; hair in disarray hanging down over one eye; beginning to turn into a werwolf ( hey it's Halloween )) . . .
bevel down planes have a less well supported blade right near the edge; SO the blade in the tapered area of the sharpened bevel can bend down minutely and actually do two things that can account for the higher resistance / requirement for horse power :
1. increase the cutting angle
2. increase the depth of cut
Without the rounding and low clearance angle the blade can go right on down into the work.
Rounding and low clearance . . . strong arguments to put this silly ruler trick to rest once and for all, for bevel up plane blades at least.
Add in the fact that a radiused blade cannot be sharpened properly with the ruler and I would call it the holly stake through the heart of the evil beast.
Good riddance. Please . . . do this for me . . . sharpen that holly stake . . . swing that mallet . . . and please . . . please let me live a normal life again . . . unaffected by the call of the blood sucking, brain power wasting, vampiruler.
: )
Hi Charles
I am citing Mr Charlesworth, who appears to have done the maths (he has discussed this in some detail on a few forums since Larry is apt to argue the point with him).
I can find references, but is it that important?
Regards from Perth
Derek
I'm beyond fascinated
....by the notion of accurately and consistently measuring 2/3rds of one degree in the context of honing woodworking tools, *perhaps* exclusive of certain highly engineered honing fixtures where the wear on the brass or plastic roller alone over time would be enough to knock it out of that sort of accuracy, if it was ever that accurate in the first place. Which I doubt.
So, are you, Mr. Charlesworth, or anybody else for that matter asserting that this level of accuracy is attainable and repeatable in the context of a thin, little ruler sitting atop a honing stone?
back bevels
I'm just a ham-fisted amateur, so take what I have to say with a grain of salt! I like simple and simple is really not fussing around with a lot of extras when sharpening. For the most part, I do not use jigs (I do for short blades, like a spokeshave).
First I flatten, and the stones used (oilstones) are in the same sequence when honing. The first is an old Washita, then a transparent arkansas and finally (depending upon my mood) a bit of stropping on a piece of horsehide with green compound. When I feel "sparkly" I'll put a bit of DuPont Perfectit III (automotive compound) on a piece of MDF to bring things to a mirror polish. If I have an old plane blade or chisel that is in rough shape, I drop back to a coarse india.
I do use a bench grinder to form the bevel, and then hone on the same stones in the same sequence (similar to the Tools for Working Wood DVD by Frasier). I also have to add that I also don't fuss a lot over angles. I've found that the less I putz around with sharpening and stay with the basics, the better job I do. With repeating and using the same simple steps, sharpening & honing has become second nature.
: )
: )
Pleased to say that your post is
pure art.
.
Yeah Ed. It reminds me why everyone moved away from Knots. Me too. Bye.
Regards from Perth
Derek
You sure....
you aren't going to stick around long enough to complain about everybody who disagreed with you and get them barred from the forum? What a *potentially* refreshing change.
What happened to :
>If am wrong I learn something. If I am right I learn something.<
I enjoyed hearing about Derek's sail boarding. Sorry to contribute to the hard feelings.
It is fun to get all excited and pound the keyboard again.
I love all this nitty gritty stuff. And it is Halloween. After all. Guess that's not a good excuse.
Well off I go to have Queenmasteroftheuniverseandbabbybunnytrainer spank me and tell me "NO".
I"ve been bad. Again.
.
Front & back bevels are good
Use of a <1* back bevel will reduce the amount of grinding required on the primary bevel by removing the back wear bevel on the prevalent side of the blade Simple geometry will provide the shim thickness depending on the distance from the blade edge for the angle desired. While this does reduce relief angle I find no concensus for what the minimum is - sources claim down to 6-7* as acceptable. Microbevels on the primary side make perfect sense & work excellently, reducing honing time and extending grit life. Back bevels ( or facets) are not in any way like "dubbing an edge" & do not "skate" on top of the wood or prevent the blade from "sinking" into the wood. The plane sole prevents the blade from sinking into the surface.
As a professional engineer I can weigh in on the effort question - with all variables held constant a BU plane wil cut with less effort due to the force generated by the chip hitting the chip breaker on a BD plane is not present. Cutting angles, weight, surface finish and other variables held constant. Dissectng the tote angle question quickly leads one to only one answer - which one do you like? There are far too many variables in the situations and humans to draw any conclusion.
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