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Continuing the Rim Thickness Inside Bowls (Read 473 times)
 
Don Stephan
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Continuing the Rim Thickness Inside Bowls
May 28th, 2017 at 10:49am
 
As I turn more bowls, my enjoyment for sanding seems to continue decreasing. Grin

I'm one of the odd ducks that likes once turned bowls, so I'm always turning green wood.  A few months ago I finally realized the value of taking the first inch or so inside the bowl to final wall thickness, then the next inch, and so on.  Especially if the wall thickness is less than 3/8", the wood is already moving (warping) in response to drying out.

My frustration is trying to pick up and continue the wall thickness where I stopped, and even more so trying to take off a whisker or so where the wall thickness is slightly thicker.  Too often where I start the cut I get a narrow groove from starting with the bevel angled too deep.

Perhaps the problem is starting the gouge at that particular spot and moving the handle to the right until the tool starts to cut?  Is it better to start higher on the wall and swing the handle to the right (to pick up the cut) as the tool tip is moving down the wall?  If so, for those able to do this do you do this in discrete increments or continually swing the handle to the right while moving down the wall, until the shaving begins?  (My vision of discrete increments would be to start above the desired starting point, move the handle a fraction to the right and move down the wall; if the tip doesn't pick up a shaving at the desired point move the tip back up the wall, swing the handle another fraction to the right and move down the wall, and so on).
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Ed Weber
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Re: Continuing the Rim Thickness Inside Bowls
Reply #1 - May 28th, 2017 at 11:46am
 
Don Stephan wrote on May 28th, 2017 at 10:49am:
(My vision of discrete increments would be to start above the desired starting point, move the handle a fraction to the right and move down the wall; if the tip doesn't pick up a shaving at the desired point move the tip back up the wall, swing the handle another fraction to the right and move down the wall, and so on).


From your description, IMO this is the best approach. If you allow yourself (leaving enough materiel) to overlap the beginning of the new cut with the end of the previous cut, you typically get a better transition. Trying to pick up a previous cut at the exact spot can be tricky and is exaggerated on a warped (not perfectly round) bowl. The slight overlapping area also makes blending the two different stage cuts easier when sanding.
I don't turn green wood if I can avoid it (I've done it and don't like it) others who do may have more/better input.
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robo_hippy
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Re: Continuing the Rim Thickness Inside Bowls
Reply #2 - May 28th, 2017 at 12:09pm
 
This is where shear scraping and in some cases the negative rake scraper (NRS) come in handy, to blend in that dang spot.... I prefer a scraper with a ) nose profile, or a round nose one, and a fresh burr, or burnished burr. Keep the handle low (so you can not contact the wood on the high side of the tool and get a massive catch), and do very gentle pull cuts. It usually takes several passes. The NRS works better on harder woods and not as well on softer woods. They also work far better for sweeping across the bottom and into the transition, but not as well on the walls of a bowl as any scraping cut will tend to pull/tear side grain.

Another part is "the bevel should rub the wood, but the wood should not know it". We all understand this, but it is difficult to put into practice. On the inside of the bowl, you push into the cut, but not into the wall of the bowl. Even the slightest push towards the wall of the bowl will make it flex.

I need to do videos on both. I had thought I had the rub the bevel part down till I watched Ashley Harwood turn her delicate 6 inch plus long ebony finials. She was not using her other finger as a steady rest on the spindle.... Ashley, I have to go home and practice my dainty skills....

Oh, part of the bowl going oval as you turn, the way I figure it any way, is because the bowl is elastic/stretchable, you have different grain patterns, and it will move more one direction than the other, and this is even more so at higher speeds...

robo hippy

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Ed Weber
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Re: Continuing the Rim Thickness Inside Bowls
Reply #3 - May 28th, 2017 at 7:23pm
 
robo_hippy wrote on May 28th, 2017 at 12:09pm:
Ashley, I have to go home and practice my dainty skills....


As Harry Callahan would say, "A man's GOT to know his limitations"  Smiley
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Don Stephan
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Re: Continuing the Rim Thickness Inside Bowls
Reply #4 - May 28th, 2017 at 7:51pm
 
Smiley Wink Cheesy Grin Thumbs Up
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robert baccus
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Re: Continuing the Rim Thickness Inside Bowls
Reply #5 - Jun 18th, 2017 at 10:00pm
 
Hence the reason for twice turning resulting in a round bowl or vase.  Way easier to sand and finish--not to mention embelish.
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David Fritz
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Re: Continuing the Rim Thickness Inside Bowls
Reply #6 - Jul 16th, 2017 at 9:01am
 
Reed, I'm confused when you say keep the handle of the scraper low. I thought a scraper was supposed to be level or handle up to avoid a catch. I would love to see a video of this as well. I have the same exact problem.
robo_hippy wrote on May 28th, 2017 at 12:09pm:
This is where shear scraping and in some cases the negative rake scraper (NRS) come in handy, to blend in that dang spot.... I prefer a scraper with a ) nose profile, or a round nose one, and a fresh burr, or burnished burr. Keep the handle low (so you can not contact the wood on the high side of the tool and get a massive catch), and do very gentle pull cuts. It usually takes several passes. The NRS works better on harder woods and not as well on softer woods. They also work far better for sweeping across the bottom and into the transition, but not as well on the walls of a bowl as any scraping cut will tend to pull/tear side grain.

Another part is "the bevel should rub the wood, but the wood should not know it". We all understand this, but it is difficult to put into practice. On the inside of the bowl, you push into the cut, but not into the wall of the bowl. Even the slightest push towards the wall of the bowl will make it flex.

