Locking a vertically sliding tube in place

[swerider]

On an outrigger design, i need a good way to lock the leg, which slides up and down in an outer tube, which is welded onto the outrigger extension arm. I want to eliminate hydraulics and have it purely mechanical. the locking mechanism must be able to handle a maximum load of 18kN.
Thanks

 

[Tmoose]

One position or infinitely adjustable?
Is Rotating machinery involved ?

Dan T

 

[alansimpson]

Screw jacks are traditional method of mechanical outrigger.
Depends on the risk level but I wouldn't trust any locking mechanism that wasn't fail safe.

 

[zekeman]

Go to an auto service station and see how they hold up the hoisted vehicle on their lift. They must be pretty fail-safe or OSHA would be there in a heartbeat.

 

[AdamPeszel]

Zekeman,
I worked part time third shift at a garage/gas station so I can answer your comment. The lockout for lifts is a small plate that can only rotate in one direction. It is pulled out when the lift is up all the way, and as the lift drops, the plate's rotation is opposite to the direction of how the shaft pushes the plate against the ground.

Swerider,
If you are only using one extension length, it is similar to carnival rides. A large pin is inserted thru the matching holes, and is held by an R-key for easier disassembly. This may also be suitable for variable positions. You would have double shear and bearing loads, but the concept is very succesful in that field.

 

[swerider]

Dan T,
infinitely adjustable would be preferred, but i could also make use of a good one position design.
On the outrigger itself there is no rotating machinery unless i use a screw jack to ensure weight is put on outrigger. the outrigger will be stabilizing a medium size crane truck.
Thanks

 

[swerider]

Thanks for the posts guys.
Here is a simple illustration of the outrigger

 

[Ron]

As AP noted, a pin through matching holes would work well. You could have multiple holes in the outrigger tube for adjustability.

 

[AdamPeszel]

Thanks Ron. After reading Swerider's last post, I have to agree with the other guys on a ball screw. The pin thru matching holes may not give sufficient range.

Swerider, I am concerned about you having to run power to a motor, as I do not know the whole design. Another possibility is to construct you outrigger like what is on some rides and fire trucks. The outrigger is one beam connected to the chassis thru a heavy pin. The foot is on a swivel and the adjustment mechanism is within the outrigger rather than perpendicular to and at the end of the outrigger. If you do not have excessive adjustment, this is tidier and more contained.

Another alternate, depending on design, is to use a handle and manually adjust, much like a trailer hitch. Small trailers are the simplest design, while tractor trailers have a gear mechanism to provide more mechanical advantage.

 

[swerider]

Ron and AP
I need more adjustability than multiple pin holes could provide. the weight of the truck must be lifted off the ground by forcing the outriggers down.
I have good idea but still need a method to lock the outer tube in position once it has been dropped to the ground. then the forcing can be applied.
Are they equations available to calculate the necessary clamping force to hold a cylinder in place under certain loading? for use in the same way motorcycle suspension forks are clamped.
Thanks a lot guys

 

[MikeHalloran]

You do realize this stuff is made commercially, right?

http://ww1.safholland.us/sites/usa/en-US/products/landinggear/Pages/HOLLAND Gooseneck Jacks.aspx

Mike Halloran
Pembroke Pines, FL, USA

 

[GregLocock]

The motorcycle fork approach is ugly as you tend to squish the tube or crack the clamp if you get your sums wrong, and it is not a 100% positive stop.

But if you use a friction coefficient of 0.1 then you should at least not slip.

However if you get grit or mud in the interface then anything could happen.





Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[waross]

There are at least three standardized designs.
1> A large manual screw jack was used for years before hydraulics became widely used.
2> Modern designs use a hydraulic cylinder with a locking check valve. The valve is part of the cylinder and apresure greater than the back pressure in the cylinder must be applied to release the check valve to allow the cylinder to retract. The operation is automatic.
3> The horizontal beam is pivoted and a large hydraulic ram is used to deflect it down. It may have manual screw jacks on the end. The cylinders are equipped with locking check valves.


Bill
--------------------
"Why not the best?"
Jimmy Carter