Flintstone Stargazing

October 17, 2009

Project: Adding a Motorized Focuser to My LXD-75

Filed under: astronomy, Equipment, project — Tags: , , , — Ed @ 8:49 pm

A bit over a year ago, I bought a Meade 1244 motorized focuser unit and adapted it for use with my LXD-75 SN-8 telescope. The 1244 unit (that I got off of eBay) is designed for a completely different scope (the ETX series), but I was convinced I could make it work with my stuff and so I got one cheap. As far as I know, there is no model specifically designed for my scope. Here’s how I did the adaptation:

Adapting the focuser shaft

After disassembling my focuser, I unscrewed the left knob from the shaft. After measuring the threads on that side of the shaft, I tapped a brass rod that I had cut to length (about an inch and a quarter) so that I could thread it onto the shaft. Once I made sure that it screwed on well, I added some Loctite Blue and screwed it in. I don’t expect it to ever come apart, but if it did, it’ll be easy for me to reattach it. I also flattened one area on the rod so that a gear set screw will have a place to hold on.

Now that I have finished the rod, I need to attach the gear that came with the 1244 focuser. The rod that I purchased had the same outer diameter as the inside of this gear. I can’t tell you what it was because I don’t remember, but I just took the gear to the hardware store and found a rod that fit nicely. Before attaching the gear, you have to slide on a plastic piece that came with the focuser first. make sure you have it facing the right way. You can spin it around, but you can’t flip it once it’s on there. After sliding the plastic piece on, I slid on the gear and then tightened the set screw. Incidentally, you’ll need a .050 hex wrench to tighten it. The 1244 comes with one.

Reassembling the focuser

Now that the shaft is complete, it’s time to reassemble the focuser. You might take this time while everything is disassembled to clean out the grease and gunk and relubricate the focuser. I added a bit of teflon tape to cut down a bit on focuser shift and I used a light coating of white lithium grease to relube everything. Next I place the focuser shaft into position:

Next, I added the cover over the “gearbox” area.

Before I put the screws on, I add the custom bracket that I made. I made the bracket from a piece of aluminum that I carefully cut to size, bent and then drilled 5 holes. To make sure the holes were in the right place, I drilled through the gearbox cover so that the four screwholes would match up. The other hole, for mounting the focuser, I marked through the screwhole in the focuser with a pencil lead (it’s pretty thin) and then drilled. Here’s the custom bracket:

While you hold the bracket in place, you screw in the four screws through the bracket and the gearbox cover into the focuser. While I start to screw them in with my cordless drill, it’s important not to tighten them too much, so I finish by hand. As you tighten them, you make it more difficult to turn the gear and it presses harder on the focuser tube. You want the movement to be nearly effortless, so make sure you test as you tighten by hand.

Attaching the Motor

It’s now time to attach the motor. I place it over the shaft and slide it into place on the plastic piece under the gear.

Next, I drop the screw into the focuser screwhole and through the custom bracket and I tighten it very tightly with a nut on the bottom.

Now, the next time I’m out, I just plug in the focuser’s cord into the auxiliary port on my telescope and I can control it with my Autostar 497 hand controller or if I’m hooked up to my laptop, with my software.

Having the electric focuser allows me much more precision in focusing and makes it easy for me to focus without touching the telescope. It now means the knob on the other side is nearly useless (though I can look at it and see if it’s turning) because you can’t turn the shaft except with the motor now. Of course, I’m always plugged in with this scope, so it’s not a big loss and if it ever broke I could just unattach it and use it manually again. I’m planning on someday in the future replacing the focuser with a much nicer one (the stock SN-8 focuser is not very good), but until that day I’ve got a much better system. Over the past year as I’ve used this, it’s really been fantastic and I’ve become almost addicted to electric focus. It’ll be hard to do without if a future focuser doesn’t have that option.


1 Comment »

  1. I was looking for a way to do this, the meade focuser is cheap and very nice. I already adapted this one to my etx-125 (the specific focuser for the 125 is rare and very expensive), and maybe will try adapting one to my sc-8 as well. Thanks again!

    Comment by billy — August 30, 2014 @ 9:50 am

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