Homebuilt 6" F15 Refractor and Mount

Intro: Homebuilt 6" F15 Refractor and Mount

Hello fellow Instruct-ables...  What better way to celebrate space than to look at it through a really big telescope? I have been an ATM for quite a while and this is my latest project, a big refracting telescope on a big mount. 

STEP 1: Gathering Parts

The mount is made from mostly easy to find scrap parts I found on line. I spent a lot of time looking for scrap pieces that were close to sizes I needed until I found that the metal merchants would cut pieces to size for pretty cheap. I used common power tools such as a small drill press, router, circular saw and chop saw. Working with aluminum is a lot like working with very hard woods, the cutting feels the same but slower.

The chassis is made of 1/2" sheet aluminum. The bearings are pillow block bearings. The Main(RA) shaft is 2-5/8" diameter aluminum and the smaller(dec) shaft is 1-1/6" steel. The large worm gear was purchased cheaply from an astronomy website. 

STEP 2: Routing Aluminum

This is a step that I thought about for a good long while. An equatorial mount has to have some adjustment for the angle of altitude in order to track properly. The angle for your location is your latitude, Where I am the mount needs to be set at 42deg. I decided to make the angle adjustable about 5 deg either way. To make these small arcs I used a circle-cutter attachment on my router and made quick 1/8" passes until I cut through each side of the chassis. 

STEP 3: Basic Chassis Assembly

I trimmed the mounting tabs from the large pillow block bearings and ground down the sides with an angle grinder. After some drilling and some tapping, I bolted the base chassis up...

I added a brace and tapped a hole for an adjustment bolt. Turning this bolt allows the angle to be adjusted then clamped down when it's right. 

STEP 4: The RA Shaft

My large pillow block bearings were sold to me as 3"ID however when they arrived they were closer to 2-5/8"ID. I was able to find 2-5/8" aluminum cylinder and had it pressed into a 6" dia 1" thick disk. Pressing the shaft in is a very strong and stiff junction but is a job for a metal shop with a press, My local machine shop charged me $20.

STEP 5: The Dec Shaft

I had the 1-1/16" dia x 24" long dec shaft pressed into a 2-1/2" x 2" x10" Aluminum bar. For the correct alignment of the tube, this unit has to be trued on a lathe. Another $20 to the machine shop. 

I felt like Thor when I carried this into the house.

STEP 6: The Dec Shaft Assembly

The dec shaft rides in two 1-1/16"ID pillow block bearings mounted to a 1/2" aluminum plate which is bolted to the RA shaft. I added a 4"wx14"l aluminum bar to mount the tube rings. 

STEP 7: Mounting of the Large Drive Gear

In a big scope the accuracy of the tracking is directly tied to the size of the worm gear. Big worm gear means smaller errors. A big worm gear also needs a smaller drive motor. This gear is clamped between two circles of HDPE which is actually cutting board material. I routed two 12" circles to act as clutch plates as well as a smaller 6" donut for the gear to ride on. This assembly is clamped tight via two threaded shafts. This clutch arrangement allows the tube to be moved anywhere while the motor turns for effortless pointing and tracking.

STEP 8: Worm Drive Assembly

The worm drive is built from pieces of aluminum bar cut from left over material. The worm gear came from another smaller drive and happened to fit. The shaft rides in oilite bushings. Gear slack is taken up by a screw that presses the shaft from the side and prevents lateral movement of the gear. Each piece of this unit took a couple of tries because to avoid binding, some precision was involved. By precision I mean drilling holes over and over until finally the shaft stopped binding! 

The motor is a synchronous timing motor which runs at a set speed from household voltage. These are used in older or simple telescope drives because it uses the frequency of your house voltage to keep accurate speed. Adjustments of the speed can be accomplished by the use of a square-wave frequency generator, a simple circuit that allows you to speed up or slow down the motor for tracking. 

STEP 9: Tripod Hub

The tripod hub is made from two disks of aluminum bolted to three leg mount bars. The top of the hub is machined flat. The bolt hods the chassis to the hub. 

STEP 10: Oak Tripod Legs

The tripod legs are built up from oak flooring boards discarded as scrap by a neighbor. They are as long as the shortest piece so abou 48"l.

