[servtech]

Those bearings worked perfectly for our build..should do the same for you. We were judicious in the use of Kluber on the spindle bearings, took our time to run them in, fine adjust them and watch the temps while adjusting.

Stuart

I agree, if there is no greasing information with the bearing, the rule of thumb is to 1/3rd fill the bearings with grease. Lightly mark 120 degrees on the bearing with a pencil and fill the bearings both sides between the 120 marks, then spread the grease around the bearing both sides. Run the spindle bearings in at 1000 rpm in 20 minute steps ensuring the bearings do not get too hot at each step.

Too much grease or too little can cause the bearings to overheat and or seize.

[CL_MotoTech]

The problem with sticking with the quill setup is that it introduces lash into the system. It's probably manageable, but I noticed a nice increase in finish quality once I got rid of it. It's also two less bearings to manage, and the machine runs quiet. Like 65dbA. Even when it is cutting, it is quiet.

If you are doing 6k or more, I highly recommend just going to a total loss oil system. Just a slow drip of oil that passes from the top through the bottom and will escape from the bottom of the spindle. Grease will get you by, but if you are doing any long run cutting the auto oil setup is far superior. I run the cheapest bearings I can find in my spindle and am now going on like at least a year at 6k RPM. I've done runtimes of nearly a day since I have the tool changer. If you have flood, the total loss system is even better because it purges the bearings as it runs. Yes, collecting the tramp oil is a pain, but it's worth it in the lack of spindle rebuilds. The ways need the oil anyways. So dealing with the oil is an issue no matter what.

I do not recommend the AC bearing change on these. That was popular before people were really starting to take hard cuts on CNC G0704's, but with one lower AC bearing they simply don't stand up. The tapered setup is better. This is why other machines use multiple AC's. The G0704 has many flaws, but sticking with the tapers is the way to go. Running at 4 cu/in/min in 6061 is pretty easy to do with the right setup on the G0704, but AC's won't do it.

[RecceDG]

The problem with sticking with the quill setup is that it introduces lash into the system. It's probably manageable, but I noticed a nice increase in finish quality once I got rid of it.

If you are doing 6k or more, I highly recommend just going to a total loss oil system.

Pics/build thread?

[CL_MotoTech]

This sort of became a build thread. Though that wasn't the initial intention.

https://www.cnczone.com/forums/bench...958-posts.html

[DJEkim33]

I concur, but that appears easier said than done.

I have a Minipro belt drive kit that is going on. It replaces 206 with a straight shaft with a longer top extension. The pulley mounts to the OD of this shaft. The inside of the shaft is broached to fit the quill spines. OEM-sized bearings (205 and 207) are pressed on to this shaft, and it looks like the Naichis I bought (6209ZZE Nachi Bearing Shielded C3 Japan 45x85x19, 6007ZZE Nachi Bearing Shielded C3 Japan 35x62x14) are indeed for this outer shaft.

They are also permanently greased from the factory (?)

But as I look deeper into this, the collet is 246 and the only way to drive it is though the quill spines engaging with the interior splines on 206 - unless 206 is replaced with a solid assembly with solid "pucks" that take the place of 205 and 207, 246 is redone with a round shaft (instead of splined) and at least one more bearing is installed at the top of the now-round 246 shaft between it and 206, to support the top of the shaft against pulley loads (as the pulley now connects to 246 instead of 206).

That's a lot of work... and I think that the existing design already does a good job of isolating driveline loads from machining loads.

The fact that the only thing keeping the 249 spindle assembly from falling out is the 236-237 quill lock is hokey, but I don't see any other way to secure it.

So that returns to this: which are the aftermarket bearings to replace 248 and 248-1? (not 251 - that's the preload nut - my bad)

For some reason I'm not getting notices when the thread is replied to. This may be late but here are some answers to your questions.

Yes the 6209 and 6007 bearings are pre greased. I would avoid letting coolant get on them however as this will wash the grease out over time. That may have been my mistake as to why mine went out recently. But I was happy with 5 years of decent use.

I also agree that removing the top gear drive assembly with these bearings isn't the best or easiest to do. Unless you are trying to really push spindle speeds of the G0704 I would leave the design alone. If you remove this setup you will still need to support the splined section of the spindle some how where it meets the pulley for the belt drive. The spindle cartridge is too flimsy and the upper bearing too low to support torque being applied 4ish inches above it via a belt drive. People have achieved 13k rpm with the G0704 and an AC motor but they braced the spline section with a 6007 bearing and used AC bearings in the spindle cartridge. They were also doing a lot of 3d contouring with small cutters. If you want something rigid the AC bearing setup isn't it for this machine. In addition the top hub of the gear drive is a great place to mount a pulley.

The 248 bearings are the 32005 and 32007 which they make a wide variety of but I have had good results with the ones I linked. My spindle TIR is less than .0003 which I believe is mostly caused by poor machining of the spindle taper itself.

[CL_MotoTech]

I understand the concern regarding the moment on the quill sans a top support, however, that concern has been invalidated by my machine and my extensive testing. I run 2.2kw belt drive at 6k. I never needed a top support, not until I added the Belleville stack. I run my spindle in proper double shear in regards to the belt drive these days, but again, the PDB changed a lot of the forces that are seen. Those quill items proved a liability, and introduce variables that simply are not needed and in fact are a negative influence. Being out of balance is a good example. I have conclusively proven that removing the quill bearings, and running the belt directly to the quill is the best spindle you can get on a G0704. 7 years of testing and replacing bearings have proven this, but for the last two years I have been really good on bearings, though the spindle is still under sized and managing heat can be an issue since mating of the spindle to the head isn’t great for transferring heat. To take it to another level add the oil drip to the spindle bearings.

My top pulley isn’t broached. It just has a single set screw. Keep in mind my spindle peaks at 4kw, I’ve never overheated it or stalled it. It’s never broken a set screw. When I have had bearing issues, it’s always the lower, usually after lots of drilling. Like I said, it’s been a while though.

If the machine is a hobby where you play with it, tune it, okay. However, if you wish to machine parts then I would suggest heeding my advice. That said, you guys do you.

[DJEkim33]

I don't disagree and made that point in my last post. As did RecceDG who was asking the question. But he was asking a specific question about a specific setup he had. He wasn't asking how to go down another rabbit hole.

The whole point of my original post was to help folks locate a better version of the original bearings used. And avoid going down the AC bearing upgrade that was popular for awhile but many of us didn't get good results from. For the current price of $115 you can upgrade your bearings, run 6k rpm with the correct motor and get great results. I have zero balances issues with my setup that maintains all 4 bearings and the drive train. I run the machine probably 20 hours a week at 6k rpm and have done so for over 5 years before needing to replace the bearings I had installed. And with this setup I was able to achieve MRR of over 8 cu in in test cuts with the correct tooling and a 1.8kw servo spindle motor.

In the end to each their own but the purpose of this thread was to help people upgrade their tapered bearings and why that had advantages. There are plenty of other threads out there for different techniques but you don't see me commenting in them to "heed my advice" because thats the only way to make parts...

https://youtu.be/j3e2mKifIyo