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making functional spiral slots on a cylinder or how to mate with slots not created as slots

Question asked by David Spencer on Jul 31, 2015
Latest reply on Apr 28, 2016 by Sindre Sorhus

I have an assembly of two concentric shafts. The outer shaft has 2 spiral slots cut into it lengthwise and which exactly mirror each other .  The inner shaft has

a pin which fits into the two slots radially. Hence, moving the outer shaft causes it to rotate about the pin. See attached screenshot. The slots could not be created

as linear or arc slots and hence SW does not allow slot mating with the pin. I kind of followed  this youtube video using a wrap/swept cut  SOLIDWORKS - Swept Cut on a Cylinder - YouTube .

 

Since the slot was not defined as a slot in its creation, no slot mates are possible so I created a tangent between the pin and the "slot" wall. This works sort of.

There are several levers and connectors (not shown) which effect the linear movement of the inner rod which via the pin causes the outer rod to rotate

. If I move the outer rod it moves, the pin moves and the mechanical precursor  linkages all move. However as I move connectors increasingly far from the pin the linkages

sometimes work and sometimes don't. Probably 50% of the time they appear to lock and 50% they appropriately move the inner rod to cause the outer rod

to rotate.

 

I had thought my PC was too gutless but this is a small assembly of maybe 20 parts.

 

I think the tangent is a poor way to move the outer rod and wondered if there is any way to create genuine spiral slots to mate with the pin such that

the movement of the inner rod causes the pin to rotate the outer rod via the spiral slot.

 

I think this approach is FAR superior to mine Straight to Helix transition cut - Slot in Cylinder - YouTube

 

But even then I doubt the slot mates will recognise this as a real slot and I will be left with using tangent again.

 

Thanks for any help.

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