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Thread: Italian mystery mills, and spindle bearings therein

  1. #21
    Join Date
    Mar 2019
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    Sorry this reply has taken so long. I've been working on modeling the whole assembly to better explain (and better understand) how it actually all fits together, and wanted to get that finished before going any further with the preload conversation.

    Quote Originally Posted by J Tiers View Post
    Given that the bearings seem to be non=preloaded, AND they are double-row..... They may have been intended to be an internally pre-loaded type. My Logan model 200 lathe uses a double row internally preloaded bearing on the spindle, which is just clamped into the headstock (it is pressed onto the spindle).
    After doing a little digging, I'm really hoping that either that's not the case, or that these folks on PM had no clue what they were talking about:
    Used to be back then and before some bearing manufacturers made precision double row angular contact bearings that somehow where assembled preloaded and ready to install.

    Early Logan lathes used similar bearings along with I suspect round dials Monarch 10EE's(for the rear bearing), essentially they were specials and have not been made for decades and decades. There is a bit of info out there on the net about Logan lathe spindle bearing issues and how simply replacing the bearings with common ones does not work."

    Browsing an assortment of other threads/forums, it sounds like Scott Logan may still sell internally-preloaded replacement Logan bearings (presumably custom-modified), but that he's the only one.

    Someone else a few posts later says:
    "RC99 is exactly right. Preload has to be built into the assembled double-row bearing, and as stated, this was an available bearing back in the day. Having come from a machine tool design background, I have used these bearings (52xx) in the distant past. Also bear in mind that the 5200 series was furnished in two geometries: externally converging contact angles (analagous to DB mount for duplex), and internally converging contact angles(like DF mounting, and probably not suitable for lower spindle bearing.)"

    I'm a little confused by this, though - or maybe he's a little confused - since 5200-series appear to still be pretty widely available (although a lot of places seem to treat 5200 & 3200 as synonymous with no mention of contact angles) and not the same thing as the Logan specials. For what it's worth, the replacement lower bearing on this spindle is a 5208.

    I doubt you would be happy long term with a loose single row (or standard clearance double-row) bearing. You would just get horrible performance and finish on parts using end mills.

    However, it may be perfectly possible to include a system for preloading such a set of bearings. It might have had that to begin with, and was subsequently modified.
    I'm still not entirely sure I've wrapped my head around the way mill spindle preloads are supposed to work, but after putting together the model I'm wondering if the spindle sleeve/liner piece pressed into the casting is actually meant to perform the same function as the bearing spacers used on Bridgeport spindles with a preload applied by the nut at the top.

    Up til now we've only been looking at the bare spindle shaft & bearings. This (minus a few nuts, bolts, zerks, scars, casting details, and the big Rube Goldberg pulley arrangement that cantilevers off the cylinder at the top of the casting) is the whole head assembly. Hopefully those of you who have a slightly better idea of how such things are supposed to work will be able to tell whether this does, in fact, work without custom unobtanium bearings, or what might be required to make it work. You can also play with the full model in Autodesk's clumsy web interface at https://a360.co/2GPtgVu (or download it, on the off chance you're actually that interested and happen to run Fusion 360).




    The question for the moment is whether your spindle is the correct size at the lowest point, or not. Since the bearing, by your description, is not an original one, it may not be correctly sized.

    I have a small add-on vertical head that has two bearings which are of different sizes, but it is a very very slight difference. Almost the sort of difference you describe. One seems to be a metric bore, and one imperial, sized like that so that the one would slide freely down the spindle to the end, where it is a slight press fit.
    I did wonder if something like that might be the case (or if a bearing like that might solve the problem) but I couldn't find any imperial double row bearings at all, never mind something like a 3 5/32" OD x 1 9/16" ID (that's 80.16875mm x 39.6875mm which would be a slightly tighter fit on the ID - where it's a terribly loose fit - and the OD - where it should probably be a tighter fit). Or have I just not found the right places to shop?

