[nadsab]

Hi,

What other types of devices would work well for vertical displacement?

I like the idea of a scissor jack because it is nice and compact when folded....are there any other alternatives to a scissor jack that can fold up into a small package when un extended?

A screw jack i think would be more robust but for my application I want to keep the device as small (short) as possible when at the lowest height.

Also is the displacement of a scissor jack linear during the entire course of extension?

Thanks.

[handlewanker]

Hi, be more specific in your requirements, IE how much lift/travel do you want, what's the tonnage......how much dough you got....LOL.

A sketch of your layout would help, maybe a photo.

Be aware that when a scissor jack is right down and flat it has neglible lift capacity as the mechanical advantage is very low, and when it's right up it's very unstable.

At all times it is totally unable to resist side loading.
Ian.

[nadsab]

Tonnage LOL. I am just trying to design a small table top jig for a tool I am designing. Tonnage is in a few pounds range at most

I need to be able to uniformly raise and lower the base of the jig up and down from zero to about 3 three inches, and the two legs that I need to raise are comprised of two 9 inch long rods approximately 3/8" in diameter. The third leg is stationairy, I just need to uniformly elevate the rear two legs a bit.

I was thinking of just building a mini scissor lift that I could rest the legs on, but that seemed a bit over kill for this - I am hoping to design something that can fit onto the legs and raise them up. The legs are not perpindicular to the table top - they are sloping - and tilted - due to the jig design requirements. The leg ends however I need to raise them up perpindicular to the table top.

About a year ago TomB posted an answer to another question I had...

...To answer the questions...Alternatives to scissors jacks include (a) wedges and cams, (b) screws, (c) inflatables like air bags or hydraulic cylinders. The link part of a scissors jack can be employed in a number of ways that seem different that a scissors jack but all use the same type equation for displacement so all are functionally equivalent.

Tom

Can anyone think of a way I could raise the bases of two non perpendicular (to a table top) rods, that is, the two rods that are part of a tripod like configuration and I only want to jack two of the three rods up a few inches.

Either by using one of the above methods or any different suggestions?

I designed one method it works, but it's kind of klunky I think - I am trying to find a slicker way to do it...

[handlewanker]

Hi....very confused information....it needs a simple sketch to clarify, and failing a graphics program and tablet, you could just sketch something in 5 minutes with MS Paint and your mouse............one picture is worth a thousand words....haven't got the time to go to a thousand words.....LOL.
Ian.

[Al_The_Man]

If the upper and lower limits are fixed, IOW you do not need to position to an arbitrary position, what about a miniature, compact air cyclinder in the centre of lift?
Also check out the Misumi catalogue, they have many jig & fixture items such as spring clamps and toggle clamps for jigs that you may be able to adapt.
Al.

[KyleCurts]

A wedge design might work in this case. Another low travel design that may work is a Cam...kinematically similar to a wedge.

Kyle