Replies

1. 
   CStanford | Jan 16, 2007 08:31pm | #1

   It's what tuning and fettling freaks do instead of simply using a scraper when the wood starts to tear out a bit.

2. 
   mwenz | Jan 16, 2007 08:45pm | #2

   In deference to Charles' characterization, back beveling allows one to increase the effective cutting pitch of a bevel down type of plane. A bevel down plane such as a Stanley plane is commonly bedded at 45 degrees with the bevel facing down on the frog.

   Bay adding say a 10 degree bevel it is effectively now the same as a plane bedded at 55 degrees.

   Each increase in effective cutting angle the plane will be correspondingly more difficult to push and the edge will wear at an increasing rate, all things being equal.

   My personal belief is it is better to simply obtain a plane with a greater bedding angle as maintaining back bevels can be a pita. I also feel it is best if one determines to do back bevels to do so on a second, thicker, after market iron rather than the thin irons which come standard on a Stanley-type plane. Increasing the effective cutting angle also introduces more strees on the edge and and can be a source of chatter.

   So I have planes with steeper beds to handle much of my difficult grained wood. However, like Charles, if those planes cannot still produce a good finish on the wood surface, I turn to scrapers and or scraper planes. But as a last resort. Most times a plane with a higher bedding angle will simply do a great job with less effort.

   Take care, Mike

1. 
   bufun | Jan 17, 2007 02:09pm | #3

   mwenz, Thank You & Charles for your replies. I was intriguied by the concept of back bevel having never read of it before. I have in my possession a very old Bailey 4&1/2 smoothing bench plane that I will after market a thicker Iron and back bevel to experiment with. My situation is this, I have some very nice crotch cherry from a tree that saved my life while cutting timber, it prevented my head from experiencing significant injury from a lateral limb that fell while dropping its neighbor. It had to go also and I had it slabbed and now wish to make peices for family members from its fletchings. I have purchased Lie-Nielsen, srub and low angle jack planes and a Lee Valley Veritas Mark2 honing guide and have experienced very positive conversations with thier reps concerning aspects of thier respective products. Its very nice to have companies whose staff are knowledgeable about thier products to the degree that they are. So, here is a very stupid question(humor an old fool). What would happen if you back beveled a bevel-up low angle plane?? Yors in DUH,GoodWorkings-bufun 

1. 
   VTAndy | Jan 17, 2007 06:35pm | #6

   Bufun,
   Don't put a back-bevel on your bevel-up blade. Picture a bevel-down blade first: it leads with the back of the blade --- therefore, putting a bevel on the back gives you a higher effective angle.
   Picture a bevel-up blade: it leads with the bevel-side of the blade. If you want to change the effective angle of the bevel-up blade, put a small, higher degree secondary bevel on the bevel side itself. Give this a shot at 40 degrees usings your honing guide, then try the blade on the face side of some wood that has been giving you trouble. You will notice a difference because you'll have a cutting angle of 62 degrees.
   Cheers,
   Andy

2. 
   mwenz | Jan 17, 2007 06:47pm | #7

   "What would happen if you back beveled a bevel-up low angle plane?? "

   Hi Bufun,

   Because the effective cutting angle is set be the bevels on the top of a BU blade, a back bevel would be on the bottom side of of a blade on a BU plane. In so doing, it lowers what is called the clearance angle of the blade.

   For instance. A BU plane which has a blade bedded at 12 degrees. If you put a back bevel on this blade of 10 degrees, it would only give a clearance angle of 2 degrees.

   If you were to plane with a plane sharpened in this manner, it wouldn't be long before the edge rounded enough the plane would effectively stop cutting. This is because a cutting tool--be it a chisel, axe, plane or anything else--when used develops what is called "wear bevels." These wear bevels develop on both sides of the cutting edge. It is formed by the abrasion of cutting.

   So once the lower wear bevel grows [the lower wear bevel forms on the back of a blade on a BU plane and on the actual bevel side of a BD plane] it reduces the ability for the cutting edge of the blade to remain engaged cutting wood. Once it grows enough, the lower wear bevel actually can ride on the wood's surface, effectively limiting the ability of the blade to cut.

   By back beveling a BU blade, one is essentially hastening this process.

   Take care, Mike

1. 
   derekcohen | Jan 17, 2007 07:44pm | #8

   Here is an observation of mine about backbevels which I do not believe has been discussed anywhere before.

