[SRT Mike]

You know the type of connection that holds your cars rear view mirror on - where it's tight enough that it won't move, but loose enough that you can move it by hand.

Does anyone know a source for buying just the two pieces of such a joint? I imagine it would be tricky to get it just right, and stay right over time.

I'm working in 6061 AL, so preferably the joint would be made of AL too.

Also, if someone knows how to machine such a joint, I'm all ears

[NC Cams]

The "trick" to that joint is that the retentive force that keeps the mirror in position is achieved by careful sizing of the ball and socket in concert with a preloading of a precisely formed spherical joint.

The preloading is done by selective crimping of the socket or use a wave washer or some other sort of preload spring to load the ball socket. This exact method is used to preload ball joints in the front suspension of cars.

The preloading of ball joints is done via a gargantuan, "boxcar" coil spring (high rate, low deflection). Another method used was to use a chunk of rubber and preload it in compression behind a 2 piece spherical cupped joint that encapsulated the ball joint (lower rate, more compression). A third method invovled using a molded nylon cup that had selectively cored out segments. The remaining colums of nylon provided the preload "spring" that pressed the female cup against the ball when the joint is jambed together.

Finally, to prevent total siezure of the parts, you need to select materials that have the proper relative hardness and metallurgical compatibility. Choose the wrong materials and they will try to gall/sieze to/with each other or prematurely wear as they rub. Choose the wrong hardness and the parts will eventually yield or prematurely wear as well.

Machinging of a true sphere involves some careful machine programming. To precisely GRIND the sphere to even better/finer levels of roundness and smoothness requires some special grinding techniques.

Google the topic "grinding spherical radius" and a number of DIY techniques should show up. It seems that there are a lot of spherically ground surfaces used in telescopes - there are a number of DIY ways to grind spherical radii that the star gazers use.

Asside from size and levels of accuracy, the grinding of a ball joint sphere and the focal length of a spherical radii for a telescope involve essentially the same type of grinding geometry.

This simple little joint ain't so simple, especially if you want it to continue to remain tight yet continue to slip-n-slide over time without wearing, siezing or yielding.

[SRT Mike]

The "trick" to that joint is that the retentive force that keeps the mirror in position is achieved by careful sizing of the ball and socket in concert with a preloading of a precisely formed spherical joint.

The preloading is done by selective crimping of the socket or use a wave washer or some other sort of preload spring to load the ball socket. This exact method is used to preload ball joints in the front suspension of cars.

The preloading of ball joints is done via a gargantuan, "boxcar" coil spring (high rate, low deflection). Another method used was to use a chunk of rubber and preload it in compression behind a 2 piece spherical cupped joint that encapsulated the ball joint (lower rate, more compression). A third method invovled using a molded nylon cup that had selectively cored out segments. The remaining colums of nylon provided the preload "spring" that pressed the female cup against the ball when the joint is jambed together.

Finally, to prevent total siezure of the parts, you need to select materials that have the proper relative hardness and metallurgical compatibility. Choose the wrong materials and they will try to gall/sieze to/with each other or prematurely wear as they rub. Choose the wrong hardness and the parts will eventually yield or prematurely wear as well.

Machinging of a true sphere involves some careful machine programming. To precisely GRIND the sphere to even better/finer levels of roundness and smoothness requires some special grinding techniques.

Google the topic "grinding spherical radius" and a number of DIY techniques should show up. It seems that there are a lot of spherically ground surfaces used in telescopes - there are a number of DIY ways to grind spherical radii that the star gazers use.

Asside from size and levels of accuracy, the grinding of a ball joint sphere and the focal length of a spherical radii for a telescope involve essentially the same type of grinding geometry.

This simple little joint ain't so simple, especially if you want it to continue to remain tight yet continue to slip-n-slide over time without wearing, siezing or yielding.

Hmm..

Well, there are a lot of guys selling motorcycle mirrors for $40, which includes machining in AL, chroming, cutting the glass, and about a 50% distributor markup. And they are made in the USA, so I have a hard time believing these guys are doing metallurgical analysis and carefully grinding perfect spheres and preloading the joints with things like wave washers or carefully designed nylon cups.

There is another way - whether it be purchasing premade parts, or a simpler method for making this joint.

I think you for your reply, but sometimes the job just needs to get done, not analyzed to the n-th degree

[spoiledbrat]

http://www.grizzly.com/products/G9812

I bought one of these to check it out.

