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Carbon tube for 10" OO mirror


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No worries about the tardiness of your reply, most of us DIY types are aware of how long jobs take, plus life in general is full of other things to occupy our days.....       BTW, Alan and myself are members of the same club.

Regarding the distance from the focuser to the front end of the tube.  One consideration is that it’s best if stray light cannot reach the inner end of the focuser.  A greater distance from the focuser to the end of the tube can fix that, but at the expense of a longer tube that may be harder to transport - my scope tubes are often transported across the back seat of my car. But it’s simple to make a slip on extension to the tube, this need not be structurally strong, just rigid enough to keep its shape.  Commonly available camping mat foam is good.

I’ll check back now and again to follow your progress with interest.

Cheers, Ed.

 

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Well, here it is, after allowing the part to stabilise for a couple of weeks the lid is finally off. The surface finish is superb, you can see that I have used a mix of standard carbon and carbon/kevl

Drive mechanics complete. Now to install the drive electronics.

The Vacuum chamber lives!!!!  Just did a trial run with a glass of water, and it degasses like crazy.  Holds a vacuum too. Pic to follow:

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The mould tool.  The end liners are 3mm polypropylene, and the same material in strip form will run down the sides vertically and horizontally to act as barriers for the flanges.  I will post the plug cradle tomorrow, which is basically this tool converted with different end caps.  Ed, thats a good reminder about tube length and car space - I must keep this in mind.  I was planning on 1200 - 1250 mm, but i better double check the rear seat width.

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Mould tool converted into plug cradle with plug installed. Now comes the fun bit..... filling, glassing, priming, glossing, cutting and finally polishing. Then convert back to mould tool to layup one side.

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Tube filled and glassed.  These are two of the most tedious parts out of the way.  Nice and cosy next to the rad, outdoor conditions not too conducive to curing today.20190425_194142.thumb.jpg.5e9a42ce9a9276bbc30cf5cdd038be06.jpg

I am very happy with the uniformity of shape and the surface of the GRP.  Still a bit rough around the edges, nothing a little finishing won't get right........

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Next stage priming.  Hopefully I will get a bit more done before I have to go back to work.

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  • 1 month later...

Just a quick update.  So I have applied a few coats of resin primer, but not too happy with the roundness now.  There is a difference of 2mm between the high and low spots.  Also, as I thought it might be, sanding the tube is very tedious.  So I have made the decision to convert the pattern jig into a mini lathe, using a router as a cutting tool.  The drive motor for the tube is a stepper motor, the transmission is a bicycle chainwheel, chain etc.  So far I have extended the ply end panels to accommodate the flange bearings that I am using to act as a bearing for the tube spindle.  I have also fitted the flange bearings.  Still have to make a spider to install the chainwheel and a drive unit to accommodate the stepper motor, bearings and sprocket.  Included is a FreeCAD model of the drive end.

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The intention will be to install a 2020 V-Profile along each side with gantry bearings and gantry to support the router.

Hopefully I will be able to get this lot up and running in the next couple of weeks to progress this build (with pictures), as once the pattern is done the mould should be quick to progress.

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Hi, sorry to sidetrack, but did anyone ever find a company that made carbon tube, I'd rather like to transfer the gubbins from my VX10 into a Carbon tube?

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  • 3 weeks later...

The mini lathe is doing a superb job so far.  The first pic shows a very nice fit with the "roundness" gauge I made while working it by hand.  Back then it was way off, big gaps everywhere (should have taken some pics for comparison) now there are none very happy with the results. The daily setup is a bit of a slog though......

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One side has a huge drop, probably where the GF laminate ended, that has been getting filled with a large amount of body filler. This has been taking a while to overcome.  It is a concentricity issue (compounded with bad roundness) which is kind of neither here nor there, however there is no way of getting away with it when turning the pattern. You can see how the router has been breaking through the GF on the opposite side. So almost there with the roundness issue slowly becoming resolved.  After that it is back to the primer, gloss coat and polishing.  I will continue to keep the thread updated. Here is a pic of the side with second batch of filler (the first batch, one and a half 250ml pots, was no where near enough!).

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  • 5 weeks later...

OK, a fairly chunky update.  I have been sanding this down every weekend since the last post, trying to get down to all the low spots is not fun.  I think the neighbours must think I have gone mad.  A couple of weeks ago I even sprayed it with gloss resin (really as much as an excuse to dabble with a resin spray head as anything else).  But today I finally got there, kind of, going through 80 dry, 120 dry, 240 wet, 480 wet, 800 wet and 1200 wet.

