Cambered blade in Veritas BUS

[Mike Holbrook]

I made a post a while back about hollow grinding larger cambers in my old A2 plane blades with my CBN wheel....

I have been doing glue ups for raised panel shutter doors. I sharpened up one of the A2 cambered blades and tried it in my BUS this morning. I was surprised that it worked as well as it did. I was expecting the LA, low angle, and wide blade to be hard to push. The camber reduces or eliminates the depth of cut at the edges, as we know. The extra blade width ends up providing more options for rough planing. The weight, low center of gravity, low grip all seem to help when working across boards taking larger shavings. The norse adjuster works quickly, on the fly, to increase or decrease depth of cut. This may be an odd choice for a scrub plane but it seems to be working.

Scrub plane.jpg

Maybe the camber works well in thick LA blades? I can see why there has not been much experimenting with this in the past as hollow grinding these blades via conventional means is quite a challenge.

[Patrick Chase]

I made a post a while back about hollow grinding larger cambers in my old A2 plane blades with my CBN wheel....

I have been doing glue ups for raised panel shutter doors. I sharpened up one of the A2 cambered blades and tried it in my BUS this morning. I was surprised that it worked as well as it did. I was expecting the LA, low angle, and wide blade to be hard to push. The camber reduces or eliminates the depth of cut at the edges, as we know. The extra blade width ends up providing more options for rough planing. The weight, low center of gravity, low grip all seem to help when working across boards taking larger shavings. The norse adjuster works quickly, on the fly, to increase or decrease depth of cut. This may be an odd choice for a scrub plane but it seems to be working.

Scrub plane.jpg

Maybe the camber works well in thick LA blades? I can see why there has not been much experimenting with this in the past as hollow grinding these blades via conventional means is quite a challenge.

Low bed angle actually *dilutes* camber. You have to put about 3.5X as much camber on a 12 deg BU blade to achieve the same center projection (amount the center of the blade extends into the wood when the corners are flush with the sole) as on a 45 deg BD blade.

I posted the math here: http://www.sawmillcreek.org/showthre...05#post2501105

It would appear that you've discovered that you like to rough with a minimally cambered blade :-). You could probably get the same results by re-cambering your BD plane blades to achieve similarly small extension.

[Reinis Kanders]

Those are pretty thin shavings for a scrub plane. Watch out for a tearout with BU plane. I like scrubbing with german style wood plane, they are light so one can really go at it.

[Jim Koepke]

It is also possible to add camber from the back side of the blade:

http://www.sawmillcreek.org/showthread.php?158373

There are many paths to the same result.

jtk

[Mike Holbrook]

Patrick, the problem I see with your math is it may not be relevant to my point. I do know how much "bite" the blade takes. Assuming your math is correct then maybe my heavily cambered blade becomes "less" cambered. Unless my math is wrong, a blade with a curved edge at an acute angle meets less resistance than a straight edge at a higher angle, which is my point. My suggestion is, if you have your doubts try it out before assuming ;-).

I figured someone would say the shavings are thin vs heavy. They do not look as thick in the picture as they do in person, maybe not the best picture/perspective... Certainly cross planing is not normally taking a full length shaving, especially early on. The shavings I get with this set up are also different than those I get with a narrower higher angled blade. Specifically, these shavings are more tapered on either side, actually leaving the edges thinner than the center section. I am able to work with a heavier camber. It is hard to sink a 8" camber full depth and then push the plane even with a narrow blade. The shavings from the BUS are wider than those I get with a #5 or #5 1/4 and in the center they are at least as deep, resulting in more not less wood being removed.

My other scrubs are a Stanley 5 & 5 1/4, with 2 & 1 3/4" blades. The Veritas scrub has a 1 1/2" blade. Less blade width makes a high angle and heavy camber manageable. My point is the BUS with the highly cambered blade seems to me to slide through the wood easier while still taking a sizable shaving. Certainly the reason for this would have something to do with the angle the blade meets the wood at and how the camber relates to that angle.

[Pat Barry]

The shavings I get with this set up are also different than those I get with a narrower higher angled blade. Specifically, these shavings are more tapered on either side, actually leaving the edges thinner than the center section.

This is what a camber blade should do

The shavings from the BUS are wider than those I get with a #5 or #5 1/4 and in the center they are at least as deep, resulting in more not less wood being removed.

This is to be expected also.

My point is the BUS with the highly cambered blade seems to me to slide through the wood easier while still taking a sizable shaving. Certainly the reason for this would have something to do with the angle the blade meets the wood at and how the camber relates to that angle.

As Patrick pointed out, the combination of camber and low angle of attack leads to this end directly.

I question why you want to use a smoother in this manner - a tad bit of camber does make sense though.

[Patrick Chase]

As Patrick pointed out, the combination of camber and low angle of attack leads to this end directly.

I question why you want to use a smoother in this manner - a tad bit of camber does make sense though.

Thanks for rewording my point in human-readable terms. What you say is basically the point I was trying to make.

I should have known better than to answer that question with a snippet of my Python code (I use it to automatically track of camber depths in my previously described spreadsheet 'o blades. Let the mocking resume!).

