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Stub Mandrel

Source of 1m of 8" Ducting

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I've ordered 1m of 200mm duct from eBay three times - to be the tube for a 150mm x 900mm Newt. The first two times my order was cancelled, I contacted the seller and they said out of stock although they are STILL listing on eBay.

Ordered from another seller, it still hadn't arrived so messaged them and... I just had another refund from the same company as the first two orders.

I suspect even the silly price sellers are the same company.

Can anyone suggest an affordable source? - my steplad has upset me by saying how much got ripped out when he was fitting kitchens.

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It seems common that some businesses trade on ebay under multiple names/accounts.  I had a look around the suppliers on ebay when I was looking for steel tube for my observatory roof and sometimes found as many as four different accounts appearing to trade from the same place.  I suspect it has something to do with evading tax/VAT.

What material are you looking for?  Plastic/steel/aluminium?  Spiral aircon ducting type stuff?

James

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Plastic ventilation duct would be ideal, I've found one direct source that will do 1m for £20, but with a 5-week waiting time.

Anywhere else is 3m minimum for £££

I suspect there is a UK-wide shortage!

At a push 200mm sewer pipe would do but will be heavier, but again the minimum 3m length means silly prices.

I might make a plywood and fibreglass pole truss as I have several old tentpoles, or I need to be on the lookout for skips at building sites.

Or an octagonal ply tube might look nice.

 

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Can you drive around any new housing developments, look for a few builders, and ask for an off-cut and throw the guy a fiver?  I got my last piece from a building site as no cost, more than helpful.  It's surprising how many people are closet astronomers.

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6 minutes ago, johninderby said:

Strange, that was the site showing ffive weeks half an hour ago.

Brainwave!

https://www.defendapack.com/Postal_Tubes_Cardboard_Poster_mailing_tubes/8_INCH_large_DIAMETER_STRONG_POSTAL_TUBES

It will need some serious waterproofing, but polyurethane varnish I already have should do the job - it won't be left out in the rain.. I can bind the ends and add reinforcement where needed.

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Just now, tooth_dr said:

Can you drive around any new housing developments, look for a few builders, and ask for an off-cut and throw the guy a fiver?  I got my last piece from a building site as no cost, more than helpful.  It's surprising how many people are closet astronomers.

I'll keep my eyes open.

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John Dobson often used cardboard tubes I believe, so you'd be in good company there.  And you could always upgrade later if you felt the need.  I have seen a few octagonal ply tubes that look quite nice though.

James

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Cardboard tube and wrap in fibreglass once its in place

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17 hours ago, johninderby said:

Some people charge more for duct tube!

But for 8" not 6"...

It will be the cardboard tube, I think, as I've ordered it.

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When I was making dobs some 20 years ago I found a local one man dust control business who made his own ducting. I had a number of tubes made by him for 8" and 10" mirrors. The maximum length he could make as a one piece was 4' ( 1.2M)  as that was the length of the rollers in his machine.

Nigel

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1 hour ago, fwm891 said:

I spotted the wrong size and that 6" tube is for an f5 so a bit short for an f6, shame as it is well affordable. Although do I want my self-made scope to say 'Celestron' on the side?

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1 hour ago, Astrobits said:

When I was making dobs some 20 years ago I found a local one man dust control business who made his own ducting. I had a number of tubes made by him for 8" and 10" mirrors. The maximum length he could make as a one piece was 4' ( 1.2M)  as that was the length of the rollers in his machine.

Nigel

Dang, I bet I could have found someone with 1m rollers, and even dropped round with some steel sheet.

Still cardboard should be lighter.

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Don't bother with cardboard.

Arrived this morning, well wrapped in cling film. One end squashed and the plastic end cap pushed down inside it and two dents. Ironically it's quite stiff and hard to get back anywhere near original shape!

I might be able to get it round again, and perhaps laminate it with something or use polyester resin to stiffen it.

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56 minutes ago, Stub Mandrel said:

Don't bother with cardboard.

Arrived this morning, well wrapped in cling film. One end squashed and the plastic end cap pushed down inside it and two dents. Ironically it's quite stiff and hard to get back anywhere near original shape!

If only they'd thought to pack it inside something that might protect it from careless handling, eh?

James

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I use galvanized steel, furniture factory, dust removal ducting.

The stuff used by furniture factories uses straight seamed tube not spiral to avoid inflammable dust sticking to the tube.

0.3mm wall thickness steel is the same weight as most other commercial telescope tubing including carbon fiber and rolled hard paper.

I've found steel tube in sizes up to 16" Ø in 2" steps so far in a furniture factory's used stock pile at beer money prices.

You just have to remember to put the straight seam at the tube ring clamp or hinge but you can't easily rotate the tube.

Cardboard tube needs to be kept round with well glued rings or it will go oval at a whim. I've tried it and given up.

Laminating cardboard with GRP massively increases the cost and the weight and ruins the appearance. Been there, done that.

Laminating two cardboard pipes over each doubles the weight, leaves a gap and it still goes oval at a whim!

Plastic ducting [thinner and much lighter than sewage pipe] is fragile when cold and will split readily with a blow or from being squashed.

Most plastic drainage pipes will sag in warm sunshine. They are also very heavy relative to other materials of the same Ø.

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On 27/11/2018 at 20:29, Stub Mandrel said:

I'll keep my eyes open.

If your heading down the M5 south anytime soon or around Leicestershire I can give you 150mm, 225mm or 300mm plastic drainage pipe to your desired length! 200mm is not a diameter used often in drainage. Can get 200mm electric ducting but not something we use. Drainage pipe will be more rigid as well.

20181201_173304.jpg

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Thanks David, I am down that way often enough, so I'll keep you in mind if I don't find a solution.

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Hi All i can thoroughly recommend the drainage pipe i have used it successfully to build two scopes,it is versatile and cost effective.

 I have also used the 10 inch to make a pier.

Regards

Mike

 

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