Re: Maximum SAFE shimming thickness under a DOVELM162 clamp set ?

Christopher Erickson

I have made shims up to 10mm thick to square-up some compound telescopes.
And make triple-sure that the scope is tightly collimated first since you are squaring to the OPTICAL axis, not the OTA structure axis.  Any change in collimation will change the orthogonality.
And any OTA structure flexure or mirror flop has to be eliminated, or at least taken into consideration when evaluating orthogonality.
I hope this helps.

Christopher Erickson
Consulting Engineer
Summit Kinetics
Waikoloa, HI 96738


From: ap-gto@... [mailto:ap-gto@...]
Sent: Friday, July 25, 2014 8:23 AM
To: ap-gto@...
Subject: [ap-gto] Maximum SAFE shimming thickness under a DOVELM162 clamp set ?

Hi Rolando,
    After gradually eliminating other causes, looks like I might actually have to “brass shim”  my RC-14 (integral) D-Plate on this saddle to fix possible non-orthogonality.
I  need to compensate about  a large 22.1 arc-Minutes  FOV shift, to re-center targets (measured) at zenith – and hopefully finally resolve the meridian flip offset problem.
    I have TWO choices for my RC-14 truss:
(1) Unbolt the D-plate from the truss, and slip in a 1.5 mm brass shim under its ring, for its short supported section (237 mm) of D-plate section. Concerned about degrading the integrity of its 4-screw attachment at one end or other. This will also require taking down the massive OTA (approx. same weight as RHA) – probably several times, to get it perfected.
... Or ...
(2) Loosen the DOVELM162 (front, or rear) saddle clamps, and slip in almost a “doubled thickness” of shim (2.6 mm) for its longer  16” saddle support span. This can probably be done safely, in place,  at Park-2 at my 45 latitude, so a lot less work. Also, much easier to test and re-adjust the brass shim thickness as required.
    If I loosen the end-most clamps (and the center pair, partially), can the end clamps still provide sufficient and safe locking with a 2.6 mm thick brass shim under the truss D-Plate, at that extreme end of the DOVELM162 ?
    Although 2.6 mm doesn’t seem like much of a saddle clamp obstruction, I worry that the end clamps won’t even latch into the D-Plate’s V-groove, and thus end up either with  OTA “wobble” during meridian flips ... or something terribly worse.
    So, what is the MAXIMUM practical and safe thickness of shim that one could place under (say) the frontmost clamps?
    Has anybody else performed an RC truss shimming,  which part was shimmed, & how ?
    It is likely the same for shimming the RHA, between its rings and saddle.
Joe Z.

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