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MI-250 ALTERATIONS

MI-250

Because Mountain Instruments didn't have a polar alignment scope when I bought the mount, I decided to alter my Tuthill Precision Polar Alignment Scope (TPPAS) to work with the MI-250.

I removed the scope from the aluminum U beam and reversed the direction that it pointed. To my surprise the holes drilled in the beam were not very square. When I got the scope turned around the 360 deg dial was about 3 degrees off! I now have to factor that in whenever I polar align with it. I am thinking of elongating the holes in the dial so I can rotate it the 3 degrees. I took the TPPAS to a machinist friend of mine to verify that the scope was a true 90 Degrees from the beam (it was). The only thing that was left to do after that was to file a couple of small 1/4 inch grooves in the beam to make room for the washers under the clutch bolts (they just barely interfere). I then calibrated the TPPAS by doing a precise drift method polar alignment, mounting the TPPAS, and adjusting the cross hairs to intersect Polaris.


I use the Dec centering stud to mount the TPPAS to the face of the MI-250. I also added the bubble level to ensure that the TPPAS was level when setting polar alignment.


This is the adapter plate that Mountain Instruments made (free of charge) to mount my MI-250 on my Meade Field Tripod. I had to make one small modification. The center hole was drilled to let the all-thread rod pass through. I had the center hole machined to 1 1/16 inch diameter and 1/2 inch deep. This allowed me to put a nut on the end. As you can see from the picture, I moved both of the handles under the support structure and use them to tighten up the tripod. I think Larry Myers (Mountain Instruments) is thinking of threading the center hole so that the all-thread rod will just screw into it, thus eliminating the need for the alteration and nut.


When I started out upgrading my equipment, this is all that I envisioned doing. I wanted to re-mount my 8" LX50 onto a mount that could be easier used for astrophotography. Well one thing led to another and I ended up with a lot more.


This little beauty is from the mind of Russ Dickman. He has helped me get through the learning curve of this new mount and suggested this enhancement. The mount comes with a 1 inch all-thread rod and two locking nuts to secure the counter weights. When you want to balance the mount you need to screw the locking nuts in or out to move the weights. The new shaft is exactly the right diameter for the center holes in the weights. The only alterations needed was to have the weights drilled and tapped for the brass rod and fastener. This arrangement holds the weights very securely and makes it easy to adjust the mount into perfect balance.


This is what the new shaft looks like assembled on the MI-250.


These are the cases that I made to transport my MI-250 mount. They are Rubbermaid 6.5 and 14.75 Gallon storage containers that I fitted foam rubber into. I cut out the various shapes using an exacto-knife. Both have handles and are easy to carry.