# Spindle Bearing Replacement For The Rf-31 Mill/drill



## mikey (Jul 23, 2016)

​
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.


​
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.


​
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.


​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.



​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:





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




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.




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




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.




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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## LucknowKen (Jul 23, 2016)

Excellent how to Mike. Good job! 
One of their (Canadian) outlets is not too far from my shop.

FAG Bearings Limited
Address: 801 Ontario St, Stratford, ON N5A 7Y2
Phone: (519) 271-3231


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## Bob Korves (Jul 23, 2016)

LucknowKen said:


> Excellent how to Mike. Good job!
> (snip)


:+1:


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## mikey (Jul 23, 2016)

Thank you, Guys! I hope it comes in useful to someone.


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## Canuck75 (Jul 23, 2016)

mikey said:


> View attachment 132814​
> 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.
> ...






Mike

Looks like you did a great job but if you will forgive me I have a couple of observations. You said that you can install the angular bearings back to back or belly to belly but not opposite. I agree that they cannot be opposite but in this installation they still have a right and wrong way. If you look at the bearings you will see a wide side and a narrow side on each inner race. The same applies to the outer races. The preload in our installation is actually applied to the inner races  as the outer races are pressed into the quill top and bottom. In my view that means the wide side of the inner race must be down on the bottom bearing and up at the top bearing. It may well work the way you installed them, but in my humble opinion you are not going to realize the maximum axial or radial strengths the angular aspect of these bearings offer. I will gladly accept any information to prove me wrong but I think I am right.

Secondly, the installation of the top nuts and notched washer is a little opposite to convention. The bottom of these two notched nuts should bear directly on the inner race of the bearing and is tightened as necessary for preload. Then the tabbed washer is put on top followed by the top nut. The tabbed washer has one inner tab and the rest are outer tabs. The inner tab is captured by the spindle spline thus preventing any rotation. Now locate a tab that is aligned exactly with a lower nut notch (after preload) and bend it down thus capturing the bottom nut relative to the spindle and preload. The top nut is just brought up snug to the tabbed washer and bottom nut. Finding another tab that is aligned exactly with a top nut notch that tab is then bent up. I beg your forgiveness but the way you have installed the tabbed washer the tabs will not reach the top nut. They are meant to capture both so nothing can move or back off.

Respectfully
Canck 75


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## Canuck75 (Jul 23, 2016)

Mike

You mentioned that the RF31 spindle has many areas that dust/dirt/chips can ingress and I agree

On my machine there is a large access hole in the bottom of the head casting just behind the quill where dust/dirt/chips can and did get in, and from there to the top bearing as it did on yours. Also going by your pictures I don't see a knockout slot in the actual spindle so therefore a R8 spindle (drawbar), but there is in the quill. These slots also provide an ingress route for crud right into the quill just above the bottom bearing when the quill is extended. It is easy to see why the unsealed roller bearings could get gunked up so easy. By the way my spindle is R8 and the quill does not have a knockout slot. Many of these machines must have had taper vice R8 spindles resulting in some mix and match of parts in manufacture.

Using the sealed bearings is going to solve much of your problem, but further to that, you should make two plastic plugs for the sides of your quill and a plate to cover the bottom opening in the head casting (assuming yours is like mine). I suggest this because it will prevent gunk from getting onto the rack and pinion area on the back of the quill which is equally important.

Canuck 75


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## mikey (Jul 23, 2016)

Canuck, 
In my communication with FAG, they made it clear that the orientation I used is what is preferred. I don't know that it matters a great deal because the spindle does not sustain a large amount of axial loading. I will give this a try and see how it goes.

As for the positioning of the castellated washer, I am following the original installation and the order of components in the manual.




Are you sure about your order? I will admit that this is the first RF-31 I have worked on but have done a number of drill presses and all of them have the same arrangement. In a drill press at least, the castellated washer locks the preload nut and the top nut serves as a jam nut. I'm willing to admit I got it wrong but I don't think so.


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## mikey (Jul 23, 2016)

Canuck75 said:


> Mike
> 
> You mentioned that the RF31 spindle has many areas that dust/dirt/chips can ingress and I agree
> 
> ...


 
Yeah, my quill has those useless slots. Those Taiwanese copied the drill press design down to the stupid slots intended to knock out a Morse taper, in a machine that does not use a Morse taper. They're nothing if not faithful copiers. When I took the quill apart there was no debris inside, unlike the rest of the machine that had dust, dirt and debris everywhere. My thought was to leave them alone and see if chips made their way in before deciding to block them off. I'll keep your advice in mind, though.

