ATM Sorbothane & Vibration Isolation

[BodyByJay@aol.com]

Take a look at www.sorbothane.com and ask for the "product guide and pricing."
This company makes sorbothane vibration mounts that could be used for a
Dobsonian I think (and cheap -- prices not much more than a hockey puck... or
two).  Basically it is a thermoset, polyesther based, polyurethane
viscoelastic material that comes in various hardnesses so you can design it to
absorb specific ranges of vibration.  There are 6 durometer types (harness
types) available.  Compared to rubber or neoprene--sorbothane has been shown
to have a lower transmissibility of vibration.  One chart shows the
transmissibilty of rubber being 10, neoprene is 7 and sorbothane is less than
2 (quite an improvment in vibration dampening capability).

I think you determine the weight of your entire Dobsonian, divide that weight
by the number of isolators you intend on using to determine the load per
isolator and then use the correct isolators to handle that load.   They
recommend 10-20% (thickness of the isolator) static deflection (preload) and
also recommend isolating your system below the lowest critical frequency to
achieve maximum attenuation.  However, I am not sure what that frequency might
be...  any ideas?   System frequencies ranging from about 20 to 70 Hz can be
attenuated which seems to also be partially dependent on isolator load (higher
loads attenuate lower frequencies) which makes such a system tunable!!

For example,  if you have a 12.5" Newt... the OTA weighs 80 pounds, the Dobson
base weighs another 80 pounds then you have 80+80 (160 pounds of load to
isolate).  Looking at the charts you might then use a 1" diameter 70 durometer
isolator bushing having a recommended load of 28-44 pounds per bushing.  You
then support the system with 5 bushings to get an load of 32 pounds per
bushing (160/5=32).  You preload the bushing using a torque wrench to ensure
equal distribution and tune out the target vibration.  

Anyway... this is my contorted Andersonian logic...  would like to know what
you think.

Jay D. Anderson