Atlas MFC spindle

A

Airpirate

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My atlas mill head spins about .009 out of true, so my cuttere basically cut on 3/4 of a revolution.
What is the most likely culprit? Bearings and cones, or bent spindle?
 
I don't use collets. I use a 1 inch arbor or a jacobs chuck. Both devices have a out of round wobble of about .006. The out of round is just on about 90 degrees of rotation and always on the same point. So when using a cutter wheel or slitting saw only about 270 degrees of rotation is doing work. You can hear it audibly like a zing zing zing.
 
Then its safe to assume you verified the true-ness of the tooling arbor then? Not saying its not what you suspect the problem is or not, just ruling out the more easily solved less expensive possibilities first.
 
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It's common for a horizontal arbor to be bent causing the problem you are decribing. A Jacobs chuck is good for holding a drill,but it in of its self has too much run out for holding an end mill. In a bind we have all used one for holding an end mill ,not a best practice.
 
At first I suspected the arbor but I have the same run out using the chuck.
I will insert a collect and a drill and check for runnout again.
 
Do you have an MT2 collet or end mill holder that you can chuck in the spindle? If so, put a dowel pin or short length of drill rod, tighten everything up with the drawbar, and indicate off the pin or rod. That should get you close enough to measuring the spindle directly that you can determine whether it is the arbor or the spindle.

You can also indicate off the back of the spindle (remove the gear cover), a dial indicator on the inside of the spindle after you clean it, which should let you know if the spindle is true. If not, well, could be bearings, could be the felt washers used as spacers, could be a loose setscrew on one of the collars ... could be a lot of things. Fortunately the spindles are not too bad to take apart; the manual is very clear on the process.
 
I do have collets so I will give that a try.
I had a morse taper insert with a 3/8 bare end on it. After cleaning the inside of the spindle and inserted the marse taper stub and measured the runout. It was only .001 out. Loaded up my arbor and did the same and duplicated the .001.
I assume .001 is within tolerance for this machine?
Could a dirty spindle have caused my earlier higher measurements?
I checked my chuck with a 1/2 drill installed and found higher runout of .004 so I assume that is integral to the chuck.
 
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It's probably because it's an Atlas. .009 is quite a bit, but both my MFC and my 12" lathe spindles hade excessive runout (~.003). I reground my mill spindle true and will probably do the lathe spindle once I get the taper attachment working. It's less important on the lathe, since I can just put in a soft center and machine the taper in situ for turning between centers, but I would like it to be right. I think it would be really hard to bend that spindle even in a hard crash, since it is quite short, fairly robust for it's size and well supported at both ends.
 
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