Spindle Bearing Replacement For The Rf-31 Mill/drill

My bearings arrived today!
Maybe I'll swap them out before I put the table back on for my DRO install.
 
Yes, they do. The 7206 has an OD of 62mm and an ID of 30mm. The 7207 has an OD of 72 and an ID of 35.
 
DavidR8 said:
I'm working on ordering a set of these bearing. Looks like part numbers have changed slightly in the intervening years.
Seems now it's as shown. The supplier is confirming that they are sealed.
Cost is $44 for the 7206 and $47 for the 7207. Not sure why they are $3 different...

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I am doing this exact same job and ended up with the same conclusion on what bearings to use before checking the forum. I could have saved a lot of time. Doh! Anyway, do you mind sharing your supplier? (PM is fine) That is a very good price.
 
Thanks for the replies fellas, I am looking through them now. I will start another thread. I don't want to hijack this one any more than I already have.
 
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mikey said:
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During my quest to eliminate the excessive runout on my RF-31 Mill/Drill I determined that the spindle bearings were a major contributor. As you can see, these bearings have seen better days. In addition to being filthy, they have not been maintained and have worn much earlier than they should have. Rather than find a direct replacement I wanted to use sealed/lubricated for life/maintenance-free angular contact bearings because the construction of the head on the RF-31 provides multiple areas for ingress of dust, dirt and chips that will eventually end up on the exposed upper spindle bearing. This is not good for longevity so I wanted to eliminate the possibility.

Surprisingly, this doesn’t appear to be a common mod as information on this subject turned up little. However, one of our very own HM members, Canuck75, did this exact job. I contacted him and he encouraged me to go for it and suggested that I provide a detailed write up for the benefit of the other RF-31 owners on our forum. This post is to honor that request.

The bearings we used are from FAG, a German maker of precision bearings:

Upper: FAG 7206-B-XL-2RS-TVP

Lower: FAG 7207-B-XL-2RS-TVP

· These bearings have the exact same dimensions as the stock bearings but are each 1mm thinner, which is a minor issue I’ll touch on later. Both are rubber-sealed on both sides and lubricated for life.

· They are single row angular contact bearings so they must be used in pairs as we are doing here in order to sustain the bi-directional axial loads a spindle experiences. These bearings have a 40° contact angle, which means they can sustain large axial loads while handling very high radial loads as well.

· The XL designation means the raceways have an improved geometry and are precision-honed to improve their load bearing capacity.

· The TVP suffix means the cage is made from glass fiber reinforced polyamide, not metal.

· They are accuracy class P5 bearings, the equivalent of ABEC 5. They are probably much more accurate than the spindle and quill are.

Cost will vary with your source and luck. I was able to find both brand new for under $100 but retail for them is somewhere around $300.00 or so.

I contacted FAG for instructions on installation procedures, preloading specifications and their recommended break-in procedure for these specific bearings. Here is what they had to say:

Normally, in a spindle, you have a break-in routine to distribute grease because the bearings are usually un-sealed. But these bearings are sealed and lubed for life, and more robust than your average spindle bearing, so there is no need for that. The newer x-life products (-XL suffix) have such finely honed raceways that there is no measurable burnishing of the surface finish. [Therefore] no special run-in required.

There are a dozen variables that could influence the running temps of your bearings, and we know virtually nothing about your system. So it is not possible to predict what temps your bearings might see. But the upper operating limit of your bearings is limited by the cage, seals, and the grease, and should not exceed 100 deg. C. A good target would probably be 75-80 C max. More than anything, you should expect to reach a steady-state temp within about 30 minutes. If you do not reach steady state, or if you rise above these temps in a short time, that might be an indication of excessive preload.

As I said, these bearings must be installed in pairs; they can be installed either back to back or belly to belly, meaning the inscribed bearing designation on one face can face in or out but both must be facing the same way – X/X or O/O but not X/0. Supposedly, X/X is slightly stronger (inscriptions facing out).

FAG emphasizes in their literature that installation forces should be applied only to the race being pressed to avoid brinelling (the permanent indentation of a hard surface) of the precision-honed races. Therefore, pressing adapters that contact only the race involved is wise. They also advise the use of an arbor press, not a hammer. (Sorry, I know us hobby guys love to use our hammers but this is not one of those times.) I used a Dake hydraulic press for this project and it worked fine, albeit with less tactile feel than an arbor press would give.

