Subject: Re: Bridgeport Spindle

From: [email-masked] (Jonathan M. Elson)
Date: 12 Jun 1996 05:34:06 GMT

Well, I've gotten that bridgeport J head mounted on my old round-ram
turret mill base.  Still a few problems.

I'vew decided to wait on any more tinkering with the spindle taper runout
until I can figure out whether the bearings are going to blow up or not.
They still feel silky smooth, but I was doing some milling and drilling
at 1750 RPM, and after a half hour, the quill got so hot it was starting
to bind in the housing (it is extremely tight anyway).  The 'nose piece'
which clamps the lower bearing was running about 110 F.  That seems really
hot, but if these are new bearings, do they need to be run-in first?

On the other hand, there was a really different 'feel' with this head as
compared to my old M head.  The M head has a badly worn spline, and tends
to chatter, but the difference seemed to be more than that - a lot more.
I was taking .050" deep cuts with a 1/2" end mill in Aluminum.  This was
about the limit of my M head, before it started vibrating and showing
surface roughness.  The J head took it like it was cutting wax.  I
definitely LIKE it!

Does anyone know if the quill is considered interchangable, or if the
quill is finished to be a matched part to the entire housing?  Why I'm
wondering is that the quill is the most badly butchered part in this
head.  Maybe I should just get a new quill, install my bearings and
spindle in it, and put it into the housing.

This model of the 1 Hp J head has a maximum speed of 2720 RPM.  If I make
up new step pulleys, with a maximum speed of 4250 RPM, say, should I
expect any problems with the spindle bearings?  (I note that variable-speed
J heads go that high.)

What is this thing called?  Is a 1 Hp J head called a 1-J?  Is the 2-J
called that because it has a 2 Hp motor, or are there other differences?

Thanks so much for the information this group has already provided.  It
has been enormously helpful in rebuilding this unit.  If it hadn't been
butchered by the worst idiots I've ever seen the butchery of, it would be
in beautiful working order now.

						Jon

---

From: Mike Rehmus <[email-masked]>
Date: 15 Jun 1996 19:38:58 GMT

>I've decided to wait on any more tinkering with the spindle taper runout

They would have been gone by now it they were going to go.

>hot, but if these are new bearings, do they need to be run-in first?

No, they don't need to be run in.  Do they have lube?  On my 2J head, 
there is an oil cup on the right side of the cast iron portion of the
head.  I don't recall where it is on a J HEAD. The cup feeds into a 
felt filter that then allows the oil to drip down into the lower bearings.

110 F. does not seem too hot after that period of running.  But I am not
an expert on Bridgeport bearing temperatures.

Tight quill.  There should be only about 0.0005" clearance for the
quill in the head, otherwise you get very interesting surface finishes 
and you can see the oil squeeze out as the quill moves in the head.

The four bolts that hold the head to the ram need to be torqued evenly
to 50 ft. lbs.  Stage each to 25 ft. lbs. first and then move up to
50 ft. lbs.  Bridgeport claims that quill movement can be affected by
this if it is too tight or too uneven.  I ignored this at first and
experienced several problems.  One of which was the head would untram 
itself at every opportunity.

Is the quill clamp loose and not falling tight.  A common problem with
Bridgeports and one easily taken care of with a few rubber bands or
the little $7.00 goodie sold to hold the dumb design in the loose position.

>spindle in it, and put it into the housing.

They are sort of matched at least to the extent that when a friend of
mine had his spindle rechromed, he had the spindle ground and the head
honed.  Course this is a guy that has a brilliant metalic gray finish
on his mill and just had all of the rotating parts and the motor in
his lathe dynamically balanced.  Still, they have to fit rather well.

>called that because it has a 2 Hp motor, or are there other differences?

According to my April 1981 Bridgeport manual, there are at least 
5 HEADS for Bridgeports if we ignore the Model II's and others:

M HEAD                     0.5 hp.       275 - 4550 rpm in six steps
J HEAD                     1.0 hp.        80 - 2720 rpm in eight steps
J HEAD Hi Speed            1.5 hp.       160 - 5440 rpm in eight steps
2J HEAD (before 1977)      1.0 hp.        60 - 4200 rpm variable
2J HEAD (after 1977        2.0 hp.        60 - 4200 rpm variable

Obviously there is a 3hp. 2J head as well.

