Can anyone identify this type of scissor jack

[Dan CarterParticipant @dancarter89683]

Hi,

Is there a specific name for this type of scissor jack:

even better, is anyone aware of how to work out the possible pivot points without me having to dust off my rusty geometry ?

The appeal is it having no need for a sliding joint as in a normal scissor lift

Thanks,

Dan

[Dan CarterParticipant @dancarter89683]

[Ady1Participant @ady1]

On a well known site they are called a lift table

[Cyril BonnettParticipant @cyrilbonnett24790]

Hi

A quick search gave the following

Industrial Scissor Lift Table

**LINK**

or a home built one.

http://imgur.com/a/7RW0n

Cyril

Edited By Cyril Bonnett on 17/11/2016 21:59:35

[Dan CarterParticipant @dancarter89683]

Cyril – that is where I found the image in the first place unfortunately doesn't help much getting the dimensions worked out.

Ady – a normal lift table doesn't have the extra/different linkage which gets rid of the need for a sliding joint, that's the bit I'm interested in

[Old SchoolParticipant @oldschool]

Surely you can scale it from the picture and then draw it up to check that you got it right.

[Cyril BonnettParticipant @cyrilbonnett24790]

The second link I posted above has a download for solidwork files

[Dan CarterParticipant @dancarter89683]

Cyril,

Sorry, only read the email update which didn't include the second link – that is extremely helpful (or at least will be once I remember how to use fusion 360 to import the solidworks model)

Old School – would have done if necessary, but the picture is of a decorative item, no way of knowing if it even works as shown

Thanks,

Dan

[norman valentineParticipant @normanvalentine78682]

Make a quick model out of mecano, if you don't have mecano cut some strips of cardboard.

[Dan CarterParticipant @dancarter89683]

Norman,

Already did (lego, not meccano). The length and position of the short linkage affect whether the top moves vertically only or also horizontally.

Am attempting to look at the model linked by Cyril to see whether it is an exact solution or not.

[JAParticipant @ja]

Except for the screw jack each pivot is the corner of a four sided link system. These are mechanism and are free to move in the vertical plane. The screw jack holds everything together because it is part of two (although only one is actually required) three link systems. A three link system is locked and is not a mechanism. I hope this makes sense.

The lift is not far removed, mechanically, for scaffolding. Unless there is a diagonal scaffold pipe in each plane the structure is very likely to collapse.

It is quite neat, though. Better than my scissors type bike work bench.

JA

Edited By JA on 17/11/2016 22:59:22

[Michael GilliganParticipant @michaelgilligan61133]

Dan,

No promises, but I think you will find this of interest: **LINK**

https://archive.org/details/howtodrawastrai01kempgoog

MichaelG.

[duncan webster 1Participant @duncanwebster1]

The name ought to be 'over complicated'. The sliding joints in my scissor lift are very simple, little wheels running inside folded channel. I have 4 lever bits and a cheap hydraulic jack, the one in photo has 12 and a bespoke leadscrew arrangement. Nuff Sed?

[Dan CarterParticipant @dancarter89683]

True, but it has more in common with a double scissor lift than a single as regards height vs length (which matters for my purpose), which would double your lever bits. In my case the bespoke leadscrew would be replaced by the guts of an electric scissor jack which I already have, so not quite as pointlessly overcomplicated as it looks

[Michael GilliganParticipant @michaelgilligan61133]

Posted by duncan webster on 17/11/2016 23:31:22:

The name ought to be 'over complicated'. The sliding joints in my scissor lift are very simple, little wheels running inside folded channel. I have 4 lever bits and a cheap hydraulic jack, the one in photo has 12 and a bespoke leadscrew arrangement. Nuff Sed?

.

Sorry, Duncan … I have to disagree

The 'Lab Jacks' that I bought for close-up photography are crude and precarious compared with what Dan shows … [because; as the elevation increases, the support becomes narrower … which is exactly what is not wanted].

MichaelG.

.

https://en.m.wikipedia.org/wiki/Laboratory_scissor_jack

Edited By Michael Gilligan on 18/11/2016 00:18:24

[Paul LousickParticipant @paullousick59116]

Dan,

What is the load capacity of your lift table ?

I can open your Solidworks model but some on this forum may not. 

Can you post a drawing with dimensions for them ?

Paul.

Edited By Paul Lousick on 18/11/2016 07:06:31

[Ady1Participant @ady1]

I presume that what makes this do it's job differently is the parallelogram within the structure?

It puts me in mind of that screwcutting attachment which the French chap posted a while back

To my mind it looks like the top left hand side has no real support compared to the right hand side, the cross member goes waaay across to the far right before it has a load bearing point

Edited By Ady1 on 18/11/2016 07:54:34

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Ady1 on 18/11/2016 07:40:24:

To my mind it looks like the top left hand side has no real support compared to the right hand side, the cross member goes waaay across to the far right before it has a load bearing point

.

Enlighten me please, Ady

I'm barely awake, but I can't see it as anything other than symmetrical.

MichaelG

.

'it' being the linkage [excluding the screw].

Edited By Michael Gilligan on 18/11/2016 08:49:04

[BazyleParticipant @bazyle]

I think he means the short arm appears to give support to the RHS. It is perfectly possible to add a similar parallelogram to the LHS.

The question we all want answered is how you decide on the length of the short arm for optimum performance without having to put in any thought effort into 'O-level' geometry.

[Dan CarterParticipant @dancarter89683]

Paul, it is not my table, the link was an example found by Cyril.

In the model, the distance between hole centres for the long piece is 20", the short distance between end hole and attachment point of the strut is 7.5" and the distance between hole centres on the strut is 7.492" (??)

However, having tried that ratio in lego, it doesn't work as I expected, the top still moves off to one side as it goes up. Possibly this is inevitable, may have to actually read Michael G's link (thanks for that)

Bazyle – I think a second parallelogram won't work unless the movement is completely vertical, which it doesn't appear to be in the example. Looking like avoiding thought may be impossible (probably would have been quicker in the first place )

[Dan CarterParticipant @dancarter89683]

Oops, schoolboy error, used 16 and 6 hole pieced rather than 17 and 7. Works perfectly with ratio as above

[Neil WyattModerator @neilwyatt]

It's congruent triangles (remember those).

As long as top and bottom are identical (but rotated 180 degrees) it should work. Changing lengths will just affect how far it can move.

Neil

[David JuppParticipant @davidjupp51506]

For those wanting to study/measure/play with the SolidWorks model, there is a free viewer program available. Handy if you don't have a CAD system that can import the files.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Neil Wyatt on 18/11/2016 10:37:38:

It's congruent triangles (remember those).

…

Neil

Do I remember congruent triangles? No.

I've always been obtuse.

Dave

[MWParticipant @mw27036]

I'm astounded by how much discussion this has caused beyond discovering it's namesake, size and tolerable load.

Michael W

[Author]

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