   As an introduction we must distinguish between micro backbevels and backbevels. The MBB is the work of David Charlesworth and involves a backbevel of under 1 degree on the back of a blade, and it is used after honing the face of the bevel as a shortcut/substitute for flattening the back of a plane blade. A backbevel, on the other hand, typically refers to a 5 - 15 (or more) degree bevel on the back of a blade, the purpose of which is to increase the cutting angle on a BD plane. The other point to be raised here is that adding a backbevel to a BU plane blade does not reduce the cutting angle (i.e. being the opposite of a backbevel on a BD plane) and simply serves to reduce the clearance angle. The necessary clearance is noted to be 7 degrees.

   That said, the question that has been going around in my head for some time has been "what is the effect of a BB on the size of the plane's mouth?".

   The answer to this is academic for planes with adjustable mouths, but it may have more relevance for planes with fixed mouths.

   Here is a drawing I put together:

   View Image

   Here the RED line represents the inner boundary of the mouth. The BLUE line represents where a backbevel would be honed.

   In the case of the BD blade, the angle of the BB would increase as the blue line moved to the right. And in the case of the BU blade, the angle of the BB would increase as the blue line moved upward.

   What may be seen here is that a backbevel on a BD plane will effectively OPEN the mouth, while a backbevel on a BU plane will effectively CLOSE the mouth.

   Of course, this has pros and cons, depending on the situation.

   Regards from Perth

   Derek

1. 
   mwenz | Jan 17, 2007 08:32pm | #9

   Hey Derek--good to hear from you.

   Actually, a BB on either plane opens the mouth, it is just that due to the low bedding angle on a BU plane, this amount is reduced significantly. Look at your graphic again <g>...However, like you mention, an adjustable mouth mitigates the increase in mouth clearance altogether.

   I try to avoid BB anymore. While they do help on wild grain, I didn't like the maintenance. Not too bad if one has an extra iron or two for a given plane should the need arise, but if one only has a single iron for a given plane one is either forced to maintain it or grind past it to remove the BB.

   So having a couple planes of different bedding in the case of BD planes is nice. With BU planes a couple irons one can have at different primary/secondary bevels increasing in angle is great.

   Clearance angles are a whole nuther ball of wax. If BU planes intended for smoothing had a higher bedding angle, say 20-25 degrees, it would go a long way to aiding longevity of the cutting edge. Which translates into longer periods between sharpening/honing and or less time sharpening/honing. I'm all for that.

   Take care, Mikeback to worky...

2. 
   derekcohen | Jan 18, 2007 03:16am | #10

   Actually, a BB on either plane opens the mouth, it is just that due to the low bedding angle on a BU plane, this amount is reduced significantly. Look at your graphic again <g>...However, like you mention, an adjustable mouth mitigates the increase in mouth clearance altogether.

   Mike, the reason why I was hesitant to raise this issue is that my spatial difficulties get in the way of reality. Nevertheless, this time I think I am correct. However my graphic could have been better (it was 1:00 am!). What I drew for the BU blade was greater than the maximum possible backbevel - one cannot have a BB that is parallel with the sole. The dark blue line now represents a more likely situation.

   View Image

   Now try "sliding" the backbevelled blades forward in the graphic. As long as there is clearance (that issue again!) then the mouth closes up with the BU blade. In the case of the BU blade, it now drops down further forward for the same shaving thickness. With the BD blade, the cutting thickness increases if the blade is moved forward to close up the mouth. Hence the BD blade must remain where it is - and the mouth remains open.

   Clearance angles are a whole nuther ball of wax. If BU planes intended for smoothing had a higher bedding angle, say 20-25 degrees, it would go a long way to aiding longevity of the cutting edge. Which translates into longer periods between sharpening/honing and or less time sharpening/honing. I'm all for that.

   Absolutely! Which is why I believe that BU planes that are dedicated to smoothing need to have higher beds. Leave the generalist BU plane with a (12 degree) bed angle that can be a "jack of all trades". A BU smoother should have a bed of at least 20 degrees, which is what I recommended to Philip Marcou  (when he was only building a 15 degree bed), and why I built a 25 degree bed into my latest BU smoother (which, with a 35 degree micro bevel for a 60 degree cutting angle, is working fantastically!). No backbevel on this smoother as it has a fixed mouth.

   Regards from Perth

   Derek

3. 
   mwenz | Jan 18, 2007 03:53am | #11

   Don't ya just love late night writing and illustrating?

