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Simple Sphere Turning Aid

Dennis J Gooding

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I recently posted to another forum a description of a simple aid for turning spheres that does not require special hardware or measuring tools or computation. It stirred sufficient interest that I was asked write an expanded article for inclusion in the Montgomery County Woodturners Newsletter. I believe that this technique will be of interest to some of my fellow AAW’ers, but rather than reposting this rather long article here, I would refer those interested to the MCW site.

http://montgomerycountywoodturners.org/Documents/Newsletters/MCWNewsletter2016-06.pdf

This article has been a joint effort with MCW member Gary Guether, who originally proposed the venture.
 

Bill Boehme

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hockenbery

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Dennis,
A nice article. Your approach is cool too measuring from the corners. I'm sure many people will find it easier than measuring from the center. Less steps too.

You get to hang out with with my old freinds Clif Poodry and Phil Brown
 

Bill Boehme

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Super-helpful! Might want to add the page number to your How-to Forum post, it took me a long time to find the article (starts on page 28).

It would be preferable to post the tip rather than linking to the article in the newsletter primarily because web links change and content sometimes disappears on other web sites.
 

Bill Boehme

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Links, especially to turning clubs websites don't seem to last for more than a few years at best. They get reorganized and upgraded and in most cases nobody thinks about links from other sites. I know that my club is guilty of this. By having original content in the How-To section, we can avoid the problem of broken links.
 

john lucas

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I use that method to start all of my spheres. Then put them between cup centers and finish them. If the sphere doesn't need to be perfect I just turn them using his technique. I carried it further. I have some large graph paper so I extended the chart so I can do up to 8" spheres.
 

hockenbery

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This is a method I have been using for a long time.
I simplify the mathematics by rounding the flat side lengths to .4 the diameter.
Makes the math simple and the error for a 3” sphere is about a pencil line width.

An aid I find especially useful is a ring to lay on the sphere. I turn them from pvc.
A ring will lay flat on the surface of sphere. If your sphere is out of round the ring will show you the high spots

This is a set of slides I use in my demos. It is easy to follow the process.
http://swat.hockenbery.net/Turning_a_ball_the_easy_way.pdf

This has some details in using the cup and flat point centers.
http://swat.hockenbery.net/turning the ball in the cup.pdf
 
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That method of marking out sections on the blank is some thing I figured out some years back... One tip that I picked up from another turner who does a lot of free hand spheres was that when the shape gets pretty close and you are rotating it between centers, he would hand spin the rough sphere and then tap it a time or two to get it more centered. It always bothered me that when rotating the sphere on the 3 axis system, that they would never go back in and center perfectly no matter what I did. With that tapping to get it closer, it worked a lot better, if this makes any sense....

robo hippy
 

hockenbery

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That method of marking out sections on the blank is some thing I figured out some years back... One tip that I picked up from another turner who does a lot of free hand spheres was that when the shape gets pretty close and you are rotating it between centers, he would hand spin the rough sphere and then tap it a time or two to get it more centered. It always bothered me that when rotating the sphere on the 3 axis system, that they would never go back in and center perfectly no matter what I did. With that tapping to get it closer, it worked a lot better, if this makes any sense....

robo hippy
That is pretty common when using two cups they tend to double any out of roundness because both push in opposite directions, I learned to use the flat point on the tail center from Christian Burchard. I just hold he ball against the cup and the flat point pushed it into the cup where I held it.

rubber chuckie cup and flat pointE2660FFF-C050-4080-A2B2-B1DF1C767145.jpeg


Wooden cup ( soft mahogany cup on a hard maple MT) A8C407AA-8D48-4364-B35A-0212E1C7A0F4.jpeg
On the first mount like this one I check the equator distance to the tool rest in each side with something like a pencil. I necessary I adjust the ball in the cup To make both sides equidistant from the tool rest.
 
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This is a method I have been using for a long time.
I simplify the mathematics by rounding the flat side lengths to .4 the diameter.
Makes the math simple and the error for a 3” sphere is about a pencil line width.

