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IndustryArena Forum > MetalWorking Machines > Benchtop Machines > G0704 Tapered Bearing Upgrade
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  1. #1
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    G0704 Tapered Bearing Upgrade

    I like many others have followed along with many recommendations found on this forum and in others while progressing my CNC build on the G0704. I don't claim to be any sort of expert but have learned a lot from experience and breaking things. There is a ton of information available for this mill and mills in this class to draw from. You may even say there is more information than is necessary which makes it difficult to sort out what to do with your own conversion. Hopefully this will consolidate some information I have gathered through my experience with bearings.

    As I looked to replace the stock spindle motor for one with more power and higher speeds I naturally upgraded my spindle bearings to accommodate those speeds. Like most I did the AC spindle bearing upgrade. The main reasons were that it was well documented and the cost was very reasonable to achieve the performance I desired. Unfortunately the results were not what I expected and I spent more time messing with the AC bearings then making parts. The TIR was also .0015" no matter how much I tinkered with the internal alignment. So I did some research and found an acceptable tapered bearing replacement.

    I started out with the stock tapered roller bearings and measured spindle TIR of .0007". This is on a used machine which I am sure was never broke in as the rest of the machine still had cosmoline all over it. The stock tapered bearings were UBC brand 25x47x15mm 32005X & 35x62x18mm 32007X They are rated at 7500 rpm and 5800 rpm respectively per the UBC catalog here.

    The upper bearings on the barrel were NWH(?) brand 35x62x14 6007RZ & 45x85x19mm 6209RZ. I was unable to find much info about these but installed the popular replacement Nachi 6007ZZE & 6209ZZE rated at 12000 rpm and 7800 rpm respectively (Links provided, click on the part number). I did not spend much time shopping around for these as they met my requirements. There is an option if you are trying to achieve speeds over 7800 rpm that I will not get into. But you can check out this link to get the general idea, this guy got 13000rpm: link

    As for tapered roller bearings on the spindle most of what I have seen is using the Nachi bearings which will limit your max rpm to 6000. Not much of an improvement above stock but a much better bearing than the UBC. I did some searching and found SKF bearings that were capable of higher rpms. The part numbers and specs are as follows:

    32005 X/Q Reference speed 11000 rpm, Limiting speed 14000 rpm

    32007 X/Q Reference speed 8000 rpm, Limiting speed 10000 rpm

    The reference speed is based on a max operating temperature of 250 degrees Fahrenheit. If you wish to go above to the limiting speed you must have a system to dissipate the extra heat generated (ie oil bath). Without going into it further there is a ton of information on the SKF website to explain what each of the numbers and ratings means. The suffix "X" at the end of the designation indicates "Boundary dimensions changed to conform to ISO".The suffix "Q" at the end of the designation indicates "Optimized contact geometry and surface finish".

    I ordered the bearings from 123bearing.com which is based in France. This was an economical decision that I do regret a bit. They had the lowest price at $38 for the set and shipping was quoted at "3-7 days". My bearings arrived 14 days later after 6 days in customs that according to FedEx was due to incorrect paperwork. So if you are not in a rush you can save a couple bucks but the bearings are available elsewhere.

    The bearings installed easily with a drift pin and some light love. I used Kluber Isoflex NBU15 from the cnc-specialty-store.com this grease is rated to 266 degrees Fahrenheit. SKF recommends that grease fill 30% of the cavities of the bearing. I was not able to find specs on how much volume the bearing had so I used the old wheel bearing packing technique of rubbing grease into the bearing from the palm of my hand. The two bearings probably sucked up 15 cc of grease, considerably more than the AC bearings. On the initial install I "pre-loaded" the bearings to a snug fit. On the G0704 spindle there is not much difference between free spinning and snug. I scribed a line on the spindle and retainer nut to mark this location for reference as needed. After the spindle was installed I checked run out and happily noticed I was barely wiggling my .0005" indicator. I would say in the neighborhood of TIR .0002".

