Cambered blade in Veritas BUS

[Pat Barry]

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.

Mike, perhaps what is needed is to understand exactly how much camber you put into your BUS blade. Can you provide the measurements you used. Then it would simple to use the calculators to see what you ended up with for effective camber on a 2 1/4" plane blade at 12 degree bed angle with the bevel angle you chose to use.

[Mike Holbrook]

Patrick, actually I asked Derek if he had tried a large camber on a LA blade since he got his CBN wheel. He said he had not, which is one of the reasons I tried it. I believe Derek has been doing much more research with the new custom planes and chip breakers recently and less with BU planes. I believe that many people, myself included, point people to Derek's page regarding how to sharpen BU planes. I believe Derek responded in a fairly recent post that all of his research on BU planes is dated in some regards and he has not taken the time to revisit it as he has moved to other interests. I am not assuming I understand all of Derek's theories. I am assuming they change as he gets more information and does further testing as just about anyones do.

Patrick are you saying you have tested BU plane blades with every radius from 3" to 24"? If so I would be interested to hear about your results. I just do not think a mathematical formula or even some chart reflects the full range of functions that are occurring when we are planing. It seemed to me that you were implying that your information was some sort of definitive answer to whether or not a highly cambered plane blade might be useful on a BU plane blade. A 8" camber is an 8" camber regardless of whether it is on a BU or BD plane. Certainly that degree of camber works differently on a BU vs BD plane which is my point. Maybe you are making the same point?

All I am saying is "facts" are only valid if applied in context. There are often more facts than we can account for in our theories. Facts may not even turn out to be facts in the face of other facts.

The possible hole in my theory has to do with tear out. Working at a low angle can cause tear out, as the blade may lift instead of cut fibers. I am also interested in whether the cambered blade helps with tear out or makes it worse.

[Pat Barry]

The effective amount of camber on a BU plane at 12 degree bedding is only about 1/3 as compared to that same camber on a blade bedded at 45 deg.

[Mike Holbrook]

Pat, my guess is the blade I am using started at around an 8" camber but I am not sure and it has been honed several times since I ground it. Lately I do not mark a camber on my blades before I grind them. I also tend to round the corners more, leaving the center section with a lesser curve. I do not necessarily believe there is mathematical formula, equation, calculation that will provide a simple answer here. I am not arguing with the math. I am just not sure that such a calculation would contain all the variables at play. Neither am I convinced that any camber or angle we might plug into any formula would be accurate. I am grinding a hollow, there is no flat surface in at least two dimensions.

[Patrick Chase]

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.

Yes, that had occurred to me long ago, enough so that I calculated the maximum resulting skew. It's:

max_skew_angle = asin(blade_width/(2*camber_radius))

For an 8" radius on a 2.25" blade (Mike's numbers earlier in the thread) that works out to 8 degrees at the very corners. That will make a small difference in cutting action, though bear in mind that the average across the entire cutting edge is less than half that.

IMO that's "homeopathic skew" - Not enough to objectively achieve anything, but if you believe in it enough it might seem to work anyway.

[Mike Holbrook]

Pat, I hate to keep referring to Derek's posts on his Blog regarding sharpening, but they are one of the better sources of information in my experience. Derek's more recent work reveals that he had a custom frog made for one of his newer Veritas custom planes. The frog he requested was 42 degrees. Apparently another very experienced wood worker, Warren, liked that frog angle too. I ordered a Custom #4 with a 42 degree frog and find I like the results I am getting.

There is only 3 degrees difference between a 45 and 42 degree frog, which started me thinking that smaller differences might be more significant than I customarily have considered. How does one accurately calculate the actual angle of a hollow ground blade, especially at the exact level as the camber? Doesn't the angle of the blade change along multiple curved surfaces? I have a Batty devise that helps me determine that I am grinding an accurate bevel on my grinding wheel. If I had to guess I would guess it is measuring at the center of the bevel which would be the high point on the wheel. That point is way above the base of the plane where the blade meets wood.

As has been discussed in detail in more recent posts, the deflection angle of the chip/shaving coming off the plane blade is a significant factor in how the blade cuts. I believe this is at least part of the argument for a chip breaker. Certainly a cambered, hollow ground blade will make a different shaving and move it over the hollowed blade differently.

[Patrick Chase]

Pat, I hate to keep referring to Derek's posts on his Blog regarding sharpening, but they are one of the better sources of information in my experience. Derek's more recent work reveals that he had a custom frog made for one of his newer Veritas custom planes. The frog he requested was 42 degrees. Apparently another very experienced wood worker, Warren, liked that frog angle too. I ordered a Custom #4 with a 42 degree frog and find I like the results I am getting.

There is only 3 degrees difference between a 45 and 42 degree frog, which started me thinking that smaller differences might be more significant than I customarily have considered. How does one accurately calculate the actual angle of a hollow ground blade, especially at the exact level as the camber? Doesn't the angle of the blade change along multiple curved surfaces?