[Patrick Chase]

It is also possible to add camber from the back side of the blade:

http://www.sawmillcreek.org/showthread.php?158373

There are many paths to the same result.

jtk

Indeed, though that brings its own issues. For starters you have to be super careful about clearance, and it may also increase susceptibility to chatter etc because the bed will now only supports the center of the blade.

[Jim Koepke]

Indeed, though that brings its own issues. For starters you have to be super careful about clearance, and it may also increase susceptibility to chatter etc because the bed will now only supports the center of the blade.

When I have done this I do not carry the 'back bevel' that far back. It only takes a little bit of bevel.

jtk

[Patrick Chase]

When I have done this I do not carry the 'back bevel' that far back. It only takes a little bit of bevel.

jtk

Ah, but then you're reducing clearance to even less than the 12 deg nominal (and weren't you one of the folks arguing for higher clearance in that other thread?).

There's no free lunch here - if you camber the underside then you must either carry that camber a fair way back uch that constant thickness is maintained throughout the cutting portion of the blade, or you must accept reduced clearance. There are no other possibilities.

[Jim Koepke]

Ah, but then you're reducing clearance to even less than the 12 deg nominal (and weren't you one of the folks arguing for higher clearance in that other thread?).

You got me there... It must be a full half degree of lost clearance. How much of a clearance angle is needed when that portion of the blade isn't cutting, touching or entering the wood?

If you want a radius on your blade, then it should be done on the bevel side.

If you want to soften the edges to reduce tracks when smoothing then a few swipes with a stone on the back of the bevel will have a similar result to 'clipping' the corners.

jtk

[Patrick Chase]

You got me there... It must be a full half degree of lost clearance. How much of a clearance angle is needed when that portion of the blade isn't cutting, touching or entering the wood?

If you want a radius on your blade, then it should be done on the bevel side.

If you want to soften the edges to reduce tracks when smoothing then a few swipes with a stone on the back of the bevel will have a similar result to 'clipping' the corners.

jtk

If you'll look back to the OP, you'll see that he's talking about using a BUS with "larger cambers" as a *scrub*. This thread is about applying significant camber, not edge-clipping, and my reply reflected that.

[Mike Holbrook]

The reason I tried this type camber on a LA plane and made the post is, I have not been able to get a response from anyone who has actually tried it. I understand the reasons. The main reason in the past has been the lack of any way to do it quickly. Derek Cohen has a very good explanation in the sharpening area of his Blog. Now that Derek and others have CBN wheels this job can be done much more quickly. I decided to try a high camber on an old A2 blade that needed a whole new bevel anyway. Having a CBN wheel made the work relatively quick. Once I had the blade, why not try it in my various BU planes?

I understand Patricks theories about how the high camber will essentially be wasted but theories are just that. Mathematics and engineering are fine but useless if ALL the “right" formulas are not being applied. It is easy to blur rather than clarify with partial facts, and who is smart enough to be sure they have accounted for all the facts? I’m one of those people who thinks you don't know until you actually try it.

I'm not sure the argument about how much the blade protrudes is actually relevant in the way Patrick assumes it is. I am assuming that the major part or all of the camber is actually in the wood as if it isn't it isn’t being used. My question becomes how much of a heavy camber can I push through the wood's surface and actually plane with at a high angle? My theory is it should be easier to penetrate the woods surface deeper with a curved blade at a lesser angle. The curved edge at a low angle slices the wood while the straighter edge at a higher angle tends to work more like a scraper.

I find it very hard to get all of a large camber into the wood at a high angle, even with a narrow blade. A higher angle blade tends to chatter at that depth. Following Patricks logic I actually need a highly cambered blade in my smoother just to get any result out of the camber.

[Patrick Chase]

I understand Patricks theories about how the high camber will essentially be wasted but theories are just that. Mathematics and engineering are fine but useless if ALL the “right" formulas are not being applied. I’m one of those people who thinks you don't know until you actually try it.

In this case the formulae are extremely meaningful. Derek's post to which you refer says exactly the same thing without the math, as do bazillions of other writeups out there. I know of at least one "online camber calculator" that spits out exactly the same answers as the math I posted. Some may find the mathless versions more comforting, but that doesn't change reality.

Also, I've tried it with basically every radius from 3" to 24". So has Derek (probably much more than I), so have many others who are trying to tell you the same thing. This isn't a theoretical exercise as you assume.

If different projection from center to edge isn't the point of cambering, then what is? It's impossible for the edge to be "in the wood" and yet "not being used" as you posit.

I absolutely DID NOT say that you "need a highly cambered blade... just to get use out of the camber". Plenty of people do roughing with nearly-straight blades, so it's obviously possible to get "use" out of minimal camber.

What I said is that you've accidentally discovered that you're one of those people who prefers to work with a nearly-straight blade (i.e. you're more comfortable taking wide-but-shallow cuts instead of narrow-but-deep). There's nothing wrong that - as with many things in woodworking technique there's a lot of subjectivity here and no single right answer.

[Andrey Kharitonkin]

Did it occurred to anyone that high camber on BU plane has more cutting effect at the sides of the blade? I mean it would be kind of skewed blade if you look at the small portion of the blade at the sides where it meets the wood. Geometry is different when compared to BD plane. I have to try that with my spare A2 blade that I've got exactly for this.