I did this changeover quite a while back but here is a write up
on it:
The standard GSO secondary spider vane assembly comes with quite chunky vanes, they measure 0.8mm / about 30thou.
This shows in images as quite imposing diffraction spikes.
Made worse because they are not really mounted that symmetrically to the centre hub. See pics 1 and 2.
I decided to change them out to thinner vanes and also turn up a better hub in the lathe. ( an old VCR head)
Firstly I used metal packing strip which I measured at 0.5mm/ ~20 thou thickness.
I then decided to go thinner again, this time using feeler strip guages which can be bought in 300mm lengths,
similar to these.
These strips are perfectly straight when under tension and harder than mild steel. My current set are 0.25mm / ~10 thou.
I had to cut the holes for the end screw brackets using a Dremel, - mainly to stop distorting them by conventional drilling, and secondly
because even HSS drill bits won't get through them.
As a set, I clamped them, then drilled them as a matched lengths to get as good as I could to
having the secondary mirror right on the central axis of the OTA.
Attaching them to the hub I used the same method that Dad and I used on the 8" homemade scope.
Wrapped around a pin, which then sat in a machined hole close to the edge of the hub.
Pins were a press fit, the whole process done on a vice.
Lastly is a pic showing how fine the diffraction spikes can get on a night of exceptional seeing.
You can see fine adjustment is still needed to make the vanes diametrically opposed to their opponent, 180 degrees opposite.
This is achieved with packers on the offending vane.
What this whole process enables me to do is image very faint detail very close to bright stars. Look at the detail in NGC 2822
which is normally lost in the glare of Miaplacidus.
I must thank my amazing father for this.
It was his idea to use feeler strip, his idea to use dowel pins, possibly his VCR alum stock, he bought me my lathe......
I love you Dad
Steve