Best regards,
Mike Rehmus
Mike Rehmus

---

From: [email-masked] (Jonathan M. Elson)
Date: 14 Jun 1996 05:42:44 GMT

Jonathan M. Elson ([email-masked]) wrote:

: Well, I've gotten that bridgeport J head mounted on my old round-ram
: turret mill base.  Still a few problems.

: I've decided to wait on any more tinkering with the spindle taper runout
: until I can figure out whether the bearings are going to blow up or not.
: They still feel silky smooth, but I was doing some milling and drilling
: at 1750 RPM, and after a half hour, the quill got so hot it was starting
: to bind in the housing (it is extremely tight anyway).  The 'nose piece'
: which clamps the lower bearing was running about 110 F.  That seems really
: hot, but if these are new bearings, do they need to be run-in first?

Oh, it just keeps getting more interesting!  I was really worried about
the bearings running hot a few days ago.  Well, I did nothing about it
except worry.  I decided to sharpen a batch of end mills on the mill,
which I have worked out a procedure to do.  I ran the mill continuously
for about 2 hours at 1750 RPM, and only at the very end was the spindle
even warm!  Very strange!  I had been filling the oil drip cup for the
spindle bearings (big oil cup, lower one) every day or two.  Finally some
oil started leaking out around the nose cap, so I know the #10 oil has
made it to the bottom.  I think there was some assembly lube on the
bearings since they were made, and the #10 finally slid down the spindle
and washed that thick assembly lube off the bearings.  Now maybe I'll
tackle the runout, being a little more confident that the bearings will
last.

---

From: [email-masked] (Jonathan M. Elson)
Date: 17 Jun 1996 06:15:35 GMT

alan anganes ([email-masked]) wrote:
: [email-masked] (Jonathan M. Elson) wrote:
: >  I decided to sharpen a batch of end mills on the mill,
: >which I have worked out a procedure to do.  

:  I know that this has nothing to do with what you where discussing, but 
: please elaborate on the above mentioned procedure you have worked out to 
: sharpen end mills on the mill. 

:  I would love to hear what you have come up with. I'm sure others here 
: would as well. Thanks, 

I really ought to do an article or two for home shop machinist.  I'll
give some rough description, but I don't think I can really describe it
so that you could do it without pictures.  In fact, the setup is tricky
enough that I have to look at my own pictures to set it up right.
The tool is held in a 5C collet in a fixture I got from ENCO for #38.99.
(Perhaps I got it for a little less on sale.)  This is on P 151 of the
95/96 full-line catalog, as #287-6840 'End Mill Grinding Fixture'.
The little picture in the 2 x 3 box on this tool is all the help you'll
get from Enco in using this - there was no paper at all in the box.
They show it on a standard surface grinder, I think.  The grinder shaft
is horizontal, but as long as the grinding is really done by horizontal
traverse of the table, all surfaces will be flat, and so the plane of
rotation shouldn't matter, I thought.  So, if I put a cup wheel in the
spindle of my mill, i should be able to grind the top of a surface, too.
Of course, it gets a little more complicated when you do serious
sharpening of mills that are badly worn or have a corner chipped off.
then you have to regrind the relief and gashing, too.  if the mill is
just slightly worn, however, just the primary relief can be done, in
under 5 minutes.

Anyway, this fixture holds the cutter in two possible positions.
When set on its flat base, it holds the cutter at about 15 degrees in
one plane, and at about 5 degrees in the other.  this is the position
you use for the primary relief, and it sharpens the cutting edge.
it also applys about 5 degrees tilt, so the point of the cutter is
just a few thousandths farther out than the center.  I never knew end
mills were ground this way - the tilt is apparently much less on a
factory-ground mill - but they work just fine this way.

So, the trick here is to have the fixture mounted on the table with
the 30 degree miter in the base facing the back, the wide part of the
base clamped flat to the table (or in a vise).  The end mill should be
set so that the hub is in a detent, and the cutting facets are lying
parallel to the X axis.  (If a 4 flute mill, then either pair lying
parallel to the X axis.)  Position the table so the rightmost cutting edge
can be fed into the front left quadrant of the wheel.  Try adjusting the
Y position so that when the wheel edge approaches the center of the mill,
it approximates the angle of the gashing that separates the two cutting
edges at the center.  After making a grinding pass, then rotate the hub
180 degrees, and make a pass on this facet to the same point on the
X position.  Examine with jeweler's loupe  (Super 8 mm projection lenses
make FANTASTIC jeweler's loupes - although they won't stay in your eye
socket) to see that the grinding goes all the way to the center.  Advance
the X a little more and check again.  When you've got it, then do all
facets until the cutting edges are all sharp all the way across the edge.

