# Made a sphere



## Bill Kahn (Apr 6, 2020)

Following Stefan’s youtube video






I made a copper sphere and a brass sphere.  (Well, sort of spheres.  I am not at all sure how to measure how close to a sphere some random lumpy shape is, but these random lumpy shapes roll pretty nicely on my granite plate.  But also, not near as nicely as a ball bearing does.)

Given copper is anitmicrobial, and that small balls are fun to roll around and just have in one’s pocket, and the times suggest antimicrobial about now is particularly useful, I combined the three ideas.  I can pretend they are not just pretty, but useful.

-Bill


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## eugene13 (Apr 6, 2020)

Like Captain Queeg (Humphrey Bogart) in the movie "Caine Mutiny"?


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## benmychree (Apr 6, 2020)

I don't think I'd count on them for protection from COVID


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## Winegrower (Apr 7, 2020)

They LOOK pretty dang spherical.    And nice finish!


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## Bill Kahn (Apr 7, 2020)

Here are some annotated snapshots of the sphere steps.  I tried to visualize what Stephan tried to explain.  But even after working out the boring bar sweep diameter, cylinder diameter and length, and the tilt angle, and carefully watching the cylinder become a sphere .01” at a time, I still don’t feel like I actually understand it. Three dimensional geometry is hard.  -Bill


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## bakrch (Apr 7, 2020)

'sphery nice.


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## Lo-Fi (Apr 7, 2020)

Really fun, isn't it! I tried my hand at it too, made some missing balls for handles on my bridgeport after watching that video of Stefan's. 

How did you manage such a lovely finish?


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## Bill Kahn (Apr 7, 2020)

Lo-Fi said:


> ...
> 
> How did you manage such a lovely finish?


Oh.  I like yours—it is useful, not just decorative.  (Even if I do like to believe my copper will ward off evil spirits.)

Finish is just sandpaper.  Mount on the lathe and start at 220 to get the machining lines off.  Then work through every grade.  320, 400, 600, 800, 1000, 1200, 1500, 2000, 2500, 3000, 5000 was my sequence.  It is just 20 seconds at each grade.  600 RPM. And it gets pretty nice.  As I roll my balls on the floor (fascinating learning that the floors of a fairly new house turn out are not actually level) I will not bother with any polishing sequence.  If you do try to polish, by holding by hand on a buffing wheel, heads up.  A fraction of a second inattention and the ball slips out and hits the concrete floor and, well, so much for a nice finish. Yeah, ask me how I know.  I love how we all just post the stuff that worked out on this forum.  I had 4 earlier (I call “study pieces”) failures before getting something to work adequately.  To get the creation navel “sphere-ized” and polished up took some fiddling.  I may make another and snap some photos to show how I did. Nothing I am proud of.  Not elegant.  But worked.  -Bill


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## tjb (Apr 7, 2020)

Bill Kahn said:


> I may make another and snap some photos to show how I did.


Would love to see that.  I'm sure I'm not alone.

Regards,
Terry


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## Lo-Fi (Apr 7, 2020)

Bill Kahn said:


> Oh.  I like yours—it is useful, not just decorative.  (Even if I do like to believe my copper will ward off evil spirits.)
> 
> Finish is just sandpaper.



Nicely done, and thanks  I left mine with the machine finish as I quite like the swirly pattern. 

I've got some video, I'll post up if it's any good.


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## Bill Kahn (Apr 7, 2020)

Lo-Fi said:


> ... I left mine with the machine finish as I quite like the swirly pattern. ...



I agree 100%—the swirly pattern is really gorgeous.  My sanded-to-polished finish is actually a cover-up.  My kludge to sphere-ize the creation navel results in a very different surface finish over the .3” diameter navel.  It may actually be nicer to leave with the navel, except one particularly attractive property of a sphere is its complete symmetry.  So, to get rid of the asymmetry induced by having the navel, I had to change the surface finish everywhere.  So, I pretend that I actually want the polish look.  If you can’t have what you want, want what you have. As the swirl pattern is, indeed, spectacular, I may make another and leave the swirl pattern (and the navel).  -Bill


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## DiscoDan (Apr 7, 2020)

I just watched another version of how to turn a ball with a boring head but it was on a lathe. It looks a little bit easier than doing it on a milling machine. Here is a link to it.


