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  • bearing overheating

    the bearings are overheating for my milldrill (the ones at the bottom of the quill) after running a 3/4 inch fly cutter (measured from center to the end of the cutter bit) on 1300 rpm at with a 0.015 depth of cut at a slow feed (just barely squeeling but thats cuz the cutter aint profesionaly sharpened) on an aluminum piece about 1.25 inch by 3 inches long. Is this normal? its gets as hot as almost to the point where i cant keep my hand around it. Sort of like holding a mug of tea front the cup instead of the handle i guess... So whats the verdict? were talking about the bigger mill drills with round column , not gearheaded

  • #2
    Sounds like the bearing is already damaged, or it was poor quality to start with. Making forced or powered table feed cuts with a dull cutter is going to create friction. I would fix the problem before the bearing gives out completely and scars a shaft that would be a lot more expensive than a $25 bearing and a couple of hours to replace it.
    For the work involved in repacking a bearing it is worth it to buy a new replacement. Instead of buying a replacement bearing from the manufacturer, and possibly getting another poor quality bearing, take the old bearing to your local automotive shop and they may be able to cross reference the bearing with a quality replacement one.
    I learned that from my first HF 3 in 1.
    Duke Reno / Yankee Metallic Metalcraft

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    • #3
      Could it be from lack of lubrication?Although the actual temperature my not be all that hot,human hands can only tolerate about 140f for a few seconds.Maybe get yourself a kitchen thermometer and see what the actual temps are before getting carried away.
      I just need one more tool,just one!

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      • #4
        It could also be too much side load on cheap bearings. Make sure the tip is sharp and try lighter feeds. Try to balance the length of your tool. Find your center of gravity for that length.

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        • #5
          Ball and roller bearings overheat more from being too full of lube than from running with a bit less than optimum.

          Too dry, they make a horrible noise.

          Does it overheat if you run it with no cutting load?

          BTW that's a 1.5" diameter, right? At 1300 rpm, that is around 500 sfm cutter speed, which is a little high even for aluminum, maybe...

          I honestly don't see how it is possible to get it over-hot with the sort of load you talk about, in the relatively short time that should take.

          The slow feed suggests hardly any big cutter load, it does not slound like you were pushing it to hog off big chips. Should have been no big deal, by the sound of it.

          Run it unloaded and see... it will probably get hot. As far as whether it is "too hot" I don't know. If it boils spit it's way too hot, that I can guarantee.

          Do you know anything about the bearings as far as lube, type of bearing as far as roller, ball, etc, open, sealed, what sort of preload is done, etc, etc, etc?
          1601

          Keep eye on ball.
          Hashim Khan

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          • #6
            1300 rpm is not exactly screaming and your cutter is not hogging material by anyone's standards. So I don't think anything you're doing is causing the heating.

            Start from the beginning, is this a new machine? Have you ever done any cutting where it didn't heat up? Does it heat up if the spindle is idling (not cutting) at 1300rpm? How about idling at it's highest speed? Is it noisy?

            The first thing that comes to my mind is the bearings are improperly adjusted, they have too much pre-load. Is there a locking nut somewhere on the spindle to adjust the pre-load? If so, back it off a bit.

            Bad bearings would probably be noisy.

            If the machine is new, there's always the possibility the bearing seats are not precisely machined. This might be hard for you to determine. Anyway if the machine is new, send it back, it should not be doing this.

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            • #7
              If I remember right,didn't you say that this machine was setup for a long time and not used?If that's the case it could be that the grease in the bearings is old and caked.That could make the bearings heat.If you can get to the top of the quill,you might try adding a few shoots of 30wt motor oil,if the grease is caked the oil should free it up with a little running.


              Oh,and there is another possiblity.You said the cutter you were using isn't very sharp.If the cutter is dull it will generate more heat,some of that heat will go into the workpiece and some will transfer to the spindle of the machine.That could be the problem also.
              I just need one more tool,just one!

