Negative Rake Scraper Angles

[Thomas Wilson80]

I've mostly used my skews as negative rake scrapers, which works well but I have a very acute angle on my skew and so it dulls almost immediately. I recently purchased a 1" x 5/8" scraper that I want to turn into a NRS but was curious what angles people use (particularly for inside/outside of bowls)? I've read anywhere from 85/15 to 60/30.

Thanks,
Tom

[Brian Deakin]

You may find the information in the attached pdf useful

https://www.woodworkersemporium.com/...ion-Manual.pdf

[John K Jordan]

I've mostly used my skews as negative rake scrapers, which works well but I have a very acute angle on my skew and so it dulls almost immediately. I recently purchased a 1" x 5/8" scraper that I want to turn into a NRS but was curious what angles people use (particularly for inside/outside of bowls)? I've read anywhere from 85/15 to 60/30.

Thanks,
Tom

Thomas,

Anything less than 90-deg will work. The "sharper" the angle, the quicker it wears. A burnished burr will far outlast a burr from the grinder in my experience.

My favorite NRS are ground at 60-deg included angle. I grind the top and bottom bevel the same so I can put a burr on either side to make left and right hand scrapers as needed. My favorite design for inside and outside of bowls and platters is a curved edge with a short flat on the end.

_scrapers_IMG_7778.jpg NRS_IMG_7907.jpg

I grind a variety of other shapes for other purposes.

JKJ

[Reed Gray]

There are two styles of NRSs. One, which has been around forever is the skew chisel type, with the angles the same on both sides, and generally in the 25 to 40 degree range, so if you have a skew chisel, then you can use that to test it out. The other style, which I use, has a steeper bottom angle, which for me is about 60 degrees, and the top angle is in the 20 to 30 degree range. I use a burnished burr on them rather than the grinder burr.

So, burrs... The grinder burr is gone in seconds. If you are using one inside a 10 inch bowl, start at center and sweep to the rim, and use all of the edge, the burr is gone by the time you get to the rim. For this cut, I use one that is like a bit 1/4 round nose profile. I haven't tried raising a new burr with the hand held hones. If I use a burnished burr and one of my 60/30 grinds, then I can go back and forth a couple of times and the edge still cuts.

From Tom Wirsing, who uses them more than I do, "This is a high maintenance tool. If you have to push at all to get it to cut, it is dull."

I seldom use them on bowls, in part because while they do work well on some woods, they don't on others. I do use them on boxes and end grain work as they work excellently on that.

robo hippy

[Russell Neyman]

Reed, if you have a 60-degree grind on one side, and a 20 degree grind on the other, why not just grind a "regular" scraper at 80 degrees (I use 85) and use that? On the occasions when you need it to be sloped downward (negative) you can raise your tool rest and lower the point quite easily. Not trying to be negative about this (pun) but I watch the NRS trend and see it as unnecessary and expensive.

I, too, sometimes burnish a burr for final passes. It certainly gives a superior cut.

[Brian Deakin]

Please watch video below from 1 hr 37 mins This provides the best explanation I have seen

https://www.youtube.com/watch?v=N7BjRcSDurM&t=5827s

[John K Jordan]

...if you have a 60-degree grind on one side, and a 20 degree grind on the other, why not just grind a "regular" scraper at 80 degrees...On the occasions when you need it to be sloped downward (negative) you can raise your tool rest and lower the point quite easily. ...

(I started writing this hours ago then got sidetracked with farm stuff. Sorry if this has already been discussed, I didn't check.)

I asked myself the same question about raising the handle years ago. Then I tried grinding a scraper as NRS and was convinced. While it seems like the result would be the same, turns out it's not. Not even close. I've since reground most of my scrapers to have negative rakes. The results of the "trend", as you say, are so impressive I'd hate to go back to using conventional scrapers. The extra expense for me is zero since I grind the scrapers myself. I mostly use scrapers made from Thompson steel and sometimes regrind skew chisels, round rods, and even made one from a Thompson shallow spindle gouge.

