Thanks Geof for the fast reply. But how do you make the cup where the ball floats in?
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 bradleybees4@gmail.com
Thank you in advance.
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.??
An open mind is a virtue...so long as all the common sense has not leaked out.
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
i don't regard this as an effort, but as the " right thing to do "; in other words, is " a must "this might seem a lot of effort just for a big aluminum ball. It is but it has a purpose
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 X0Parting off is not advisable because when your spinning sphere drops down and bounces around inside the machine the surface gets damaged
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
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 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
pls check attached document : it shows a kyocera tool, designed for this, starting from dia16The 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
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
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 )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
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
is ok to have an external thread, but threaded assemblies have tolerances that, if not controlled, may lead to misalignment ...The holder is the cylindrical part with an external thread ...
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