Recently I purchased an APM 100mm Apo Binocular with the APM center mount. While the center mount is nice and compact and works well I found that as I increased the magnification to 60x and beyond, the vibration was just a bit too much. Thus I started thinking about building my own fork mount.
The difficult part for this was coming up with decent bearings for altitude and azimuth. So I got to thinking and looking at the commercial APM fork mount, it seemed that the azimuth bearing is quite close in appearance to the center mount bearing. So I decided to use the existing az bearing and find ways for the Alt bearings.
Looking through the McMaster Carr catalog turned up the following 4 parts:
I used a teflon bearing that fit a flange mount 3/4" shaft that had a 5/8" thread at the end. A thrust bearing made out of 1/8" teflon sheet provided the perfect spacing through the 1/4" aluminum arm. On the other end, I added a 3/4" inside diameter roller bearing and then 3d printed a knob that held a 5/8" bolt. The result, assembled looks like this:
That took care of the azimuth. I then purchased some 20x80 and 20x60 aluminum extrusions as well as a nice vixen dovetail mount from ebay.
I wanted to have shaft encoders to use with a Nexus DSC so I drilled out and tapped one altitude axis and placed an AMT 101 encoder there with a 3d printed support.
The azimuth axis turned out to be more challenging. I first started to drill through the shaft for the azimuth thinking I would add a shaft through the existing bearing. Well the main shaft was far to hardened for me to do anything with it. So instead I 3D printed a GT2 pulley which was a press fit on the outer azimuth bearing casing and designed a support for a smaller pulley with a shaft through to the azimuth encoder.
The resulting complete fork mount looks like this:
The black box under the mount is the Nexus II DSC which I use with an Android tablet and Sky Safari.
Total cost was around $320, a lot of which was postage ordering the things from all over the place. So here in Canada I saved a cool $1000 or so over the commercial cost. (Money's gone. I bought a mini-lathe with the savings) The aluminum arms were done on a Shapeoko 3 CNC mill but you could do the same with hand tools if you have the patience.
Hope this helps some adventurous ATM's.
Edited by tomb18, 11 January 2020 - 07:39 PM.