You can easily and accurately determine that angle in one of 3 ways:

1. If like Derek you hone by "balancing" the hollow-ground face on the cutting edge (face-to-back intersection) and top edge (face-to-top intersection) then resting a protractor across those edges and the back gives an extremely accurate measurement of the tip angle. That's the beauty of Derek's approach - the edges where the hollow-ground face meets the top and back constitute a built-in guide, and you can easily measure its angle. Precisely controlling the angle (via tool rest setup) is a bit harder in my experience, which is the only reason I don't use that approach.

2. If like Charlesworth you grind a secondary bevel on only the face-to-back edge with a jig, then you can easily determine the jig's angle in the usual way (by measuring extension from the guide).

3. If all else fails, it is possible to directly measure the angle of a secondary bevel with a good protractor, strong backlight, and lots of magnification. It's a pretty bone-simple exercise as metrology goes.

I have a Batty devise that helps me determine that I am grinding an accurate bevel on my grinding wheel. If I had to guess I would guess it is measuring at the center of the bevel which would be the high point on the wheel. That point is way above the base of the plane where the blade meets wood.

As has been discussed in detail in more recent posts, the deflection angle of the chip/shaving coming off the plane blade is a significant factor in how the blade cuts. I believe this is at least part of the argument for a chip breaker. Certainly a cambered, hollow ground blade will make a different shaving and move it over the hollowed blade differently.

It's different all right, but not in a good way. To avoid tearout you want a sudden *increase* in angle just behind the edge. A bevel-up blade with a hollow grind provides exactly the opposite (the angle decreases behind the micro-bevel, and doesn't significantly increase again until well back from the cutting edge).

[Mike Holbrook]

Patrick, as far as I am concerned you are making the same case I am. You name three ways to determine the angle. Two different ways for two well known woodworkers..Apparently there is no "standard", which is my point. In my experience more people do not measure any of those angles than measure them. Derek has mentioned in threads and his blog that one of the reasons he does not like to use his method for sharpening BU planes is he can't do it by hand. It requires a MkII and set up time to sharpen.

I'm not sure I just accept your evaluation of what makes a reliable chip breaker angle either. The information on that subject that I have read is not well defined or consistent enough to base much on as far as I know. I have not seen any testing that defines exactly where and at what angle an object needs to be to deflect a specific kind of wood chip. I believe the type of wood certainly affects the elasticity of that wood and how it will deflect. Sure it seems that setting a chip breaker close to the edge works better, and there are posts suggesting that rounding the deflecting surface may help but what "angle" is the curve at? Doesn't how "rapidly" a hollow ground blade curves up relate to how thick the blade is and at what angle the bevel is ground?

[Jim Koepke]

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.

He also mentioned:

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.

My post merely offered another option for experimenting. If the OP wants to try experimenting with a very slight round tapered bevel on the back of their bevel down plane, I would hope he will post the results.

jtk

[Mike Holbrook]

Jim thanks for the link and another idea worth experimenting with. I liked something you said in that thread which is also a goal of mine:

"The pursuit is finding a blade that holds an edge long enough so we can do enough work so that the sharpening seems like a quick break from the more difficult work at hand."

I do not mind taking a while when I first get a new blade to grind the kind of bevel I want, but when I am working I want to pop the blade out of the plane swipe it across a stone and maybe some buffing compound and get right back to work. I don't want to have to haul out jigs, rulers, protractors, squares...I don't like to interrupt the rhythm of the work. I think there are a good many people who feel the same way.

[Jim Koepke]

Jim thanks for the link and another idea worth experimenting with. I liked something you said in that thread which is also a goal of mine:

"The pursuit is finding a blade that holds an edge long enough so we can do enough work so that the sharpening seems like a quick break from the more difficult work at hand."

I do not mind taking a while when I first get a new blade to grind the kind of bevel I want, but when I am working I want to pop the blade out of the plane swipe it across a stone and maybe some buffing compound and get right back to work. I don't want to have to haul out jigs, rulers, protractors, squares...I don't like to interrupt the rhythm of the work. I think there are a good many people who feel the same way.

Thanks Mike, I think you have gotten the full meaning of my comment. Sharpening should be quick and simple, not a drawn out ritual.

jtk

[Mike Holbrook]

I hate to resort to my own math here as I don't believe we have accurate numbers to work with. However, the "pertinent angle" of my BUS is not the 12 degree bed angle.

The pertinent number is actually the bed angle, 12 degrees + the angle of the camber of my blade. I have two cambered A2 blades, one at 25 and one at 30. I am not exactly sure 25 and 30 are "correct" numbers either as they are cambered and I am not sure exactly where and how one measures a meaningful number on these blades. However, assuming my Batty devices is correct and I have 25 & 30 bevels. The actual pertinent number for comparison is 12+25=37 or 12+30=42. 37 is only 8 degrees from 45, 42 is only 3 degrees from 45. In a response to Andrey above Patrick states:

"For an 8" radius on a 2.25" blade (Mike's numbers earlier in the thread) that works out to 8 degrees at the very corners. That will make a small difference in cutting action, though bear in mind that the average across the entire cutting edge is less than half that.

