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Shear Scraping (Read 2,211 times)
Ron Sardo
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Shear Scraping
Oct 4th, 2015 at 5:10pm
 


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John Grace
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Re: Shear Scraping
Reply #1 - Oct 5th, 2015 at 11:11am
 
A very enjoyable and knowledgeable piece...learned a lot.
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Glenn Roberts
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Re: Shear Scraping
Reply #2 - Oct 5th, 2015 at 9:43pm
 
Seems to me, as a neophyte at this stuff, that the shear scrape would be very similar to a sharp gouge. Why would the shear scrape be superior to the gouge on end grain in particular. Doesn't scraping just  "break" the grain instead of cutting it? A shear scrape would tend to cut the grain as would a gouge, but that's what a gouge does I thought: cut the grain. With tear out being more prominent in softer woods, wouldn't the gouge be the superior tool? I did see the example, but it appears that the shear scrape is the slower process, and a bit unstable - the scraper doesn't seem supported when it is tipped at the pictured angle. What if the gouge went that slow? Doesn't make sense to me.
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robo_hippy
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Re: Shear Scraping
Reply #3 - Oct 6th, 2015 at 2:39pm
 
Lots of misconceptions about scraping, gouges, and shear scrapes. I have been wanting to do this video clip and it has been in the planning stages for a year or so. Both scraping and bevel rub gouge use is 'cutting' the wood. Tear out mostly comes from trying to cut the wood so fast that it tears before it gets a chance to cut. Dull tools does the same thing, pretty much with out any relation to speed. The idea of 'shear' is almost as old as woodworking itself with hand planes that have angled blades, or even the card scraper that you move across the wood at an angle to the grain. I compare it to going over speed bumps in the parking lot. Hit it square on and you get a fairly good bump. This would be scraping with the scraper flat on the tool rest. Hit the speed bump at a 45 degree angle, and you get much less of a sudden bump, but the bump is still there. Going at a 75 degree angle and the bump almost goes away. So, the shear angle is better at getting under the wood fiber more gently to lift it away. A bevel rubbing cut with a gouge is at a shear angle, most of the time in the 45 degree range. Shear scraping can be done with both gouges and scrapers. The shear scrapes are for clean up work, not for heavy stock removal. So, for bowl turning, first you get a rough shape, then you refine it with a pass or 5 with a bowl gouge. Then you use a shear scrape to clean up all the little tool marks and bumps and humps that maybe you could sand out, but it is easier, and most of the time faster to shear scrape. To get these marks out, you don't do it in one pass, but take several. Also, since this cut is so light, you can generally go with or against the grain. The higher the shear angle, the more gentle the lifting of the shavings is. I would say that the biggest difference between a shear scrape and a bevel rubbing cut is that with the shear scrape, the tool rest is your fulcrum. With a bevel rubbing cut, the tool rest supports the tool, and your bevel rub is the fulcrum. The bevel rub may help hold down the fiber as you cut it. It also does leave a some what burnished surface. Jimmy Clewes made the comment that he always shear scrapes because when you start to sand, the first thing you have to do is sand off the burnishing. I hadn't thought of it before I heard him make that comment, but it seems to be true. With the bevel rubbing cut, remember that 'the bevel should rub the wood, but the wood should not know it', so keep the pressure very light. I also like the shear scrape if I want a 'perfectly' round bowl. Most bowls will have a run out of maybe 1/16 inch, which means plus or minus 1/32 of an inch. Over about 1/8 of an inch thick, and no one will notice. Under that, you need to even it up in ways that you can't do with a bevel rubbing cut because when you rub, you get a tiny bounce from going uphill (against the grain), down hill, up hill, and down hill for each revolution. The shear scrape, since you are not rubbing the bevel does not seem to do this and you can get almost perfectly round, after reversing the bowl. I have a bunch of bowl turning clips up here and on You Tube, type in or search robo hippy

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Ralph Fahringer
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Re: Shear Scraping
Reply #4 - Oct 6th, 2015 at 3:42pm
 
Do you ever give classes? I'd consider coming back out to Oregon for that.
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robo_hippy
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Re: Shear Scraping
Reply #5 - Oct 6th, 2015 at 4:20pm
 
Ralph, I don't really do classes, but have people in the shop for 'mentoring'. Funny thing about mentoring is that more people don't take advantage of it. I am good for half day or so sessions. If you are ever up this way, let me know. I will be in Atlanta next summer for the Symposium, and in KC the year after. I actually have family in that area. Where are you?

