The 14" build is finally underway

[Dave_D]

So, now i've got my CNC kicked into shape, it's time to start my 14" dob build. I've had the optics since i was 21... i'm now 52 HAHA so yeah...

Anyway, i've got the rocker box designed (see the vid linked below) and the 18mm water resistant Medite Tricoya arrives in a couple of days, can't see anything that would cause a problem but opinions are welcome.

https://knowledge.autodesk.com/community/screencast/8ff926f8-95a9-4b09-bb89-37a5fb6cf8dc

and the mirror cell is 80% complete

I was originally going to 3D print the blocks and have already made a test version which seems plenty strong enough but it's a load of faffing about and i'm sure a simpler method would be less of a headache to make all the parts. I'm really not sure yet how i'm going to do the truss attachments so if anyone has any good ideas...

Edited November 11, 2018 by Dave_D

[westmarch]

Dave,

Respect! Anyone who can put together a dob from raw materials deserves awe. Good Luck with your build, I look forward to following your progress.

John

[hughgilhespie]

'So, now i've got my CNC kicked into shape, it's time to start my 14" dob build. I've had the optics since i was 21... i'm now 52 HAHA so yeah...'

I am so relieved - it's not just me then. I've been sitting on a 12.5 inch conical mount mirror from R F Royce and a matching carbon fibre tube for the past 5 years. OK, it's not quite so extreme but I still feel the guilt. My mirror cell is also about 80% complete. One day.............

Regards, Hugh

[Dave_D]

right... that's the truss attachments sorted and no 3D printing involved

https://knowledge.autodesk.com/search-result/caas/screencast/Main/Details/fcb30d12-54c4-4908-b6b2-2eaa95ab07f4.html

[Dave_D]

bit of a delay with the medite delivery ? will have to wait til next weekend. thought i'd do a tolerance test on a couple of the rocker box parts. To give clearance to the truss poles, i've added a crescent shaped insert into the main runners to move them 10mm away from the mirror box and inserted 5mm into the main runner so i can glue it for a good solid joint. for some very odd reason when i cut the pieces on my CNC, i had to make the pocket 0.45mm larger than the insert. not sure if it's just me being a fusion360 noob and not setting up the tool paths properly or some other issue... 

 

enlarging the pocket worked well though on a bit of scrap MDF

 

Edited November 17, 2018 by Dave_D

[Dave_D]

Secondary holder coming along nicely... just eed to get the right length bolts

[mapstar]

Nice to see another home build gracing the pages of SGL. Seems to have been a while since one appeared.

If you're going to be using a shroud make sure you've enough clearance between to truss pole and the bearing to get it over and down to the bottom.

Just a couple of suggestions for the secondary holder. It looks nice, not sure what the central spider boss is made from? but it looks nicely profiled to mount the spider vanes.   I find 4 screws easier to adjust than 3 and mounting the screws further out increases the accuracy of adjustment and gives more stablility to the secondary.  Keep the screws as short as possible. 

Truss mounting is always something to ponder. I've changed idea's a few times whilst trialling them out in the field.

I need to become more practiced with the CAD and nice to see it being used in scope design.

Hope that helps keep up the build as I think it's about time it was completed after sitting on the optics for so long. 

 

[Dave_D]

material has finally arrived...

first runner off the CNC

[Dave_D]

Forever on the quest to find much cheaper options for astro gear, because as we all know, as soon as an item is labelled for astronomy, the price shoots up a few hundred percent, i stumbled across these on fleabay

https://www.ebay.co.uk/itm/Diving-Lights-Ball-Butterfly-Clip-Arm-Clamp-Mount-For-GOPRO-3-4-5-Xiaoyi-Gitup/323380801421?_trkparms=aid%3D555017%26algo%3DPL.CASSINI%26ao%3D1%26asc%3D55149%26meid%3D7d9a06518b1e4247bab881ab505969ad%26pid%3D100505%26rk%3D1%26rkt%3D1%26%26itm%3D323380801421&_trksid=p2045573.c100505.m3226

looks plenty sturdy enough for truss pole fixings... and WAY cheaper than anything i've seen elsewhere

[saac]

Dave I noticed that your truss tube blocks are similar to the Moonlite blocks but that yours are are split while the Moolite are one piece. Your socket also looks to be deep enough to fully capture the ball.  I'm guessing this means that you would need to unscrew the two block halves to allow insertion or removal of the ball. I can see that this would be a bit of a faff on assembly/disassembly.  With the Moonlite design the socket is not as deep as yours so the ball can be inserted and removed freely; the socket is also slightly oversized for the ball.  A single threaded hand turned screw is then used to secure the ball in the socket on assembly. I wonder if this would help with the faff you mention concerning the blocks or was that to do with the printing process. In either respect your blocks look pretty neat and maybe worth pursuing.