    From what you say, I expect the issues are with the area that was mucked with, that area is probably oversized, Bubba did not get it cut down far enough with the angle grinder and flap wheel.
    The mucked with area definitely has a patch that's oversized (although just a patch, not the entire diameter). Aside from the evidence that the inner race slides (and turns) freely on either side & polished the high points on the way off, it's so tight when passing that region that the outer race couldn't turn smoothly (or even as smoothly as the damaged balls would normally allow).

    Get out the micrometers and give us the diameters at various places other than the part Bubba has been at. The lowest area, where the nose bearing goes, the area where the top bearing goes, and any original area in between. Measure a couple different angles around the spindle, so it can be seen if things are consistent. You might also measure a couple around Bybba's work as well, one diameter including the "polished" area.
    Unfortunately those numbers are going to have to wait a little longer, while I shop for a new (or old) mic. While I've got a variety of 0-1" mics, I never had a pressing need to pick up a 1-2" before.

    Of course, why I didn't pick one as soon as I discovered I had a >1" problem is a little harder to justify, but... err... moving right along...

    I suspect that the top and bottom bearing areas may not be identical diameters, and that (aside from Bubba) the spindle is set up to allow the bottom bearing to slide down fairly easily.
    Now measurements with that sort of precision I can make! There's a 10mm difference between the upper and lower bearing ID. (I guess it wasn't entirely apparent in the photos just how & where the two bearings mounted - hopefully the model clears it up)

    As far as the fit along the nominally-40mm portion of the shaft, though, there is a very slight taper from the top to just above the Bubba bit (from ~39.95mm at the top to 40mm - or as close as I can read on a vernier caliper - at the bottom). The fit at the very bottom - Below Bubba - actually seemed a little looser than immediately Above Bubba. It still shows the same turned finish, though (as above, so below), rather than being worn smooth from spinning in the race.

    It may even be that ol Bubba looked at whatever arrangement was in there and said "whayt's thish hea?", determining that the "newfangled nonsense" could be replaced with something else, since he didn't understand it, or could not get the right part down at the auto parts place in the nearest big town.
    This would surprise me not at all. Whoever Bubba was, he wasn't much for precision. There are a couple slots made for the pulley assembly that I'm fairly certain were cut with the same angle grinder that attacked the spindle - except this time being wielded left-handed so the right could work its way through a 12-pack. Then again, there are also some parts that seem to have suspiciously crude or imprecise workmanship for a factory, but seem significantly more advanced than Bubba's work. For example the spindle endcaps are extremely rough on the inside, have uneven or arbitrarily spaced pin spanner holes on the outside, and an odd mix of thread pitches (not to mention lacking the stamped "45" that's on nearly all of the other factory parts), but clearly weren't hand-hewn by stoneage tools (or angle grinders).

    That aside, I've been forced to assume the original probably had the same dimensions as the replacement 5208 just because I haven't found any trace of bearings that are close to that size without being that size. I've seen occasional references to undersize & oversize bearings, but have yet to find anywhere listing them for sale (although, again, this could point to deficiencies in my shopping technique rather than the obscurity of the bearing sizes).


    -Bats
    (I'm going to feel really terrible about all of this when I some day meet Bubba and learn about the extraordinary conditions he was working under when he did all this... and that he'd lost his right arm in the war... and that a combat medic grafted on an angle grinder in place of his left hand)

  2. #22
    Join Date
    May 2013
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    Alvin Texas
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    Bats,
    Iíve been a machinist and machine rebuilder for many years. I ran the machine shop in several businesses that rebuilt electric motors. It was nothing to remove a electric motor shaft and make a new one. As to the shaft on the mill, I would definitely make a new one. It has been welded on so it is most likely bent. If the bearing spins on the shaft, the fit is to loose. When you run the machine at operating speeds the bearing inner race will spin on the shaft generating excessive heat and will gall the race to the shaft. Iíve had to repair that many times usually by making a new shaft. We welded up the shaft as a last result because 9 times out of 10 the result would be a bent shaft. Any repair job is worth doing right the first time. You donít want to have to tear it down in a few months to re-rebuild the machine!!

    Barry


    Sent from my iPhone using Tapatalk

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