Carbon Composite tube upgrade questions

[DavidU (Dave)]

Ian, to make the focus area stiffer why not do a few more wraps about 5" wide around the ota where the focuser is fitted?

[Ian Robinson]

Originally Posted by DavidU

Ian, to make the focus area stiffer why not do a few more wraps about 5" wide around the ota where the focuser is fitted?

That's probably a good idea , I was thinking a good idea is to stiffen the tube where the cell is bolted on, where the focusor is and where the spider bolts on by applying at least one extra layer of unidirectional CF with the fibres orientated parallel with tube circumference , this will I think enhance hoop strength and make the tube extra resistant to deformation and compression in those sections (ie the bottom 300mm , the top 300mm and maybe once I've got the new DEC torques sorted (for the DEC balance) do something similar for where the two tube rings compress the tube.) .... cripes my tube will only be 1.27m long , and if I don't cut the unidirectional CF cloth circumference reinforcements , then I may as well just do the whole length of the tube in 2 layers of 0o unidirectional on top of the first 90o layer of unidirectional ....

This sound right ?

[Tandum (Robin)]

Originally Posted by mch62

Ian have a look at FPI Protostars blacklight tubes. 27gr/cm weight and the flocking is extreamy dark.
My 10'f3.8 Astrograph comes in at 11kgs total but that is with a conical mirror.
The 1200mm long tube weighs 3.28kg. It's very stiff and with a small amount of body filler to fill in the spirals and a nice shinny appliance enamel paint job looks a treat.

http://www.fpi-protostar.com/blite.htm

Mark

These are pretty cheap and worth a look but they say they will not ship outside the US. How do we get our hands on one?

[Ian Robinson]

mch62

What are the Outside and inside diameters of your blacklight tube from Protostar ?

Have you checked how it holds collimation by observing how collimation shifts when you move the tube about and into different orientations (via a laserbeam type collimator) ?

[Ian Robinson]

Originally Posted by Tandum

These are pretty cheap and worth a look but they say they will not ship outside the US. How do we get our hands on one?

Tandum,

I asked Protostar about getting hold of a 1.27m x 12" BlackLite tube and have been informed the shipping will be 180USD.

Too bad no one here in Australia stocks them (hint ... hint ... any retailors reading this as this is what the response was -

Re: BlackLite 12" tube‏
From: Bryan Greer (bgreer@fpi-protostar.com)
Sent:Thursday, 8 October 2009 3:07:11 AM
To: ian robinson (ianinoz76@hotmail.com)

Hi Ian,

Unfortunately, it is not practical to ship these tubes out of the USA. It costs hundreds of dollars to do so, so is just not worth it. It is the length of the tube that causes the shipping to be expensive. Mail will not allow anything over 46" in length, and even then it must go by Express Mail International which costs about $180.00. I wish I could find a way to ship these abroad, as there is a lot of interest in them.


Sincerely,
Bryan

Unfortunately my tube needs to be 50" long.

[Ian Robinson]

I asked Composite Components , Bibra Lake, Perth for a quote to make my 314mm OD , 1.7mm thick CF tube , they estimate about $1000. Scrub getting the tube made by them .

Will likely source my unilateral 3K CF cloth, and plain or 2x2 twill weave 3K CF cloth and 2 part epoxy , make my own mandrel and have a crack at making my own CF tube.

In the meantime while I'm sourcing my raw materials , I've queried Vixen Japan re how well the New Atlux servos will cope with my 7.25 kg.m RA tangent arms eithe side of the RA pivot point (assuming I stick with my heavy OTA tube and buy 10.5kg of extra counterweights).

[mch62 (Mark)]

When i got my 46"x 12" blacklight tube back about 12months ago i don't remember it being $180 for shipping ?? But I went for the Blacklight tube because it was the most economical lightest and least messing around & quickest compared to making a CF tubes. I have made them before as well as FG ones.
The cost of $115 for the tube and remember this is pre flocked + say $180 for shipping is still a resonable price. When I got quoted the shipping it was for the tube boxed + what ever fitted inside the tube for transport so I got a secondary , spider and heated secondary holder end caps trims and a couple of meters of the extra blacklight cloth for future projects.
Add a mirror and focuser and presto a Telescope.
I think if you need it longer that is when they won't ship outside US ???
As far as stiffness goes holding collimation when moving from horizon to horizon no problems there. The tube is very stiff and not prone to squashing. Actually much stiffer than steal or aluminium tubes for the weight/thickness ratio.
It has the feel of a CF tube.
I am using a Conical mirror which reduces overall weight and means the mirror does not need to be colliminated once originally done , only the secondary as required. Also at f3.8 thermal expansion appears to be quite low and have found refocusing to be minimal over a coarse of a night.
I only wish they made tubes to suit larger mirrors although i would most probably go a double truss again for larger mirrors.
I experimented with my Green laser at different angles and different materials and paints as well as the inside of the Blaclight Tube and the BL flocking gives the least light scatter I could find.
Mark

[mch62 (Mark)]

P.S. Ian I have to eventually cut 3" off the bottom off my tube ,you can have that + 46" only 1" short
Mark

[Ian Robinson]

Thanks Mark,

That was interesting and useful information , I'll keep that in mind, expectally now the AUD is getting better.

I can probably shorten my tube requirement by a few inches if push comes to shove.

I've not bothered shortening the threadbar that holds the secondary holder (maybe 3" there) , kept it as the extra bit of tube beyond the focusor helps keep stray light out and maybe a bit of dew.
But being a "skinnyer" tube , my focusor will be closer to the primary so I'd need to move the primary further away from the secondary.... need to model that to work out how far.

I've had a quote from company in China for some unilateral 12k CF, plain and 2x2 twill 3k CF which is 230USD including postage for enough for 4 layers of CF.
Just a matter deciding on how to make a mandrel , $70 for some thin polycarbonate from Specialised Wholesale (Lambton NSW) , getting a quote for aluminium tube (1.6mm thick sheet rolled to a tube = 5.28kg) a possible alternative OTA tube (?).

Enough Protostar SA flock to do the entire inside of the aluminium tube or a carbon fibre tube , 80USD.

2 litres of 2 part acrylic to make the carbon fibre tube $49 from FMS (Broadmeadow NSW).

[AlexN]

I'd love to move my 80mm F/6 objective into a carbon fiber tube... Would make a difference both in thermal expansion (focus drift due to temperature) and also reduce the weight of the scope... I would love to do it..

[Ian Robinson]

Originally Posted by AlexN

I'd love to move my 80mm F/6 objective into a carbon fiber tube... Would make a difference both in thermal expansion (focus drift due to temperature) and also reduce the weight of the scope... I would love to do it..

Woudn't cost much to do the CF tube for a 80mm refractor.

Wouldn't need much 12k unilateral or 3k 2x2 twill cloth and not a lot of epoxy.

The 12k unilateral cloth comes 300mm wide.
The 3k 2x2 twill cloth cames 1m , 1.27m or 1.5m wide.
You can buy small lots on Ebay (I need more than a 12" long or 1m long sample, and I've not seen unilateral cloth on Ebay unfortunately).