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TGTool
02-27-2008, 04:13 PM
I received a question recently on whether the up and over ball turning tool could also be used to form concave radii. At first I thought not, but on reflection realized that all the necessary movements were there if the tool could be positioned. The regular straight-in tangential cutting tool was out, but with the right holder a cutting edge could be presented.

Voila.

http://i48.photobucket.com/albums/f244/TGTool/P1010026.jpg

Not something I'd want to do with any regularity, but it's cute to know that it can be done. (RIP #4 tap)

DickDastardly40
02-27-2008, 04:31 PM
My ball turner has a internal cranked holder shown loose (not tried it myself yet).

http://i199.photobucket.com/albums/aa317/DDastardly/Picture050.jpg

TGTool
02-27-2008, 05:14 PM
Some nice features of that design. I like the coarse and fine feed settings. It gives up the tangential cutting that Radford's original had which could simplify toolholding for diameters larger than the hub and might give a little more rigidity. Thanks for posting.

DickDastardly40
02-27-2008, 05:24 PM
I've posted some pics of this before, here is the whole thing and a photo'd page of the instructions:

http://i199.photobucket.com/albums/aa317/DDastardly/Picture049.jpg
http://i199.photobucket.com/albums/aa317/DDastardly/Picture.jpg

Al

Evan
02-27-2008, 07:22 PM
Now that I have a lathe on the CNC mill I'm going to try diamond turning a mirror from aluminum.

This is the parametric code for a parabola.

%
O8010(PARABOLA SUB)
#100=.5934
while[#100GT.0081]DO1
N1#101=SQRT[#100*15.168]
#102=.132*#101
#103=[#510/#102]*2
G1U-[RO[#103]]W-#510F.01
#100=#100-#510
END1
M99
%