Negative rake scraper

[Brian Kopp]

I realize I’m a latecomer to negative rake scrapers but this is worth noting for those who haven’t tried one yet.

I have a French curve negative rake inside bowl scraper I got two months ago that, along with a Hunter Hercules #3 cupped carbide, I used extensively on this bowl this week.

To be honest, I was using a Sorby heavy inside bowl scraper, to deepen the inside bottom corners, and got a bad catch. That in turn broke off a section of the mortise, and the bowl partially came out of the Supernova2 chuck jaws but fortunately didn’t fly off. (Yes, I’m still learning, I started turning 14 months ago.)

Enough of the mortise remained that I simply adjusted the jaws and started again. However I couldn’t afford another catch or the stress on the mortise of continuing with the Hunter cupped carbide cutter.

So I finished the inside of the bowl with a negative rake French curve inside bowl scraper I got two months ago, which puts very little stress on the mortise since it only takes off thin ribbons at a time.

I could only take a couple passes at a time, then I would need to resharpen the negative rake on my 8” slow speed grinder to raise another burr. I was only sharpening the bottom bevel, not the top.

It took another two hours of very slow progress to finish the inside of the bowl using this process but it was worth it, to save this bowl; I had no other handy way to hold it on my lathe. Plus the negative rake scraper reduces the need for sanding dramatically, as many have already discovered.

Since part of the side of the mortise was completely broken off, and I had other way to mount a 12” bowl, I had to finish the bottom by hand, with 3” sanding discs on my 55• drill.

But for a bowl that initially broke off part of the mortise and came off the chuck, I’m thrilled I could salvage it and really happy how it turned out.

I couldn’t have completed it without this negative rake scraper.

I could easily have converted an extra skew into one of these on my grinder but I decided to splurge: I wanted to try one of these “fancy” Cryo treated chisels.

12” wide, 4 1/2” thick ash and walnut salad bowl. A friend requested this as a Christmas gift for his wife.

 

[Alan Heffernan]

Nice bowl! I have seen that CryoTek offered for sale.

I would have thought you'd get more than two light passes before needing sharpening. I would be interested to know what others have experienced in that regard.

 

[Brian Kopp]

Nice bowl! I have seen that CryoTek offered for sale.

I would have thought you'd get more than two light passes before needing sharpening. I would be interested to know what others have experienced in that regard.

I used it a good bit after it really needed sharpening each time, but I’ve read multiple comments that a French curve negative rake scraper takes on a very small burr, which is regularly gone in 15 seconds. I’d say that was accurate. The longer I did this, the more often I was sharpening, and I was getting pretty good at sharpening that French curve chisel.

 

[Emiliano Achaval]

Lots of torn grain, lots of room to improve. With a NRS I usually leave my Baldor grinder running, sharpen every 10 seconds or so. Any pressure and you will have torn grain. Or, if you go past the the burr…

 

[Ron Solfest]

@Alan Heffernan - I only have one NRS (yet) that I’ve sharpened with a long full curve (French?). It’s one of the newer exotic steels and I find that it does better if I only use a section of the cutting burr for a few seconds (kiln dried, glue laminated). I’ve gotten very good at using different parts of the edge to prolong use between sharpening, still I resharpen on my 180grit Cbn before use each time, and during use if I need more than a few seconds (not often).

 

[Brian Kopp]

@Alan Heffernan - I only have one NRS (yet) that I’ve sharpened with a long full curve (French?). It’s one of the newer exotic steels and I find that it does better if I only use a section of the cutting burr for a few seconds (kiln dried, glue laminated). I’ve gotten very good at using different parts of the edge to prolong use between sharpening, still I resharpen on my 180grit Cbn before use each time, and during use if I need more than a few seconds (not often).

That’s a good explanation, thanks. That’s exactly what I found myself doing with this Cryo French curve NRS.

If nothing else, I quickly learned how to sharpen it properly to get a good burr.

 

[Brian Deakin]

These links are the best resource I have seen on negative rake scrappers

https://www.woodworkersemporium.com/content/NRS-Instruction-Manual.pdf

and I would also take a look at Stuart,s website

Stuart Batty Tools

stuartbattytools.com

and this link takes you to Stuart,s videos and articles

Stuart Batty Tools

stuartbattytools.com

 

[Aaron Harris]

So here's a question for you fellows who refresh the burr on the grinder every time? I keep a heavy, handled carbide rod handy, and just frequently pull the burr back with a few firm swipes around the edge. I like to cant my D-Way 1 and 3/4" round-nose NRS down for some gentle cutting, and then lighten up for the super-fine final finishing cuts. When I'm cutting like that instead of scraping, I like to pull a pretty heavy burr and just control it by feel if it gets too aggressive.

The question is, am I losing anything by pulling the burr probably 90% of the time, and just going to the grinder when I can no longer get a good burr raised? I feel like I'm saving steel doing this, but I'm still very much in learning mode on this endlessly-fascinating tool. TIA for any experienced opinions here.

 

[John Hicks]

I've had better results turning a burr with a carbide rod than what I can get from the grinder.

 

[hockenbery]

The question is, am I losing anything by pulling the burr probably 90% of the time, and just going to the grinder when I can no longer get a good burr raised?

You are probably getting a better burr. I often strike a burr with a diamond hone. Less aggressive than a rolled burr.
Polish the top to remove the old bur and run the dianong card across the bevel a few times to raise the burr.
After 4 or 5 I hit the grinder.

 

[robo hippy]

I have been needing to do a video on NRSs for a while, and I think I have figured out what works best for me. The grinder burr on a skew chisel type of NRS is gone in seconds. Part of the reason is that there is not enough metal under the burr, due to the acute angles, to support it. The second is that a grinder burr just isn't very strong. In the words of Tom Wirsing, (hope I spelled that close to correct), it is a high maintenance tool. If you have to push at all, your tool is dull. I have settled on a 65/25 degree angle for mine. I also prefer a burnished burr, and use a carbide rod in a handle. I generally use the grinder burr for a bit, and then burnish it down and then back up a few times before going back to the grinder. They do excel on end grain, leaving a surface that 400 grit will rough up rather than smooth out. On bowls, they work fine for sweeping across the bottom, but not as well for the transition and going up the sides of a bowl. This can vary a lot depending on the wood you are turning. They are still scrapers, and will pull more at the fiber when compared to a gouge sheer cut. I still prefer a shear scrape for my final passes on a bowl.

As with all tools, 'individual results may vary'....

robo hippy