PM1236T Spindle Stiffness

[NickelOrBust]

Hi Folks-

I was mounting my new Bison 5C collet chuck my 10 day old PM1236T tonight. I noticed that by leaning on the chuck i was able to generate about .001 of movement on the indicator. That much movement surprised me but I'm still learning the moods of the machine. Is this typical? I really dont have any baseline to go by, but it seems like a lot even when considering my admittedly not so slender weight.

On the upside, the Bison dialed in to less than .0002 of TIR, and the head stock alignment via taper cuts is better than .0001 per inch.

 

[darkzero]

Well, don't lean on it!

 

[mksj]

That sounds about what one might expect. I had the 1340GT, could get around 0.0005" movement with not much pressure on the chuck. Still, I could easily hit tolerances under 0.001" without much effort. Rechecked my Bison 5C today on my lathe after some work and it repeated at 0.0002" TIR near the collet, what you will find is 5C collets tend to have a bit more skew as you measure further away from the chuck. I also index my chucks to the spindle so they always mount up in the same position. Make sure on the 5C collets you do not over collapse it, they have a narrow clamping range. Keep the collets clean and the internal clamping area free of oil to minimize slipage, I put a little way oil on the threads when I insert the collet.

 

[Janderso]

I would be curious to see what kind of movement you would get after the bearings came up to operating temperature.

 

[COMachinist]

Well, don't lean on it!

Good point. My 12x36t has little less than .001 when pressure is applied perpendicularly with the spindle stopped. How ever I think when the spindle is turning there is nil if any deflection. Even with heavy cuts the dial and mic, agree with repeatable results. I have had my 12x36t for over a year now and it is consistently holding tolerances of less than .001 in any material from 6061 o 4140 and the surface finish is great as well. You may want to run it up to normal operating temp then check again, and try to keep the OCD in check.
CH

 

[NickelOrBust]

Good point on temps, I’ll definitely check that.
I’ve been really pleased with the accuracy I’ve achieved so far. I hit .3148 on the nose the other day as measured by some .00005 mitutoyos. So that’s why I was surprised to see the spindle deflect .001.