Tube builds for 8" f/5.9

[dana]

I'm a new Istar forum member from S Africa. The 8" f/5.9 looks to be the scope of my dreams and I've pretty much come terms with the Household Finance Advisor on the pros (me) and cons (her view of the monthly budget). I won. It'll cost me a new rose garden in addition to the scope. Familiar?


It looks like the lenscell, focuser, & etc will come from the USA but the tube might have to come from Ales's plant in the CR. S Africa is not an easy place to import large, expensive-looking things into. To us it looks like a telescope tube, but to the customs here it looks like a wallet, mine. I may have to consider my own tube build. Anyone on the forum done a tube for a lenscell that size and f.l.? Does anyone have views re. the thermal properties of wood -vs- metal tubes? I have an 8" Mak and know how long it takes to cool a metal one to equilibrium. Will  wood tube minimize that?

Thanks . . . Doug Bullis

[Mike]

Doug, the main concern is the lens itself reaching equilibrium. I don't know if the tube material makes a difference. Maybe someone else would care to comment on this. Check out:

wood tube scope

Also to be taken into consideration is the lens and cell weight of a 204-6 which is 11 pounds. A fairly short tube but it needs to be stable and without flexure.

Mike

[boomboom]

Hi Doug,
I'm building a 6" f12 and have found 152mm wide 3mm thick round aluminium pipe available in Australia easily. Are there no steel /metal workshops in SA ? For under $200 Australian dollars there is a 203mm 3mm round Al tube 2200mm long that could be knocked up into a telescope tube. I'm doing cells out of hardwood.
Matt

[bn1777]

Hi Doug and welcome to the club Mate , woaw! 8 inch , cool .
I am with Matt on this , there must be a supplier of the 203mm x 3mm thick aluminium tube some where in South Africa , look at HVAC ( Heating Ventilation and Air Conditioning ) companies , also ship repair/building use this as well .
You need about 1200mm or so , so maybe you will find an off cut ? and save a few Rand .\

Good luck and we all await to see your progress , lots of photos please .

Brian.

[criverside]

Doug here in the U.S. thrifty ATM's have used alum. irrigation pipe from Hastings Irrigation Pipe Co. for years, they will sell short lengths just for ATM's. Try to find a irrigation pipe mfg. close to you, ---------Craig

[Mike]

It is true that many use the irrigation tubes. However, the problem with them is they are not very round. I talked to Danny Crawford a few months ago. He was machining a back plate and counter cell for a guy. He said he had a hard time because the tube from Hastings was so out of round.

Mike

[dana]

Hi again, all . . . There are indeed tube suppliers and custom machine shops in SA but I've checked prices and it may make more sense financially to buy direct from Ales in the CR. Really, though, financial sense is less the issue than build quality. Local metal shops can't match the baffle fitting and perfectly round tube that an experienced optical artisian working from original CADs can do. Better to expand the wallet than reduce the quality. Thanks to all for the tips. =Doug in SA