How much is too much mini lathe spindle run out?

macardoso said:
One more thought. ER collets center best when properly torqued to spec. This torque is wayyyyy more than you'd expect. For an ER32 collet using a standard (non-bearing nut) you need to torque to 100 ft-lbs. I doubt many of us actually do that, but it does improve TIR when using good collets and nuts. My cheap collets deform under much less torque while the Techniks stay true.
Click to expand...
That's good to know. I torqued it down, but not that much! Might have only been 20 ft-lbs. The ER32 spanner wrench I have is short and I haven't even made a tommybar to fit the chuck yet. I was using a hex key as the tommybar. Now that I know the chuck is ok, I'll make a bar.
 
WobblyHand said:
That's good to know. I torqued it down, but not that much! Might have only been 20 ft-lbs. The wrench I have is short and I haven't even made a tommybar to fit the chuck yet. I was using a hex key as the tommybar. Now that I know the chuck is ok, I'll make a bar.
Click to expand...

You *probably* don't need to get it that tight but just making you aware that these do come with a manufacturer recommended torque.
 
Seriously, 100 ft-lbs is a lot of torque! Yes I could do it with my weight, but one has to be in the perfect position to do this. I wouldn't be able to do this in my current setup. I'd have to make some long bars and a long wrench, at least 12" long each. @12" I'd need 100 lbs of force. Doubling the distance would halve the force. That would be a crazy ER32 spindle wrench to be sure!

My takeaway from this is to tighten the collet a lot tighter than you thought you should have.
 
I am going to suggest something that some might consider sacrelige........

If you wan tthe ER chuck to run true, you are going to need to machine some clearance on it (whatever is preventing it from moving wrt spindle)
and then tap it into true as you torque the bolts holding it to the spindle.

Sort of like traming a vise on a milling table, but in rotation instead.
 
Mitch Alsup said:
I am going to suggest something that some might consider sacrelige........

If you wan tthe ER chuck to run true, you are going to need to machine some clearance on it (whatever is preventing it from moving wrt spindle)
and then tap it into true as you torque the bolts holding it to the spindle.

Sort of like traming a vise on a milling table, but in rotation instead.
Click to expand...
I thought I might have to do that, but was really hoping it wouldn't be necessary.

I don't know yet the repeatability of the chuck TIR. By that I mean remove the chuck assembly, remount on the spindle and measure the TIR. At the moment, I'm just amazed at ~0.00001" runout. 1/10th of a tenth. So I'm not anxious to remove it today. (I'll move it, but not today!) I have the location marked, but it's only a sharpy, which can be easily rubbed off. When I'm a little more sure the location is a keeper, I'll punch the location to mark the assembly plate. That way I won't have to guess each time.
 
WobblyHand said:
I thought I might have to do that, but was really hoping it wouldn't be necessary.

I don't know yet the repeatability of the chuck TIR. By that I mean remove the chuck assembly, remount on the spindle and measure the TIR. At the moment, I'm just amazed at ~0.00001" runout. 1/10th of a tenth. So I'm not anxious to remove it today. (I'll move it, but not today!) I have the location marked, but it's only a sharpy, which can be easily rubbed off. When I'm a little more sure the location is a keeper, I'll punch the location to mark the assembly plate. That way I won't have to guess each time.
Click to expand...

Not trying to be mean, but let's double check that TIR. How are you measuring it and can we verify the indicator is not bottomed out? That kind of runout would put you in the ultra precision class of lathes seen only in laboratories.
 
Not bottomed out, I checked for that. However, I could very well have made a mistake! And I'm not afraid to admit mistakes. Witness this thread.

I have a Noga indicator holder. It is magnetically attached to the top of the headstock. (Not the cover to the headstock.) I have a Federal 0.0001" dial indicator. (The dial indicator was my Dad's, when he worked as a technician at the MIT Radiation Laboratory just after WWII. He helped build their cyclotron among many other things.) I have positioned the dial indicator so that it touches the taper of the chuck near but not on the edge of the taper. I adjusted the indicator so that it pushed in by about 0.005". (So I can easily tell if I "fell off the indicator") Rotated the dial face to read 0. Grabbing gear end of spindle, rotate the spindle by hand 360 degrees. Measure difference between minimum and maximum setting. Rotate a few more times, just to see if the measurement effectively repeats.

I'll measure it again, since it does seem too good. Next post with a picture of the set up and measured results.
 
WobblyHand said:
I've partially mislead people. CRS. The real amount of spindle play is 0.002" on a static spindle. Just went down and measured it again. If I push and pull the gear end of the spindle in the horizontal plane, I measure 0.002 play in the horizontal plane at the rod end. (The gear end is opposite end of spindle from chuck.) This is as much as the TIR. Does this point to the spindle bearing being the dominant issue?
Click to expand...
I've no idea what brand of mini lathe you have, but I know a mate of mine replaced his spindle bearings in his mini lathe with branded ones - nothing expensive, fancy or precision - and it transformed the machine. He had 0.005" static play before and around 0.0002" after. I'd bet that $15 worth of bearings will probably do similar for you.
 
I'm not discounting the bearings yet. Need to go downstairs and measure stuff again.
 
If you do have that good of runout, good for you. I'm jealous!
 
You must log in or register to reply here.
Back
Top