IMO that's "homeopathic skew" - Not enough to objectively achieve anything, but if you believe in it enough it might seem to work anyway."

If 8 degrees of difference is "homeopathic","Not enough to objectively achieve anything, but if you believe it enough it might seem to work"... then I guess the entire difference between the BU planes combined bed angle and the bed angle of a BD plane, 3-8 degrees, is insignificant, following that logic.

I do not agree, I admit I have no idea how much angle may or may not be significant which is why I tried cambering old blades to see what it actually does. I think Andrey's comment has merit and I do not find 8 degrees to be insignificant. I have actually moved toward working the edges of my cambers more like Andrey and Jim suggest.

The other reason I made the test is a BD plane blade is dead flat where the shaving comes off the blade. Certainly one of the functions of a chip breaker is to move the shaving. My hollow ground BU blade, however, has a curve built into the bevel of the blade where the shaving comes out. Any BU blade presents a bevel at some angle to the exiting shaving. The shaving is "handled" at some distance behind where the shaving is made. A chip breaker needs to be very close to the leading edge of the blade to function. My question is whether or not we know where and at what angle the shaving is best dealt with? I'm not sure that a hollow ground blade might not deal with the shaving more efficiently than a chip breaker.

[Derek Cohen]

The other reason I made the test is a BD plane blade is dead flat where the shaving comes off the blade. Certainly one of the functions of a chip breaker is to move the shaving. My hollow ground BU blade, however, has a curve built into the bevel of the blade where the shaving comes out. Any BU blade presents a bevel at some angle to the exiting shaving. The shaving is "handled" at some distance behind where the shaving is made. A chip breaker needs to be very close to the leading edge of the blade to function. My question is whether or not we know where and at what angle the shaving is best dealt with? I'm not sure that a hollow ground blade might not deal with the shaving more efficiently than a chip breaker.

Mike, if you believe that the hollow bevel has a function to play on a BU plane, something akin to a chipbreaker, then you need to compare a BU plane with hollow grinds at different angles, and with another blade with the same bevel angle but on a secondary micro bevel on a flat primary bevel. This would help determine whether it is the hollow grind is making a contribution distinct from the cutting angle.

Regards from Perth

Derek

[Pat Barry]

One thing you can imagine that is happening, if you have a significant camber on your blade, is that the left and right edges of the blade will slice into the wood at a complex angle as compared to the center section of the blade which will be head on to the work. The result of this is further lessening of the apparent bevel angle (at the edges) - couple this with the fact that the edges of the blade are less engaged in the material due to the camber and you can see that this will make your work easier of course. No one will refute that. I'm in no position to say whether the hollow grind by itself creates some sort of chipbreaker substitute but I can say that the hollow grind lowers the effective angle of the bevel at the edge. The effect of this is dependent on the depth and breadth of your hollow grind. The angle right at the edge after grinding and before honing can approach tangency to the bedding angle. That's why its important to talk about bedding angle. A question that comes to mind is how can we quantify your hollow grind and how can we quantify the amount of honing you do? Would you say that the hollow grind is about 1/4" in breadth? What would you say is the width of the honed edge, 0.010"? Having a few dimensions will remove the ambiguity in the math.

I did find an interesting website on the topic of camber, calculations etc. Here is a link to it

[Patrick Chase]

I hate to resort to my own math here as I don't believe we have accurate numbers to work with. However, the "pertinent angle" of my BUS is not the 12 degree bed angle.

The pertinent number is actually the bed angle, 12 degrees + the angle of the camber of my blade. I have two cambered A2 blades, one at 25 and one at 30. I am not exactly sure 25 and 30 are "correct" numbers either as they are cambered and I am not sure exactly where and how one measures a meaningful number on these blades. However, assuming my Batty devices is correct and I have 25 & 30 bevels. The actual pertinent number for comparison is 12+25=37 or 12+30=42. 37 is only 8 degrees from 45, 42 is only 3 degrees from 45. In a response to Andrey above Patrick states:

We're talking about different things. The "8 degrees" I cited is a skew angle, i.e. about the Z-axis (axis normal to the wood surface). The angles you cite above are bed/cutting angles, i.e. about the Y-axis (axis perpendicular to the plane's long axis and tangential to the wood surface).

Andrey (correctly) pointed out that grinding a camber into a BU blade causes the edges to make a slightly skewed cut. I replied with the math for that amount of skew.

Pat correctly points out that the skew at the edges does also reduce the cutting angle a teeny tiny bit (by <1 deg @ 8 deg skew)