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paul11
professor emeritus
Reged: 01/30/06
Posts: 577
Loc: Essex UK.
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Hi Ian in this image the mandrel has a single layer of CF and then a layer of 3mm Coremat ( the white layer ) that has been saturated with Epoxy Resin and the I put on 2 more layers of CF. Did you get my PM Ian?,,,,,,,Paul.
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LX90-10" Canon 350D Toucam 840K Barn-door tracker
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Ian Robinson
Pooh-Bah
Reged: 01/29/09
Posts: 1165
Loc: Gateshead.NSW Nth Coast,Austra...
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An idea that struck me last night is as follows :
Buy some slightly over length thin polycarbonate (as acrylic wont bend and is too brittle) sheet (thin enough to form a tube ie the mandrel but it will be permanently bonded with 1st carbon fibre cloth acrylic composite layer.
Before forming the mandrel from polycarbonate sheet, coat one side with ProtoStar self adhesive flock while it's flat.
The with the flock on the inside surface,form the tube mandrel using precut MDF disks on a pipe.
Staple the end disks to the acrylic mandrel and proceed to build up the tube with sufficient layers of CF cloth impregnated with 2 part acrylic.
When done , simply unstaple the end disks , and push out the centre disk (if it's needed) and trim back the excess acrylic sheet and square up the CF tube.
This way the mandrel essentially is a permanent part of the tube , so no releasing agent is needed and the task of flocking is made heaps easier and the flock should adhere very nicely as it'll not be under tension but inder compression.
Only I'm not sure how well acrylic will bond to polycarbonate ????
How's that sound ?
Edited by Ian Robinson (10/09/09 12:31 AM)
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Ian Robinson
Pooh-Bah
Reged: 01/29/09
Posts: 1165
Loc: Gateshead.NSW Nth Coast,Austra...
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Yep , got the PM.
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Ian Robinson
Pooh-Bah
Reged: 01/29/09
Posts: 1165
Loc: Gateshead.NSW Nth Coast,Austra...
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Done the sums again on a 1.6mm thick aluminium tube :
--- that'll work out at 5.3kg (a big improvement over 11kg for UPVC) for a slightly over long tube (1.3m , I need 1.265m long to be exactly the same length as my existing tube).
--- my mate at Accufab Solutions (Sydney) is fishing about for jobs , so I've asked for a quote to roll me a tube from 1.6mm thick aluminium sheet with a hole for the focusor at the appropriate spot , if that works out too flexible and bendy (it's only 1.6mm thick) I'll convert it to a mandrel and make a carbon fibre tube with it, wont flock the entire interior surface until I've testes how well it holds collimation (will only flock opposite focusor with some of the left over self adhesive flock I've got stashed away).
See attachment for properties I found on the Exel site.
Aluminium is 3x stiffer than PVC and 10x stronger , while CF composite is more than 20x stronger and stiffer than PVC.
I'll need a mandrel anyway .... so I'll hold off buying any carbon fibre from the Ebay sellers and FMS (Broadmeadow NSW) until Accufab respond.
A 1mm thick polycarbonate sheet to make a mandrel (even if I can't incorporate into the structure if good bonding of acrylic and polycarbonate is not possible) will set me back $70 + a cutting fee.
Don't know how much a 1.6mm aluminium tube will cost me yet.
Unilateral 300mm wide 12k CF cloth will cost me 15USD/ yard + postage from the USA (www.fibreglast.com), or 30AUD / m locally. Not available on Ebay.
3k Plain weave CF or 3k 2x2 Twill weave CF (drapes better on curves than plain weave ??) will cost me 170USD (www.fibreglast.com) for a 3 yard offcut + postage of 1.27m (50") wide fabric or 90 AUD/m locally. May be cheaper if I buy some sample lengths from Ebay sellers .
2 lites of 2 part epoxy will cost me 49AUD locally.
plus I'd need some plastic sheeting to cover my work table and concrete floor in the garage , and some glassing rollers and other bits and sods.
And another batch of Protostar self adhesive flocking material to do the entire interior of my tube , no matter which way I go (aluminium tube or carbon fibre tube). About 80USD .
Wont be cheap.
Edited by Ian Robinson (10/09/09 03:14 AM)
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Ian Robinson
Pooh-Bah
Reged: 01/29/09
Posts: 1165
Loc: Gateshead.NSW Nth Coast,Austra...
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I'll track down some dacron cloth.
I've decided to progress my CF tube plans , found a company in mainland china who are willing to send me 3sqm of 12k 1m wide unilateral CF cloth and 3m of 2x2 twill weave 3k CF cloth for 260USD including EMS shipping , which is much cheaper than buying it locally or from the firms I found who sell small lots over Ebay or to hobbyists (in the UK or USA).
Locally the unilateral CF cloth is only available in 300mm wide and sells for 30AUD / Lm. And 2x2 twill 3k CF cloth sells in 1.27m wide at 90AUD / Lm .... WAY TOO EXPENSIVE since I need 3 sqm of unilateral (2 layers and a bit) and 3 sqm of twill for my project.
Will produce a tube 1.27m long x 305mm ID and with a tube wall thickness 1.2mm , except where I reinforce it. I can add another layer if I need it later.
I'll source some 0.8mm thick aluminium sheet for my mandrel , will likely have this cut ready to form the two halves of my mandrel (top and bottom) which I'll secure to MDF or plywood reinforcing forming disks (2 . maybe 3).
Car body bog will fill the joints , or maybe paper drafting tape over some silastic may be all I need to keep it together until the first layer of CF is epoxyed and cured.
Will 0.8mm thick aluminium sheet be flexible / bendy enough so I don't need to have the sheet rolled to form a perfect tube , then slitted ?
Any suggestions on suitable bonding material for curing at ambient temperature (not vacuum forming) , should I just stick with 2 part epoxy or use something else ?
I'll blacken the entire interior surface prior to assembling the OTA with Protostar self adhesive flocking material.
Edited by Ian Robinson (10/15/09 08:30 AM)
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mark Jimenez
sage
Reged: 01/08/07
Posts: 339
Loc: Atlanta GA.
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Hi Ian,
The .8mm Al sheet will be plenty stiff once formed into a tube, but it wont like it!! depending on the alloy, it will be very resistant to perminent bending (spring back). It would be MUCH easier to take it to a shop with a slip roller and have them form it to the correct dia. This should only take a pro a few mins.
You can weld, rivet or glue the seam, and proceed as you discribed.
I would stick with West Systems 2 part epoxy, will work just fine.
The dacron fabric (peelply) Is used as a covering for fabric airplanes, if you cant find it anywhere else, look to your local aviation community (they are often also quite experienced with lightwieght composite construction).
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Celestron ASGT
Astro Tech 8" f4 Newt
QHY8
Meade DSI pro
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