Negative rake on Tracy Owens tools

[Guy Mueller]

I have a set (3) of Tracy Owens round stock scrapers, has anyone tried to grind them into negative rake?

[Reed Gray]

A friend did it with a Doug Thompson fluteless gouge and it works fine. If I remember correctly, Tracy's tools are the same, only bigger. Should work fine.
robo hippy

[John K Jordan]

I don't know Tracy Owens but I grind negative rakes on a number of small scrapers, including those I've made from round stock. These are some of my most useful tools for finish cuts on detailed areas especially in end grain.

This picture shows a couple from round Thompson steel stock, the second ground from a spare shallow detail gouge, round except for the very top.

scrapers_small_thompson.jpg

JKJ

[David Gilbert]

John, can you measure the included angle of your negative rake scrapers. These look to me like they are greater than 90 degrees. It was my understanding that the included angles need to be less than 90 degrees. I have several that are around 60 degrees +/- 5 degrees and they work fine.

Cheers,
David

[John K Jordan]

John, can you measure the included angle of your negative rake scrapers. These look to me like they are greater than 90 degrees. It was my understanding that the included angles need to be less than 90 degrees. I have several that are around 60 degrees +/- 5 degrees and they work fine.

Sure, I'll try to tomorrow. I may actually get to spend some time in the shop! (Yikes, I guess I'd better, I have to prepare for a demo later this week.)

I believe the angles are less than 90 but I don't think I've ever measured. I just eyeball, grind and use.

Sharp angles do work well. I use these inside and outside of bowls and things (ground from Thompson scraper and skew chisel steel):

scrapers_neg_rake.jpg

BTW, I like the symmetrical grind on this shape since I can burnish a burr either way as needed to make a scraper left-hand or right-hand.

JKJ

[John K Jordan]

John, can you measure the included angle of your negative rake scrapers. These look to me like they are greater than 90 degrees. It was my understanding that the included angles need to be less than 90 degrees. I have several that are around 60 degrees +/- 5 degrees and they work fine.

David,

I measured the included angle of the small scrapers: they are all 88 degrees, +/- about 0.5 degrees.

I like the way they work now but maybe when I get time I'll experiment with a sharper angle. I never measured the angles, just eyeballed them when I first ground them and tried to see how they worked, then set the tool rest to match when sharpening. BTW, I grind the top (the neg rake part) freehand, off the rest but also to match, 600 grit CBN wheel. Also, I think I mentioned this, but I always remove any burr from grinding then add a burnished burr.

Just for fun I also measured the rounded scrapers in the other picture: they are all between 59 and 60 degrees.

JKJ

[David Gilbert]

Thanks for the info.

I sharpen all my scrapers (regular and negative rake) on my 80 grit CBN wheel and then use it right off the grinder. I'll try your way soon.

Cheers,
David

[Reed Gray]

John,
Looking at the top Thompson NRS's, I would guess the lower bevel to be 70+, and the tops in the 20 to 30 degree range. That would have included angles of 90+. As far as which work better, I am still experimenting. The more blunt ones, with a burnished burr work much better in end grain than they do in bowl/side grain. The more acute/pointy ones seem to do better on bowls, but they seem to work better with a grinder burr rather than a burnished burr. Some one commented that the NRS is a high maintenance tool, which means you have to sharpen it a lot more often than any other tool. Some prefer 20/20. I have one 25/25, several 30/30, and a couple of 70/30. I have been trying some standard scrapers with the burr totally honed off. One thing for sure, if you have to push with them at all, they are dull, which means you get the lightest possible touch to the wood, and if shavings are not coming off, then it is dull. If you will be in Portland next summer, I will have a lathe, wood, and lots of different toys to play with. ! will also have a 400X camera and screen to play with as well....

Oh yea John, that last tip seemed to get rid of the Gremlin strange figures....

robo hippy

[John K Jordan]

I hope you are taking good notes and photos so you can write that amazing magazine article on scrapers! I know the way I sharpen my small scrapers works incredibly well on end grain (mostly what I use them for) giving almost glass-like surfaces. But I haven't tried changing the angles. I do have a number of spare rectangular and round Thompson stock so there's not much excuse to not try some variations.

I like reading the quotes rather than the quote codes! Glad it worked. I hate the intricacies of software sometimes, even though I spent years on the creation end!

JKJ

John,
Looking at the top Thompson NRS's, I would guess the lower bevel to be 70+, and the tops in the 20 to 30 degree range. That would have included angles of 90+. As far as which work better, I am still experimenting. The more blunt ones, with a burnished burr work much better in end grain than they do in bowl/side grain. The more acute/pointy ones seem to do better on bowls, but they seem to work better with a grinder burr rather than a burnished burr. Some one commented that the NRS is a high maintenance tool, which means you have to sharpen it a lot more often than any other tool. Some prefer 20/20. I have one 25/25, several 30/30, and a couple of 70/30. I have been trying some standard scrapers with the burr totally honed off. One thing for sure, if you have to push with them at all, they are dull, which means you get the lightest possible touch to the wood, and if shavings are not coming off, then it is dull. If you will be in Portland next summer, I will have a lathe, wood, and lots of different toys to play with. ! will also have a 400X camera and screen to play with as well....

Oh yea John, that last tip seemed to get rid of the Gremlin strange figures....

robo hippy

[John K Jordan]

David,

I did a couple of experiments while turning some walnut this morning. It was on the outer circumference of a face turning so it was alternately cutting side and end grain every revolution. I compared an 88-deg NRS with a 60-deg NRS. Both had a burnished burr.

