12 dob counterweight ... How heavy?

[Fraunhoffer]

Hi all.

I'm taking the opportunitybto tinker with my 12" flextube whilst it's cloudy and going to add a counterweight. Rather than mess about with the clutch nut, I wondered what a good approx weight to start with might be.

I would like to get the top heavy balance better than it is, but not too worried about perfection. Thinking of using some old dive trim weights and a weightbelt.

What approx weight are people using?

[Ships and Stars]

I have a truss dob but since your lower OTA is solid it might be relatively close overall. My 500p came with 4.5kg (3x 1.5kg discs). Too little, so I added another 1.5kg which seems about spot on. It changes slightly depending on eyepiece/barlow etc but mostly on how much dew or frost accumulates on the fabric shroud - it gets quite heavy if saturated and adds a lot of weight. 

One time I left my counterweights at home and used a tie down strap to secure a small tool bag to the underside. That's one of the best alignments I've had!

I thought if I tried that again and got it spot on, I could take my small digital luggage scale and see precisely how much counterweight it liked.

Someone on here with a SW flex tube (or Orion UK solid tube?) OTA had a clever idea to use a magnetic weight they could slide up and down the OTA to fine tune, that or a velcro strip? Might have been John? A nice solution I thought...

 

 

Edited December 14, 2019 by Ships and Stars

[John]

My counterweights go on a magnetic knife strip attached to the lower part of the tube of my 12 inch dob. The 2 weights are 750g and 1500g respectively. With my heaviest eyepieces (wich weight 1.3kg) and the scope at a relatively low angle I need both of them.  I have two positions on the strip that I can place them so that provides more weight variation. This is a DIY solution as I expect you have guessed !

In this pic the lighter of the two weights is in the upper position on the strip:

[Mark at Beaufort]

I have used these strong magnets together with a weight and place them to get balance - https://www.ebay.co.uk/itm/2-of-Vehicle-MagPad1-super-strong-magnet-for-roof-signs-taxi-driving-school/183856185790?epid=1205420445&hash=item2aceaec1be:g:btcAAOSwx4ZakVOw

Not much good for an Orion (UK) scope as the OTA is aluminium but great for my metal OTA.

[Fraunhoffer]

Thanks. Looks like I'll start with 1kg, and work my way up to 2 kg and see how it goes.

There's probably just a bit of play in the altitude, if I don't do the bolt right up , to feel when I'm getting close.

Edited December 14, 2019 by Fraunhoffer