Dob base build

[mdstuart]

Contact expert...Dennis Steele of dob stuff for dimensions....tick

Plywood bought.....tick

Some parts cut out.....tick

How do I cut a nice 8 inch hole! Ok will ask a friend..

Decided to go for the dark star chunky base rather than the curved stylish lightweight approach..

Mark

Sent from my HTC

[swamp thing]

Using a router and trammel will cut nice accurate round holes.

http://woodworkingtips.com/etips/etip030201wb.html

[mdstuart]

Oh I see...I am hoping a friend will do this bit for me but if not I will get a router and have a go.

I found the straight lines hard! I eventually worked out I got better lines using a flat piece of wood with my jigsaw. You see as an accountant I am not that practical but I love having a go.

I did not have enough wood so I need to get a 55cm square piece for the base.

Now arms..I might go wood again as I suspect aluminium will be beyond me.

Mark

[cotterless45]

If it works out on the heavy side , you can always cut loads of holes in it ,

Nick.

[mdstuart]

I think my dark star has a white Teflon? Pad running on Teflon pads...is that a good approach to an az bearing or should the pad be made of something else?

[swamp thing]

I used 'Ebony star' worktop edging glued to my alt bearings and PTFE (teflon) pads on the rocker box Mark. 

You really want a laminate with a texture on the alt bearings this helps to avoid stiction. 

I'll see if I can find a picture to illustrate it, if you would like?

[mdstuart]

I was more interested in the azimuth base bearing...I will use Teflon pads but what surface should I use on the base of the base? Teflon as well?

[Astrobits]

As Steve (swamp thing ) said, "Teflon" against textured Melamine laminate, for both bearings. "Ebony Star" is an American trade mark for melamine laminate. You can control the ease of movement, particularly on the altitude bearings, by trying plastics other than "Teflon" ( another American trade mark for PTFE ). You can try Acetal, High density Polyethylene and Polypropylene. This can be combined with changing the diameter of the altitude bearing, small diameters giving a more delicate balance and easier movement while a larger bearing diameter giver a more robust balance better able to handle large differences in eyepiece weights and a stiffer movement.

Some Dobsonians from GSO in the 90's had altitude bearings of injection moulded plastic against PTFE and they would not hold altitude when a Plossl eyepiece was removed from the focusser. Changing the PTFE for Polypropylene gave enough extra friction to make the dobs useable. In America springs were added to increase the force on the bearings to make them more controllable.

Nigel

[swamp thing]

As Nigel said Mark. Any textured laminate will work

For the azimuth bearing I've used the formica equivalent of ebony star and PTFE pads on my scopes, and it works nicely. I'll see if I can find the exact laminate number of what I used and I'll let you know.

[steppenwolf]

I was more interested in the azimuth base bearing...I will use Teflon pads but what surface should I use on the base of the base?

I used a vinyl LP as the bearing surface for mine - works a treat.

[mdstuart]

Thanks all for the ideas and information...I will let you know how it goes.

[mdstuart]

Had a look on ebay..

Laminate ike this?

http://www.ebay.co.uk/itm/FORMICA-1200-x-600-Sheet-Textured-Grey-Formica-Laminate-Light-or-Dark-Grey-/261714560968?pt=UK_BOI_Building_Materials_Supplies_Carpentry_Woodwork_ET&hash=item3cef6747c8

And then three 1 inch square ptfe pads.  Is this enough to carry my 16 inch scope?

Mark