The 60-deg cut better and made beautiful fine streaming shavings. The 88-deg did not cut nearly as quickly or make the same streaming shavings but had extremely fine and tiny shavings. HOWEVER, although the 88-deg was a lot slower the resulting surface was much better than the 60-deg. This is not to say the 60-deg surface was bad, there was no tearout, but the surface was not as smooth.

When I get time I plan to regrind some small negative rake scrapers to different angles and try some more careful tests. I suspect there is a better compromise somewhere between 60 and 88-deg.

JKJ

[Reed Gray]

John, are your 60 and 88 degree meaning the combined angles, as in 30/30, and 44/44? I may have to go out to the shop to play a bit. I have a nice piece of myrtle that has some nasty grain. The burnished burr seems to cut better on a 70/30 than it does on a 30/30. A totally honed scraper surface, top and bevel also can leave a really nice surface though you can feel minimal (220 grit will take care of it) tear out. I do have one 25/25 NRS and when doing peeling cuts, it seems to leave a better surface than the 30/30.

robo hippy

[John K Jordan]

John, are your 60 and 88 degree meaning the combined angles, as in 30/30, and 44/44? I may have to go out to the shop to play a bit. I have a nice piece of myrtle that has some nasty grain. The burnished burr seems to cut better on a 70/30 than it does on a 30/30. A totally honed scraper surface, top and bevel also can leave a really nice surface though you can feel minimal (220 grit will take care of it) tear out. I do have one 25/25 NRS and when doing peeling cuts, it seems to leave a better surface than the 30/30.

robo hippy

Included angles. The 60 is 30/30 but the 88 is different, I didn't measure the angles independently but it's probably closer to 60/28. I was using the small flat scraper in the photo I posted with the three small scrapers, two round. I'm not sure the orientation of the included angle on the scraper makes a lot of difference, at least not with the 88. I say that since I tested it with the tool held horizontal as well as angled a bit up and down and didn't see a big difference although holding it horizontally was easier to control. (I use most "finish" scrapers, NRS or otherwise, with no handles unless I'm using one for hollowing or deep inside a box.)

The 25/25 NRS sounds like a skew chisel laid flat on the rest!

As we discussed before I don't use ground burrs anymore on any scraper but raise an edge with the carbide burnisher. The shavings from the curved 60/60 with a VERY slight burnished burr are kind of amazing, especially in cherry. Too much burr and it might get grabby. This is on very old, very dry cherry. It seems to me that any experiments with scrapers should be repeated with both dry wood and wet. (I don't often turn wet so all my tests are with dry.) I often hear people talk about some tool or method with "A works better than B" while others say "B works better than A" but they don't always say what kind of wood and use and conditions. With the scrapers, it would be nice to know if there was a difference, best compared with the exact tool!

BTW I made a handle for one of the little carbide rods I got from you - it's probably a little easier to use than the larger one I've been using for years. I took some rods to a club meeting and barely made it home with some spares!

burnisher_IMG_6767.jpg carbide_burnisher.jpg

JKJ

[Fred Belknap]

There is so many variables that it is difficult to make positive statements. I have been experimenting with NRS for the last year and have change my mind about them quite a few times. My experimenting is mostly with large scrapers like 3/8" and 1/2" Sorby and Henry Taylor tools. The top angle is ground with a RoboRest set in the last hole and according to my measurement is 25 degrees. The bottom angle has been changed several times when I think I can get a better cut with a different grind. As of now I have pretty much settled on 80/25 degree. I use NRS for finish work mostly and do most of the work with gouges. The 80 degrees is not the combined angle but is the setting I use on the RoboRest. I find that a burr off the Veritas seems to work better than one straight off the grinder but the grinder burr is almost as good but doesn't seem to last as long. I find to get good results I need to sharpen them frequently. I sharpen with a 120 grit D-WayCBN that is a few years old.

[John K Jordan]

There is so many variables that it is difficult to make positive statements....I find that a burr off the Veritas seems to work better than one straight off the grinder but the grinder burr is almost as good but doesn't seem to last as long. I find to get good results I need to sharpen them frequently. I sharpen with a 120 grit D-WayCBN that is a few years old.

Another variable not always considered is the specific wood. I get better results with certain scrapers on some woods than others. An analogy is what I discovered years ago turning very thin spindles with a skew chisel. The grind that worked very well on one wood, say, rosewood or cherry or even oak, was totally useless on osage orange. The osage would chip and tear badly unless I used a skew with a much blunter grind. It always cut smooth as glass with a sharp spindle gouge. Of course it might even have been that particular tree - all of my dry osage came from the same tree.

What I like to do is have a variety of grinds on tools - I often experiment with several different grinds while turning to find which works the best for that case. Even the angle of the grain to the surface makes a huge difference some times in what works best. I suspect it may be more art than science. Tool grind analysis sure would be a lot simpler if wood were consistently homogeneous like most plastics and metals!

BTW, long ago my own tests convinced me a burr raised with a carbide burnisher lasted far longer than one from the grinder and could be just as effective if not under- or over-done. One look at a ground burr with the microscope explained why - it simply looks fragile. I grind, hone, polish, or strop away the burr, then burnish. I find the burnished burr can usually be removed and re-burnished several times before regrinding.

JKJ

[Fred Belknap]

JKJ I want to thank you for posting about the Stewart McDonald scrapers. I got the one and liked it so well I ordered the other two. The square one is great for the outside of NE bowls and the small one is great for smoothing up the bottoms of bowls. I use them on almost every bowl I make.