Azimuth Section #1
The azimuth section is a simple ring manufactured from 3 layers of 25mm ply laminated together provides all the support necessary for the OTA. Essentially it is a 70x75mm (3"x3") solid circular beam with a Laminpanel plate on the bottom (which in theory should make it stiffer, but not really necessary). Originally my design was just a ring with no center pin, but as it came together there was really no reason not to put a thin plate on the bottom, so I did, mainly because the plate adds another barrier to creepy crawlies.
The most difficult bit to do was cutting the altitude bearing recesses. Several reasons. First there was no straight edges to work from, and at the time no bottom plate with a center point either. Second I didn't have a tool that could make the cut in a single set up. And third I didn't take enough care building a jig and relied too much on measuring, clamping, unclamping, marking and realigning everything to marks. Consequently the cuts didn't align as well as I expected and needed some rework.
Mounted in jig from behind
Jig from front showing angle grinder with 4" saw blade mounted in jig
This is about as dodgy and vicious as it looks. I had to take the guard off to use it and was terrified it would bite and grab and do something really evil. In practice it was as smooth and easy to use, gave no hint of grabbing, and I just shaved the job a few millimeters at a time. This involved lifting the entire cutting assembly to slide up its defining point and then slowly let gravity work its way down slice after slice. Unfortunately with only a 4" cutting blade it soon interfered, hence the step cut to clear space. This meant I had to locate the job 4 times and the saw 4 times, which is not a recipe for repeatability and precision.
So the lessons learned for next time were:-
1. take the trouble to make a very good jig - much better than the photos show
2. buy a 6" angle grinder and saw blade
3. build a better safer jig for the saw
I would also think about hogging most of the material out on the tablesaw with a dado set beforehand, and just using the swinging angle grinder jig to fair the final shape.