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kman-oz
17th August 2007, 11:48 AM
I've had a quick read around regarding the planing of curly timbers and discovered an array of methods to minimise tear-out... most of them involve another mortgage, but I understand a york or higher pitch on a bench plane will get the job done reasonably well. To my mind the only practical and in-expensive way to do this is with a back bevel on the plane iron.

The timber I'm working with at the moment is some old growth Spotted Gum from nothern QLD, and the No.4 & 5 planes have made a real mess of it. Thus, I have two questions:

1) Can anyone suggest a versatile back bevel angle that could be used on either of the No. 4 or 5 bench planes for working with curly timbers? I'm thinking 60-65 degrees (15-20 degree beck bevel), and

2) What sort of depth of back bevel should I apply to the iron? Do I make it deep enough that the chip breaker is completely redundant, or narrow enought that the chip breaker can be postioned close to the cutting edge as normal?

Many thanks for your help folks.


Dave.

jisk
17th August 2007, 02:15 PM
I've also got some curly spotted gum. I was planning on buying a Metabo Duo ROS to finish it.

I'm no expert (I seem to be saying that a lot lately) - I'd just go with 60 - 70 degrees effective angle as that's what HNT Gordon seem to use.

scooter
17th August 2007, 04:21 PM
Try PMing apricotripper or searching back through the threads he has started, he put up a comprehensive thread a fair while back on back bevelling.

Edit: I think I'm thinking of this thread (http://www.woodworkforums.ubeaut.com.au/showthread.php?t=23798) here, maybe check it out them send PM for more info.


Cheers...................Sean

silentC
17th August 2007, 04:36 PM
Have you tried a scraper on it?

kman-oz
17th August 2007, 05:21 PM
Thanks Scooter, did a bit more searching and found another thread by apricotripper that was helpful for the first question. Good little guide for making a very low angle back bevel guide too :)

Still have no idea about the second question though.


Have you tried a scraper on it?

Don't have one, this being the primary reason for experimenting with back beveling. On the other hand would a bevel up attempt with the iron primary bevel ground to <20 degrees work?

silentC
17th August 2007, 05:24 PM
I'm sure someone has tried it.

I made my scraper from an old saw blade. It's a very handy tool to have and the finish is like glass. Great for removing tear out and machine marks but not so good for flattening or removing lots of material.

kiwigeo
17th August 2007, 05:31 PM
Silent, scrapers are only for whiley old farts like you and me :D

kman-oz
17th August 2007, 05:40 PM
Ah, I misunderstood, I though you meant a scraper plane. Either way the tearout generated with the No.4 plane bevel down is almost 1mm deep. Not suited to a hand scraper me thinks. When I said a mess.... I meant a MESS! :(

silentC
17th August 2007, 05:40 PM
You can tell us from the rest by the crooked thumbs :)

silentC
17th August 2007, 05:46 PM
They can be made to cut quite aggressively. I used mine the other day to remove some tearout lovingly introduced by my thicknesser. Probably not 1mm deep but still pretty nasty. Might be worth a try before you muck up one of your good plane blades :wink:

BTW regarding backbevel, I've got a spare #4 that has a 15 degree back bevel. I haven't spent enough time with it to really test it out but it seems to cut a bit better in some situations compared to the one with the 5 degree bb. The back bevel is only a couple of mm. I don't think it needs to be any more - not sure, one of the other guys will know for sure.

kman-oz
17th August 2007, 06:28 PM
...The back bevel is only a couple of mm. I don't think it needs to be any more - not sure, one of the other guys will know for sure.

My thinking is the same. It make sense to me for the back bevel to be <1mm deep so that the chip breaker can be positioned the same way on the iron. Of course this also limits the geometry change so it won't effect adjustments much either. I've got a spare iron and the smaller I make the back bevel the easier it is to remove later too :)

I'll take a couple of pics on the timber tonight so you can see what I'm talking about.

scooter
18th August 2007, 03:49 PM
kman, I think the backbevel only needs to be very small, read < 1mm. Sure I saw that somewhere.

Paul Chapman
26th August 2007, 08:20 AM
To my mind the only practical and in-expensive way to do this is with a back bevel on the plane iron.



