Collimating a Diagonal/Eyepiece Combination?

Good Evening,

I've been playing with a small MAK and tonight when I was testing the optics I noticed that it had very poor collimation. Guessing that it was not the scope, I began loosening and re-tightening the diagonal and eyepiece. At certain points the collimation is right on, but when the screws tighten down it goes off again.

Any suggestions as to how to keep the thing collimated? My first thought is to insert a very thin piece of plastic sheet around the diagonal before inserting it to center it better with the scope.

Thanks,
Ed

This is a deffinate universal problem. I would think that a shim would be a good way to try and keep it centered, It sure can't hurt and it is cheap.
EPs are a problem because they are made undersized and the focusers or adapters are made oversized! This is something that is hard to get around. Almost seems like someone needs to make a shim material that is self adhesive and could be wrapped around the EP or focuser barrel until it achieved the right size. Some thing made of teflon or even aluminum in a roll like tape would be OK. I used to have some aluminum tape like this years ago. I have no idea where you can find it today.
Floyd