Knee Mill How To Tips
  Bridgeport Mill Parts and Service |
variable speed upper housing | variable speed lower housing | quill housing |
leadscrew assembly | step pulley housing | base machine assembly |
Knee Mill Service - How To Tips
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These are tricks or tips I use when working on a Mill

These are intended for informational purposes only and not responsible for any injury or damage to the machine

Removal of motor on a variable speed head
Turn the spindle on and crank the RPM's down to the lowest RPM
Shut off the spindle disconnect the power to the machine
Remove the drum switch from the left side of the machine
Underneath the motor is a half moon shaped cover. Take out the
three 10-32 screws that hold the cover on.
Looking up in the opening you will see a collar with a spring above
Using two of the 10-32 screws stick them through the two holes in the collar
and thread them into the varipulley. This secures the compressed spring.
(If you cannot thread them this means that the key in the varipulley is broken
and you will have to carefully force the belt off the pulley)
Now crank the spindle RPM handle to the highest RPM. This loosens the spindle varipulley
Remove the two bolts that hold the motor onto the housing and lift motor up and tilting
it slightly. This loosens the belt on the spindle varipulley. I usually rest the motor
on the adjusting screw sticking up through the housing. This now gives you enough room
to slip the belt off the motor pulley and remove the motor.

Easy removal of the head T-bolts or head tilt adjusting Screw
Put and clamp a vise onto the table (If you have a riser block
on the machine you may have to block up the vise)
Now crank the knee all the way up to the bottom of the head.
Position the table with X and Y cranks so the spindle nose goes into the vise jaws
Crank the knee up so the bottom of the spindle sets inside the vise jaws
Clamp the vise jaws onto the bottom of the spindle. You will see that there is
small flat spot underneath the Micrometer rod. I clamp the vise there.
You may want to use blocks of Aluminum or wood inside the vise jaws to clamp with.
At this point you can loosen the four head T-bolt nuts. Now carefully crank the Y-axis handle
and the whole head assembly will go straight out and straight back in again.
Be carefull the head assembly is top heavy you may need assistance to balance the head.
With it out you can replace the T-bolts (part# 1431), Head tilt adjusting Screw (part# 1097)
Head tilt worm gear (part# 1096), on page quill housing
You can also replace Quill housing adjusting gear (part# 1186) on page base machine assembly

Replacing bushings and keys inside Motor Varipulley
With the Spring collapsed on the motor varipulley, I put the varipulley in an Arbor Press.
Holding the spring collapsed with the Press (You may need a block to access the bolts)
Take out the two 10-32 screws and slowly release the press and the spring
Be careful the spring wants to fly up the press handle.
Take the spring and the collar off the assembly
Take the old Plastic Bushings and key out of the varipulley
The bushings should be black, if they are green they cannot be replaced and you have
to buy a new Pulley assembly. (part# 1036 for a 2 HP and part# 1037 for a 1 1/2 HP)
The pulleys I supply have the replaceable bushings and keys.
You will notice inside the bore of the varipulley that there will be some glue left inside
This needs to be removed. I use a Dremel type grinder with a drum sander and a Keyway cutter
to grind away the glue. The keyway cutter removes the glue inside the groove of the varipulley
I clean out the keyway with a screwdriver blade and then run a file in it.
Once I've cleaned up the bore, I put the new bushings and key inside the pulley and set it
on the motor shaft to see how it fits. If too tight, grind some more glue out. It should
be a snug fit. If it fits way to loose the bore may be wallowed out and the pulley replaced
Mix up some epoxy (I prefer JB weld the five Minute type)
Spread the epoxy on the Bushings and key and set them into the varipulley
No need to glue in the 2HP varipulley key it is held in with a 10-32 screw
Quickly set the pulley on the motor shaft and let the epoxy set-up
Put the asembly back in the Arbor press and collapse the Spring and collar
thread in the two 10-32 screws back on the varipulley so the spring stays
collapsed. Put the assembly back on the motor.
On the 2HP varipulley there is a small bore for the 10-32 screw that holds
in the key. If it is broken out I countersink a larger bore and put a washer
behind the 10-32 screw and reassemble.
All parts can be found on page variable speed upper housing

