Using oring to maintain small shaft vertical position

[buzzedge]

I'm working on a retractable handle, vertically up/down, and looking for the best way to keep it from falling down when its pulled up to any position. Normal approach would be to use a spring but I'm limited as far as space goes and can't fit a spring under the shaft or inside the shaft where it would extend against the inner base. So, I'm thinking of using perhaps an oring, or another friction object, which sits near the top and makes contact with the shaft putting enough pressure so that it doesn't fall down on its own.

Below is a rough drawing of the concept, the green circles are where the oring would be placed making contact with the shaft. All materials involved will be anodized aluminum. The handle will be fairly light, maybe couple hundred grams at most. It will be moved maybe several times a day which isn't much but I'm still concerned about longevity and how long it will last before it starts to lose tension against the shaft. Perhaps oring is not the best for this?

Any suggestions/ideas would be appreciated.

Thank you!

 

[Mech1595]

You mention it needs to be held in any position. How critical is the positioning? i.e. what are the consequences of the handle moving on it's own? Will help determine how robust your design needs to be.

Edit: What's the diameter of the handle shaft as well?

 

[buzzedge]

It's not critical, it's more of a convenience thing. The shaft diameter will be about 9mm so its fairly small, the handle is 80mm long and about 15mm wide.

 

[LittleInch]

The issue with an O ring is that it works on friction.

My usual phrase is that friction is like an unreliable friend. Never there when you need it and turns up unannounced when you don't.

So several times a day will wear the Oring, polish the shaft or maybe get oil or water and not have enough static friction to hold the handle in place. Or get some debris or scratch and get harder to retract.

Some form of adjustment, multiple o rings or maybe a chevron seal to make it easier to pull it out than retract it?

Or some sort of twist and pull ratchet type arrangement?

Or maybe some sort of recessed lifting hook?

 

[MintJulep]

Flip-Lok™ Quick Release Clamp On Stafford Manufacturing Corp.

Browse Flip-Lok™ Quick Release Clamp in the Stafford Manufacturing Corp. catalog including Part Number,Bore Size,Material,Width

shaft-collars-couplings.staffordmfg.com

https://www.amazon.com/Dairrr-Fuuu-Telescoping-Replacement-Universal/dp/B0CYBZLW18

Products

C Style internal Cam locks are internal and twist to close. This lock is ideal when one handed operation is necessary. Available in 1/2 through 1-1/4 diameters. Not compatible with non-rotational tubing. Bearing lines are pro

www.testriteoem.com

 

[drawoh]

buzzedge,

Hunt through Parker's website for data on O-rings. I had a copy of a graph that showed the compressive forces on O-rings. The forces get very high, very quickly. You need some sort of spring element that exerts acceptable forces throughout your range of compression. You need to do some engineering here.

 

[Mech1595]

I have a vague memory of seeing a t-handle with a rubber expansion mechanism on the end, similar to a boat drain plug. When the handle was squeezed, the compression on the rubber was released, allowing the handle to move. Might be an idea worth investigating, I can't for the life of me find an example though.

 

[TugboatEng]

O-rings are a challenge to achieve consistent force with because they require lubrication and lubricants affect the dimensions. I strongly suggest using a PTFE based grease for this as they are non-reactive and will not change the dimensions of the o-ring.

 

[buzzedge]

Thank you for the feedback guys.

I'm now considering using a small spring ball plunger on the shaft and then have as many engagement spots inside the cylinder as will fit. Will have to do some testing to see if something this small will support the weight of the handle.

 

[LittleInch]

Still relies on friction. And will score and mark the shat over time, might squeal or make a high pitched noise if you get dirt or rust in there. Seems like a poor option to me.

 

[3DDave]

The typical solution is to add a release mechanism to the handle for either an indexing or friction lock. This prevents the wear of the locking system while sliding but then releasing the mechanism restores the resistance to motion.

A button on the shaft that goes down to a tapered cone, spring loaded to engage a split bushing, for example. One can get a large mechanical advantage that way.

Look for "ball lock pins" as an example for a possible indexing solution.

 

[dgeesaman]

O-ring for a friction grip presents a few limitations:
1) easily damaged by dirt/grit
2) friction can change drastically by water/oil/dirt/grit
3) o-ring material hardness and size varies with temperature and can swell or harden with chemical compatibility issues.

All bolting and clamping technologies rely on friction. So friction can be highly reliable when excess is tolerable. 3DDave has a very good point in that a mechanism that releases all clamping when you move and restores all clamping when it's in position is going to be reliable.

With the o-ring and set screw I think you're relying on Goldilocks friction - not too much and not too little. So having a user adjustment and spring-loaded ball points makes sense to me. Or if you add a feature that allows the user to easily adjust the compression on the o-ring (say, a wedge shaped collar that squeezes the outside of the o-ring into the shaft and has a threaded adjustment to get the right amount of squeeze).

 

[LittleInch]

Still relies on friction. And will score and mark the shat over time, might squeal or make a high pitched noise if you get dirt or rust in there. Seems like a poor option to me.

If you incorporate a groove oe grooves in your shaft then you might have a point, but not for a position anywhere.

 

[buzzedge]

Ok so back to a spring. I could sacrifice a bit of vertical travel under the shaft of about 10mm if I could find a corrosion resistant spring that can compress that much and still offer 35-40mm of travel in under 12mm O.D. Quick searching I do see some springs except they use music wire which is not corrosion resistant.

 

[LittleInch]

How does a spring work?

More force required as you push it in surely?

There are a lot of turn, pull,the turn back to lock systems. What's wrong with that?

I don't understand why you need it to be any position though. What purpose is it doing unless you're at the end of the shaft.

 

[TugboatEng]

Ball detents are a common solution. They work well. The only time I have trouble with them is when the operators burry the set screw so hard it scores the cam plate or causes the ball to get a flat spot from no rotation.