Step 2 is to grind the second relief, if needed.  Now, tip the fixture
onto the 30 degree facet, with the 30 degree facet to the left.  Hold
in a vise or clamp to the table.  To make clamping easier, I cut a flat
in the top of the fixture's bottom plate which is level when the fixture
is on the 30 degree facet.  I can place a clamp on that flat.
Now, with the end mill approaching the same quadrant of the wheel, bring
the tool slowly into the wheel from the front, with the Y feed.  Adjust
X position until the tapered side of the cup wheel clears the cutting
edges while grinding down the secondary reliefs.  This is particularly
tricky on 4-flute mills.  This work is not as critical as the primary
relief, which is actually part of the cutting edge.  The secondary relief
just provides room for chips to escape.

Gashing is used to make the center of a center-cutting end mill somewhat
like the point of a drill bit.
Gashing is necessary for major repair to an end mill, when .050" or so
has to be ground off the length.  This is done with the fixture set up
as for the second relief, but the table is moved so that the end mill
approaches the wheel from the FRONT side.  Turn the hub a few notches
counter-clockwise, one notch less than 90 degrees. (Should be 5 detents.)
This has the 2 cutting edges almost parallel to the X axis, but the left
edge is a little back, the right edge a little toward the front.
Now, pass the mill back and forth with the X axis, while slowly stepping
the table back with the Y axis.  Observe the wheel cutting closer and
closer to the right cutting edge.  Stop before you cut into the right
cutting edge, but get slose enough to eliminate the large flat land at
the center of the mill.  Look at a new 2-flute mill to see what you are
trying to achieve.  What you want is this :

        xxxxxxxxxxxx
        xxxxxxxxxxxxx gash here
        xxxxxxxxxxxxxxxxxxxxxxxxxxx
            gash here xxxxxxxxxxxxx
                       xxxxxxxxxxxx

This is the trickiest part by far!  I have made several messes, had to
repeat the first part after bad gashing attempts, etc.  But I also have
made a few end mills look just like they were absolutely new!  I wish
I had video taped those grinding attempts, so that I could see how I
did it!  But, I am getting better, and I can now routinely make end mills
that will plunge properly.

I suggest getting a book on end mill sharpening from a good library if
you can.  I would have never figured all this out without a good
illustrated text.  Try the library of a university with a mechanical
engineering department, a tech school, or high school with a vocational
depertment.  These books will show how to do it with a cutter grinder,
almost always with a cup-type diamond wheel.  I am using a 'flaring
cup' type wheel of alumina (Aluminum Oxide) abrasive.  This is actually
similar to what is frequently used on a cutter grinder, and so makes
translating the pictures on the book a little easier.  The Cup-type
wheel is essential for gashing.  That side relief makes it possible to
get UNDER one cutting edge to gash the other one.  I am using a wheel
similar to Enco's # 391-1153.  These are fine grain, hard abrasive,
which seemed to be the right material.  I take a swipe across the bottom
of the wheel with a diamond dressing point before starting.  Hold the
diamond in a vise, or possibly in the collet of the fixture, and use the
table feed to pass it under the wheel.  Take off just a thousandth or so
each pass, and the diamond will not show any visible wear.

Start with really blitzed end mills, of which we all probably have a few.
Keep the nearly good ones for last, so you can look at them
and follow their contour.

As I say, it would be a lot easier to describe this with pictures!
If you want to try this and need clarification, let me know.

						Jon

---

From: alan anganes <[email-masked]>
Date: 16 Jun 1996 16:31:26 GMT

[email-masked] (Jonathan M. Elson) wrote:
>  I decided to sharpen a batch of end mills on the mill,
>which I have worked out a procedure to do.  

 I know that this has nothing to do with what you where discussing, but 
please elaborate on the above mentioned procedure you have worked out to 
sharpen end mills on the mill. 

 I would love to hear what you have come up with. I'm sure others here 
would as well. Thanks, 
                       AL