Thread: Bevel down, bedding angle and primary bevel

I don't have any evidence for you monoman, but I will instead express my experience.

I little while back I played at length with back-beveling of bevel-down plane irons on standard 45 degree bedding. From a presented angle of 45 degree through to 70 degrees with clearance angles varying from 10 to 45 degrees using standard Stanley plane irons my conclusion was this: a) clearance angle bore no relationship to how well the edge lasted, and b) clearance angle factors heavily in how long I could use the iron before resharpening.

If you've read these last statements and wondered whether I've lost the plot, please read on.

I'll give an example to explain my finding. I take a stanley plane iron with a 25 degree primary bevel and a 15 degree back bevel, this give me a 60 degree presented angle with 20 degree clearance angle. With this configuration I can happily go at a hardwood board for roughly the same length of time as I would any standard configuration. At some point it stops cutting so it's time to resharpen.

Following this I took another plane iron and turned it bevel up with a 20 degree primary bevel, resulting in a 65 degree presented angle and 45 degree clearance angle. Of course, you'd expect the edge to deteriorate pretty quickly given the primary bevel, but the surprising part was that this didn't stop the plane cutting. In fact, I noticed that the shavings were getting thinner as I went. I rightly concluded that this was because the edge was wearing out... so I wound on a little extra depth to the iron, and it keeps going. In the end rather than the blade no longer cutting, it starts producing a poor finish, then it's time to re-sharpen. Even more surprising is that it seems to have lasted longer.

I can't say I absolutely understand this, but the experience leads me to believe that wear on the edge will make a plane iron cut poorly, but lack of clearance angle stops the plane cutting at all. I can only imagine that a lack of clearance angle means that as the edge wears more of the primary bevel comes into contact with the work. This may result in a larger surface area of steel in contact so that the iron skips over the surface instead of penetrating. On the other hand, a larger clearance angle (or smaller primary bevel depending on you perspective) angle will result in a smaller surface of steel exposed to the work peice, which can be further forced to cut more easily. This seems to explain why the higher clearance cut longer, but produced a poorer finish as it wore out.

That's about all I can say from that experiment.

EDIT: I spent all that time writing that and you found you answer already? Damn! From this experience I'd agree with Terry too.

So what causes the lower wear bevel to form?

Originally Posted by silentC

So what causes the lower wear bevel to form?

About the simplest answer to that questions is, pushing the blade through wood.

Both upper and lower wear bevels form at the same time, only the upper wear bevel is always about 3 times bigger.

Yes I realise that

But if the fibres are cut off at the height of the cutting edge, how do they exert enough pressure on the bottom of the blade, which angles away by virtue of the clearance angle, to produce any wear at this point? Wouldn't you just expect to see the top edge rounding over?

Actually I still don't really get how a plane works to make a surface flat, because if you look at the bottom of it, the "in feed" and "out feed" are in the same plane, with the blade sticking out. Explain to me how that results in a flat surface.

However maybe that has something to do with it.

Originally Posted by silentC

Yes I realise that

But if the fibres are cut off at the height of the cutting edge, how do they exert enough pressure on the bottom of the blade, which angles away by virtue of the clearance angle, to produce any wear at this point? Wouldn't you just expect to see the top edge rounding over?

They well may be cut off at the top. Only the iron in the blade doesn't know that it should only wear on the leading edge, so some of the wear also occurs on the trailing edge. Maybe it's cause by the metal trying to curl under against the pressure of the cut.

Originally Posted by silentC

Actually I still don't really get how a plane works to make a surface flat, because if you look at the bottom of it, the "in feed" and "out feed" are in the same plane, with the blade sticking out. Explain to me how that results in a flat surface.

However maybe that has something to do with it.

When you are typically taking shavings between .001" and .010", I don't think it makes much difference if it is slightly dished or bowed. The finished thing is flat enough.

Originally Posted by silentC

Actually I still don't really get how a plane works to make a surface flat, because if you look at the bottom of it, the "in feed" and "out feed" are in the same plane, with the blade sticking out. Explain to me how that results in a flat surface.

In absolute terms you probably don't. However the tendency to form curves is counteracted by technique. Putting more weight on the front of the plane and only easing off at the end to prevent rounding over.
I'm glad you raised the point because I now understand why I was taught that way
Jim

See http://planetuning.infillplane.com/h...ker_study.html

This will dispel may myths regarding chipbreakers. But I am posting this because it contains microscope video footage taken during planing show chip formation and, amazingly, nothing whatsoever going on behind the cutting edge. By nothing whatsoever I mean no mysterious springback

I am not sure if the research on chipbreakers is really helpful here - I will return to this later after I have read it again (last done some time back). I would also want to search out info on spring back and wear bevels - I am very interested in these issues. Steve Elliott (from whom the link comes) is a great bloke.

You may be interested to read two links, neither of which will provide definitive answers, but both informative (for different reasons).

The first is a link to Brent Beach's research on wear bevels on different steels. This has some photographic information.

The second link is a discussion on wear bevels and BU verses BD planes on Sawmill Creek (similar issues to this thread). There are several members involved, notably Larry Williams (of C&W planes), who has a hatred of BU planes and here "offers" his opinion why they are crap. There are opposing views

Regards from Perth

Derek

Absolutely agree about the chipbreaker discussion not being relevant. I included it because of the excellent photos of chip formation which fail to show any evidence of springback. If you know of some evidence regarding springback, I would love to read it.

I thought you for one would want to read the article I offered.

BTW. Know of any chipbreaker discussions going on?

Only not relevant because it is essentially about chipbreakers, but interesting because of the pictures that show planing and possible insights on springback because of these pictures. I need to re-read it when i have enough time (still at work). I fear that it did not focus on what was going on behind the bevel, per se.

There is also info in Leonard Lee's book ("The complete guide to sharpening"). This contains many research papers on sharpening.

http://books.google.com.au/books?id=...esult&resnum=2

Regards from Perth

Derek

Hi Monoman.

Why not just grind a blade as far as you think you can push it bevel wise and see how it goes?.. Maybe start flush with the bed of your plane and take it up a bees whisker untill you get results and then leave it at that for a while.

I think it'll be a pain to hone without guides.. but then I think that's the whole point.

on a side line.. I'm sure I read something about a zero bevel plane being made briefly around the whole Bailey era.. the blade sitting up under the bed dead flat with it's back against the workpiece.. didn't sell well I don't think.. may have been on leeches better mouse trap page.

Originally Posted by derekcohen

I am not sure if the research on chipbreakers is really helpful here - I will return to this later after I have read it again (last done some time back). I would also want to search out info on spring back and wear bevels - I am very interested in these issues. Steve Elliott (from whom the link comes) is a great bloke.

You may be interested to read two links, neither of which will provide definitive answers, but both informative (for different reasons).

The first is a link to Brent Beach's research on wear bevels on different steels. This has some photographic information.

The second link is a discussion on wear bevels and BU verses BD planes on Sawmill Creek (similar issues to this thread). There are several members involved, notably Larry Williams (of C&W planes), who has a hatred of BU planes and here "offers" his opinion why they are crap. There are opposing views

Regards from Perth

Derek

Hi Derek.

Your remarks on the importance of a well balanced plane versus having extra weight alone, was pleasing to read. Using the back purchase point as the fulcrum , most of a hand planes weight is nearly always forward from this point. Improving the overall balance has been an direction I have worked on, with the wooden bodied planes I make.


Thankyou again for your input on this subject, including the core issue raised by monoman.

planemaker:

Originally Posted by Slow6

something about a zero bevel plane

Here it is.