Slightly off balance

[CraigD1986]

Hi all. Just looking for a little advice on how to get the balance right on my slightly overloaded setup. It’s not far off but just not quite perfect. In an ideal world, I’d get an EQ6 mount but my wife says we need a new shed and thats apparently much more important (boooooo).

Anyway, I’ve got a Skywatcher 72ED with an ASI533 MC Pro on the back (spacers and flattener between). There is an ASI120MM camera and mini guide scope mounted on the shoe of the 72ED and an ASIAir Plus on the top of one of the clamshells.

I’m very slightly off balance in RA but have got the dovetail bar as far down as possible (blue circle in image)

I’m also very slightly off in declination as the scope is back heavy. I bought a long skywatcher bar to try and combat this but I can’t push the scope any further up the bar due to the focus locking screw (red circle).

Any advice on how to improve the balance?

Thanks in advance!

[astronymonkey]

Hi ,

Can you not rotate the tube in the rings to allow the focus screw to clear the end of the bar.

As for the other axis, would a bit more counterweight give you the adjustability you need ?

Hope you get sorted.

Cheers

[CraigD1986]

Ah, thats a good idea, thanks. If i turn the scope upside down, all of the focus knobs should clear the bar. A bit more counterweight would probably help the RA balance. It would be idea if i could push that hole bar up a little to allow for more clearance above the mount. Any idea on what to use as a weight? Preferably one that won’t slide along the rod.

[astronymonkey]

I guess the first thing would be to put the scope where you want it and then add weight to the end of the bar to see how much you need. I'd only slide the scope up a 5 or 10mm as the further you go the more weights you will need.

As  a starter you could just blutac some weights to the end to get an idea , or use some coins the weight them on the kitchen scales once you get the balance .

You then have a few options, get a weight made up at a metal fabricators,  add some washers to the bar if that's all you need  , or just tape the weights on to make it more permanent.

I'm sure others will join the discussion  who have more experience of a eq mount. As a dob user we have different balance issues but I made mine by working out the weight I needed, calculating the volume of lead that would lake, then I cast some in a sand mould in the garden. I then wrapped them in self amalgamating tape so they were protected and bolted them to the mirror cell.

Final option is a longer bar, but that may increase vibration and flex.

Cheers

[newbie alert]

Tell her that you will build a shed to store the scope in... And call it a obsey..

[CraigD1986]

1 hour ago, newbie alert said:

Tell her that you will build a shed to store the scope in... And call it a obsey..

lol, I very much doubt she would go for that.

[CraigD1986]

Quick update on this. After a lot of tinkering and moving bits and pieces around to more evenly distribute the weight, here is what I came up with:

Moving the ASIAir off the scope removed some weight there and helped with the counterbalance on RA. I custom designed and laser cut a mount for the top of the brackets to house the guide scope. It’s made from 2x 5mm thick pieces of acrylic so the shoe of the guide scope fits in a snug recess and then is bolted in for extra strength. This also moved some weight forward on the scope. I’m planning on adding a ZWO EAF soon so that will be more weight on the back.

Just got a little bit of cable management to do now.

[Elp]

The way I did it with a 60mm refractor is mount the scope at the front of a long dovetail bar so you have all the balance adjustment available at the back of the dovetail. I also had a slight problem of the focuser fouling with the saddle clamp knob of the mount so sandwiched a mini dovetail on top of the main dovetail for that added 15mm odd height clearance under the scope.