800 grit (wet)

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I actually went down to 1200 grit wet, but didn't take a pic.  Anyway the polishing process went not too bad, cutting gave a fairly shiny finish with a brand new pad, but it dulls as it loads up with compound.  The actual polish doesn't give that great a finish, I think the pad may be too soft:

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You can see that the surface is scratchy, it must be from the 80 grit I was using to get down to the low spots.  There are also a couple of remaining low spots. I think I can deal with the scratches and low spots in the female as they will become positives, so carefully buff the gelcoat in the female with 800 grit wet or something.  Anyhoo, This weekend is ideal for mould production (warm with low winds) so the plan is as follows:

Saturday (tomorrow, 24th August) am: swap out the pattern ends for the mould ends and install all the barriers.

Saturday pm: prep the mould, and lay up the first half.

Sunday: flip the mould and lay up the second half.

Monday: Drill holes in the flanges and crack it open.

I will keep the forum updated, stay tuned for an exciting weekend!

 

 

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No surprise I didn't quite complete the schedule for today, however the pattern is in the mould frame with barriers and registrations.  The process of applying release agent is ongoing as I type this.

Pattern in mould frame, note the exchanged end panels otherwise it's all the same.  These end panels are full size and lined with polypropylene.

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And here it is with a complete set of barriers and registration dimples.  Note the modelling dough to fill in the gaps to prevent leakage.  Tonight I will complete the release application and first thing tomorrow the first coat of gel coat will be applied.

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Coupling Coat applied (100g CSM)

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 And Tooling resin with 450g CSM.  This side is complete:

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Flipped to start the other half tomorrow:

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The flanges have turned out really nice, with their registration dimples. Will continue and hopefully complete the mould tomorrow.  Stay tuned!

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Thought I better post a quick update.  So the side in the above pic has now been gelcoated, but I ran out of time so didn't manage to reinforce it.  The soonest time for the next session will be the weekend commencing 13th Sept. so fingers crossed for some decent weather around that time.  I must own up to a couple of bungles learning points during the lay up of the first half.  First, release agent was applied to the pattern after the barriers were applied, as this seemed the most intuitive time to do it.  However the release agent should really be applied to the pattern as a whole before barriers are applied (in case of barrier leakage).  I did get barrier leakage at one small section, where the gelcoat brush displaced some moulding dough and through to the unreleased pattern.  It is fairly minor I think I have managed to get away with it, just.  And, second, The reinforcement panels were cut too big, which induced slight bridging at the flange/pattern interface (you can make this out in the top pic of the previous post).  The panels should really butt at the flange/ pattern interface, but I cut them oversize.  The heavyweight cloth panels were also a bit unwieldy with may have induced slight de-lamination.  Hey ho, it's good experience though, it might all be OK in the end.  If not I will just mould up another one, its not the end of the world.  Chances are when I apply a vacuum it will all be OK.  Anyway no more updates for a while, but when I get the second half complete and the mould split, you can be sure I will update so you can get a good look at the interior.  I am fully expecting voids and bubbles in the gelcoat, but these can be repaired easily.  On a side note, and while I remember, if anyone is wondering why the pattern has that strange brown/grey finish, the brown is tangerine pigment that was applied to one of the layers of grey primer.  I was dabbling with pigment in the primer as an aid in the rubbing down process.

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  • 2 weeks later...

Hi Mark, good question, apologies for the late reply. The reasons for the mould are several: Good external cosmetic finish, it is a great beginners composite project, easy release when cured, dimensional accuracy, and yes, if anyone is looking to purchase a tube then that would be great too. Plus I just enjoy getting stuck in to a multi discipline project like this. Hope you are enjoying the posts.

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  • 2 weeks later...

Mould complete (kind of).  So I have laminated the other half and split the mould.  Apologies for the lack of interior surface detail pics, today was a bit hectic.  Anyway I propped the mould up against a chair to take a few basic pics.

 

The parting line looks quite good in the pics, but it is bigger in reality.  I don't know how the tube will end up, as long as the cloth doesn't get pulled in, I can live with a bit of slightly proud resin.  My barriers weren't as good as they could have been at the flanges (too far away and so too much modelling dough), and also I put on the release post barriers so I didn't get good penetration at the barrier interface and ended up with a bit of adhesion.

 

When I said the mould was complete, I still have to dress up the rough edges and clean up the inside.  Couldn't do it today, my angle grinder was being naughty.  I will also wet and dry the interior to get rid of the scratches (now positives, so shouldn't be too bad) and polish it up. 

 

The work will continue, again in a couple of weeks because of work etc.  The next step will be to build up a carrier out of the left over mould timber to hold it upright for infusion.  Think I might do a single or maybe double layer laminate with cheap cloth as a trial run, this could come in handy for a honeycomb core trial.

 

Anyway enough of my ramblings... here are the pics (these ones aren't great, I will get some better ones up sometime).

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