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Hello Leo, hope you are well. There seems to be a few differing opinions on collimating your refractor and apart from using a laser to align the focuser using the method described by doug mc, you don't need the laser to collimate the lens cell. I am assuming that the 2 lens elements are a snug fit in the cell and the spacers between the elements are all the same thickness and are equally spaced around the lens circumference and the retaining ring is allowing just a little movement. If you gently shake the cell you should be able to hear a slight movement of the lens in the cell, meaning the ring is not overtightened and pinching the lens'.
All you need now is an cheshire eyepiece inserted into the focuser drawtube , with a light shining on the reflecting surface of the cheshire, leaving the dew cap on the dew shield, look through the cheshire and you should see a series of faint concentric reflections, all being well. If the reflections aren't concentric, gently adjust the 3 sets of collimation screws around the outside of the lens cell until they are concentric again. I own several refractors, all the achros are home made and have used the described method to collimate them after having removed the lens for cleaning, the pollution around here tends to leave an oily film on the outside lens surface and needs to be cleaned ocassionally. Hope this helps, it's not too different from collimating newts, just have to get all the reflections as concentric as possible.
Jeff
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