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## Lo-Fi (Apr 7, 2020)

I did wonder if removing that was part of the reason. 

It should be possible to make some interesting patterns by doing the first op, popping in the lathe to part, then mounting on a superglue arbor with the pip facing out and doing another pass. Could be pretty cool. Changing the angle would change the overlap in the middle


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## Bill Kahn (Apr 10, 2020)

tjb said:


> Would love to see that.  I'm sure I'm not alone.
> 
> Regards,
> Terry


OK.  Here is the best explanation I could come up with for how I got rid of the navel.  It is a kludge from start to finish.  As a beginner I just try stuff.  The failures (many) go into a box I call “study pieces.”  Now and then, something works.  This one worked.  But I would love to learn how real machinists machine a (complete) sphere.  I will try to past all 24 annotated pictures here.  If a single message can’t take so many pictures, I’ll just see what it took, and then post the rest.

-Bill


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## tjb (Apr 11, 2020)

Bill Kahn said:


> OK.  Here is the best explanation I could come up with for how I got rid of the navel.  It is a kludge from start to finish.  As a beginner I just try stuff.  The failures (many) go into a box I call “study pieces.”  Now and then, something works.  This one worked.  But I would love to learn how real machinists machine a (complete) sphere.  I will try to past all 24 annotated pictures here.  If a single message can’t take so many pictures, I’ll just see what it took, and then post the rest.
> 
> -Bill
> View attachment 320490
> ...


Thanks for the excellent write-up.  Very impressive work.

Regards,
Terry


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## Lo-Fi (Apr 11, 2020)

Interesting, mine didn't come out with the oddly shaped tip. I set up a CAD drawing where I can set the desired sphere and holder radius and it spits out the angle and other measurements for me, which saved a lot of potential calculation errors. 

Thanks for the excellent write up.


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## Bill Kahn (Apr 11, 2020)

Lo-Fi said:


> ...I set up a CAD drawing where I can set the desired sphere and holder radius and it spits out the angle and other measurements...


That is very cool.  I do not understand the multiple parameters.  I get that I set the cylinder diameter (D) and tab diameter (d).  I then set the boring bar sweep diameter to be (a smidge under) the cylinder diameter.  I set the the cylinder up-angle so it is horizontal from where the top of the tab touches the cylinder to the middle of the cylinder.  I center the mill’s Y on the cylinder.  Maybe I am not positioning the X correctly?  I position so the boring cutter just touches the center of the end of the cylinder. (Well, as Stefan said, a smidge inside the cylinder of that position.  I have the sense that the centrifugal force on the boring cutter expands its diameter a bit.  I feel like it is a few thou.  But maybe it is more?). I am not really sure how long the cylinder should be.  I have guessed it needs to be longer than the diameter.  Maybe like 1/(cos(atan(d/D)).  But I am not confident this analysis is correct.  Other than that tiny axial end knob everything else ends very spherical (well, constant diameter, which is not really the same, but I’ll pretend).

What system do you do the CAD in?  Is there a way to post your logical construction process (not simply the drawings)?

-Bill


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## Lo-Fi (Apr 11, 2020)

Actually, I can share my OnShape document. All you need is a free account and you can tweak the parameters to suit. No prior knowledge required, just put you numbers in and the drawing will update itself. If anyone is interested, I'll do a little video explanation. Stefan's was great, but he missed some of the basics like setting the cut radius and lining up. I'll get on it


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## Lo-Fi (Apr 11, 2020)

Bill Kahn said:


> Maybe I am not positioning the X correctly? I position so the boring cutter just touches the center of the end of the cylinder



Actually, just re-read this. I did the same, then moved X so the cutter was going to be 0.1mm inside. I reckon that's maybe where you might improve the end. It just seemed like the right thing to do, if that makes sense?