An aid I find especially useful is a ring to lay on the sphere. I turn them from pvc.
A ring will lay flat on the surface of sphere. If your sphere is out of round the ring will show you the high spots

This is a set of slides I use in my demos. It is easy to follow the process.
http://swat.hockenbery.net/Turning_a_ball_the_easy_way.pdf

This has some details in using the cup and flat point centers.
http://swat.hockenbery.net/turning the ball in the cup.pdf

What are you using for the rings? Regular pvc? Sounds like a great idea, I’ll need to try it.

Paul
 

hockenbery

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What are you using for the rings? Regular pvc? Sounds like a great idea, I’ll need to try it. Paul

HS Geometry I learned a Cut on a sphere leaves a circle.
In Christian Burchard’s I learned I could use the cup ball chuck to gauge roundness.

Then a round 2000 I saw Soren Berger use a ring in a demo and that was a big improvement on being able to spot the out of round parts.


I make most of mine from 1.5 ID thick PVC pipe like below.
Thin pipe will work too but it can be flexed into fitting easier.

An old flashlight hood will work pretty well too. One important thing is for the contact edge to be thin or the shadow from a thick contact surface will hide the light you are trying to see peak under.

This is one in progress. Pvc you have to ride the bevel. Also the shaving is miles long or so it seems.
Be careful not to let the shaving pull across you hand or finger- I think it would cut your before breaking.
The generally just wrap around the pipe and the chuck.

F6EA22E2-BD1B-4B88-BBD2-6F67724DB48E.jpeg
 

john lucas

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Question for everyone. When you make your cone centers what shape is the inside. I'm bought a piece of 3" solid plastic bar and want to make some cone centers that stay perfectly round (my old ones are wood and move a little). One thought I had was to make the hollow portion V shaped so a sphere of any side would fit in it. The way I've always done it before was it was a cove shape so only the outer edge touched the wood. This works fine for sphere of certain range of sizes. I think the V shape would also be somewhat limiting but I was thinking of making a few with wider V's for larger spheres. I like Al's idea of the small flat cone on the tailstock end and may go with that this time around. I have about a foot long bar so I can make several.
 

hockenbery

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make the hollow portion V shaped so a sphere of any side would fit in it. The way I've always done it before was it was a cove shape so only the outer edge touched the wood.

I want the ball seat against the rim of the drive cup. This gives a better hold and drive than a cone shape.
the cone has negatives the ball will always be on a smaller diameter drive radius than you want, the ball would be more likely to slip when being cut, and anything below the rim of the drive cut cannot be turned,

one of Don Doyle’s (rubber chucky) prototypes was a cup with little rings on the inside so that you had different size rims to seat against. This took away too much working room on the smaller balls.

I turn out a bowl shape not quite as deep as a hemisphere. Don’t want the ball to tough anything but the rim.
Ideal diameter is about 1/3 of the. The most secure drive would be just under 1/2 the diameter but there is no working room on the ball. 1/3 is a good compromise between hold and working room.
I soften the inside rim to a gentle curve.

I also like to use soft maple, mahogany, Camphor for the cup. These are woods that are softer and less likely to mark any balls I turn. They might leave a ring mark on Camphor but it goes away after sanding with 220.

plastic may be too hard for a good drive cup.
You can always put foam on the rim,

I use PVC vacuum chucks on large balls. I use the foam with them both to protect the work and improve the drive. in working when Don to perfecting the hardness of the ball chucks he made a couple that too hard and a couple that were way too soft and would flex and then he made it just right.

it’s always fun to experiment with materials but it’s hard to beat wood. I have been using some of the same wooden cups on wood MTs for 20 years. I rarely have to true the rims but I do check them every time.
wood chucks used in chucks need to be trued a lot.
I have a bunch of rubber chucky cups but rarely use them for balls. I do use the a lot for holding the seed jars I have been turning the last few years.
 
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I have purchased several boxes of 2-inch diameter and 3-inch diameter Delrin end drops off of eBay at a good price compared to buying continuous length material at retail cost. These work great for making jamb chucks and cone centers etc. A few machine shops get rid of their shorter pieces that they are unable to use for their regular production pieces by selling them on eBay at a discount.
 
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