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I have a shaft inside a bushing, the shaft has a gear on one end that is supposed to provide resistance to other gears it is driven with.

I'm having a hard time finding the correct term for the sort of grease or fluid, or in more lay-man's terms a "goo", that will provide increased friction between the shaft and the bushing, rather than reducing friction, as it is with regular oil or grease.

Essentially a tar-like substance, that isn't as messy as actual tar. Perhaps also similar to tree-sap, except more manageable in terms of putting it into a mechanical device. Also tree-sap gets hard over time, I'd like to keep its mechanical properties, like viscosity, etc.

In case you're wondering, this is going to be part of a soft-open gearing, such that a small door doesn't fling open when the lock is released, instead it provides some resistance.

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    $\begingroup$ It sounds like you're looking for increased damping, not friction per se. There's a lot of shock-absorber and dashpot designs out there; it may not be worthwhile to reinvent the wheel. $\endgroup$
    – TimWescott
    Commented Mar 28, 2019 at 2:59
  • $\begingroup$ I totally agree! There is absolutely no reason to reinvent the wheel. I would stick to a solution that already exists. $\endgroup$
    – Daniel H.
    Commented Mar 28, 2019 at 15:29

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They are called haptic greases. Used on knobs and levers to provide stiction but very smooth movement when actuated.

Here's an explanation from Nye Technologies - https://www.nyelubricants.com/motion-control

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  • $\begingroup$ "haptic damping grease" did the trick. Finally, I'm not poking in the dark anymore, thanks! $\endgroup$
    – polemon
    Commented Apr 23, 2021 at 15:00
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That made for some interesting links... You may be looking for shear thickening lubricant. According to the Wiki page, some of these products can also be called non-Newtonian fluids, but I would not suggest cornstarch and water for your application.

Additional research resulted in a question posted "elsewhere" that suggests the product you seek is rare, uncommon and difficult to find. One application listed is as projectile defense in body armor!

I have seen slow opening devices which use a cylinder linkage in which the cylinder allows "normal" fluid to travel through a circuit with a restricting opening. Think about a syringe in that you have a large diameter plunger and a small diameter needle. Plenty of force does not result in rapid travel.

One can create a closed system similar to a syringe using air as the working fluid, if one can drill a small enough hole in the restrictor plate.

Additionally, I have seen speed limiters that use a high gear ratio assembly to spin a simple squirrel-cage impeller fan. Similarly, there is arresting gear for exiting a building that also uses a spinning fan of paddle wheel design.

Because you used "small" in your question, I suggest paddle wheel or squirrel cage fans may not work well in tiny scale, but a cylinder and orifice can be reduced and still be effective. You can get away with a clean wall cylinder and a piston with such tight tolerances that the entire perimeter is the orifice. If properly machined, no seals (o-rings) would be needed, only a light lubricant and possibly periodic lubing.

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  • $\begingroup$ I've seen similar things in cassette decks that had one of these soft-open things. it was essentially a little stick that slid in and out of a little receptacle filled with a resistive fluid like that. The stuff should be stable, i.e. not slowly leak out, etc. The only thing I could think of right now, is using blobs of paper glue, they keep their gooey and sticky texture at least for a long while. $\endgroup$
    – polemon
    Commented Mar 28, 2019 at 1:03
  • $\begingroup$ Glycerin is a liquid that does not harden in the same manner as glue and is of reasonably high viscosity. It's slippery but not really a lubricant for mechanical purposes. It will make your skin silky and soft, however. $\endgroup$
    – fred_dot_u
    Commented Mar 28, 2019 at 13:17
  • $\begingroup$ Well, I'm not making a lotion, it's supposed to provide friction without stiction. $\endgroup$
    – polemon
    Commented Mar 28, 2019 at 19:00

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