So there I was machining a piece of 304 cres on my Bridgeport to make
a belt tensioning handle for my Heavy 10 lathe because I didn't have
the good sense to use a piece of aluminum. I waS using a 3/4" end
mill, so I was running the mill in the low speed range at 210 rpm.
The head was making a slight knocking sound, not loud enough to be
obvious as I was cutting metal, but noticable as the machine coasted
to a stop after I shut off the motor. The endmill didn't appear to
jump as it cut, so I don't think any gear teeth are missing. However,
after running the mill for about fifteen minutes, the drawbar gets too
hot to touch. I don't have this problem with the mill head running in
the high speed range. Any idea what the source of my trouble is? I
have an operators manual for the machine which contains helpful
exploded views but doesn't really tell me how to take the head apart,
or more importantly, put it back together.
Well, this essentially can apply to the 1J or 2J head, but there are
some more things on the 2J that can affect it. I think, possibly,
the direct drive clutch is not fully disengaging, and the clutch
teeth are banging together. The direct drive clutch is partly on
the bull gear and partly on the driven pulley up in the belt housing.
There is a linkage between the back gear engagement and the direct drive
clutch on the 2J. (They are separate handles on the 1J.)
I think there are adjustments on the linkage, so you can synchronize the
two levers. So, there may be some bending of the rod or something that
has gotten it to the point that the direct drive clutch is no longer
disengaging. It lifts the whole bearing assembly of the driven pulley
to pull the clutch teeth apart when disengaging the direct drive.
This is accomplished by a cast iron cam with two angled slots in it.
Two pins in the pulley bearing ride in the cam. These pins wear out,
and also have a tendency to rip out the threads in the bearing nest
that they are supposed to lift. So, you might inspect the pins and cam,
too. I just made new pins for mine, and made the threads in the bearing
nest the next size up with a tap.
But, this may not explain your heating. Maybe it does, if the clutch
teeth were rubbing on each other. But, there may be another problem in
the uper bearing that is causing both problems. The top thing in the
head is the bearings that hold the driven pulley. So, if the top of the
drawbar is hot, and especially if the whole housing is hot up there, it
indicates a problem in that bearing. I'm more familiar with the 1J than
2J, and have never torn down a 2J. I know there are a few extra
procedures to get the motor belt off, etc. because that is the
vari-speed drive belt.
Anyway, before pulling it apart, you can do a couple of simple tests to
isolate the problem. First, put it in back-gear and fiddle with the
upper end of the range-shift linkage and see if you can get the knocking
to go away by making the lever move farther into the low-range position.
That may indicate the rod has bent, or the pins in the cam are going out.
If you can make the knocking go away, it is almost positive you have a
problem with the clutch not disengaging, and can stop testing and try
to fix it. Once you get rid of the knocking, see if it still runs
hot. If not, it was entirely the clutch dragging.
If the direct clutch mechanism can't stop the knocking, try putting the
range selector in neutral, and see if it still knocks. This will leave
the direct clutch out, but not engage the back gears. The spindle will
not turn, So, the bull gear and its bearings, and the entire spindle
will not be turning. Only the motor, driven pulley and the toothed
belt drive to the back-gear pinion will be running. If the knocking
stops, it indicates it is the bull gear bearings or the spindle.
(I think it is not these, as the heating sounds like it is the top
bearings or clutch, in your case.) Oh yeah, if the spindle runs with
substantial torque, that also indicates the direct drive clutch is not
If it still knocks in neutral, go to high range. If no knock here, it
has to be the direct drive clutch that was knocking because it can't
To disassemble, there are some special procedures for getting the belt
off the vari-speed pulleys. I'm pretty sure this is in the book, as
it is a reasonable thing for a user to do. Remove the motor bolts
and take the motor off. Then, there are 3 vertical bolts with nuts
under the belt housing on the top of the main spindle housing. Remove
the nuts. There is a linkage on the speed range handle, remove it. You
can now pull the whole belt housing straight up and off the spindle.
Half the direct drive clutch will be in the belt housing, half on the
bull gear. So, you can now inspect these parts. Remove the socket head
cap screws on the bottom of the belt housing, and it splits in half.
There is a steel plate inside the belt housing with about 8 screws in
it. Remove the screws and you can lift the plate and inspect the
back gears. Mine sounded fine, but I'm glad I inspected inside there.
All the shields and spacers had been blown out of the ball bearings and
run through the gears some time ago! Yikes! These bearings are real
cheap to replace.
That's most of what I know about the Bridgeport J heads.