Hi Dave,

I don't know whether you ever see the UK magazine "Furniture & Cabinet Making" http://www.thegmcgroup.com/ccp51/cgi-bin/cp-app.pl?&act=&aff=&pg=prod&ref=1010FC#thumb In the May 2007 issue there was an excellent article on this by David Charlesworth, which covered the subject very comprehensively. Well worth reading if you can get hold of a copy.

Cheers :wink:

Paul

kman-oz
6th September 2007, 12:48 PM
Thanks to all who replied, you've been a big help. I'm happy to say the back bevel operation was much more sucessful in both the No.4 and 5 planes, with only the slightest tearout at 15 degrees and only a few furry bits at 25 degrees. I also had a go at hand scraping the surface using the plane iron from a No.6 (2 3/8") and the result was very nice indeed. Still no sure how to get that gloss back, but I'm infinitely better off.

Thank you all again! Now I'm going to attempt to build a high-angle smoother/scraper plane :)

P.S. As soon as I get my camera back I'll provide some shots of the result.

kman-oz
21st September 2007, 11:29 AM
I thought I'd update this thread with newer results since the last attempt at some curly timber; further refinment of the back-bevel operation has made me question the need for a HA plane at all.

The last back bevel I tried on the No. 5 plane used a primary bevel of 25* and a back bevel of 25* for a total iron cutting angle of 50*! Some research tells me this may be too high, so I've tried a few different configurations since then with even better results. First I left the back-bevel and ground a primary bevel of 20*.... smoother but no less effort to plane, i.e. lots of energy expended. Next I tried the back-bevel at 20*.... no less smooth, but less effort to plane. So, progress then?

In further iterations of this process I've now got both bevels at 15 degrees for a total iron cutting angle of 30 degrees, or roughly the same as a standard primary bevel with an additional micro bevel. Results: much easier to plane with only the slightest degradation of finish using a deep cut. Wind the blade back a little for a see-through thin shaving and the finish is almost perfect; nice semi gloss with no tear-out at all. A quick once over with some 1200 grit silicone carbide paper and Tung oil reveals a beautiful patina.

It seems that this method only really suffers when I attempt to take more than a medium to thin shaving. When attempting a heavy shaving the tear-out comes back and it becomes increasingly difficult to eliminate chatter, presumably because the un-supported edge has become considerably longer due to the very low primary bevel angle.

I'm not sure how much interest there is in this department, but in the interest of sharing knowledge (this is a forum isn't it :) ) I've added this for future reference for other cheapskates like me.

silentC
21st September 2007, 11:56 AM
OK, trying to get my head around this.

With a bevel-down plane, like the Stanley #5, without a back bevel, the cutting angle is the same as the bed angle. The primary, secondary or micro bevels that you put on the blade actually make no difference to this, as they are clearance angles and don't affect the angle of blade presentation to the wood.

When you grind a back bevel however, this does change the cutting angle, which is a result of the combination of the bed angle and the back bevel. So a back bevel of 15 degrees would give you a cutting angle of 45 + 15 = 60 degrees, regardless of the bevels on the other side of the blade.

However, the clearance angle has a bearing on the life of the edge and I think it may also have a bearing on the degree of difficulty in pushing it through the wood. So a sharper angle is easier to push but will be less durable than a more obtuse one.

kman-oz
21st September 2007, 12:20 PM
... the clearance angle has a bearing on the life of the edge and I think it may also have a bearing on the degree of difficulty in pushing it through the wood. So a sharper angle is easier to push but will be less durable than a more obtuse one.

Exactly, this has been my experience. I can't say I completely understand all of this but the upside of the sharper iron angle also seems to be less need for a higher over all cutting angle. In my example I've gone from a presented cutting angle of 70 degrees to a cutting angle of 60 degrees with no significant effect on finish while the effort involved was considerably lower.

I'm going to continue building a HA plane anyway to verify my results against. With a 60 degree bed and 30 degree primary bevel the presented angle and clearance angle will be the same as my experiment, then I just need to see if the results differ.

silentC
21st September 2007, 12:22 PM
Well let us know how it goes and don't forget the photos!

Caliban
22nd September 2007, 10:59 PM
You can tell us from the rest by the crooked thumbs :)

and the unmistakeable smell of burning flesh.:o