Holbrook T13 - Lathe Spindle Plane Bearings - Page 2
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  1. #21
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    Mat,

    I can lend you an MT 4.5 to 3 MT nose adapter which would enable you to use a 3MT Test bar if that's of any help ?

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    Quote Originally Posted by Tray View Post
    Mat,

    I can lend you an MT 4.5 to 3 MT nose adapter which would enable you to use a 3MT Test bar if that's of any help ?
    That will save me trying to make one :-) can you PM me and we can sort it :-)
    cheers

    Mat

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    Default The lower bearing Halves.

    img_6525.jpg

    Front bearing lower half - no transfer to upper half.

    img_6526.jpg

    Rear bearing (bit heavy on the blue - but next to no transfer to upper half.

    I repeated the dti over the spindle with the bearing halves in place and nipped up.

    I got 0.07mm - or just shy of 0.004" lift on the journal at the front of the front bearing. Not too bad at all.

    Ive checked side ways and get around half that - so I suspect the original sizing was in the region of 0.002" i.e. 0.001" all round or a tad less.

    As for where the original 'reading' of 0.035" came from - I have a number of possibilities which could have given rise to it ranging from play in the chuck being lifted and dti sat on, extension forward of the front bearing, upper portions of the bearings not being nipped up (I cant recall how tight they were when I removed the spindle on site in the small hours of the night rushing to get it out of the guys work shop. However, I am favoring the following - ' the 'old hand' I had with me - was involved in buying and selling machine tools along with rebuilding - it would not have surprised me to find out that he had a tenths dti with a thou' face to it - for 'site visits and valuations' .... or maybe he just pulled out the first clock to hand and told me 35' meaning tenths and I understood thou' - guess I will never know.

    This does reduce the likelihood of remaking the white metal bearings, line boring etc etc - bringing me back to the original question of how best to go about scraping the worn bearings back into close tolerance bearings.

    Mat

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  5. #24
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    Upon seeing your last post, it looks as though it can be saved. Your gear mesh in previous posts is straight horizontal, or so it looked, therefore making it much more forgiving. I would still check gear pattern with bluing when your done as that could render the lathe irreparable should the gears go bad.
    It's not ideal to have no shim, and even less ideal to have to grind or mill clearance into the bearing caps to make room for shim, but given the circumstances, I dont see any other option but to rebabbitt the bearings. If your going to do it give yourself enough clearance to have adjustment later. But not so much you greatly offset the true hemisphere each bearing half should have. I will note, doing it that way is not how a professional rebuilder would do it as it permanently alters the true geometry of the bearing. On machines I've repaired there is usually anywhere between .060 to .125 thick spacer between the caps that you can grind for fit up and then you shim back your running clearance, you dont have room for that. Without being there to inspect it myself you'll want to stay in a range that you can adjust with shim stock alone, say .010-.020 thousandths.
    Once you have clearance to the cap faces your babbitt surfaces will be tight to the spindle so you dont have to worry about clearances affecting your readings for alignment.
    As you start bluing and scraping, you will lightly snug the cap, finger tight on the bolts, and take a rub. Now, fair warning, if you grind or mill clearance on the cap or spindle casting itself, then it would make sense that you cant draw both sides of the cap down tight right? Dont make the mistake of randomly tightening the cap and taking a rub, as there is nothing keeping the cap parallel to the longitudinal axis of the spindle. You must run the bolts on ONE side of the cap down so the mounting surface touches, along its length, the lower half of the bearing housing of the spindle. THEN gently snug the other side of the cap until the babbitt portion is contacting the spindle and stop. Effectively, you want all of your gap on one side as you are bluing the spindle, maintaining full contact with one side of the cap housing to the lower half of the bearing, this maintains the bluing pattern parallel to the long axis of the spindle. This is a common mistake among first timers, they randomly lay the cap on top and snug all the bolts with a random gap on both sides and nothing to keep the mating surfaces parallel. Then once they have their pattern where they want it, they shim in the clearance and call it good but the shims land the cap parallel to the mating surfaces of the steel portion of the cap and the babbitt surface they just scraped now has more clearance at one end of the bearing than the other.
    There are a few more tricks but I'll wait till you get that far, I hate writing novels.
    Regards
    Chris

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  7. #25
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    Quote Originally Posted by ironsmith89 View Post
    Upon seeing your last post, it looks as though it can be saved. Your gear mesh in previous posts is straight horizontal, or so it looked, therefore making it much more forgiving. I would still check gear pattern with bluing when your done as that could render the lathe irreparable should the gears go bad.
    It's not ideal to have no shim, and even less ideal to have to grind or mill clearance into the bearing caps to make room for shim, but given the circumstances, I dont see any other option but to rebabbitt the bearings. If your going to do it give yourself enough clearance to have adjustment later. But not so much you greatly offset the true hemisphere each bearing half should have. I will note, doing it that way is not how a professional rebuilder would do it as it permanently alters the true geometry of the bearing. On machines I've repaired there is usually anywhere between .060 to .125 thick spacer between the caps that you can grind for fit up and then you shim back your running clearance, you dont have room for that. Without being there to inspect it myself you'll want to stay in a range that you can adjust with shim stock alone, say .010-.020 thousandths.
    Once you have clearance to the cap faces your babbitt surfaces will be tight to the spindle so you dont have to worry about clearances affecting your readings for alignment.
    As you start bluing and scraping, you will lightly snug the cap, finger tight on the bolts, and take a rub. Now, fair warning, if you grind or mill clearance on the cap or spindle casting itself, then it would make sense that you cant draw both sides of the cap down tight right? Dont make the mistake of randomly tightening the cap and taking a rub, as there is nothing keeping the cap parallel to the longitudinal axis of the spindle. You must run the bolts on ONE side of the cap down so the mounting surface touches, along its length, the lower half of the bearing housing of the spindle. THEN gently snug the other side of the cap until the babbitt portion is contacting the spindle and stop. Effectively, you want all of your gap on one side as you are bluing the spindle, maintaining full contact with one side of the cap housing to the lower half of the bearing, this maintains the bluing pattern parallel to the long axis of the spindle. This is a common mistake among first timers, they randomly lay the cap on top and snug all the bolts with a random gap on both sides and nothing to keep the mating surfaces parallel. Then once they have their pattern where they want it, they shim in the clearance and call it good but the shims land the cap parallel to the mating surfaces of the steel portion of the cap and the babbitt surface they just scraped now has more clearance at one end of the bearing than the other.
    There are a few more tricks but I'll wait till you get that far, I hate writing novels.
    Regards
    Chris
    Thanks Chris - that all makes sense. For your information, the gear mesh to the spindle is just below center line - i.e. the spindle sits higher than the driving gear set. I will check this again to be certain. So if my understanding would be that the gears will move in to mesh as the spindle is lowered a thou' or so.

