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1/2 wit idea

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GK1918

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#1
I have never had a need to turn a radius, a ball but would like to know. I read somewhere
(cant find it) it is possible on what you have in being a standard tools. If my compound rest
would only turn 360, but it won't. There was somebody on Utube doing it by feel & I cant find
that either. I can't afford an attachment that would be nice . This is not my priority but just
a cabin fever thingy. sp
 
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Moderatemixed

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#2
“Build something cool”, formerly “metal tips and tricks” Dale Derry on Youtube did the “freehand” radius. Lots of other videos showing radius tools etc. Good luck.


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mcostello

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#3
Hey, if it wern't for 1/2 wit ideas, some of Us would have no ideas at'all.
 

tcarrington

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#4
The short explanation I would use for this method and it may well be 1/2 wit is use a form tool. Grind a concave radius that you wish and "apply" it in as many places as it takes to make the ball,, or whatever portion that you wish. The compound would be rotated to allow the form tool to come in from the correct angle to connect the first radius to the second, then third, etc. The complex portion is positioning the tool so that you come into the right position.
since the compound does not pivot on the center of the ball, the carriage and cross slide will require some fiddling to successively apply the form tool. Roughing it in somehow will make all this work a lot easier.
Liberal application of successive grades of abrasives will help make the ball look better.
As to 360 degrees on the compound, you need at most 180. If the form tool spans say, 20 degrees, then you need just 160. You may need even less by creative positioning of the form tool in the tool holder. "on the fly" and adaptive metal removal is your friend here.
 

tcarrington

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#5
Should have looked up Mr Pete first. He and may others show a full radius form tool. Great for features small enough to existing on the lathe bit. But maybe this will give you the idea.

 

Video_man

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#6
It's possible, if a little tedious, to rough out a ball by making parallel cuts of different depths with a cutoff blade. Then smooth with files and abrasive paper. I've done it, it works, and made an Excel spreadsheet to calculate the cuts, if it's any help. Guy Lautard described the process in one of the Bedside Readers several years ago.
 

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whitmore

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#7
I have never had a need to turn a radius, a ball but would like to know. I read somewhere
(cant find it) it is possible on what you have in being a standard tools. If my compound rest
would only turn 360, but it won't.
Shouldn't that be 'turn 180'?

If you can attach a tool/holesaw/shell reamer driven on a second axis, that can
do it, too <
>
 
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