Friday, November 25, 2016

Another Machining Lesson Learned

I have developed enough confidence in my knowledge of feed rates and depth of cut when milling acetal on the top surface to start it up and come half an hour later to a completed operation.  I am currently trying to side mill aluminum to square off a tube.  (Yes, I should do that on the lathe, but machining steel dulled my carbide tool and of course I had no spares.  Next time, ten of them, which also gets a 20% discount from Sherline.) 

What happens if your finish end mill gets stuck and stops turning?  I shudder to think what happens on a gear-driven vertical mill.  On the Sherline, it burns out the drive belt--a $5.50 part.  But it takes an hour and myriad temptations to swear.  The cleverness of the Sherline design makes some replacements very hard.  No more trusting it until I have run through attended at least once,

1 comment:

Will said...

Most of the typical knee mill types use some type of belt for the final drive of the head, which can slip if needed, I suppose. The Bridgeport has two different setups, depending on if variable adjustable or pulley change type. Neither is a toothed belt type connection.

With the availability of VFD controllers, the pulley change type is no longer an also-ran in the desirability area. Less to wear out or break, and belts are cheaper, and the VFD gives you the speed control. Changing the pulley setup just gives you a different speed range to play with. IIRC, the VFD gives one the capability to spin them in the range of current CNC units (8-10k rpm), but the headstock bearings are the limiting factor. I don't know if they can be upgraded to handle that sort of load.

The VFD was less than the price difference between the two Bridgeport versions, I think. I'm a bit out of date on my data on this subject.