Magnetic Knife Rack

[kirkster501]

Can someone suggest one of these they have used to balance a Dob please (12" in my case). There are quite a few of these about so eager for some recommendations please? Also what weights did you use? I have some 1kg cast iron weightlifting weights kicking around the garage. I may need something smaller to "fine tune" the balance....

Thanks, Steve

[crashtestdummy]

I was looking at then but none seemed to hold the weight I was after so I drilled my tube,placed a round holder through it and I drop a plastic coated weight over it kinda like the weight on the end of the bar.I needed 4kg though so had to be more structural

[nameunknown]

I used a "Gold Block" baccy tin full of lead sheet folded and a big round magnet out of an ancient telly.

Was rubbish....

P

[Bart]

I use lump hammer heads taped to a magnet with a cloth underneath. Slides nicely around the OTA

Barry

[John]

I use a relatively cheap magnetic knife rack which I got from eBay for around £7 delivered I think. I use 1 and 2 lb iron kitchen weights with it but the magnetic strips won't hold the weight on their own so I've added some thin bolts sticking up through the rack at the bottom end and around halfway up which act as barriers to the weight sliding down the length of the knife rack. I've found having the options of the two weights (or none) with the options of two positions along the knife rack covers all the balance issues that I encounter up to and including using my 2.2 lb 31mm Nagker eyepiece.

My knife rack is held to the tube using extra strong double sided adhesive pads.

[astrokoma]

I did something like John's project. The only diference, is that i drill many 5mm holes at the bar (every 2cm), and i fit a little cylinder 4,5mm diameter at the weight.

I used to moove the weight till the right position, and put the little cylinder at the hole.

( i used double insulated "foam" tape also to install the project).

[kirkster501]

I have rebuilt my 12" SW Truss Tube Dob mount entirely. I scrapped the Goto - hideous on a Dob IMO and inaccurate - and turned it into a manual - wonderful! What I find with the balance is that if I balance it such that its correct when viewing object at say 45 degrees altitude its fine with weight at the bottom near the mirror. But if I then shift to an object near the Zenith the Dob wants to go vertical and I have to remove the weight. And same the other way round. Is this the typical issue with balance on Dobs ? Some form of neat rubberised magnetic weights would be ideal, in a range of 500g and 1Kg sizes!!! Or the knife rack idea of course!

[crashtestdummy]

On my 300p I used verlcro and those ankle weights and just removed weight when near the zenith

[Merlin]

A problem with most commercial Newts on a Dob base is that the side bearings are too small, causing the 'scope to suddenly lurch backwards at higher elevations.

The solution seems to be to make the side bearings about the same diameter as the primary mirror.

[earth titan]

I had a magnetic knife rack on the back of a 16" LB I owned (not fitted by me but by a previous owner).

The weights used were metal weightlifting dumbbells.

Worked a treat.

[Damo636]

I had a magnetic knife rack on my 12" but have since found a much simpler approach. I use a 1kg lump of steel (roller from a very large bearing) painted up & with a strong magnet on the back. I then stuck a felt chair pad over the magnet to stop the tube getting marked. It works a treat and I can slide the weight anywhere about the tube with ease. Its particularily useful when viewing close to zenith as I slide it opposite the focuser to stop the ota wanting to go completely vertical.

[kirkster501]

A problem with most commercial Newts on a Dob base is that the side bearings are too small, causing the 'scope to suddenly lurch backwards at higher elevations.

The solution seems to be to make the side bearings about the same diameter as the primary mirror.

Indeed. Thats exactly my finding. I had to order a new side mounting ear for the tube and some mounting bushes to replace the bits where the Goto Altitude motors went. £20 delivered from China All fine and works nicely. Just need to sort out this balance issue and I shall be sorted. I will post some pictures what I did later.