Truss/Flex tube Dobs, how?

[Mr Bond]

Anyone got a pic of a flextube collapse mechanism, rods, bearings, locks etc?

I'm planning an attack on a 12" Dob and want to duplicate their mechanism.

No photos I've seen show the way it works and holds collimation.

Can you help?

Thanks, Phil.

[Mr Bond]

Nobody can help?

That's not like SGL.

:-)

[Gina]

Sorry, I know nothing about Dobs.

[Moonshane]

don't know about the flextube ones but the ones here are very high quality and someone with your skills could easily replicate?

TELESCOPE TRUSS CLAMPS

[swamp thing]

don't know about the flextube ones but the ones here are very high quality and someone with your skills could easily replicate?

TELESCOPE TRUSS CLAMPS

These are indeed excellent quality truss clamps, but I seriously doubt you'll ever get the tube to slide through them as they grip onto it like an angry Pitt Bull.

They have to be opened to move the tube about. Not sure that would be of much use to your Flextube ideas.

Although I've no experience with them, these look like they could easily be modded to accommodate a sliding pole.

Maybe worth sending them an email.

MoonLite Telescope Accessories

Regards Steve

[Mr Bond]

Excellent. Thanks, that is handy.

Anyone know how Skywatcher do theirs?

[Cornelius Varley]

You might be able to work it from the illustrations in the manual Flex-tube dobs

Peter

[calibos]

Have a look here.

http://www.cloudynights.com/ubbthreads/showflat.php?Cat=0&Board=reflectors&Number=5028653&fpart=&PHPSESSID=

He used Moonlite clamps and ball and socket clamps for the top of the struts. I'll be converting my 16" Lightbridge from its current truss system to the collapsible 3 strut system. However with the greater Focal length and shorter height of my Lower OTA I'd be pushing the flextube type system (longer struts) beyond the point where it would hold autocollimator precision level collimation un-aided. As a result, I'll be adding a steel cable string tensioning virtual truss system. with a threaded bolt system in the struts so that I twist the 3 struts to tension the strings.

[Mr Bond]

Thanks chaps.

More research to do me thinks....

[JamesF]

I guess the key to keeping collimation is "repeatability". That is, the scope opens to exactly the same position each time. The Skywatcher Flextubes appear to have the truss rods firmly fixed at the top end and then just run through collars on the base, with a stop on the end of each truss so they open to the same place every time. Each truss is then just held in position by a bolt. As long as the truss rods are rigid enough to hold everything firmly in position I imagine it wouldn't be that hard to duplicate. Could be very similar to the counterweight bars from an EQ mount, come to think of it.

With a self-build I think I'd be inclined to make the scope easy to collimate (ie fit decent adjustment knobs all round) in any case. If it's easy to adjust then it's probably not going to be a big deal just to drop a collimating laser/eyepiece in every time it gets used so the collimation can be checked. If it's a pain in the neck then I imagine it's less likely to get done...

James

[Mr Bond]

Thanks James. I think my best bet might be to take a ride over to see one in a shop. Take mental note or even sneaky phone camera pics.

We have a Green Witch opened only 50 miles or so from us and it'll be an excuse to look at the EPs and scopes anyway.

Thanks for great input. Much appreciated.

[JamesF]

Definitely be worth checking out the diameter of the truss rods and getting some idea of whether they're solid or hollow if you're going to actually see one in the flesh, though there must be someone on SGL who could help with that by measuring their own if necessary. I've been wondering whether standard 15mm copper tube as used for plumbing would do the job. It would have the convenience of lots of available fittings if it would, and can be bought with a chrome finish if that's what floats your boat.

James

[Mr Bond]

I was thinking of curtain rods, 25mm. For the same reasons of easy availability (B&Q etc).

I think 15 or 22mm copper might be weak. It's annealed to bend easy.

[swamp thing]

If tubing is what you're after these people are where I bought my truss poles from.

Aluminium Round Tube | Aluminium Tubing | Aluminium Warehouse

[JamesF]

That's handy. What size did you use, for what size (focal length/aperture) scope?

James

[swamp thing]

That's handy. What size did you use, for what size (focal length/aperture) scope?

James

I would use 1" 16 swg for a 12" f/5 scope. You might be able to use 18 swg for a shorter f/ratio.

Unless you are going to go with the moonlight clamps these will require the 1.25" tube.

I used larger 1.5" 16 swg for my scope but that's a 20" f/4 this would be far to big for a 12" scope.

Regards Steve

[Mr Bond]

For reference, I'm building a f5.3, 12", Orion optics (UK).

I thought to use the curtain rail tubing as I can get it locally, it's chromed steel, designed to be rigid, and I have a choice of the larger diameters.

Some of the fittings might work out too.