clamping force on 1/2" dia rod

[bob96808]

thread404-396097

sounds like i may have a similar question to this previous inquiry.
Am working with a 1/2" dia smooth rod that runs thru the center-line of a compression spring. In compression, the spring is exerting a nominal 450N force.

I need to restrain the rod with a clamping device, open/close via a cam action on clamp. Clamp width (contact with rod) is nominal 1/2". The rod dia would be reduced by 1/16" where it would contact clamp. Hence a 1/2" wide notch running circumferentially is created in rod to inhibit slipping.

If this design is realistic, then I assuming the force required to open the cam and release clamp could be controlled by the length of a lever arm on the cam, which would snap the clamp open or closed.

 

[MikeHalloran]

Since you're notching the rod, your problem is not similar to the exemplar you have quoted.

... except that you have provided only a small sample of the information required to solve whatever your actual problem is.



Mike Halloran
Pembroke Pines, FL, USA

 

[bob96808]

ok, basically I'm looking for the LEAST amount of circumferential force required to restrain the 1/2" rod, given that in a cocked mode their is 450N spring force trying to push it. so i see 3 options:

1. notch the rod
2. don't notch the rod
3. add a hard rubber coat on the inside of clamp to improve static friction.

this site is basically what I'm trying to do, but totally different application & size:

http://www.fitnessbodyequipment.com/images/bars_collars/lock_jaw_one_regular_1_collars_pair_b.jpg

 

[MikeHalloran]

You don't have a 'design', you have several disjoint cloudy ideas.

WRT to the image provided,

I think I've seen similar clamps, used by gaffers.
... except not with over-center cams, but with relatively large half or full wingnuts, so that a pretty fair amount of clamping force can be generated.
I'd bet they'e expensive.

I've also had occasion to buy connecting clamps for building laboratory frames.
Most of them are garbage, sold to idiots who will buy anything shiny.
The best/least_awful of them comprise nickel-chrome plated zinc saddles, heavy stainless steel half-circle saddle clamps, and ridiculous poorly made wing-screws that can be easily replaced with stainless socket head screws. Even those clamps cost ~$15 each, 20 years ago.

But 450N, if I'm converting it correctly in my head, is a lot of force to be restrained by a friction clamp of any kind. If the rod were threaded, you could use a nut. If the rod were machined with a series of grooves, like a thread with zero pitch, you could use a sort of half-nut clamp, closed by an easy to operate toggle if you wish. I'm not aware of any such thing for sale now, but it seems achievable.

How many will you need?


Mike Halloran
Pembroke Pines, FL, USA

 

[bob96808]

"If the rod were machined with a series of grooves, like a thread with zero pitch, you could use a sort of half-nut clamp, closed by an easy to operate toggle if you wish. I'm not aware of any such thing for sale now, but it seems achievable."

yes, i see your point. good idea. i'm probably looking at having to fabricate something like this. Am prototyping an idea (better mouse trap concept)and this clamp would also have to RELEASE quickly. Didn't mention before, since didn't want to add confusion. So the clamp would be functioning as a "trigger release" mechanism.

probably looking at fabrication of say 4 initially.

Know any fabricators in south Florida? I'm in Sarasota.

 

[EdStainless]

Look at a bike quick release leaver clam mechanism.
It won't snap open but they clamp tightly and release quickly.
I am thinking of the QR seat post clamps and such.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[MikeHalloran]

I have a friend in the upper reaches of Miami who rebuilds wire-drawing machines, and takes on a little manufacturing on the side.
I'll check if he's still alive and in business.



Mike Halloran
Pembroke Pines, FL, USA

 

[bob96808]

that would be great, thks

 

[77JQX]

It sounds like you're describing the lever locks sometimes used on trekking poles to adjust their length. Like this?

 

[bob96808]

regarding trekking poles - am familiar with these. only issue i see with that currently is the lock/unlock method requires a twisting, circular motion. Right now I don't see this practical for my particular application. good thought, though. The bike seat clamp seem most appropriate so far.

 

[77JQX]

The trekking pole lock I posted uses a cam like a bike seat post clamp, not a twisting action. They have an adjustment screw to set the force, and a cam lever to lock it on the pole. It comes in 14mm, 16mm and 18 mm diameters, and costs $2.48. I can attest that they can clamp sufficient to resist the force a 200 lb man can generate in a fall, yet open easily through the cam lever. Link.

 

[bob96808]

i ordered 1 each of the 3 different sizes. so we'll see how it goes with the trekking pole clamp.

 

[EdStainless]

You may need to play with surface finish in the clamping area, too smooth and it wont hold and too rough and it wont slide.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[bob96808]

will do.

 

[MikeHalloran]

Bob, my friend Charlie T. can be reached at { charlie at commercialprocessing dot com }.
He does a lot of prototype machining in most materials.


Mike Halloran
Pembroke Pines, FL, USA