Best way of turning rotational motion into linear motion?

[bendo112]

Hello everyone,

I am not an engineer, so I apologize if this is a relatively simple question. What's the best way to turn rotational motion into linear motion under the following circumstances?

1. Rotational motion is driven by a vertical bolt.
2. When turned, the bolt will extend a bar horizontally to apply pressure to an object.
3. The bar should remain fixed unless the bolt/screw is turned (there will be constant pressure exerted against the bar).

Hopefully I explained that clearly. Here's a link to a quick sketch:

https://www.dropbox.com/s/djyrgydd2j59b9l/drawing.png?dl=0 (sorry it turned out kind of small)

In my searches I came across a rack and pinion which looks like it could possibly work. However, it's not entirely clear to me if it can be designed to satisfy point #3? I look forward to your suggestions.

 

[billy_joule]

A scissor jack converts rotational motion into linear motion in the arrangement you want. You probably have one in your car boot.

Also google bottle jack, F-clamp, trigger clamp, (many vice jaws can be reversed to do expansion rather than compression, including trigger clamps & F clamps) for other ideas.
Failing all those, if you can provide more specs (travel, force applied, force exerted, cost etc etc) we can offer better/more suggestions.

 

[bendo112]

Thanks for the quick reply. I should have mentioned some additional specs initially.

As far as additional specs, the housing containing the item will be a fairly small square at approximately 3"x3" and approximately 1/2" thick. So something low profile is ideal. An object will be attached to the housing and the idea is for the housing to be able to expand to fit multiple spaces which vary in size by up to 1.25", so the travel distance would need to be just above that. As far as force exerted, I'm not sure what the numbers look like, but I'm basically just looking for something that has enough force so that the housing stays in place if someone was to give it a strong tug to try and pull it out. It won't be used to support weight. For force applied, I'm not sure on that either, I was looking for something that could be tightened by a standard screw driver. For cost, the lower the better. I'm imagining it will have to be made out of metal or some type of strong plastic.

 

[billy_joule]

OK. At that scale I'd look at little scissor jacks, something like this:

http://www.ebay.com/itm/4-Stainless-Steel-Lab-Stand-Table-Scissor-Lift-laboratory-Jiffy-Jack-100-100mm-/182107453008
or this
http://www.stewmac.com/Tools/Clamps,_support_tools/Scissor_Jack.html

 

[Baluncore]

The rotating bolt could drive an eccentric or a cam. That could lock when over-centre.
Is the required extension always the same? If not, then consider a spring loaded pressure plate so as to fix the extension.

 

[jack action]

The simplest (and cheapest) method would be to thread the shank of your brown part, mating with a threaded hole in your black part. All you have to do is to turn the brown part to make it go in or out. If there are no large forces involved, you might even be able to do it by hand instead of needing a screwdriver. A jam nut may be added if vibrations are involved, to lock everything in place.

 

[bendo112]

Thanks for the suggestions everyone. The required extension will be variable. I considered a spring loaded plate, but due to the height of the object the housing will be placed in, I think it would be difficult to use. The limiting factors are the height of the housing (needs to be around 1/2" high) and the height of the object the housing will be placed in (4" is a rough estimate). Here is an updated drawing with some addition explanations.

https://www.dropbox.com/s/cx3mtit0cnyusl7/updated drawing.png?dl=0

I also included an idea that appears like it should work, but maybe someone can offer some comments/suggestions.

 

[boneh3ad]

You could also have your rod that applies pressure attached to a lead or ball screw and then turn its corresponding nut using a bevel gear attached to your bolt that you turn. Lead screws and ball screws can apply a very large axial force for a given torque used to turn it. That also means that pushing back against it would likely not move it since it only takes a little friction in your bolt to hold the lead screw steady.

 

[Baluncore]

Lead screws and ball screws can apply a very large axial force for a given torque used to turn it.

A lead screw will lock if the tangent of the thread angle is less than the coefficient of friction.
A ball screw is a rolling ball mechanism so it is reversible, the coefficient of friction is then irrelevant.
That excludes ball screws from consideration as locking devices.
A fine threaded lead screw will lock.

 

[boneh3ad]

A ball screw would still work. I was referring to friction in the bolt that the OP mentioned turning to control this mechanism, not the lead or ball screw itself. That friction would potentially provide the torque necessary to prevent the nut from turning. If it couldn't, then you would need something that would lock all on its own.