It is quite rigid when you tighten the knob. When loose, the two end ball joints become loose, as does the "elbow" joint that the knob runs through.

Anodized aluminum, could possibly be cannibalized and made into two adjustable-stiffness ball joints.

[NC Cams]

The "how to" part of the reply was to help the folks who may, at some time now or in the future, want to MAKE such a joint - no more, n0 less. After all, this is a site where a lot of DIY'ers ask for such help and do so time after time.

In light of the fact that a cheap source for such a joint was already known, ergo a motorcycle mirror, why bother to even ask for a source in the first place???

By the way, the less sophisticated sphericalmirror joints that i've seen are/were molded with a split if they did not have a compression bushing contained therein - I checked before I replied the first time. In that design, they use a tightening screw to set/adjust joint compliance tension.

Even so, I do hope that the "how to" reply in this and the prior post are helpful to SOMEONE outside of that of the original posting member.

[Geof]

You know the type of connection that holds your cars rear view mirror on - where it's tight enough that it won't move, but loose enough that you can move it by hand.

Does anyone know a source for buying just the two pieces of such a joint? I imagine it would be tricky to get it just right, and stay right over time.

I'm working in 6061 AL, so preferably the joint would be made of AL too.

Also, if someone knows how to machine such a joint, I'm all ears

6061 is not necessarily a good choice particularly if you machine both parts out of it; aluminum rubbing on aluminum may gall up. You can get it hard
anodized with a teflon coating.

Do you want it for a mirror mount or is that just an example? We make, and have over the years made thousands, of adjustable ball joints in a couple of sizes. How much load do you want to carry, what size ball are you thinking about, what is the environment it will be used in, how much articulation do you want, what end connectors?

[spoiledbrat]

quote from SRT MIKE: " Does anyone know a source for buying just the two pieces of such a joint?"

Seems like someone looking for a means to an end to me.

My post was only meant to illuminate a possible source for an adjustable ball-joint; cheaper and with adjustable friction too. Even comes with a disposable magnet.

Cheers.

[NC Cams]

As I stated in my original post Geof elaborates upon in his post, there are a few more details needed that were initially lacking in order to come up with a properly functioning "custom" joint for this vaguely defined application - especially if an "off the shelf" one can't be found that is totally suitable.

I'd contend that the info cited in the original post is insufficient to spec out anything other than generic solution potentials for the application. This is why both Geof and I posted a number of considerations that need to be better defined in selecting and/or making such a joint.

If too much detail and technology is getting involved to suit the inquiring member, perhaps the aforementioned motorcycle mirror ends up being the better/most viable option. To those interested in making such a joint in the future, it is hoped that the info provided helps with their problem solving efforts.

[skmetal7]

how about something like this? i am experimenting with making a ball joint for a project and thought this up.

its a 3/8 steel ball drilled and pressed onto a .1875" shaft, the socket is a .5" drill rod drillled and then i took a ball endmill and rounded the blind hole for a hemisphere shape. i turned the od to .420" and used a homemade die to roll the lip over the ball. its a loose fit only because i want it to be, and it should be made out of brass or bronze since it will be in a high wear applicaton (i dont like steel on steel) but i dont know how it will form like steel does. or maybe i could use a brass/bronze ball instead.

[Geof]

how about something like this? i am experimenting with making a ball joint for a project and thought this up.

its a 3/8 steel ball drilled and pressed onto a .1875" shaft, the socket is a .5" drill rod drillled and then i took a ball endmill and rounded the blind hole for a hemisphere shape. i turned the od to .420" and used a homemade die to roll the lip over the ball. its a loose fit only because i want it to be, and it should be made out of brass or bronze since it will be in a high wear applicaton (i dont like steel on steel) but i dont know how it will form like steel does. or maybe i could use a brass/bronze ball instead.

Make little brass cups. They can both be identical because it doesn't really matter if the inside bottom has a hole; actually sometimes you can get a smoother action. Then you make the steel socket flat bottomed and roll the rim down onto the top brass cup.

We doing the rolling process in a different manner. Three rollers are mounted on a spindle in milling machine and the workpiece is stationary. The stem on the ball goes up a hole in the spindle during the rolling. This gives a balanced pressure which is what is needed when you are rolling down onto a cup covering the ball.

[widgitmaster]

I found steel ball ends with delrin sockets here:

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