    I did a break in incrementally using a heat gun and my spindle drives load meter. Starting with 1000 rpm for 10 minutes then 2000 rpm for 10 then 4000 rpm for 10 followed by 10 minutes in reverse at 1000 rpm. When you do this break in I would recommend extending the quill out all the way. You will need to take a temperature about halfway up the quill for the upper bearing and for the lower you will be reading about 1 inch up from the lower retainer nut. If you can't do this you can get a reading from inside the casting but I have noticed the cast iron builds heat faster and holds it longer. A few minutes into the 4000 rpm segment I noticed the load meter creeping up and once it broke 10% I shutdown the spindle, allowed it to cool for a moment and then ran it in reverse at 1000 rpm for 10 minutes. The temperature when this happened were 155 upper and 130 lower.

    I let the spindle cool off and removed it. I adjusted the pre-load to about 1/32 off from where it was checked TIR at .0005" and then ran another cycle. This time was 2000 and 4000 rpm for 10 minutes each. Temps reached 145 and 120. I let the spindle cool for 10 minutes then ran 3000 and 6000 rpm for 10 minutes each followed by 1000 in reverse for 10 minutes. Temperature spiked at 150 and 125 during this set and the load meter never moved off 0. At the conclusion of the test I checked TIR at .0002".

    Overall I am happy with the results and will run one more break in lap tomorrow to double check things. I would like to give credit to lcvette and russtuff for starting down this path already. I am open to suggestions if anyone notices issues with how I did something or a better way to go about it. I will update this as time progresses to see if it holds the run out and how much maintenance is required.

  2. #2
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    Re: G0704 Tapered Bearing Upgrade

    Thanks for a good scientific report.

    Don

  3. #3
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    Re: G0704 Tapered Bearing Upgrade

    I ran the last break in cycle today at 3000 rpm, 6000rpm and 1000rpm reverse for 10 minutes each. Maximum temperature on the upper was 116 and the lower never passed 83.

    I let it cool off while I setup. I then ran parts for 40 minutes straight with everything at 6000 rpm. It was all light cuts with a 3/16" .06 DOC and .1" WOC followed by some cleanup and chamfer. Temps did climb on the upper bearing to 135 but the lower stayed under 90 the whole time. Would say they are pretty well broke in now. I have a few hours of parts for tomorrow planned. If the temps hold for that I am calling this good.

  4. #4
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    Re: G0704 Tapered Bearing Upgrade

    I find that above 2,000 - 2,500 RPM bearings, even good ones lightly loaded, do start to get warm. It's the flexing of the steel surfaces.

    Cheers
    Roger

  5. #5
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    Re: G0704 Tapered Bearing Upgrade

    135 is fine. Expect some heat with any moving parts.
    A lazy man does it twice.

  6. #6
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    Re: G0704 Tapered Bearing Upgrade

    Hi,

    Thinking of pulling the trigger in these bearings and was just wondering, did you use the standard number/size shims with these bearings?


    Dust

  7. #7
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    Quote Originally Posted by 6696 View Post
    Hi,

    Thinking of pulling the trigger in these bearings and was just wondering, did you use the standard number/size shims with these bearings?


    Dust
    These bearings are a direct replacement of the factory bearings and require no shims. Just make sure to pull and replace the old bearing races with the ones provided.

  8. #8
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    Re: G0704 Tapered Bearing Upgrade

    Nice! Thank you

    Hope this cuts down on the heat of my originals. I swear I could heat the garage after just a few minutes. :-)

  9. #9
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    Re: G0704 Tapered Bearing Upgrade

    Quote Originally Posted by 6696 View Post
    Nice! Thank you

    Hope this cuts down on the heat of my originals. I swear I could heat the garage after just a few minutes. :-)
    That is the motor, drives and power supplies running too.
    Milling itself creates heat.


    Sent from my iPhone using Tapatalk Pro
    A lazy man does it twice.

  10. #10
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    Re: G0704 Tapered Bearing Upgrade

    Well, I'm gonna start here :-).

    After about 15 minutes at 2000K the spindle is so hot I can't touch it. I can't imagine this is normal. Once I get the Bearing in, I thing a belt drive may be on the wish list.

