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Elninio
02-28-2011, 12:32 AM
While looking for tangential tool designs, I found a page of a man who produced his own QCTP using only a lathe, and this design of a sphere cutter that I've not seen before;

http://peake-engines.com/resources/Lathe_Modifications/QCTP/QCTP%2035.jpg.opt631x473o0,0s631x473.jpg

His page here: http://peake-engines.com/quick-change-tool-post.php

randyc
02-28-2011, 01:32 AM
The means of creating spherical shapes are limited mainly by imagination, LOL. Did this male ball-joint part a few weeks ago with a hole saw held in an ER-40 collet (photo is of the "proof" piece, made from aluminum).

http://i97.photobucket.com/albums/l219/randy9944/P1020346.jpg

An angled rotary table was used to generate the sphere although normal procedure would have been to use a boring head rather than a hole saw. (This experiment worked out well BTW, removing material about three times as fast as the boring head.)

Carbide router cutters can also be useful to form special profiling shapes in the lathe, including spherical ones. The cutters are inexpensive and all that's required is to make a toolholder for the 1/2 shank diameter... I use them in the vertical mill as well.

Cheers,
Randy C

Elninio
02-28-2011, 02:29 AM
Ooooo that's slick! Does it produce a nice finish like in the picture - or is that a camera effect from the oil?

Forrest Addy
02-28-2011, 03:41 AM
Used to hone monel and titanium submarine sea valve balls with a similar but scaled up arrangement. A radius rotated around one axis will generate a sphere on another intersecting and rotating axis at an angle to the first. I designed and built the ball honing machine but then I had to run it. Boring job honing corrosion damage off corrosion resisting valve balls.

Used to hold the round to 0.0005" if I felt like taking on the challenge.

Ed P
02-28-2011, 08:11 AM
This design of spherical turning tool is a take-off of the J. A. Radford design. I know because I made one identical to Radford's. See "Improvements & Accessories for Your Lathe" by J. A. Radford. Its advantage is the very quick and simple setup time. Slap it in your toolpost, adjust the cross slide until the cutting tool is on the centerline, bring the tool down to the workpiece, move the saddle over, rotate the turing tool 90 degrees and touch the end of the workpiece and lock the saddle. You're ready to go.

Ed P

TGTool
02-28-2011, 11:00 AM
I've made one that's a variant on the Radford design that looks like this:

http://i48.photobucket.com/albums/f244/TGTool/b683a16f.jpg

I've also got drawing sets and kit of materials and components required. Designed around AXA but the dovetail can be enlarged for BXA if required.

randyc
02-28-2011, 12:18 PM
Ooooo that's slick! Does it produce a nice finish like in the picture - or is that a camera effect from the oil?

Mainly from the cutting oil - when a hole saw is used, some polishing is normally required. Using a HSS boring bar with a polished radius produces a better finish and finer tolerances can be achieved.

FWIW, here's a sketch that I made for producing ball-joints that have been useful to me. The dimensions are "normalized" to one inch. Any ball diameter can be produced by multiplying the constants in the sketch by the desired diameter:

http://i97.photobucket.com/albums/l219/randy9944/millballturn.jpg

randyc
03-01-2011, 01:01 AM
Coincidentally, this same topic came up on PM tonight and reminded me of a few other similar operations performed recently. This is a 3-1/2 inch diameter workpiece with a concave radius of 22 inches.

http://i97.photobucket.com/albums/l219/randy9944/P1020349.jpg

http://i97.photobucket.com/albums/l219/randy9944/P1020354.jpg

A decorative addition using a router cutter in a vertical mill; the workpiece is rotated in a rotary table. By angling the rotary table, other interesting shapes can be produced.

http://i97.photobucket.com/albums/l219/randy9944/P1020331.jpg

Another router cutter in a shop-made 1/2 boring bar holder in the lathe.

http://i97.photobucket.com/albums/l219/randy9944/P1020319.jpg

randyc
03-01-2011, 01:02 AM
Producing a spherical radius on the end of a steel crank handle in the lathe with inexpensive router cutter.

http://i97.photobucket.com/albums/l219/randy9944/P1020272.jpg

Router ball cutting tool mounted in a hastily-constructed aluminum toolholder:

http://i97.photobucket.com/albums/l219/randy9944/P1020277.jpg

Plunging the ball cutting tool into the steel handle (radiused with the router cutter shown above) plus a couple of additional operations results in a small crank handle in less than 1/2 hour:

http://i97.photobucket.com/albums/l219/randy9944/P1020282.jpg

Making radius on the end of a steel rod, incrementing the carriage .005 at a time and the cross-slide by the amount computed from a spreadsheet (made years ago) for decorative balls of odd diameters. Parting tool is used to plunge to depth, after which the ball is blued.

http://i97.photobucket.com/albums/l219/randy9944/P1020293.jpg

randyc
03-01-2011, 01:03 AM
Ten or fifteen seconds of filing removes almost all of the blue markings.

http://i97.photobucket.com/albums/l219/randy9944/P1020294.jpg

Another twenty seconds of polishing with emery cloth and the ball joint is ready for the next operation.

http://i97.photobucket.com/albums/l219/randy9944/P1020298.jpg

Fun stuff and sometimes useful for other than decorative purposes !

Randy C

TheAndroid
03-01-2011, 11:24 AM
Coincidentally, this same topic came up on PM tonight and reminded me of a few other similar operations performed recently. This is a 3-1/2 inch diameter workpiece with a concave radius of 22 inches.

What is the math behind this? I understand the offset of the piece, but is the head tilted? What exactly generates the 22" radius?

randyc
03-01-2011, 01:52 PM
What is the math behind this? I understand the offset of the piece, but is the head tilted? What exactly generates the 22" radius?

The angular relationship between the mill head and the rotary table and the radius of the flycutter determines the finish configuration - in the photo of the large concave part, the rotary head was tilted while the mill spindle remained vertical. In the photo depicting the small ball produced with the hole saw, both the spindle axis and the rotary table axis were angled. This wasn't strictly necessary - as I recall it was a matter of convenience to prevent interference between the tooling and the jaws of the chuck or some such trivial matter.

Making this type of set-up using spherical calculations is not something that I would be anxious to do - they just aren't required very often. For me it's much quicker and easier to work these types of problems graphically, using a CAD application. In post #7, I linked a drawing of the most common set-up that I use to produce small balls (for sockets, I generally use a ball end mill or router cutter and ream to shape). The sketch is normalized to one-inch diameter balls. By multiplying the desired ball size by the constants shown, any ball of that configuration can be produced in a vertical mill with the rotary table or dividing head angled at fifteen degrees.

Here's an interesting discussion of the process from a guy in Britain who does this routinely (and from a few of the forum members who observed the process):

http://www.practicalmachinist.com/vb/general/generating-spherical-surfaces-139400/

I have no access to the measurement equipment he mentions so the absolute sphericity of the generated surface of large spheres is not known to me - I can only calculate the spherical radius from the length of the chord across the part and the distance from the center of the chord to the concave surface at its deepest point. There is a table in my old edition of "Machinery's Handbook" that simplifies the calculation (normalized table of circular segment properties).

Apparently this is a common technique for some ... one of the guys that commented in the above thread mentioned using the process to create molds for cannon balls. (Although I've made accurate small ball-joints using the above methods, I've never tried mating large concave/convex surfaces like the one shown above.)

Elninio
03-03-2011, 05:51 PM
Found a video of a really really cool sphere turning QCTP:
http://www.youtube.com/watch?v=u2cqmSFYRDE&feature=related