# G0704 CNC mill spindle rebuild.



## COMachinist (Jan 8, 2021)

Hi every one.
I have a G0704 CNC conversion and the spindle bearings need replacement. I have decided to go with Nachi tapered rollers this time. The angular contact bearings, I used during the first build had about 2 thou run out for some time now. I have seen the Nachi bearings being use in rebuilds and new conversions. So I have ordered the Nachi bearings. I have been trying to figure out preload and how to set it. I will be using Kluber lub and will be making a better top retaining nut to better load and keep preload consistent over the long haul. I have seen run out number in the mid tenths of a thou. I found the angular contacts to have a higher than I like maintenance need. Any help with this rebuild will be greatly appreciated.
Thanks for looking.
CH


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## macardoso (Jan 8, 2021)

I went through the rebuild of the G0704 spindle in this thread, right at the beginning. The process isn't too bad. I went with the AC bearing route, and have 0.0003-4" TIR at the spindle taper. I am pretty confident that most of this is error in the taper grind and not the bearings. The ones I purchased ($120 for the pair) should have ~0.0001" TIR when properly installed.









						G0704 CNC AC Servo Rebuild (Picture Heavy)
					

Hi All,  About 5 years ago I completed a CNC conversion of a Grizzly G0704 milling machine. Like everyone at that time I chose to go with the Hoss Machine style conversion as there were not many options on the market. I was not comfortable designing my own system at the time since I was just...




					www.hobby-machinist.com
				




I built a set of tools to disassembly the spindle nuts which are currently in the possession of @bakrch, I am pretty sure at least. If he is done with them, I am fine with you borrowing them at your expense of shipping. They aren't anything fancy, but it might make your life easier.

Preload is set by the "adjuster nut" in the spindle. A very light preload is all that is needed or the spindle will get HOT.

You should probably invest in Kluber IsoFlex NBU35 spindle bearing grease. It is expensive but appropriate in this application. I found a company selling portioned out quantites of it for $35 or so. You'll also need a dosing syringe (if you have a pet, grab a few from your vet) to measure the correct fill of grease (~30% of the free space of the bearing).


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## COMachinist (Jan 8, 2021)

macardoso said:


> I went through the rebuild of the G0704 spindle in this thread, right at the beginning. The process isn't too bad. I went with the AC bearing route, and have 0.0003-4" TIR at the spindle taper. I am pretty confident that most of this is error in the taper grind and not the bearings. The ones I purchased ($120 for the pair) should have ~0.0001" TIR when properly installed.
> 
> 
> 
> ...


Yeah I went the AC route twice and none last long at all. The original set started out great great about .0006, but after about 10 projects they ended up with .004 run out. The second set has less than 15 jobs on them and finish sucks big time. So it is Nachi and back to tapered rollers. Factory rollers last 3 times as long as the AC sets. Hey thanks for the tool use offer, but I have long since made pin spanners for both ends of the spindle. I think the problem is the adjuster nut, it just want stay tight. The nut will nut fit tight and every time I did maintenance on the spindle the nut just was not tight. So I‘m going to make a good fitting 2 piece single point threads 24mm 1.0 . I wish I could find a beeper or better machine spindle to fit it. I sa one on you tube from a guy out in Kaliforina, that looked beefier and longer but he is a west coast nut, he never tells you the facts of part numbers, sizes or any thing else. It is worse than finger nails on a chalkboard with constant “So Yeah’s” I his farther did all the machine work on his G0704, it is really a nice machine, but he don’t really know thread sizes, or pitchs. I think he is an idea man and has his work done by real machinist. So if you know of a better spindle for it please let me know. 
l been wondering if the PM25MV or PM 727 spindle would interchange, they are made by the same factory I think.
CH


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## bakrch (Jan 8, 2021)

I do have @macardoso 's tools. Funny timing. I also had issues with my AC bearings (figuring it was my fault, though) and ready to put the Nachi 32005/32007 in.


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## macardoso (Jan 8, 2021)

bakrch said:


> I do have @macardoso 's tools. Funny timing. I also had issues with my AC bearings (figuring it was my fault, though) and ready to put the Nachi 32005/32007 in.



Interesting. I smoked my first set from being way too tight, but this second set is running beautifully so far. Please share the taper roller bearings you select. I had a hard time picking out precision ones when I looked years ago.


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## COMachinist (Jan 8, 2021)

bakrch said:


> I do have @macardoso 's tools. Funny timing. I also had issues with my AC bearings (figuring it was my fault, though) and ready to put the Nachi 32005/32007 in.