The press fits are only about 0.0002” so there isn’t a lot of force involved. However, alignment and the application of force to the right area is critical so I made pressing adapters from solid aluminum rod as I had trouble finding pipe of the appropriate size – that’s a lot of boring! The largest adapter is 2.8” OD.

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The adapters on the left and center are used on the lower bearing. The one on the right is used on the top bearing and engages both inner and outer races at the same time; this is fine according to FAG since the two races are the same thickness and pressure applied to both races at once will not stress the internal bearing surfaces. Each adapter is sized to just fit the width of the race it is intended to contact.

Procedure:
Remove the quill from the head. This is a simple job that involves removing the depth stop, quill return knob and quill return spring along with the spring anchoring screw and quill alignment pin. Be sure to lock the quill before you remove the pinion shaft. Once the pinion is removed, catch the quill as you unlock it. The locking cotters can remain in the head.

With the quill removed from the mill, remove the little cap overlying the lower bearing. Mine is aluminum and is a right hand thread that comes off easily.

Now the spindle can be pressed out of the quill from the top. This leaves the lower bearing still on the spindle and both bearing races in the quill. The upper bearing just lifts out and off the upper spindle.

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After pressing the lower bearing off the spindle the next step is to remove the races from the quill.

The lower race comes out with some judicious tapping with a 3/8” steel rod and hammer behind the race. There are two access slots in the quill casting to allow a good angle for this. Tap alternately on both sides until the race releases.

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Removing the upper race is problematic because you can’t angle a drive rod behind the race. Fortunately, I previously made a race removal tool to do this very job on sport bike steering stem bearings and it came in really handy.

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The tool is inserted so the fingers face the race. As the tool is pulled up through the quill the fingers snap in behind the race and engage at four points. Then a few solid taps with a hammer on the head of the tool and the race pops out easily. The tool is just a length of thin-gauge stainless pipe with two through-cuts made on the band saw. The fingers are bent outward by hand, and the head is an aluminum slug. It isn’t something you’ll use often but when you need it, you need it.

Once everything is cleaned, the bearings can be installed. The manufacturer makes a big deal about cleanliness when installing their bearings. I wiped each contact surface with alcohol until the paper towel came away clean and then used a microfiber towel before I blew the area out with air and applied a light coat of oil. The bearings were unwrapped just before installation.

Here, the smallest adapter is being used to press the inner race of the lower spindle bearing in place:

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Then the lower bearing outer race is pressed into the lower end of the quill:

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Once the lower bearing is installed, the upper bearing can be pressed onto the upper spindle. The upper bearing is supported underneath by the aluminum adapter that rides on the rim of both the inner and outer races. I applied force to the lower bearing rim with the large adapter and got the upper bearing in but had to also apply a little follow up pressure on the spindle nose to be sure both bearings were bottomed out.

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Again, these bearings are installed back to back so that their inscriptions face out.

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Recall that I said these bearings are 1mm thinner than the tapered bearings they replace. It turns out that this matters because the preload nut has a limited amount of downward travel. At this limit there is about a 1mm space between the bearing and the tabbed washer so the bearing cannot be preloaded. Therefore, a spacer with the dimensions of 1.4” OD X 1.2” ID X 2mm thick was made from 6061-T6 Aluminum to take up this space. Aluminum is fine for this purpose – it just needs to solidly take up space between the inner bearing race and the tabbed lock washer. You can just see it under the tabbed washer in the pic below.

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The castellated tabbed washer is placed on top of the spacer (Note: the castellated washer has a downward-pointing tab that must fit in a groove in the spindle) and the preload nut is threaded on – LEFT HAND Thread; the beveled edge of the preload nut faces the bearing. As these bearings do not have a specific preload value I just snugged the first nut very firmly with a spanner and a spindle wrench and engaged one of the washer tabs. The second nut is firmly tightened down on top of the first one and the spindle is complete and ready for installation in the mill. The Luminar 28mm spindle wrench held the spindle solidly while tightening the preload nut and I can recommend it.

I checked runout at the bench with the quill clamped down firmly. Runout was less than but close to 0.0001” TIR. The quill was then installed and the bearings were run at 1800 rpm for ½ hour.

I checked the temps directly at each spindle bearing with an infrared thermometer to be sure that preload wasn’t excessive. Both bearings leveled out at 41.9°C at 25 minutes and then the temperature remained stable.

Run out was checked with a Compac 215GA inside the R8 taper after the bearings were hot; it was 0.002”TIR. While this was disappointing I knew the spindle was running pretty true so the runout I was seeing had to be due to the drive sleeve bearings, which it was. Runout after the drive sleeve bearings were changed dropped to less than 0.0001” TIR. (I’ll discuss the drive sleeve bearings in another thread.)

