Two collar test - how close is close enough?

I did a search on here, there were several posts on ones that others have made. Richard told me that if I wanted to make one that it was not a trade mark infringement or patent or something like that as long as I am not selling them. I had to make 2 different sizes, the first one I made was about 1.25" in diameter, with a half inch groove, I made the one in the picture about half that size and it fit my lathe quite well. I also bought several different clamps, 2 more starret mag base posts that were threaded where they screw into the way alignment fixture. I have 3 or 4 different DTI's but only 1 is .0001 the rest are .0005. My next purchase is an alignment shaft for my lathe. I need a MT4.5 to fit the spindle so when I start scraping the head I can get the head alignment close so I am going to get it from Millers machine tools, they claim no run out and .0001 or less for straight and conconcriticy. Tim
 
Thanks, Tim. Rich is a great guy, unsparing of his time and always willing to help/educate others as you doubtless know ! A few weeks ago, for example, he went to a seller's home to evaluate a lathe for a newbie who was considering buying it. He'd never even met the potential buyer except on a forum !
 
If I understand correctly you got no difference running the indicator across the top from collar to collar but you are measuring .003" difference in the collar diameters. To me, it indicates bed wear because the indicator followed the dip the carriage dropped into when it made the cut. I've seen worse, I inherited a lathe that had .025" wear as received, it took a lot of scraping to fit that one.

to get 0.003 difference the wear would have to be huge at 2" diameter.
 
My non hardened Rockwell bed was worn .0087 near the head stock. So its possible. Tim
 
o.k., vertical wear 0.01": 0.01*2 + 1*2 = 1.0001. root of that is 1.000049. (pythagoras.) so radius has increased by 50 milionths for 2" stock. besides carriage will average out.

not much help to op though. maybe think about it some more and take a straight edge to the ways. or the level, i believe you have one. maybe the problem is with the jaws. they might be gripping in the back only. to check, take two round pieces of same diameter (preferably ground) or make them, with a hole in them. attach a rod on one and slip it through the other one. chuck them up with moderate force, one in back, one in front and see if one moves (probably the front one). if that how it is, get a cbn insert, make a boring bar for it and hard turn the jaws. be shure to preload them, look that up or i can elaborate.

oh, and check the jaws in the middle too, as they can be worn round.
 
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