Dob Base Query!

[Damo636]

I have a couple of weeks holidays coming up during that time I am going to try my hand at a more sturdy base for the dob, should be interesting!! I am thinking of the box cradle design (something like the pic below) & have a couple of questions for you guys that have been down this road before.

First of all. Obviously the cradle has to be fairly snug around the ota but how is it tube secured so that it doesn't slide out under its own weight when pointed high in the sky? Am I correct in thinking I would need a tube ring or similar positioned at the upper end of the cradle assembly or is there a simpler approach?

Secondly, is there any advantage to have the altitude bearings seated as below or would they work just as well seated in a V cut out?

[swamp thing]

I built my 10" Dob similar to the one in your pic. With sonotube the tube cradle can be made 1/8" undersized. This allows it to grip the sonotube very firmly indeed. It won't slip.

My homebuilt 10"

Ugly but it works well.

If your tube is metal have a look at Shanes 16" Dob and how he got round it. Very nice job he made of it too.

A vee cut out would work equally well but doesn't look so aesthetically pleasing IMO.

[Damo636]

Cheers Steve. My tube is metal so will need some sort of additional support. I might be able to use the existing holes in the tube when the alt bearings are removed to fix the cradle assembly in place. It will be a case of trial and error but luckily I have sourced a load of old plywood to experiment with!

[yesyes]

My homebuilt 10"

It's an iDob !

[Carbon]

I'll be following this thread as I am in the process of modifying my stock Lightbridge base, among a few things I am in the middle of installing pebbled laminate strips (substitute for ebony star) around the stock alloy altitude bearings and some teflon stips in place of the stock felt strips. I'm just curious as to exactly where to place the short strips of teflon. I am thinking at the 4 and 8 O'Clock positions? I realize the wider you separate pads the more friction they create.

[Moonshane]

hi Damo

if you can upload a pic of the tube and how the alt bearings currently fit then I might be able to suggest something. if you can get tube rings then this would give you more options, I don't think they are that dear for the Synta ones.

re the rocker shape, I also prefer the aesthetics of the arc sections but you could get away with a V cut. you'd need to ensure that the V was quite shallow though as the best motion comes with teflon pads placed at approx 70 degrees apart from the centre of rotation. i.e. 35 degrees from centre each side either side of a vertical radius.

I could do a drawing if you want to explain.

[Starflyer]

This was my attempt, a different design but the thread may give you some ideas

[Damo636]

Thanks guys. I have uploaded a few pics to show the main problem with the supplied mount. The supplied needle thrust bearing (at least thats what I think its called!) although very smooth, is just too small in diameter for the size of the base. When in operation there is a lot of roll (yaw)

and especially at high powers gets very irritating! I have tried fitting a few felt pads but they haven't really helped that much. I think an Ebonystar ring and some teflon pads in addition with the bearing would sort it out perfectly. The altitude bearing system actually works very well and it might be a simpler approach to build the new base around the existing design but with better wood and focus the improvements on the azimuth end of things.

[Moonshane]

most independent kitchen shops will be able to obtain 0.8mm sheets of formica and try to get one with a slightly dimpled pattern - the one near me sells it for about £2 per square foot. glue this to the underside, add three teflon pads above each of the feet, and maybe another around the central bolt and then wax the formica. this will sort out the smoothness of the azimuth markedly.

[Damo636]

Cheers Shane. We have a couple of local kitchen retailers I could try for the Formica, fingers crossed I get something suitable.

[Saleratus]

Hi Damo,

One of the more solid and elegant dob designs I have seen for scope in the size range of yours is the Starmaster Oak Classic. I have one of these and it's wonderful to use. Here's a photo just in case it provides some inspiration.