I need to do videos on both. I had thought I had the rub the bevel part down till I watched Ashley Harwood turn her delicate 6 inch plus long ebony finials. She was not using her other finger as a steady rest on the spindle.... Ashley, I have to go home and practice my dainty skills....

Oh, part of the bowl going oval as you turn, the way I figure it any way, is because the bowl is elastic/stretchable, you have different grain patterns, and it will move more one direction than the other, and this is even more so at higher speeds...

robo hippy


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Ed Weber
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Re: Continuing the Rim Thickness Inside Bowls
Reply #7 - Jul 16th, 2017 at 9:14am
 
David Fritz wrote on Jul 16th, 2017 at 9:01am:
Reed, I'm confused when you say keep the handle of the scraper low. I thought a scraper was supposed to be level or handle up to avoid a catch.


I'm sure Reed will comment at some point but until then,
What he's saying is in this circumstance you're using a scarper BUT you're using it in a different fashion, shear cutting.
When the handle is lowered (roughly 45 degrees or more) the cutting edge is now being  presented to the wood at a angle where it can no longer scrape but needs to berolled on it's side to "slice " across the fibers.
This is very similar to the way some (like myself) will use the wing of a bowl gouge in the same way.
Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register Scroll down 3/4 of the page or so until you get to the section, Shear Scraping.
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David Fritz
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Re: Continuing the Rim Thickness Inside Bowls
Reply #8 - Jul 16th, 2017 at 9:31am
 
Thank you Ed. That's really helpful.
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robo_hippy
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Re: Continuing the Rim Thickness Inside Bowls
Reply #9 - Jul 17th, 2017 at 10:16am
 
Each tool can be used to make basic cuts, which are pretty much bevel rubbing cuts, scraping cuts, and shear scraping cuts. These are pretty much describing how the cutting edge is presented to the wood.

So, bevel rubbing cut, mostly used with bowl gouges and skews, the bevel very gently rubs the wood as the edge cuts. Most of the time, the cutting edge is at a shear angle to the rotation of the wood. A peeling cut with the skew is similar, but is more square to the wood. Note here, skews, gouges, and scrapers can all be used with a bevel rubbing cut.

A scraping cut is with the cutting edge at 90 degrees to the spin/rotation of the wood, which also is a cut with 0 degrees of shear angle. Most common is a scraper flat on the tool rest. A skew chisel is a negative rake scraper and can be used this way. A gouge, held level, with the flutes rolled all the way over on the side is also a scraping cut.

A shear scrape is another cut that really is not a scraping cut. I will be doing a video on just shear scraping.... Anyway, the shear/sheer (according to Lyle Jamieson) is with the cutting edge at an angle to the spin/rotation of the wood and the bevel is not rubbing. So the cut isn't really a scraping cut at all because the cutting edge is at an angle to the spin. I don't think the name we have given this cut applies correctly, but can't think of another name for it. The idea behind this cut is for clean up of tool marks and some tear out. The higher the shear angle is, the cleaner the cut, so most of the time this is in the 60 to 80 degree range vertical. Mike Mahoney just did an article in the AAW magazine about it and there is a video link to it. Most use gouges for this cut, but I prefer scrapers. The idea with the high angle is kind of like speed bumps on the road. Hit them square on (like a scraping cut) and you get a pretty big bump. Hit them at a 45 degree angle, and the bump is still there, but it is smoother to go over. A 70 degree angle makes the bump almost disappear. So, a high shear angle does a better job of gently lifting the fiber as you cut so you get less tear out. Also, since you are not rubbing the bevel, it does a great job of getting rid of the little bump that is in every bowl (from cutting uphill/downhill/uphill/downhill on every rotation) so you can get it pretty much perfectly true. On the outside of a bowl, you drop the handle to get the high shear angle. On the inside of a bowl, you can't drop the handle much because you run into the banjo, or the bowl rim, or the lathe. This is where I use a ) profiled nose shape on my scraper. With that nose shape, you have to drop the handle a bit and work on the lower half of the tool edge because if you try to work on the high side, the tool is not balanced, and that edge will catch. If you have ever used a skew, this is a mistake we all have made, several times. I have seen a couple of well known turners who when using a scraper to shear scrape the inside of the bowl keep the handle high because "Well, I am using a scraper." "Yea, but you are not doing a scraping cut....". On one of my videos where I am using scrapers, with the big ugly tool (not the ones on the Big Ugly tool), where I am shear scraping the rim, and as I come from the inside rim to the outside of the rim, I get high sided..... Nice catch!

I do have a video 'robo hippy turns a bowl using just scrapers' in the video section here, or up on You Tube. Along with many others dedicated mostly to bowl turning.

Hope this explains things better....

robo hippy
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Ed Weber
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Re: Continuing the Rim Thickness Inside Bowls
Reply #10 - Jul 17th, 2017 at 10:32am
 
Thanks Reed
I understand how/why it's done but I'm going to stick with my gouges  Grin
robo_hippy wrote on Jul 17th, 2017 at 10:16am:
I don't think the name we have given this cut applies correctly, but can't think of another name for it.

IMO
I think this is what starts the confusion, people read scrape and it put a preconceived notion in their head about scraping cuts.
To me, it's what I call a slicing cut, regardless of the tool used. Actually any time where the cutting angle is beyond 45 degrees (more vertical than horizontal) I think of as a slicing cut.
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Don Stephan
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Re: Continuing the Rim Thickness Inside Bowls
Reply #11 - Jul 17th, 2017 at 11:28am
 
Very thorough exploration Reed.  Thanks.  Sounds like an outline for a very useful video for all skill levels!
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