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IndustryArena Forum > MetalWorking Machines > Benchtop Machines > G0704 New Bearings, Still Gets Hot!
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  1. #1
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    Oct 2015
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    G0704 New Bearings, Still Gets Hot!

    Hey Guys,

    So I just finished the belt conversion from Benchtop Precision and as part of it, I replaced the spindle bearings (roller) and the upper larger ball bearings around the barrel they recommended. Bought some of the Lubex grease that everyone is using for the spindle bearings, the barrel bearings were sealed so no grease was added. I pressed all the bearings in with my press with the exception of the upper spindle roller bearing. This was pressed in by screwing the top nut down onto it until the spindle had no play between the upper and lower bearings, then I gave it another 1/4 turn which incidentally stopped the nut as I must have hit the end of the threads. After assembly I ran the new setup at 1000 RPM increments each for 10 minutes up to 4500 RPM which is where it topped out. I went to work on my first piece and after 20 minutes of milling at 4000RPM the spindle was so hot that I couldn't hold onto it for more than a few seconds. I have an infrared temperature gun that was only picking up 90 degrees but that can't be right as the casing above it was 112 which I had no problem touching.

    So, where did I go wrong? Cheap bearings? Too much preload on the spindle bearings? I used more grease than everyone on the spindle bearings but I don't think I over did it? I read that I may need to remove the bearings and re grease now that they are broken in but I hate to stress them pressing them in and out. Any suggestions?


    The upper ball bearings as suggested are:

    6007ZZE Nachi Bearing Shielded C3 Japan 35x62x14
    6209ZZE Nachi Bearing Shielded C3 Japan 45x85x19

    And the spindle bearings are:

    32005 X/Q Reference speed 11000 rpm, Limiting speed 14000 rpm
    32007 X/Q Reference speed 8000 rpm, Limiting speed 10000 rpm

  2. #2
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    Jan 2005
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    11890

    Re: G0704 New Bearings, Still Gets Hot!

    Quote Originally Posted by 6696 View Post
    Hey Guys,

    So I just finished the belt conversion from Benchtop Precision and as part of it, I replaced the spindle bearings (roller) and the upper larger ball bearings around the barrel they recommended. Bought some of the Lubex grease that everyone is using for the spindle bearings, the barrel bearings were sealed so no grease was added. I pressed all the bearings in with my press with the exception of the upper spindle roller bearing. This was pressed in by screwing the top nut down onto it until the spindle had no play between the upper and lower bearings, then I gave it another 1/4 turn which incidentally stopped the nut as I must have hit the end of the threads. After assembly I ran the new setup at 1000 RPM increments each for 10 minutes up to 4500 RPM which is where it topped out. I went to work on my first piece and after 20 minutes of milling at 4000RPM the spindle was so hot that I couldn't hold onto it for more than a few seconds. I have an infrared temperature gun that was only picking up 90 degrees but that can't be right as the casing above it was 112 which I had no problem touching.

    So, where did I go wrong? Cheap bearings? Too much preload on the spindle bearings? I used more grease than everyone on the spindle bearings but I don't think I over did it? I read that I may need to remove the bearings and re grease now that they are broken in but I hate to stress them pressing them in and out. Any suggestions?


    The upper ball bearings as suggested are:

    6007ZZE Nachi Bearing Shielded C3 Japan 35x62x14
    6209ZZE Nachi Bearing Shielded C3 Japan 45x85x19

    And the spindle bearings are:

    32005 X/Q Reference speed 11000 rpm, Limiting speed 14000 rpm
    32007 X/Q Reference speed 8000 rpm, Limiting speed 10000 rpm
    More than likely you have set to much preload Nachi is a good bearing brand although I don't recommend using any bearings the are ZZ shielded they should be 2RS, ZZ are not shielded very well

    Another thing that can cause over heating is to much grease
    Mactec54

  3. #3
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    Oct 2015
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    Re: G0704 New Bearings, Still Gets Hot!

    Thanks for your reply,

    I have a feeling I over greased the spindle bearings. I watched a video and the guy used 1cc for the large and .5cc for the small bearing. I wasn't even able to hit each roller on the large bearing with 1cc. I pulled the spindle and ran the mill with just the barrel. After 50 minutes at 4300 RPM (max) the temp of the top barrel bearing was 122 degree's. I don't think that's too bad, course the weight of the spindle will no doubt effect this variable. As for the spindle, it spins more freely than when initially installed, I can get a full rotation before it stops spinning it by hand, My next plan of action is to pull the nut and wipe out any excess grease and check the preload.

    Dust

  4. #4
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    Re: G0704 New Bearings, Still Gets Hot!

    The bearings will have a break in time but I'm sure its too much preload.

    You set the preload by how much rolling resistance with a fancy torque wrench that cost way too much.

