You insert the shaft of an accessoir like a drill or diamond bit and tighten the collet nut to hold the accessoir in place. The accessoir is supposed to be centered automatically.
I want to use it to engrave a rather delicate ornament into glass. During my first tries with this tool I noticed that the diamond bit often isn't centered in the collet and creates a very wide line with chipped edges instead of the fine lines it should produce. When I start the tool I can actually see how the tip of the bit isn't centered (it looks like a double image):
When I notice this, I have to stop the tool, loosen the collet nut and wiggle the diamond bit around in the hopes of centering it by chance, then start the tool again and see if I was successfull.
How can I insert a bit into the collet straight on the first try?
I have bought high quality bits, so I assume they are straight. I always use the collet that is just big enough to insert the bits and always push the shaft all the way in. Since I get it right sometimes, I assume the machine itself is not to blame.