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#1 stephanm

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Posted 29 October 2013 - 09:39 AM

I recently purchased a Vixen Porta II mount and am having some issues with it. I am using it with an AT72 refractor.

When turning either slow motion control, they bind for about half of a rotation of the knob and then free up for the other half of the rotation. I have tried adjusting the radial adjustment screws, but that didn't seem to make any difference. I have tried to loosen the axial adjustment nuts, but neither one will budge. Does anybody have any suggestions on how to adjust this binding out?

I am also trying to adjust the scope so it will balance in altitude. Is anyone doing this? Do I need to attach a dovetail bar to the scope?

#2 Binojunky

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Posted 29 October 2013 - 11:22 AM

Have you tried the two axis adjustment screws on the axis bodies? the two allen keys under the rubber plate are for this, a dovetail will help with balance issues however if either of the two screws are tightened down too much it can cause binding,ajustments are very minor and a small one will make a big difference,DA.

#3 stephanm

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Posted 29 October 2013 - 01:55 PM

Yes, I have adjusted them for the balance issue. This did help, but the little scope is back heavy with larger eyepieces. I am looking at a Manny Myles plate and attaching a dovetail bar so I can slide the scope forward more.

#4 Binojunky

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Posted 29 October 2013 - 02:26 PM

I put the Manny conversion on mine at a later date, it moves the dovetail clamp from a side position to a horizontal position however it stays the same in relation to the position of it over the centre of the tripod and head, it may lower the centre of gravity a bit, for the scope you mentioned a longer dovetail plate will do the trick, your focuser rotates so you can spin it to get the knobs horizontal.
On my Zenithstar 71 I just use the longer plate attached to the foot with one allen screw securely tightened.
If you are imaging then removing the foot and using rings and a dovetail is the way to go,hope this helps, Manny Miles stuff is very good by the way, DA.

#5 stephanm

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Posted 29 October 2013 - 05:59 PM

Does anyone know how to loosen those axial adjustment nuts on the slow motion controls? To loosen, do they turn counterclockwise or clockwise?

#6 Don Taylor

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Posted 29 October 2013 - 11:53 PM

Does anyone know how to loosen those axial adjustment nuts on the slow motion controls? To loosen, do they turn counterclockwise or clockwise?


I was playing with the Porta a couple of nights ago in an attempt to lighten the stow motion controls somewhat but ran out of time to fully disassemble and understand the inner workings.

It seems though, that the small set screws hold the adjusters which controls engagement of the worm to the main gear and the set screws also restrain them which controls axial end play of the worm.

Try loosening one set screw and then work the slow motion backward and forward. When I would do this the adjuster would begin to protrude from the housing and the worm gear would gain axial play.

The adjusters also have two spanner recesses to allow worm to main gear mesh adjustment by rotating the adjusters.

Long answer but in summary I believe the adjusters are not threaded, just simply retained by the set screws.

Hope this helps.

#7 stephanm

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Posted 30 October 2013 - 08:50 AM

Don, thanks for your reply. That makes sense now, what I thought were radial adjustment screws are actually set screws holding the adjusters in place. I will play with it again tonight and see if I can even out the movement.

#8 SteveG

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Posted 30 October 2013 - 12:48 PM

On mine, one of the slow-motion spanner nuts was coming loose, which caused a lot of backlash in the control. I was able to tighten it and everything has worked well since.






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