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              • #8
                the mill is used and it doesnt overheat on regular use. The cutter is sharp but i dont think the angles are perfect is what i meant. Also when i first started the machine for the first time on a speed higher than 1000 rpm there was oil that shot out of there. I'm almost sure that these are sealed ball bearings but either way these bearings are pretty huge and i didnt feel any resistance in the hand wheels. If bearings of this size overheat like this normally then the bearings in my bmx bike would have melted my hub by now. Well, tomorrow im heading to get a vise and some tooling, then converting the motor to 220volts (also this is un upgraded motor which didnt come with the mill), and ill take a look at those bearings. Ill keep you guys informed..

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                • #9
                  Your bike is not spinning 1300 rpm........ hence it would NOT overheat.

                  It is not for sure that yours is "overheating" anyhow, but let's assume it is hotter than it should be.

                  You say that "oil shot out of there". That could be grease that separated, or it could be oil that was poured in to "rejuvenate" the old caked grease (or disguise the problem). In my experience, that does NOT work well...... pretty much like putting a banana in the differential to get a car sold...

                  If teh grease is caked and cruddy, the spindle will likely turn roughly by hand. May feel "coggy"... I don't know that that would cause it to overheat all by itself.

                  Possibly if there were not sufficient (like not any) good grease left, and the bearings are actually dry, then it might.....

                  If the workpiece was hot, it might have been friction heat conducted up.

                  How long was it cutting? More can be told from how fast it heats up than just from what the temperature was.
                  1601

                  Keep eye on ball.
                  Hashim Khan

                  Comment


                  • #10
                    I would pour about 1.46 gallons of gasoline in there, crank it up to 3,000 RPM, and let it burn all that grease out of there, you may have to leave the room though. When the flames die down, inject light grease and have fun.

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                    • #11
                      If it stays cool when not loaded we can prob. eliminate to much pre-load (which was my first guess),,, if your cutter is not responsible for transmitting the heat then your bearings either have poor lubrication or are damaged, J-tiers has a good point of the bearings posibly being to full of grease but this will show up in a free run, One other thing i would check is are they to loose? Loose will cause misalignment and that can cause the bearings to run out of true and create "scuffing" on there races esp. whilst under side loads from an offset cutter, this could make the bearing run cool in a free run yet create the heat when under load, while this effect is huge on taper rollers it is still a factor for ball bearings as well..Most mill head designs have zero side load on spindle bearings in a free run because the spindle drive pulley runs on separate bearings and the spindle is driven internally by splines.

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                      • #12
                        Originally posted by J Tiers
                        Your bike is not spinning 1300 rpm........ hence it would NOT overheat.

                        Well im almost sure that my bike wheels have spun at that speed because usually when i go to the skatepark i blast down this really steep street, at about 60kms an hour because im keeping up with the cars. The piece that i was facing wasnt as hot as the bearings, i will inspect tonight, right now the machine is being converted from 110 volt to 220 volt, cheers =)

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                        • #13
                          everything is as it should be( they are not lose or anything), right now im just guessing that the cutter was transmitting heat up to the bearings. If its the cutter thats transmitting all this heat then atleast ive learned something new because i didnt know that that was possible. Ill post some pics tomorrow too if i can.

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                          • #14
                            Originally posted by Elninio
                            Well im almost sure that my bike wheels have spun at that speed because usually when i go to the skatepark i blast down this really steep street, at about 60kms an hour because im keeping up with the cars. The piece that i was facing wasnt as hot as the bearings, i will inspect tonight, right now the machine is being converted from 110 volt to 220 volt, cheers =)
                            I know this wont help your bearing problem but for what it's worth a 28in. tire rotating at 1300 rpm= 108 mph!
                            Good luck tracking down the bearing heat...keep us posted.
                            Home, down in the valley behind the Red Angus
                            Bad Decisions Make Good Stories

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                            • #15
                              I just re-read your original post,did I read correctly that you WERE able to hold your hand on the quill and keep it there?

                              If so there is nothing wrong since that will be less than 130*f.Above 260*f is where you would begin to worry,that's the point when grease lube starts to fail.
                              I just need one more tool,just one!

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