Difference Between Skew & NR Scraper?

[Mike Goetzke]

When I look at quality tools like Thompson/D-Way looks like skews and negative rake scrapers are becoming similar if not the same tool when the NRS has shallow grind top & bottom. What am I missing?

Thanks,

mike

[Roger Chandler]

The NRS should have a small bevel on top and a larger bevel underneath........with the top bevel too far down, it makes the handle angle go too far right at times. This may or may not be an issue depending on the size of the turning, I think it is easier to get a shear scrape angle with just a small top bevel. This is referring to inside bowls especially. For spindle work it might not make much difference on the bevel length, just adjust the presentation angle to get the tool cutting as desired.

[John K Jordan]

When I look at quality tools like Thompson/D-Way looks like skews and negative rake scrapers are becoming similar if not the same tool when the NRS has shallow grind top & bottom. What am I missing?

You can grind a negative rake scraper from almost anything. Most skews are made from thinner steel so the thicker scraper stock might be better. I personally don't see any difference in function between those ground with equal bevels on both sides and those ground with a smaller bevel on top. The angle of the grind is usually less acute than that of a skew.

These are some I ground from Thompson square scraper stock, two 3/4" and one 1" (I think) for the insides of bowls and such:

scrapers_neg_rake.jpg

I made these little NRS guys from a round rod from Doug Thompson, one of his shallow detail gouges, and from a 1/2" Thompson flat bar. I use them a LOT on smaller work, especially end grain, and on detail on bottoms and rims of bowls and things - they leave a finish on end grain that is so smooth. I use them without handles. The round ones let me easily rotate them to any angle as needed. I have a pile of these since I make special shapes as needed.

scrapers_small_thompson.jpg

BTW, some people rely on the burr from grinding to make negative rake scrapers work. I prefer to raise a cutting burr with a carbide burnisher. I sharpen with a 600 grit CBN wheel.

JKJ

[Bob Bouis]

A burr for one thing.

[Mike Goetzke]

Thanks for the replies. Should mention I have an 1-1/4" Thompson scraper that is flat but I want it curved for inside of bowls. Just read some posts about NRS and think I will try that grind on it.

John- I see your scrapers have the grind swept back pretty far. What angles do you use and do you just continue to carry the tool around the rest to achieve the form?

Mike

[John K Jordan]

Thanks for the replies. Should mention I have an 1-1/4" Thompson scraper that is flat but I want it curved for inside of bowls. Just read some posts about NRS and think I will try that grind on it.

John- I see your scrapers have the grind swept back pretty far. What angles do you use and do you just continue to carry the tool around the rest to achieve the form?

Mike

I'll have to measure next time I go to the shop. I copied the grind I saw a demonstrator use at the TAW symposium, both the curve and the approximate angle. (I sketched a diagram while there) I'd have to check my notes but I think it was Glenn Lucas.) He shows one on this video https://www.youtube.com/watch?v=c0RDG4A6yh8 but the ones he had and was selling at the symposium were Thompson scrapers and were ground further back than the one in the video. I ground the curves a little further down the side than he had (with the grinder rest at the same angle) but the sharp edge runs out pretty quickly. Sorry, I'm not sure what you mean by "carry the tool around the rest."

I like the idea of grinding the same bevel on the top and the bottom. If I want to use it inside a bowl on the other side with the lathe in reverse all I have to do is burnish a small burr going the other way. BTW, I don't think the included angle is all that critical. I just eyeballed it and made it look kind of like what I saw and had sketched.

JKJ

[Reed Gray]

Well, digging into the NRS, the first ones were skew chisels, and I picked up that one from Allen Batty in a story about making billiard balls from elephant ivory. Stuart Batty says the best ones have an 'included angle' of no more than 90 degrees, so if you have a 45 degree bevel on both sides it works fine, but if you have more, then it doesn't work as well. I haven't proved or disproved that one to myself yet. I think the Glenn Lucas NRS is 33 degrees. Most used to have a symmetrical grind, so the same grind on both bevels, and a more skew shaped nose, so some were straight across, and some had a little sweep, and some had a more swept back profile. The more broad nose ones, ) shaped are better for sweeping across the bottom of a bowl, but not so good for going through the transition. The more swept back profiles are better for the transition and going up the wall of a bowl. The idea with a symmetrical bevel seems to be that some times you want the burr on one side, some times the other, depending on what type of curve you are going through. Perhaps also easier to sharpen since you can sharpen both sides without having to adjust your grinder platform. With the asymmetrical bevels, it seems to be a more specialized tool, but maybe not. You do have the burr only on one side, so you may need several different shapes for different curves. Most of the time I refresh the top shallow bevel free hand. I do think the burr is more important than the included angles, but I need to play with that some more. Going beyond the 90 degree included angles would make for a much more blunt surface, and more difficult to burnish the burr. The burnished burr, which is new to me after watching an Eric Lofstrom demo, is much stronger than the grinder burr, and I can't tell if it is any sharper than the burr from a 600 or 1000 grit CBN wheel. Pretty much the same with the honed burr, but again, the burnished burr is the strongest one. No idea about Glenn Lucas's 'French Curve'. Looks pretty much like an inside bowl scraper profile to me. French curves to me were the old plastic mechanical drawing tools for different parabolic curves...