Overall, this is a very simple maintenance step that will reduce runout and the need for bearing maintenance for the useful life of the bearing. Once the pressing adapters were made it was done in under 5 minutes.

Once again, my thanks to Canuck75 for doing the legwork to find the correct bearings!



Mike
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Hi Mike, and thanks to all that have this machine and all the great advice and option to do with it.

I am sorry that I am about 5 years late to this party, (LOL) but I just got a used RF-31 (made in Taiwan) that I had written you (MIKE) and a few of the others about a few weeks ago. I have also decided to replace these bearings, but am going to use the same tapered one that came with it.
these are numbered, 30206JR and 30207JR by Koyo. waiting for them to arrive.


My questions are, being from a grease monkey's point of view, so please take it from where it comes. Everything you folks will tell me here is a learning curve as I am a newbie (machinist) at this and would love to get as much info as possible.

1. I am having a hard time seeing how you preload these bearings because once installed, both of them sit on the lip ( or a shelf )of the shaft that appears that the bearings are pretty much locked into position. So wouldn't that make it a predetermined distance that already exists?

With a vehicle, if you're doing a brake job that has those types of bearings, the back bearing is up against the spindle lip, which holds that bearing in place. and the front bearing is pushed up against the race by the castle nut which allows the rotor to be pushed into place so you can set preload.

2. the way mine is set up, when I disassembled it if it differs from other RF-31's, is that upon reinstallation, you install the lower bearing and seat it against the lip and insert the shaft into the quill, and then the top bearing has to be pressed on down to the lip where it seats?
once that is done I believe that the preload is set??? and the nuts just hold the bearings in place? because you can't go any further down past that lip? when you press the upper bearing into place which squeezes the shaft in place? unless you only press the bearing down far enough and install the first nut to set preload allowing the nut to seat the bearing? If so, than why have the lip there at all? also, the upper bearing was pressed onto my shaft.

3. According to the manual, the castle washer is put on top of the bearing. then the 2 nuts follow. As you have in the picture. mine was as follows, 1st nut over the bearing followed by the washer than 2nd nut. the castle washer was pinned up against the top nut. I don't know which is right?
The machine was made in Oct 2002, I believe that it was never serviced. So, If not talking to you guys I would think the nut, washer, nut sequence was correct?


4. The bottom bearing is the larger one which the small side of it (35mm) faces up toward the top of the quill and the upper bearing which is the smaller bearing and the smaller face of it (30mm) faces down toward the tabletop, that is what allows you to preload?

I hope I explained in enough detail and did not throw too much junk in. ALL advice would be wonderful and greatly appreciated! Thanks, Jay
 
This is a most enlightening thread and very helpfully instructive. However, I was uncomfortable with all the discussion about pre-loading. It seemed difficult and I wasn't sure about how necessary it might be. I went looking on the internet. It didn't take that long to find this instructive video from H&W Machine Repair in Ft. Wayne, IN: youtubeDOTcom/watch?v=UPJhq9POdAA Barry rebuilds (among other machines) Bridgeport Milling Machines – for a living! Barry looks like he's been doing it for a while. He shows every step and he explains every step. OK, Bridgeports are not round column Chinese RF30 mill-drills. Chinese RF30 mill-drills are like Volkswagens. You can do almost anything with them and to them. Watch the video. You'll recognize a lot. Near the end of the video, as he's reassembling the spindle into the quill he says that Bridgeport has no torque specifications for tightening and locking those big flat nuts that hold.the bearings in with the tabbed locking washers.

Bridgeport has NO torque specifications for tightening and locking those big flat nuts that hold the bearings in with the tabbed locking washers.

Bridgeport

Let that sink in.

So what does Barry do? He goes on to say (and show us) how he just snugs them up.

Bridgeport! Barry does this for a living. He never once said, "pre-load."

I got Timken bearings for my main drive shaft and NTN Japanese bearings (ntnamericasDOTcom) for the spindle. I don't really figure I can "make a silk purse out of a sow's ear." I already did the main drive shaft. Soon I'll complete the spindle bearings. I'm 70 years old. I will have only done this once – probably the only time in my entire life. But I'm comforted by having Barry from H&W Machine Repair in Ft. Wayne, IN show me what I did and DIDN'T have to do. I'll post when I'm completely done. If I screw up, everyone can say whatever.
 
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