Veritas scraper burnisher questions

[Raif Harik]

Well after being inspired in a previous thread, or filled with envy, whatever, I got the veritas burnisher. It seems to work pretty awesome. However, after some use I'm starting to have some questions.
a) how long can I keep re-burnishing a NRS? I feel like I may have hit the limit. But how do you know, or is there a rule of thumb?
b) when I go back to the grinder, should I then remove the grinder but with like a 600 grit diamond "stick"? As I mentioned I'm using NRS and it's kind of hard to file of the bur on a round scraper. If the were ... No rake scrapers or whatever it would be a lot easier I guess.

I think that's it but I'm probably forgetting some other problem
Thanks,
Raif

 

[Brian Gustin]

To roll a burr on a scraper (be it a card scraper or NRS or any other scraper that cuts with a burr) you do need to start with a very fine perfectly squared up edge, so of course you do need to hone off the old burr from the top before grinding your new square edge on the front of the scraper. On a microscopic level, the finer you are able to bring the 2 corners where the burr is formed to a perfect point (razor's edge) the better of a burr you are able to form. For most turning purposes, the rougher burr resulting from grinding (even if the ground burr is removed and a new one formed with burnisher) with be perfectly suitable. Mos of the time such an edge can have the old burr polished off and a new burr formed several times (3 to 5 maybe) before the corner becomes too rounded over (from forming new burrs) and has to be refreshed at grinder.

For things like card scrapers (fine woodworking, luthiers, etc) often the scraper will be honed and polished to as fine as 8000 grit (it just has to be perfectly square for those double sided edges, but could of course get a burr on only one side in which case squareness isn't important) and a rather delicate but extremely sharp burr can be formed that will draw shavings thinner than a human hair from even really hard woods (resulting in a surface that is so smooth on some woods that you'd ruin it by sanding it even with 1000 grit paper)

Important thing is to understand what the burnishing is actually doing at the 10x magnification level (if you have a magnifier to study your edges before & after, it can help you to improve your skill at burnishing too!) what you're actually doing is taking a keen edge corner and pushing that corner with the carbide rod to "stretch" the metal a little and roll it slightly to form a hook (think of a fishhook) which is the burr (the actual cutting edge) so how often you may need to refresh your burr at the grinder can depend on a lot of factors, not only the quality of the metal in the scraper, but how keen your refreshed edge is, and how aggressive of a burr you pull with the burnisher (Obviously heavier more aggressive burrs will necessarily be using more of the edge faster, so more frequent trips to the grinder)

 

[Bill Alston]

I find I can go back to the burnisher two or three more times before going back to the grinder.
I use an 800 grit belt on my scrapers to get a nice polished edge before burnishing.

 

[robo hippy]

I can go 2 or 3 times, but generally go back to the grinder after 3 times, at the most. Mostly the burr gets worn out from bending down and back up again. It takes very light pressure, even with the M42 and V 10 metals to turn a burr. These metals are harder than the standard card scrapers. Supposedly, with the card scrapers, you want the grinder burr or sharpening burr to be removed before you burnish a burr on it. I have found with my plane irons that there is still a burr at 8000 grit. Maybe a burr at 16000.

robo hippy

 

[Jamie Straw]

Though I own a Veritas burnisher, I've never used it on a negative rake scraper. These scrapers are sharpened with Jimmie Allen's upside-down method - the platform is tilted down and has an auxiliary plywood piece (photo later). If I need a frequently refreshed burr (like every minute or less) I just leave the grinder running, makes 10 seconds to refresh the burr. Might be interesting to try the burnisher.