Need help deciding on ideal ID for animatronic spring guide

I am helping my son construct an animatronic design of his. He is having trouble finding a formula to help him determine the proportion of cable to spring guide. He is working on a small scale, so he is using 0.85mm/0.0335" thick, 80# test monofilament. He wants to learn how to determine the ideal ID of the spring this will run through. He would appreciate help to determine what would be the ideal amount of play for quick action. Should the gap be in 1000ths or hundredths of an inch?

Also, I'd like suggestions for thin flexible tubing to cover this spring.

I appreciate any suggestions you might offer. Thank you.


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    Hi Barry,

    The inner diameter does not need to be too specific. It just needs to have enough clearance that the cable/string/etc is able to move freely without generating too much friction.

    With push/pull cables you also want to make sure it's not too loose a fit so the cable does not bend when being pushed.  

    But with monofilament you are using pull only, so any housing that does not bind or create friction should be fine. 

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