6205z bearings on MkII 6"

I would have expected under 0.0002" TIR with ABEC 5 bearings in there, John. What is the condition of the spindle taper?
 
The spindle taper isn't good but the .002 was at the 3 jaw, it's closer to .0002 at the outside of the spindle near the headstock where I could measure.

I was thinking of getting a reamer for the taper but I'm not really sure when I'll be turning anything between centers on this machine. Two thousandths at the chuck seems reasonable and probably getting a 4 jaw would be a better use of money than trying to fix the taper.

John
 
Also I'm still trying to learn how to measure properly ;)
 
Let me offer a procedure that might help. You will need an indicator stand and a decent DTI, ideally a 0.0001" DTI. All measurements are done while NOT under power and cleanliness is paramount - tip of the DTI, spindle taper or surface where it contacts.
  • Find a surface from which to take your measurements. Ideally, you want an undamaged surface inside the spindle taper but if that is not available then somewhere near the taper that is a structural part of the spindle itself. Clean it well.
  • Place the indicator holder on a non-moving surface, like the bed/ways. Bring the tip of the DTI into contact with your chosen reference surface on the spindle and try to position the tip of the DTI at about 6 O'clock. Keep the extension of the arm/arms of your indicator stand as short as possible while still allowing you to maneuver around it. Preload the DTI by about 0.015" or so and zero the dial.
  • Mark the spindle and a non-moving but adjacent surface with a Sharpie at 12 O'clock. As you turn the spindle the mark on the non-moving surface will remain steady and the mark on the spindle will rotate and can be realigned with the non-moving mark. Now, with the DTI preloaded and zeroed and your two reference marks aligned, turn the spindle by hand and go one full revolution around. When your two marks are aligned again the DTI should be exactly at zero. If it is, then you can rely on the set up. If it is not, then rearrange the indicator holder so it is more rigid and try again until you get the DTI to return to exactly zero. Once it does, you can rely on it.
  • Now make one more revolution of the spindle but this time you are looking for the minimum and maximum deviations from zero. As you slowly rotate the spindle, mark where the high and low spots are (make a mark across from your static reference mark at 12 O'clock) and make a note of their magnitude, then realign your original two reference marks. The DTI should again be at zero. If this is true, then make one more slow revolution and see if the high and low deviations are at the same place and of the same magnitude as before. If they are and your DTI again returns to zero when your two reference marks are realigned then you can rely on those measurements.
  • Now subtract the minimum deviation from the maximum deviation and that will give you your spindle TIR. Make a note of this and put it somewhere you can find it.
Now that you know what the accuracy of your spindle is you can tell what the accuracy is for anything else you put on that spindle, like a chuck or a center. You measure the accuracy of these things the same way as the spindle; you do NOT do it under power. Remember that each thing we attach to our spindle increases run out and every interface there is with the spindle will add its own run out.

You can probably see why adding a drill chuck to a spindle and measuring the run out of a rod sticking out of the chuck under power like we often see on the forum adds absolutely zero useful information. We have at least 4 interfaces between the spindle and the chuck - the morse taper, the chuck itself, the jaws of the chuck and the drill or rod. Then you add rotation to that mess and who knows what it means?

Anyway, give this a try and let us know what you find. I bet that spindle is far more accurate than 0.002". If it is not then the spindle is bent or the spot you measured from is not accurately ground.

Mike
 
Thanks Mike,

I have the first part of this process but can see where marking the spindle will give much better information. From what I could tell the spindle is pretty decent, I did re-install the original one I had to free the chuck from not the eBay special which seems to have some sort of tar like material in the taper.

I've put the gears and such back for now so I'm going to make some chips and see how accurate it is in use. My other lathe is a Seneca Falls 9" Star which is far more substantial than this one but it's 2000 miles away right now.

John
 
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