I just got my first telescope a couple months ago and have learned a lot about collimation. I purchased a Celestron combo tool (Cheshire/sight tube) but it is way too long form my telescope (F4.7 10 in. dob). I can't see the whole secondary/mirror clips in the tool. I have now been thinking further about making a combo tool specifically for my scope by cutting down a long combo tool.
I am going to use the paper tube method + collimation cap to try and figure out the correct length for the tube. I will attach a 1.5 in. paper tube to the collimation cap and determine how long a tube I need to see just see the 1) edge of the primary in the secondary, 2) edge of the secondary and 3) edge of the sight tube as closely spaced concentric rings. I will then cut down the length of an inexpensive combination tool (Cheshire) to make it the correct length and then install new cross-hairs in the end of the tube.
Will this work? Am I missing anything?