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Vixen Super Porta

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#1 Don Taylor

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Posted 03 March 2013 - 01:06 PM

What's a "Super Porta"? Well, some CN'ers have updated the tripod legs or tripod of the Vixen Porta and Porta II altazimuth mounts. Another has updated the saddle with an ADM product.

I've done both. I had a Celestron ASGT (CG5-GT) tripod left over from another project and I ordered a Porta II head to go with it, to serve as the basis for a grab-&-go telescope.

Also, I have the 6" long ADM saddle on my Celestron ASGT (CG5-GT) mount and like it. It's secure and doesn't chew-up the dovetail bars. Here on CN someone used the other ADM saddle for the Porta, a short, single knob unit that accepts both Vixen style and Losmandy style dovetail bars. I used the 6" two knob saddle, although it's sold for use on Takahashi mounts.

So, I put them together. The results are quite sturdy.
Super Porta!


One problem I discovered when mounting the Porta II head to the tripod: there were only 3 threads engagement between the tripod center bolt and the head adapter (the black piece that comes with the Porta II head). I took the washer off the tripod center bolt and that helped a bit (now 4 threads) but I'd like more, as the center bolt has approximately 8 threads. To do that, I machined off about .150" from the lower face of the head adapter, which increased the engagement to about 7 1/4 threads. I have a small milling table on my drill press and it's not the best but it does work with very light cuts and feeds:
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The ADM saddle is p/n VSAD-TAK8 which is designed for Takahashi mounts and is drilled for 8mm capscrews on 35mm centers. It's a direct bolt-on (appropriate fasteners are provided with the saddle):
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Here is the ETX90 OTA mounted.
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The rig will mainly use an 80mm F11.3 Astro-Physics guidescope. I'm waiting on tube rings from Crawmach. Other OTAs can be used too, the ETX as shown, the ST-80, and even the Vixen VMC200L although it only reaches about 80 deg elevation. The 102mm long tube refractor seems a little too much, even with the beefy tripod and saddle.

#2 Agatha

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Posted 04 March 2013 - 02:57 PM

Don,

That is a very nice job. I, too, am always concerned about the amount of thread engagement. I have replaced bolts on various mounts to longer ones for just that reason. And I always use a light coating of grease on the threads. Many pieces of equipment come with dry screechy threads. :shocked:

Thanks for the great pictures. Nice mod.

Best, Linda B.

#3 Don Taylor

Don Taylor

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Posted 04 March 2013 - 07:26 PM

I was quite surprised at the small engagement. I wonder how many have done this conversion and never checked just how secure the attachment is.

Could have just used a longer 10mm bolt but the Celestron uses an extended bolt that also tensions the tripod spreader. So just a bolt wouldn't quite do it. I also considered machining off the shoulder on the extended bolt - it's like a spacer made integral, but that is a job for a lathe (which I don't have).

By the way, I too make certain to lightly grease the threads. Also used low strength Loctite on all the other bolts for attaching the head to the black adapter and for attaching the ADM saddle.

Thanks for the kind comments.






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