Re: [ATM] Mirror Cells - Springs vs. Push/Pull

["Don Clement" <clement.focuser@verizon.net>]

>  Don't forget some obvious but often overlooked ways to
> make adjustments finer.  These may be easier to implement.
>
> 1. design your collimation screw locations as far apart as possible.
>
> 2. Buy fine thread screws.  The standard US inch size screws usually
> come in at least two different pitches, e.g 1/4-20 and 1/4-28.  Use the
> higher pitch number.  (Of course you have to get nuts to fit.)

The Standard 3/8-32 UNEF thread size could be substituted for 3/8-24 UNF
size previously mentioned. Taps are readily available for UNEF sizes. The
larger diameter 3/8" is much stronger that 1/4"  diameter used for support.
Three 3/8" diameter collimation bolts are located at each apex of 9" long
triangular sides of the moving mirror focuser and adequately supports  the
focuser with 14" mirror.

Also there must be some sort of allowance for the angle change or tip-tilt
of the bolt during collimation. That is what the  flexure machined  into the
bolt if for. To allow for tip-tilt but be axially  and radially rigid.



Another advantage of larger diameter fine pitch bolts is the thread helix
angle is smaller so that given the same coefficient of friction of the
threads there is less of a tendency for overdrive or loosening to occur
after collimation.



Don Clement

Running springs, California

Happy Thanksgiving.

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