    I am very appreciative of your comments - as i am flying in the dark on this one - no oars, paddles or safety net !
    Mat

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    Quote Originally Posted by ironsmith89 View Post
    Upon seeing your last post, it looks as though it can be saved. Your gear mesh in previous posts is straight horizontal, or so it looked, therefore making it much more forgiving. I would still check gear pattern with bluing when your done as that could render the lathe irreparable should the gears go bad.
    It's not ideal to have no shim, and even less ideal to have to grind or mill clearance into the bearing caps to make room for shim, but given the circumstances, I dont see any other option but to rebabbitt the bearings. If your going to do it give yourself enough clearance to have adjustment later. But not so much you greatly offset the true hemisphere each bearing half should have. I will note, doing it that way is not how a professional rebuilder would do it as it permanently alters the true geometry of the bearing. On machines I've repaired there is usually anywhere between .060 to .125 thick spacer between the caps that you can grind for fit up and then you shim back your running clearance, you dont have room for that. Without being there to inspect it myself you'll want to stay in a range that you can adjust with shim stock alone, say .010-.020 thousandths.
    Once you have clearance to the cap faces your babbitt surfaces will be tight to the spindle so you dont have to worry about clearances affecting your readings for alignment.
    As you start bluing and scraping, you will lightly snug the cap, finger tight on the bolts, and take a rub. Now, fair warning, if you grind or mill clearance on the cap or spindle casting itself, then it would make sense that you cant draw both sides of the cap down tight right? Dont make the mistake of randomly tightening the cap and taking a rub, as there is nothing keeping the cap parallel to the longitudinal axis of the spindle. You must run the bolts on ONE side of the cap down so the mounting surface touches, along its length, the lower half of the bearing housing of the spindle. THEN gently snug the other side of the cap until the babbitt portion is contacting the spindle and stop. Effectively, you want all of your gap on one side as you are bluing the spindle, maintaining full contact with one side of the cap housing to the lower half of the bearing, this maintains the bluing pattern parallel to the long axis of the spindle. This is a common mistake among first timers, they randomly lay the cap on top and snug all the bolts with a random gap on both sides and nothing to keep the mating surfaces parallel. Then once they have their pattern where they want it, they shim in the clearance and call it good but the shims land the cap parallel to the mating surfaces of the steel portion of the cap and the babbitt surface they just scraped now has more clearance at one end of the bearing than the other.
    There are a few more tricks but I'll wait till you get that far, I hate writing novels.
    Regards
    Chris
    Getting ready to start rescraping the headstock spindle bearings this week so re-reading the thread and many others on babbit bearings in the forum.
    I have re-scraped the bed and headstock seat. As things lay, the spindle is 0.0004mm forward at 12" from the spindle - measured to a test bar up the spout. Vertically it sits 0.0009" at 12". This is twice that recommended in Schlesingers book for a tool room lathe. I figured, as the front bearing is 'bell mouthed' and worn more than the rear, I can scrape the wear away and lower the spindle without shifting as much material at the rear. As for internal gear mesh - the gears sit toward the front half of the spindle - so I am mindful of the fact they will see the best part of 0.0004" pivot down. I shall adjust my plans accordingly as things progress.
    Mat

  9. #27
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    A bit of progress with the bearing re-scrape.
    Working the lower halves to give alignment first then Ive been looking to address the contact area.
    Alignment wise, a test bar at 12" is 0.01mm high (thats 0.00039") and 0.015mm forward (0.00059") at the free end . Which as I read things is max' for a Tool Room Lathe. It is incredible how little material has to be removed to shift either of these dimensions. A single pass at the rear will shift me out of alignment, leaning too much on a face etc etc. On the plus side Im getting swifter at checking the alignment !

    img_8009.jpg

    The scrape marks are very shallow - max 0.0002" mostly half that or less, making the printing with blue increasing tricky. the last few cycles Ive been using next to no blue and minimal rotation say 20 degrees. Sorry the image is 90 degress - no idea why ?

    Mat

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  11. #28
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    Quote Originally Posted by Lurk View Post
    Sorry the image is 90 degrees - no idea why ?
    Some pics deserve to be the right way up

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  13. #29
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    I have put a video together of the progress made and while the video isn't the most enthralling, the comments posted by viewers below have been helpful.
    The actual scraping starts around 20 minutes in, showing the roughing in to alignment. As has been posted above - this isn't the approach recommended by professionals - re-making the babbit bearings would be that route - however, if you read through the comments below the video and my replies, hopefully it will provide some further information to anyone facing a similar worn set of bearings - scrape back to good v's re make.


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