Dob base build question

[aerobrake]

Hi all,

Just about to build the base of my 18in dob which I have been building using Kriege/Berry dob building bible.

Am having a bit of a confusion with the base that will rest on the ground board. I have the 3 teflon pads that go on the ground board and was wandering if I'm correct in assuming the bottom of the rocker box is entirely covered with a laminate that will rest on the teflon pads?

Also what are you guys using as the laminate? Are you using one big piece or several pieces (not ideal) to cover the bottom of the rocker box?

Thanks
Mike

[mental4astro]

Hi Mike,

First, the easy part: yes, you cover the entire surface of the rocker box in one single piece of laminate. This will assure that the Teflon pads will have the maximum span to work on.

You also place the pads to give you the maximum diameter the rocker box will give in a circle. Remember that the optimum pad size to weight is 15lb per square inch. You will need to weigh the fully assembled OTA with finders and your biggest eyepiece, and the completed rocker box to give you the weight you need.

Now the hard part. The heavily textured laminates we like to use have been discontinued by Formica and Laminex. The 'Ebony Star' from Wilsoncraft is available, but you need to by a full sheet (3.6m X1.8m), and off-cuts are very hard to come by. My experience anyway.

However, you may still find some off-cuts and full sheets of the textured Formica and Laminex range. The textured range of these two companies are, including the colours the 'good book' recommends:

Formica: Quarry finish

Laminex: Dimensions.

Within each there is a range of colours, but the texture is the essentially the same. I found my Laminex off-sut at a cabinet maker. Check out the cabinet makers near you for these off-cuts. Cheap too. My 1.8m X 1.2m was $20. The uglier the colour, the cheaper it is as the off-cut has been around for a while.

Calculate the diameter of your altitude bearings as this will be the absolute minimum that you will need in the length of the off-cut: half the circumference. The width of the off-cut will need to cover the rocker box and allow for at least 8 strips for the alt. bearings to allow for errors in cutting. This will leave you a left over piece about the same size as the one for the rocker box.

Mental.

[aerobrake]

Thanks Alexander, thats great info. I'll start hunting down the laminex asap.

Cheers
Mike