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  • mill/drill spindle bearing re-greasing

    i posted a few weeks back about this UP mill/drill i picked up. it has a Frejoth motor on it (not Feioth), and after doing some searching i think it is an old Acra mill/drill (the motor has a 1978 manufacture date). it is your standard two-belt, three-pulley design.

    i noticed the spindle gets very warm after a short time and was reading prior threads on spindle bearings and related topics. if i just turn the mill on for a few minutes and run it without making any cuts, the lower spindle still gets hot, so it isn't due to heat transfer from the endmill. i have no idea what speed it is running as there are no speed charts on the mill, but it is probably on the third-highest speed or so. i have never operated a mill/drill, so i don't know if my machine is louder than it is supposed to be, but it doesn't sound like rocks are rolling around in the spindle when it runs, and the spindle turns smoothly, but it doesn't spin as easily as the spindle on my old lathe.

    this mill sat in the former owner's garage for several years before i bought it. it was never powered up the entire time and the garage was unheated/uncooled. there is no rust on the machine anywhere. is it possible the bearings just need to be relubed?

    i have gone through Tim Reidhead's Bridgeport spindle rebuild, and it looks pretty similar to what i'd have to do for my mill/drill.

    http://members.cox.net/tangoromeo/mill_upgrade.htm

    any other tips or ideas? i went through many pages of old threads (especially the more recent ones), but if there is a certain one that contains all this info and i missed it, feel free to redirect me.

    andy b.
    The danger is not that computers will come to think like men - but that men will come to think like computers. - some guy on another forum not dedicated to machining

  • #2
    Andy, it sounds like either the bearing pre-load is set too high, or more likely, that the grease on the tapered roller bearings is old and cruddy.
    Assuming your Acra mill/drill is like any other Chinese/Taiwanese mill/drill, you can drop the spindle out, clean and re-lube in about 1/2 hour - 45 minutes.

    After you re-lube with some clean NGLI 2 spindle grease, run it for awhile and if it still gets hot, you'll want to reduce the bearing preload a bit.
    "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

    Comment


    • #3
      but whats too warm for a bearing? if you look in the threads in here its above 90C. Greases are commonly rated to 120C+.

      All of these temps are not warm but hot to the hand...

      Comment


      • #4
        it isn't getting over 100C, but i bet it's close. i wouldn't be able to grab the lower spindle ring in my hands and keep my hand on it for more than a second. if it got this hot after running it for an hour taking heavy cuts, i wouldn't worry, but the fact it will get this hot after a few minutes with no load at all on the spindle, just spinning, is what concerns me. i have never ran the mill more than a few minutes so i don't know if it will get to a certain temperature and just stay there, or if it will just keep getting hotter.

        i think i'll try re-greasing the bearings, run it, and make an adjustment to the preload if needed. besides, it's supposed to rain saturday by me, so this gives me a good indoor project.

        i'll report back what happens.

        andy b.
        The danger is not that computers will come to think like men - but that men will come to think like computers. - some guy on another forum not dedicated to machining

        Comment


        • #5
          Originally posted by andy_b
          it isn't getting over 100C, but i bet it's close. i wouldn't be able to grab the lower spindle ring in my hands and keep my hand on it for more than a second. if it got this hot after running it for an hour taking heavy cuts, i wouldn't worry, but the fact it will get this hot after a few minutes with no load at all on the spindle, just spinning, is what concerns me. i have never ran the mill more than a few minutes so i don't know if it will get to a certain temperature and just stay there, or if it will just keep getting hotter.

          i think i'll try re-greasing the bearings, run it, and make an adjustment to the preload if needed. besides, it's supposed to rain saturday by me, so this gives me a good indoor project.

          i'll report back what happens.

          andy b.
          try measuring the temperature to be sure
          Btw After you have regreased you need to let it get rid of the excess grease while its doing that it will get hot.

          Comment


          • #6
            Gettin' ya bearings right

            Originally posted by lazlo
            Andy, it sounds like either the bearing pre-load is set too high, or more likely, that the grease on the tapered roller bearings is old and cruddy.
            Assuming your Acra mill/drill is like any other Chinese/Taiwanese mill/drill, you can drop the spindle out, clean and re-lube in about 1/2 hour - 45 minutes.

            After you re-lube with some clean NGLI 2 spindle grease, run it for awhile and if it still gets hot, you'll want to reduce the bearing preload a bit.
            I'd go along with that lazlo.

            But I think I'd slacken off the pre-load first and see what if feels like. I'd strip it down as well just to see that there was no spalling on the bearing balls, rollers or races and if in doubt, replace them. If the mill hand-book (if you have one) doesn't give the pre-load I'd suggest having a chat - in person, phone, email - or on the web, with the bearing vendor or manufacturer for guidance on initial setting for the pre-load.

