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Author: Subject: how to grip onto a smooth shaft (ooh erhh)
bi22le

posted on 15/5/17 at 11:20 AM Reply With Quote
how to grip onto a smooth shaft (ooh erhh)

I am trying to design a product for work that needs to lock onto a vertical pole, 25mm dia.

I can think of a few ways of doing it but also know I have used various grip methods in the past. I am just thinking I can use the principles from a tried and tested product and develop them for my use.

It needs to be hand adjustable, no key ways or none circular profile poles allowed. It has to be a non metallic part (medical device). Rubber is allowed but will increase complexity.

I remember using a few clever little locking devices, twisted a tread to climb a conical prong (therefore reducing dia) and one way bearings to name a couple.

Google throws up little more than weight lifting techniques and re-gripping golf clubs!!

One for you guys to ponder on.

[Edited on 15/5/17 by bi22le]





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loggyboy

posted on 15/5/17 at 11:28 AM Reply With Quote
how locked are you talking?
What weight etc.






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nick205

posted on 15/5/17 at 11:46 AM Reply With Quote
My drill press table clamps to the circular pole that holds the drill head itself. There's a split collar on the table tightened/loosened with a thumb wheel. Granted it's a metal assembly, but it could be re-created in other materials no doubt. The clamping force is friction, but I've seen the same approach fixing car front uprights to ball joints and McPherson struts so it's pretty secure.
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redturner
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posted on 15/5/17 at 11:54 AM Reply With Quote
My new clothes line prop, although steel has a plastic fitting at the end which allows the inner tube to lock to the outer tube with half a twist. I haven't a clue how much weight it will stand but even in the strongest wind it never moves.....
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r1_pete

posted on 15/5/17 at 12:00 PM Reply With Quote
Look at shower risers, should give you some ideas.
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Toys2

posted on 15/5/17 at 12:15 PM Reply With Quote
It sounds to me that you're looking for some kind of split collet clamp/chuck

A cable gland springs to mind, they use a type of split collet with an internal taper driven over to clamp, most clamp down onto a rubber ring, but this is mainly for the IP rating, but obviously helps with the grip too
In the picture below the "body" and "claw" are often 1 peice



My other thought it to look into the mechanism for walking/trekking poles, they use a simple twist to look

[Edited on 15/5/17 by Toys2]

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Toys2

posted on 15/5/17 at 12:19 PM Reply With Quote
I found this for trekking poles, the gripping mechanism is on the end of the inner pole



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gremlin1234

posted on 15/5/17 at 12:45 PM Reply With Quote
how about a mechanism like on the top of some garden umbrella bases
http://www.homebase.co.uk/en/homebaseuk/resin-parasol-base---green-196253

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nick205

posted on 15/5/17 at 01:55 PM Reply With Quote
quote:
Originally posted by gremlin1234
how about a mechanism like on the top of some garden umbrella bases
http://www.homebase.co.uk/en/homebaseuk/resin-parasol-base---green-196253



That takes me back!

I've got one of those you were supposed to fill with water. Mine leaked so I mixed up some runny cement and filled it with that. Granted it's quite heavy now, but it certainly doesn't leak any more

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trextr7monkey

posted on 15/5/17 at 03:45 PM Reply With Quote
Spring loaded pins as in the everyday humble crutch - simple and tried and tested and cheap!
hth
Mike





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Angel Acevedo

posted on 15/5/17 at 03:58 PM Reply With Quote
Cam-Locks?
Like used on Plate elifting Clamps or sailboats for control lines?
Cam Cleats are called on boats.

[Edited on 5/15/2017 by Angel Acevedo]





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MikeRJ

posted on 15/5/17 at 04:11 PM Reply With Quote
Can't you just use a split clamp which is pulled together with a wingnut i.e. a plastic version of a scaffold clamp?

Take a look at Go-Pro handlebar/seatpost mounts and also Sat Nav mounts for motorcycles.

[Edited on 15/5/17 by MikeRJ]

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bi22le

posted on 15/5/17 at 05:47 PM Reply With Quote
Great response peeps, I often get less response than this phone posting car related stuff!

Forces - vertical approx 80N nominal but we run a 4x test.
Rotational - hard to tell but around 10Nm.

The suggestions are similar to what I have come up with but I could not think of examples.

