Now for the Tangent Arm. Gotta admit I had heard the term before but had no idea what this was or how it worked....ATMing is a learning curve for sure
As with the RA slip clutch it was read read read look and try to understand what's what. I came across a nice idea from Jim Sapp. The penny dropped some where along the way and it was into the shed for aluminium shavings everywhere again. Building a pillow block mount from scratch would have made all this so easy...retro fitting means I'm limited with what I could do, so this is what I came up with.
Photo time: L to R Tangent arm showing the cylinder block with the threaded rod through it. The cylinder block is two cylinders one in the other that keeps the threaded rod straight as the arm moves through an arc....simple right?
From the front and next the solid blocks that are part of the clamping mechanism around the mounts DEC axis. Last photo the dovetail and tube rings which are bolted to the Dec shaft...turning the threaded rod moves the dovetail around 10º in either direction while the clamp keeps it all clamped down on the dec housing with cork inserts for a bit of grip. Whew.
A lot harder to describe than it really is.
Thinking of putting an electric motor on this too and as I can move it by hand quite easily, possibly a focus motor will do the job? Gonna try it any way. My first version of the arm was twice as long as it is now and it sagged under it's own weight. Rather than rebuild it with a counterweight out the front of the dec axis a I have seen on some old 19th Century refractor's I went with the shorter length and a motor will make adjustments easy...I hope.
Still need to get the scope up on this but it works with a smaller scope on it in my shed.
I feel that I have missed out on quite a few details of the build here so I'll add more along the way.
Matt