centering springs

[iconoclastica]

I am making a micro led lamp that can be centered from two concentric rings of aluminium tube. The evident part of the centering mechanism are two screws. What turns out to be less easy are the counter springs.
I thought two blobs of silicone rubber would do, the material is easily compressed after all. This works to some extent indeed, but I discounted that the elasticity decreases with increasing compression. So in the sketch below, it moves the inner ring well to the top-right, but it's hard to impossible to turn the bolts to move it to the bottom left.

So I guess steel springs are a better option, but I do wonder: what kind or shape of spring would work best? Also given that I will have to fix them in position inside the tube somehow.
Another design issue is wether it is wise to have the screws at 90 degree angles. From my trials with the silicone rubber, it seems that one bolt turned tight prohibits the dislocation of the inner tube by the other bolt. Is that why the centering mechanism of the condenser has the screws at 120 degree angles?

outer diameter: 65mm; zigzag denotes spring position

[PeteM]

Couple thoughts.

First, consider using a 3 point suspension; such as is near universal for microscope heads, condenser mounts, etc. Simpler and less prone to jamming. You'll have one plunger located in a detent on the inner part and two centering screws.

For the plunger you can buy off the shelf spring plungers from sources like (in the US) McMaster Carr. There's surely an equivalent supplier in your part of the world. These have a threaded outer diameter, an inner spring pin or ball, and are easy to install. You'll want one with a long range (rounded pin, not a ball detent).

[Pau]

I concur with Pete

Zeiss used both systems in their Standard series microscopes of which I have many components, the 3 points system in most cases works better than the 4 points one, despite the 4 points system movements seems more intuitive (orthogonal displacement)

[iconoclastica]

I concur with Pete

Zeiss used both systems in their Standard series microscopes of which I have many components, the 3 points system in most cases works better than the 4 points one, despite the 4 points system movements seems more intuitive (orthogonal displacement)

Thanks, this well confirms the gut feeling is was beginning to get.

[iconoclastica]

Couple thoughts.

First, consider using a 3 point suspension; such as is near universal for microscope heads, condenser mounts, etc. Simpler and less prone to jamming. You'll have one plunger located in a detent on the inner part and two centering screws.

For the plunger you can buy off the shelf spring plungers from sources like (in the US) McMaster Carr. There's surely an equivalent supplier in your part of the world. These have a threaded outer diameter, an inner spring pin or ball, and are easy to install. You'll want one with a long range (rounded pin, not a ball detent).

So, that would be like a pin, with the head inside the tube, and the shaft outside and pulled inward. That's even easy to make myself. Is the size of the head important?

[PeteM]

These are examples of spring plungers; which would work fine for one point of contact:

https://www.mcmaster.com/spring-plunger ... -plungers/

The other two can just be thumb screws, with springs under the heads if you wish to eliminate backlash. There are plastic thumb screw caps made to turn an ordinary (stainless etc.) socket head screw into a thumb screw. They press on and are surprisingly storng. Just bought 50 of them for under $10 to replace missing 4mm screws on Olympus scopes.

https://www.mcmaster.com/thumb-screws/s ... nt~metric/

[iconoclastica]

Thanks, I just bought a couple of these, which have a nice long travel distance. I can't find 'm closer at hand for I haven't the remotest idea how we call them...

[iconoclastica]

This works well and took about five minutes to install.
Only now another design flaw becomes apparent: In the wo dimensions as drawn above it works perfecty. But it derails in the third one. I suppose I must make a kind of double flange to restrict movement to one plane.

[patta]

yes, a bit late
such centering mounts are usually made with conical dovetail and one reference surface against which the ring press.
One flange may be enough for you, if Gravity is pushing down (if is on side, no, you need two flanges..)

[iconoclastica]

Brilliant solution! Now let me think how I could make that. Perhaps two ridges would do as well in this case.