Thread: Bridgeport spindle grinding

Originally Posted by Geir T Simonsen

R 8 Spindle regrind - YouTube

Good youtube .. You may have to set angle off the quill if the held part is running out due to condition of taper ID or quality of the collect, and I would blue-in check the taper but not with a collect but some type of a gauge, perhaps my best end mill holder or make a gauge on the lathe or grinder. (Near new (name brand) collect filled with the proper size part not Ok but better than nothing)

Good he shows still having .0006 run out because the perfect spindle does Not make everything run perfect

Thanks for the info guys, it is definetly not falling on deaf ears, one thing I didnt think of mentioning is the 4hp series II Bridgeport is a 40 taper not a R8, and it has a very finely adjustable factory power knee.

My other option would be to pull the spindle back out of the machine and do it on my Brown and Sharpe 13, I just thought it wouldnt be to bad to do it on the mill but maybe I will rethink it.

Seems like most advise the mill spindle horizontal and long table travel with cross in-feed..That would give better control of tweaking the angle with the mills big head rotate protractor..or spindle horizontal and down tilted for angle and knee for feed..job is a piece of cake on a 13 grinder..

you could also do it with diamond compound on a taper. difficulty here is to locate taper properly, so you can move it into the spindle by hand. i would try freehand and see what is does.

btw, last time i got a quote on regrinding, they said they would use a diamond wheel. why is that?

Don't forget to dress the stone with a diamond

I did some testing today and the best I could do moving the X axis was .0005, but what seemed very controlled was using the quill which being at the angle it is has a very fine infeed moving along the X.

Mike

You could place a sine bar to quill OD or to the spindle-end and get very close to the exact taper..you wan't to be close at start so not needing much/many tickle changes.

Michiganbuck, in my first post I stated that I set to angle using a sine bar to the outside of the quill, well I went to the shop this afternoon and ground the spindle, Michiganbucks suggestion of having a plan for movement of the grinder contact was spot on, I went the route of lowering the quill a .001 at a time which translates to about .00028 horizontal movment of the quill, I used the power knee to control the feed till it ran off the end of the taper up in the spindle then powered it down rinsed and repeated till complete.

I ran the bridgeport spindle at 150 rpm, grinder spindle at about 40000 grinder running opposite of the bridgeport spindle.

The final result was almost full contact on the taper, about the last 1/2 has no contact, probable could grind some more but there may be diminishing returns.

At this point should the spindle have 0 runout? As of now I'm picking up .0003-.0004 is this due to the spindle bearings? Should I worry about it? The spindle has no decernable movment with the indicator and runs quiet and cool, BTW I am not making parts for NASA on this thing.

Thanks for everyones advice, it came in very handy.

Don’t give me any extra credit we all were tossing out good ideas trying to help…Glad it worked for You. You might pull the keys from any mill cutter holders and tickle grind them if .002 or so out and mark then to a spindle mark..with a + on the high face side or 0 if flat..so any cutter will be place best position..

Put a mill cutter on the RO with a tickle angle that would grind all inserts a small tweak for height but still leave the pocket set still good for turning the insert..Yes if a good enough finish make one run with inserts not ground ..then ground in the second use. Yes tickle the mill sharpening stub arbor and mark it for set position so it goes back the same spot radialey..Some times a .004 or so tickle will make most all hit and give better tool life and better finish..High blade might tickle much and low blade only tickle a tweak and that is fine. (120 to 320 wheel Ok.)500gt better for aluminum but often overkill and may heat check some carbide. .

Learned the RO from Ray Nixon one of the designers of that machine..

You might try a mill cutter with a .010/.020 end-flat (with clearance)then the normal dish perhaps 2* or what...

*Yes you could have posted a photo of set-up, what diameter, grit and hardness of wheel? did you diamond, stone or abrasive roller wheel dress the grinding wheel? About how long did it take once set-up?

Buck

qt dain : btw, [last time i got a quote on regrinding, they said they would use a diamond wheel. why is that?]

I have no idea..

I have used CBC wheels for such work but think AO is the best..Anything that might heat and burn would be taking a dangerous chance..CBN is dangerous for that..I have put fine grit compound to a taper and compound rub marked a blued up taper..

1. Royal Oak internal spindle (persise brand?)
2. 3/4 aluminum oxide mounted point, Grit unknown, on a 3 inch arbor extension out of 1/2 TGP
3. dressed the point freehand with a dimond nib started as a coned cylinder dressed the back of the stone so it was a double cone, high part in the middle.
4. feeding up 2 minutes down 2 minutes so about 4 minutes total per pass, I believe it was 8 passes.
thanks Mike

This is the only picture I took while I was doing it, BTW how do you rotate a picture so its the right way?

Originally Posted by Mike Hill

BTW how do you rotate a picture so its the right way?

Never once had that problem, but.. I bring up the original on-screen, rotate it if it needs that, then take a "screenshot" and save for upload as a .png file.

That because the original .jpeg's here are waaay to high-res, high byte-count to upload.
(cheap, but effective Nikon Coolpix L32)

Originally Posted by Mike Hill

This is the only picture I took while I was doing it, BTW how do you rotate a picture so its the right way?

Fixed that for you.



Regards Phil.

QT [0003-.0004 is this due to the spindle bearings?]
could be .. think Richard mentioned that.. I think you should mark the high side to the spindle OD with any mark. with that if having a fussy something and indicating an end mill or something you can rotate it to the low side..even a best collect often has .0002 or better error and end mill holders often have a wash-out opposite the lock screw so your 3 or 4 tenths should not be any problem. IMHO

Originally Posted by Mike Hill

At this point should the spindle have 0 runout? As of now I'm picking up .0003-.0004 is this due to the spindle bearings? Should I worry about it? The spindle has no decernable movment with the indicator

Not BAD numbers, but your description seems contradictory.

Picking up .0003" to .0004" runout, but having no discernible movement on the indicator?

Which is it?

Or did you just use two indicators, one more sensitive than the other?

Guessing between the lines should not be needed. "Tenths" and "half tenths" indicators are cheap and available enough.

ANY indicator, one DOES have to pay close attention that they themselves have a really stable holder and mounting, are not reading flex somewhere else in addition to whatever runout the spindle has.

If the runout is caused by the rotating elements (i.e. balls, cylinders, etc.) of the bearings, the high and low spots will be at different positions at each revolution. One more reason to mark them to understand what causes the runout.

Paolo

I just re read the OP #1 post.. He said he rebuilt the head, so I know am assuming that meant new spindle bearings. And the taper was last thing he was going to do because it took a pounding. So if he has the skill level he could give it a go I suppose.

(wrote before the re-read)

To me it seems like you have a lot of time on your hands if your going to grind a spindle that runs out .0003 to .0004" when you haven't replaced the bearings. Grinding the spindle taper on a Milling machine and expecting zero when done to me seems silly. Think about the multiplication of error or division in size Bottom ID to cutter ID. The spindle is what 2" diameter at bottom. and your using a 1" cutter then you have .00015 or .0002"?

I was just looking up some spec's. It says the "Standard National Milling Machine taper" is 3 1/2" per ft. which is an included angle of approx. 16.5 degree's.

I guess I need to clarify a few things, before I started you could see a tool wobbling around by eye, I replaced everything except the spindle bearings in the head, Im satisfied with how the job turned out.

thanks for the help guys
Mike

I know this is a old thread but I finally finished my spindle job, I made new drive keys for the spindle they were missing when I bought this basket case, which I believe was the root cause of the beat up spindle taper. This project has been moving at glacial speed.