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Dob mount build.


foundaplanet

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Hello,

I will be starting to build myself a dob base tomorrow night for a 10" newt. I shall be using 25mm birch ply.

I have read various good threads on this but would like to ask a couple of questions please.

I shall be making the alt bearings and would like to know if there is an ideal or best size for these relevant to size and weight or is it the bigger the better?

Then where these seat on to the mount I notice teflon/ptfe is applied and that the alt bearing often has a piece of formica applied, is this the best way?

I have ordered a 12" lazy Susan and think I pretty much have the az base figured (no doubt I haven't).

If anyone has any top tips or pointers with anything regards to sticktion, friction or common errors or anything to be wary or careful of I would be very grateful.

Thank you.

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hi.ive not built a dob base as you intend doing but i have added a 12" lazy susan to my skyliner.so regarding stiction it was recomended to me on this thread -> http://stargazerslounge.com/topic/118946-just-finished-modding-my-dob-base/ to use some slide glides. i used four with some thin plastic to bring them up to the right height to get the amount of stiction required.

i have some going spare if you need them.

good luck with your build.

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my first reaction is that 25mm Birch ply is a little OTT and will be quite heavy. 18mm would be more than enough and I'd suggest 12mm in many places.

my recommendations would be no more than 12mm for the top cage rings, the mirror box sides, the rocker box back and front and the ground board. the mirror box bottom, and the rocker sides and bottom and the alt bearings I'd say no more than 18mm. birch ply is heavier than hardwood ply and also much stronger so the above would be more than adequate. you could even potentially use 9mm instead of 12mm (but I'd keep the 18mm).

my other recommendation is buy the Kriege and Berry book The Dobsonian Telescope. it's not known as the bible for nothing.

good luck - it's great to see others having a go.

my recent thread might help as this is for a 10" mirror.

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Thank you for replies.

Rory, thank you very much for the offer, I picked some up at the weekend...:)

Carbon, cheers, very useful.

Moonshane, I would agree but I have had this sheet for 2 yrs and it has nothing else to do, I am hoping that by cutting some bits out it will not be to bad.

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Nearly doubling the mirror diameter for sizing altitude bearing work for smaller scopes up to a certain point. Balance becomes less critical when you increase bearing size on small scopes.

But I think as you go with much bigger scopes the bearing size formula becomes less critical with bearings sized only as large as their rocker boxes. For instance, weight differences between the lightest and heaviest eye pieces become a non-issue for the most part relative to the size and weight of the monster dobs, not requiring huge bearings.

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hought I'd post a progress pic..

So far I think its going okay. I went for bearings at x1.8 and whilst I was routing them I thought they seemed huge, and they are! Though I'm pleased with them now they are on the base.

I'm hoping that Susan will turn up tomorrow but I reckon she will arrive Thursday.

med_gallery_13491_1204_3025062.jpg

Thanks.. :)

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This is my effort at trying to make do with the rings I have.

I have made another dovetail plate out of timber and which slides into a female dovetail housing on the bearing.

I was going to buy some more parts but then the light went on. At the moment it seems to work quite well but does need a little tweaking which, may be as simple as a bit of silicone spray.

post-13491-0-25281200-1352893154_thumb.j

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ps it's good to see that others work on a try something and develop it as it goes, kind of method!

That pretty much sums things up so far.. :) I felt like I was taking a bit of a chance but If it all went wrong I'd figure it out..

I have been wanting to make one for so long. The goto is great at times but when I was a kid I knew the sky so well, and it is that that I miss. Very much looking forwards to being lost again, so to speak.. :)

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The lazy susan did not arrive so I have put it together without for the moment. I put some textured polyrey laminate on the base and have some of the grey teflon glides. I noticed that they are not strictly flat so I taped some 240 grit silicone paper to the table to flatten them off. It seems to work very well but I have little experience of dobs so I will have to wait for the first clear sky. Certainly a better glide than prior to flattening them.

post-13491-0-27858900-1352984178_thumb.j

As I had not ordered any teflon strip I wondered if I could get away with using the remaining 4 from the pack. I screwed them on at around 68' (thanks Moonshane :) ). Then placed some of the 240 grit between the bearing and the glide and gently, if rather awkwardly rotated the bearing whilst holding the paper to shape them. This seems to work very but I do have 25 mm sides so its probably not always applicable as the glides are 26 mm.

post-13491-0-06614100-1352984666_thumb.j

Thanks.

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