pivots

[wayne quigleyParticipant @waynequigley28540]

Hi Guys

not actualy boat related,but I am a member of a amdrame group and have a stage prop to make.it is a machine which swings out 2 arms.

I intend to have a solid round pole suported at the bottom by a 3 plate washer which 1 of the plate has ball bearing on to reduce friction.the top will be a bracket it suport

the arm will be positioned at 90 degrees to the pole.

the means of turning will be by a string wraped around the rod and a weight via a pulley,as the weight drops it will unwind the string turning the rod and arm.

does any of the enginnering guys see any problems with this

cheers

Wayne

[wayne quigleyParticipant @waynequigley28540]

[Bob Abell 2Participant @bobabell2]

Hello Wayne

I would suggest the contraption will need a top and bottom bearing, the thrust bearing will be ok for taking the downward load only

A nail top and bottom in the pole and two plates fixed from somewhere solid

Bob

[Paul TParticipant @pault84577]

Hello Wayne

Without knowing how long the arm is or what function / weight the arm has to support it is difficult to give any advice however from you description I can say that the weakest point of the design would be the junction between the vertical and horizontal pieces.

The stress on this part is dependant upon the length of the arm, the weight of the arm and any weight that the arm has to carry, the turning speed of the supporting vertical section and finally the breaking / stopping system that controls the rotation.

Could you provide a sketch of what you envisage.

Paul

Edited By Paul T on 28/12/2012 08:26:32

[wayne quigleyParticipant @waynequigley28540]

Hi Paul

sorry for late reply but we went away.and while we were there I change my approuch.I picked up a 3 plate washer for the bottom of each pole 1200mm long(the washer is basicly a washer with ball bearing inserted and 2 grooved washers.the top is now supported by a threade rod inserted into the top and it turn easly.

the turning of the rod is still by means of a string wriped around the rod and a weigth pulls the string please see photos.

Wayne

[Paul TParticipant @pault84577]

Hello Wayne

The feasability of the whole structure still depends upon the strength of the arm and its supporting joint.

Without knowing what the arm is going to do or what weight it is intended to support it is difficult to pass further comment however given the evidence of the photos I can comment on the materials.

The arm appears to be made from slate batton which is notoriously weak and prone to failure when put under tension, this problem is compounded by the fact that there is a large knot in the arm adjcent to the point of connection,(image 2) this knot is a weak point in the timber and at a position where the arm will be under maximum stress.

Paul

[wayne quigleyParticipant @waynequigley28540]

thanks Paul

the arm is to hold another piece of 6mm ply to form a L shape.the arm is not going to carry any weight apart from it own weight.the machine is to open out and the L shaped arm is to go behind a person to give the affect of trapping them to the audience.the arm attached to the black enamel rod is 2 pieces of ply fastened to each side of the rod and there will then be a further piece added to make the L shape.

so strength not an issue

cheers Wayne

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