Further on platform sharpening

Re: Further on platform sharpening

Don Orr

Glad to see it is working for you. I still have yet to try it.

Re: Further on platform sharpening

David Walser

I can see that there might be advantages with this method, but it looks dangerous to me. It appears to be self-feeding and there's a (small) risk that the tool could become wedged between the platform and the wheel. At least, I seem to recall my shop teacher telling us not to set up the grinder like that. (We won't go into how long ago that was and whether there's any possibility my memory could have failed me. I mean, I'm sure I remember every thing else he ever said with perfect clarity.)

Re: Further on platform sharpening

John C Lucas

I had the exact.same thought. It wouldnt take much to get the tool trapped between the stone ad tool rest. Free hand without a platform would be safe but that way looks dangerous. I use the Roborest set at 40 degrees for my version of the Batty negative rake scraper and im. Utting wboe center.

Re: Further on platform sharpening

Paul Grenier

I also attended a presentation by Jimmy Clews where he espoused doing a negative grind this way. You MUST have the tool rest VERY close to the wheel to avoid a potential trapping situation. I'm talking about a 1/16" gap.

If you are using stone wheels, you have to remain very aware of how much of the stone is wearing away during the grinding. With CBN wheels, they don't wear smaller like stone wheels.

Re: Further on platform sharpening

Joe Fleming

I think the next time I see Jimmy, I'll let him attempt to explain why this is safe, then give him a ration if his explanation doesn't hold water.

For me, this is in the realm of using a tablesaw without a splitter. Or not using a zero-clearance insert. Sure it can be done safely in the right hands, but the inherent risk is always there.

Re: Further on platform sharpening

John C Lucas

It is safe as long as the platform is that close. The problem is new turners dont always listen. Well they do but often get so much information the little bit about how close it needs to be can easily be ignored. Then they gradually get more and more lax at keeping the tool rest.close untul an accident happens.

Re: Further on platform sharpening

Ron Bauer

Same things I said the first time looked at a bicycle. I must have rode a thousand miles that first summer.

Jimmy doesn't do things half way

john lucas

He is a turner I highly respect. What he is showing is simply another version of raising a burr. Several people have tried running wheels or sanding belts backwards or uphill to raise a burr and it does work. How much better is arguable. I don't use scrapers much anymore but still play with burr raising. Reed Gray has played a lot. What I find is different steels, and maybe the hardness or toughness of the steel, changes how a burr will be raised. For example I find that using the ceramic stone John Jordan sells will raise a fantastic burr on his shear scraping tool. It raises a really lousy burr on most of my other scrapers. Some of them work really well using a medium diamond hone. Some of them raise a better burr straight off my 120 grit Aluminum oxide wheel. I've had to experiment with what works best on each tool.

Since I don't use a scraper much I'm looking for a quality burr that cuts clean. I don't need longevity of the burr because I will stop and resharpen it as often as possible. On some tools I prefer the matching bevel on both sides because I can simply flip the tool, hit the grindstone, and that establishes a burr on the other side Learned this from Stewart Batty and it works great. However one tool that I love for doing boxes has a long grind down the left side. It is very hard to get that shape on a thick tool and have the same bevel on both sides. I find it much better to have a more blunt angle on the bottom and then very slightly grind the top for the negative rake. On this tool I raise the burr using a diamond hone.

Of course on boxes now days I use the Hunter #5 to clean up the edges so my old scraper never gets used. Try scraping with a freshly sharpened skew on it's side and you'll see why I like the Hunter tools as scrapers.

to burr or not to burr

John K Jordan

I've seen Clewes and others grind this way.

There is no need to use the inverted grinding on a scraper if you don't rely on the grinder burr for turning. I remove any burr from scrapers with a hone or leather strop then raise an edge with a swipe or two from a burnisher. This smooth burnished edge is similar to the fine cutting edge used on traditional cabinet scrapers by fine craftsmen everywhere. My experience is this sharp edge lasts much longer than the fragile ragged burr of deformed metal left by the grinder.

The burnished edge does take a bit of experimenting to determine the amount of force needed which may be related to the diameter of the burnisher. It doesn't take much. I use a carbide rod maybe 1/4" or 5/16" in diameter, mounted in a handle. Too much force will turn up too much edge and the tool might be more aggressive. I learned this about 15 years ago when using a heavy hand while burnishing large scrapers with the Veritas burnisher. The Veritas tool works well, but in the long run I found it quicker and easier to burnish by hand and no longer use the Veritas.

If interested, this article describes using the Veritas scraper burnisher:

http://www.leevalley.com/US/shopping/Instructions.aspx?p=41670

JKJ

Re: Further on platform sharpening

robo hippy

It has been a while since I have seen Jimmy demonstrate, but he likes that up side down grind for his scrapers because, according to him, it leaves a better edge. This was before he had CBN wheels. That raises another point of the burr from standard wheels is not nearly as strong as the burr from the CBN wheels, and to me, not nearly as sharp.

So, for the up side down grind, you get a burr that is dragged down off the top edge. To me this is more of a wire type burr that is more fragile, though I guess it could be pretty sharp. With the right side up burr, I figure that is more like burnishing since you are pushing into the top edge, though not positive. When you hone a burr on, do you go sideways, push up, or push down??? I generally go sideways, which would be almost like burnishing depending on how fine your hone is. However, I pretty much never use a honed burr.

If the tool rest is at or pretty near center height of the wheel, I wouldn't expect any jamming problems. This is a very gentle push into the wheel, and not a big push to build a heavy duty burr.

Most of the time, on most woods, the burrs from the 80 or 180 wheel is fine for just about every thing. There are times where you need the finer edge, and for me, that is where the 600 and 1000 grit CBN wheels come in handy. Great for finish cuts, lousy for heavy roughing cuts.

I have been using the burnished burrs a lot for shear scraping, all of which I do with scrapers, and not gouges. It does seem to leave a finer edge. I use an 1/8 inch carbide drill bit in a rod. It takes very little pressure to turn a burr, and about 2 passes (shown in my new platform sharpening video). I can turn it down and raise it a couple of times, just like card scrapers. I can't remember if I have used it for the heavy roughing cuts, so may have to make sure I do that next time out to the shop. In the recent AAW magazine, Mike Mahoney talks about shear scraping. He prefers gouges to scrapers for this task. There is an short video about this. When he shear scrapes with his gouge, he uses a swept back gouge, and has it at about a 70 or higher degree angle. When he does it with his spear point scraper, he has the scraper at about 45 degrees. I have to chat with him about that...

Another point that I got from Eric Loffstrom is that you get very different burrs from M42HSS and V10 because of the differences in the metals. Now I have to experiment some more. Out of curiosity, I put the burnisher to my Big Ugly tool, which has tantung (particle metal) as the cutting edge. It raised a very nice burr. I have been told it is impossible to raise a burr on carbide like all the flat carbide cutters use. I have to get my hands on a dull one and try that one out as well. I would think some thine will raise if I use carbide or a ceramic burnisher on it.

Don't think I will ever get done experimenting.... Just too curious...

robo hippy