Back bevelled jointer blades

[Wongo]

In his show David Marks said that back bevelled jointer/thicknesser blades cut better and reduce chip out.

I would like to give it a try on my jointer and thicknesser. I thought I would ask you guys first. Have you have tried it or do you have any opinions.

Also what is the angle? I am thinking about option 3 and the actually angle is not that important BUT I want to hear what you have to say. Thanks very much.


http://www.woodworkforums.ubeaut.com.au/attachment.php?attachmentid=72853&stc=1&d=1210031031

[silentC]

Haven't tried it, but when I heard him talking about it, I was thinking only a very flat angle of a few degrees, like with a plane blade. Personally I think those angles are all too steep.

[silentC]

Google turned up this: http://www.woodweb.com/knowledge_base/BackBeveling_Tips.html

[Geoff Dean]

Wouldn't the back of the blade need to be perfectly flat also?

Does anyone go to that degree with jointer knives?:D

[silentC]

Not if you back bevel because the back of the blade is not part of the cutting edge any more under that scenario.

[Wongo]

Like this one silent?

On the show he did show a picture and it looked like option 3. As he described option 3 gives a scraping action rather than cutting action. Hmm..


http://www.woodworkforums.ubeaut.com.au/attachment.php?attachmentid=72854&stc=1&d=1210032901

[silentC]

Yeah I was thinking 10 degrees but like I said, haven't tried it and that was just what I thought he meant. He doesn't actually say what angle.

But you would need to make sure that whatever angle you use clears the in feed table, you don't want the bottom of the bevel where it meets the back (front) of the blade coming into contact with the timber before the cutting edge.

Also I think the steeper the back bevel, the more force required to push through the cutter. One bloke in that woodweb link mentioned using a power feeder. So it's probably a trade off, like with a hand plane.

[Wongo]

But you would need to make sure that whatever angle you use clears the in feed table, you don't want the bottom of the bevel where it meets the back (front) of the blade coming into contact with the timber before the cutting edge.


Very good point.



I am really troubled by the concept now. On one hand if the angle is too small then it might make no difference at all. On the other hand, if the angle is too big then the machine has to work a lot harder to crape the wood off.

[echnidna]

are you having any troubles with tearout Wongo?

[Wongo]

No not really.:p but isn't it for the more difficult grains?

[echnidna]

if you're getting good results why bother.

If it ain't broke don't fix it!

go and make some sawdust instead

[Toolin Around]

Doing a back bevel would be similar to a negative rack on a saw blade. It would reduce tear out, prolong the edge somewhat but it would also compress the fibres in the timber - which could come back and bite you if your finishing technique isn't up to scratch.

[Wongo]

I gave it a go on the jointer knives last night. I cut the back of the knife as a very small angle, just like option 1 above. Thne I tried it on a piece of jarrah which has irregular grains and a piece of rosewood. The results were pretty but I wasn't sure whether it was because the knives were newly sharpened. I did feed that I had to push the wood harder but the extra effort is insignificant. I think I will do the thicknesser knives too this time and see how it goes.

Cheers

[silentC]

There's got to be something in it I guess. Otherwise people wouldn't do it. I suppose it's a matter of finding the right bevel angle.

I searched through all my books and couldn't find a single mention of it, including Leonard Lee's sharpening book and my old WW textbooks. Might be a matter of trial and error. Just hope you don't grind all your blades away before you find it...

When you find the best angle, let us know :)

[Wongo]

Silent, I am not sure if I would waste my time to find the correct angel. What is the correct angle anyway?

You know I am not like those who must get the blade angle to the nearest 0.0001 degree. :D No I am not.

[silentC]

Yeah but you'd think there would be an angle that gives the best scraping action with the least amount of back pressure. Maybe someone will come along and tell us what it is.

[Wongo]

Yeah but

If 0 degree gives you the best cutting action and say 30 degree gives you the best scraping action the any angles in between will give you the combination of the 2. Whatever it is you won’t be worse off.

So 12.25 degree gives you a bit more cutting action then scraping action, right?? :D

C’mon you and I should unit on this one. When was the last time you sharpen your plane blade to the exact angle David Charlesworth suggested. :D (Is that sarcasm)

[silentC]

True. I'm not into the microscopic analyses either. If it works, that's good enough. Maybe there's a range, like <5 degrees - might as well not bother; >15 - too much vibration, that sort of thing.

I think it's hard to be definite with these things though because all wood is different. Maybe you'd have to keep a set of blades without the back bevel and try both on the same board to see if there was a difference in finish.

Or you could just do what you've done and rely on how it feels. You must have pushed enough boards over it by now to know if it makes a difference. :)

[Wongo]

Seriously, what I do like about it is the fact it takes less effort to get a sharp edge. I will keep you posted mate. :2tsup:

http://www.woodworkforums.ubeaut.com.au/attachment.php?attachmentid=72951&stc=1&d=1210125046

[Wongo]

I did the thicknesser knives last ngith. It took me less than 30 mins to sharpen 3 blades. Usually I would take me a lot longer. The picture above shows there is a lot less metal to cut to achieve a sharp edge.

I am very happy for a different reason.:2tsup:

I even managed to cut my finger.:C

[silentC]

How do you sharpen them?

[Wongo]

Tormek.

[routermaniac]

Wongo I am no expert at this, but does this mean that the finish on pine might not be as good? (especially the higher the backbevel angle gets?). On the other hand I would expect that the finish on hardwood should be much better due to the scraping action.:?

I got the planer jig 2 weeks ago and I must admit I couldn't wait to get stuck into the thicknesser blades. It does a very good job and I was surprised how quick it is. I think I cut my self three times before I managed to reinstall the jointer blades! :-

Just out of interest at what angle do you grind your primary bevel at Wongo?

regards

Marios

[Wongo]

Wongo I am no expert at this, but does this mean that the finish on pine might not be as good? (especially the higher the backbevel angle gets?). On the other hand I would expect that the finish on hardwood should be much better due to the scraping action.:?


I am not sure. The back bevel angle is very small so I guess the scrapint action is very small. I am just happy now I can sharpen my 15" blades very quickly.



Just out of interest at what angle do you grind your primary bevel at Wongo?


I don't really know.:- I never see it as important. I eyeball the set up each time.