Behavior of the dull (?) blade (bevel up vs. bevel down?)

[adrian]

At risk of duplicating the question in another recent thread, I ask the question. How sharp does an edge need to be and how can you tell when it's not sharp enough? And do different woods behave differently in terms of how sharp the edge needs to be?

I surfaced about 40 square feet of rough sawn American cherry with my hand planes. I'm not sure how often I sharpened tools, but I went several hours (ten? fifteen?) between sharpenings without noticing a problem. (Maybe I'm oblivious.)

Lately I have been working in canarywood. It is surfaced already, but badly, and is not flat. I was working with two planes, a bevel down plane (45 degree cut angle) and a bevel up plane. The bevel down is sharpened at 30 degrees with a 32 deg microbevel and set for a thicker shaving (maybe .004 inch). The bevel up plane is sharpened at 45 deg (microbevel at 47), effective pitch 59 and set a thin shaving (about .001 inch). Both planes are Veritas witih A2 irons. Both blades are cambered.

At a certain point the bevel up plane just stopped taking a shaving. It wouldn't cut. I usually blame this sort of event on the shape of the wood. But at a certain point I decided I needed another explanation, so I inspected the blade. It had an accumulation of fine dust from the wood on the edge. When I stroked the edge with a fingernail it felt smooth. It would bit into the face of my fingernail reasonably well at an acute angle, though not quite as well as when the plane was freshly sharp. But I wouldn't have considered it dull. I sharpened the edge and went back to work and the plane would cut again. For 20 minutes or so. Then it again stopped cutting completely.

Meanwhile, I can't even remember the last time I sharpened the bevel down plane. After I finish surface jointing a board I figure it must need some attention. I remove its blade and inspect the edge. It's clearly in far worse condition than the other blade. The fingernail stroked along the edge reveals a lot of roughness. I can see some micronicks with the naked eye. It flunks the test for biting into the fingernail. This is clearly a dull blade. But this blade was still cutting when I took it out of the plane. This plane is sharpened at 30 degrees with a microbevel of about 32.

When working with the cherry I sometimes suspected that my finish surface was suffering due to the blades getting dull, but I don't recall noticing this phenomenon even though I went far, far, longer without sharpening.

Presumably my sharpening procedure isn't to blame, since it's the same for both blades. So what explains this difference in behavior?

 

[Racers]

Hi,

You need sharper tool to cut soft wood, think soft tomato and a blunt knife.

Pete

 

[adrian]

Canary wood is harder than American cherry. The latter is fairly soft, as hard woods go. Janka hardness for canarywood is 2200. For the cherry is 950.

 

[Racers]

Hi,

Sorry I thought is was soft stuff

Pete

 

[Paul Chapman]

I'm not sure how often I sharpened tools, but I went several hours (ten? fifteen?) between sharpenings without noticing a problem.

Sounds to me like you are not sharpening your planes often enough. Furthermore, if you can plane for ten or fifteen hours without noticing a problem, then possibly you don't know what a really sharp plane feels like.

It's difficult to say how often you need to sharpen because woods vary so much - but I think you need to sharpen a lot more frequently.

Cheers :wink:

Paul

 

[woodbloke]

I'm not sure how often I sharpened tools, but I went several hours (ten? fifteen?) between sharpenings without noticing a problem.

Sounds to me like you are not sharpening your planes often enough. Furthermore, if you can plane for ten or fifteen hours without noticing a problem, then possibly you don't know what a really sharp plane feels like.

It's difficult to say how often you need to sharpen because woods vary so much - but I think you need to sharpen a lot more frequently.

Cheers :wink:

Paul

Beat me to it I sharpen the iron, bevel up, bevel down whatever every twenty minutes or so, sometimes sooner. If your planing teak, it needs to be done every 5 minutes and that's pushing it! - Rob

 

[adrian]

I'm not sure how often I sharpened tools, but I went several hours (ten? fifteen?) between sharpenings without noticing a problem.

Sounds to me like you are not sharpening your planes often enough. Furthermore, if you can plane for ten or fifteen hours without noticing a problem, then possibly you don't know what a really sharp plane feels like.

Well, I'd like to think that the blades are sharp right after I sharpen them, in which case I have a period of time where I feel a reall sharp blade. If they aren't sharp at that point...then sharpening more often isn't going to help a lot.

The only thing I can offer as evidence of sharpness is that I can get a smooth surface, free from tear out, on curly maple and with grain reversals in the cherry and canary wood.

