Bevel up blades and how long they stay sharp

Re: Bevel up blades and how long they stay sharp

Frank D. in Montreal

>Yes, but I think I already told you that somewhere else...

My next smoother will be bedded at 20 degrees so I can get an angle of 30 degrees on the blade. I find 12 degrees a little low for most woods (except some soft woods or softer hardwoods like teak where I might want a planing angle between 40 and 45°) because the blade skips over the wood sooner.

Was it something I said?

Frank D. in Montreal

>Sorry to monopolize the thread like this ydb1md, I thought my response would be drowned out by the others. I guess nobody really uses their bevel-up planes. ;)

Re: Bevel up blades and how long they stay sharp

Norman (Ottawa, Ont.)

>Hello Frank,

I'm not clear on how you're going to change the BU bedding angle

from 12 to 20 degrees. Isn't the proper procedure with BU planes to increase the angle of the blade bevel from let's say 25 degrees to 35 or 40 degrees to achieve 45 -50 degrees .

Norman

Like this Norman 

Frank D. in Montreal

>

Re: Like this Norman

Norman (Ottawa, Ont.)

>Thx Frank, nice infill gloat :) Yours??

After I posted I realized I was refering to LA BU planes, when

it doesn't necessarily need to be a LA variant at all, although

they seem to dominate the BU plane market.

Norman

Re: Like this Norman

Frank D. in Montreal

>Not mine yet,

Still waiting for the kit...waiting...YAWN...

Re: Was it something I said?

Greg Sloop, Portland Oregon

>I'll hop in here...

I don't personally find any significant correlation between the grind angle of the blade and how quickly it dulls.

That certainly doesn't mean it doesn't exist, but that I haven't seen much evidence of it.

The factors compounding this are these:

A) On the pieces where I have the highest angles, the wood has the most figure and is the most sensitive to a dull blade, which will cause tear-out. Thus, how can one compare a lower angle blade, which will produce tear-out to a higher angle blade?

B) I suppose that one could use a higher angle blade on more straight grained wood which would also produce good surface finish with a lower angle blade and see which worked better... But, what would that point be?

*IF* the result truely was, and I'm not making any assertion that it would be so, that the higher angle blade's edge retention was poorer, that wouldn't be much help. It would I guess tell you that you shouldn't use a higher angle than required to get a good surface finish, but that's been a given in my book for a while. But for more figured surfaces, you'll have to use higher angles anyway.

C) I would tend to believe that higher included angles would tend to be less susceptible to edge fold-over. Theory: like a mortise chisel needs higher angles to survive, I suspect to some degree, the higher angle will be a benefit.

However, there’s more resistance for the higher angle, so at some point, this the increased resistance/abrasion would overcome the more support of the higher angle and the result would be a net loss.

It would be an interesting academic exercise, but I’m not sure it would result in any great useable information for those of us with LA BU planes.

Cheers,

Greg

Re: Was it something I said?

ThomD

>I always wondered whether the 30 degree angle for greater edge retension on mortising chisels made any sense. You chop a dovetail, and they give you a really low angle chisel, sometimes just a sliver. You chop a mortice, and they give you this blunt thing. But in both cases you are making basically the same cut. But the objective isn't the same, you are perfectly happy to cut through ont he doevetail with the minimum effort, not so on a mortise. What the blunt thing does is diplace the chisel sideway, which shears out the wood in a mortise.

You could argue tha metal grain orientation is less optimal for tangent loads in a bevel up.

Re: Was it something I said?

Frank D. in Montreal

>Hi Greg

The way I see the difference is when I go from a standard bench plane to a bevel-up plane. They both have similar planing angles but the bevel on the blade in the BU plane has an angle of about 38°, vs. 30° for the bench plane. The blade in the BU plane (38°) resists minor chipping better but it seems to me that it loses the sharp edge that allows it to penetrate the wood more quickly, so when planing hard maple (the wood I use the most) it'll skip out of the cut and slide over the wood after less BF than the 30° blade. So I guess the edge rounds over more quickly. That's obviously just an impression, and it's not a real problem. I talked to one other person who had the same impression.

FWIW (not much...)

Re: Was it something I said?

Pam Niedermayer - Austin, TX

>The first dovetail chisel cut is quite different from the first (and some subsequent, depending on how you do it) mortise cut. There's significant give in the dovetail since the other sides have been sawed loose. Not so for the mortise cut into the midst of a piece.

Pam

Re: Was it something I said?

ThomD

>Thanks. I forget about the blade. I have a blue steel blade on my Record 07, and it is fantastic. Early impressions of LV A2, don't compare. However the point you make is well taken, and the difference relative to the blade that came on the 07 are probably night and day. I guess i will just try it out to see what it can do. I bought an early version of the first bevel up plane they built. I had already bought the LN Jack from LV when they were a dealer. I didn't feel it compared well. But with this plane, assuming execution on the design, their design seems better than the LN's without the mouth adjust and so forth.

Re: Was it something I said?

ThomD

>Agreed, but I have hard time seeing that as a cause of "edge fold over". Just as the poster mentioned, that get's talked about relative to the morticing chisel. What you are talking about isn't caused by the edge, it's caused by the fatter bevel not wanting to penetrate. The solution to that problem would be less angle not more. But mortising is about more than cutting deep. You have to be able to work the bottom of the mortise (forgeting various trick tools for the moment), not so much the flat bottom as in shoji, but the high aspect ratio problem as you go deeper relative to width. And you need to cut out the sides without paring in some applications. People do this either by cranking on the bevel, which does fold the edge by using it as a scraper. Or they do it properly by exploiting the bevel geometry which both displaces the chisel sideways during the cut, or let's you work lateral angles because you have 5 degrees more angle. These uses aren't all that hard on an edge, and are pretty similar to what happens with dovetails, unless one wastes a lot of time spliting out each cut. I think the main reason for the geometry is not to do with the edge retention. If it were one could just use a micro bevel with equal success.