            If a "strip-down" is required, I'd barely put any pre-load on it, see if it is smooth and if so "run it in" at no load for 10>20 minutes and see how it sounds. After stopping, see how it "feels". If OK, set the pre-load and check again. If OK, put a cutter in and try it out.

            I keep wondering why the mill was left aside and not run. I wondered if it had anything to do with the spindle bearings.

            If re-packing the grease, use the correct grease and the correct amount - too much grease can almost be as bad as none at all.

            Comment


            • #7
              My Background -
              My first job involved computer simulation of bearing lives of vertical inline directly coupled pumps with roller, taper roller, spherical roller, angular contact ball and deep groove ball bearing races.

              later : Commissioning 10Kw to 30Kw Radial Fans for pollution control on steel and cement works as well as paint treatment ovens.

              So i have literally over the years spent weeks looking the SKF data books (but none recently I use the web site)

              Some facts:
              predicted bearing life at zero load is zero (well close enough) -
              Upper Operating temperature limit of bearings is the minimum of the lubricant and the bearing. (this usually means the lubricant)


              Note the ISO Standard reference temperature for bearings is 50C above ambient. thats 70C or 158F SKF link

              And of course "A temperature peak may occur during the initial start-up of a grease-lubricated bearing. Therefore the bearing may have to be in operation for up to 10 to 20 hours before it reaches the normal operating temperature."

              So 70C ~ No problem

              But too low a grease temperature can be a problem. If you trawl around the SKF site you will see you shouldnt run the bearings below 20C for too long on standard grease.

              For standard greases the green zone is from 20C to about 120C and the red zone is above 175C skf-link

              remember 70C/158F feels very very hot indeed to the hand but thats just normal temp ~ measure the temperature

              Why not back off the preload?. Because in a mill you are presenting a varying radial axial load and if you dont have enough preload you can get a zero load condition on one set of the bearings - not good and at speed very badSkf link

              Comment


              • #8
                Originally posted by oldtiffie
                But I think I'd slacken off the pre-load first and see what if feels like. I'd strip it down as well just to see that there was no spalling on the bearing balls, rollers or races and if in doubt, replace them. If the mill hand-book (if you have one) doesn't give the pre-load
                Agreed, although if it's an old Mill/Drill, it wouldn't be a bad idea to pull the spindle and clean it up, just for peace of mind.

                The spindle preload wasn't described in any of the Mill/Drill manuals I could find -- I had to go by the instructions posted on the Yahoo Mill/Drill group. I started off with light preload, and kept increasing until the quill sleeve on the outside of the tapered bearings got pretty hot after running for 30 minutes or so.

                The problem I had with the manufacturer's preload recommendation is that they specify the preload in ft/lbs, and the preload nut on the Mill/Drills are one of those pin spanner nuts, so it's not a simple task to convert foot pounds to torque on that castle nut.
                "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                Comment


                • #9
                  man, i need to get my head out of my anus.
                  i'm sitting here reading through the replies some more, and i just realized i have a temp sensor i use to measure the head on the nitro engine on my radio control truck. i'll fire the mill up tomorrow and take several measurements over a five or ten minute span and see what it shows.

                  also, the reason the mill sat for so long was just that the guy never got to set it up. the previous owner worked with a friend at a small gun shop. his friend had the mill and would do some small gunsmithing projects on it and eventually bought a larger mill. the guy i bought it from bought it from his friend to do the same. he brought it home and put it in his garage and wanted to eventually move it into his basement. the garage only had 110V outlets, and the motor was wired for 220V so the guy never fired it up in the garage. jump ahead a few years and the guy decided it would be too big of a hassle to move it to the basement. then he and his wife were in a traffic accident and recently got out of the hospital. he and his wife are moving out of the area to live with a daughter of theirs, so the son was helping sell things off after the house was sold.

                  anyway, the mill looks to be in very good condition, except for this "hot" spindle thing (which maybe isn't as hot as i think, but i'll know soon enough).

                  andy b.
                  The danger is not that computers will come to think like men - but that men will come to think like computers. - some guy on another forum not dedicated to machining

                  Comment


                  • #10
                    Some folks may be missing part of the point........

                    Yes, bearings get hot.

                    But they should not get real hot real fast...... if it can warm up that much in just a few minutes, the rate of power input to the bearing sounds way too high.

                    A client has a bearing that he wants to run at high rpms, probably 20 times higher than the mill drill will ever see. THAT bearing has a break-in cycle (although I already know that isn't their problem) which they have to do to reach high speeds.

                    But the slow spindle on a mill-drill, going maybe 3000 rpm, should not be so fussy. And, it should not get hot enough to scald you in a few minutes......

