Constructing a dob

Trevor,

Meant to ask you: how did you cut the circles of wood for the secondary cage? Do it yourself and get it done in a workshop?

Thanks,

Hey Michael,

I used a cheapish router for the circles. I had a photo somewhere but can't find it but here's one of me cutting the arc for the rocker. Same process just with the metal jig in the centre of the piece of plywood. The trick is to only cut about 5mm deep at a time and you'll get nice rings.



I also had a hell of a time trying to get decent Ply. It's all WBP it seems, which is a softcore ply. Because of that my mirror box walls are 18mm with large solid Oak gussets for support. The UTA rings are 24mm each. Now I checked with a bunch of building suppliers and it seems that this is just about the only stuff around, but I since found that Noyeks Newmans have Marine Ply, which is a good deal better.

For hardwood I was lucky enough to find that O'Higgins' joinery in Galway have Mahogany and Oak, so if there's a joinery near you that could be your best bet (again I was told by most suppliers that I would be lucky to find this stuff anywhere :shock: ).

I could not for the life of me find Aluminium anywhere so after a long think I build a pretty solid mirror cell from solid Oak. Very chunky, but my UTA is about 2.2 Kilos with an EP so it will actually probably help with the balance. The primary is attached with a silicone caulk to eliminate the sling and it's arranged in a 9 point floating cell manner (the daubs placed according to Plop). It seems to work - the epoxy is REALLY strong and hopefully this arrangement will eliminate astigmatism. It's also flexible and the mirror is held a few mm from the holder at all times.

here's the primary holder. I really hope it works out. The caulk daubs were placed at the dots I have drawn onto it.



and on the 2" high Oak cell.



Not sure about wood for the cell but I've seen others have had great results with it.

Oh yeah, the groove for the split blocks were made on a cheap Aldi table saw (€50). A word of warning though, this was the scariest device I have ever used

Hope that helps.

Trev

Trev,

For the mirror cell itself, I'm just using steel tubing. Not easy find aluminium tubing, and besides, the steel will be more rigid.

In terms of wood, 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. I might end up buying one sheet and making all the scope from it. Will need to draw it up first though to make sure I can get it to work with only one sheet. I would also need to buy a router then, which adds further expense to the project. At least I will have it for later use I suppose. When cutting the rings for the secondary cage, I will be left with two circles. I must see if these size circles wil be the right size for use as bearings. Would be neat if they were.

Thanks,

Following correspondence with Dave Kreige, I've ordered the following from Obsession:
Upper truss tube clamps for 1.25" tube
8no. 1" tube inserts
2 no. split bolts
Total cost including postage and feess for transferring the money electronically to him worked out around €138. With the euro-dollar exchange rate so good, now is a good time to buy from the US. Let's just hope customs don't hit me.

Mike.
It looks like you are making great progress there!
With regards to the timber...
Be very careful if you do buy plywood.
I'm sure you know this already but I'll say it just in case.
You will want high grade (A-A) marine ply.
This type uses the best adhesives and is manufactured to the highest standards.
Do not use anything else no matter what
When moisture resistance is a priority.
Also make sure the grade is an industry standard and not a 'store' grade.
I've seen pathetic sheets of junk labeled all sorts of grades in those big diy places.
If the sales guy is unsure then walk.

If you don't end up going for ply then there is a company I order timber from at work from Dublin called Excel.

They make bespoke cabinets in Oak, Cherry, Ash & Walnut.

They can source any thickness or size sheets.
(Ash I'm told is one of the hardest timbers)
I know the owner quite well and he has sourced sheets and cut sizes for me in the past and I know from first hand experience
the quality of the timber, cuts & lacquering is excellent.
(Moisture treating &Lacquering bieng very important in bathroom furniture due to the problems that expansion or warping could cause)

If you want, you can send me a drawing of exactly what you need and I'd be happy to get a price for you.

Coool! Thanks Frank. I appreciate that.
Still trying to decide what size of mirror box to use. The bigger the box, the heavier it is. I'll post up a couple of drawings here later this evening and explain the dilema.
Thanks,