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rsser
25th January 2009, 03:25 PM
A recent American Woodturner mag reported a test of how cleanly various scrapers treatments left end-grain poplar.

The winner was one with a lapped top and a burr or hook turned up with a diamond hone. 2nd place went to one lapped with a hook turned up with a burnisher. A dry ground burr performed poorly.

I had a play with a dry English Ash spindle blank comparing the second two in cleaning up the cylinder which had been trued with a forged spindle gouge. (Which btw left a cleaner finish than a roughing gouge). The scraper was 3/8" thick Record steel 1 1/2" wide, initially square-end but now slightly radiused for this kind of application.

The Ash as you'd know has distinct spring (wide) and summer (narrow) rings.

The summer grain ran somewhat unevenly through the piece, with some forming an elongated oval at the surface, while the rest ran in planes parallel to the spindle axis. The first I'll call unsupported grain and the 2nd supported.

So the result was this: the dry ground burr left a cleaner finish on the supported grain and a worse finish on the spring wood adjacent to unsupported grain compared with the burnished scraper.

It may be that a finer burnished hook would change this result. On this occasion the hook was distinct and produced with 3 swipes on the Veritas turning tool burnisher, and there was some evidence of the 'self-feeding' noted in the instructions with that unit.

I've still to do the planned tests on the durability of edge treatments.

Hope you find this of some slight interest :rolleyes:

Skew ChiDAMN!!
25th January 2009, 04:40 PM
Out of curiosity Ern, do they mention what brand tools they used? CS or HSS?

I wish good luck to anyone trying to burnish an edge on a P&N HSS scraper! :D I suspect that trying to burnish a hook on 'em simply removes the existing grinder burr and doesn't accomplish much else.

Which'd help explain your findings with the English Ash; you're actually comparing with burr and without, not grinder burr & burnished burr.

Have you got your microscope up 'n running again yet? So you can actually check this?

On the other hand, Ashley Iles (for example) tools are ideal for this sort of thing and there's a noticeable improvement by burnishing. Pity their steel is too soft for most Aussie woods. :rolleyes:

rsser
25th January 2009, 05:19 PM
Yup Skew, HSS. Only a few bearded trogs still use CS these days :rolleyes:

FWIW I've found the Record HSS pretty good, and it wasn't hard work turning a hook on the scraper (give or take a slice through the thumb pad). The Veritas burnisher pins are carbide IIRC.

The Veritas instructions insist that you lap the top of the scraper before each new turning of a hook, and I did that carefully on a fine DMT diamond stone (and can't recall the grit rating on that, which is also a variable).

I've posted elsewhere some 'scope pics, and the burnished edge is somewhat more consistent than the ground (sigh, OK, a good deal more). Another variable would be the angle of a dry ground burr vs that of the burnished. Suspect that the latter would be closer to perpendicular to the tool shaft.

There are pics too in Leonard Lee's book on sharpening.

We can also speculate about how typical English Ash is. You get those wide spring-growth rings in Oregon and Pine but these timbers are much softer.

The theory in Lee's book and his burnisher instructions is that a dry ground edge is really like a saw tooth edge, while the burnished job is like a knife and so has a slicing action. He claims the dry ground edge is weak and the teeth break away readily; that's not borne out by Farrance's test where he found on a spindle gouge that it was in fact difficult to hone away the burr. Course we're mixing up tool types here.

Should've have said in post 1 that the poorer finish from the 'hook' edge at the supported grain equalled chipping out.

Course I didn't control force, tool presentation angle, or direction of travel. Just did what I normally do; get the shavings off. Each of these if varied might produce a different result :?

Time for a cuppa tea, a Bex and a good lie down :wink:

Skew ChiDAMN!!
25th January 2009, 05:37 PM
Yup Skew, HSS. Only a few bearded trogs still use CS these days :rolleyes:

Now, now. Be nice. :p


Course I didn't control force, tool presentation angle, or direction of travel. Just did what I normally do; get the shavings off. Each of these if varied might produce a different result :?

Time for a cuppa tea, a Bex and a good lie down :wink:

Yeah. it can be like that when you're trying to compile empirical results.

And even if you managed a way to cancel all those variables out, it's possible that although a burnished edge may give a better finish at a given angle, a rough edge may give better results over a wider range of angles or some other unexpected result. Or mebbe not. :D

The best we can really expect is "in use I get a better finish with..."

rsser
25th January 2009, 05:53 PM
Zaccly.

Grain orientation is also worth figuring out the variables.

So take a bowl or goblet hollowing task and put your fertile vision to work ... all tool variables aside .. how would you describe the various grain orientations?

I don't have the tech language.