Hot Head on Mini Mill

[Me2]

Hello all,
I picked up a Demo Mini Mill at an auction for a very good price. I was very surprised to find the drive gears are made of plastic. The low range gear is totally striped, this is going to be replaced free of charge by the agent for the mill along with a few other sundries. I have totally stripped the head and replaced all the bearings with NTN units, set the backlash on the taper roller bearings and lightly greased. Running on the high range gear it runs extremely smoothly. The one thing that bothers me is how hot the motor runs, its 1000W and a variable speed unit. After ½ hour of running it’s so hot I can’t hold my hand on it, the heat dissipates down to the spindle where it’s uncomfortable to hold whilst doing tool changes. When in neutral everything is free and easy to turn so I’ve ruled out sticky or tight bearings. Has anybody else experienced this problem on their mini mills or is this just normal running?

Thanks Cam

[sansbury]

after ½ hour of running it’s so hot I can’t hold my hand on it, the heat dissipates down to the spindle where it’s uncomfortable to hold whilst doing tool changes. When in neutral everything is free and easy to turn so I’ve ruled out sticky or tight bearings. Has anybody else experienced this problem on their mini mills

Yes. Search on my name here for my posts on the subject. Some people solve the problem by replacing the bearings. I was not one of them. I pulled the seals off my bearings and they run at full speed with a belt drive (~4000rpm) with a lot less heat buildup. They could run at normal gear drive speeds (~2200 RPM) with less heating. You might try backing off the preload but my suggestion would be to give up and just run it. The bearings are not that hard or expensive to replace.