Takahashi EM-1S Ersatz Polar Scope

I bought an old Takahashi EM-1S mount from Yahoo Japan, but it did not come with a polar scope.  Since this mount is 25+ years old, I was not even sure if a polar scope could be bought for it. Also, the Takahashi polar scope is expensive, and since I got the EM-1S fairly cheap (for a Takahashi..) I figured it would not be worth it to buy the current polar scope.

As luck would have it, I had a Celestron 6x30 "Long Eye Relief" finder scope, and I thought it might be possible to adapt this finder scope as a primitive polar scope for the EM-1S. The outer diameter of the eyepiece portion of this finder is about 24mm, and the barrel itself is 32mm in diameter. After three attempts, I came up with this design for an adapter, and 3D-printed it. The finder scope is a bit of a loose fit, so I added two masking tape shims:

There are three 3mm diameter holes in the circumference of the adapter, which must be tapped with an M4 tap and grub screws inserted to hold the finder scope in place.

Here is the ersatz polar scope in position. The adapter is a very tight fit in the Takahashi mount's RA bore. A strap wrench would be needed to remove the adapter. So it is important to place the finder scope into the adapter, and secure it with the grub screws, before inserting the adapter into the mount's RA bore. Some whacking was necessary to get the adapter to seat (although a previous version I made did not require whacking, so it's probably down to non-repeatability at sub-mm level in the 3D printer).

The polar scope manhole cover (cap) still threads on nicely: