Ballscrews?

[Bear G 1Participant @bearg1]

[Bear G 1Participant @bearg1]

Hi, looking for advice on ballscrews. I have to make a scissor lift but it has to be screw driven. Can anyone advise me what I should look for/at when buying one? I knopw there are two different types of nut but there seems to be no obvious way of telling which is the stronger?

Bear

[Paul LousickParticipant @paullousick59116]

Which types of ball nuts are you refering to ? Details ?

Ballscrews used on milling machines, etc can have an adjustment to reduce back lash but would not be required for a simple scissor lift application.

Paul.

Edited By Paul Lousick on 29/05/2019 09:39:23

[Bear G 1Participant @bearg1]

Hi Paul,

I was look at those listed as "SFU2005" on ebay but there seem to be so many variations and I need the strong one. I can't use hydraulics nor linear actuators for this project due to weight (circa 300kg capacity with a severe weight restriction). I did try looking around for a ready made lift but they were all either too small or too heavy.

C7 grade seem to be better?

Bear

[Mike PooleParticipant @mikepoole82104]

My experience of ballscrews and scissor lifts is that they are bloody dangerous, failure of the nut has been sudden and catastrophic. Guarding to keep everything from fingers to people is essential, never work on it when raised unless it is positively secured.

Mike

[Nick HulmeParticipant @nickhulme30114]

Posted by Bear G 1 on 28/05/2019 20:35:48:

Hi, looking for advice on ballscrews. I have to make a scissor lift but it has to be screw driven. Can anyone advise me what I should look for/at when buying one? I knopw there are two different types of nut but there seems to be no obvious way of telling which is the stronger?

Bear

Step 1 is not to buy a cheap Chinese screw and nut for an application like this, then you can ask the supplier/manufacturer for something with specifications which meet your needs.

[HOWARDTParticipant @howardt]

As Mike says, dangerous in this situation. I would use a simple trapezoidal or acme thread, perfect for occasional movements. Ballscrews are used for applications where in continual movement. While the load is perfectly acceptable you would need some sort of safety device to arrest. There are many types of ball nut for different mounting ways and accuracy, a simple reversed flange nut would do what you want. Also need to consider the dirt that is around, fine particles would soon wear the ballscrew even with wipers. Best to look up a UK manufacturer and give them a ring for advice. I used ballscrews in machine tool designs for years, and although some were rebuilt at service rebuild time most outlasted the component the machine was producing.

[Bear G 1Participant @bearg1]

Thanks for the replies.

I've looked and looked and I cannot find any information on either load ratings or detailed specs. I've asked the only company with prices nearly on this planet and they never responded.

The Chinese sellers with just tell you anything to get the sale.

I'm hoping someone on here can tell me how to recognise a good one from a bad.

Bear

[KWILParticipant @kwil]

HOWARDT gave the best answer, don't use a ball screw. You have not given any reason why you wish to use a ball screw as opposed to any alternative.

[BufferParticipant @buffer]

If your not using it for CNC and you have made no calculations of load you might as well not worry about good or bad ones. Just get a big one and hope no bits of your little pink body are near it.

[Bear G 1Participant @bearg1]

Posted by KWIL on 29/05/2019 11:05:46:

HOWARDT gave the best answer, don't use a ball screw. You have not given any reason why you wish to use a ball screw as opposed to any alternative.

I have, weight. All other options for driving it are too heavy or ridiculously overpriced.

[Stuart Smith 5Participant @stuartsmith5]

Would these be suitable?

Accu

[HOWARDTParticipant @howardt]

You have weight?? A car jack uses a screw about 16 mm dia to lift a quarter of a car!

[HopperParticipant @hopper]

Have a look at motorcycle lifts and lift tables. They are right in the 300kg range and upward to 4 or 500. There is a fair variety available. Might be something that suits your needs. Typically they are hydraulically operated.

But I definitely would not use an unknown rating ball screw. That is just begging for catastrophe. Typically they are used in CNC machines and other production equipment where loads are not huge. If those tiny little balls escape from that flimsy aluminum body your nut all of a sudden becomes a sliding sleeve.

Acme threaded rod and solid steel nuts are readily available not too expensive.

Edited By Hopper on 29/05/2019 12:06:07

[Alistair Robertson 1Participant @alistairrobertson1]

Ballscrews should not be used to carry/hold weight. They have no locking capacity unlike an acme or trapazoidal screw which is (usually!) inherently self locking.

I used to make lifting mechanisms and ALL ball-screw applications need an efficient braking/locking system.

We made a system to lift 5 ton ingot ladles and the braking system cost twice as much as the lifting system!

[Paul LousickParticipant @paullousick59116]

Hopper, beat me to it. Lots of motorcycle lifts available on ebay.

