Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Porta II mount - stiff slow motion

  • Please log in to reply
6 replies to this topic

#1 Michael11

Michael11

    Messenger

  • *****
  • topic starter
  • Posts: 461
  • Joined: 24 Jun 2006
  • Loc: Israel

Posted 28 September 2016 - 05:58 AM

I've got a Vixen Porta II mount for my 80mm ED telescope. For some reason thr slow motion controls are really stiff. Is there an adjustment to fix it? Or will replacing the grease help? I don't mind taking the mount apart.
Also the manual movements aren't quite smooth. Even after I released slightly the allen adjustment screws on each axis.

Edited by Michael11, 28 September 2016 - 06:04 AM.


#2 rhcrooks

rhcrooks

    Vostok 1

  • *****
  • Posts: 131
  • Joined: 28 Aug 2013

Posted 28 September 2016 - 08:43 AM

First, there is a clutch-screw on each axis. I assume you have adjusted those. If the handles are still hard to turn then the most likely culprit is that the bearings that hold the worm are rotated in such a way that the worm is too tightly meshed with the gear.

 

There are 4 grub screws per axis that loosen the bearings so that you can turn them and set the worm engagement (the holes in the bearings are slightly off-center), two are visible close to where the handles attach, and there are additional hidden grub screws under a metal plate on the opposite side of the exposed ones. To remove the plate will require disassembling the mount.

 

Once you take the mount apart (you'll need to pry off the cover with the vixen logo to open the altitude axis), you'll be able to pry off the plates to expose the grub screws. When taking the mount apart I would try to retain as much of the original grease as possible. I took mine apart and removed the grease - and had a heck of a time finding anything that even approximates the smoothness of the original stuff. Definitely not Super Lube or white lithium - both are inferior to the stuff you already have in there for this application. I ended up using some stuff that was recommended for greasing a Losmandy mount, but I forget the name of it.

 

Good luck tuning up the mount. You should be able to get the slow-mo controls working nice and smooth, unless there is something really wrong with your bearings or worm.


  • Jon Isaacs, Michael11 and teashea like this

#3 Michael11

Michael11

    Messenger

  • *****
  • topic starter
  • Posts: 461
  • Joined: 24 Jun 2006
  • Loc: Israel

Posted 28 September 2016 - 12:00 PM

Thanks a lot for the detailed answer,
I'm trying it when I'll have some free time.

Edited by Michael11, 28 September 2016 - 12:01 PM.


#4 Michael11

Michael11

    Messenger

  • *****
  • topic starter
  • Posts: 461
  • Joined: 24 Jun 2006
  • Loc: Israel

Posted 12 March 2017 - 02:17 PM

A little bit late - but I've followed your recommendation and it worked perfectly. Now the mount moves smoothly.

The only problem is that I've ruined the aluminium cover plate while trying to remove it, however it's my own fault.



#5 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 91,219
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 12 March 2017 - 02:30 PM

The cover just gets in the way.. 

 

Jon



#6 rhcrooks

rhcrooks

    Vostok 1

  • *****
  • Posts: 131
  • Joined: 28 Aug 2013

Posted 17 March 2017 - 10:56 PM

Glad it worked out for you, Michael. And as far as the covers go - I forgot to replace mine after reassembly once and left them off with no issue  - I guess it exposes the gears to crud.. might be an issue if you are in an area with lots of wind-blown stuff flying around. Here in Maryland the covers are totally unnecessary.



#7 rederikus

rederikus

    Sputnik

  • -----
  • Posts: 26
  • Joined: 20 Oct 2017

Posted 05 June 2018 - 01:06 PM

Another resurrection of this thread.  I just got a Porta II mount.  It had some backlash and I read several threads about how to adjust the worm gear.  Finally I took it apart on my work bench.  On each end of the worm, there are two (yes, 2) separate adjustments. Both ends need both adjustments to be just right in order to obtain a smooth, no backlash, no effort drive.  The procedure I used, which worked, is as follows.

 

Vixen ED80S Refractor Telescope with Porta II Mount
Album: Vixen Porta Mount II
22 images
0 comments

 

The picture shows one end of the worm.  There's a screw on the top and there's an off-center bush around the shaft.  Starting at one end, I slackened the top screw.  I took some needle nosed pliers and turned the bush to tighten (or loosen) the worm onto the gear.  I then tightened the top screw.  It then did the same on the other end.  I repeated this until the drive was smooth and easy to turn.  I also found it necessary to tap both bushes inwards to ensure they were fully inserted and there was no end play in the worm.  This helps reduce non-worm backlash.  You'll need to repeat the adjustment making tiny rotational adjustments at each end and then tightening the top screw several times before it feels right.

 

The whole process took me about 10 minutes and my drive is now backlash free, smooth and easy to turn.

 

Before I got to this happy stage I freely admit to having spent at least ah hour getting it very wrong indeed.  Have patience.  This works.


Edited by rederikus, 06 June 2018 - 10:16 AM.



CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics