[cncz]

Hello all. What's the best method to accurately cut or shave 7/16" diameter flats into 5/8" brass balls? Need smooth finishes.

I may get a decent milling machine for other operations, but I'm wondering if there's a more suitable method than a milling machine for this. Thanks.

[txcncman]

Have you considered a Norelco ball shaver?

[cncz]

ya but it didn't work so well on brass. Any other ideas?

[fizzissist]

It might help if you'd show us your balls.

[cncz]

Can't do that. Don't want to scare you away.

I'm thinking a fly cutter on the mill would be the best method.

[txcncman]

For the size, I would use a 0.500" diameter 4 flute uncoated carbide end mill running about 2500 RPM and 20 IPM done in a single pass.

[Geof]

How many are you doing, fewer than a hundred or many thousands? You could do it in either case on a mill or a lathe. Probably your biggest challenge will be making something to hold the ball securely enough to machine it without putting marks on it.

[cncz]

Thanks txcncman for the help. With your suggestion, would I be cutting the top surface of the ball or the side surface of the ball? In other words, would the end mill bottom surface be doing the cutting or would the end mill side surface be doing the cutting?

Also, I prefer to stick with a mill that fits in a small space, but could get the job done without a fuss. Would the Grizzly G0704 be suitable or do you recommend something bigger?

Geof, I will be doing a few hundred. I've read of people having success bracing the balls with washers between the ball and the vice.

[txcncman]

I would set this job up for cutting the top of the ball off. I would use a vise with aluminum soft jaws. I would cut a flat bottom hole 0.350" minimum depth, in the vise jaws, spaced with a 0.0625" minimum gap, off center, up to 0.250", so that the ball will rest on the flat bottom and not the gap. I would provide some means to eject the part from this hole when machining is completed, such as a piece of wire.

[fizzissist]

.... Now that we know how many balls you have...

Starting out with a 5/8" ball mill, I'd take an aluminum rectangular bar and spot indents into the bar at about 2 to 3" intervals for the fixed clamping surface. (centered about .220 below the top edge of the bar so there's a few thousandths of clearance between the cutting surface and the bar)
Mount this bar with the indents facing sideways (for a conventional vertical mill) on a plate. On a similar, preferably thinner bar do the same thing with the ball mill, then cut it into segments with 2 indents/segment.

Using horizontal DE STA CO clamps ( Manual Clamps : DE-STA-CO ) or something similar, mount 1 clamp per segment such that it presses the middle of the segment against the stationary jaw with a ball secured in each "pocket".

The aluminum is soft enough to not mar the brass if you keep it clean between cuts, and the spherical pocket will give you a good clamping surface.

This way, you can easily have a row of 10 balls clamped, and with a 1/2" endmill face off the tops in one pass ( a 2nd light finish pass if your machine isn't real rigid). Clamping only 2 per segment with the force in the middle of the segment will assure uniform pressure, and should make loading the fixture easier. 10 up at a time means that you wont' be spending a week doing this job, and you've got a fixture for the next time you run it.

[cncz]

Thanks guys!

Instead of horizontal clamps, how about these (2 balls each)...


or...


Not sure how the latter would mount to the mill table.

[fizzissist]

To put this in perspective.....
Most of the suggestions you're getting here are from guys who are thinking short run production with tolerances in the +/-.005" range (or tighter!), surface finishes of 32micro, and picky QC people who will check for damage to the body of the part as well as dimensions.

Those vises shown will leave indentations in your balls when tightened enough to allow for safe machining. You need soft jaws that the balls will feel all warm and fuzzy in.

.................................

Turning in lathe:
Another method would be to make a "collet" type of clamp, with fingers that are tapered on the outside and have a spherical cup in one end... a correspondingly tapered sleeve can be pushed over the area of the cup with the ball inserted, then the whole contraption is placed in a lathe and secured in a large collet or chuck.

[cncz]

As per your suggestion, I would use aluminum flat bars between the vice and the balls, with "pockets" in the aluminum for the balls to brace between.

[cncz]

(Double Post)

While I'm at it, I gotta say that finding these kinds of solutions is exciting. I really appreciate the help.

[fizzissist]

We're not helping. We're coercing you into spending money to support your habit. It starts with the small tools.....

Muwahhhhhhhhhaaaaahhhaaaaa.....:bat:

...Then we talk you into buying the really expensive stuff.....

[cncz]

Yes I know. That's pretty much how I do everything I get into. The last thing I did this with was a bicycle, ended up spending 7k to do some riding with freinds, and I have very little money.

I'm learning. I'm spending my free time researching everything about the Bridgeport J head so I know how to inspect them and spot a great deal. Would eventually want to CNC a decent bridgeport so I can do my projects in house.

[TechGuy5002]

What about machining a custom concave cutter the diameter of the ball size, then plunge the custom tool into the brass, then flip the workpiece and plunge on the other side. This would permit you to cut the workpiece as two hemispheres.

I think this might be easy to machine a cutter. Cut a piece of flat bar steel into a square piece. Weld it to a rod (so it can be clamped into the spindle, Square up the flat with the welded rod (assuming you didn't get lucky with a perfectly square weld). Then side cut the flat steel square with an end mill as the same diameter of the ball size, so you have a half circle cut out.Hardened the steel and create cutting edges using a grinder. Just go slow (rpms) in case it binds up so if the weld gives away the cutting edge doesn't fly off and embed into your flesh.