Well it is nice to know that I am not the only one. But I have learned something interesting. I tried to do an etch with the wobbly chuck and it worked just fine. I really could not understand this until I was going to sleep last night. Then it came to me. The laser treats light much the same way a camera does. The focal distance is not the only issue. There is also focal depth - that is, the space where focus is achieved. It is not a flat plane. It has depth. In the case of the laser, this focal depth could be up to 1/2”!
You can sort of demonstrate this to yourself. Hold your hand palm down in front of you and move it up and down about 1/2”. From the side, this is a pronounced movement. Now face your palm toward your face and move the palm 1/2” toward and away from your face. See what I mean? The movement is much less apparent. I believe the laser “sees” in a similar way.
So while I am still trying to get these Chinese vendors to make good o delivering a faulty rotary (good luck) I am delighted that I can actually use the thing. It works much better than the roller rotary I was using before.