I also have a hole in the head casting behind the quill and have made the template for a block-off plate to stop ingress of chips and debris. I'm trying to clean my shop up so I can move again and I'll get the plate done.


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## TomS (Jul 24, 2016)

mikey said:


> Yeah, my quill has those useless slots. Those Taiwanese copied the drill press design down to the stupid slots intended to knock out a Morse taper, in a machine that does not use a Morse taper. They're nothing if not faithful copiers. When I took the quill apart there was no debris inside, unlike the rest of the machine that had dust, dirt and debris everywhere. My thought was to leave them alone and see if chips made their way in before deciding to block them off. I'll keep your advice in mind, though.
> 
> I also have a hole in the head casting behind the quill and have made the template for a block-off plate to stop ingress of chips and debris. I'm trying to clean my shop up so I can move again and I'll get the plate done.



On my RF-31 clone I made a thin wall sleeve that I pressed into the quill to block off the slots.  I also made a seal carrier that replaces the lower bearing cap and a plate to block off the opening in the head casting.  All three mods work great at keeping swarf and coolant out of the lower bearing.  If you want to see pictures let me know and I'll post some.

Tom S.


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## Canuck75 (Jul 24, 2016)

Mikey.

Sounds like you have a good handle on the issues at hand. I'm now going to look at the drive pulley bearings to make sure they are okay.

With regard to the angular bearing orientation, this crosssection drawing shows what I am referring to. I don't understand why FAG suggested otherwise. In our particular installation, and the way you have installed them, the preload is driving the bearing races apart. The way I have installed mine, the preload drives the bearing races together - big big difference!     




Really appreciate trading ideas and information. These are great little mills. Here is a pic of mine hard at work making 1 1/4" wheel spacers for my Ford Ranger.


Cheers 
Canuck75


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## mikey (Jul 24, 2016)

TomS said:


> On my RF-31 clone I made a thin wall sleeve that I pressed into the quill to block off the slots.  I also made a seal carrier that replaces the lower bearing cap and a plate to block off the opening in the head casting.  All three mods work great at keeping swarf and coolant out of the lower bearing.  If you want to see pictures let me know and I'll post some.
> 
> Tom S.



Thanks, Tom. Yes, I would very much like to see what you've done. As simple as these machines are, there isn't a whole lot of info on this site about them. I'm thinking that the more we share and innovate the better off we, and all those that follow, will be.

I meant to credit Canuck75. He has shared what he's done and I hope to follow that example.


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## mikey (Jul 24, 2016)

Canuck75 said:


> Mikey.
> 
> Sounds like you have a good handle on the issues at hand. I'm now going to look at the drive pulley bearings to make sure they are okay.
> 
> ...



Yeah, I had a rather long discussion with my local bearing company last year about this very subject (bearing orientation). The gist of it was that the  configuration of the races are near mirror images of each other but there are small differences. That is why they suggest you install them either way but both must face the same way. I argued that this meant that if the bearing inscription pointed down on one bearing then it should point in the same direction on the other bearing - down. I was told no, if one faces down then the other should face up. I was doubtful but I listened to the guy. When it came to this project I asked FAG about it and they said it doesn't make a lot of difference either way but did confirm what the bearing guy said. I wish I kept that email but I tend to keep my inbox clean and I dumped it. Didn't seem important at the time. 

I think this is something we'll just have to wait and see. If my bearings fall apart and things go totally awry then I'll readdress it at that time. For now, I'm comfortable with what I understand and have done.

It seems like the RF-31 is a great little mill and a lot of people seem to like them. I don't know much yet but I will soon. Much of what I do is done for other people and I've been able to hold some of them off because my Sherline mill was too small. Now I don't have that excuse. Thing is, my Sherline is very accurate, is fully tooled up and has handled 90+% of the things I do. It has about 0.0001" of runout but has maintained it for over 20 years. I seriously doubt the RF-31 will be as precise as my Sherline but then again, I can do bigger stuff now. We'll see.


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## xman_charl (Jul 24, 2016)

castellated tabbed washer

notice there is a lot of variation in those tabbed washers.

shinny is from Grizzly, other is enco






Charl


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## Canuck75 (Jul 24, 2016)

Mikey
I'll just say one more thing on the angular bearings and then leave it alone. Look at that crossection and visualize how the load on one side, vice the other, affects the amount of inner/outer race contact with the balls. When the races are pushed together on a specific bearing the balls run on a large surface on both races. This is by design. When the races are pushed apart on a specific bearing (as in your installation), the angular contact angle flips, and the running surface contact with the balls is greatly reduced.

