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saac

16 " Open Truss Dobsonian Build

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saac    799

Some photographs to show the setup for the Schlieren imaging above.

 

Jim

 

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Chriske    111

To determine the distance between Primary and secondary cage I always use dummy poles. Thin square wooden poles, or whatever I have  at hand. I fix one set of poles to the secondary cage and the other set of poles to the primary cage. I fix them together with clamps. It's all very basic, don't even think collimating, see to it you can focus on the moon or a bright star, just find the correct distance. If it's not correct just loosen the clamps and slide a bit further. You need clamps, lots of them. If you don't have clamps just screw them together.

While removing clamps PROTECT YOUR MIRROR...!!!

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saac    799

That sounds good Chriske, it's what we were really trying to do at school but we didn't have the means of securing the upper OTA well enough. So clamps it is :)

Jim

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saac    799

I made some further progress today and managed to finish cutting out of one of the altitude bearings. I'll look to cut out the rest of the second bearing tomorrow and then get them trimmed and ready for gluing up.  I wonder if anybody could point me in the direction of a supplier for ptfe strips.  I found some sheets on Amazon but the delivery cost was more than the sheet itself!  

Jim

large.5980cc40d619c_AltitudeBearing.jpg.e33d3ca5454c26e857ba4aa1b32efc26.jpg

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mapstar    5,456
47 minutes ago, saac said:

I made some further progress today and managed to finish cutting out of one of the altitude bearings. I'll look to cut out the rest of the second bearing tomorrow and then get them trimmed and ready for gluing up.  I wonder if anybody could point me in the direction of a supplier for ptfe strips.  I found some sheets on Amazon but the delivery cost was more than the sheet itself!  

Jim

large.5980cc40d619c_AltitudeBearing.jpg.e33d3ca5454c26e857ba4aa1b32efc26.jpg

Ptfe sheets? Or laminate/formica sheets? 

Ptfe/teflon is normally used for small pads that the formica/laminate on the bearings run on. Ptfe can normally be had quite cheaply on fleabay 

Edited by mapstar

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saac    799
44 minutes ago, mapstar said:

Ptfe sheets? Or laminate/formica sheets? 

Ptfe/teflon is normally used for small pads that the formica/laminate on the bearings run on. Ptfe can normally be had quite cheaply 

It's the ptfe I'm trying to source Damian, I already have the formica. I may just bite the bullet and go with the supplier on Amazon but it seems a wee bit overkill for what I need.

 

Jim

Ptfe Sheet

Edited by saac

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saac    799
38 minutes ago, brantuk said:

These guys are usually at most astro trade shows and I've used them a couple of times via mail order. They're also very good with advice if you give them a call:

http://www.awrtech.co.uk/miscprod.htm#PTFE

 

Thanks brantuk that looks useful. I'll give them a call tomorrow. :) 

Jim

 

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mapstar    5,456
6 hours ago, saac said:

It's the ptfe I'm trying to source Damian, I already have the formica. I may just bite the bullet and go with the supplier on Amazon but it seems a wee bit overkill for what I need.

 

Jim

Ptfe Sheet

Just an example the same as what I have used in the past. Being 6mm thick you can drill and countersink it so you don't have to use etched stuff to glue on. 

http://m.ebay.ie/itm/360978773408?_mwBanner=1

If you want thinner material I have some 3mm sheet in the garage somewhere I could sort you out with. PM me if you are interested.

Damian :thumbright:

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saac    799

Thanks Damian that's another good source; the 6mm dim looks ideal as well. :) 

Jim

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saac    799

Been a wee bit busy at work so progress on the Dob has been a bit slower than I would have hoped.  These things always seem to take longer than planned ;)  Anyway, I finally have both bearings cut and the bearing supports mounted on the base board.  The photos below show a trial fit, the outer faces of each of the bearings have yet to be glued hence the clamps. At the moment, the mirror box is simply sitting on the bearings, but everything moves smoothly so far.  I hope to sort out an attachment arrangement for the mirror box to the bearing assembly next weekend together with finishing the ground board; I have some thrust bearings and a few router bits being delivered mid week hopefully :)  So far, no major snags; everything is moving along, just taking a wee bit longer than planned. We are hopefully still on track to have it ready for the return after our Oct mid-term.

Jim

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Edited by saac
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saac    799

I also picked up a nice SW 2" EP (28mm) from AstroBoot, I thought it would set off the scope nicely.  I'm also keeping my eye out on AstroBoot for a focuser, my own scope is missing its Moonlite now that the sky is getting dark. No real urgency, I still have my ED80 mounted so should keep me happy enough :) 

 

Jim

 

large.WP_20170910_22_53_23_Pro.jpg.0d3dc3d8ab5cace66bf562f5db45cbda.jpg

Edited by saac

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MikeCM    43

Just picked up on your thread Jim. So this is the telescope Euan has been telling me about - Looking pretty impressive so far and look forward to seeing pictures of the final article.

Regards Mike

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Paul73    2,407

That looks really impressive. I really like the mirror box(?) / Rocker assembly. Yes. Telescopes should be found!!!

How much the bottom section weigh (box,rocker,base and mirror)?

Paul

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saac    799

Hi Mike, yes this is the monster. I had thought it would have been completed  before Euan left but I underestimated the time needed. All being well, it should be ready for the return from the Oct half term. I'm busy looking for a good dark site in the local area for a first light test - Kingsbarns near St Andrews looks promising, good car park site down by the beach.  I've got a group of 5th year students itching to get their hands on it so when we are ready to go you and Euan are more than welcome to join us. After that, the plan is to take a trip out to the Scottish dark sky observatory down in Dumfries and Galloway or maybe up to Skye.  I must admit, I'm getting quite exited now, I've never looked through a large aperture scope so I'm hoping for a big difference.  

 

Jim

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Beulah    2,523

Fabulous work. I've not seen the multi-laminated rings before as a primary mirror box; very original!

I have found out that Flexi ply is the best thing since sliced bread!

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saac    799
17 minutes ago, Paul73 said:

That looks really impressive. I really like the mirror box(?) / Rocker assembly. Yes. Telescopes should be found!!!

How much the bottom section weigh (box,rocker,base and mirror)?

Paul

Paul,

Thanks Paul. I'm trying t o emulate the Waite Research design as much as possible although I've had to make some changes due to use of hand tooling and my woodworking skills.  I must admit, I do like the look of the circular mirror box, it's my intention that it will also serve as the mirror storage box when off the telescope.  The lower OTA , with mirror and cell, is heavy; I haven't got around to weighing it properly yet, maybe do that at the weekend and have a look at the turning moments as well. I fitted the azimuth bearing yesterday and it rotates really smoothly in both azimuth and dec. There is something quite pleasing watching a big scope move around - simple things I know :) 

 

Jim

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saac    799
2 hours ago, Beulah said:

Fabulous work. I've not seen the multi-laminated rings before as a primary mirror box; very original!

I have found out that Flexi ply is the best thing since sliced bread!

Thanks, Beulah. I spent some time, perhaps too long, looking at different designs before I settled on this. I found a few that used a circular box but the Waite Research design caught my eye.  It is a more expensive and time consuming way of doing it (as DIY) vice a rectangular box but it is supremely strong and aesthetically pleasing. I've used FlexiPly in the upper OTA, akin to a monocoque design where the main loads are carried by the ply. First time using FlexiPly and I must admit it's a fun material to use; I need to find something else to build with it :) 

Jim

Edited by saac
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