As for the best cut quality, I am more in the school of shear angle giving a cleaner cut than a scraping angle. A shear scrape is more difficult to use for removing ripples than a NRS, which may be why the NRS is becoming so popular. A lot of turners use scrapers to sweep across the bottom of a bowl to clean up the ripples, just the easiest tool to use.

robo hippy

[Curtis Myers]

Cindy Drozda has a two page handout on the subject of Negative Rake Scrapers on her web site.

http://www.cindydrozda.com/handouts_...20scrapers.pdf


All the Best
Curt

[John K Jordan]

I'll have to measure next time I go to the shop.

I measured. The curved NRSs shown in the first picture have a 60-deg included angle, 30-deg each side.

I also saw that I had ground one of the 3/4" scrapers from a Thompson skew chisel which is rounded on one side. (It's the one in the middle) It is a little thinner than the others but still works OK.

JKJ

[Brice Rogers]

This is an interesting thread.

I am a learning wood turner with perhaps 3 -4 years of experience. When I started, I used a scraper in the scraping mode a lot. It worked but required more sanding to get rid of tearout. Then I became more comfortable using a bowl gouge and did less sanding. About 6 months ago I began to appreciate using a round-nosed scraper with a fresh burr - - I started using it to get rid of tool marks and tear out that was still (at times) challenging with the bowl gouge (especially inside of bowls near the transition. Recently I discovered that if I took my scraper and put a fresh burr on it, that it also worked very well, especially for flat areas. I found that with a fresh burr that it acted a lot like my round-nosed scraper.

[John K Jordan]

This is an interesting thread.

And a fascinating hobby! I think we all have used methods, abandoned them, then found them useful again perhaps with small variations. I've been woodturning about 15 years now and I still learn something new almost every day, often by reading things here and on other forums. Sometimes by experimenting, some from books. The possibilities with turning wood are nearly infinite.

A good friend of mine did a lot of wood turning in the '70s and '80s then quit to focus on BIG pottery. When he visited my shop he was amazed that we were all making good use of scrapers and various scraping cuts. In "his day" scrapers were a strict no-no, never touched by the experts and respectable turners. What will they think 30-40 years from now about how we work now?!

BTW, for removing tool marks, I've mentioned this before but for certain things I have found nothing better than using hand-held (mostly) curved card scrapers, such as on the inside of platters and bowls. A ripple in near the center? No problem, scrape it away with the lathe off. Tool marks on wings of non-round pieces that sometimes can't be avoided? A gently curved card scraper fixes it with no sanding. Very long and thin spindles that insist on giving me a problem on a finish cut? Shear scrape with a straight edged card scraper works magic.

I recently saw a turner show a stunningly beautiful platter, a collaboration between a turner and another artist. Then when he turned it and the the light caught it I was horrified - it had 2 or 3 concentric ripples near the middle, shallow and well sanded, but so unnecessary. If he couldn't get it right with the gouge or NRS, three minutes with a good light and a hand scraper would have made it perfect. Sigh.

JKJ

[Brice Rogers]

Thanks John for your comments. Based on some of your previous comments on scrapers, I am actively in the process of selecting and buying a set.

I notice that there are several sets (including one from Rockler) that consist of three scrapers - - one like a french curve, a rectangular one and a rectangular one with a single significantly concave end. I'm wondering for the outside of bowls if I might want a mild concave shape. Would I just take a rectangular one and reshape it? Is there a particular set that you would recommend??

Thanks in advance for your guidance.

