Sherline spindle to 30k RPM -- am I crazy?
I am in a dilemma. I run mostly "fine step" contouring in aluminum, and I'm wanting to get faster feedrates. I have run a Taig spindle (Maxnc machine) around 15k rpm with my own 2+HP DC motor, and also a KaVo 500W 40krpm spindle. The surface difference between the KaVo and the Taig/Maxnc is like night and day. The KaVo leaves a beautiful surface, but it has little to no torque for some of the more heavy duty cutting I do on the same part. Swapping spindles for every part is out of the question.
So, I am looking to build my own "fix all" spindle. I am trying to go for the smallest (desktop mill sized) spindle yet still maintain precision... which leads me to the Sherline industrial line of spindles with an ER-16 cut directly into the spindle. However, after talking to a Sherline rep, he assured me I would have problems pushing the stock spindle with stock bearings up to 30krpm. So, I am looking at getting the sherline spindle, replacing the bearings with PN 35435023 from MSC (Nachi grade ASME-7 matched set 13* contact angle, rated 35krpm). These have the same dimensions and will drop right into the Sherline spindle, and would be driven, via pwergrip GT belt drive, by my 2hp DC motor geared up aprox 4:1 to get very close to 30krpm at the spindle
My main question is, AM I CRAZY? :) or should this work ok? with the angular contact bearings being held about 3" apart on each end of the spindle (in "sandwich" configuration), will thermal expansion over the length of the spindle be too much to maintain a percise enough runout? (stock bearings they run 0.0003" runout @ 10krpm).
please help!
Thanks-
Colin
Further on spindle cooling
Found this in "Manufacturing Talk" today: http://www.manufacturingtalk.com/news/fid/fid111.html
It's a nice reminder that reducing spindle bearing wear by cooling them with water sometimes can be a problem in itself. I still smile each time I walk by one of my chilled air cooled lil beauties. BTW bearing makers distinguish between "seals" and "shields" and I chose metal "shields". Regards, Terrence