Worried about security of Vixen dovetail mount

[Zermelo]

I have a new scope on a Skywatcher mount with a Vixen dovetail type mount.
The scope is a lightweight F/5  150mm Newt.
The mount has a single screw that braces the inserted OTA 'wedge' against the opposite side of the dovetail recess.
There is no other mechanism to prevent the inserted wedge slipping, so it's basically relying on friction (and on a single, unlocked screw) when the scope is vertical. The first time I used it, I had tightened up the screw as tightly as I dared, but half way through the session I felt the scope slip slightly when pointed upwards, and managed to catch it, but only just!

I'm not very happy with this design. My previous refractor had a similar dovetail arrangement, but it had a slightly recessed area to receive the screw, which meant it was more secured against slipping out. I'm thinking of doing something similar with the new scope - countersinking a *very* shallow hole in the centre of the OTA wedge to give the screw something to bite into. An alternative (or additional) ploy might be to line the inside of the mount dovetail recess with some variety of thin, rubbery self-adhesive strip that would grip the OTA wedge more firmly than the existing, smooth metal-against-smooth metal.

Is there any reason I shouldn't perform this mod? (other than voiding any warranty, obviously). Clearly I'd be establishing a "preferred" position for the OTA in the mount, so if I needed to rebalance it in future, for whatever reason, then I'd need to repeat the procedure (the OTA has no rings, the wedge is attached directly to the tube).

[dobblob]

Does the dovetail have an overhang, one end or the other beyond the shoe? Usually there is a hole or two that will accept a screw/bolt (1/4 x 20 ?). A screw of the right length into the dovetail may prevent it dropping out completely. I have done this and it has saved my a** more than once.

[Skipper Billy]

Or get one of these?

https://www.firstlightoptics.com/adm-replacement-saddles/adm-vixen-style-saddle.html

[John]

1 minute ago, Skipper Billy said:

Or get one of these?

https://www.firstlightoptics.com/adm-replacement-saddles/adm-vixen-style-saddle.html

That's what I use. Very secure

 

[johninderby]

Or if you don’t want basic black there is Primaluce. 🙂

https://www.firstlightoptics.com/dovetails-saddles-clamps/primaluce-lab-plus-big-dovetail-clamp-for-vixen-losmandy.html

Edited June 23, 2020 by johninderby

[Cosmic Geoff]

You probably just need to tighten it up a bit more. Thousands of scopes use this system without reported problems.  Including several of mine.

[michael.h.f.wilkinson]

The original Vixen pucks have two screws to tighten: One at right angles to the dovetail and one under about 45 degrees. I first tighten the one at right angles, and then the secondary one. I have found that if the first is loosened, the other one won't turn and loosen, but locks. As a result, my telescopes (8" SCT, 80 mm triplet and 6" F/5 Schmidt Newton) have never slipped in any of my mounts, provided the second screw is also tightened.If you puck only has one screw, something is missing, I would say

[johninderby]

Lot of the newer saddles only have one locking screw and no safety screw.

[Zermelo]

Thanks all, for the replies.

The "saddle" I have is actually integral to the mount, it's one of these:
https://www.firstlightoptics.com/skywatcher-mounts/sky-watcher-star-discovery-wifi-az-goto-mount-tripod.html
so I don't think there's a way to replace it with a third party version.

dobblob, the bar/puck attached to the OTA has no overhang or holes, it has an identical section along the entire length (hence my concern about its ability to slip unhindered through the mount). But your point is valid: I could probably drill and tap a single hole at the eyepiece end of the bar, insert a machine screw, and that would catch the OTA against the saddle if it did slip. It might still shake up the optics a bit though! (but the closer I placed it to the saddle clamping screw, the less it would fall).