It's difficult to say how often you need to sharpen because woods vary so much - but I think you need to sharpen a lot more frequently.

Paul

I agree that more frequent sharpening wouldn't be a bad thing. In the past I could expect to spend 45 minutes sharpening one plane. This doesn't encourage frequent sharpening. If everything is going well I have been able to do it in something like 5-10 minutes lately, but things don't always go well. In the latest case I've started experimenting with only going back to the polishing stone, and that seems to work OK and is quite fast. But is that good enough?

And so far the replies have focused on this problem with my work practice. But I'd like to understand why I'm observing such different behavior with the two different planes. Why will my bevel down plane still cut when it's really quite dull and the bevel up plane stops cutting entirely when the edge is much sharper?

 

[Paul Chapman]

In the past I could expect to spend 45 minutes sharpening one plane. This doesn't encourage frequent sharpening. If everything is going well I have been able to do it in something like 5-10 minutes lately, but things don't always go well.

When a plane gets blunt, the end of the blade becomes rounded over. If you go on planing as long as you do, it will get more and more blunt and more rounded. Re-honing a blade shouldn't be taking 45 minutes but by leaving it so long between honings you are probably having to remove a lot of metal. Re-honing a blade should only take a couple of minutes at most, but that requires you to re-hone as soon as the sharpness starts to wear off.

If I were you I'd review your honing regime - I think that's where the problem is.

Hope this helps.

Cheers :wink:

Paul

 

[Steve Maskery]

Canary wood is harder than American cherry. The latter is fairly soft, as hard woods go. Janka hardness for canarywood is 2200. For the cherry is 950.

Well that doesn't accord with my experience. Canary whitewood (AKA Poplar, tulipwood) is much softer than cherry. Yes, cherry is not the hardest of hardwoods, but it's noticeably harder than Canary. Just hit a piece of each with a hammer and see which has the biggest ding. You can easily dent Canary with your fingernail.

I wonder if there is more than one type of canary whitewood?

S

 

[adrian]

Canary wood is harder than American cherry. The latter is fairly soft, as hard woods go. Janka hardness for canarywood is 2200. For the cherry is 950.

Well that doesn't accord with my experience. Canary whitewood (AKA Poplar, tulipwood) is much softer than cherry. Yes, cherry is not the hardest of hardwoods, but it's noticeably harder than Canary. Just hit a piece of each with a hammer and see which has the biggest ding. You can easily dent Canary with your fingernail.

Canary whitewood sounds like something else. The canary wood I'm talking about is an exotic from Central and South America in the genus Centrolobium. http://curiouswoods.com/wood--Canary-Wood--CW. It's clearly a lot heavier than the cherry, and I doubt I could dent it easily by fingernail (though I don't have it handy at the moment to check).

 

[adrian]

If I were you I'd review your honing regime - I think that's where the problem is.

Since I honed the two blades using exactly the same method, my honing regime (or lack thereof) cannot explain the difference between the blades. One blade cuts for 15 minutes and then stops completely while still sharp enough that the edge is smooth and it bites into my fingernail. The other one cuts for hours even after the edge is ragged and the edge skitters across the fingernail surface without biting. The dull blade still cuts and the sharper one does not.

Why?

 

[Mike H]

Cherry is really fairly soft as temperate hardwoods go, but it is not totally the strength of the wood wich dictates how long the blade will last.

For example a long stored air dried piece of english oak will often plane better that a brittle over kiln dried softer import. I had a batch of American Ash 2 years ago wich resisted most attempts with the plane, I reckon they had it in the oven too long and too hot.

Also some woods plane fine one one face, but the figured face, even ignoring tearout, is really hard on the blade. Try for example Silky Oak on the lovely but deadly show face.

If you are not sure when to sharpen, then try this experiment with two blades equally well sharpened. Plane away for a tad too long with the first one, then change to the fresh blade. At the first stroke you will probably fall off the end of the bench and realise why you were dripping with sweat before! Suddenly the planing turns back from chore to shear pleasure. That is my yardstick.

With a heavy plane, say a 5 and a half, resting it on the wood and just pushing should produce a good shaving, if not the blade is getting blunt or the shaving is too thick for one pass.

I purchase quite a few blades for my main planes and gang sharpen. With one blade I would be likely to go less than 30 minutes. Less with end grain or to get a high angle bevel up to sing.


Mike

8)

 

[adrian]

With a heavy plane, say a 5 and a half, resting it on the wood and just pushing should produce a good shaving, if not the blade is getting blunt or the shaving is too thick for one pass.