    The best way to see how much preload you have is by how hot it runs, too hot, too much preload.

    The grease will move out of the way in the first few minuets.
    youtube videos of the G0704 under the name arizonavideo99

  5. #5
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    May 2005
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    3920

    Re: G0704 New Bearings, Still Gets Hot!

    I have to agree a preload problem.

    You do not want to over do it with preload and your description of the lock not stopping indicates to be that you went too far with torquing that down.

    As for grease too much can be a problem in machine tools, especially in fine cyclodial drives or bearings with not breathing room. However unless the assembly traps the grease, it is pretty hard to over grease roller bearings. At least for the limited speed range of these spindles.

  6. #6
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    Re: G0704 New Bearings, Still Gets Hot!

    I agree that it sounds like preload issue.

    A comment on IR thermometers - most people that use them do not get accurate, repeatable readings because they don't understand how they work - here's why:

    1. Accuracy of IR temperature measurement is significantly affected by the IR thermometer's distance to spot ratio - in simple language the further from the target, the larger the area being measured. IR thermometers measure the average temperature of the spot, so get as close as possible and straight on to the target.

    2. The emissivity of the object being measured greatly affects the accuracy of the measurement. Most IR thermometers, especially inexpensive ones, assume an emissivity of between 0.9 & 0.95 (1.0 is a theoretically perfect IR emitter). Measuring and compensating for the emissivity of a surface in order to get an accurate measurement can be a complex task. The easiest way is to control the emissivity of the target by applying something of very low mass and known emissivity to the target to be measured. For example, masking tape has an emissivity of approx. 0.92 and black electrical tape an emissivity of approx. 0.95, so either could be applied to the target surface to get a more accurate measurement.

    Also, remember that regardless of the method used, you are measuring the surface temperature - the actual internal temperature is going to be higher.

    Hope this helps.....

    Tim
    Meddle not in the affairs of Dragons - for thou art crunchy and taste good with ketchup!

  7. #7
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    Re: G0704 New Bearings, Still Gets Hot!

    Thank you gentlemen,

    I cleared out all the excess grease and when tightening the lock nut down onto the bearing I applied just the lightest touch and tightened down the two hex bolts. I ran it for about 30 minutes at 4000RPM and while it still gets hot, it's definitely cooler than before. I think I'm just going to run it and see what happens. I do appreciate your replies.

    RTTIM, I think your a few step ahead of me in the infrared department ;-) . However I thought about the reflectivity of the spindle causing a false reading. My solution was to put scotch tape on it which did not yield much difference. I will try electrical tape as you suggested and see what changes that may make.


    Thanks guys,

    Dust

  8. #8
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    Re: G0704 New Bearings, Still Gets Hot!

    Good luck with it Dust!

    Don't forget to get the IR thermometer as close as you can when you take your readings, as with most of the garden variety units the measured spot size increases dramatically with distance......

    Without getting too technical, you're correct that IR surface reflectivity is an issue to be aware of - simply put it is the percentage of the surface that reflects IR energy vs the percentage that emits it - E+R=1.0. With IR, a surface that is 50% emissive is also 50% reflective - which means that only half of the IR energy the detector sees is from the surface temperature and the other half is reflected from the background. FYI, the emissivity of unoxidized or polished steel ranges from 0.1 to 0.3 (10% to 30%).

    Didn't mean to get going......I'm a recently retired reliability engineer and vibration analysis, IR thermography, ultrasound and strain analysis are tools of the trade......old habits die hard.

    Tim
    Meddle not in the affairs of Dragons - for thou art crunchy and taste good with ketchup!

  9. #9
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    I have a G0704 with a cnc conversion. I'm controlling the stock board and motor with UCCNC and get about 3200 RPM with "stock board and motor". Also have a 3d printed fan shroud and fan on top and that keeps the motor cool.
    The spindle is another story - runs very hot. During a 20 minute CNC job with a ball end mill at max rpm it got so hot that it melted the plastic spacer that mounts the quill to the digital readout scale. I've since replaced it with an aluminum one. Last night I removed the quill (took about 6-7 minutes) and knocked the shaft out of the quill, cleaned the stock bearings and sparingly repacked them with Kluber NBU 15 and re-assembled. I took care to tighten the preload nut lightly until all end-play was eliminated and tightened the locking screws. My spindle runs cool now - barely gets warm and the whole job took about an hour and a half.

  10. #10
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    Another note:
    take them time to make the "Russtuff" spanner wrench - it made the job of setting the pre-load very easy.

  11. #11
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    Re: G0704 New Bearings, Still Gets Hot!

    Wow! what a great post, by the way, I like this Mens Leather Jacket and I will definitely recommend others too.

  12. #12
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    Re: G0704 New Bearings, Still Gets Hot!

    I'm happy by reading your enjoyable article, Keep uploading more interesting articles like this. Bearings.

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