Which produces the better finish?
Figure a fresh sharp edge on the shear scrape and a nicely raised burr on the negative rake.
Figure a fresh sharp edge on the shear scrape and a nicely raised burr on the negative rake.
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Is a shear scrape finish better than a negative rake scrape?
- Thread starter Hugh
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I'd say it depends on the wood, the lathe speed, and the turner. Some turners might get a near perfect minimal sanding surface with a neg rake scraper and swear by it on the woods they use, while others may get better results with shear scraping - Some woods react better to a slicing cut as in shear scraping, while some may react better to the negative rake scraper - Much like hand planing a flat board - some woods you can get a glass smooth surface with just the plane, and other boards you might get tear-out and have to resort to your card scraper (which takes much finer shavings at a higher angle) I don't think there is any one BEST tool for all woods and all situations.
In my opinion the shear scrape leaves a better finish.
Can you really compare the two? The negative rake scraper is a tool. Shear scraping is a technique. You can shear scrape with a negative rake scraper.
The surface will tell you what works best with that particular wood and tool.
Jim McLain
Artist
On some woods I shear scrape with a negative rake scraper. I feel that it leaves a better surface on some of the softer woods I use.
Well, a NRS is still a scraper, so it will pull on the wood fibers as it cuts. For sweeping across the bottom of a bowl, they are great. For going up the walls and through the transition, they are not as good, again, because they are scrapers. The 'shear/sheer scrape' is not a scraping cut. The reason it is called that is because the bevel is not rubbing, rather than how it is applied/presented to the wood. On my bowls, and any time I am having problems with tear out, I use the shear scrape on the transition and and walls of the bowl. I prefer a burnished burr. I even use it on spindles some times, but that is mostly because I am a bowl turner, and don't do tons of spindles. What I do like about the shear scrape, is that because you are not rubbing the bevel, you can nibble off any high spots which allows you to get a close to perfectly round bowl form. I figure the gouge bounces as you turn bowls because of the uphill/downhill grain orientation. The shear scrape evens that up a bit. This is really only important if you are turning really thin, like 1/8 inch or less. Jimmy Clewes started me shear scraping. He commented that with a bevel rubbing cut, you actually burnish the wood a bit, and when you start to sand, first thing you have to do is cut through that burnished surface. I think there is at least a little truth to that.
robo hippy
robo hippy
Complete and accurate @robo hippy - I couldn't have said it better!
john lucas
AAW Forum Expert
I just did that on a piece this last week. I used the negative rake scraper with a light gentle touch. Surface was not quite as good as I wanted so I tilted the tool.up and shear scraped with it. Noticeably better. That was hard maple.
As many have said much depends on the species. I run two basic types of scraper 3mm thick HSS 20' and 90' . The 20' can be inverted to become a negative in the positive, its the most aggressive and the 90' also can be used as a negative by lifting the handle. But its more often used in a shear action, and at the end of the day you have to find what works for you. Mine work well for me, but not all my friends would agree with me.
Good stuff folks. Thanks for the answers. Stuff to make the mind wiggle a bit. Always good to wiggle the mind.
I do both when I am turning. Depends on the mood of the day and the cut I am trying to make.
I do like the burnished burr on the NRS.
I was just interested in how others thought about the two different methods.
Thanks.
I do both when I am turning. Depends on the mood of the day and the cut I am trying to make.
I do like the burnished burr on the NRS.
I was just interested in how others thought about the two different methods.
Thanks.
Same as others - depends on the wood and what I'm trying to do. Some woods like willow don't tolerate NR scraping at all but a sheer scrape cut with a sharp gouge works well. On hollow forms it can also depend on where you are on the form. Straight side grain around the middle or mostly end grain around the top and near the bottom. I'll try both to see what gives me the best finish and what I can manage for the task. If I'm trying to refine a curve or a transition then a NR scraper helps without creating other marks, especially around the high sides of a natural edge bowl. If I'm trying to get rid of a bounce due to my error or the piece moved then a sheer scrape works best for me, usually.
Any advise on how to shear scrape the inside of a bowl with a bowl gouge. I've not had good luck with this.
odie
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Is a shear scrape finish better than a negative rake scrape?
In my opinion......yes!
-o-
Edit note: I'm going to go against dominant opinion here, and say that it is not dependent on the wood species. In no case that I'm aware of, the negative rake scraper cut is ever the equal of a well planned and executed shear scrape cut....while using a manually raised bur for the shear scrape.
.
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lots and lots of practice first, and a very delicate touch.
you need to be able to "translate" the different perspective of the gouge positioning (angle and presentation of the edge) it needs a somewhat different technique for inside a bowl than outside.
I started out with just mastering the outside shear scrape until I could get a smooth continuous curve and a hand covered in extra fine angel hair shavings (as opposed to dust which means you're scraping but not shearing) and then you probably have enough practice you can start over on inside preferably starting at rim and working down but NOT into the transition which is where you can get some horrible catches.. ask me how I know!
It is probably that high tendency to get awful catches when you stick the nose a little too far down into the transitional curve near the bottom that is why many turners will simply tell you to NOT shear scrape inside of a bowl.
I'd already been doing that inside shear scrape with some success before I read somewhere from some "Pro Turner" that said you should never shear scrape inside of a bowl..... and at this point, I can even manage a very very delicate shear scrape (or maybe it is just one of Odie's "Zen" cuts - close to but not quite a catch ) through the transition , but there can be no vibration in the bowl (wobble from movement of the wood) to get that precision cut done... and even after tons of practice, it only takes VERY tiny miscue to get a catch that digs in halfway through the bottom of your nearly complete bowl (if it doesn't blow it apart for you) so I suspect that is why most will not recommend shear scrape inside a bowl using a bowl gouge. I'd say, it is possible, but it requires a lot of practice and, I suppose, a sense of "Zen" being at one with the whole... to make it any better than a good sharp freshly burred scraper (or BOB gouge)
With the end grain boxes I do, I can get surfaces on the inside of the box that do not need sanding. It does take a bit of practice. On the lid and the bottom, same thing. On the outside, I generally use the skew, and then sand to 400. For bowls, what Odie said.
robo hippy
robo hippy
Brian, that's my experience trying this is to have a catch and ruin something almost done. I'm ok on the outside of the bowl getting the angel hair cuttings
I believe that the results of either are dependent on your skill level with either tool. Either can produce the desired effect.
Using NRSs for shear scraping depends. If you are using the grinder burr, the burr will be gone in seconds. If you have a burnished burr, it will work fine. I still do all of my shear scraping with dedicated scrapers. I quit using swept back gouges years ago. One thing they do excel at is shear scraping with that long wing.
robo hippy
robo hippy
I was practicing scraping and shear scraping today on a rough out bowl, figured that's a good place to practice instead of a finished product. I figured out what I was doing wrong with the gouge, the gouge I was using and got catches with had a flat wing. The one I used today had a convex grind on the wing and it worked perfect. Thanks for the tip on the burnished burr robo, it does work better for shear scraping with a negative rake scraper. I used a combination of the bowl gouge and negative rake scraper on the inside of the bowl depending where I was scraping. The nrs worked better on the bottom of the bowl because I couldn't get the handle low enough on the gouge without hitting the bed of the lathe. Hope this helps someone.