Looking forward to the rest of your build you look on track to end up with a fine truss tube set up.  I'm envious of your CNC machine  

Jim 

 

Edited November 25, 2018 by saac

[Chriske]

Dave,

Can we have peek how your CNC cutter looks like. Most curious, my pal Marc is busy building one.

Chris

[Dave_D]

Making steady progress, and yeah, had to add the text to the front of the mirror box   and with a 14" mirror, it better HAD be full of stars lol

It's a bit dark cause the camera on my tablet is rubbish

and Criske, this is the machine. An Ooznest 1000x750mm Workbee. using a proper spindle instead of a trim router cause trim routers are noisy as hell...

I've also removed the T-slot bed i added (and damn expensive too ? ) and used a piece of MDF which i can skim easily as i was having trouble levelling the T-spot accurately enough

Edited November 25, 2018 by Dave_D

[Dave_D]

Mirror cell fits juuuuuust nice...

just remembered i have to hinge the bottom of the mirror box, otherwise the mirror will be getting a life sentence lololol

[Mick J]

Looking great Dave,  that MDF is new to me - replacement for marine ply, looks useful but expensive but then...........

[Dave_D]

3 minutes ago, Mick J said:

Looking great Dave,  that MDF is new to me - replacement for marine ply, looks useful but expensive but then...........

it's moisture resistant medite exterior MDF and supposed to be far tougher and more dimensionally stable than standard MDF... cost me 60 quid or so for a 8' x 4' sheet. no point skimping and have the scope fall apart because of this lousy climate

[fwm891]

Quote

 

Looking good Dave - I have a 750x750 screw-driven WorkBee - great machines ?

[Dave_D]

for the truss poles and attachments, i've decided to go with these

they're ball butterfly clamps in aluminium and i can get them for £4.50 each. for the balls, my local wood supplier has 25mm diameter drawer handles in nickel plated steel that will screw into a plug in the end of the truss poles for £4 for 2 so a hell of a lot cheaper (similar to this but a much better finish)

[mapstar]

17 hours ago, Dave_D said:

it's moisture resistant medite exterior MDF and supposed to be far tougher and more dimensionally stable than standard MDF... cost me 60 quid or so for a 8' x 4' sheet. no point skimping and have the scope fall apart because of this lousy climate

Bit of a health warning to those considering using MDF

Hope you have decent extraction and ppe as MDF is carcinogenic and far worse than the usual birch ply used for constructing scopes. 

It's banned in america but good old britons get to use it with no health advice given when buying the stuff. 

Be careful out there peeps.

[Dave_D]

4 hours ago, mapstar said:

Bit of a health warning to those considering using MDF

Hope you have decent extraction and ppe as MDF is carcinogenic and far worse than the usual birch ply used for constructing scopes. 

It's banned in america but good old britons get to use it with no health advice given when buying the stuff. 

Be careful out there peeps.

I look like Bane when i've got my respirator on

[Whistlin Bob]

Great project, and love the quote! I have a 14” (manufactured, and nowhere near as beautiful as I suspect yours will be) and it is indeed full of stars. 

[westmarch]

7 hours ago, mapstar said:

Bit of a health warning to those considering using MDF

Hope you have decent extraction and ppe as MDF is carcinogenic and far worse than the usual birch ply used for constructing scopes. 

It's banned in america but good old britons get to use it with no health advice given when buying the stuff. 

Be careful out there peeps.

I don’t think it is banned in America.   Any dust is harmful so I agree be careful.

http://www.hse.gov.uk/woodworking/faq-mdf.htm

John

[Lurcher]

Looking absolutely brilliant. I like the wording you've added. I hope it continues to go well, and I look forward to seeing more updates.

[mapstar]

4 hours ago, westmarch said:

I don’t think it is banned in America.   Any dust is harmful so I agree be careful.

http://www.hse.gov.uk/woodworking/faq-mdf.htm

John

Apologies you are quite right when referring to the newer types John.

I'm talking from experience with the older type of MDF which so many 'diy' programmes used 15 years ago. It was banned from production in the US. 

Glad that Dave is wearing ppe and encourage others to always put their health first when using it. 

[Dave_D]

taking shape...

[Dave_D]

almost ready to paint the mirror box

 

just need to machine an inset into the rear panel so the hinges can extend fully