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## Bill Kahn (Apr 11, 2020)

Lo-Fi said:


> Actually, just re-read this. I did the same, then moved X so the cutter was going to be 0.1mm inside. I reckon that's maybe where you might improve the end. It just seemed like the right thing to do, if that makes sense?


Yes.  I did follow Stefan and moved it a smidge inside.  Maybe I need to move it two smidges.


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## Bill Kahn (Apr 11, 2020)

Lo-Fi said:


> Actually, I can share my OnShape document. All you need is a free account and you can tweak the parameters to suit. No prior knowledge required, just put you numbers in and the drawing will update itself. If anyone is interested, I'll do a little video explanation. Stefan's was great, but he missed some of the basics like setting the cut radius and lining up. I'll get on it


Thank you so much.  Yes, I have an OnShape account and have played with it a bit.  Have enjoyed it.  I will learn a lot in looking how you set this up. Thanks.  -Bill


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## Janderso (Apr 11, 2020)

Maybe I missed it, what angle are you putting the spin indexer device?
Is it even that critical?


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## Bill Kahn (Apr 11, 2020)

Janderso said:


> Maybe I missed it, what angle are you putting the spin indexer device?
> Is it even that critical?


What I do:  Let d=diameter of the tab.  D be the diameter of the cylinder.  The _angle_ I use is atan(d/D).  At this _angle_ the cutter is just starting to cut the top of the tab at the same height as it is (finally) also cutting the very middle of the cylinder.  If the angle is less than this (a flatter cylinder) then the cutter starts to cut into the tab before it has quite gotten low enough to round the middle of the cylinder.  Connected to this is how long the cylinder is.  What I do is L=D/cos(_angle_).  So, if you set the angle to be greater than _angle_ you find your cylinder is not long enough and to save the piece you raise the boring bar, reduce D, and come down again.  (Yeah, ask me how I know.)  Effectively you are back solving for D given the (too large) angle you did set.

Now, all this being said, I am not a geometrician.  So this is just me noodling and doodling, and having now made 6 of these (3 not working out for various reasons). If anyone on the list can do the math more carefully, I would love to see the correct solution.  (https://meta.wikimedia.org/wiki/Cunningham's_Law      Cunningham's Law)

-Bill


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## Janderso (Apr 12, 2020)

Gosh Bill,
I’ll need to noodle and doodle a bit to work out your formula.
You make it look easy.


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## Bill Kahn (Apr 17, 2020)

My 7th sphere now made.  Aluminum this time, so, no antimicrobe properties.  BUT, this one is *3.4”* in diameter.  Which is much much bigger than the 1” and 1.2” ones I had been making.  Of course, a picture of a sphere of any size always looks the same, but here is a snapshot anyhow.  ThE size required some adjustments to my method—nothing big, but it is interesting how some machining operations do not scale.  This sphere came out more spherical than any of the others.  3.400” +/- .002”. So, far from ball bearing quality, but rolls on the surface plate just like a ball bearing.  No way to tell it isn’t a sphere by feeling it, watching it roll, or looking at the reflections.  You really do need (long jaw) calipers.

You can see I worked on the surface finish.  Aluminum polishes up nicely.  For the final polish Mother’s Billet polish worked well.  The snap shot catches the overhead recessed lights, which are close to point sources.  And you can see diffraction spikes coming out in a few directions.  This indicates that on one of the (many) sanding steps, I did not take enough time to get the previous sanding gouges out.  Actually, I think it was the very last step, going from 2500 to 3000 grit.  So, it would not really be that much work to take it back to 3000 again and repolish.  But, this is a sort of geeky thing.  If you are not looking for diffraction spikes off of point sources, it is really quite shiny.  And, maybe a small point of physics instruction someday for some teen-aged aspiring scientist.

So, (in addition to many other things) I have now machined all five Platonic solids.  And spheres.  Three years in now and still loving this hobby.

-Bill


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## Lo-Fi (Apr 17, 2020)

Fantastic! That finish is incredible! 

Sorry I've not got round to posting up drawings and suchlike yet, I've been way too wrapped up in a little project myself. I'll get something sorted over the weekend.


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