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Stevelr
10-18-2003, 02:44 PM
Here's a question for the professional and experienced machinists from a amateur.

Is it possible to make a sphere/ball on a lathe?
(between .5 and 1 in) Is special tooling required? What kind? Where can I get information on machining such an object?

Thanks for any advice and help.

Steve

Evan
10-18-2003, 02:50 PM
Short answer is yes. Have a look at this page. There is a mistake on the page, the caption for the first picture is wrong. It is really a boring bar holder.

http://www.statecollegecentral.com/metallathe/MLA-13.html

SGW
10-18-2003, 03:27 PM
Here's another kit for a ball-turning attachment: http://www.jerry-howell.com/Radius.html

You can also buy ready-made ball-turning attachments, of coursed, but the price will likely make you choke.

It's also possible, if you have something like a South Bend on which the comound pivots on a spigot, to set the tool "behind center," loosen the compound locking screws, and turn at least a partial radius by rotating the compound. It's pretty difficult to set that up accurately, though.

As you may surmise, it's not possible to turn a *complete* ball, there has to be at least some amount of neck left to hold onto it with, but that can be made pretty small. Some ball-turning attachments are better at doing a complete ball than others (the clearance provided by their design).

wierdscience
10-18-2003, 08:52 PM
Not a complete ball,but you can finish 2/3s of it,saw it off and then chuck the ball in a collet or spigot chuck and finish of the stub.

Dr. Rob
10-19-2003, 04:35 AM
Two things come to mind...I hope nobody has forgotten the sharpened tube trick: Take a steel tube, sharpen the end, and rock it back and forth and around the roughed-out workpiece. Depending on material, it works rather well.

Second, really decent steel balls are available commercially for so little $, that it often isn't worth the effort. (ball bearing suppliers or ball handles from machine / fasteners suppliers)

John Stevenson
10-19-2003, 06:21 AM
As people have remarked yes it can be done and there are various ways to do it.
A simple way for doing a few or lot of the same size is the old file trick.
Take an old file and soften the end in a fire, drill a hole to the size you want the ball and cut a slot in the side to the width of the stem, reharden, temper and grind and stone the top face.
To use it, place a bar in the toolholder to just stick out and using this as a pivot point start the lathe and lever the file upwards against a crude precut ball. This will then shave to a perfect sphere.
As they say a picture is worth a 1000 words so here's 2000.
http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/ball1.jpg
http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/ball2.jpg

Another lathe method is the radius attachment type but here you can cheat and instead of moving in a horizontal plane and going round the ball side to side you can use an el cheapo boring head and go vertical, top to bottom. Another 1000 words.
http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/ball3.jpg

Balls can also be done on the milling machine by using the dividing head set to an angle and a flycutter. Kinda hard to explain but the pic shows it all.
http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/ball4.jpg

HTH
John S.

[This message has been edited by John Stevenson (edited 10-19-2003).]

SGW
10-19-2003, 08:43 AM
Can you elaborate on the dividing head and flycutter a bit? Dim as I am, I don't follow that one.

wierdscience
10-19-2003, 12:19 PM
Love the boring head setup,I have to build one.

John Stevenson
10-19-2003, 05:33 PM
<font face="Verdana, Arial" size="2">Originally posted by SGW:
Can you elaborate on the dividing head and flycutter a bit? Dim as I am, I don't follow that one.
</font>

SWG,
There is a formula to use to work out the angle based on the diameter of the ball [2r] and the shank diameter [b]
You then set the dividing head to this and set the boring head to the diameter. Then bring the boring head down to the centre of the ball and lock off.
Then rotate the ball using the dividing head crank, what is low on one side will be high on the opposite side after it has done 1.2 a turn. By the time the DH has done a full turn you will have generated a perfect sphere.

This sketch came out of a book called 20 [ or 50] simple machining setups. Unfortunately I went to find it tonight to get the formula and I can't seem to locate it.
The problem is I have too many books http://bbs.homeshopmachinist.net//biggrin.gif
I have a good idea which room it's in but it's hiding. I really need to catalogue these books, when something happens to me someone is going to have a field day http://bbs.homeshopmachinist.net//frown.gif

John S.

Stepside
10-19-2003, 07:10 PM
With just a lathe and Guy Lautards description in his bedside reader or his tables for turning balls and spheres book you can turn a ball.
Or: if you have a CAD program just draw the Diameter required and then draw a line from center to "6 o'clock quadrant". array this line every .010 each direction from its starting point until you have covered the entire ball. Measure the distance from the circle to the end of the line and record the values. The recorded values are your "X" travel and each .010 is your "Z" travel.
I use a travel indicator in each axis. I also start at the far left or ouboard value and cut in increments going to the equator and then move to the far right and do the same excep that I leave a spigot where it is in the chuck. The next step is a coat of blue layout dye and then file while it is moving. When the blue is gone you have a pretty decent ball. I use a .010 increment but you could use a greater distance --It would require more filing and would result in less accuracy. For a cutter I use a cuttoff tool.