The secret to cambering Bevel Up plane blades

Wiley Horne · Posted: Fri Oct 12, 2007 5:30 am Post subject:

Denis,

I'll write you offline, as I have unwisely jumped into the middle of Derek's story with an explanation--when he is infinitely more qualified than I to explain his results!

Wiley

Derek Cohen (Perth, Oz) · Posted: Fri Oct 12, 2007 5:54 am Post subject:

Hi Denis

Let me start by saying that your questions are good ones. Even more than good - they are important and must be asked and answered.

The problem centres around the grind (a term I prefer when removing metal rather than polishing it) a significant camber on a bevel up blade. And to take this the important next step, to do so on a BU blade with a high bevel face, such as 50 degrees.

It is contended generally that a BU blade requires a greater camber for the same effect than a BD blade. This is due to the geometry of the bed, 12 degrees for BU and 45 degrees for BD.

It is my contention that there is less metal to remove - which makes the process viable - on a BU blade with a 25 degree primary bevel and a 50 degree secondary (micro) bevel. The foundation for this argument is that a microbevel is .. well, micro .. and a camber on the full face of a 50 degree primary bevel has considerably greater volume.

I would suggest that you try cambering a full face 50 degree bevel by hand and, if you can, do the same with a 50 degree micro secondary bevel on 25 degree primary bevel , and report back your experience.

Keep in mind that we are talking about creating shavings for not just a smoother, but especially for a fore plane - so see the camber profile that is needed to do this. The camber resembles that of a scrub plane with a BD configuration.

Regards from Perth

Derek

David C · Posted: Fri Oct 12, 2007 8:22 am Post subject:

Andy,

Thank you so much for that encouraging story!

David

AHoman · Posted: Fri Oct 12, 2007 12:17 pm Post subject:

promhandicam · Posted: Fri Oct 12, 2007 1:07 pm Post subject:

ivan · Posted: Fri Oct 12, 2007 2:39 pm Post subject:

I understood Derek to mean "metal removed on the honing stone". If you have a 25 deg primary bevel you don't have to remove much steel to hone it - it's a microbevel, even if honed at 50 deg. If you grind at 50 deg, you then have to remove metal from the whole face of the bevel to hone it (also at 50 deg). This right?

dchenard · Posted: Fri Oct 12, 2007 3:14 pm Post subject:

Derek Cohen (Perth, Oz) · Posted: Fri Oct 12, 2007 3:49 pm Post subject:

Steve

Thank you for clarifying that point. It is amazing in how many ways the same sentence might be (mis)interpreted.

Here is what I originally wrote:

dchenard · Posted: Fri Oct 12, 2007 4:54 pm Post subject:

ivan · Posted: Fri Oct 12, 2007 5:15 pm Post subject:

PS. I assume there's little advantage in using the JET cambering jig? This one looks a good deal more affordable....

David C · Posted: Fri Oct 12, 2007 9:23 pm Post subject:

Ivan,

I have been using that New Jet jig, (which fits Tormek) and have written about it and camber in general, in the issue of F&C which is out about now.

It does a very good job on gentle and medium camber, may or may not do enough for a scrub plane, didn't have time to find out.

I like it a lot.

David Charlesworth

ivan · Posted: Sat Oct 13, 2007 10:54 pm Post subject:

Thanks, David; I'll keep a lookout for the mag. but newsagents are a rare item in these 'ere parts.

David C · Posted: Sun Oct 14, 2007 8:40 am Post subject:

Ivan,

There is one at the bottom of Bideford high street!

Where are you?

David

bugbear

David C · Posted: Tue Oct 16, 2007 7:49 am Post subject:

BB,

I was going to point out the same thing.

The skill required is to keep the long stick at the same angle.

A support at the top end of the stick would help to maintain consistent angle, would it not?

best wishes,
David