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

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

> >From: "Donald Good" <donald.good@comcast.net>
>
> >WARNING!  Simply making hachsaw cross-cuts in your collimation bolts will
> >leave scratches in the bolts at the thinnest part (at the bottom of the
> cut)
> >creating stress risers.  Stress risers are locations in materials that
lead
> >to concentrations of stress forces leading to fatigue failure, something
> >that you do not want in your collimation bolts.  The most common cause in
> >the fabrication process is sharp corners or scratches while making load
> >bearing parts.
>
> >For such modifications in critical load bearing parts like collimation
> >bolts, it is strongly recommended that scratches and tool marks left at
the
> >high stress parts be polished out....
>
> Thank you for the warning.  However if I use this approach in collimation
> bolts...and I subject the collimation bolts to relatively little bending
(a
> couple degrees?)...is this fatigue failure less likely to happen?
>

I agree with Tom on this. I have made many dozens of collimation bolts and
similar mechanisms with solid flexures machined in having both sharp corners
and with rounded contours. Since collimation bolts and the similar
mechanisms  don't see high loads or much bending over a couple of degrees,
there have been no failures due to stress fatigue. I always run parts like
this though many hours of vibratory deburring ( like shot or ball peening)
that does relieve some stress though only on exposed edges where the media
can contact. It's not like a collimation bolt is used in critical aircraft
or spacecraft applications that might see extreme loading and high
vibration.



Ever see a bolt made for high strength applications such as  the high
strength bolt with a twelve- point head bolt, the type of bolt with MD111
prefix for example? These high strength bolts are forged, have rounded
contours, stress relieved by shot or ball  peening and have rolled threads.
Even the head shoulder on this type of bolt has a rounded fillet.



Don Clement

Running springs, California

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