Sharpening a round nosed scraper question

[Brice Rogers]

I'm a little embarrassed to ask this question as it is a pretty basic question. It may actually be kind of a stupid question.

At a wood turner's club meeting, a senior member mentioned that he grinds his round-nosed scrapers upside down on the tool rest. That creates the burr on the bottom side. But his tool rest is angled downward and with the tool upside down he ends up with the desired included angle and forms the burr. That differs from the several videos on-line that I've watched. The videos show the wheel coming down to the tool, the cutting surface of the tool is on the top. So that brings up my question - - to make a good burr, should the grinding wheel be approaching the leading (cutting) edge directly (sharp side up with wheel coming down to cutting edge) or is it better to make the burr on the trailing edge (tool upside down)?

I have a HF Carbide tool grinder (a clone of a Baldor) that I use to touch up my scraper. It has a switch to control the direction of rotation. So I can hold the tool with the cutting edge visible but can sharpen in either direction. I've sharpened the scraper with the burr edge in the (traditional?) leading edge position and also with the wheel going in reverse. Surprisingly, both seem to work and produce a usable burr. But it would seem that the biggest burr would be created on the trailing edge. Maybe a large burr is not what is needed?

Am I overthinking this? Are there any other people out there who grind their scrapers basically upside down?

[Mark Greenbaum]

I think your way seems safer, as long as you wear eye protection. Having the guide table pitched downhill seem dangerous and risky at best.

[John K Jordan]

Brice,

There are various opinions on sharpening scrapers. Here is mine: I sharpen the scrapers with the cutting edge up. I hone the top flat, or hone away any burr on the bevel, then burnish with a carbide rod to raise a cutting "burr". This is the same rod I use to raise a cutting edge on my cabinet scrapers. When the edge is burnished it doesn't matter which way you grind.

For me this edge lasts far longer than the burr from any kind of grinding. In all of my wood turning I have never relied on a grinder burr. When I tried it it only lasted a few seconds. Look at the burr with a microscope before and after one cut and see how it holds up. I suspect the properties of whatever type of steel a specific tool happens to be made of will make a difference in the structure and life of a grinder burr, as might the type and grit of the grinding wheel.

Reed Grey is experimenting with burnishing scrapers; he discusses this in other threads.

Also, except for certain special scrapers such as for the inside of turned boxes, these days I grind my scrapers with a negative rake. Much more controllable and nearly impossible to catch.

Here are some Thompson scrapers ground with a negative rake.

340867

I used to use this for all my scrapers but I haven't yet tested it with the negative-rake scrapers:

http://www.veritastools.com/Products/Page.aspx?p=122

JKJ

[Brice Rogers]

John, thanks for the suggestion on burnishing with a carbide rod. I will begin to try that technique. I will also pick up a set of scrapers. How much force and how many strokes do you use with the rod to raise the burr?

BR

[Jamie Straw]

[Snip] But it would seem that the biggest burr would be created on the trailing edge. Maybe a large burr is not what is needed?

Am I overthinking this? Are there any other people out there who grind their scrapers basically upside down?

From what I've read, a large burr could be overly aggressive and unpredictable, especially in tight-grained woods. To me, the risk and awkwardness of sharpening a scraper upside-down doesn't really have an up-side. They work quite fine when sharpened traditionally. I think it's good you thought to ask here about the method, can't hurt to get a variety of opinions.

[Reed Gray]

Jimmy Clewes is one who sharpens his scrapers up side down. He feels it gives a sharper burr. I tried it a few times, and can't say that I noticed any difference in sharpness, but for sure it was gone much sooner than the burr when sharpened right side up. The burrs from CBN wheels are far superior to the ones from standard grinding wheels, and are what I use for all of my heavy roughing on bowls, and some times even spindles. I do push into the wheel rather than just kiss the bevel. I feel that this almost burnishes a burr onto the edge, similar to honing a burr onto the scrapers. I do hone off or burnish off the old burr before sharpening a new one on. I can see little difference between the 180 and 80 grit CBN wheels for durability and sharpness, but stepping up to the 600 or 1000 grit CBN wheels makes a big difference. The burrs from the finer wheels are much better for fine finish shear scraping, but there isn't enough there to make them work well for heavy roughing.

As for which scraper, to me, anything more than 3/8 thick and 1 1/4 wide is too much metal. Doug Thompson has a 1 inch wide by 5/16 thick scraper from V10 metal that works great. I can stall my Beauty with it. The much wider and thicker scrapers are overkill for me. Turners talk about 'stability', and if you are having stability problems, move the tool rest closer. Larger scrapers means the possibility of getting more metal into the wood at one time, which I think at least contributes to catches and just getting overpowered.

I am still exploring the NRS, and burnished burrs, or maybe I should say exploring them again/some more. See the thread about Oh no, more experimenting ahead.

John, what angles are you using on your NRSs'?

Oh yea, my brother in law is a GrEy, my side of the family is GrAy. He gets teased about not knowing how to spell.......

robo hippy