Bridgeport spindle grinding
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  1. #1
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    Default Bridgeport spindle grinding

    Hi all I have a 4hp series II Bridgeport that I bought several years ago, I rebuilt the head last year all I have left to do is grind the spindle taper then it will be a usable machine. The spindle didnt have the drive keys in it when I got it and it looks like the taper took a pounding because of it.

    So my plan goes like this, I set up a sine bar on the table with the proper blocks under it for a 3 1/2 to a foot taper, brought the quill all the way down to the sine bar then used a presision square to tilt the head along the x axis till it was square to the sine bar locked the head down at that point.
    Then I removed the internal grinding spindle from my RO grinder and mounted it to a block on the table so it is vertical.

    After all that my hope is to run the grinder up into the taper on the side of the taper that is now vertical using the power knee on the machine take some light grinds and blue up a holder see how it fits, if its off tilt the head till it blues up correctly.

    Am I missing anything, is there a better way?

    Thanks Mike

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    Sounds good to me. Do you have an accurate piece to do a contact check with using bluing? Having the large vertical travel sounds like a real plus so you can lower the table, inspect the work, then go back to exactly where you were (if you haven't bumped any handles.)

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    Make sure that the axis of the spindle and the one of the grinding wheel are on the same plane.
    In other words, you need to be very careful in Y axis location for your grinding head. Otherwise you'll be grinding an elliptical surface.

    Paolo

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    Also check the spindle bearings for shake, be sure the knee gib is snug and X, Y and quill is locked. The columns seldom get worn much but o be sure check the short distance or travel of the column against a blade square. I was also thinking the same as Paolo be sure to grind the same side you indicate. If you are replacing the spindle bearings you could probably have a grinding company with a Heald ID grinder do it pretty cheap.

    Also I bet if you Googled this with Practical Machinist in the search words, you could find how someone in the past did it. Have you checked You Tube?

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    Thanks for the tips guys, I assume when grinding I would want to spin the spindle in the opposite direction as to the grinder spindle and on the mill spindle are you better off spinning it fast or slow.

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    Tricky grinding.. You don’t want to burn or be forced to take way too much off due to correcting the angle. Using the knee you need to know if it leans one way or the other due to direction of feed..if so you may wish to in-feed at one end or the other.. feeding to a still-in-cut end stop is tricky as you don’t go off the grind at one end for cooling…
    You can have the mill spindle vertical or horizontal with deciding what feed will allow a .0001/.0002 in feed..What travel is best the long table travel or the knee..No mill feed axis is anywhere near as close as a grinder feed axis..
    And I am the Jury rig guy and think you have to be very careful.. even consider mounting or making a precision slide or bring some one with the right equipment..

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    Default

    img_0386.jpg
    This is what I was thinking

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    Guess with deciding to try it I would catch the angle with indicating.. then try the very best in-feeding (with not yet trying grinding)to see that I could in-feed .0002//if not then to try grinding is taking a dangerous chance..Getting a hard burn in the grind will make a mess of it.

    Guess you might make a spring back screw..Cut up an old micrometer by cutting away about 2/3 of the frame.. mount that to a angle plate so the micrometer spindle pushes against the grinder motor mount..Then with an indicator set to the grinder practice cranking the micrometer until you get a feel for in and out feeding .0001 to .002.. with this you use the mill to feed .001 0r .002 still missing the grind and use the micrometer to in feed .0001 /.0002 and the like with having still the option to crank out any time you wish…Yes almost any grinder motor set-up will spring to .003 or so and allow controlling .0001... Yes you may have to play with it to get the feel and to be sure of controlling the in-feed and back away from the grind. May need to put a small vise grip on the micrometer.

    Perhaps you can just use the mill dial with not having the spring-back screw..But you have to be very sure of that or lose the job. best to be able to say "I can in-feed .0001 / out feed and then return to my same place"…Likely you want to be counting sparks..that means there are spaces in the spark trail.. not a yard of sparks.. close or tight sparks will burn and suck-in the job.

    [Am I missing anything, is there a better way?] Guess I would eyeball the ID as it is now
    .. de bug by hand grinder and round hones to blue fit an arbor to see how good it runs then decide to grind or not.

    Yes normal is slow turning with wheel direction into the feed. Wet would be best but wet wont stop burning if feed is too great.

    Yes you might mount a small diamond and dress the wheel OD and then hand dress a small lead and follow break.

    OH..IMHO

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    Thanks for the thoughts Michiganbuck, I think I will mount a tenths indicator on the X travel and see if I can reliably move it, if that doesnt work I will try your cut down micrometer idea, when you say you would catch the angle with a indicator what do you mean, if I am following you right are you suggesting to check it on the existing taper, if thats the case its bell mouthed badly, and there is bad galling farther up the taper so I wont be able to reliably check it that way.
    thanks Mike

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    When I did mine I laid the head all the way over and used the x to run the grinder in and out and the knee for depth of cut. I used my tool post grinder. It came out good, full contact on the taper and 0 runout.

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    QT: [you would catch the angle with a indicator?].. with nothing better a pivot arm going up into the existing taper to see the knee travel will make the wheel follow the taper for starers, then to a blue in fit..