If you compare using a NRS ground at a given angle and a standard scraper ground at the same angle and tilted in use, you will probably, like many, quickly see the difference. Used flat on the rest with the tool held horizontal, the NRS is more stable and easier to control than a conventional scraper tilted down. This is especially true of round-nose scrapers and scrapers ground with a curve such as I showed in photos earlier in this thread. Just imagine swinging the curve around a piece on the lathe with the NRS held flat, then think of what happens to the intersecting geometry of the edge and the wood with the same profile on a conventional scraper with the handle raised and the tool down, ESPECIALLY if using the long edge of one of the scrapers shown. The angle would be wrong for removing fine shavings and the control would be difficult in comparison.

The NRS in use on a curved section, held flat against the rest and horizontal.

NRS_curved.jpg

After a bit of hand scraping with the lathe off I can usually start with 320 or finer paper. I haven't power sanded with rotating disks for years.
The flat I grind at the end of these scrapers is great for smoothing the wings when cutting air. I've had people tell me you can't use scrapers like this but they leave an excellent surface.

NRS_IMG_7515.jpg

BTW, in the pics above I'm making pieces like this:

penta_maple_ellis_c_IMG_5435.jpg penta_plate_walnut_IMG_46.jpg penta_jatoba_IMG_7636 - Copy.jpg penta_platter_cedar_IMG_7434.jpg

I also like to use NRS on end grain with hard fine-grained wood (bottom or lid of a box, etc) - leaves a surface like glass.

JKJ

[Reed Gray]

Well, Stuart does change the things he says, and all of us learn...

So, first off to answer Russel's question, A standard scraper does not cut like a NRS, no matter how you present it to the wood, and raising the handle does not let it cut like a NRS. Best explanation of that was from Woodturner's Resource where the comment was that you get a 'trailing cut' by raising the handle. A trailing cut is what happens if you are using a card scraper, and I have blistered my fingers a number of times with them. You start to cut with one by rubbing the bevel, then angle the tool into the wood just until you start to cut. If you keep angling the tool more and more, you get the trailing cut, where you are raking the fiber rather than slicing it. I have seen a scraper with a honed edge so there is no burr used on hard maple and get a glass smooth cut. That works on hard maple, and so does a NRS. that doesn't work on the softer woods. It does work on end grain pieces like box tops and bottoms.

I will have to ponder Stuart's comment about the NRS burr 'abrading' the wood. As far as I can tell, it cuts, not abrades. I have never seen shavings from any abrasives. Part of why I prefer the burnished burr is that it really cuts well. No clue as to how it would work on ivory though.

robo hippy

[John K Jordan]

...
I will have to ponder Stuart's comment about the NRS burr 'abrading' the wood. As far as I can tell, it cuts, not abrades. I have never seen shavings from any abrasives. Part of why I prefer the burnished burr is that it really cuts well....

My experience too with a burnished burr. Thing is, burnished burrs can be larger or smaller and different angles. At the sweet spot shavings come off the NRS so fine they float through the air. No evidence of any abrading. I didn't see the abrading comment but to me abrading is either tearing the fibers, as with coarse sandpaper, or digging out fibers, as results in tearout. Neither come from a well prepared NRS in good wood. All bets off in rotted, punky wood.

[Russell Neyman]

My experience too with a burnished burr. Thing is, burnished burrs can be larger or smaller and different angles. At the sweet spot shavings come off the NRS so fine they float through the air. No evidence of any abrading. I didn't see the abrading comment but to me abrading is either tearing the fibers, as with coarse sandpaper, or digging out fibers, as results in tearout. Neither come from a well prepared NRS in good wood. All bets off in rotted, punky wood.

