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Re: Status Report on WA3 Rebuild

Amazing what you can find with a google search.

A compression spring is designed to get shorter when a load is applied to it. Examples are vehicle suspension springs, mattress and upholstery springs, and springs used in switches, controllers, and so on. Many compression springs are cylindrical in shape but others are conical (tapered) or hyperboloidal (hourglass/barrel) with a variable coil diameter. One advantage of noncylindrical springs is that their spring constant varies during compression. The larger diameter coil windings collapse and become inactive first, followed step by step by the smaller diameter windings, thus keeping the action of the spring constant. Another advantage of shaped springs compared to cylindrical ones is that higher effective spring constants can be attained with less voluminous springs, requiring wire of a smaller diameter.

Another source I found stated that the coils of a conical spring collapse inside of each other so they don't bind like a helical spring would. Maybe this along with the variable spring constant referenced above makes them the best choice.

Kirk

Re: Status Report on WA3 Rebuild

My education in spring technology began with a broken coil spring in garage
door mechanism...the horizontile coils on shaft above door. I thought I knew
what I was doing...afterwards I knew better. I have had to deal with broken
spring three times in 30 years...the original installation was marginal for
an over length wood door...so about every 7,000/10,000 cycles a spring breaks...and usually in Winter.
Lessons learned:
1) if one spring breaks replace both...spring life related to up and down cycles of garage door...identical springs will have close to same failure point...plus or minus a relatively small number.
2) ALWAYS bear in mind STORED POTENTIAL ENERGY...a sudden release of this
energy due to a wrench or bar slipping out of engagement or a wound spring breaking can be shocking even if you are clear of danger.
3) Internet article by an engineer goes thru the steps to arrive at longer
lasting installation...begins with knowing weight of door...once that is a
known to plug into calculation formulae the life of door springs of several
wire gages can be determined....no surprise that the small diameter wire
that is "standard" gives least number of life cycles...use of slightly larger gage wire gives expotential increase...formulae factors include
weight of door, diameter of wire coil, number of effective coils cable drum diameter,lift distance and wire gage of spring...the stuff engineers dream of
and the rest of us dread.
May seem(and is) far off subject of outboards but springs obey certain rules and knowing those rules takes the mystery out of making a spring.
Next time you need a broken garage door spring replaced ask the technician
about expected number cycles before failure...and cost to upgrade spring
to obtain longer life...extra cost should be nominal. Pay a little more
now and a lot less later.
Outboard related springs (in theory anyway) should be possible to make given basic spring knowledge, a source of material and some basic tooling.
Louis