    *But but see you think the taper not worth picking up...

    also see if it has an attitude like shifting one way or the other with going up or down..You need to know how Goofy or good the knee travel might be.

    *Moonlight what grit wheel did you use?

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    Quote Originally Posted by michiganbuck View Post
    QT: [you would catch the angle with a indicator?].. with nothing better a pivot arm going up into the existing taper to see the knee travel will make the wheel follow the taper for starers, then to a blue in fit..

    *But but see you think the taper not worth picking up...

    also see if it has an attitude like shifting one way or the other with going up or down..You need to know how Goofy or good the knee travel might be.

    *Moonlight what grit wheel did you use?
    Whatever was on the grinder at the time, got a real nice finnish though so it was probably pretty fine.

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    Quote Originally Posted by michiganbuck View Post
    ...
    *But but see you think the taper not worth picking up...

    ...
    I see your point that, on a worn machine, the knee could tilt one side going up and the other side coming down. It's a very good point, which the OP could check running an indicator (secured to the table) against the column, measuring a few inches above the table: if it moves when inverting the motion, this is proportional to what will happen while grinding.
    However, I think that the tapered portion of a R8 collet is far too short in order to get a reliable reading.

    Paolo

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    You will/should know if the knee is a good enough travel by running an indicator along something straight attached to the head, perhaps a parallel or a sine bar You may find the vertical position OK.. You may find the head horizontal and long travel better.(?)..
    Do measure the tube ID to see what stock removal will make clean-up. Consider how much grinding the taper will need ,and how much the collect will go up into the tube with full clean-up..Perhaps you may not be able to get full clean-up so will stop short of full clean-up. You can trig that out or simple draw it 10 scale to see how much the grind will go up the tube..If I remember right the taper is about 5/8 long and it starts about 3/8 inside. With this you may need perhaps 1 ¼ wheel arbor stub to your grinder so the heal of the wheel will pass the end of the taper..To use end mill holders or collect you want them to only go so far up the tube. Perhaps full clean up would not be necessary. The far up the tube is/should be clearance but not bugging the collect tube off angle.
    Hope I am not being a worry wort on this just trying to think of the variables and hazards.
    You might extend the quill and check the taper with a sine bar to the side..but it may change when drawn back. sine the bottom should be Ok with an early blue in check.
    Good also to know how you are going to move away to make a blue check easy.

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    What's the old saying? Measure twice and cut once?

    I would definitely do a few or a dozen dry runs before grinding it. OP never said anything about the bearings. I suppose if the bearings are worn or quill housing is worn and if the bearing runs out less then a thousand that would be OK for most. I always say "practice makes Perfect" I also like the idea of not using the knee to feed. The table feed would be easier and more precise. Be sure to tighten the gib or at least check the table shake. When I used to grind 50 tapers in 8" HBM's I would mount a tool post grinder on a compound slide jury rigged to the machine table. So much easier to control then a hand crank on the knee of a Bridgeport. I like the IMHO of Bucks...so if the OP screws up it's his fault, not ours.......lol
    Good Luck but I would rather see you send the spindle to buck and have him do it on a Heald. G-Day

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    Still another tricky thing is how you will tweak your angle.. it is not that easy to tram a head to zero and so it may be a bugger to tweak the head angle a few tenths..play with that a time to know how you can best do it.

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    It would take a little time, but if you are concerned about the possible outcome, you could make up a test piece that can be mounted in one of your holders and finish grind the taper on that to see what type of results you get. Rough the taper on your lathe and finish on your mill with the grinder. This would give you a feel for proper feed per grind pass as well as let you fine tune the taper angle so when you start on the spindle you'll already have that set.

    Just a thought,
    Ted

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    With the old grease pencils we would get perhaps .002 or more grease layer on a part..Then we would come in to just grind the grease a few times with not yet touching the part, so setting our angle and our zero. You can't do that with the new pencils because what they call grease is to hard...

    Not suggesting you do this but once I made a simple precision slide with grinding Vs long ways in two plates..The over lap side edges was just enough to make a close fit to keep out dust.
    In the Vs I set precision balls so the slide was like floating on air..but yes it was gravity set so not much good for a vertical set-up. That rig if set on a sine table to rise .005 (for the grinding feed) could have made a decent spindle grinder. Yes likely start .0025/,005 low so the arc would come to center line.

    Yes over-kill as a scraped oil way slide would have been as good ,likely better. I always thought an oil way smoother than balls.

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    Guess you could measure the existing taper as best you can so having a rough idea the bell mouth condition so to expect that you need .001/.002 or what ever off the smaller end to make good..then watch your grind hit to see it hits in the correct area and looks like about that is being ground..then with enough to to blue (perhaps 1/16 or 1/8) check the taper...then with adjusting the angle adjust about half of that.. that may be enough or will at least hit above the first grind to make another blue check. You may need to set an indicator somewhere about your spindle head to see that you made a move in the right direction. The distance away from the pivot point will make the move different from that of the taper's need, so perhaps check the move close to the taper..

    re: [adjust about half of that] What you take from one end of a taper you put back at the other end]


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