Re: Safely installing a heavy OTA onto an AP900


Joe Zeglinski
 

Hi Mal,

Thanks for the info,

I went through the AP accessory list, and came across Roland's
justification, as you describe. The DOVEM2 is a nice design because as you
say - simply set the dovetail horizontal and flip the matching plate into it's
bottom edge, lock the knobs. However, I think there is also a "design flaw"
in the manufacture.

O.K. - please forgive this bravado, from a total newbie, however, I have
just attached the DOVEM2 dovetail and noticed what seems a bit of a problem -
not a deal breaker, but certainly an inconvenience.

I attached the DOVEM2 with the "offset hole pattern", such that it sits
higher up on the face of the DEC end face, so that the approx. one inch of
excess moment will be "towards the front of the MAK/SCT OTA (which is mirror
end heavy). If I were to flip the DOVEM2 around 180 degrees, the off centre
hole patter, would be towards the back of an SCT,, making the mirror end
moment even worse, and thus decreasing the adjustment range of the mating
plate, before it slips out of the bottom end, lock knob. I know, it could be
moved to a centre hole, but that would make the DOVEM2 effectively half
length, and the OTA "rocky".

I hope I am being clear, so far. Surely, those with SCT's must be aware of
this situation.
Please bear with me.

The bad news, if the DOVEM2 is bolted in, high up, as I started to
describe, and you then set it horizontal in preparation to receive your SCT
and plate, the lock knobs are now along the bottom edge. Also, the bottom
V-groove where you will drop the plate into for first contact is actually a
shallow, milled down channel (not a full notch, like the other side). So
basically, the SCT's mating plate edge is initially resting on just two
points - the two brass locking pins. As you then tip the horizontal SCT up, to
be fully inside the DOVEM2 channels, you must now screw the two locking knobs
"upward" against the entire weight of the SCT.
Note: I am intentionally not talking about a "refractor", here. This is an
awkward way of installing a mirror end heavy SCT or a MAK like a Questar-7,
correct?

The only other way to make this still viable, is to rotate the DOVEM2
"counter clockwise" instead, so that the knobs will be along the top, and you
will dip the SCT plate into the other, FULL V-groove, which now is along the
bottom edge. This is almost perfect, since after you tip the SCT into the
DOVEM2 surface, the lock knobs are loose, and can easily be screwed downward,
into a full lock, while the SCT's dovetail plate fully occupies the full
V-groove.

Perfect ... right?

Not quite. The problem in making this compromise - rotating the high
bolted DOVEM2 counter clockwise, is that you first have to remove your very
heavy SCT (C9) or a MAK (like my Q7), from the transport case, and flip it
around "hand over hand" (end to end), so it is facing now LEFT.

Problem is - my Q7 sits in it's case "facing right", and I suspect that
all telescopes, are placed in their travel cases with the objective or
corrector lens facing to the RIGHT. The alternative, to avoid hand over hand
flipping of a heavy scope, is to bend over from behind and over, the case lid,
and lift it out that way, backwards - back killer!

The solution:
Roland should have drilled a third "4-hole pattern", in the opposite
direction, relative to DOVEM2 centre. That way, everything I have meticulously
described above, will work correctly, with the lock knobs at the top, and the
SCT lifted from it's case, facing to the right, as you install it, and the
DOVEM2 dovetail will no longer be back end heavy, giving you more room to
shift the SCT balance in the saddle. We can't sacrifice any loss of adjustment
position for SCT's, because there will also be heavy eyepieces, and possibly
cameras, making things even worse for loss of adjustment range.

Looks like I am going to need a machine shop to drill 4 more holes in the
standard DOVEM2, for use with SCT's and MAK's.

I think that Roland may have chosen the "current direction" for the offset
hole pattern, is because he was thinking of AP "refractors", which are lens
end, forward heavy, and the DOVEM2 being eyepiece end heavy, provided more
latitude for adjusting a refractor's balance point.

As I said - I may be WAY OFF on this, since I haven't had my AP900 fully
configured, but at this point, the DOVEM2 seems not to be particularly made
very well for it. Certainly, it makes mounting an SCT inconvenient.

Fortunately, this can be easily remedied on future DOVEM2 production, by
simply drilling one more 4-hole mount pattern, on the opposite side of centre.

Perhaps, you or someone else in the group can explain if I am totally
mistaken. Your experience with the DOVEM2 will be much better than mine.
Certainly, after an evening of playing with the DOVEM2, to see how it will
seat itself on the end of the DEC axis, and how I would lift up my heavy MAK
OTA, I can see no easy procedure.

Please comment, and save me a trip to a machine shop. I hope I have explained
myself fairly clearly, above. Sorry for such a long post.

Thanks,
Joe

----- Original Message -----
From: "Mal Speer" <mal@malcoprecision.com>
To: <ap-gto@yahoogroups.com>
Sent: Friday, April 13, 2007 10:02 PM
Subject: [ap-gto] Re: Safely installing a heavy OTA onto an AP900


AP and Cassidy both make newer upgraded saddles with a much better
locking system using two large knobs. The reason for only a dovetail
on one side is that that is a tip in saddle. You don't have to slide
a heavy scope in from the end, just tip the scope into the dovetail
drop it down and lock it in.
Mal

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