Of bedding and burnishing angles

[ivan]

It's often surprising how often we cannot recognise what we already know!

It is easy to think of a plane with a very close set cap iron, as having the same cutting geometry as a scraper, with the useful addition of a mouth. It took till this morning to recognise that the obverse is also true. A scraper plane, sharpened at 45 deg and burnished from 45 increasing to 75 deg, when mounted in in the scraper plane sloping forward at ~20 deg, is mimicing a bench plane bedded at about 80 deg with the cap iron set very close.

More interesting for discussion, consider a 112 or 212 scraper plane (with adjustable angle), sharpend at 45 deg and burnished to 90 deg as LN suggests. If the blade is mounted vertically in the scraper plane, then the clearance angle is ~zero. This setting is somewhat academic, mimicing a low angle plane with an imaginary zero clearance. However, the adjuster allows you to tilt the blade forward as desired, putting control of the cutting angles in the hands of the user. In effect, the scraper plane cutting geometry mimics a close set plane with adjustable bedding angle. This seems a useful way to clarify what is often, in texts, a rather grey area - that of choosing burnishing and bedding angles for a scraper plane. It's intriguing to think that a low angle plane (has to be bevel up) cannot actually have a cap iron, but that such an effect can be realised with a scraper plane.

Examination of a LN 1/8" blade burr (30x) suggests that the cutting edge included angle is not much changed fom 45 deg by the burnishing. A thinner blade might well burnish to a finer cutting edge (cf. cabinet scraper) giving rise to additionl settings.

 

[Philly]

Interesting stuff, Ivan!
I find the name scraper to be off-putting. As it should cut and not scrape regular pitch/chip type should apply.
Cheers
Philly

 

[David C]

Ivan,

Since when have L-N been recommending burnishing to 90 degrees please?

This is news to me.

News no longer........ I have just checked their use and care section.

This is not consistent with the advice which will be in my Cranky Grain dvd due possibly before Easter. How odd...........

David C

 

[ivan]

Lets be fair here, I don't normally burnish as far as90deg, but remembered seeing it printed in the LN leaflet, and it makes a better point re. scraper geometry mimicing an unrealisable low angle plane with cap iron.

On reflection, cabinet scrapers sharpened to 90 deg produce a much finer cutting edge (ie much less than 90deg) as a result of burnishing. The burnishing stretches out the metal. You might get a finer cutting edge sharpening to say 70 odd deg. (30 - 45 deg sharp edges may be thin enough to just bend over under the burnisher). A finer edge and lower equivalent angle might help to reduce that "scraper dullness" and/or give a better result on softer timbers.

 

[Rich]

Right chaps and ladies, can we hold it right here? all this talk of angles and burnishing is confusing me, it's to be expected as I'm still trying to come to terms with 25, 30 degree angles, even 15 was mentioned on another thread (phew), anyway a while back I bought my eldest lad a self build guitar kit which he duly assembled, he sprayed it with a metallic blue paint, then he decided he did'nt like it .
So, he proceeded to scrape it all off with a stanley knife blade held between fingers and thumbs, took him about 3 hours but he done it and finished the surface with a green scotchbrite pad, turned out smashing, now, what about the angle of a stanley blade, 75 degrees?
could one of you lovely people post a picture or diagram of what your saying to each other, I'd be much obliged so I can be on the same wavelength.
Regards, Rich.

 

[David C]

My apologies, but my skills do not run to the cad drawings required...

I have described scraper plane blade sharpening, in depth on page 110-113, of my second book, with photos and diagrams and words.

It has always seemed sensible to me to follow the Stanley instructions for the no 80 Scraper plane. This means sharpening and honing the blade at 45 degrees, (with very slight camber) and then burnishing or turning the hook, by stroking with the burnisher, very lightly, from 45 degrees to 75 degrees.

In other words the edge is deformed through 30 degrees, when creating the hook.

It also means setting the blade at the same forward lean as the 80.

Rich,

The Stanley knife blade is yet another form of scraping but with different geometry.

best wishes,
David Charlesworth

 

[Paul Chapman]

I have described scraper plane blade sharpening, in depth on page 110-113, of my second book, with photos and diagrams and words.

David, I've followed your methods as described in your book (but without the cambered blade and ruler trick) and found them very successful. I've also found that it is possible to re-form the hook a couple of times without going through the whole honing process, with some success.

Cheers :wink:

Paul

 

[David C]

Paul,

Good to hear that, thank you.

I have spoken to Thomas and I think those care instructions will be changed in due course.

David