I've been at this craft for about 16-17 years, so my perspective is backed by a degree of experience. I'll repeat the advice I have so often given in teaching and demonstrations: Be pragmatic. Experts only give you a way to do somethins, but it's not necessarily THE way. Use common sense and figure it out for yourself. If it works for you, use that method. I haven't ground my expensive scrapers with the fashionable negative rake because I rarely have catches with my 85-degree grind and I'm satisfied with the results. Experiment and try various methods and use what works for you.

[John K Jordan]

... Experiment and try various methods and use what works for you.

Many of us certainly agree with that. I often try a variety of methods on a piece, bowl, vessel, or spindle, to see what works best for that shape made out of that wood - different tools, lathe speed, burr angles, etc.

One of the best turners I know told me he works like me - while reducing a diameter towards the desired shape, for example, we both often switch to a different tool or a different presentation to see the effect. We sometimes make beads and coves in spindles for practice then cut them away and practice finishing cuts while still a long way from that final pass. This is especially helpful so I teach it to students - making multiple finishing cuts with the best control you can manage will set you up so your eye, hands, arms, and body are well practiced for that one cut that matters. This method may not be attractive for production or the person who dreams of winning speed-turning contests.

[David Walser]

... I haven't ground my expensive scrapers with the fashionable negative rake because I rarely have catches with my 85-degree grind and I'm satisfied with the results. ...

Russell -- I understand the reluctance to regrind an expensive tool, particularly when you're satisfied with the results its giving you. Here's the thing: Lots of very good turners also felt there was nothing to gain by using a NRS. They were already getting satisfactory results with their traditional scraper grind. But, for some reason, they tried a NRS (perhaps they borrowed one from another turner or reground an inexpensive Harbor Freight tool). After experimenting with a NRS for a short time, the results from their traditional scrapers were no longer satisfactory. They were consistently getting better results using a NRS, so why would they continue being satisfied with the finish from a regular scraper?

Too often NRS are touted solely on the fact that they are less likely to produce a catch. That may be true, but I doubt that's why John K. Jordan uses one. It's certainly NOT why I use them. I wasn't getting catches with my traditional scrapers, so the fact a NRS scraper is less likely to catch provides me with zero benefits! I use them because the finish off the tool is simply better. I use a skew for planing cuts for a similar reason -- it leaves a better surface than I get with a spindle gouge. So, why not try a NRS for that reason? Don't regrind one of your expensive tools. Borrow a NRS from a friend or use a cheap chinesium tool. (Try the chinesium tool both as a regular scraper and as a NRS to keep the quality of the steel out of the equation.) If you get better results with the NRS, that's your reason to regrind some of your expensive tools.

One other data point to add to the question of whether NRS produce better results: If you turn acrylics and other resins, you know that they are prone to micro-fracturing on the surface. The only tool in my arsenal that all-but eliminates this problem is a NRS. A regular scraper in a trailing position still produces the fractures. So does a spindle gouge or a skew (in bevel rubbing mode). But, a skew held flat on the tool rest produces a clean result. So do other negative rake scrapers. Somehow the plastic can tell the difference between a scraper with the handle raised and a NRS.

[Reed Gray]

As for getting catches with standard scrapers, most of the time it comes from biting off more than you can chew, which is either trying to hog off hard wood way too fast or from using a huge scraper and getting too much cutting edge into the wood at one time. See my video 'Scary Scrapers'. On bowls, I seldom use the NRS as I can get a better surface with a shear scrape from a scraper with a burnished burr. The one exception to that is with Madrone, which cuts like butter. On boxes, I love the NRS as it leaves a glass smooth surface. No clue about plastic or acrylics.

I have too many tools.... I have reground some old scrapers that I didn't use any more, mostly because all I want to use is V10 and M42HSS. They are specialty tools, like for boxes...

robo hippy

[Jim Hipp]

He seems to be saying that a burr is necessary for the NRS to perform.

Or am I misunderstanding it?

[Paul Heely]

Came across this today and thought it was appropriate for this discussion. SB Tools NRS Scraper Manual: https://www.woodworkersemporium.com/...ion-Manual.pdf