[Tailgunner]

Thanks Geof for the fast reply. But how do you make the cup where the ball floats in?

[Geof]

Thanks Geof for the fast reply. But how do you make the cup where the ball floats in?

If you mean the cup that the water is pumped into this is just a cylinder with a square end. This I assume would be made on a lathe; I was just referring to making the ball.

[Jarith1993]

Here are the pics.

The partial sphere is first turned with a thick neck then the neck is thinned down before cutting it off. If the neck is made too small the ball bobbles around during the turning and chatters.

The holder for the finishing is held in the chuck and the inside liner skimmed true before use. This makes sure the partial sphere is held true.

Just enough protrudes to turn off the neck and finish the sphere.

This might seem a lot of effort just for a big aluminum ball. It is but it has a purpose. I am establishing the procedures for making aluminum spheres from around 2.4" diameter up to 3.4" both solid and hollow with varying wall thickness. I am working with a guy to start manufacturing really big ball Trackballs for computer access by people who have a physical disability so they cannot operate a regular mouse or trackball. We want to experiment with different size balls with different weights. Some potential users will have Cerebral Palsy so they cannot control fine motor function; for them a heavy ball that does not spin readily may be preferable. Other users may have Muscular Dystrophy or another muscle weakening disorder and they may find it better to have a very lightweight and easy to move hollow ball.

And maybe the whole venture will fall flat on its face and I will be left with a whole bunch of aluminum marbles to play with .

Hey Geoff I know this is an old post, but if you could shed some light on this process you would make my day.

I have so many questions with regards to this process.

I’m currently undergoing the same thing in work, where we’re turning the slug to 65% of a ball in the first operation.

But we’re having trouble holding the work when turning it around.

If you can let me know what tools etc you’re using and or a video of your process that would be a massive help.

If you’d like to contact me via email: my email [email protected]

Thank you in advance.

[Geof]

I cannot give much more explanation other than what I included with the pictures in an earlier post. The holder is the cylindrical part with an external thread and a replaceable aluminum insert. The insert is matched to the same as the ball and as I mention in another post this operation uses the same Z work offset as the ball finishing does. The ball with stem is then clamped in the holder with the stem protruding through the cap. I did not show this, just the finished ball in the holder. I machined past 65% to have more ball in the holder.

To do this of course you need tool compensation correctly setup and this could be part of your problem because you need to know the tool nose radius very precisely. I knew the nominal nose radius and experimented using different values for the nose around the nominal value until things worked. Maybe there is a more sophisticated approach such as using CAD/CAM but I am not that competent. I also really cannot remember any more detail because it was so long ago and after spending a large sum of money it the project did fall flat on its face.??

[deadlykitten]

hy geof, hi jarith, i will share a few things in this thread, including aspects for the 2nd fixture

jarith, i believe you should consider the solution shared by geof. If in doubts, then discuss it with the veterans inside the shop where you work ... also feel free to ask whatever you wish

this might seem a lot of effort just for a big aluminum ball. It is but it has a purpose

i don't regard this as an effort, but as the " right thing to do "; in other words, is " a must "

Parting off is not advisable because when your spinning sphere drops down and bounces around inside the machine the surface gets damaged

a parts cathcer may be used, and this parts cather has to be kept clean and lowered only when the cutting tool gets close to X0

the key for lowering the parts catcher at a later moment, just before the drop-off, is there in order to avoid filling it with chips

also, the parts cather should have a smooth advance/retreat movement, so to handle the "ball" with low cinetic energy, thus gentle

some parts catchers mechanisms may allow adjusting the advance / retreat speed, in order to smooth out the movement

also, after the parts catcher retreats, there has to be a box or something that allows the ball to fall without bouncing

some lathes have a part catcher that always bounces parts, thus there are some big distances between the "retreat position of the parts catcher" and the " collecting box, or conveyer belt, etc " .... for spheres, and other parts with fine threads eg, there sould be no "bouncing", in order to avoid damaging the parts

in some situations, is required to avoid "damaging" the part after/during the cut-off operation

The trueing up is done on a replaceable aluminum insert in the holder and trueing up is only needed at the start of a batch of spheres so you do whatever is the batch size each trueing up

this works but what about a setup, during which is not needed to "true up" by cutting ? also, that "aluminium insert" means an extra part inside the assamble, so, removing it, will remove all the plays betwen this part and it's neighbours less play means less tir ...

The difficult part with boring a full hemisphere is going past zero, or even getting to zero, on the X axis. The boring bar needs clearance and of course the sphere gets in the way

pls check attached document : it shows a kyocera tool, designed for this, starting from dia16

for diameters < 16, gang tools may be used

but, ... there is a but for holding a sphere, in order to finish it, is not needed to go towards 0 ... if the fixture goes towards 0, then stability is lost

Both the truing program and the sphere finishing program used the center of the sphere as Z zero; once a cut had been taken it was certain that Z zero was at the center

even if this works, is not ok to "cut", in order to set the zero ... consider that the fixture is true, or at least tir is within tolerance; in such a situation, if the fixture is cut, then it becames disposable ( in time, after 2-3 .. 50 cuts, etc )

fixture tir has to be adjustable, without cutting, and zeroing requires a calibration part / gauge ... this eliminates a few variables, and also assures the repetability among a greater period of time

The holder is the cylindrical part with an external thread ...

is ok to have an external thread, but threaded assemblies have tolerances that, if not controlled, may lead to misalignment ...

in other word, the contact between the nut and the part is not always located in same "geometrical space", and the "part" + "nut" are always tilting, thus their axis are not colinear with the main chuck ... but, in some situations, this may work

someday, i will share examples about how to achieve lower & repetable tir on a lathe, for 2nd operations, including ( but not limited to ) finishing spheres / kindly