I think some of the problem is the poor machine work on the spindle. I know my adjuster nut threads on crooked It’s like they used a die witch was not strait and kind of cross threaded. The preload is not even across the bearing and puts uneven loads on the spindle. I looked on the parts list on Grizzly sit and they list a v2 spindle part #PO 704246 V2.08.11 $90.00. Mine is just the worst machining I have ever seen. Before I just never looked at it close enough.
CH


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## macardoso (Jan 8, 2021)

COMachinist said:


> Yeah I went the AC route twice and none last long at all. The original set started out great great about .0006, but after about 10 projects they ended up with .004 run out. The second set has less than 15 jobs on them and finish sucks big time. So it is Nachi and back to tapered rollers. Factory rollers last 3 times as long as the AC sets. Hey thanks for the tool use offer, but I have long since made pin spanners for both ends of the spindle. I think the problem is the adjuster nut, it just want stay tight. The nut will nut fit tight and every time I did maintenance on the spindle the nut just was not tight. So I‘m going to make a good fitting 2 piece single point threads 24mm 1.0 . I wish I could find a beeper or better machine spindle to fit it. I sa one on you tube from a guy out in Kaliforina, that looked beefier and longer but he is a west coast nut, he never tells you the facts of part numbers, sizes or any thing else. It is worse than finger nails on a chalkboard with constant “So Yeah’s” I his farther did all the machine work on his G0704, it is really a nice machine, but he don’t really know thread sizes, or pitchs. I think he is an idea man and has his work done by real machinist. So if you know of a better spindle for it please let me know.
> l been wondering if the PM25MV or PM 727 spindle would interchange, they are made by the same factory I think.



The spindles should be interchangeable but I don't think anyone is going to guarantee that for you. You can learn for the rest of us 

I've thought about turning my own and having it heat treated and ID/OD ground but at the end of the day it is just a G0704 and I guess I've gotten lucky and been OK. Spindle runs a touch hot but otherwise I still have 0.0004" TIR and it leaves good finishes. I figure if I want something better, my best bet will be to buy a purpose built CNC machining center and refurbish it. 

Be careful with the spindle threads. At least the ones at the end of the spindle for the retaining cap are non-standard. I had to measure them for pitch and PD over wires to make a mating piece. I'd worry the adjuster nut threads would also be non-standard.


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## COMachinist (Jan 9, 2021)

Well I looked at the parts list from original 704 and it just listed a 704246 spindle on a later 704 parts list it lists that part “no longer available” the list shows the V2 as the replacement.  Anyway I’ll let you know when it comes.
CH


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## bakrch (Jan 11, 2021)

macardoso said:


> Interesting. I smoked my first set from being way too tight, but this second set is running beautifully so far. Please share the taper roller bearings you select. I had a hard time picking out precision ones when I looked years ago.



I just grabbed these, looked good enough for my purposes. I was a little rough installing the AC bearings, so I can't tell if it was that or too much preload. 

For these I will make wooden guides to keep the heat from sinking out too fast, then I'll slam them down nice and quick.  I may even take the spindle into work and polish or turn it down a bit on a big/rigid CNC. 









						32005 Nachi Tapered Roller Bearings Japan 25x47x15
					

32005 Nachi Single Row Tapered Roller Bearing Made in Japan One Bearing 32005 is nachi single row tapered roller bearing, the cage is Chrome Steel, 32005 inner diameter is 25mm, 32005 outer diameter is 47mm and 32005 width is 15mm. Item: 32005 Nachi Ball Bearing Type: Nachi Tapered Roller Ball



					www.vxb.com
				












						32007 Nachi Tapered Roller Bearings Japan 35x62x18
					

32007 Nachi Single Row Tapered Roller Bearing Made in Japan One Bearing 32007 is Nachi single-row Tapered roller bearing can support a combined radial and axial load, the cage is Chrome Steel, 32007 inner diameter is 35mm, 32007 outer diameter is 62mm and 32007 width is 18mm. Item: 32007 Nachi



					www.vxb.com


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## COMachinist (Jan 13, 2021)

Ok I got the new V2 G0704 spindle to from grizzly. Does look like it is nicer machined work on it. Here is a photo. I have not done and inspection on ityet just by the seat of the pants look and a photo side by. I‘ll get some mics and DTI do a comparison of the spindles. I got 1/2 the Nachi bearings today as well. From the look of them there won’t be any need for shims like we used on the AC bearings. The new on left


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## macardoso (Jan 13, 2021)

If you have vee blocks, can you roll it on the front bearing race to get a runout reading of the taper?


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## COMachinist (Jan 15, 2021)

I got the Nachi bearings tonight in the mail box. Now, do I need to shim the Nachi bearings like we did the AC bearings that are much thinner than stock tapper bearings? I have the shim washers from the AC bearings and just need to know if they need to be shimmed to preload them? As always help is greatly appreciate. It looks like the new spindle is the same dimensions as the older spindle just better machined.
thanks for looking
CH


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## COMachinist (Jan 16, 2021)

Never mind found a post on another forum, these are direct factory replacements. LOL HSM.
CH


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