STEP 11: Mount Assembled

All the different assemblies together as a mount head. 

STEP 12: Finished Mount

After some fiddling, refitting, stiffening sanding and painting, the finished mount....

STEP 13: The Heart and Soul....

Ah, now it's time for the cool stuff... The Objective!  This lens was made by Istar Optical, at the time a relatively new manufacturer of telescope optics. The lens has shown itself to be an excellent performer, especially for the price. Currently the objective in cell costs about $515.  

STEP 14: The Tube...

The tube is a section of aluminum tube made by Hastings Irrigation. I had to special order the size as shipping an 8' l tube costs as much as the tube itself...

The focuser is a Synta refractor focuser painted blue for looks. 

The interior is baffled via 7 knife-edge baffles spaced 12" apart. The baffle assembly was built from plans I drew of the optical path. The baffles are kept out of the light path by about 1/4" or so.

STEP 15: Objective Cell Mounting

The objective needs to be mounted in a collimatable ring. This ring was routed from three pieces of HDPE drilled and tapped for three push-pull screw arrangements.

STEP 16: Sliding Dew Shield

Traveling with a 9'l tube is tough, traveling with an 8' tube is much easier, fits right in the mini-van. To make things easier the dewshield slides over the objective to shield the lens from stray light.

STEP 17: How Does It Perform?

This refractor is an achromat which normally would not be suitable for photography. Due to it's large focal ratio (f15) and long focal length(2276mm) this scope is a superb planetary performer.  This is a photo of Saturn taken with a Celestron Neximager, a webcam-based imaging camera. This photo is a stack of 1000 frames in Registax. There is a white blob which is a storm imaged on the surface of Saturn from 3 blocks outside of Chicago! 

Comments

[Beerwiser]

Where did you find the worm gears?

[jwoodward8]

Does it work

[Astrochef]

WOW! Thanks everyone who voted! I am proud to be a part of such an active building community. Thank you Instructables and Celestron, I'll put the scope to good use!

Hopefully my wife will let me spend a little more time in the shop now!

Sean

[Mechanic2011]

For building a telescope:

Do you know of anyone that has used a section of the heavy Green plastic sewer pipe which is available in diameters starting at 10 or 12 inches for this?
I have found the white PVC pipe locally that is 8 inches approx. in diameter.
Anything 6 inches or less is available in the plumbing supply / home improvement stores .

The problem is that once you get to the green commercial PVC piping the gets buried underground a ways , it also gets very heavy as the wall thickness is quite thick as it is schedule 30 or 40 so it won't crush when buried in the ground.
The Blue PVC underground piping is for water mains and has an even thicker wall on it than the green sewer piping as it needs to be schedule 80 and be able to take the municipal water pressure continuously .

[Astrochef]

In terms of strength vs weight vs cost, Aluminum wins most of the time. I have used PVC for smaller scopes for the kids but after a certain length/diameter, it starts to sag. A 10" diameter rolled Aluminum tube will run about $100 + 30 shipping. I am also a big fan of sonotube which can be bought from your local building supply for $10 and wrapped with fiberglass or reinforced for added strength. The holy grail of scope building is Carbon fiber but it is awfully expensive and messy to do yourself(correctly, anyways)

If you know some one in the business and can get thick-walled PVC, go for it. You won't find a cheaper easier-to-work material and you won't have to go to the gym again ever!

[Mechanic2011]

Yes, I was thinking about the weight of the scope tube .

Once the lenses are installed into it the tube I am very sure that the weight of these sizes of lenses won't be very light either.
I figure that it is going to take 2 people to set the scope up of that size on site anyway.
The ground or earth base , the mount system and then the scope tube and other parts will need to be assembled in pieces to be able to handle them .

In theory it could be "portable" with some work involved with the set up.

If you were going to make it portable and transportable what length and diameter of tube would you consider to be a maximum for such a project ??

What would a person use to anchor the thing into the ground without a hard pad to set it on?
Perhaps 3 of those large 36" or 48" tent spikes with plates welded on the ends that could be leveled ??
Would that give a steady enough base to install such a powerful telescope onto without worrying about vibrations etc.??

What kind of clock drive system would be best for tracking the stars OR moon for these larger scopes ??

