Back Beveling of jointer and thicknesser knives

[lesmeyer]

G'day,
I have trawled thru the posts about back beveling of blades, but all the posts w.r.t. back beveling are about hand plane and chisel blades. Recently I have observed some TV programs (Wood Works and NY workshop) where the guys reckon that back beveling of the jointer and thicknesser knives provide a smoother finish/action and also keep a sharp edge for longer. When I spoke to one of the sharpening specialists at the Perth wood show, they say this is the first they have heard about it.
Does anyone out there have any experience in this regard - would love to hear about it.
Regards
Les

[Harry72]

This is about all I could find...

"Back beveling is effective when the angle of the knives in the planer head is not sufficient. By back beveling, you make the knife more slender and more likely to chip the grain, over-heat, and dull, so care must be used. Back beveling has been used for softer woods (aspen cottonwood, basswood, etc.) only, in my experience."

This page has a bit about blade angles on jointers
http://www.woodweb.com/knowledge_base/Knife_Grinding_and_Woodworking_Manual_6.html

[routermaniac]

I just think that it would be tricky to get both blades exactly the same, as if its not bad enough setting blades that are identical, these would be worse!

Also, the benefits are likely going to be minimal, the manufacturer would have presumably chosen the best compromise between finish and longevity when setting the angle of the blades, back bevelling the right angle would be a trial and error process, not sure whether it would be worthwhile...

The above is not based on any personal experience so take it with a grain of salt.

[JDarvall]

This is about all I could find...

"Back beveling is effective when the angle of the knives in the planer head is not sufficient. By back beveling, you make the knife more slender and more likely to chip the grain, ........

Am I visualising this wrong ? Why does the blade get more slender when you backbevel ? ....When there's a backbevel doesn't that final bevel get larger ??? ....or am I missing the point :D ...no, seriously, I'd like to understand this better.

And I agree with Routermaniacs points.
Backbeveling with hand planes is practical, IMO, because its a relatively quick process trialling different effective pitches until there's no tear. Be so much different I guess when setting jointer blades because that can be quite time consuming......but hangon, I forgot......Harry's got a great blade setting process with magnets (gota try it myself).

I wonder how often you'd have a need to backbevel them anyway ? I machine a lot of teary timber, and that scooping cutting action of jointers and thicknessers seems to give a clean result 99 % of the time. ???

[Harry72]

apricotripper, did you have a look at that page i mentioned, it explains about different angles for different woods.

[JDarvall]

apricotripper, did you have a look at that page i mentioned, it explains about different angles for different woods.

No, I was too much in a hurry and missed. Just looked at in now, and it looks good except for a lack of pictures :D .....Got to go to work right now, but I'll read it latter. ...ta.

[sinjin1111]

About a 100 yrs ago when i did my apprenticeship. We had some very large machines. And one of the things you notice is the dia. of the cutter heads are much larger than machines i seem to be seeing now. I personally bought a 20" over the 15" for 2 reasons. One the extra throat depth and the larger dia cutter head. Sure it has to be larger for the extra width for the same stiffness. But to me the biggest advantage of larger cutter heads is the included angle at which the knives hit the wood. So by back beveling aren't you effectively reducing the size of the cutter block. What i mean is the back bevel makes the knives hit the wood at the stepper angle. I agree the edge would last longer for sure. But like Jake i'm really missing the point about how the knives would be slimmer.
Sinjin

[NewLou]

Gidday lesmeyer:D

Heres the drum straight from marksey himself!!!:

Tip: Jointer knives should not only be sharp, but for best results they should also be back-beveled. The same is true for the planer. Back-beveling the knives causes the cutting action to be more like a "scraping" action , thus reducing chip-out and save time from fixes and sanding. Back-beveling is an added cost, but will payoff in the finished wood products produced with the jointers and planers.

David J Marks Master Woodworker

REgards Lou

[lesmeyer]

Thanks for the input guys.
As I said in my post, the TV shows state that one should do the back beveling, but the sharpener here in Perth has never done so. I agree with Routermaniac that it is difficult enough to set the blades, let alone trying to back bevel. Having said that, I intend to experiment with the HSS blades once the 18% tungsten blades are in the machine. I will hone the HSS blades with my Veritas Jointer blade sharpener. Then add a back bevel of about 10 deg. If this does not work, not much lost as I will not be using the HSS blades again.
Regards
Les

[cray54]

Here is some more specific information from David Marks regarding the back bevel on jointer / planer blades from American Woodworker, February 1996:

http://books.google.com/books?id=o_YDAAAAMBAJ&lpg=PA12&ots=3u-K5OgTK7&dq=jointer%20%22back%20bevel%22&pg=PA12#v=onepage&q=jointer%20%22back%20bevel%22&f=false

Thanks,
Chris