How to fit a second dovetail to 130pds?

[billyharris72]

Hi all,

Seems like a stupid question and I guess I'm missing something very obvious, but just how am I supposed to do this? The supplied tube rings have holes in the top, but they are not the same size - only the one that comes fitted with the useless, wobbly screw mount thingy is the correct size to take a bolt that will thread through a Vixen dovetail bar (the other is smaller), so how does the second bar fit to the other ring? Come to think of it, what is the other hole supposed to be for?

As I say, I'm probably missing something obvious, but can someone enlighten me? I'm trying to work out how to fit a guidescope and getting nowhere.

Billy.

[Waldemar]

You can buy new tuberings from a better quality, like these:

[Louis D]

2 hours ago, Waldemar said:

You can buy new tuberings from a better quality, like these:

Or find a local machinist to drill and tap you new holes in your current set of rings to match your needs.

[Waldemar]

2 minutes ago, Louis D said:

Or find a local machinist to drill and tap you new holes in your current set of rings to match your needs.

Those SW rings don't leave a lot of flesh for that... They are very flimsy I think.

[Macavity]

I tend to drill out the "photo threads" with an M6 Drill.
So, if you have some ability to use a power drill + bits...

In that way, you can attach many things to some degree 
of precision/rigidity -- with an M6 countersunk bolt / nut!

Some of the larger rings have a more extensive FLAT part?
If so, then use a half-height (locking) nut on the top. This
fits under the curved side of Skywatcher bars, if you mount
the bar "upside down". You can then attach a *variety* of 
gear with other dovetail clamps... which are movable! 

This shows the general idea. I have removed one end of 
the upper bar to reveal the half height nut! You can also
see how I use aluminium U-channel to fit a *lightweight*
solar finder to a MAK150 via M4 nuts / counter sunk bolts. 

[Macavity]

P.S. It does occur to me to add a quick reminder to CLAMP the
ring firmly before you start any drilling! They are an awkward
shape and can bind themselves to the drill bit and spin round. 

You don't want any digits... lumps of flesh removed etc. etc.  
These days I mostly use Step Cone bits for drilling such things. 

https://www.amazon.co.uk/MOHOO-Titanium-Precision-Drilling-Different/dp/B06XXPNTWF/ref=sr_1_2?ie=UTF8&qid=1507299512&sr=8-2&keywords=cone+drills

[billyharris72]

Thanks for the feedback all. I can drill out and tap a hole on the dovetail easily enough. Just wanted to check I was not overlooking something really obvious.

It does make me wonder what the smaller hole in the other dovetail is for.

[Luna-tic]

16 hours ago, billyharris72 said:

It does make me wonder what the smaller hole in the other dovetail is for.

Safety stop, maybe?