Hey, aren't you going to get a knee done?

robo hippy
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Ralph Fahringer
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Re: Shear Scraping
Reply #6 - Oct 6th, 2015 at 4:39pm
 
I'm up here in Maine..the opposite end of the country.

Yup, the operation is scheduled for Dec 15th.  Still trying to get the shop finished before going in.
I expect  to start making shavings & chips & dust very soon.

Ran a 4" PVC pipe thru the wall to the old shed next door for the dust collector and another smaller one next to it for the air compressor hose and the wiring for it and the collector.

More room for me and less noise. Win- win. Thumbs Up

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Glenn Roberts
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Re: Shear Scraping
Reply #7 - Oct 6th, 2015 at 8:24pm
 
Robo, Thankx for the more detailed explanation - very much appreciated. Would a round carbide tool be able to do a shear scrape? Maybe a square carbide? Or is it the long flat nose of the scraper that makes the difference between a gouge and a scraper in shear scraping? 
Maybe a reason mentoring is not taken advantage of as often maybe because the "mentee" may feel like he (or she)  is taking too much off the mentors time.
Thankx again for the explanation. Maybe I'll ride to Oregon  with Ralph ... That would be an experience(!!)
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JimQuarles
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Re: Shear Scraping
Reply #8 - Oct 6th, 2015 at 10:18pm
 
I've done shear scraping with EWT tools.
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Mentor Basics, Pens, small stuff, Acrylics, EasyRougher.
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Ralph Fahringer
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Re: Shear Scraping
Reply #9 - Oct 7th, 2015 at 9:35am
 
Glenn... I drive a Mercedes ML350 so the ride would be verrrry niiiice!
It made the Kessel Run in less than twelve parsecs, so a trip to Oregon should be  a piece of cake!! Thumbs Up Thumbs Up
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Ed Weber
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Re: Shear Scraping
Reply #10 - Oct 7th, 2015 at 11:11am
 
Not to get into too much granularity, but...
To shear something is to cut it. Woodturners have adopted their own definitions of this word.
Shear = lightly cut
Shear = cut at an angle
It can get confusing trying to explain a procedure when one word has multiple meanings.
I personally believe you either shear or scrape, you can't do both at the same time.

In a nutshell, if at all possible try to cut (shear) the wood fibers an an angle (slice not chop) regardless of the orientation of the piece.
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robo_hippy
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Re: Shear Scraping
Reply #11 - Oct 7th, 2015 at 3:51pm
 
Okay, where was I???? Some where directly over the center of the earth...

Shear cut vs shear cut. Only real difference is one cut uses a bevel rub, and the other does not. Both remove shavings. I have always considered shear 'scrape' to be inaccurate. A scrape is with the cutting edge at 90 degrees to the spin/rotation of the wood, and does not use a bevel rub. It does tend to pull at the fibers more. I haven't been able to come up with any better term though.

For shear scraping, most of the carbide tools I have seen will work. I would consider them excellent for the insides of boxes where the small size would fit better. I would not consider them to be good for bowls where a longer edge would offer more surface area and cutting area.

Ralph, if you want an additional reason to come west, and yes, every thing is west from you, we will be having the second Oregon Woodturning Symposium in 2017, March some thing, kind of around spring break time. Probably not the best time to be driving cross country. Last year, Lyle Jamieson had to take a 300 mile detour to get around a heavy snow storm. I will have a booth there, and of course, making a big mess in the area, and may demonstrate. We had a pretty good line up last one. We are alternating with the Arizona Woodturning Symposium which is also in March. Summer time through mid July is crazy busy time for me.

Also a side note on your knee. Ask your doctor about the 'honey comb' bandage, aka Opsite Post Op Visible Dressing. HUGE improvement over gauze and tape. My healing time was about a week faster than with the old style bandage. It is a honey comb type piece of closed cell poly about 1/8 inch thick, with a wide piece of clear tape over it. It stays on for a week, and you can take showers with it. You can also see inside if some thing is going on that you don't want. I got kicked out of therapy after 6 weeks. Most others are up to 12 or more weeks. Tai Chi!

robo hippy
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Ralph Fahringer
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Re: Shear Scraping
Reply #12 - Oct 7th, 2015 at 4:31pm
 
93 more miles east and I'm in Canada.
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Glenn Jacobs
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Re: Shear Scraping
Reply #13 - Oct 8th, 2015 at 1:51pm
 
Ralph, at that point you may as well keep going east to get to Oregon. Roll Eyes
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John Cepko
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Re: Shear Scraping
Reply #14 - Oct 12th, 2015 at 7:50pm
 
3350 or so miles. according to Bing.
A nice Sunday drive.
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