[Astrochef]

This scope was limited by how long of a tube I could fit into my vehicle, so 8ft. The scope weighs about 30lbs, which is fine for me weight-wise. The mount breaks down into components no heavier than 75lbs, my personal limit. I really wanted it lighter but each time I rebuilt it, I wanted it stiffer which meant more weight.

No joke: when I started to get a feel for how heavy this thing was going to be I started lifting weights and doing back exercises so I wouldn't kill myself lugging it around. I have to drive about 45 miles to get to dark skies so the scope travels a lot. So far, no major issues but I hesitate to go larger/heavier without permanently installing it in my yard(not possible at this time)

With a scope as large as you suggest, a clock drive of 12" or better would be minimum, they get pretty pricey if you buy them off-the shelf. Last time I looked they ran from $900 to around $3,000.

If your scope is of Newtonian design, I would suggest an "Equatorial Platform"
Easy to construct on your own with good enough tracking even for basic photography. Google it to see what they look like.


Thanks,
Sean

[Ignacio_Ramirez]

I think, guys, that your discussion should move away from 'homemade telescope' and start into 'installing an observatory at home on a budget'.

Just saying.

[Mechanic2011]

I believe that the main point of this article was the scale and size of equipment to make it "portable" and transportable to locations away from the city and light pollution and also to cut the costs down associated with such a hobby .
Most of us do not live way out in the country .
But your point is well taken and I am sure that someday "someone" would come up with an instructable for building a stationary observatory facility at home.
Are you game?
I wonder WHAT the building inspection office will tell you when you go in to get your building permit for such a facility ,LOL .

How are you going to make it rotate to track the stars?
There will be all kinds of other structural questions they will ask of you.
They will probably tell you that you cannot design it yourself and you will need to get the service of a qualifies architectural and structural engineer.
I KNOW our building inspection office would tell ME that .
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[georgeATM]

Beautiful scope! I am surprised you went with oak on the tripod legs. I Built an 8" f/15 refractor and used all aluminum except for the alt-az box on top of the tripod.

[Astrochef]

Thanks George! I went with oak because that's what I had around. My intention is to permenantely mount it to a pier but that day is a few years off....

I like the minimalist design of yours. I camped next to an 8" f15 once at a star party and it's huge size made me decide on a 6" for myself... Who made your lens?

[maewert]

Also, you may find that the oak dampens out vibrarions better than aluminum... at least that's what you can tell people :-)

Best Wishes.

[georgeATM]

D&G optical. Air spaced achromat fully coated.

[Astrochef]

Geez George, that glass deserves a tube!

[Mechanic2011]

Where did you find the aluminum tubing of that size?

[georgeATM]

The "tube" is made of aluminum angle both 2" and 1". It is actually two 5 ft sections that I designed to slide together. The legs are 2" square and again, 5ft pieces that slide to size. i bought it all from a local aircraft/metal supply shop.

[jmacdonald6]

Very nice work indeed bro. Congratulations. But I found those instructions are so imprecise to the inexperienced (myself) that I could as easily end up with a vertical lawn mower or letter opener for giraffes. Not only that, this project could be impossible in many other countries: one bemoans e.g. in the UK the lack of DIY venues -- of junkyards, 'local machine shop guy', spare materials, shops, suppliers, space, of ANY PERSON within 1000 miles 'discarding' any hardwood in size and number bigger than a single chopstick. Thus MY assessment: life is tough in the US now but appreciate that you don't need to crop your own talents as in Europe. Keep on building and posting!

[Astrochef]

Our streets are paved with gold, don'tcha know....

I set out with this project to prove that you didn't need a full-on engineering degree to make an accurate large mount. Frankly, Imprecise is my middle name, I measured very little during this project. It was more important for the parts to be square with each other rather than specific sizes.

Everyone's access to materials is different all over the world. One of the largest homebuilt refractor's (a dialyte)is in the UK with an objective of 32" or so. During the first year I was gathering parts, no dumpster was safe! I remember measuring pipe in my restaurant's basement for a pier I was thinking about mounting the scope on!

[pcgate]

just plain ole wow. good job.

[raul38]

Thanks for share your excellent works