[ Ref. John Grant in 201018 MMDigest ]
After submitting the design for this spring to over ten custom
manufacturers, I have gotten two bids that seem reasonable. With
apologies to Allen Ford, I find that the correct terminology for
the geometry is, indeed, a "torsion" spring. One manufacturer even
called it a triple torsion design, although I would quibble with
that description since the smaller diameter coils are really just
mounting anchors for the torsion element and do not themselves serve
any spring-force function.
It turns out most of the manufacturers are reticent to guarantee the
deflection-force parameter I specified from measuring an original
sample, however the second lowest bidder (which was not significantly
higher that the lowest bidder) agreed that if I provided the sample,
they would manufacture as closely as possible to that parameter, so
I am inclined to give them the order.
Unsurprisingly, the only way to get an acceptable price is to
accept a relatively large quantity, in this case 100 pieces, so I am
proposing a subscription based acquisition. In talking this up with
friends locally, I have confirmed demand for 8 pieces, so if I can get
commitments for 92 more, the order will go forward. Please consider
your own (and your customers') Model "B" needs, now and for the future.
Experience says this spring fractures relatively rarely, but when it
does, there is no easily engineered, durable work-around that I am
aware of, so you may want to have some spares.
Bottom line is I can offer these for $6.50 each, postpaid (U.S.
domestic), two for $12. Foreign shipping at actual cost. This is a
one-time purchase and time is of the essence as the quote will expire
Nov. 30th, so subscription will end on 11/20/2020. Production time
estimated at 5 weeks. If sufficient subscriptions are received, I will
notify subscribers by 11/23/2020 and pre-payment must be received not
later than 11/27/2020. Payment is preferred via PayPal (Friend/Family),
Venmo, Zelle, or Cash App (details to be provided.) Please use my email
address above to enter your subscription, specifying your desired
[ Model "B" Transmission Torsion Spring