[pmrid (Peter)]

I'm about to embark on a long-delayed project to refurbish a fast 10"newt I have had sitting here for some time. I've reached the secondary mirror section now and am wondering about the relative stability/strength of the various alternatives out there. This unit uses a secondary mirror with a 3 inch minr axis so it's a relatively heavy unit. When you take the weight of the secondary holder into account, that's half a Kg or better that has to be supported/held by the spider assembly.

I've had some serious disappointments with different spiders I've bought for this scope. The worst faults I've encountered so far have included (in no particular order):

The mirror-holder shaft made of plastic that flexes when the scope moves - impossible to hold collimation or that strips its own threads when you tighten the hex nut;

The captive brass threads in the spider centrepiece that slip around in their housing preventing any proper tension on a collimating screw;

Captive brass threads that actually have a different thread from the collimating screw (yep, I've had one of those).

So I've become more than a bit cynical about these products. So I'd be glad to have some thoughts from others about how to identify a decently made, reasonably solid and reliable secondary/holder combination that will actually hold collimation.

Peter