Posts Made By: P. Lee Stock

Three beads will do it. I make sure each squished blob of silicone has contact approximately equal to a 1/4" to 3/8" diameter circle. You could probably do less.

I asked this forum a couple weeks ago if I could take my freshly siliconed secondary out the same day and a few dare-devils said they'd taken theirs out only a few hours after gluing with no problems. I let mine cure for perhaps 14 or 16 hours or so before installing in the scope and it was solid. Normally I'd give it a day or two but I wanted to use it that night.

Removing is a piece of cake: a razor will slice right through it and scrape it from both surfaces.

Short version: It works really well--what was I worried about?

Longer version: At 305x (4mm ortho, 8" f/6) an image placed in the center FOV moves around a little bit--perhaps 1/3 of the total available FOV in a ~45-degree apparent field eyepiece over about 45 seconds. In other words, you won't be doing astrophotography with it, but it works really well, even at high powers.

After straightening the threaded rod to the point where turning one end only resulted in movement of around .01" at the other end, and making a really tight connector, a dial indicator measuring the movement of the table showed a steady drop over approximately .08", then a couple second pause, then the steady movement again. No backtracking.

By far the greatest challenge with tracking was simple polar alignment and first-time leveling. Once these were close (via drift method--could hardly find Polaris in the sky glow tonight), everything simply worked.

It is surprising how forgiving and easy the EQ platform concept is. Yes, I was careful in designing and building, but this was my very first attempt at one and the thing worked great right out of the chute. I even got the motor speed and threaded rod per inch thread count right.

Only thing to improve is I need a better potentiometer--I placed slightly too much resistance on the circuit to power it down to a range my available pot could deal with and during the last 5 or 10 minutes of "climb", the motor doesn't have quite enough speed/torque to keep up--and if I bypass the pot and run full speed, it tracks just slightly fast. So I need a speed just shy of "full", something not available as currently wired. For the other 60 or 70 minutes (of 90 total), it tracks just great.

Oh, and the best part... I reset it 3x tonight and that took around 5 seconds total, counting all 3 times ;^). NO rewind procedure to clutter up the observing experience--just like I wanted.

Center knob, to right of carry handle, is a long screw that holds the platform together during transport. It stores away conveniently during use.

Top-side feet help raise my scope close to eye-level at zenith (my preference). Protruding brass screws fit into divots in my telescope's feet to prevent the scope from sliding off.

Behind the motor, a circuit breaking plunge switch mechanically cuts power when the table reaches the end of its run--didn't want to worry about the table pulling itself apart if I left it running accidentally.

Power to the table comes from the telescope above via a 12v 7ah battery. I made a brush-type power transfer system to get power from the battery housed in the rocker box to the telescope's ground board, where a short cable crosses down to the platform--no dangling wires and unlimited rotation.

Motor speed control is via a potentiometer in a control box at the end of a cable velcroed near my eyepiece (not shown). It is connected to the telescope mount, not the platform, so it wouldn't be a dangling cable liability, and to keep the control at the eyepiece where it would serve its purpose best.

Details of the ball bearing assemblies. South bearings were conveniently and inexpensively purchased for $5/pair as screen door hardware--rubber O-rings fit perfectly around the bearings. Half-nut, tensioning spring, bronze bearings also shown. The hole in the maple block (foot) is where I slide the long "transport screw" when the table is actually being operated.

Top/side view. I included a compass (only place it wasn't affected by magnetically charged metal strips, motors, screws, etc.), bubble-level (the center section of a $4 Stanley torpedo level), top-side carry handle, top-side scope feet matched to my telescope--I have been trying to raise my scope to eye-level with this project as I prefer to stand when observing, especially when it's cold. I seem to notice the cold less when I move around more.

North feet are very adjustable: for leveling, to raise the platform as discussed above, and to permit use of the platform a good distance N & S of my Salt Lake City home.

Aluminum channel is decorative, protective and structural--I wanted it to look sort of finished until I finalized a drive option (and the current one might just be it). Then I'll finish the wood black to match my telescope.

I'm guessing this platform would work for a scope well over a hundred pounds and with virtually any center of gravity, so it ought to (hopefully) work for that minimalist 18" to 20" scope I have planned ;^).

I chose a 3-point bearing support system over four--it's just easier to align three points.

The rear bearing block here at the South end of the table is also the only part that required some wittling and re-making--until the table was level, until the N & S bearings attached to the block had full contact with both sides of the cylindrical bearing, etc. I'd do it this way again, no question.

So... this is how I did it. I've been wanting to make one for years and am glad I finally did. I can't recommend this ATM project highly enough--it was really fun!

Cut a wooden mounting plate the inside dimensions of the mirror box. Route or cut a circle out of the center of it about the same size as the the mirror cell. Screw three wooden blocks or metal "L"-shaped brackets (Stanley-brand hardware would work) around the perimeter of the circle corresponding to each of the mounting screws. Screw the plate into the mirror box and the cell onto the brackets.

Here's the bottom of my ground board showing the RCA connector. Pretty ugly, I know, but no one ever sees it.

They often do...

;^)