[Reed Gray]

Oh, the dreaded bottom of the bowl ripples..... The inside is always more difficult to get ripple free than the outside. When I have some, I do clean them up with a NRS, or start sanding with 120 or 150 grit on a firm pad as that will level things out. When cutting with scrapers, if you are sweeping back and forth across flat grain, you can get a fairly good surface that requires less sanding. If you are cutting down through the grain, like a plunge cut down the side and wall of a bowl, the part on the wall will have a lot more tear out due to the fibers not being properly supported during the cut. This is also why you can get better/cleaner cuts in end grain with scrapers than you can in flat grain.

For shaping the outside of a bowl, and doing clean up, I prefer a swept back design on my scrapers, almost identical to the ones in John's top pictures. The nose for the heavy stock removal, and the swept back part/wing for shear scraping. Since I prefer to shear scrape rather than use a NRS on the outside I don't sweep quite that far back because the wing can dig into the tool rest. If you get 3 different scrapers, I prefer a half round nose, a swept back, and a ) shaped nose, and these will cover just about all your needs. If you have some that are dead square across the nose, rather than having a tiny arc across the top, they can leave a bit of tear out with the square edge. John, what do you use that one for anyway?. I would not use a concave shaped nose, in part because it would be difficult to sharpen, but possible with a radius edged CBN wheel. It may work though.

I do have a video clip up on You Tube where I go through the different scrapers I use.

https://www.youtube.com/watch?v=ZM4ak8ygzS4

I need to do one on the NRS, but figure I still have a lot to learn about them...

robo hippy

[John K Jordan]

Reed, I use the small one that is square across to make narrow flat details and recesses, mostly on end grain but also on the bottom of face turnings, and to clean up in corners. I use the wider one on some small convex surfaces and some wider flats. The small scrapers I use the most have a radius on the front. Both the round and flat are great for things like this:

bottom_IMG_5346.jpg bottom_IMG_4687.jpg

I recently ground a small negative rake on a beautiful little 1/2" Ashley Iles scraper (a present!) and use it a lot for detail work. It works great to refine tight curves in some of the colored acrylic I've been turning lately.


The wings on the larger scrapers actually don't make a sharp edge very far along the side (you might be able to see this on the one in the center) but it looks like it from the top since for even a tiny extra curve takes a lot more off the side (unless you just stop grinding abruptly). Also, I don't know if you can tell from the picture, but instead of a flat on the end I curve the edge back very slightly towards the tip. I'm not yet sure if this is better than having it flat. I do occasionally angle these on the rest (and have used them in the air, off the rest) but generally prefer shear scraping with the wing of a gouge. If I need to shear scrape deeper on the inside than comfortable with these scrapers, I switch to the Sorby with the teardrop scraper on the end, one I bought maybe 10 years ago.

Brice,

I do not find a concave card scraper very useful, besides being harder to sharpen as Reed mentioned, a flat scraper moved steadily across the outside will do the same thing. The two convex curves on one on the left of the picture are what I use most often for wings and the flat or slightly curved insides of larger bowls or platters.

scrapers_.jpg

I use smaller curved scrapers on the inside bottom of smaller bowls and things and to remove occasional tool marks on the insides and near the rim, especially if I can't reach it easily enough with shear scraping with the wings of a bowl or spindle gouge. For the outside of a bowl or goblet I almost always use a gouge for shear scraping. I almost always finish turn dry wood so I might do something different if I turned green.

I have several sets of the small curved scrapers and use them a lot. However, for the best quality steel the larger scrapers are better, especially the better quality scraper furniture makers use since the steel is thicker and holds an edge longer. Unlike scraping flat wood where you need to bend the scraper to put a slight curve it in, I don't bend any of these so the thicker steel is fine. The nice thing about having a bunch of small scrapers is when one is dull I can grab another one without stopping to sharpen!

I've cut some smaller scrapers from large card scrapers using a metal cutting disk on a Dremel. I try to keep the steel cool. If I knew someone with a water jet system I'd probably try to get some cut that way.

This is one I cut from a the end of a larger curved scraper with the Dremel. This is the first one I made and used and did almost everything I needed for several years until I lost it one day, probably in a pile of shavings.

scraper_PB054025_s.jpg

I bought a set of good Lie-Nielson scrapers I plan to cut up into a variety of shapes. I shape the edge with the Tormek then file (or hone) and raise a burr with a carbide burnisher.

JKJ

[robert baccus]

The combined use of a sharp bottom feeder and followed bt a heavy hand scraper is very effective.