A friend of mine has a Bridgeport knee mill making a loud clicking or knock
ing sound in the head. I could not find any obvious reason. So I sorta just
said sorry man I can't find anything. Well about 2 weeks later Karma I gue
ss, I have a large Jet knee mill 3 phase started doing the exact same thing
.So I am telling myself the same thing, (sorry man can't find anything ). H
as anybody got info as to a guess what it is ? I am not a machinist just a
hobbiest. Thanks for any input you might offer.
Is it a varispeed head (2J)? If so, it is likely to be the plastic bushing
on the varispeed cone pulleys. I think the one on the motor can tear up the
motor shaft, so you really want to get it fixed. The plastic piece is not
expensive, and it dosn't take a massive amount of dissasembly.
cking sound in the head. I could not find any obvious reason. So I sorta ju
st said sorry man I can't find anything. Well about 2 weeks later Karma I g
uess, I have a large Jet knee mill 3 phase started doing the exact same thi
ng.So I am telling myself the same thing, (sorry man can't find anything ).
Has anybody got info as to a guess what it is ? I am not a machinist just
a hobbiest. Thanks for any input you might offer.
It is not a Varispeed.
Are these pure step-belt pulleys for speed control, or variable
speed pulleys? If the latter, the moving half of each pulley has a
black plastic (Delrin) sleeve inside it and a key on the shaft screwed
to the inside of the pulley with a Delrin cover over it to minimize play
and friction in the keyway. These eventually wear out, and need to be
replaced. If you don't replace them, the key starts wearing the keyway
in the shaft wider and wider, with a loud "CLACK" as the motor is
started or stopped.
If the step belt pulleys version -- I don't know, but perhaps
the spline which couples the upper pulley to the spindle is dry and
If the bearings in the front pulley are worn, belt tension can pull the
face coupling out of alignment. This will cause a knocking sound in
direct drive, that will go away in back gear. Had a Millport with this
Oh, well, that BLOWS that theory! So, this is a 1J (4 step pulley)?
There is a 1" belt that is the first stage of the back gear reduction.
The belt is held on one of the pulleys by a flange that is bolted to the
face of the pulley. That could be working loose, or the belt could be
disintegrating. Take a look at that assembly, rotating by hand and looking
with a flashlight.
Disengage the feed worm (little crank on right front of head).
Put the direct-drive clutch in neutral (push lever on top clockwise looking
down from top, it raises the driven pulley about 1/2") and spin the spindle
as fast as you can. Does it still knock? If so, bad news, that sounds like
Doesn't knock? There are a bunch of commodity bearings in the head, in the
back gear assembly. First, remove motor (it's heavy). Then, remove nuts
under belt housing, and you can lift that straight up and off the spindle
spline. The back gear is under a metal cover with a few screws. If the
bearings are blitzed, the ball retainers will have crumpled up and been spat
out. That's how mine were. Also, the motor bearings could be bad. Thay
are relatively easy to replace.
I can't say if your Jet is built the same way, but it probably is fairly
OK, two more things to think of. If the spindle spline is badly worn, it
will clatter when taking short (as in along the length of the cutter) cuts.
What I mean here is that the cutting flute is not continuously cutting
workpiece material, like when cutting 1/8" sheet with a 1" end mill, for
instance. Each cutter flute digs in and the comes free. This will rattle
the spline. Easy to check, just twiddle the spindle nose and see how much
it can be turned CW/CCW before it hits the other side of the driving spline.
This will generally only rattle when cutting, and run totally quiet when
running without cutting.
One other thing is a shot V belt. If the V belt has started to break down
in one spot, it will ride lower in the pulley V groove. As the thin spot
alternately rounds the driven, then the driving pulley, it will cause large
speed-up/slow-down of the spindle. It can actually start the whole machine
shaking! I saw this on a lathe once, it was QUITE dramatic.
On top is the lever arm that rotates a ring with two
grooves at an angle in which there are pins
attached to the part that engages the low range
gears. When the lever is moved to high range
these pins pull up on the engagement cogs for
low range. These pins can work loose enough that
the cogs are not fully disengaged in high. That's
the rattle you hear, the cogs hitting each other
ever so slightly.
Oh, I think a cracked ball will go from bad to worse at a very rapid pace.
Possibly a dinged ball in the backgear assembly (like when it ran over the
bits of the retainer cage) could just get noisy and stay that way for a long
time. That's the kind of shape my back gear bearings were in, and they
generally made a loud whirring noise. But, a really cracked in half ball
ought to be fairly disasterous.
I heard a report that Wieber was rushed to the ER after a freak
accident. Seems he was confused about which end of his screwdriver
stethoscope was which. In addition to the hearing loss, the fluid leak
was lapped up by a few dogs, causing them to be "adopted out," if you
know what I mean.
BTW, here's an "engineering" tip: I store my 7 to 13 screwdriver
stethoscopes with the correct end out of harms way in a sort of
hammock made from something I found on sale for $1.99 at HF. Not sure
what it was supposed to be, but it's various bits of tubing connected
together. There are also some plastic gizmos that can be repurposed as
earplugs if you block the little holes in them.
That is a lie! It was only an infection caused by ear mites. Everybody
gets them now and then. And there's nothing wrong with my 20
dogs either. Im not trying to brag but how many dogs do you
have...Hmmm? Sucks to be you.
You think your funny, but I know all the best stethoscopes. The one
your talking about isnt 2 bucks its four! And I can prove it.
that kind of money? Cash is very... very tight right now. So
screw you pustilant leftist! Im submitting your name to the
listkeepers again. When the People drag you out and hang you
from a bit of barbed wire after kicking you off a lawn chair..Ill be
very happy. In fact..I hope the doers send me a video clip of your
ending. Knowing you were disposed of, along with the many thousands of
your bretheren..and knowing that you will be gone into a mass grave
somewhere along with the rest of the trash who have tried so hard to
ruin America..will allow me to believe that America will indeed
survive Get your affairs in order you mentally ill welfare queen.
Gunner, Coyote Engineering
Machinery Repair Tech.