Keep them coming





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Please read my ring story:
http://www.locostbuilders.co.uk/forum/13/viewthread.php?tid=139152&page=1

Me doing a sub 56sec lap around Brands Indy. I need a geo set up! http://www.youtube.com/watch?v=EHksfvIGB3I

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Slater

posted on 15/5/17 at 07:40 PM Reply With Quote
prusik knot





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coyoteboy

posted on 16/5/17 at 12:29 PM Reply With Quote
Something akin to a taperlock pulley?





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ReMan

posted on 16/5/17 at 12:45 PM Reply With Quote
Thinking from my Gym, these grip nicely

https://www.amazon.co.uk/Lock-Standard-Inch-Barbell-Collars/dp/B006TKKJ1A





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Matt21

posted on 16/5/17 at 03:44 PM Reply With Quote
I'm struggling with ideas as I don't know the exact purpose of what you need it to do other than just grip the tube.

How about a 25mm O ring, and a plastic collar above it with the bottom edge tapered so it forces the O ring into the tube as more force is added.





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nick205

posted on 17/5/17 at 08:17 AM Reply With Quote
One further idea - something like a bicycle seat tube clamp. Usually I see them in Aluminium alloy, but they're also around in Carbon Fibre. Sometimes with an Allen bolt tightening, but also with a lever action tightening. From experience if they'll hold a bicycle seat tube in place they'll support a fair bit of weight and force. You may even be able to buy one online for little money to try first.
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02GF74

posted on 17/5/17 at 05:47 PM Reply With Quote
quote:
Originally posted by nick205
One further idea - something like a bicycle seat tube clamp. Usually I see them in Aluminium alloy, but they're also around in Carbon Fibre. Sometimes with an Allen bolt tightening, but also with a lever action tightening. From experience if they'll hold a bicycle seat tube in place they'll support a fair bit of weight and force.



Hmmn not exactly sure that is correct. They clamp around the seat tube and it is friction between the seat tube and seatpost that supports the riders weight. The clearance betwwen post and tube is very small so the area in contact is more than that of the clamp. If you clamp it directly around the seatpost, which is how it would be used in the op application, i doubt it would hold the same weight.

Thats not to say it wont work since i dont recall the weight to be supported





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coyoteboy

posted on 9/6/17 at 02:23 PM Reply With Quote
Nah bike seat contact area is fairly small (the bulk of the tube doesn't deflect, they only use a pinch area about 20mm height) but the contact pressure is very high. Happily supports 1KN+. Carbon frames actually struggle a little because you can crack the carbon with the clamp and you often need paste to increase the friction in that area though.





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bi22le

posted on 9/6/17 at 10:18 PM Reply With Quote
Due to the massive response and interest I thought I should update you all.

I ended up not being part of the design team and it has gone down the route suggested by Matt21. The o ring is to control slide when loose though and plastic fingers tighten around the shaft as the tapered collars come together.

quote:
Originally posted by Matt21
I'm struggling with ideas as I don't know the exact purpose of what you need it to do other than just grip the tube.

How about a 25mm O ring, and a plastic collar above it with the bottom edge tapered so it forces the O ring into the tube as more force is added.


The way I would design it is far stronger. Inspired by a similar product I would use a spring coiled around the shaft, spring and shaft axis are co-centric. The ID of the spring is about 1mm less than the shaft and so it grips onto the shaft locking very tight. To release the lock you twist the spring opposite to its coil direction, increasing ID.

Simple, auto locking and rediculously strong.





Track days ARE the best thing since sliced bread, until I get a supercharger that is!

Please read my ring story:
http://www.locostbuilders.co.uk/forum/13/viewthread.php?tid=139152&page=1

Me doing a sub 56sec lap around Brands Indy. I need a geo set up! http://www.youtube.com/watch?v=EHksfvIGB3I

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daviep

posted on 9/6/17 at 10:30 PM Reply With Quote
quote:
Originally posted by bi22le
The way I would design it is far stronger. Inspired by a similar product I would use a spring coiled around the shaft, spring and shaft axis are co-centric. The ID of the spring is about 1mm less than the shaft and so it grips onto the shaft locking very tight. To release the lock you twist the spring opposite to its coil direction, increasing ID.

Simple, auto locking and rediculously strong.


In my line of work it's called a "spiral grapple overshot" and used to retrieve pipe or tools from oil wells, as you said it is ridiculously strong.





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