So you mean without any downward pressure (except the weight of the plane)?

With one blade I would be likely to go less than 30 minutes. Less with end grain or to get a high angle bevel up to sing.

A high angle bevel up would get dull faster?

 

[lwilliams]

...The bevel up plane is sharpened at 45 deg (microbevel at 47), effective pitch 59 and set a thin shaving (about .001 inch). Both planes are Veritas witih A2 irons.

At a certain point the bevel up plane just stopped taking a shaving. It wouldn't cut. ... I sharpened the edge and went back to work and the plane would cut again. For 20 minutes or so. Then it again stopped cutting completely.

Meanwhile, I can't even remember the last time I sharpened the bevel down plane. ...

... So what explains this difference in behavior?

What you're experiencing is the accelerated wear caused by too small a clearance angle. The 12º clearance angle is marginal at best and then for a relatively acute bevel angle and very light cuts in a relatively soft wood or for end grain work. Increasing the bevel angle to 47º only increases the difficulty in cutting the wood. This increases deflection of wood fibers ahead of the cutting edge and the resulting spring back of the fibers which rub on the back of the iron and increase dulling wear.

You can verify this by using a more acute 30º bevel angle and you'll see the edge life is greater. If you had an O-1 iron you could go to a 25º bevel and increase edge life even more.

The best approach though is to go to a plane that offers 15º or more of clearance behind the iron. The steeper the pitch, the more resistance to cutting and more deflection so you need even more clearance with steeper pitch planes.

 

[adrian]

What you're experiencing is the accelerated wear caused by too small a clearance angle. The 12º clearance angle is marginal at best and then for a relatively acute bevel angle and very light cuts in a relatively soft wood or for end grain work. Increasing the bevel angle to 47º only increases the difficulty in cutting the wood. This increases deflection of wood fibers ahead of the cutting edge and the resulting spring back of the fibers which rub on the back of the iron and increase dulling wear.

You can verify this by using a more acute 30º bevel angle and you'll see the edge life is greater. If you had an O-1 iron you could go to a 25º bevel and increase edge life even more.

Of course I raised the bevel angle quite intentionally, as the wood has some grain reversals that tend to give tear out with a 45 degree cutting angle. So I don't want to go to a more acute bevel angle. I'd rather not deal with adding a back bevel to increase the clearance angle if it can be avoided.

Another observation is that the blade doesn't seem to have worn at a faster rate, but to have stopped cutting at a faster rate. Is it possible that the dust that sticks to the bevel is decreasing the clearance and interfering with the cut? (I have noticed that with the canary wood the blade tends to accumulate a layer of dust around the edge that cannot be removed with just a dry cloth.)

The best approach though is to go to a plane that offers 15º or more of clearance behind the iron. The steeper the pitch, the more resistance to cutting and more deflection so you need even more clearance with steeper pitch planes.

Veritas sell a high angle blade for their plane with a 12 degree bed angle. Is this not a combination that can be expected to work well? I don't think I've seen a bevel up plane with a 15 degree bed angle.

 

[Steve Maskery]

Canary whitewood sounds like something else. The canary wood I'm talking about is an exotic from Central and South America in the genus Centrolobium. http://curiouswoods.com/wood--Canary-Wood--CW. It's clearly a lot heavier than the cherry, and I doubt I could dent it easily by fingernail (though I don't have it handy at the moment to check).

Hmm OK, well at least we agree we are not talking about the same thing.

But do yo know what I think has happened? I think that the person resposible for that web entry is confused. Or at least, there is general confusion.

OK. AFAIK< there is only one commercially available Canary wood inthe UK. Canary whitewood, tulipwood, Americam Poplar. It's all the same. I don't have a botanical reference.

BUT. There is another timber, with all the characteristics of that described, called TULIPWOOD. It's botanically very different, it just shares the same name. I think I have a piece somewhere. Now that IS harder than cherry. I've only ever come across it as turnery blanks from Craft Supplies.

So, I would suggest, either Craft SUpplies got confused between Tulipwood/ Tulipwood or Canary/canary. about 15 years ago (which I dare say is entirely possible), or these people have now.
But the picture and description in that link bears no resemblance to Canary that you would find in any commercial timberyard.

I know that this a bit of distraction from the main thrust of the thread, I just want to be sure about what we are talking about.