    Thanks guys,

    Dust

  11. #11
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    Re: G0704 Tapered Bearing Upgrade

    Did you break them in fully? They do get hot on initial run in, but that will subside after the break in process and also be sure you have properly preloaded the bearings according to the mfg recommended setting. Will need a clean and regrease after break in along with a resetting of the preload

    Sent from my QTAIR7 using Tapatalk

  12. #12
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    Re: G0704 Tapered Bearing Upgrade

    The spindle cracked on my G0704 a few weeks ago and I figure that I should also do this bearing upgrade while I'm replacing it. I have all of the new bearings and Kluber grease ordered and the old spindle removed. So, from what I understand I'll need to 'break in' the new SK spindle bearings and then completely remove them, clean them, re-grease them, and re-install them...that seems like a lot of work! Are there any tips/tricks to make this go easier?

    Thanks,
    JJ

  13. #13
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    Re: G0704 Tapered Bearing Upgrade

    Hi,

    I by no means know what I am doing, but I did not remove the bearings after break in. I figured the added stress to the bearing, pressing them in and out, was not something I wanted to tempt fate with. I went through the "break in" procedure and found that I was still getting more heat build up than I was comfortable with. I decided to just let it run and found that as I continued to use my mill the spindle ran cooler and cooler. In retrospect I think I used too much grease but at this point I have several hours on it and it is running as cool as I could hope for.

    Hope my experience helps,

    Dust

  14. #14
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    Re: G0704 Tapered Bearing Upgrade

    I did not like the way the large bearings on my mill spindle were getting hot when the RPM went above - say, 2,600.

    So I bought a length of thin copper tubing (5 mm?) from ebay and wrapped it around the bearing region and clamped it tight on with a formed metal cover and some large hose clamps.
    Then I bought a submerged spindle pump and some matching silicone rubber tubing from ebay and a plastic tub from the local HW store, and hooked them all up.
    Finally (Mach3), I modified the M3 and M4 macros to assert an output pin when activated, and M5 to de-assert that pin. The pin drives a Crydom 240 VAC solid state relay which drives a stock power outlet. The pump plugs into that.

    So now the spindle is automatically cooled when running. It gets warm but not hot, even at 3,300 RPM.

    Cheers
    Roger

  15. #15

    Re: G0704 Tapered Bearing Upgrade

    Bearing heat is normal, and in fact, they should build heat as that increases viscosity of your lubricant and helps to spread it evenly in the bearings.

    I've run my G0704 spindle as fast at 8,000 rpm. It gets warm, in fact, it probably gets too hot to really hold on to. And on long runs the entire head will get warm. There is absolutely nothing wrong with this as long as the bearings are within their accepted operating range. Bearings in engines for example are similar temp to the the oil, often 220F or more (most oils break down at 275F or so).

    The issue is that you need to account for the change in preload over the temperature range. A spindle that's going to get to 150F will usually be tighter than when it was at 65F. This is why spindle warm up is required, though on these relatively small spindles it doesn't take long, just a minute or two at 65% max spindle speed will do if everything is adjusted correctly. Spindles that aren't building some heat aren't preloaded quite enough. However, it is somewhat horsepower dependent, I know with my small spindle motor it would tend to stall more often with more spindle preload, but with less preload I would struggle with surface finish. I now run a much larger spindle motor, and I also run more preload. I get slightly more heat, but stalling is no longer and issue, and I get a better surface finish too.

    I've also moved away from greasing my spindle and instead it gets oiled. That allows higher spindle speeds, but it also resulted in a quieter and cooler spindle despite higher preload. Right now I just pipe in way oil using the automatic oiler. At machine startup I open just the spindle port and run the pump for about 15 seconds. It gets oiled every 20 minutes like the ways do there after. It's been working very well.

    The G0704 spindle fit is fairly loose to the bearings, IMO. They are press, but only just so. I generally use a brass punch and a ball peen hammer to take races on and off. It's about a 20 minute rebuild process these days. Getting the preload right is the tricky part, and just a few degrees on the nut makes a big difference. With grease, it's really hard to get a feel for what's loose, what's tight. So running an oil system has allowed me to clean the bearings up a bit with some brake clean before building out the spindle, then when it comes time to preload it's a lot easier to get it right just by feel.

    I've gone back and forth between the tapered bearings and AC bearings with my G0704. I definitely prefer tapered bearings. I find them to be quieter, easier to adjust, and longer lasting. It's also nice not dealing with a bunch shims and other B.S. during rebuilds. But with lower horsepower spindle motors, the AC's are probably the better option as they do seem to have less parasitic drag.

