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  • June Project of the Month (Click "x" at right to dismiss)
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Jet Mill Jvm-840 Pf (kao Fong Kf Vo-2af) Project

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Jim_Z

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Oct 31, 2015
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#1
I picked up a little Jet Mill last summer that had been sitting for several years and was in need of some TLC. The mill is a knee mill with a turret head, just a little bigger than a Clausing 8530. The spindle and quill assembles were pretty stiff, but spraying things down with some PB Blaster and squirting copious amounts of diesel fuel and 20w oil down the head oil cap loosened things up. The quill and spindle bearings freed up OK, but were rough so I disassembled the head and ordered new SKF bearings for the spindle and quill. Today I got the new bearings installed. Both assemblies are really smooth with the new bearings. Something has me puzzled though, the quill uses a pair of 7207 high angle contact ball bearings. I am wondering about how much preload should I put on these bearings. I am going to to proceed with assembling the head and can adjust final preload in situ.

I found a couple of good photo essays on rebuilds of these mills, but have not found good documentation on setting the bearing preload. Can anyone on the forum enlighten me on this?

Once I get the head assembled, I will move forward with powering up the mill. I was going to use a VFD, but am going with a rotary phase converter instead. The mill has a 1.5 hp 2 speed 3 phase motor to power the quill and uses a little 1/4 hp 3 phase motor to power the gear train of the power feed. It is my understanding that VFDs don't like that type of setup. I will post a couple of pictures in a later post.

Jim_Z

Logan 1825 lathe
Jet JVM-840PF milling machine
 

sanddan

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Jan 22, 2012
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#2
Call Jet customer service and they should be able to help you.
 

calstar

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Sep 26, 2013
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#3
Finding the correct preload is pretty tough, I hope Jet can help you out. I've replaced the spindle bearings on 2 8530s and could not find any preload numbers, Clausing couldn't help me, just went with what I felt was just tight enough. I did not use a matched set because of cost, but when a matched set is used you snug up the two bearings until the the two "beveled" inner races touch. FWIW one of the mills had been running with a couple of cheap $15 plain bearings for more than a few years(hobby use) with very little runnout and zero noise, go figure. Got a picture of the mill for us??

Brian
 
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