Lifting threads?

Russell wrote on 18/04/2007 :


Let me try to describe the layout a little better....
There is a 50mm square stainless steel vertical post. Attached to that is the slider which is basically two 6mm steel plates drilled with 4x holes in each plate corner, to take 10mm threaded rod. These four link the two plates and take all of the side thrust weight.
The slider plates extend down from the post at 45 deg to where the plates attach to the main lifting beam. On the 10mm rod between the plates I have used a piece of tube against which the 10mm rod is tightened, with a second slightly larger diameter, but shorter tube to form a roller running against the post.
In addition to the 4x 10mm threaded rods, I have welded in a piece of 6mm steel linking the two sides of the slider at the top. Through this latter item I have drilled a 20mm hole to take the 20mm threaded rod to provide the lift, with its nut free to rock about, but not turn.
So the 20mm rod is located between post and the bike, but there is no sideways stress at all on the rod or its nut, only the weight it has to lift. The rod is about an inch clear from the post to allow for the rollers, where as the bike centre line is about 16 inches. If you imagine sitting on the bike, with it all set up to be lifted, the vertical post would be by your elbow.
Hope the description makes sense?
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Harry (M1BYT) (L)
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Harry Bloomfield wrote:

Hi Harry
Yes that's quite clear thanks and it sounds a reasonably sensible way to do it.
I agree as other posters have suggested that there are issues over friction with the studding and I'm clearly in a minority here in looking at bits other than the thread. As nearly all the effort you're putting in is to overcome friction I think it's worth looking at other parts of the mechanism.
Unless the tube that you're using for the rollers is very thick walled then I'm not sure that they will reduce friction very much. Have you greased the rollers? Is there any way you could reduce friction here? The bottom bike side and the top far side ones will be crucial. If the tube is only thin walled then you are just transferring the sliding friction from the outside to the inside of the tube. If it's thick walled then the amount of sliding needed is reduced.
I'm not sure from your description how the nut is free to rock but I think it will work better if it's loaded centrally - ie if it rocks then it has to do it in a way that doesn't load one edge of the nut.
I hope this helps.
Russell
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Harry Bloomfield wrote:

Hydraulics would be an easy solution, envisage how a forklift works. By using a cable or chain anchored on one side of the ram and the other end passing over a sprocket/pulley fixed to the ram end, the cable end being then fastened to the carriage to be lifted. Because of the 2 : 1 purchase, for every inch of ram movement, the carriage will rise 2 inches. Your 30 inches would require a 15 inch stoke ram, cheap chinese long stroke jacks abound these days, engine hoists have them as well. However if you wanted to be cheap you could use a 7.5" stroke jack and cable. With a double sheave mounted on the ram and one underneath, the diameters being big enough that the cable cleared the jack body, you would have a 4 : 1 advantage to lift to 30". Be aware that there are no free lunches and a 2 ton jack will only lift 1/2 ton in this instant.
Tom
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An acme thread, with a roller trust bearing at the top should work. This was a common arrangement on aftermarket American car jacks. These were bumper jacks, which could support well over 2,000 pounds. They had a simple crank at the top end of the screw. I still have one somewhere!
Steve R.
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wrote:

The jack of the Deux Chevaux was like that with bevel gearing so you didn't swing the wheelbrace into the body. Long while before the wheel you were changing left the ground. About 2ft lift.
<rummage>
Yep, got one here, bit rusty - lot of cobwebs. Can deliver in that condition. I'll be travelling Redditch to Sittingbourne area via M40/M25/M26/M20 tomorrow or Friday, shall I drop it off somewhere?
<No, Tony, I'm not fly tipping>
Ray
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wrote:

And then (with apologising for following up self) you come across this: http://cgi.ebay.co.uk/48-FARM-JACK-HIGH-LIFT-4-X-4-OFF-ROAD-CARAVAN-TRAILER_W0QQitemZ190102674237QQihZ009QQcategoryZ108783QQrdZ1QQcmdZViewItem
<sorry, no idea about tiny url>
and you wonder if you've been going about it the hard way. Not a thread in sight, just old lever technology. Ok, you need some room to swing that lever, but it comes already painted.
No connection, just thought it was interesting. And if you need a rabbit hutch, a pair of MP3 sunglasses, or a rucksack, he seems to be the bloke.
Ray
Don't believe everything you think
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Harry Bloomfield wrote:

Not particularly cheap, but marchantdice, an ebay seller, does 20x4 mm acme threaded rod at 1.86 per 100 mm, so a meter would cost 18.60. They also do nuts, but these are expensive at 19.50. BTW, why would you need two nuts?
Put a bearing on the thrust end of the rod though.
--
Peter Fairbrother


