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Skywatcher dovetails and their tube rings


Ajohn

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Don't know if I am being stupid and have missed something but I bought 90mm tube rings and a 210cm dovetail.  I'm sure I have read that the dovetails are drilled to accept the rings but it doesn't look that way to me. The base of the rings have a flat thin protrusion that would sit on the rims on the dovetail plus there are no threaded holes to use at the ends of the dovetail bar for this anyway.  There are 2 M5 holes at each end but nothing to match on the riings,

There are a couple of 1/4 whit holes near the centre of the bar but all of the supplied screws seem to be M5 and M6.

Looks to me that I am going to have to drill the rings to match the 2 M5 holes at each end of the bar.

Bar

http://www.optcorp.com/media/catalog/product/cache/1/image/400x400/9df78eab33525d08d6e5fb8d27136e95/1/3/13280-l_1.jpg

Rings

http://www.365astronomy.com/SkyWatcher-76mm-Tube-Mounting-Rings.html

The centre holes at the end of the bar aren't tapped and if those were used to hold the ring in place they would break or bend the tube ring.

?????? Arggggggggggg.

John

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I had problems with that set up loosening some time ago - eq some low number and a refractor that was really too heavy for it. It really needs something to prevent the rings from turning in my view. They could do that with a small change to the rings. I'd still be worried about them loosening though. Looks to me like they could do that and make use of the 2 M5 holes using the screws they provide for those. I don't think the hex drive heads on these will foul the rings,

:embarrassed: Anyway I concluded it must be that way and suspect I will use it to hold the things together while I mark through the 2 M5 holes in the dovetail.

I just did that by hand with a drill that was a nice fit in the tapped M5 holes  :grin: and found that the core size on one side is distinctly different to the other, What quality. Hope  I am right about the screw heads not fouling.

I want the set up to extend the rail on something as it barely balances with 2in eyepiece gear on the end so I will need to drill for a ring that has to be positioned part way along the rail anyway.

Thanks, I must have had the past problems with this set up in my mind when I looked at what was supplied.

( And yes if some one in particular is reading this I still want a smaller refractor - just hope the car bill is the lower one.)

John

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What I have done is this -  :shocked: hasn't Rick's shot changed since yesterday ??

It really needs a bench drill and vice to match the tapped holes at the front. I did it with a hand drill for some reason, the drill wandered a bit and I had to file a little. I did the back one with bench drill but as the tapped holes needed in the dovetail bar can be spotted through it might be ok with a hand drill.

post-2035-0-67918700-1425744299.jpg

I'll probably add a camera rail to the top at some point

:sad: Taken with a Philips CCD web cam. Looks like something a little better would be a good idea.

John

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