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

["RodShea" <RodShea@comcast.net>]

There is also an animal out there called a round edge joint file.  It looks 
like a flat file, except that the narrow edges, which do have teeth, are 
rounded, and the wider, flat "faces" have no teeth.  the ones I have seen 
have been pretty thin, and would fit into the kerf left by a hacksaw blade, 
allowing you to round the bottom of the kerf w/o widening it.

Question,  how deep should the cuts be to give a good balance between 
strength and flexibility, for, say, a 3/8 NF, or finer, threaded SS rod?

Thanks,

Rod

----- Original Message ----- 
From: "RodShea" <RodShea@comcast.net>
To: "Donald Good" <donald.good@comcast.net>; "'Tom Krajci'" 
<tom_krajci@tularosa.net>; <atm@atmlist.net>
Sent: Saturday, December 03, 2005 8:39 PM
Subject: Re: [ATM] Mirror Cells - Springs vs. Push/Pull


> 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
>>>
>>
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>
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