Anyway, back to the point.....
S

 

[Wiley Horne]

Hi Adrian,

My experience is that if a plane 'just stops cutting'--meaning downward pressure won't hold it in the cut--then you're out of clearance angle.

With the bevel up plane (unless it's a Holtey 98), the plane will be bedded at 12 degrees, which means you have a max. of 12 degrees of clearance. According to Leonard Lee's results in his sharpening book, you need a minimum of 5 degrees in hardwood, or else the plane will not work. If you are not sharpening frequently, it's pretty easy to lose the cushion of 7 degrees of clearance to accumulated wear on the lower blade surface, or rounding due to stropping on the back of the blade. Others have reported (sorry, I don't have the links to hand right now) that planing with a high attack angle, like 59 degrees, will accelerate the wear noticeably, compared to the same plane at, say, 50 degrees.

Some combination of infrequent sharpening, high attack angle, stropping of the blade back, etc--may be causing you to lose your 7 degrees of available clearance rapidly. It's not sufficient, when clearance is limited, to have the blade feeling sharp. It can be fairly sharp to the touch, yet the plane won't cut, if the blade back has in the ballpark of 7 degrees of rounding or wear at the microlevel.

Here's a suggestion: Do you have a grinder? Or a belt sander? If so, get a fresh start on the bevel up blade by removing some metal. Take a square and mark the blade back about 1mm up from the current edge, and grind back to that line. That should get rid of any rounding or excessive wear on the blade back near the edge. Then, going forward, sharpen more frequently so that you are removing the wear and not allowing it to accumulate over sharpenings. And to control what your sharpening may be doing do to the blade back, use David Charlesworth's ruler trick (and no other stropping or microbevels) to limit the clearance loss to 1 degree.

Wiley

 

[David C]

I think Wiley has given an excellent answer.

If the timber is remotely hard or abrasive, I would be sharpening every 15 minutes or so.

best wishes

David Charlesworth

 

[Steve Elliott]

I'd like to understand why I'm observing such different behavior with the two different planes. Why will my bevel down plane still cut when it's really quite dull and the bevel up plane stops cutting entirely when the edge is much sharper?

The difference in clearance angles between the two planes is only one degree and that's not the entire cause of the difference in performance. I've found when I'm using a very dull blade that taking a thicker shaving will keep it working longer. With a thick shaving there's downward pressure from the wood hitting the front of the blade that helps counteract the upward pressure due to loss of clearance. The plane will be hard to push for three reasons: increased force to push the rounded edge into the wood, more force needed to take a thick shaving, and increased downward pressure needed to keep the blade in the cut. But it's still possible to take a thick shaving. If the same blade is retracted to take a very thin shaving it becomes harder to keep the blade in the cut at all. This is where the plane just stops cutting.

Since your bevel-up plane blade has a 47 degree bevel angle it might be hard to take a .004" thick shaving even if the blade was sharp.

My block planes are among my favorites and of course they're bevel-up. Even with the low angle block bedded at 12 degrees I've been able to use blades that were fairly dull for fitting work, typically taking a thick but narrow shaving. A bevel-up smoother would be used for taking thinner shavings so it would need a sharper blade.

 

[adrian]

Canary whitewood sounds like something else. The canary wood I'm talking about is an exotic from Central and South America in the genus Centrolobium. http://curiouswoods.com/wood--Canary-Wood--CW. It's clearly a lot heavier than the cherry, and I doubt I could dent it easily by fingernail (though I don't have it handy at the moment to check).

Hmm OK, well at least we agree we are not talking about the same thing.

But do yo know what I think has happened? I think that the person resposible for that web entry is confused. Or at least, there is general confusion.

OK. AFAIK< there is only one commercially available Canary wood inthe UK. Canary whitewood, tulipwood, Americam Poplar. It's all the same. I don't have a botanical reference.

Perhaps it's significant that I'm not in the UK.

But the picture and description in that link bears no resemblance to Canary that you would find in any commercial timberyard.

The picture is a bit bland, but looks reasonable. The description seems reasonable. My first experience with this timber was from a mail order supplier who claimed it weighed 31 lbs/ft^3. But the board felt heavy so I weighed it and the actual density was 45 lb/ft^3. This supplier seemed to have mixed up this wood with tulip wood.

I tried pressing my thumbnail into it. If I press as hard as possible it leaves a very faint mark. On American cherry the thumbnail leaves a clear indentation. The cherry is definitely softer.

More pictures of the wood I have can be seen here: http://www.hobbithouseinc.com/personal/woodpics/canary.htm