Burnishing A Burr On Scrapers

Recently I attempted to burnish a burr on a round scraper I had just sharpened on a 600 grit diamond Tormek wheel. The angle I use is approximately 70 degrees. I found that the burr, after burnishing it, wasn't as effective as the burr I got after merely sharpening on the Tormek. This leads me to assume I'm doing something wrong when burnishing.

Questions -

1. When burnishing, should your hand holding the burnisher be toward the beveled part of the scraper or the flat side?
2. Is there angle to use as a goal to get an optimum burr?

I can't remember for sure, but I think I cover that in my platform sharpening video. So, for burnishing a burr on high speed steel, your burnishing tool needs to be harder than the steel. With the standard burnishing rods for the card scrapers, they may be a tiny bit harder, and don't work all that well. I did better with the triangular shaped one than I did with the round ones. I now use a small diameter carbide rod for burnishing. There is also a tool from Lee Valley/Veritas tools that screws down to your bench top and it has carbide rods, but I prefer hand held because I use a lot of different angles, and some tend to apply too much pressure when using this tool. There are carbide rods available on the internet, or old router bits can work well also. All it takes is a couple of light strokes across the bevel. The angle you should use, for a 70 degree bevel scraper would be 5 to 10 degrees more than that. If you have the burnishing rod at a much steeper angle, you can actually turn the burr over so it barely cuts unless you really raise the handle for roughing or end grain cuts, or roll the tool way over on the side for shear scraping. I do all of my roughing cuts on bowls with a grinder burr and the Big Ugly tool. For shear scraping, I prefer a fresh edge and most of the time I will turn/burnish the grinder burr down, then back up. If I am doing finish cuts in end grain boxes, I will hone the grinder burr off, then burnish a light burr up on that. I do burnish my NRSs also. I have found that a 60/30 NRS burnishes up with a little less effort than on a 70/30 NRS, and I have tried to burnish one on an 80/30 'hardwood bowl NRS' from Sorby tools, and found that difficult.

robo hippy

Quote:

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Originally Posted by Randy Heinemann

Recently I attempted to burnish a burr on a round scraper I had just sharpened on a 600 grit diamond Tormek wheel. The angle I use is approximately 70 degrees. I found that the burr, after burnishing it, wasn't as effective as the burr I got after merely sharpening on the Tormek. This leads me to assume I'm doing something wrong when burnishing.

Questions -

1. When burnishing, should your hand holding the burnisher be toward the beveled part of the scraper or the flat side?
2. Is there angle to use as a goal to get an optimum burr?

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I hold the burnisher in my right hand with the scraper bevel to the right. The angle is just a few degrees - I lay the burnisher against the bevel then raise the lower end a little off the bevel. Some advocate starting with just a degree or so of angle then increasing the angle with each of several successive passes.

Another way is to put the scraper in a vise and use two hands on the burnisher for more pressure. Card scrapers are often laid flat on the workbench with the edge off the table a bit and burnished with the burnisher held a few degrees off vertical.

The angle, the pressure used, and the number of passes with the burnisher depends on the radius of the burnisher and how aggressive I want the edge. A small radius burnishing rod will create a larger burr with the same pressure. A triangular burnisher effectively has a very small radius. My burnishers are carbide but I have used the side of a HSS gouge in a pinch.

After burnishing you should be able to feel the burr when dragging your finger across the top face of the scraper or across the upper bevel of a negative rake scraper. If it doesn't cut as well as I want I burnish again with more pressure. I've experimented a lot over the years to come up with the angle and pressure I use. I don't know of any easy way to tell someone else other than to suggest just trying things.

Note that before burnishing I almost always remove any grinder burr with an extra fine diamond hone.

The Veritas burnisher Reed mentioned can be quite aggressive with minimum effort - the angle is fixed but should be fine for a 70-deg flat-topped conventional scraper. Not useful for the negative rake scrapers I almost always use now. https://www.woodturnerscatalog.com/p...aper-Burnisher

I just remembered I wrote about burnishing in a thread a few months ago. It was about negative rake scrapers but the principle is the same.

https://sawmillcreek.org/showthread....13#post2910113

JKJ

Still a little confused (but that is a problem sometimes) . . . I am using the carbide rods I got from you so that shouldn't be an issue.

What I'm unclear about is when you say "5 to 10 degrees more than" the scraper bevel. Does that mean the burnishing angle should be be 80 degrees or 60? I'm not sure how to ask the question clearly.

I think I understand why my first effort wasn't very successful. I will experiment with a little better understanding now. Thanks to both Reed and John.

I grind my scrapers upside down on the grinder and use the burr off the grinder. I made a template to set the grinder table and use an 80 grit CBN wheel. Quick and easy just takes a few seconds.

If all else fails, get thee to a club meeting or open shop for hands on demo. BEST way to learn it. Bring a piece of wood that's round and ready to put on a lathe to play with.

Quote:

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Originally Posted by Randy Heinemann

... Questions -

1. When burnishing, should your hand holding the burnisher be toward the beveled part of the scraper or the flat side?
2. Is there angle to use as a goal to get an optimum burr?

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Start with your burning tool flat against the bevel top to bottom. Then open a small gap at the bottom ... so now the burnisher is touching at the top of the bevel and there is a small angle, perhaps about 5° at the bottom. Then just make a single sweep from one side to the other using light to moderate pressure ... about like a polite handshake. This is important: JUST ONE PASS. Making multiple passes runs the risk of rolling the edge over, but even worse is that multiple passes will work harden the edge, in other words it will become brittle and not last long before it breaks off. I prefer M2 high speed steel for burnished burs.

If your bevel angle is 70 degrees, you want your burnishing rod to be at about 75 degrees. If you have it at 90, it tends to curl over like a breaking wave. It doesn't take huge amounts of pressure, and generally a few light passes are all that is necessary. I have tried the upside down burr, and while it works, the burnished burr is better, if for no other reason, it lasts a lot longer.

robo hippy

Thanks guys. I know what I was doing wrong the first time I did this. I confess I was having a lot of success without burnishing though, but given the endorsements of burnishing on this site, I am going to try it for awhile and see what happens. I am always willing to try different things and then choose the way that works best for me.