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12x36 belt drive import expectations for depth/width of cut

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  • #16
    Originally posted by Yondering View Post
    One more comment on spindle bearings for these lathes (still assuming yours is like mine and BCRider's) - the inner bearing races may be a pretty tight press fit on the spindle, so the lock nuts can feel tight without actually causing much preload. Mine was tight enough that even with the nuts backed off, I had to use a dead blow hammer on the back of the spindle to loosen the preload from it's originally over-tightened condition. This also meant that when re-tightening it to the final position, I had to tighten the nuts quite a bit more than I expected.

    The spindle bearings in mine do warm up in use now, but have enough preload that it doesn't matter if they're warm or cold. I never have any need to warm up the lathe before cutting.

    I'll also point out that when experimenting with preload on mine, in the "too loose" condition that caused chatter like you describe, there was still no measurable play in the spindle, the bearings warmed up slightly when running, and the lock nuts felt pretty tight. It just vibrated and chattered with anything but light cuts. I had to just tighten preload a little bit more at a time until the chatter went away.
    Just curious, how tight the bearings were after factory ie how hot they got in use?
    (I'm assuming that bearings heating up was the reason you had to loosen them)
    Location: Helsinki, Finland, Europe

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    • #17
      Great news, you guys were right. I backed off the lock nut and gave the main castle nut maybe another 16th of a turn. Ran it at the new high speed of 1700rpm (VFD at 90hz) for 15 minutes. Front and rear bearing temps both only still around 110F, perfectly acceptable. Instant improvement in cutting. With the same 1.375" 12L14 chucked up I made several parting cuts at 800-1000 rpm and several turning passes with carbide up to 0.125" on the radius, maybe even more. I had hints of chatter here and there but could often feed harder through it. I'm going to let things cool over night and try it out cold and see how she does, tempted to snug up just a little more.

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      • #18
        Originally posted by MattiJ View Post
        Just curious, how tight the bearings were after factory ie how hot they got in use?
        (I'm assuming that bearings heating up was the reason you had to loosen them)
        The spindle had a lot of drag when I got it; enough that it was blowing breakers when trying to start the lathe. Once it was running and in use for a little while, the spindle bearing area became hot enough that it was uncomfortable to keep my hand on it. That was with new spindle bearing oil too.

        That may have been the reason my lathe had a little surface rust but very little sign of use. It was a good find, all said and done.

        JCByrd - that's great, glad it worked out. Nothing wrong with snugging it up a little more to be sure. It's amazing how much difference that preload makes, from "should be tight enough" to "really tight enough".
        Last edited by Yondering; 03-22-2018, 07:10 PM.

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        • #19
          JCByrd, I am happy for you. Spindle bearings is a special application. You basically sacrifice bearing life to gain rigidity. Without spindle rigidity you don't have a lathe.

          Another application for tapered roller bearings is automotive wheels (at least it used to be). There you adjust the bearings leaving some clearance in assembly. This is because you need long life under heavy load and rigidity is not that important.

          Another word of advice - you may want to check your spindle bearing lubrication system. In my lathe there is no oil pump. The headstock gears are submerged in oil. When they turn, they create an oil mist. It would condense on the top gearbox cover and then run towards the walls and enter the oil channel, running all the way around the top of the gearbox. Deep drilled holes go from the channel to the bearings and provide oil for lubrication. Excess of oil drains back to the main sump. What an ingenious system! But Chinese decided to cast the channel to save money and did not clean the casting properly, so casting sand could enter the bearings with oil. Fortunately I decided to take the lathe apart before using it, so the bearings are still alive after 12 years.

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          • #20
            Mike,

            Thanks for the advice. I'm familiar with tapered wheel bearings as I owned a couple of first generation Ford Explorers with just such bearings. I also liked to run them through mud and water so I got good at cleaning, lubing, and resetting them. It was nice to me that a set of bearings cost $25 instead of a unit bearing that's $200 and not serviceable. Similarly my trailer has tapered bearings. Regardless, with my experience what I thought was enough pre-load was clearly not enough. Luckily I've had my spindle out and my lathe was of early enough vintage that it was clean and the bearings are of good quality. What I found though which is consistent with others is that the sight glasses are useless. A single hole from mid-height in the bearing cavity enters the sight glass cavity. The sight glass cavity can be full while the bearing cavity could be empty from a leak through the seals. Or vice versa. Out of cowardice for drilling into my lathe and contaminating things I did not drill another hole at from one cavity to the other at the bottom when I had the spindle out, a mistake in hindsight. The sight glass is now just the overflow. I'll add a few drops of oil every once in a while until I pull the spindle again.

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