i'm trying to mill (or whatever) a seat for a 2 in. steel sphere in a plate. the only way that comes to mind is to mill it with a ball end mill of the same diameter, but a mill cutter this size will cost hundreds of dollars. are there any other ways to get the job done? thanks for any help!
rtv
What is the size of the plate? Ray Mueller
Suggest that you think of using a 'church steeple' design instead of 2 matching spheres. The church steeple is a cone into which fits the 2 in steel ball. The problem with the seat and the ball both being spherical is that the 2 spheres will never match perfectly, either too tight or too loose.
Roger
I agree with other posts that you're more likely to get a precise fit with either a cone (church steeple) or just a round hole -- but I don't know your application. If you want a spherical cavity, it can be done with tooling you probaby have on hand.
As Brent suggested, you can mill a spherical cavity using an endmill or boring head and a rotary table. Either the rotary table must be tilted at an angle or you must tilt the head of your mill.
I've written this procedure up in an article for Guy Lautard's next volume of "The Machinist's Bedside Reader" (TMBR IV) but I'm certainly free to share it with others since Guy doesn't pay me for my contributions. I'm mostly retired and am in "give back" mode now.
I've no doubt Brent could write it up as well and maybe better.
I didn't invent this procedure; it was written up in a magazine (not HSM) some years ago but that article left "the math" to the reader. All I did was reduce it to a procedure that anyone who can use a calculator with trig functions could follow. I've made a number of things, both parts of spheres and spherical cavities so I know it works. It can and has been done to optical precision as Brent noted.
Let me know by email if you'd like to see the article. It's written in MS Word. Note that it is copyrighted material, but feel free to use the described procedure to make all the parts you'd like.
If it saves you hundreds of dollars then token compensation would be nice but certainly not necessary or even expected.
You'll need to get past the spamblock in my email address, no apologies for that.
The optics industry uses an interesting technique to generate spherical surfaces in glass using a flat ended diamond wheel. I googled to find some good pictures of the process, but I didn't find any that would make sense to someone not familiar with the process. If you have a milling machine with a rotary table, (cnc control isn't necessary) it would be possible for you to make the feature you want with a much smaller, conventional flat end endmill. In fact, I remember seeing an article on the process in "Home Shop Machinist" where the author uses a fly-cutter to generate a ball end, which is basically the same process reversed. If you're interested in doing it this way, I could try to describe it for you. I've never tried it myself, so I haven't thought through the process you would have to go through to set it up.
Brent.
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