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Thread: A brief history of the burr
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22nd September 2018, 02:35 PM #16
Without the original images this thread is useless (the images disappeared at the time of great image vanishing episode). Having referred to it in another thread, here, I thought I should attempt to reconstruct at least part of it with the original images that I have on file.
Here we go....
There is an excellent article (now here on page 67) by Alan Lacer and Jerry Wright that examines the effectiveness of the different methods of scraper preparation. One of their key findings was that the level of polish on the face of the scraper is a key determinant of the finish off the tool. However, they didn't cover the durability of the burr if left on a scraper.
Brendan thinking is that the burr off a grinding wheel is too fragile to last last long enough to be useful in cutting wood cleanly, but thought it worthwhile taking a closer look at the burr after a short periods of use to confirm this.
The scraper I used was one of these. It had the advantage of being detachable so it could easily be put under the digital microscope. The grind angle was about 80deg.
The wood was native cherry, a dense hardwood, running at 1500rpm. A shear angle was used of approx 45 to 60 deg.
The face of the scraper was polished to a level where no scratch marks could be detected under magnification.
The following images are at 200 X magnification and show an area approx 1mm wide.
Scraper - 200 X - #120 burr.jpg
Burr from #120 diamond wheel before use.
Scraper - 200 X - #120 burr at 30 secs.jpg
Burr from #120 diamond wheel after 30 secs use.
Scraper - 200 X - #120 burr at 60 secs.jpg
Burr from #120 diamond wheel after 60 secs use
The burr off the #120 diamond wheel could be felt but not seen with the (my) naked eye. The scraper continued to readily produce fine gossamer shavings for about 30 secs when I stopped and took an image. As can be seen, the burr appears reasonably intact, but could only just be detected by touch. The serrations were starting to lose some of their sharpness.
By 60 secs there was a noticeable change in performance. Another image was taken that shows the burr in effect has gone.Stay sharp and stay safe!
Neil
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22nd September 2018 02:35 PM # ADSGoogle Adsense Advertisement
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22nd September 2018, 03:01 PM #17Hewer of wood
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Thanks for the rehabbed thread Neil.
I'd forgotten how well the hooked scraper went.
And there was a piece of Rock Maple I tried scraping with no burr or hook at all that produced a cleaner result than a burr.
BTW The V burnisher is FS if anyone's interested. Was pretty much only used for this test. Make me an offer.
Veritas Tools - Sharpening - Scraper Burnisher for TurnersCheers, Ern
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23rd September 2018, 02:39 AM #18GOLD MEMBER
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Thanks for bringing this back.
So much timber, so little time.
Paul
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