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Porta Mount altitude axis is loose

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#1 _Z_

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Posted 19 September 2012 - 09:33 PM

My Porta Mount's altitude axis is loose, but it's not that it spins too easily, because I know how to tighten that down. I can pull the portion that rotates a small amount away from the arm and push it back in place, so there is a little slop now, and the weight of the scope pulls it slightly away from the arm, so the worm gear doesn't grip as well.

When I rotate it in altitude I can hear more noise in the axis than I remember, you can tell the worm gear isn't gripping the best because it barely turns with weight on it, despite being tightened down.

I tried tightening down everything else and it didn't make a difference.

Here's a shot of the gap i'm talking about.

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#2 _Z_

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Posted 21 September 2012 - 06:27 AM

Nobody knows? I contacted Vixen support about another thing and they're a little slow to respond. Hoping I don't need to go through them for this too.

Do you need to remove the vixen logo and service something under that, or is it related to that big screw that appears to have been locked in place with a nail?

#3 davebuechler

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Posted 21 September 2012 - 02:54 PM

Hi Zeldaboy

Yes the blue plate is glued on and can be removed. You then can access a nut that holds the assembly together. You may be able just to tighten the nut, but while you are there you might as well disassemble, clean & re-grease everything and adjust the worm while you're at it.

#4 _Z_

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Posted 21 September 2012 - 03:32 PM

Is there a trick to removing that blue plate? It looks like it's on there pretty good.

#5 SteveG

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Posted 21 September 2012 - 04:24 PM

Are you sure it's not the worm gear coming loose? This caused a little play in mine, and was an easy fix.

#6 dlpville

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Posted 21 September 2012 - 06:05 PM

I had this on a used Porta II I bought. On mine, the Blue Plate stuck so hard that I had to actually cut away some of it to remove the blasted thing (really old adhesive on the back.) After that, there are three socket head cap screws holding it to the angle arm (same as the azimuth axis.)

Remove the axis and you'll find a center nut holding down a large washer plate, which covers the spur gear. On mine, the center nut is a nylon locking (Nylock) nut, and if the nylon insert is too old, it may have lost the elasticity needed to lock it down (the nut is NOT fully turned to seat.) I believe these are standard 6mm nuts, a trip to the local hardware store should find some new ones. If not, a good way to substitute for one is to get a half-height nut (erroneously called a lock nut). The half-height nut is placed on the post FIRST, then the full-height nut is turned to torque on top of it. Some experimentation may be required to get just the right tension, but that adjustment is not terribly sensitive.

After that, you should be good to go.
davel

#7 _Z_

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Posted 21 September 2012 - 06:11 PM

Are you sure it's not the worm gear coming loose? This caused a little play in mine, and was an easy fix.


I had tried tweaking it before and had no luck. I just tried it again and it looks like it has to be just right, the slightest tweak one way has so much slop and the other way is too tight to turn. Looks like that fixed the altitude problem. Thanks!

#8 davebuechler

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Posted 21 September 2012 - 10:01 PM

Zeldaboy

The blue plate has a sticky adhesive back but only the the outside 1/8 inch or so is actually making contact all around the outside edge. The inside is recessed in the metal so the blue plate doesn't make contact.

#9 Eric38

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Posted 29 September 2012 - 12:47 PM

I have the same problem and it is not the outside tensioner set screws or the worm gear axis spanner rings; both accessible from the outside. This looseness is from the mount side of the bearing and gear. The grinding is the outside of the housing against the bearing mount. I am afraid that removing the "pretty" blue sticker is the only way to get into the guts of the thing. I have avoided this because I like to keep things stock looking as long as possible but I can't put up with the lack performance any more. :smash: Time to tinker!

As you can now see below; I have tinkered. There are two layers if 1/8" aluminum that must be dealt with. The sticker is toast by the way. I will probably paint the area and put a plug in the whole. First hole drilled was a 5/8" that revealed the lock nut through a much smaller hole. Too small to get a socket or nut driver into. I widened the second hole enough to get a grip on the lock nut and unscrewed the assembly by applying pressure on the dovetail with a twist. I had to the retrieve the lock nut from the nut driver with a tap from a nail set while clamped in a vice using a random screw of the correct thread pitch as a fulcrum. Good time to clean out the goo grease too. All back together and fully adjustable now. Works like new if not better. :jump:

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#10 Eric38

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Posted 29 September 2012 - 03:36 PM

Update: I noticed inside the housing that there are 3 allen head screws. Only one way to get them in there. Turns out that the sticker is on a glued in plate covering the access to all of the hardware. Only way to get it loose is probably to drill a hole in it like I did and pry it out. Hope this helps if you find the same thing happening to you.

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#11 _Z_

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Posted 01 October 2012 - 07:03 AM

Thanks for the photos Eric! That's a shame vixen didn't make it easier to tweak their mount, but i'm glad to see it's possible. Tweaking the worm gear helped a lot with the slop that was there. There is still some, but i'm going to see if it still performs alright as is before I tear it apart. If it does need to be tweaked more though, i'm glad to see it can be done with some work.

#12 Eric38

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Posted 01 October 2012 - 11:49 AM

I took it entirely apart after that pic. There is a bent washer inside that looks as if designed to compensate for the slop, like a spring, over time but it is not nearly strong enough. I tend to load down the end of my scopes with bino viewers, paracors, barlows and big EP's so I also am glad to be able to adjust the altitude tension at the main bearing point. Once that main axis is tight (to suit), the other tensioner (large set screw on the outside) works a lot better. Then fine tune the tension on the slow mo controls. Works better than new and will hold up The ED 80 APO from ES, with Bino viewers, no drop!






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