back bevels

[engineer one]

the latest issue of the merricun magazine Woodworker's Journal
has an article by Ian Kirby about putting a back bevel on plane blades.
he makes the point in a different way from DC, and the drawings are
interesting.

anyone else think this works better than Frank's treble bevel?? :wink:
paul

 

[MikeW]

hey Paul,

I'm not a member of the flat back society, and I don't generally care to use back bevels (they are for making one not need to flatten the back. They don't help in edge retention enough to do them for that), neither do I usually do micro (or multiple) bevels, except the ones I end up with while working and honing freehand...I guess I'm the wrong person to answer :lol:

In fact, the only planes I think I take the time to ensure that their edges are done as good as I care to get them are my molding planes and the couple smoothers I still have. And all I care about those is to make sure they are sharp enough.

Take care,

Mike
the writer of this totally worthless post

 

[engineer one]

yes mike but what's sharp enough. (hammer)

the more i study all this, the more i know that i need to stick
to a smaller number of woods, and make smaller things,
then maybe tear out won't affect me as much as it seems to
others.

i think that in conversation, dc makes a good case for a flat back,
but maybe in print it seems a waste. and at the end of the day
if your plane does what you want, then it is sharp enough.
its just that Ian Kirby seems to be an american DC, and his
views are interesting.

maybe i'm spending too much time thinking again
and not enough working :lol:

paul
you know it is never the question that is wrong, only the
answer you thought was needed.

 

[Anonymous]

Isn't Ian a Brit?
I think everyone develops a variation they like. I use 3 bevels and a backbevel on most bench plane blades simply to reduce the time and metal removal. Blades and abrasives last a long time.

 

[MikeW]

Hi Paul...to me, sharp enough is an edge tool that produces the desired result.

Don't get me wrong, things are pretty darn sharp (whatever that is as well). It is probably more accurate for me to say I don't refine the edge as much on some planes as others.

I think that sometimes people can take fettling and preperation of a plane blade to its ultimate expression--which is perfectly fine by me--but if the issue is planing wood it may be to greater tolereances than the person or material is capable of.

I know of one person who has his plane blade backs surface ground to save time, the soles of his [metal] planes scraped. I'm only surprised he hasn't figured out a way to consistently torque his lever caps to the same degree of tension as when the where flattened.

How far we take preperation of the tool itself is a personal thing. There is a point in that process that the tool will actually perform the required task, though. That, to me, is enough.

Take care, Mike

 

[bugbear]

Isn't Ian a Brit?
I think everyone develops a variation they like. I use 3 bevels and a backbevel on most bench plane blades simply to reduce the time and metal removal. Blades and abrasives last a long time.

Are you using a tiny back bevel to minimise back lapping (say < 1 degree) or a significant back bevel to increase effective cutting angle (say >= 5 degrees) ?

Confusion between these 2 (similar, but distinct) ideas is rampant!

BugBear

 

[Anonymous]

Usually tiny (about 2º and .01" wide). I still flatten the backs just not quite as carefully.

 

[Wiley Horne]

Hello All,
Just a small note, in light of the increasing popularity of bevel-up planes, esp. the 12-degree bedded ones. I suggest using back bevels only on bevel-down plane blades. Bevelling or rounding the back of a bevel-up plane blade will cause a significant loss of clearance angle.
#2: I really like Ian Kirby's instruction--always extremely practical and to the heart of the matter. I think us 'Murricans ought to just proudly claim him as our own, since he's been in the States so long.


Wiley Horne....always enjoying this forum and out of lurk mode for a bit

 

[Chris Knight]

Hi Wiley,
Nice to see you here in the flesh so to speak - welcome!

 

[Alf]

Wiley Horne....always enjoying this forum and out of lurk mode for a bit

Who is that masked galoot?! :lol: Welcome into the light, Wiley.

Cheers, Alf

 

[Waka]

Wiley Horne

Welcome to the forum, good contribution already.

 

[Derek Cohen (Perth Oz)]

I suggest using back bevels only on bevel-down plane blades. Bevelling or rounding the back of a bevel-up plane blade will cause a significant loss of clearance angle.

Hi Wiley

The ease with which we make our international visits makes it harder to know whom is the visitor and whom is the visitee! Nice to have you vocal.

DC has a lot to answer for regarding the use of "mini" backbevels on plane blades. This is my term - would that help separate our the angle-changing from the blade-straightening types? The fact is that there really has been little discusion about backbevels and their effect on BU planes. Perhaps it is time that our collective wisdom is used to write the book.

Let's take the angle-changing type first. A backbevel of 5-10 degrees on a bevel down blade is used when there is a desire to increase the effective cutting angle of the plane. This is a well-known, established method for BD planes.

Use this same degree of backbevel on a BU plane and you could be in trouble. From memory (never a good thing in my regard) the minimum clearance angle for a BU plane is 6 or 7 degrees. So, take 5 degrees (the backbevel) from 12 degrees (the bed angle) and you have 7 degrees. Ouch.

Now the mini-backbevel is a different kettle of fish. Using the "ruler Trick", it is only about 1 degree. It is not intended to alter the planing characteristics. Rather it is intended to clean up the back of the blade. It is an alternative to the hours that might go into flattening the back of a plane blade (since, as we all are aware, you ain't goin' to create a sharp edge unless it is a single edge).

A second use for DC's mini-backbevel (in my view) is that is does a better job of removing the wire edge from A2 blades than just rubbing the back of the blade back-and-forth on a waterstone (or your own favourite poison). The effects of a poorly removed wire edge can be heart breaking. So the use of a mini-back bevel on BU planes is quite desirable and is a separate matter from the issue of flatness, per se.

On a BD plane, a mini-backbevel is going to pose no problem at all. On a BU plane, a 1 degree bevel should have no effect whatsoever on the clearance factor.

The question remaining is what effect does the mini-backbevel have on the planing characteristics of a BU plane? I am not clear here. My logic says that it is similar to the effects of a backbevel on a BD blade, that is, it will increase the cutting angle by its amount. Still, I cannot see 1 degree making much of a difference. Can someone clarify this point? And, of course, comment on the others I make.

Regards from Perth

Derek

 

[Chris Knight]

The question remaining is what effect does the mini-backbevel have on the planing characteristics of a BU plane? I am not clear here. My logic says that it is similar to the effects of a backbevel on a BD blade, that is, it will increase the cutting angle by its amount. Still, I cannot see 1 degree making much of a difference. Can someone clarify this point? And, of course, comment on the others I make.

Derek,

I think you are now going to have to give your definition of cutting angle. It will make the edge (angle) of the blade less acute but the angle between the surface of the main bevel and the wood won't change of course. In terms of the difference it might make, I shall be interested to hear from someone but I am not going to try it on my own BU planes which have a 12 degree bed angle thus a 1 degree micro-back bevel is about an 8% change in clearance which I reckon is quite a lot. Of course I could grind it out if I don't like it but perhaps one of our intrepid experimenters will test the water first!

 

[Derek Cohen (Perth Oz)]

I think you are now going to have to give your definition of cutting angle.

Hi Chris

Well, the cutting angle of a BD plane is the angle of the frog (ignoring the alterations made by a backbevel). So a plane with a 45 degree frog has a cutting angle of 45 degrees (regardless of the bevel angle of the blade).

On a BU plane the cutting angle is the bed angle plus the bevel angle of the plane. So 12 degrees (bed angle) plus 25 degrees (blade bevel) = 37 degrees of cutting angle.

So the cutting angle is the angle that is presented to the wood.

But of course you know all this.

It will make the edge (angle) of the blade less acute but the angle between the surface of the main bevel and the wood won't change of course.

This was what I originally believed, but I am no longer so sure.

Here is a related issue: honing a camber on a BU blade. Do you hone it as you would a BD blade (at the front of the bevel), or would you hone the backside? I'd like to say more about this now, but it is after 1:30 am in Perth and my brain has suddenly gone numb! I look forward to reading the discussion tomorrow.

Regards from Perth

Derek

 

[MikeW]

BU BB...semi interesting issue. Or what the heck, BBs anyway.

There are more issues involved than merely altering included/combined cutting angles on a BD plane or relief angles for a BU plane.

One of the issues involves wear bevels. That is, a plane blade bevel wears on both the front and back. Depending on the bedded angle, this is a more or less than proposition.

A lower bedding angle--for instance a BU plane--wears more quickly on both sides of the bevel due to its attack (bedded) angle.

Combined with this is the fact that the more steel in thickness as the bevel(s) near the very edge, the more rounded the wear bevel becomes more quickly. The more obtuse those to planes meet, the duller/more rouded the wear bevel.

