Re: Lifting threads?
- From: Russell <russell@xxxxxxxxxx>
- Date: Thu, 19 Apr 2007 08:53:07 +0100
Harry Bloomfield wrote:
Russell wrote on 18/04/2007 :Hi Harry
If I've got those sums right then there's a lot of friction in the
system and I've been trying to get my head around why friction on the
thread should be greater going up than down and I don't think it should
be. You don't say much about the sliding arrangement and it strikes me
that there will be a lot of out of balance forces as it's a single post
lift. Is there anything you can do to reduce friction there. I think
that may be the main difficulty. Is there any arrangement to ensure
that the nut doesn't go out of alignment under load as that would
increase friction dramatically too.
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?
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
.
- References:
- Lifting threads?
- From: Harry Bloomfield
- Re: Lifting threads?
- From: Guy Griffin
- Re: Lifting threads?
- From: Harry Bloomfield
- Re: Lifting threads?
- From: Russell
- Re: Lifting threads?
- From: Harry Bloomfield
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