Replacing Collet Alignment screw inside spindle
Bring the quill down about two inches
Look on the back side of the quill and you will see a small set screw. Remove it
This holds in the nosepiece on the bottom of the quill
With set screw removed you can unscrew the nosepiece. I use an adjustable spanner wrench
You will find two holes on the bottom of the nosepiece for this. You may need to use
a punch and hammer to get it started.
Right hand thread for Bridgeport mill, left hand thread for Imports.
If the nosepiece does not unscrew this means the threads of the nosepiece are bad
You may never get it off without damaging the nosepiece and or quill. It can be very
expensive to replace both nosepiece and quill. At this point most people live
without the Collet screw and just put it back together
With the nosepiece removed you can get to the Collet Alignment screw (part# 1137)
and special socket set screw (part# 1424). You may need to tap on the drawbar to
bring the spindle down a bit farther so you can access the Collet screw.
Replace the Collet screw and may need to replace the Special Socket set screw
I put an R-8 collet in the spindle and adjust the collet screw by screwing the
alignment screw in until it touches the R-8 collet and then back it off so the
R-8 collet slides out of the spindle without hanging up.
I use blue Loctite on the collet screw and Special set screw just for insurance
Then I tap the spindle back into the quill with a rubber hammer and thread the
nosepiece back on. Making sure it is up tight.
There should be a small gap between top of the nosepiece and the bottom of the
quill anywhere from .003" to .010". This insures the spindle bearings are seated
in the quill. If not check out how to reseat spindle bearings below
Before replacing the set screw in the back of the quill, drill a setpoint into
the set screw hole.(I use a handrill and a #8 drill) This puts a dimple in the
threads of the nosepiece. If you don't you will smash the threads and never be
able to get the nosepiece off again. It also allows the set screw to in farther
and not stick out catching on the quill housing.

Spindle Runout
Use the same disassembly instructions as replacing the Collet Alignment Screw above.
When you get the nosepiece off. Take the Drawbar out of the top and put at least a foot
long rod about an inch in diameter in place of the drawbar.
Tap on the rod at the top and the complete spindle assembly falls out of the quill.
I put a block of wood on the table so when it falls out it bangs on the wood
and not the table
Now crank the knee down and Y-axis back so you can get the spindle out.
At this point keep everything clean, don't get dirt into the bearings
Looking at the spindle assembly you will see that there is a pair of precision
thrust bearings with a two inch spacer in between, then there is a long spacer with
another precision bearing, on top of that there is a spider washer and a spanner nut.
If the short spacer is loose between the thrust bearings you will have runout.
To tighten, find a tab on the spider washer that is bent into the spanner nut.
bend it back down and out of the way. I clamp the spindle at the splines in a bench vise
I use blocks of Aluminum or wood to clamp on in the vise jaws so not to crush the splines
Tighten the spanner nut on top of the spindle. I use an adjustable spanner wrench or you
can use a punch and hammer. Tighten until it will tighten no more.
Adjust or tap with a hammer the small spacer between the thrust bearings so that it
will align between the two thrust bearings exactly. I use a six ruler to check the
concentricity. If the spacer sticks out to one side or another you'll still have runout.
Once you have adjusted the spacer then bend the spider washer tab back into the spanner nut
Before putting the spindle back in the quill look up into the quill and you will see
a felt washer (part# 1164) in the top part of the quill. The spindle has to go back up
through the hole in that felt washer. Be sure to get it through the hole or it will
damage the felt washer. The washer is there to keep dirt from getting into the spindle.
Now replace the spindle into the quill. After the spindle goes through the felt washer
you will feel the splines of the spindle engage the splined gear hub. Just move the spindle
around until they mesh together and the spindle goes all the way up.
I have found that sometimes the top of the spindle has mushroomed out from years of use of the
the drawbar being tigthened. If that is the case you may need to clean up the splines with a
file at the top of the spindle. It may also be difficult to get the spindle out because of this
Tap on the spindle with a rubber hammer until the nosepiece engages the quill. Tighten the
nosepiece with the same instructions as assembling the collet screw above.

