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

[George Anderson <tillerman1@videotron.ca>]

How about drilling out the bottom before making the cut? You would have
to do a bit of filing on the threads first but you could make a nice
round bottom. Or drill through a mating nut (flats are much easier to
drill) and then thread the bolt through to the correct depth and use the
nut as a guide during drilling. You may want to add a second nut to lock
the bolt position during drilling. Just a thought.

George Anderson
Montreal Canada

Clear skies and good health

RodShea wrote:
> 
> Might be worth making the cuts, then rounding over the lateral edges of the
> teeth of the hacksaw with a sharpening stone, making the cutting profile a
> semi circle.  I realize there would be no relief, but I bet you could round
> out the bottom of the cut pretty well.
> 
> Rod
> 
> ----- Original Message -----
> From: "Donald Good" <donald.good@comcast.net>
> To: "'Tom Krajci'" <tom_krajci@tularosa.net>; <atm@atmlist.net>
> Sent: Friday, December 02, 2005 10:46 PM
> Subject: Re: [ATM] Mirror Cells - Springs vs. Push/Pull
> 
> > 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.  In this particular case, simply round
> > off the back edge of the hacksaw blade and use the finest grade grinding
> > grit and then polishing compounds (from your mirror making supplies)in the
> > cut with the hacksaw back edge as the polishing tool.  Take special care
> > that the polishing strokes are linear (don't rock the hacksaw blade) and
> > that the thickness of the material remaining at the bottom of the cut is
> > constant along the full length of the cut.  Use a strong magnifying glass
> > (e.g. jeweler's loop) to examing the cut.  The bottom of the cut should be
> > an even high-gloss or shiny (not necessicarily mirror shiny) for the full
> > length.  Also make sure that the bolts have a non-threaded shank portion
> > and
> > that these cuts are made there.  The threaded portion have stress risers
> > already (the threads themselves) that may compromise the strength if the
> > cuts are made there.
> >
> > If you want proof, make a test (round, not threaded) rod with a set of
> > cuts
> > as described by Arjan with just the hacksaw and right next to those, an
> > iddentical set of cuts (same final thickness) that are polished out.  Then
> > repetedly flex the rod until it breaks and see where the break occurs.  If
> > made equally, the polished out cuts will survive.  Then continue to flex
> > the
> > polished out cuts to see how much longer til they break.
> >
> > Don
> >
> >> -----Original Message-----
> >> From: atm-bounces@atmlist.net
> >> [mailto:atm-bounces@atmlist.net] On Behalf Of Tom Krajci
> >> Sent: Sunday, November 27, 2005 3:39 PM
> >> To: atm@atmlist.net
> >> Subject: Re: [ATM] Mirror Cells - Springs vs. Push/Pull
> >>
> >> >From: "Arjan te Marvelde" <arjan.te.marvelde@hetnet.nl>
> >>
> >> >> However, I still don't know what Don's flexural U joint
> >> looks like in
> >> >> his collimation cell....
> >>
> >> >I guess that you could make those for example by making cuts with a
> >> >hacksaw on opposite sides of the screw, almost meeting
> >> eachother at the center.
> >> >Repeat the process 1mm along the screw, but at 90deg angle.
> >> The result
> >> >is a cross-coupling which gives some flexing but keeps axial
> >> position.....
> >>
> >> Thank you!  This sounds reasonable, and fairly easy to accomplish!
> >>
> >> Tom Krajci
> >> Cloudcroft, New Mexico
> >>
> >
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
> >
> 
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