Vixen Porta Mount / ADM Dovetail Adaptor Issue

[Dragons Egg]

I've just come into possession of a Vixen Porta 2 Mount, only to realise that that the saddle that comes with it is inappropriate for the dovetail bars that my two scopes use. I therefore went to replace the saddle for a spare ADM "Vixen style" dovetail plate adaptor I happen to have (see link below). It seemed a simple enough solution, but for an unforeseen problem. The Porta 2 mount's outer threaded bolt holes don't line up with those of the ADM plate adaptor. A partial solution is to use two of the mount's four inner bolt holes instead. These do line up with those of the ADM adaptor in question. . . but now there's another issue - two in fact: 1) The Porta 2 mount's bolts are all in Imperial! 2) Meanwhile the mount head's inner bolt holes are visibly larger than the eight outer ones (which appear to be 1/4"). How much larger I don't know for certain. . . 5/16"? Also, are they UNC or UNF? I have tried to contact Vixen by email, but for some reason the link on the company's webpage doesn't work for me. 

So it comes down to this: does anyone know what size (and type) of bolts I need to get? Thanks in advance. 

https://www.rothervalleyoptics.co.uk/adm-vixen-style-dovetail-plate-adaptor.html

[johninderby]

You could just get a short photo type dovetail and bolt the saddle to that then fit it to the strandard saddle.

Here’s one I did  on an AZ5

 

Edited October 9, 2019 by johninderby

[Dragons Egg]

Hi johninderby. Thanks for getting back to me. Your suggestion looks like a good workaround, but I'm concerned about the extra weight. The Vixon saddle on my Porta 2 mount (which looks somewhat different to your one?) plus a photo-type dovetail, could add nigh on half a kilo to the overall weight, and I'm already pushing the boat out with my current OTA/EP setup. Still, I'll certainly consider if all else fails. Nice photos. 

PS. I'm pretty sure the bolts I need are 5/16" UNC. I'll find out for certain in a few days time, and I'll post the results, come what may. 

 

[pete_gamby]

On 09/10/2019 at 16:07, GrahamKnott said:

So it comes down to this: does anyone know what size (and type) of bolts I need to get? Thanks in advance.

The larger bolt holes on the Porta II are M8 with 1.25mm thread pitch. The smaller ones are 1/4" with 20tpi pitch.

HTH

Cheers, Pete

Sales Manager, Opticron - Vixen UK Distributor

[Dragons Egg]

Pete - just to say, many thanks. . . much appreciated. 

Gray