  16. #16
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    Re: G0704 Tapered Bearing Upgrade

    I've read across CNCzone many times about "preloading" bearings according to the manufacturer's specifications, but I've never actually had anybody describe the process that they have used. I just read this article for the SKF bearings I have ordered: https://www.skf.com/binary/30-299896..._12-299896.pdf

    After reading this, I am confident that virtually nobody has ever measured the axial spindle bearing force on their G0704 mill when installing bearings. So, other than the approach of 'tighten the nut up until you just start to feel some resistance while turning the spindle' method, is there any other real-world advice in how to approach this?

    I'm also inclined to punt on cleaning/regreasing them after break in. I just don't think the juice will be worth the squeeze and I bet very few people actually go through this trouble unless they are shooting for super high spindle speeds. My spindle won't even get to half the rating of these bearings. Any contrary opinions?

  17. #17
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    Re: G0704 Tapered Bearing Upgrade

    I installed the new spindle and bearings last night and it went quite well. If it helps anybody, here are some observations and notes:


    • I was able to do all the work without the use of a press or pin spanner wrench, but did require a couple aluminum tubes of proper diameter to tap the bearings in place. The larger aluminum tubing was about 1-5/8" O.D. and about 1-3/8" I.D. and the smaller tube was about 1" I.D. thin wall tubing. Both were just scrap pieces I had laying around that happen to work.
    • I installed the 'lower' bearing (SKF 32007 X/Q) first and used the old bearing outer race as a guide tool to help seat the new outer race in the bottom of the quill housing. This race seats firmly against an inner lip in the quill housing.
    • I used the larger tube to seat the 'lower' bearing rollers/inner race onto the bottom of the spindle. This is supposed to seat firmly against the top of the spindle 'head'. It went on easily using the tube and taps with a dead blow hammer until it was about 1/8" from being fully seated...then it didn't go any further. I didn't notice that most of the shaft was a just-slightly smaller diameter than the very bottom, where the diameter is sized just a little larger in diameter for the bearing. My tube was a near perfect fit, but just for the upper section of the shaft...it started to hit this slightly larger diameter once I reached it. I took a dremel tool and carbide burr to grind away at the I.D. of the larger tube to give me clearance for this slightly larger diameter region.
    • The outer race for the upper bearing (SKF 32005 X/Q; that's what I ordered off Amazon and they actually sent me an SKF 32005-XVB015...I used it anyway) fit into the upper region of the quill housing with a slight tap using the old race to guide it. It seats against an inner lip in that housing.
    • The rollers/inner race for the upper bearing would not slip over the region of the spindle shaft by hand. I think they are not supposed to be a 'press fit' here because they nut that goes on top if it is what provides the preload and it would be a PITA to tighten otherwise. I checked on my old spindle and it was also a tight fit, so it must supposed to be pretty tight. I used the smaller tube and the old bearing to tap it into place and get enough tension to not have any noticable Z axis play and not let the spindle spin more than about a half turn when spun by hand. This was my 'pre-load'. I then tigtened the nut onto the bearing, gave it a little tap on the spanner pin hole and screwed down the two screws which I assume are there to 'bind' that nut in place so that it can't loosen on its own.
    • After putting it all back in to the G0704 I did the standard spindle bearing break-in procedure and it has acceptable runout with 0.0003" T.I.R. and they didn't heat up much at all after 10 minutes at 2400 rpm. (I have not done the spindle pully upgrade to higher RPMs yet).


    Hope this helps,
    JJ

  18. #18
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    Re: G0704 Tapered Bearing Upgrade

    Interesting, thank you.

    the very bottom, where the diameter is sized just a little larger in diameter for the bearing.
    Was that deliberate, or was it just poor machining due to a chuck with a significant TIR? Me, I would guess the latter. A G0704 is not a precision German or Swiss machine.

    Cheers
    Roger

  19. #19

    Re: G0704 Tapered Bearing Upgrade

    Its like that by design.

  20. #20
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    Re: G0704 Tapered Bearing Upgrade

    Its like that by design.
    That would be interesting.
    Source for information?

    Cheers
    Roger

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