Machining a ball


My Garmin NUVI 500 for my bicycle uses a ball mount. The one that I
purchase from a third party is hollowed plastic and broke from
vibration. I adapted the broken piece to my light bar and it broke
again at the ball.
I toyed with several methods. One buy a ball turning tool, two find a
ball and mount it to a post. The ball was .670 inches and I didn't
find any one that size.
I decided to make a form tool for a section and move around the ball
shape. The critical section is smooth as the female move up to the
major diameter and that the major diameter size is maintained. The
down side also needs to be smooth for a short distance.
I Machined a rectangle piece of aluminum leaving the head 3/4 inches,
in three direction. The post section is 3/4 X 1/2 inches. Pictures are
here.
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Reply to
mac
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It would have been 17mm
Mark Rand RTFM
Reply to
Mark Rand
It looks like this worked well enough for you.
In the optical lens industry, spheres and spherical sections are generated using a cup-shaped grinding tool. The workpiece is rotated, the tool axis is at an angle to the workpiece and spun more quickly. The edge of the cup is aligned over the apex of the workpiece, and then the tool is moved into the work parallel to the workpiece axis. Here is a rough diagram of how it works:
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radius generated will depend on the diameter of the tool and the angle. It can make very precise spheres that are the ready for (very) fine grinding and final polishing. Perhaps you can do this with a tool post grinder on a metal lathe.
Reply to
anorton
Making a bunch of taper cuts to rough out the sphere, then filing it 'round' on the lathe may work well, too.
Your technique works, obviously, and would be the way to go if you need to make a ton of parts. Probably makes a more precise ball, too, if you get the contour of the tool correct. (In fact, this may be a good way to make something like a Cox engine connecting rod).
Reply to
Tim Wescott
========= or see
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some ideas on how to make your own.
Unka George (George McDuffee) .............................. The past is a foreign country; they do things differently there. L. P. Hartley (1895-1972), British author. The Go-Between, Prologue (1953).
Reply to
F. George McDuffee
Om a metal lathe..CNC..it can be done in one simple operation.
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If you think there may ba a market for your new mount..Id be happy to turn you onto people who could make these and other parts cheaply and quickly. You might have a new product!!!
Gunner
Whenever a Liberal utters the term "Common Sense approach"....grab your wallet, your ass, and your guns because the sombitch is about to do something damned nasty to all three of them.
Reply to
Gunner Asch
That's exactly how I did it. It's not a precision thing, doesn't even have to be very round. Mine is still a bit oversize and tight. I'll whittle it down a bit more if I find that it needs it.
Wayne
Reply to
wmbjkREMOVE
le.
The history of my home machine shop, It was a belt sander and drill press with a cross slide vise. I had help a friend set up his three in one machine. I thought that if I could come up was a reason I would buy one also. A little while later I read about a free coasting gearing for a tandem bicycle. I shopped around for a unit to modify our tandem bicycle. A bicycle shop wrench, that the name they go by, said that this type is just a couple of BMX free wheeler mounted. The shop wanted 500 dollars for the set of gears. That was my excuse to spend 1500 dollars for the three in one. Bolt circles and other calculation made for a fun take off for my shop. I docketed many of the projects on my web page and posting on in this group.
Thanks, but I don't see a market, Several are made for motorcycle that are stronger.
Reply to
mac
mac explained on 1/24/2010 :
Get a good mount?
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've used their mounts for a different model. I did make an addition so the mount could rotate on the bars
Wayne D.
Reply to
Wayne
Neat Bill, and good to hear from you. It's been a while.
Reply to
Don Foreman
Thanks Don; Good to see your ping also.
Reply to
mac
A long time ago in American Machinist, there was an article that showed how to make a perfect ball on a Bridgeport (actually half a ball). Tilt the head at 45 deg. Put in a fly tool with exactly the radius you want, mount the part on a rotary table and start moving the tool to the part very slowly, while turning the table. Said to make near perfect hemispheres. In a small size, wouldn't take all that long, I'd guess.
Karl Pearson
Reply to
aslub
I developed and expanded on this in an article I wrote to go into a next version of Guy Lautard's "Machinist's Bedside Reader" which never happened. It's mine to share, ping me if you'd like a PDF of it by email.
Reply to
Don Foreman
If you have a mill, a tiltable indexing head or rotary table and care to provide a valid email addy, I'll send you an article I wrote, in PDF format, about making balls and spherical cavities with a flycutter. I didn't invent this technique and I acknowledge and credit the previous article mentioned by another poster. I merely tried to discover and teach how to do it since previous documentation was vague. I derived the various formulae I presented, and verified them both theoretically and in the shop.
I have reported examples of my work with this technique to RCM by reference to my website. I've since removed in favor of more current activities but will rehost if anyone is interested.
Reply to
Don Foreman
Yes, please.
--Winston
Reply to
Winston
I's like a copy. The above email is real.
Perhaps it would make a good addition to the Dropbox?
Thanks,
Joe Gwinn
Reply to
Joseph Gwinn
OK
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I'll leave it up for a couple of weeks.
Reply to
Don Foreman
I'll respond by email. I don't want to put it out on the internet because I want to respect Guy here. I wrote it, gratis, for him to include in a forthcoming Machinist's Bedside Reader -- but that was a decade ago and TMBR4 still hasn't happened. The only version I still have contains some editing by him, though no material content. He did tell me he had no objection to my sharing it with individual interested metalworkers. I've not heard from him for several years now but he's still alive, his website is current.
Reply to
Don Foreman
Extremely cool.
Thanks Don!
--Winston
Reply to
Winston
I got it; thanks.
Understood.
Joe Gwinn
Reply to
Joseph Gwinn

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