Constructing a dob

I did see Birch plywood in B&Q Liffey Valley. Only available in 18mm thick sheets of 2440mm x 1200mm, one sheet cost €55, which seemed expensive to me.

That's a shocking price Michael. But I bet if it's not marked as Finnish, Russian or Baltic that it's really just a veneer over a soft core. If it's the genuine article I think that would be the price to expect though.

By the way, I've seen many sheets of 18mm WBP ply in that size which have warped and split. I'd follow Frank's suggestion. One of the problems with the ply I used is that it has a tendency to split because of the enormous number of voids in it. Fully 2/3rds of the sheets I looked at were junk. Just had to pick the best ones from the stock that were in the store.

Very tempted to order those clamps from Obsession myself, but am going to wait a bit test out the current ones. 1.5 hours of clear sky in two months so I don't know when that will be though

Trev

Trev,

I've seen several examples of warped and damaged sheets of plywood in those diy stores alright. To be fair to B&Q though, with the birch plywood, it was only one stack of sheets that were marked as "birch plywood". All the others were simply labeled as "plywood" and priced alot less.

Here's a drawing of the secondary cage:

www.astroshot.com/Dob/4.jpg

And here's the mirror box:

www.astroshot.com/Dob/5.jpg

This drawing isn't quite complete yet as the side bearings aren't shown yet. Once they are sized up, part no. 4, the side of the ground box, will increase in height and form a support ring for the side bearing.

As you can see from the last two drawings, it's getting very wide. I'm now thinking of having no mirror box - attach the side bearings directly onto the mirror cell.

What do you think??

What is dictating the size of the gap between between the walls (6) and the mirror ?

I thinking of you not having a mirror box but having a shroud about 2 feet long to protect the mirror from light and mishaps, it would save on weight.

What is dictating the size of the gap between between the walls (6) and the mirror ?

The mirror cell, and in particular, the bolts holding the sling.