   There is another issue involved with BU planes and back beveling and that is iron extension. IE, it is possible to put too much BB on a BU iron which is bedded at 12 degrees and not get good extension/depth of cut on the iron *if* the plane has a fixed mouth. Think LN low angle jointer unless the mouth is significantly open--and I don't have one to review.

   Trying to not pick nits, the illustration still shows the BB affects the mouth--but is moot on a BU plane one can adjust the mouth on. The extension is the issue. If the actual edge climbs on the top bevel [i.e. adding a BB] then the iron needs to slide that much more forward/down in order to project below the sole the same amount as an iron without a BB.

   This means the mouth must be opened and then adjusted to the desired degree of open/closed. Thank goodness most all LA/BU planes have an adjustable mouth else taking a ranker cut would get more problematic with potential clogging.

   But--and here's the thing. There is no good reason to generally add a back bevel to a BU plane. There is only one plausable reason because the effective cutting angle is controlled with the primary bevel side of the iron. That is to add strength to a very low primary bevel. But I think the subsequent maintenance of the BB negates any gain in less honing--which without a BB doesn't take but a couple minutes and doesn't require jigs 'n' rulers to keep a moderately accurate BB.

   Take care, Mike

4. 
   derekcohen | Jan 18, 2007 04:11am | #12

   But--and here's the thing. There is no good reason to generally add a back bevel to a BU plane. There is only one plausable reason because the effective cutting angle is controlled with the primary bevel side of the iron. That is to add strength to a very low primary bevel. But I think the subsequent maintenance of the BB negates any gain in less honing--which without a BB doesn't take but a couple minutes and doesn't require jigs 'n' rulers to keep a moderately accurate BB.

   I totally agree Mike. The only type of BB I would use on a BU plane is a microbevel (ala "Ruler Trick"), and this is so small as to minimise any effects on the mouth. However, I hear of some who believe that they have converted a standard angle block plane (e.g. such as a Stanley #18) into a low angle block plane by adding a backbevel. I cannot get my spatially-challenged head around this one. In my mind, it is the upper face of the bevel that pares the cut, the upper face of the bevel that determines the cutting angle, and that therefore giving the lower face a BB will not alter the cutting angle.

   Regards from Perth

   Derek

   (PS  - has the postman made a delivery from Perth as yet?).

5. 
   joinerswork | Jan 18, 2007 04:14am | #13

   All,

   I have used a back bevel for a reason not yet mentioned: to salvage an otherwise unusable antique iron with some significant rust pitting on the back of the blade.  A back bevel effectively polished out the pits at the edge, without necessitating re-surfacing the back of the laminated blade.

   Ray Pine

6. 
   mwenz | Jan 18, 2007 04:44am | #14

   Hi Ray--it was briefly mentioned somewhere--else I dreamed it.

   I do this also on my BD vintage irons, much to the same degree and aspect as Charlesworth describes with the ruler method.

   Take care, Mike

3. 
   ptu | Jan 17, 2007 05:17pm | #4

   Could someone explain exactly what a back bevel is, and where on the blade it is? I doesn't make sense to me, the way I envision it.
   Pedro

1. 
   Samson | Jan 17, 2007 05:53pm | #5

   Instead of the back of the blade being flat, a bevel is ground on the back side as well as the front.  When you consdier the front bevel, back bevel and bed angle, you arrive at an effective cutting angle.  That angle is made steeper by grinding a slight back bevel on your plane.  The steeper angle handles troublesome grain better (like a York pitch frog effect).  HTH

1. 
   ptu | Jan 19, 2007 05:06pm | #15

   Thanks, Do you use them? Would you have two irons, so you swap back and forth?

1. 
   Samson | Jan 20, 2007 04:52am | #17

   Sorry, Pedro, I don't use them.  If I ran into a significant tearout issue, I'd use my scraper arsenal.

1. 
   ptu | Jan 20, 2007 06:14pm | #18

   Samson, I'm like you, I use scrapers when things twitch. I don't think I want to change any of my Irons.
   Pedro

4. 
   bigfootnampa | Jan 20, 2007 12:31am | #16

   Just to add a little consideration for those interested in planing troublesome figured woods... try dampening the surface of the plank just before planing it.  The lube effect, possible fiber softening, and swelling of the fibers, will make your planing task far easier... with ANY plane.