But as in most things, there are trade-offs involved. The thicker the plane of those two angles--the angles both the front and back of a plane blade meet--the stronger the edge itself is. While this does not have an affect on the rounding, it does prevent premature edge failure in the way of knicks and edge folding. A very good thing on harder timbers.

The thinner bevel towards the edge--the meeting of the front and back bevel planes--the less wear bevels have an impact on loss of apparent sharpness. In other words, the cross section of the wear bevel is thinner as it develops and seems to present a sharper (thinner) edge as it develops. But it also knicks more easily and can, if too acute and angle of the primary bevel is used, literally fold the edge.

So the point? I have no idea. Practically, we all establish our own idea of edge durability (more obtuse combined bevel angles) verses fragility and apparent sharpness (more accute combined bevel angles).

My personal opinion is that I will forego flattening of backs as a matter of course, prefering instead to do small micro back bevels regardless of whether it is BD or BU plane.

Take care,

Mike
who is too lazy anymore to go through all that work...
and who desperately needs to go sharpen more saws...

 

[Chris Knight]

Here is a related issue: honing a camber on a BU blade. Do you hone it as you would a BD blade (at the front of the bevel), or would you hone the backside? I'd like to say more about this now, but it is after 1:30 am in Perth and my brain has suddenly gone numb! I look forward to reading the discussion tomorrow.

I produce camber by honing the blade as I would with a normal bevel down blade. I only flatten the back. If one were to attack the back then there would be a changing clearance angle across the blade which makes my reluctance as mentioned above even stronger!

 

[Alf]

<snippage of much technical stuff>

My head hurts.

 

[Wiley Horne]

Well, my bevel up planes are shoulder planes and a skew block, so this is kinda abstract. But on the face of it, it seems that Derek would want to camber his bevel-up planes on the primary bevel side, and not the back, for the reason given by Chris.

On the micro-bevel point, the highly-qualified will surely be able to manage their available clearance. My original suggestion was directed more toward those getting their start in hand planing with bevel up planes, because changes made to a blade back are hard to undo. If you have 12 degrees of gross clearance, and approx. 7 degrees of that is a working minimum, then you have 5 degrees of usable clearance, which the lower wear bevel begins to chew away at as you plane. So a 1 degree micro bevel takes 20% out of the usable fraction--the 7 degree base is fixed. And if 1 degree becomes 2 through some imprecision of technique or stropping, etc, then that's 40% of the available. This would not be noticed on the initial planing strokes, or initial 'wow' factor, but would bring about re-sharpening faster than if the back were left dead flat.

A follow-on query is whether clearance angle affects the speed at which the lower wear bevel develops. In other words, does the clearance angle that you start with affect how many feet of shavings you can put on the floor before it's time to re-sharpen? Seems like it might, because at a real low bedding angle, wear on the lower blade edge will rapidly expose more metal (and more wear). In the bevel-down world, the Japanese are very careful about honing angles and bevel-flatness for this very reason. In the bevel-up world, more data and experience will shed light on whether this is of practical concern. In this connection, Mr. Holtey bedded his No. 98 at 22.5 degrees for some reason.

Wiley ... hoping Alf doesn't punch my ticket and send me to the corner for a while.

 

[Frank D.]

A follow-on query is whether clearance angle affects the speed at which the lower wear bevel develops. In other words, does the clearance angle that you start with affect how many feet of shavings you can put on the floor before it's time to re-sharpen? Seems like it might, because at a real low bedding angle, wear on the lower blade edge will rapidly expose more metal (and more wear). In the bevel-down world, the Japanese are very careful about honing angles and bevel-flatness for this very reason. In the bevel-up world, more data and experience will shed light on whether this is of practical concern. In this connection, Mr. Holtey bedded his No. 98 at 22.5 degrees for some reason.

Wiley ... hoping Alf doesn't punch my ticket and send me to the corner for a while.

Wiley,
IMLE (L for limited) the bevel angle affects how long a blade holds its edge. A blade with a higher bevel angle, like the 40° or so that you might need on a plane with a 12° bed, doesn't stay sharp as long as a blade with a 30° bevel, that you'd be likely to put on a blade with a bed that sits 10° higher. I ordered a handled mitre plane kit from Shepherd (which I'm still waiting for...) with a standard angle bed (20°) for this very reason.
Just a thought,

 

[Frank D.]

Actually Wiley I was just thinking about your post in the shop, and it never even struck me that the difference I perceived might be caused by the clearance angle; I thought it was the bevel angle that made the difference. I'll have to observe my blades with this in mind.