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Peter Fairbrother was thinking very hard :

One fixed solidly on the top of the rod, the second one captive under the slidy bit.
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Regards,
Harry (M1BYT) (L)
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Harry Bloomfield wrote:

Chris Heapy says that adding a proper thrust bearing to a vice tightening screw is so effective you have to watch for stripping the thread.
(site archived here: http://kansai.anesth.or.jp/gijutu/kousaku/easyweb.easynet.co.uk/chrish/wrk_tips.htm )
BugBear
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As you have discovered and others have written, screw threads are not very efficient and this is why "up" is harder than "down". Galvanised studding (probably zinc plated, actually) is not ideal but for moderate contact stresses (say < 1000 psi) and with a moly grease you may get away with it. A bronze nut would be better than steel, but I've seen them wear at an alarming rate when overstressed and/or under-lubricated. Acme threads should be a bit better, but studding is cheap and easy. You need two ball bearing assemblies to take the thrust.
(Tribologist)
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bugbear wrote:

http://kansai.anesth.or.jp/gijutu/kousaku/easyweb.easynet.co.uk/chrish/wrk_tips.htm )
I'm slightly surprised by that. I've seen a vice (Record No1) overtightened and the front jaw snapped off.
Russell
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Apologies for my apparent absence from the thread for a while, this was due to Tiscali's problematic newserver and the fact that I had other more pressing things requiring my attention.
I would like to thank you all for the suggestions and ideas - I will soon get around to testing the suggestions for the lift to reduce the effort required to operate it.
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Harry (M1BYT) (L)
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Harry Bloomfield formulated the question :

Just thought I would let you know///
I have now obtained and installed a roller thrust bearing, which at a guess has reduced the effort required by approximately 1/3, it also runs quite a bit smoother.
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Harry (M1BYT) (L)
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Harry Bloomfield wrote on 24/04/2007 :

If anyone fancies a look at some pictures of this beasty...
http://www.bikersoracle.com/vfr/forum/attachment.php?attachmentidF241
http://www.bikersoracle.com/vfr/forum/attachment.php?attachmentidF242
http://www.bikersoracle.com/vfr/forum/attachment.php?attachmentidF243
http://www.bikersoracle.com/vfr/forum/attachment.php?attachmentidF244
--

Regards,
Harry (M1BYT) (L)
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On Apr 24, 10:31 pm, Harry Bloomfield

Hi Harry,
Cheers for the pics! Looks cool.
Erm...I don't mean to be picky, but which bits of the bike are you going to work on with it lifted? And, how are you securing the bike to the lift? Is it intended for you work on it or just to get it out of the way and a second bike underneath?
I'd love to be able to stack bikes up in my garage. would make things ever-so-much easier. As they used to say about Spitfires, it'd make much more space if you could hang 'em up by the tails.
Zed
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snipped-for-privacy@gmail.com explained :

Had it just been to allow me to park a second bike under it, I would have used a vertical post permanently fixed to the wall to lift on.
This is intended to allow me to lift the bike to a level where I can work on it in comfort and to be able work on all parts of the bike, once I have made up some lifting adaptors.
Once lifted up, the bike is almost completely clear of any obstructions to accessing it to work upon it. There is just the main lifting spar running below and to the side of the bike slightly in the way down one side.
I'm now working on the next stage, which is a means to actually keep it up right when lifted by its wheels - which I was looking at yesterday evening.
One way is to clamp the extended side stand to the lifting frame, but that makes it rather awkward to get the bike set up to lift it. It means you are rather forced to have the vertical post always on the left hand side of the bike. Basically balancing the bike whilst attempting to slide the lift under it, then dropping the side stand down to clamp it. You can't slide the lift under the bike from the left hand side of the bike if its on either the side or centre stand.
Instead I have decided to fit another bit of box section at right angles to and bolted on top of the main lifting spar box section - such that it passes under the folded centre stand close to its pivot point. On top of that box section I will weld two short bits of angle to pick up the tube of the centre stand, then put a bolt down through a clamp and the centre stand. That clamping through the centre stand should be more than adequate to keep it steady, vertical and it offers the possibility of lifting it with the rear wheel removed.
This was another reason why I made the thinner F frames which lift it by the wheels, so they could be slide completely out when they are not needed to lift it by its wheels.
--

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Harry (M1BYT) (L)
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snipped-for-privacy@gmail.com brought next idea :

You need a similar idea, but with the vertical post permanently fixed to the garage wall top and bottom - so no need for the H frame to support the vertical post. Instead of the F brackets to pick the bike up by the the wheels, you need some U channel wide enough for the wheels to run in, then a simple bracket to rest the side stand on.
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Harry (M1BYT) (L)
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