Paul

[Bear G 1Participant @bearg1]

Posted by HOWARDT on 29/05/2019 11:53:14:

You have weight?? A car jack uses a screw about 16 mm dia to lift a quarter of a car!

You are intentionally misunderstanding what I have written. THE FLOOR CANNOT TAKE THE WEIGHT.

I have to build this then ensure the beams don't deflect more than they are already. If then do I have to reduce the weight further. I have already started making the mounts for the forty eight m8 feet to spread the load out as much as possible.

Thanks to Stuart Smith for the link, ouch those are expensive!

Others have mentioned load calculations something I haven't got a clue how to do. My normal way is to over-engineer.

I know quite a few toolmakers and have learnt from them how to make the easy difficult!

Thanks to others who have brought up motorcycle lifts, way, way, too heavy! Hydraulic platforms are just too small. I've been researching for months and what I'm trying to build is the only way it can be done.

Bear

[Paul LousickParticipant @paullousick59116]

Bear

Details of what you are trying to make would help us to make relevent suggestions,

Paul.

[Mike PooleParticipant @mikepoole82104]

I am not really visualising what you need to do, I am getting that the floor is not strong and the load you wish to lift is 300kg but how big is it and how high do you want to lift it? I am also a guesstimate worker but this often makes things over engineered and heavy and your situation sounds as though you want it to be as light as possible to do the job. I have experience of two scissor lift with ball screws failing, one was picked up by maintenance as being noisy but as it was a show stopper to repair it the decision was taken to grease it and see if it would get to the weekend maintenance window, needless to say it didn’t but it did give time to get the spares and gear needed into position to minimise the downtime.

Mike

[Bear G 1Participant @bearg1]

Hi Paul & Mike,

It's a tiered model railway fiddle yard with traverser. I simply cannot fit the traditional fan of sidings in the space I have and get enough length/capacity and a traverser on its own would be even less.

The traverser is built with four levels two feet by ten sat on a frame 1200mm wide by ten feet. This will sit on the top frame of the scissor lift (920mm by 2500mm) the scissor itself will be made from 2M lengths of ally and the bottom frame is 12ft by 920mm in two halves.

Yes, I have worked out how to automate the switching and I have a mate to weld the scissor assembly when I get to that stage.

I know people will call me utterly mad for coming up with this concept and despite it's physical size it is a space saver; it holds over twice it's width and if the slope of the ceiling doesn't cause an issue more tiers might get added if the floor can take it hence the number of feet to spread the weight.

Mad Bear

[Paul LousickParticipant @paullousick59116]

Bear,

You have mentioned 46 x M8 feet. 3D printers use M8 screws and nuts which are available as either Trapezoidal and as ball screws.

Banggood sell an M8 ball screws and nut for Au$30.21 ( £ 17). Trapezoidal thread type much cheaper.

Banggood

Paul.

 

Edited By Paul Lousick on 29/05/2019 13:38:17

[Neil WyattModerator @neilwyatt]

Posted by Bear G 1 on 29/05/2019 12:29:19:

Posted by HOWARDT on 29/05/2019 11:53:14:

You have weight?? A car jack uses a screw about 16 mm dia to lift a quarter of a car!

You are intentionally misunderstanding what I have written. THE FLOOR CANNOT TAKE THE WEIGHT.

That seems a bit unfair. You havn't been very clear about what the application is but appear to have specified the weight to be lifted, 300kg, but not how far it needs to be lifted or exactly what the limiting factors are (OK we now know you have a weak floor).

A car jack will lift more than 300kg and only weighs 2-3kg. It can be welded in the centre of a metal plate to spread the load, so repurposing one would be my first suggestion.

[John HaineParticipant @johnhaine32865]

One thing to remember with a scissor lift is that when it's "collapsed" the load on the screw can be many times the weight you are lifting. In fact, if it's completely collapsed the initial load is infinite! So the strength of the screw can't be based on simply the load being lifted.

Also with ballscrews: if I detach the stepper motor from my lathe cross slide and just push it hard, the ballscrew spins merrily away as the slide, well, slides!

I would suggest that a better approach would be a simple vertical screw, motor driven, not a ballscrew, in compression, that does the lifting. Then you need some way to do the vertical guiding.

[HOWARDTParticipant @howardt]

With those sort of dimensions a four post lift would be possible with ball screws in each corner connected by chain or possibly toothed belt. For simplicity you could hand turn them. The problem is the supporting frame for each panel to prevent them bending. I think you need to sketch it out to see what you actual loading is on the floor, you may be adding more weight than you think. Could you slide the panels under the rest of the track and slide and lift one into place at a time, possibly with a simple cam action lever, this would lessen the weight being moved.

[BazParticipant @baz89810]

Being an ex toolmaker and therefore highly skilled at making the easy difficult, would it not be better to get the floor strengthened rather than faff about with with 46 x M8 feet and trying to make a scissor lift or something like that, that weighs next to nothing?

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