Dob base - wide or slim?

[gooseholla]

Hello,

I recently constructed a base for my dobsonian scope. The base is 60 x 60, but the uprights are only c. 42 x 42.

Is it better to have this wide base, or could I trim it flush with the uprights? It is a bit cumbersome to move, and when it turns can smack the legs if not paying attention.

I guess wide is stable, but would it being smaller make it less stable, able to topple over?

Any help appreciated.

Thanks

John

[John]

Here is my Orion Optics 12" F/5.3 John. The mount was built in 18mm baltic ply by Shane (Moonshane) along the rough dimensions used by the Orion Optics dob mounts. It's very stable and I've used 400x - 500x on with scope target / seeing conditions allowing without undue vibration issues. Underneath the square section rocker box is a circular base of around the same diameter with 3 feet. I guess this is quite a narrow mount.

[Moonshane]

as you say, wider is more stable but personally, and assuming it's like the one in your avatar pic?, I'd trim to a square base. my own is similar but with square footprint. I also cut out two of the sides to allow the wind to blow through, reduce weight, add 'style' and also it gives you a place to grab.

here's a pic of the style I use, again with an OOUK 12"

[Moonshane]

LOL - as you can see John's is 'similar'.

[gooseholla]

Thank you.

Yes it is the one in my picture.

Both those mounts look great! Hopefully one day I'll be able to make something a little less rough than this!
 

My neighbour - who helped me build it, has all the saws required, so I think i'll talk to him when I see him next, take it round and chop it down a bit, perhaps even round off the bottom board.

[gooseholla]

Hi,

Was wondering if another question could be answered.

My base spins on 3 bits of teflon 120 degrees...ish... apart near the central bolt. It also has 4 bits on the extremities of each side. If/when I cut my dob base down, is it best just to leave the 3 central bits in, or replicate the set up now? Or is there a better way to do it?

Thanks

John

[Moonshane]

three pads make a plane. anything else will create sticking issues. I'd just have three pads at 120 degrees and put these at a radius equal to the side bearings. you want them widely spaced of course but ideally the weight put on the side bearings of the rocker should pass directly though the teflon pads to the feet (which should be under the pads) to the ground. I have a round groundboard. 

[AlexB67]

Always reminds me your mounts are a beautiful looking bit of craftsmanship Shane, I am going to  attempt one some time for my own skywatcher, do it slowly bit by bit while I have a working one. I doubt it will come out that nice knowing my success with hammers and stuff

[8kids]

My ground board is circular and flush with the sides, it has three Teflon pads above the 3 feet. I did have it wider but it caused some flex because the Teflon pads and feet were not in line.

[gooseholla]

Thanks for the replies.

If I understand it correctly, I am looking to place just 3 teflon pads over 3 feet, and 2 of those pads should be as near as possible to the vertical boards where the telescope moves in altitude?

 

[Moonshane]

not quite. space them equally at 120 degrees. this shows a round and a square groundboard - I use round but the pads will be in the same place no matter what shape

board.bmp

[gooseholla]

Thanks for that.

I don't think I'd be able to make my base circular, but I am certainly contemplating cutting both down to the size of the mount this weekend.

Thanks

John

[Moonshane]

hi John. Triangular works too for the groundboard. the shape is irrelevant in some respects as it's the three points that matter. draw a circle. mark your points and then cut a triangle around then.

a bit like this

[swamp thing]

Never even thought of that Shane. I need not have routed out that circular groundboard after all.

Triangular would have been much quicker. Ah well!

[gooseholla]

Wow! That is a great idea. Triangle it is then. That will make the 3 points easier to locate as well, and knock the weight down considerably.

[gooseholla]

Hello there,

Well, with my neighbour we managed to cut down the base to a more suitable design.

There are 3 feet underneath the teflon pads (not shown).

Thanks

John

edit: Oh, another question... The telescope came with a box around it (as seen in pictures) but I can't work out actually what it does, or if it is even needed! The bearings for the altitude are bolted to the scope itself!

[swamp thing]

Looks like the box is simply providing a flat surface to mount the bearings against.

[gooseholla]

It just seems kind of cumbersome and adds weight. However, it is useful for helping to carry the scope and attaching a wixey to! I may change it out for ply wood one day and match it to the base.

[swamp thing]

Looks good though

All the best turned out solid tubes have a box around them (can you guess what my 10" looks like )

[gooseholla]

Well I've been out tonight and used my 'new' base. It is so much easier to move from the shed to the garden for a start. It is also easier to control. I have been tracking objects with no effort for 30 minutes tonight. Before, a slight nudge sent the object out of the view, but now it moves tiny amounts. It is so much smoother to turn.

Now I only have to sort the focuser out and it will all be nice and smooth!!

Thanks for your help guys, especially Moonshane.

John