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Starblast 6 Dob Mount

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#1 Ratchet

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Posted 18 July 2013 - 10:02 PM

I'm trying to cure one of the pitfalls of a 6" F5 scope, which is you either need a GEM, or you sit on the ground with the OEM base, or you bring a table + scope.

I had some 1970s old mass produced desk wood lying around in 1" and 3/4" thickness oak veneer plywood. It is a very odd ply with thick, unidentified lightweight wood plys. The 1" ply weighs about the same as 1/2 B/C ply from the big box stores.

My base circle is 17.5", eyepiece height is a couple inches shorter than the XT10. The bottom isn't finalized, nor are the bearings or wood finish. The bearings will be teflon riding on some surplus material I found labeled as "ABS plastic sheet" at Skycraft in Orlando. The only parts glued so far is the rectangular section. I hope to finish it this weekend and attain a final weight around 15 lbs. I made templates for the side panels which are cut on the router table and front/rear panels are joined with stub tenon and groove (stop dado?). The dowel is 1.25" and inset into the side panels. It adds some stiffness, provides a handle, and acts as a bump stop for the OTA. I'll probably condition the wood with a water/glue mixture and use india ink for dye and treat with a topcoat of something or another for sealing the plywood against moisture. I have some epoxy, but might try some water based poly. Ignore all the pencil and marker marks for now.

I know a 6" F5 dob is a compromise. Since the base needs to be so tall most people will say "just get an 8" F6". But this will still be nice because there will be room in the bottom to line with foam and add a lid for built in finder and eyepiece storage. One less thing to carry, right? I was hoping the OTA could turn 90 degrees, lower and sit/lock between the side panels, but it's not possible with my current rings. Still, it doesn't take up much space.

I'm building this for a member of our club who is having trouble with their vintage 6" F5 Meade mounted to a GEM. She wants to just be able to set the scope on the ground and start star hopping without all the fuss of polar aligning and dealing with old style GEM gears/clutches/brakes and rickety legs.

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Ratchet

#2 Mirzam

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Posted 18 July 2013 - 10:30 PM

Looks great if you ask me! Nicely proportioned and a practical solution to the height problem. I'm gonna steal your design for my 6" mirror.

JimC

#3 Ed D

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Posted 19 July 2013 - 04:49 AM

I have often thought about building a small Dob just like yours. It's awesome, and I'm sure it will perform as good as it looks. Don't forget to post pics of your finished masterpiece.

Ed D

#4 Tom McDonald

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Posted 19 July 2013 - 06:00 AM

Nice design and your woodworking skills are commendable!
I should build something along those lines for my 6" Starblast. I got rid of the original mount before I moved.

Congrats! And keep us posted on how it works.

#5 BigC

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Posted 19 July 2013 - 08:52 AM

Excellent work there!

Putting the focuser at a more comfortable height for the user ought to be a design goal of manufacturers.

In order to invert the scope for storage you'd have to remove the crossbar that adds much to the mounts rigidity.Or make it easily to remove and install.

#6 Ratchet

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Posted 04 January 2014 - 12:26 AM

I finally got back in the garage to work on the dob conversion some more. Been busy lately with a newborn boy peeing and pooping all over me.

The dob conversion is still far from finished, but I'm making good progress. I decided to try using some cutting board material for a combination thrust bearing and brake. All I have so far is a pic of me cutting the disk and I probably won't have the completed altitude bearing for another couple of weeks.

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The scope pictured in the first post above is my Starblast 6 which I was using for mock-up of the base dimensions. This first conversion I'm doing is for a Meade 6600 so I had to make a cradle for the scope since Meade doesn't use a flat spot on one of the rings. I drew up something in CAD and made some layout lines on a 9" plywood square and just cut to my layout lines and trimmed out the corners.

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The two rings are joined by 4 tenoned struts. Once I get all the burn marks sanded off, I'll glue it up and cut right down the middle of two opposite sides to make it a clamshell.


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#7 cheapersleeper

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Posted 04 January 2014 - 01:31 AM

I love 6" f5. I love them so much that I will be working on one this weekend.

B

#8 StarStuff1

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Posted 04 January 2014 - 04:29 PM

Looking really good! I especially like your clamshell/rings.

A coupla minor recommendations. A hole could made in the front board to reduce weight a little further. And a wooden eypiece holder could be easily added to the base. Just sayin.

#9 Geo.

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Posted 06 January 2014 - 02:35 PM

Found this stuff at Lowe's. It's HDPE plumber's tape that I needed for rerouting the dryer vent. $7 for 50'. It's pretty slippery and may work well for bearing material.

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#10 cpr1

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Posted 06 January 2014 - 10:23 PM

Nice design!! and skills. I never really liked the tabletop mounts for these small scopes. What you have done should make your scope much more user friendly. :waytogo:

#11 Ratchet

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Posted 16 May 2014 - 07:47 PM

Finally finished the scope. It operates considerably smoother than my XT10 and I think it will be a handy little scope. I had no problem tracking Mars last night at 200x while sitting comfortably in my chair. The integral eyepiece case is definitely convenient.

I returned it to its owner today and she was pleased beyond her expectations. Her scope was the beta test for the design and I'll be building something similar for my 6" F5 and/or 8" F4.9.

Concerning stability, a little bit of care has to be taken due to the width vs height, but this concern is mostly eliminated with choosing firm level ground. Turning near zenith can induce tipping if you only grab the upper end of the scope and pull haphazardly. The entire scope is very light weight so it is best to use two hands on opposite ends of the OTA when tracking near zenith. Using a more dense plywood may help, or using a lazy Susan bearing.

All the bearing surfaces are teflon riding on textured plastic. The plastic was marked ABS and purchased at a surplus store. The outer disks on the altitude bearings as well as the altitude brake are made from polypropylene cutting boards. The brake was reinforced with an aluminum strip. I think there are better ways to make a brake, but this one works well and could compensate for some dimensional errors I accidentally created :o.

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#12 Geo.

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Posted 18 May 2014 - 10:20 AM

Nicely done! Couldn't understan how you keep those garage doors straight, bu I guess you aren't plowing a lot of snow near them

I have a 114mm f/11 and picked up an Otion base for it cheap. My problem is supporting the tube with something that is narrow, yet strong enough. I think your cage is just the thing. Thanks for the update.

#13 Ratchet

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Posted 19 May 2014 - 06:05 AM

No snow here, so they can make our garage doors out of aluminum foil.

#14 Ed D

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Posted 20 May 2014 - 04:40 AM

WOW, I'm really impressed how your project turned out. :bow: :bow: :bow:

Ed D






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