Has anyone compared scraping and shear-scraping with conventional scrapers and shear-scrapers with scraping and shear-scraping with negative-rake scrapers? My rough-and-ready trials indicate that negative-rake scrapers leave less tearout. If others confirm my findings, then it would seem sensible to convert one’s conventional scrapers and shear-scrapers to negative-rake versions by grinding a 25 degree top bevel a couple of millimetres wide on them. Any thoughts?
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Negative-rake scraping
- Thread starter Mike Darlow
- Start date
In reference to scrapers, all I use are NR. Both store bought and regrinding regular scrappers. I do a lot of open segmented work and NRs come in very handy for me.
A disclaimer about me. I am not trying to be the best turner in the world. I like making things and using whatever is the easiest to use. I use mostly carbide cutters and NR scrapers.
A disclaimer about me. I am not trying to be the best turner in the world. I like making things and using whatever is the easiest to use. I use mostly carbide cutters and NR scrapers.
Before they were in vogue, 20-some years ago I ground one to negative rake on the advice of a traveling turner presenting at a club meeting. But I never felt it offered anything superior to a normal scraper with a proper burnished hook held "handle high", or held with the edge tilted on an angle in shear mode. That tool pretty much sits untouched in a drawer.
yep, confirmed. only have one negative rake scraper and it does a much better job.
Havent converted mine as yet, but tend to lift the handle into the negative position, it works for me. But then I think it depends on the species you are turning.
I haven’t tried ‘shear scraping’ (angled up on side) with my NR. One of the benefits I’ve found with NR is it’s simplicity to use - just bring in level and it leaves a very clean cut.
Years ago I scared myself with a scraper up on its side; it caught and slapped the tool rest *hard*. Additionally I’ve had occasions with a scraper angled down where it self-feeds at the bottom of a bowl.
I still use scrapers, but not as much as the NR. There are uses for both, but you can’t beat an NR for a simple light cleanup.
Years ago I scared myself with a scraper up on its side; it caught and slapped the tool rest *hard*. Additionally I’ve had occasions with a scraper angled down where it self-feeds at the bottom of a bowl.
I still use scrapers, but not as much as the NR. There are uses for both, but you can’t beat an NR for a simple light cleanup.
I have thoughts!
I've done such comparisons. I my opinion the NRS are far better for smoothing, no tearout on good wood, very controllable, can make incredibly smooth surfaces and surface refinements with little effort. Unlike potentially aggressive conventional scrapers, I can hand a negative rake scraper to a first-day beginner and with 30 seconds of introduction they are instant experts! The aggressiveness or delicateness depends somewhat on the burr added after sharpening.
When I first started reading about NRS I tried converting one. Ooo! I converted most of my scrapers to NRS then bought some more square-end scrapers and skews from Doug Thompson and ground those into NRS with various shapes. I've made small NRS from spindle gouges. and round stock. I do keep a couple of conventional scrapers now but the rest are now NRS, from a tiny Ashley Isles radiused scraper to a 1.25" wide curved scraper, probably about 10 different shapes and a few duplicates so I can quickly pick up a "fresh" one. I still have the John Jordan double-ended shear scraper but gave away the massive long-landled scrapers I didn't think would make good NRS.
I've tried different top and bottom bevels and found most work about the same as long as the included angle is less than 90-deg.
BTW, I shape with a 60 grit CBN wheel and sharpen with 600 grit CBN, remove any grinder burr with an extra fine diamond hone and/or the leather stopping wheel on the Tormek. Then use a burnisher to create the burr. Can refresh the edge multiple times before going back to the grinder.
I experimented a lot with various edge shapes and the curved NRS in the first photo below have been the most useful for me - I grind a long curve down one side and a short flat on the end, unlike any I'd seen. (I do know some who made this shape later.)
I grind these with an equal bevel on both sides (a bit like a skew) so I can make them "left" or "right" simply by changing the direction I burnish the burr. The second photo shows the view from the sharpened edge and the little platform angle-setting gauge I made for this style.
This shape lets me remove gouge marks from bowls, platters, and "dished" platters. The burnished burr will take off amazingly fine shavings. The second photo show just one reason for the flat on the end - to gently smooth the wings/corners when "turning air." A conventional scraper on the corners might be a problem.
These work so well I haven't reached for a conventional scraper for years. So far two students have asked me to grind one for them with this shape.
To double-up on scrapers, I almost always grind a different shape on the other end, whether it's a narrower NRS on the tang or different shapes on both ends of 1/4" and 3/8" round stock. I don't put handles on any of these. Used the only way I know, there are no significant forces on the tool - could hold and guide one with just the thumb and one finger of each hand.
If anyone is interested, I've tried various methods of burnishing a burr and now only use the Arno burnishers - they have several advantages for both NRS and conventional card scrapers.
Amazon.com: Arno French Carbur 2 Double Sided Carbide Cabinet Scraper Burnisher 115508 : Tools & Home Improvement
Amazon.com: Arno French Carbur 2 Double Sided Carbide Cabinet Scraper Burnisher 115508 : Tools & Home Improvement
www.amazon.com
When useful, I use a different type of scraper for spindles.
(I realize this is more than you asked but hey, someone else might be interested!)
JKJ
Video, at the 17:50 mark is a good explanation of shear scraping with a conventional scraper.
View: https://youtu.be/vguvnSEhokE?
I didn't mention that on occasion I will lay down a skew on its side for a quick scraping action, so in essence it is a negative rake scraper. Usually it would be to define a tenon for chuck mounting, or some similar limited action. I would not drag a skew across an entire surface.
I didn't mention that on occasion I will lay down a skew on its side for a quick scraping action, so in essence it is a negative rake scraper. Usually it would be to define a tenon for chuck mounting, or some similar limited action. I would not drag a skew across an entire surface.
A big thankyou to those who have contributed to the debate on comparing conventional scraping with negative-rake scraping. The consensus seems to be that the latter is better. No-one has mentioned any disadvantages from negative-rake scraping, so it does seem to be worthwhile converting all your conventional scrapers (except those used for parting).
I started this thread because I’m preparing a second edition of Sharpening Woodturning Tools and was conscious that I had rather neglected scraping in the first edition. Also trials which compare techniques can be inconclusive.
I have a second query which I’d be grateful for some input on. The sharpening angles recommended in books for conventional scrapers range from 45 to 80 degrees. A conventional negative-rake scraper has two bevels, both with a bevel angle of 25 degrees, giving a sharpening angle of 50 degrees. Is there a particular sharpening angle which is optimum for conventional scrapers? and can the bottom bevel of a negative-rake scraper be steeper without adversely affecting performance?
Thank you, Mike Darlow
I started this thread because I’m preparing a second edition of Sharpening Woodturning Tools and was conscious that I had rather neglected scraping in the first edition. Also trials which compare techniques can be inconclusive.
I have a second query which I’d be grateful for some input on. The sharpening angles recommended in books for conventional scrapers range from 45 to 80 degrees. A conventional negative-rake scraper has two bevels, both with a bevel angle of 25 degrees, giving a sharpening angle of 50 degrees. Is there a particular sharpening angle which is optimum for conventional scrapers? and can the bottom bevel of a negative-rake scraper be steeper without adversely affecting performance?
Thank you, Mike Darlow