DIY Equatorial Telescope Mount

[macona]

hjd1964, a member of the CloudyNights forum, has been working on the code to get his OnStep software package working on a Teensy 3.1. It is working for the most part so far.

I powder coated the last batch of parts for the scope mount last night and mounted the dovetail today. Now comes the fun part of pulling the OTA off the old forks. Whee...

Here is the breadboarded Teensy 3.1, line driver, and bluetooth module:

Scope mount control prototype by macona, on Flickr

I did some gizmo triage and recycled a bunch of stuff, I now can see some of my desktop:

Parts powdered and ready for baking. by macona, on Flickr

Here are the parts just after being coated and ready to bake. 400F for 30mins.

Parts powdered and ready for baking. by macona, on Flickr

The dovetail mounted on the OTA. Funny thing, I went to bolt it down and I found my holes to be 1/16" off. I milled out one end turning the holes into slots and reinstalled it. Now the bolts fall in to where they were supposed to before. I have no idea what happened. Oh well.

IMG_8909 by macona, on Flickr

[RichR]

For your application, quite understandable. In my friends case, there's a stop on the mating piece, so it can't slide all the way through, and gravity holds it
against the stop. The two 1/4 20 screws I used only get finger tightened to take out any side to side movement.

[macona]

All of the commercial saddled use a clamp of some sort. A screw will dent the surface no matter how polished it is. With a clamp like mine or other you get a lot more pressure and surface area to hold, with several thousand dollars hanging off it I dont want it to slip!

[RichR]

I considered doing that on a dovetail mount I made for a friend. I opted to drill and tap on an angle so the end of the screw came down perpendicular to the face
of the dovetail. I then filed and polished the end of the screw so it required very little pressure to hold and would not mar the dovetail.

[macona]

Yes, it clamps against the dovetail. After the dovetail was cut I set up a 1/8 thick slitting saw in an arbor and sliced leaving about 1/8" at the bottom the bolt squeezes it in place. The bolt is only temporary, I have a handle that will go on there.

[RichR]

Hi macona
Nice work. The piece with the cap head screw looks interesting. I guess that squeezes the dovetail smaller when tightened?

[macona]

I made the dovetail and saddle for the telescope today. Figuring out where to put the holes to match the existing accessories hole on the scope was kind of a pain, no documentation anywhere on the hole spacing and angle. The dovetail should be compatible with Losmandy type accessories.

I am probably just going to paint these. We will see.

Machining the dovetail on the telescope side.

Losmandy style telescope dovetail and saddle. by macona, on Flickr

The four parts I made today:

Losmandy style telescope dovetail and saddle. by macona, on Flickr

Assembled.

Losmandy style telescope dovetail and saddle. by macona, on Flickr

[macona]

I got the declination fine adjuster installed last night. It came out of an old Sperry Gyroscope Tool Set I got a couple years ago. A little overkill but it should work fine. I also made up the clamps for the Dec adjuster as well.

Next is the dovetail saddle for the scope and the mechanical portion of the scope will be done. I need to start ordering some parts for the control system, a couple AM26LS31 line drivers for the step/direction inputs of the servo drives and the bluetooth module for the controller. A guy at the local Dorkbot meeting gave me one of the Orbital LK204 serial LCD/button modules. I might try to use it as a control pendant.

http://www.matrixorbital.com/product_info.php?products_id=207

The adjuster, should barely clear the scope, it came out bulkier than I had hoped:

IMG_8779 by macona, on Flickr

The kit the parts came out of. I had just bought it for the case but figured the rest might come in handy someday.

Tool Set, Gimbal Positioner by macona, on Flickr

[macona]

Cant claim the design, I copied a little Newport rotation stage for optics.

Its an Anthro 5/32" Hex driver. Its propping up the right ascension drive.

[Euph0ny]

Very nice! The anodising looks very smart. I think using the two opposing screws to fine-adjust the lever is ingenious.

That looks a lot like a Brownell's gunsmith's screwdriver in the last photo - bug or feature?

[macona]

On the tripod, this is a standard Meade Field Tripod:

IMG_8775 by macona, on Flickr

Other side:

IMG_8776 by macona, on Flickr

[macona]

I got my parts back from anodizing today and assembled what I have so far.

I think I have created a monster.

I inserted the bearing cup into the base, a bit of a tight fit but it pressed into place and trimmed the spud to it's final length. I lubed up the two bearings with Krytox 240AC, a nonreactive teflon based grease, and put the base together. I glued the spud into the post mount with some Hysol 1C epoxy. Hopefully that will keep it from turning. I may have to pin it in place.

Everything went together pretty well, one spot I ran into interference between the bottom plate of the main harmonic drive mount and the Az fine adjust bar, it will only get in the way at low altitude settings which will never happen so I am not too worried right now.

Next up, figure out the angle lock and fine adjustment. I have a section of worm gearing that might work nice. I also need to make the dovetail saddle and buy the dovetail kit for my telescope, that will attach the scope to the mount. Then I need to get working on the control.

The taper bearing in place and lock nut:
IMG_8769 by macona, on Flickr

The fine adjuster in place:

IMG_8770 by macona, on Flickr

Side plates on:

IMG_8771 by macona, on Flickr

A view of the base:

IMG_8772 by macona, on Flickr

[macona]

Everything ready for anodizing:

Last batch of parts by macona, on Flickr

[macona]

Another batch of parts finished for the telescope. I have decided to just buy a saddle and dovetail kit from ADM, I dont want to mess with that.

Needed a piece of aluminum rod for the bearing spacer/axle. Couldn't find anything but I did have a piece of titanium, close enough...

Untitled by macona, on Flickr

Making the spud that the base rotates around. I used some 17-4 TGP stainless I had left over from an old job years ago. Found an insert that would actually break chips with this stuff which just created tiny super hot little chips flying everywhere. Ouch!

I am using a large ball thrust bearing for support and a taper bearing on top of that. The spud ties it all together and also serves as what the fine adjust presses against. I single pointed 5/8-18 threads for a nylok to tighten up the bearings.

Untitled by macona, on Flickr

This piece is the fine adjustment arm, two Vlier fixture screws will push on either side and allow it to move around it's axis. It is slit down the middle to clamp on the spud and can be loosened for rough alignment.

Untitled by macona, on Flickr

Untitled by macona, on Flickr

[macona]

I got the parts back from anodizing today. I decided to go ahead and send out what I had done since I need to press in the bearings and once they are in I was worried I couldn't get them out. Cant anodize them with steel in them.

They came out pretty nice. I decided not to anodize the main drive, I didn't want to take it all apart. Some pics of it all together below.

The thing is getting pretty heavy. I am kind of thinking of getting a small trailer and mounting it to that. The trailer would have outriggers to level it and get it off the wheels.

Also need to start thinking about a polar scope. A polar scope makes alignment much easier. It attaches to the mount and you use Polaris to get the mount lined up.

I plan on making the base this mounts to this weekend. It will pivot on two taper bearings and then sit on thrust bearings for polar alignment.

IMG_8565 by macona, on Flickr

IMG_8563 by macona, on Flickr

IMG_8560 by macona, on Flickr

IMG_8559 by macona, on Flickr