Single piece, simple ball turner.

[tonyfoale]

I need to make some engine pushrod ends with a ball shape. In the past I have done this with carefully ground form tools. There can be two problems with this approach. Firstly, form tools can cause chatter and secondly there is a question of how accurately the shape is.
I have been thinking of building a ball turning attachment for several decades but there has rarely been a real need. i only make tools when I have a current need.
My initial ideas centred around "conventional" devices but as I was searching for suitable lumps of metal a much simpler and minimal work idea emerged. Most/all systems that I have seen pictures of don't seem to have a means of fine diameter adjustment. This is an important requirement for me. I guess making door knobs or lathe handles doesn't need it. Then I thought that I needed something like a compound rest slide to mount the tool on for diameter adjustment. That idea led me to ask why build something else when the cross slide can be rotated and is probably more securely held than the small pivots used by many designs of ball turners? So this meant that I only had to make a single piece, a tool holder that would put the cutting edge near the rotation axis of the compound rest. Job done.
Before use I'll need to clock up the the hole that the compound rest pivots on to centralize that using the cross slide and then lock it in place. That will put the rotational axis on the same longtitudinal vertical plane as the centre of the work piece, ensuring a circular ball rather than a distorted circle with pointed ends as is often seen on winding handles. Perhaps I should make some form of stop to eliminate the clocking each time.
There is one principal disadvantage with this design. The cutting edge of the tool is set a fair way back and the saddle can't get close enough to a chuck without a lot of workpiece overhang. There is also a compound rest rotational clearance problem ​with a normal chuck. Not so much of a problem with 25 mm and above material if the work piece is long enough to give enough overhang. For smaller diameters I have found that an ER25 collet chuck with a 5C shank held in a chuck on the parallel section works well. This ball turner is suitable for a wide range of ball diameters up to around 40 mm diameter, which is far larger than any anticipated work.
So i dug out a suitable steel block from the scrap bin and did the minimum amount of milling to enable tool holding and to give work piece and collet chuck clearance. I like to leave the maximum amount of metal in place for rigidity and general mass. I decided to build it to take 1/2" square insert lathe tools because it will give me great flexibility in the choice of cutting tool shapes. I machined the height of the floor of the tool mounting to put the cutting edge at the centre height of the work piece.


The machined tool holder block compared to the original lump of steel.


The block bolted in place on the compound slide in place of the usual tool post. The odd shapes milled away are for clearance as the compound rest is rotated.


Machining a 25 mm diameter ball end. Note the required overhang and the closeness of the fixed section of the slide to the chuck.


Machining a 12 mm ball end held in the ER25 collet. Since this photo was taken, more clearance material has been machined away and the overhang from the collet has been greatly reduced.

I don't claim that this is anywhere near the best ball turner out there but it does a great job and it must be one of the simplest to make and it is a solid and rigid implementation. I love simplicity and minimum work.

[tonyfoale]

here are a couple more pix. making a pushrod end, the base reason for making this ball turner. I mentioned that one of the reasons for making it to accept insert type lathe tools was the choice of cutting edges that can be used. Here I am using a round insert which leaves a smooth finish and blends nicely into the rest eliminating stress concentration.


Two views showing the turning of an 8 mm ball for a pushrod end cap. Click images for full size versions.

[olderdan]

Nice simple sturdy solution, I use my boring head in the up and over mode but do not have the precision requirement that you need, mostly for acorn nuts.

[tonyfoale]

Nice simple sturdy solution, I use my boring head in the up and over mode but do not have the precision requirement that you need, mostly for acorn nuts.

i did actually consider using a Criterion style boring head instead of making the tool holder but on balance i decided against it.

A memory damaged by age is a terrible thing. i remembered as soon as I finished it that I had previously considered two other methods for making ball ends.
1. i described a T & C grinder that I made in an earlier post to this forum. If I change the grinding wheel for an end mill then I could make balls on that.
2. I could put the work piece in the mill spindle and a lathe tool in the vice, sprinkle in a bit of G-code and hey presto.

Why wasn't it before I made this ball turner that I remembered these almost zero work options?

[DIYer]

Thanks tonyfoale! We've added your Ball Turning Fixture to our Machining category,
as well as to your builder page: tonyfoale's Homemade Tools. Your receipt:

Ball Turning Fixture by tonyfoale

tags: ball turning

[Toolmaker51]

(abbreviated) A memory damaged by age is a terrible thing. i remembered as soon as I finished it that I had previously considered two other methods for making ball ends. Why wasn't it before I made this ball turner that I remembered these almost zero work options?

Well you mentioned considering a ball turner for decades. Both other solutions are feasible, perhaps turning beats milling by eliminating 1 axis?
Any how, it seems memory is subject to more than just age...Few of us can create items quicker than conceive them.

[tonyfoale]

...... Both other solutions are feasible, perhaps turning beats milling by eliminating 1 axis?

You have lost me there, I see 3 axis involved either way.
In the lathe you have the rotary workpiece Z axis, the rotary Y axis of the compound rest to describe the ball circle and a linear axis of the compound slide for diameter adjustment.
On the mill you have the Z workpiece spin axis, the linear Z axis to traverse the work and either the linear X or Y axis (user or G-code programmer's choice) to trace out the shape and size.
If you have a rotary 4th axis on the mill then you would still need 3. The spin of the 4th axis, the traverse of the X axis and the linear Z axis for the shape and size.
I don't have a 4th axis yet but I have my eyes open for a small lathe head which I would drive either with an induction motor to use it as a high speed lathe or a stepper motor to use as a CNC 4th axis. A change of belt or a dog clutch would allow rapid swap between the two modes. Although my mill had only 3 axis control I took the precaution of setting up the control stuff for 4 axes to allow easy addition of a 4th.

[Ralphxyz]

I am just getting started with using a lathe and have a ball turner on my list of things to do.

Where is the pivot on you tool? Sure wish I could could see things live, posible a video of it in action would help.

But thanks!!

Ralph

[Toolmaker51]

You have lost me there, I see 3 axis involved either way.

I'm thinking along the set-up, manipulating knee and quill Z's [prior to locking] wherein lathe that's more 'built-in' addressing centerline. Maybe better size control too? Can think of last occasion to ball turn, no-one had the lathe version, used a boring head though. Difficult to get proper finish, heads aren't too great for decent corner radii on cutters. I wouldn't spend effort on form tool even with means to generate accurate cutter, on something like a push rod.

[Y-geo]

Ralph,
from my "library " :-

It is one of the variant "ball making Jigs " available commercially I have not seen (so far ) a how to make your own ball making jig/fixture.

PS you are in luck this is ONLY 23 mins long lolz