Adjusting the quill downfeed
After years of use your quill downfeed lacks power and slips. You hear a clicking noise
On the left side of the quill you see a round cover. It has a black "S" shaped arm out of it
Take out the two long 10-32 screws that holds this round cover in place
There you have the quill downfeed clutch assembly. You notice there is a spring with a collar
You are suppose to tighten the spring to adjust the clutch but this rarely works
What I do is take out the two small pins that holds the "S" shaped black arm on the clutch assembly.
The "S" shaped black arm is made of brass. The less "S" there is, the tighter the quill feed is
I put the "S" arm in a vise and gently clamp on the brass arm. This takes some of the "S" out
I usually do a gentle clamp with the vise the first time. Then reassemble the clutch
and try it out. I test it by engaging the quill feed and pulling down on the quill handle.
It should have some give and you will hear some clicking of the clutch but should have power
enough to put a drill into your part. You can be your own judge.
If I still don't have enough power I clamp the "S" arm a second time.
I've had some that did this procedure 10 times until I got the right amount of power.
Things to watch for. If you straigthen it out to much you'll find that you will have
a clicking noise and feel when the quill feed is not engaged. Then you have gone to far
Then I put the "S" arm in the vise and clamp on the O part of the arm and use an adjustable wrench
to bend or put more "S" back in it.
Another thing to be careful with is there is two tabs that stick out from one end of
the arm be careful not to bend or brake these off. If all else fails you can purchase a
arm (part# 1388) Overload clutch trip lever - page quill housing

Adjusting the quill feed tripout
Adjusting the quill feed that doesn't trip out when engaging the Micrometer stop
Looking at the front of the quill you see a Micrometer rod. At the bottom of it, there
is a trip lever (part#1033-02). You have to look under boss that the micrometer rod
goes through. On that lever there is a small set screw. Adjusting the set screw gives
more or less trip out depending which way you thread in the set screw.
Sometimes you will find the Trip lever all loaded up with chips and you have to take it
out and clean it up. There is a small pin that holds it in place.
Make sure the micrometer rod is loose. I spray WD-40 on it.

Replacing a broken Ball trip lever at the top of the Micrometer rod
All I can say is good luck!!
The first piece usually comes out easily. I use a small screw or tap and thread into it
and pull it out. You will use profanity on the back piece. Sometimes you can use a small
magnet to get it out. Usually I get it out by blowing air around the top of Micrometer rod
and moving the micrometer rod around at the same time and it pops out. I have worked on
some for hours never getting it out and giving up. (part# 1033-03) on page quill housing

Adjusting the clutch arm on a Bridgeport power feed
When you engage the power feed it makes a rattling sound, especially when in rapid
and you change directions. Two gears are not engaging and they make the sound.
Take the cover off the front of the power feed gearbox. It usually has the name Bridgeport
on it. Be ready there is about a half a cup of oil in it. So have a pan ready to catch
it so it's not all over the floor. Also have some shop towels handy.
Looking in the gearbox you will see a spring attached on one end to the gearbox housing
and the other end to the clutch arm. Take the spring loose from the clutch arm.
There is a 1/4-20 shoulder bolt that holds that clutch arm in. Undo the bolt and get the
arm out. On the clutch arm you will see two roller cams. One on the end that the spring was attached
the other back cam engages two gears inside the box. Notice the back cam is in a slot on the clutch arm
It usually backs off and doesn't let the two gears mesh in together. I take the back cam off and then
mill the slot a little farther to the left so when I reassemble the clutch arm it keeps the
the two gears together. I then drill and tap a 6-32 hole in the edge of the clutch arm.
This way when I put the roller cam back on the clutch arm I put the 6-32 set screw in so
it pushes the roller cam to the left and never backs off again. Reassemble the clutch arm
and put it back in with the shoulder bolt. Attach the spring on the clutch arm and put the
cover back on. Put about a half a cup of heavy oil, preferably 90 weight in the gearbox
through the set screw in the top.

Replacing Cam Ring Pins on Step Pulley Head
If you have trouble getting a step pulley head to go into back gears.
Most times the Cam Ring Pins (Item #10 part #1109) are stripped and need to be replaced.
There is not much to replacing the pins, but one thing to look for is not only are the
Pins stripped but the Spindle Pulley Bearing Sleeve (Item #11 part #1128) that the pins screw
into may also have stripped threads. Get up on the machine table and look down at where
the Pins screw into the Bearing sleeve. You will see a couple of small set screws that
screw into the Cam Ring Pins and hold them in place. Look off around 30 degrees and you will
see another set of holes for those set screws. Bridgeport drilled another set of holes
in the Pulley sleeve. Just take the old pins out and rotate the pulley sleeve with a
spanner wrench or a punch and hammer and put in the new Cam Ring Pins.

Arch City Service 314-630-3575 * 800-746-9550 * fax 866-219-3613 * please leave message  parts@archcity.net

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