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Using Scrapers Inside a Bowl (Read 1,609 times)
 
Don Stephan
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Using Scrapers Inside a Bowl
Mar 6th, 2016 at 8:17pm
 
I am so envious of Richard Raffan - on his bowl turning video he shows repeatedly how he glides a curved scraper across the bottom of a bowl without digs and catches.  I have similarly curved the ends of my scrapers, but get a dig if the shaving is more than wispy thin, even in shallow bowls.  The scraper bevel is 70 degrees, flat on the tool rest, and always angled down perhaps 5 degrees from horizontal.  I'll never be as skilled as Richard, but I would like to be more effective and efficient with these scrapers on the inside bottom of bowls.
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Bert Delisle
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Re: Using Scrapers Inside a Bowl
Reply #1 - Mar 7th, 2016 at 10:01am
 
I agree Richard always make it look so easy. I am fortunate to be in a workshop with him for a week in the near future. I intend to ask him for guidance on that exact tool skill.
This will be the second workshop with Richard, the first one was like a blur sooooo much info, but fantastic inspiration and education.  I just got a copy of Richards latest book "all new Turning Projects", great projects book. I have some questions for him when he is here in person. Hope to have him show us the lamp and shade project live.
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Al Wasser
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Re: Using Scrapers Inside a Bowl
Reply #2 - Mar 7th, 2016 at 10:44am
 
For sure I am not in a class with RR.  Scrapers can be catchy.  For me the key to making thin, catch free cuts, is having the tool rest close.  If you  reach much beyond the tool rest you will get more catches
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robo_hippy
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Re: Using Scrapers Inside a Bowl
Reply #3 - Mar 7th, 2016 at 1:01pm
 
First video and book I ever looked at was Richard Raffen, and I thought every one turned like that... If you have seen my videos, I use scrapers way more than most people. If I am sweeping across the bottom of a bowl to clean up ripples, I use a shear scrape: scraper up on its edge rather than flat on the tool rest, handle lowered, working below the center line of the tool/lower half, and on the inside I use a ) shaped nose rather than swept back or round nose. You can use a big scraper, and scraping cut, and like you said, you are taking tiny whisper cuts. However, a smaller scraper works fine. If you are getting catches, I would guess it is when you sweep from the center bottom of the bowl  over to the transition. Common catch because you hit the transition area, you end up with both the nose and wing of the scraper getting into the cut at the same time rather than just the nose. If this is the case, remember to pivot/rotate your body as you come into the transition so you keep the same amount of metal in the wood. A negative rake scraper works very well for this cut and it is almost catch proof. It does work better on harder woods, and not as well on softer woods.

robo hippy
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Glenn Jacobs
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Re: Using Scrapers Inside a Bowl
Reply #4 - Mar 8th, 2016 at 1:30pm
 
Also if the wood is singing, you'll get more catches.
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Al Wasser
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Re: Using Scrapers Inside a Bowl
Reply #5 - Mar 8th, 2016 at 2:26pm
 
If the wood starts singing you are likely creating tear out.
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Larry Matchett
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Re: Using Scrapers Inside a Bowl
Reply #6 - Mar 8th, 2016 at 10:59pm
 
I changed the angle on my scrapers to 85 deg.  Works much better.  I also use an 80 grit grinder to put the burr on.  That also resulted in less catches.  For my negative rake scrapers I grind upside down and the angle is more like 60 deg.  Like others have said tool overhang causes catches.  I admit I only use scrapers when a gouge won't do the job.  Reed is probably a better source for info on scrapers.
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robo_hippy
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Re: Using Scrapers Inside a Bowl
Reply #7 - Mar 9th, 2016 at 2:18am
 
The wood singing is what happens when you work a scraper flat on the tool rest near the rim of a bowl. As some one once said, "my bowl started making this strange screeching and howling noise, and then it blew up". Since there is no mass behind it, working near the rim, more so on bigger bowls, the walls start to vibrate. If you don't pull off or change cutting pressure to almost nothing, it vibrates more and more till you get a big catch.

I have my scrapers at a 70 degree bevel, which as near as I can remember, is how they came, and that was 18 years ago. I have seen less, and more, but have learned with them as they are... I do sharpen on CBN wheels, and the burr from the 80 and 180 grit are fine for heavy roughing, and pretty good for shear scraping. I just got a 600 grit CBN wheel, and the burr from it isn't good for heavy roughing, but excellent for shear scraping. For any clean up on bowls, I prefer a shear scrape to a negative rake scraper. Negative rake scrapers excel on end grain, like box lids and bottoms.

I will have a shear scraping video later this year, and hopefully a sharpening video next week. Some final editing to do....

robo hippy
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Tim Hyatt
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Re: Using Scrapers Inside a Bowl
Reply #8 - Mar 9th, 2016 at 12:33pm
 
i find I have a LOT more "catch" problems the more overhang there is.   so keep your rest close and your overhang to as small as distance as you can reasonably manage.    Does mean sometimes you have to change rests to get in the right place/depth, but it's worth the few moments....
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Jeff Vanden Boogart
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Re: Using Scrapers Inside a Bowl
Reply #9 - Mar 9th, 2016 at 7:55pm
 
Robo, have you made a "big ugly" inside the bowl scraper yet?  Thinking about trying it..........just because Smiley
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lloyd harner
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Re: Using Scrapers Inside a Bowl
Reply #10 - Mar 9th, 2016 at 9:29pm
 
what would "big ugly" be i have a 5/8 slab of cpm10v overr an inch wide that im working at being a scraper?
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Re: Using Scrapers Inside a Bowl
Reply #11 - Mar 10th, 2016 at 12:30am
 
Lloyd...
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Don Stephan
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Re: Using Scrapers Inside a Bowl
Reply #12 - Mar 10th, 2016 at 8:50am
 
Not sure what to make of the suggestions to keep the rest close.  I've seen statements that the rest needs to be perpendicular to the bed ways, which would seem to rule out using a curved rest when using a scraper.  The tool post will keep the rest away therefore a distance slightly more than the depth of the bowl.
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lloyd harner
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Re: Using Scrapers Inside a Bowl
Reply #13 - Mar 10th, 2016 at 8:59am
 
ok now i get it the 6k holds a toothy edge and also forma a nice bur to work with
knife makers hate the stuff cause it is a bugger to grind nicely
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Al Wasser
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Re: Using Scrapers Inside a Bowl
Reply #14 - Mar 10th, 2016 at 2:38pm
 
Don, I don't know where you read that.  You need to be perpendicular to start the bowl hollowing process, but after that either angle a straight tool rest into the center or go to a curved rest.  If you don't move the rest in you are really  fighting the process, especially with scrapers.
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