                    Added note:
                    The first speed of the break-in cycle which I mentioned, is well above mill-drill speeds.......
                    Last edited by J Tiers; 10-24-2008, 08:14 AM.
                    1601

                    Keep eye on ball.
                    Hashim Khan

                    Comment


                    • #11
                      Torque-ing-up

                      Originally posted by oldtiffie
                      But I think I'd slacken off the pre-load first and see what if feels like. I'd strip it down as well just to see that there was no spalling on the bearing balls, rollers or races and if in doubt, replace them. If the mill hand-book (if you have one) doesn't give the pre-load I'd suggest having a chat - in person, phone, email - or on the web, with the bearing vendor or manufacturer for guidance on initial setting for the pre-load.
                      Originally posted by lazlo
                      Agreed, although if it's an old Mill/Drill, it wouldn't be a bad idea to pull the spindle and clean it up, just for peace of mind.

                      The spindle preload wasn't described in any of the Mill/Drill manuals I could find -- I had to go by the instructions posted on the Yahoo Mill/Drill group. I started off with light preload, and kept increasing until the quill sleeve on the outside of the tapered bearings got pretty hot after running for 30 minutes or so.

                      The problem I had with the manufacturer's preload recommendation is that they specify the preload in ft/lbs, and the preload nut on the Mill/Drills are one of those pin spanner nuts, so it's not a simple task to convert foot pounds to torque on that castle nut.
                      lazlo,
                      the torque to be applied can be at the loading ("castellated") nut (indirect) or to the shaft (direct).

                      If you want to apply it to the castellated nut "C" spanner, just fit a male or female 1/4", 3/8" or 1/2" square to the handle of the spanner, measure the distance from the centre of the shaft to the centre of the fitted square and set to torque using the pics/scans in these links, 1>4 are for general information - there is no number 5 - and 6 and 7 are specific to this instance:

                      http://i200.photobucket.com/albums/a...ie/Torque1.jpg

                      http://i200.photobucket.com/albums/a...ie/Torque2.jpg

                      http://i200.photobucket.com/albums/a...ie/Torque3.jpg

                      http://i200.photobucket.com/albums/a...ie/Torque4.jpg

                      (There is no No. 5)

                      http://i200.photobucket.com/albums/a...ie/Torque6.jpg

                      http://i200.photobucket.com/albums/a...ie/Torque7.jpg

                      Comment


                      • #12
                        Thanks

                        For derekm:

                        Derek,
                        that SKF reference you posted at:
                        http://bbs.homeshopmachinist.net/sho...40&postcount=7
                        is a very good read.

                        Many thanks.

                        Comment


                        • #13
                          oldtiffie,

                          you're a crazy man. i am not sure why you posted photos of head tightening specs and old torque wrenches, but you certainly always post interesting things.

                          anyway, i guess i'm a big pansy because i took my spindle temperature readings and this is what i came up with. the readings didn't seem correct as i was taking them, so i started taking readings of the back of the spindle and then the spindle bore to see if the shop lighting was affecting the IR temp sensor i have.

                          Minutes--Front----Back-----Spindle Bore
                          0-------65.8F
                          1-------73.7F
                          2-------86.4F
                          3-------94.3F
                          4-------99.6F
                          5-------102.8F
                          6-------104.1F
                          7-------100.1F
                          8-------97.9F-----109.2F
                          9-------95.8F-----106.9F
                          10------96.3F-----107.8F----120.2F
                          11------95.4F-----104.2F----118.8F
                          12------94.1F-----103.3F----117.9F
                          13------92.1F-----102.3F----116.9F
                          14------92.3F-----103.6F----116.6F

                          i then filled a cup with the hottest water from my faucet and put a meat thermometer into it which gave a reading of about 155F. when i aimed the IR temp sensor at the water it read about 127F, which is about what i expected since the water is very reflective (the IR sensor reads best on dull objects, black is best). when i put my hand in the water, it was HOT, and i'd say yes, it felt hotter than my spindle.

                          SOOOOOOO, i guess i don't have anything to worry about. i did find it interesting how the spindle temp went down after a certain warm-up period.

                          i'm thinking i'm not going to do anything to the spindle for now and just run it as is. what do you guys think?

                          andy b.
                          Last edited by andy_b; 10-25-2008, 03:35 PM.
                          The danger is not that computers will come to think like men - but that men will come to think like computers. - some guy on another forum not dedicated to machining

                          Comment


                          • #14
                            Temps go down when the grease "channels" and gets out of the way of the rollers/balls.

                            Those temps are no problem. use it.
                            1601

                            Keep eye on ball.
                            Hashim Khan

                            Comment


                            • #15
                              Yeah, you're fine Andy -- fire-her up!
                              "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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