Re: Safely installing a heavy OTA onto an AP900


Joe Zeglinski
 

Hi,

Just got my "modified" DOVELM2 saddle back from a local machine shop, and
the original design oversight, is now very nicely resolved.

I had the original "4-hole bolt pattern" for the AP900 duplicated (mirror
imaged) on the opposite side of saddle centre. Now the OTA can be safely
clipped in place, with the "lock down knobs" along the top of the saddle.

As I had reported previously, the problem begins with how your OTA sits in
it's foam padded field case. It seems that most cases - from the manufacturer,
or a supplier like JMI - usually have the eyepiece draw tube on your "right
hand side", as you face the open case. When you lift it up, it is already
oriented to clip into the saddle correctly.

However, a brief search has shown that this is NOT always true - there are
field cases where the eyepiece end is on "your left hand side", as you lift.
This makes it impossible to drop the OTA into the DOVELM2 groove directly,
with the knobs at the top, V-groove on the bottom - because of the DIRECTION
of offset in the bolt pattern.

You are faced with one of the following options:

(1) Put the OTA down on the ground (snow, dirt, etc.), walk around it to
reverse hand directions, before picking it up again.

(2) Or, flip it over end-over-end, in the case. You will do the same as you
dismount the OTA, slippery with dew, at the end of the session, when packing
it back into the case.

(3) Or, continue to use the unmodified saddle, and be forced to tighten the
knobs, "upward", against the weight of the OTA, since in that orientation, it
will always drop into the notches in the knob pins "along the bottom". That is
also a rocky, initial 2-point contact.

I have a Questar-7 OTA, which sits in it's foam lined case, as I
described, eyepiece end "at the left hand" - and this situation was
unsatisfactory. It is not only unwieldy, but you also LOSE a couple of inches
of plate adjustment range, because the saddle ends up shifted below DEC axle
centre if you use the "unmodified" DOVELM2. There is also nearly 2 inches of
saddle, overhang weight at the eyepiece end, in this situation, which you
don't want since you will already be bottom end heavy with cameras etc. Thus
OTA centering is affected in two ways.

Now, with the duplicated bolted pattern, the DOVELM2 can be used correctly
for ALL OTA field case designs - left or right handed.

Some may say that this is a picky point, but I disagree. I think there
should be as standard, TWO bolt patterns - one shift left and the other
shifted right of the DOVELM2 centre line.
I suppose this might also apply to other saddles.

Roland, I recommend you consider this on future production runs of the
DOVELM2, and perhaps offer the mod on present stock, depending on which
orientation (eyepiece on left or right hand side) the user's field case comes
in. When you designed the offset approach, you could not have possibly
realized the potential conflicts with OTA case designs, out there.
The "offset bolt pattern" was a good idea - just wasn't fully implemented.

Joe

----- Original Message -----
From: "Joseph Zeglinski" <J.Zeglinski@rogers.com>
To: <ap-gto@yahoogroups.com>
Sent: Saturday, April 14, 2007 12:00 AM
Subject: [ap-gto] Re: Safely installing a heavy OTA onto an AP900


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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