Just for interest I have made the following mods to my mill:

a. quick release belt tensioner
b. angular quill bearings
c. longer X and Y adjustable nuts
d. rack accurately pinned to the column with tight guide blocks on the head to maintain X setting after head height adjustment
e. locking screws on the back end of the gibs to reduce dovetail clearance
f. windlas system inside the head to exert return pull on the quill instead of the pinion to get rid of Z backlash
g. torrington thrust bearing on the drawbar to improve the tightening force on the collets
h. 3 axis Yadro DRO system
i.  motor reverse witch
j. cover plate for the bottom hole in the head casting      
k. grade 8 head clamp bolts vice the grade 5 (or less) originals

Cheers
Canuck75


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## mikey (Jul 24, 2016)

Maybe do some pictorial "how to's"? I think there is a silent group of RF-31 guys out there who would be interested, including me.


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## Canuck75 (Jul 24, 2016)

Mikey

I too am interested in anything H-M members do to theses machines. Regards to some of the mods that I have done, surf this forum for any threads posted under Canuck75. I tried to enclude as much detail as possible and photos. Always happy to answer questions.

Canuck75


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## TomS (Jul 24, 2016)

mikey said:


> Thanks, Tom. Yes, I would very much like to see what you've done. As simple as these machines are, there isn't a whole lot of info on this site about them. I'm thinking that the more we share and innovate the better off we, and all those that follow, will be.
> 
> I meant to credit Canuck75. He has shared what he's done and I hope to follow that example.



I'll take some pictures tomorrow.  Worked all day in the shop in 107 degree heat.  Not anxious to go outside at the moment.

Tom S.


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## TomS (Jul 25, 2016)

mikey said:


> Thanks, Tom. Yes, I would very much like to see what you've done. As simple as these machines are, there isn't a whole lot of info on this site about them. I'm thinking that the more we share and innovate the better off we, and all those that follow, will be.
> 
> I meant to credit Canuck75. He has shared what he's done and I hope to follow that example.



Here are the pictures.  I did these mods about five years ago.

Tom S.

The lower seal housing is made out of aluminum.  I sourced a double lip seal that fit the spindle snout then made the seal housing to fit the seal.  I added a couple of holes for a spanner/pin wrench.





The cover plate was made from a scrap piece of 18 or 20 gauge steel.  



Sorry for the fuzzy picture.  You can see the sleeve through the slot.  As I recall I had to bore the quill then make the sleeve.


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## mikey (Jul 26, 2016)

Thank you, Tom. I had intended to make the plate under the head. Now that you and Canuck have both recommended sealing the quill ports I guess I'll have to take a good look at how to implement that, too. 

That's a serious seal you made to cover the lower bearing. I don't think a chip could get past that!


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## Ludvigsen (Mar 5, 2019)

Thank you guys, it is very helpful information. By the way, do any of you replaced the ball bearings on the spindle taper sleeve and can give any information on the ball bearings? I have just removed the quill and spindle and removed the ball bearings and trying to find a supplier for it. So now I can't take off the spindle taper sleeve as I have nothing to hold back on to remove the nut. I would like to buy bearings for the spindle taper sleeve also so then all should be i top shape.

By the way the drawing for the the spindle shaft is wrong, on mine Rong Fu RF31 mill, the tabbed washers was in between the two nuts, not like on the drawings, below the two. but it only locked to the top nut but I guess you could just as well lock both nuts with the tabbed washer.

thanks for the help.

Brg Knut Erik


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## Investigator (Mar 5, 2019)

Do you mean the drive sleeve bearings?

Drive sleeve bearing replacement


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## mikey (Mar 5, 2019)

What he said ^^^

The tabbed washer's function is to maintain the position of the preloading nut, whether it sits above or below it. As long as the lower nut maintains its position, it works.


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## Ludvigsen (Mar 6, 2019)

Investigator said:


> Do you mean the drive sleeve bearings?
> 
> Drive sleeve bearing replacement


yess..


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## Ludvigsen (Mar 8, 2019)

Hi Guys

I thought I make an addition to the information found here. I have spent most of the evening figuring out all the dimensions on the quill and the spindle, and made a rough drawing of it as to help myself to get an understanding of the positions of the upper and lower bearings in relation with the quill.  I have made some notes on the sheet but the picture didn't come out so good so I think it might be an good idea to write it here to.

When the lower bearing have a race of 17mm. and the original has 18mm. the result is then that the spindle goes 1mm. deeper into the quill.
This gives us 229mm. from the lower bearing to the shoulder where the upper bearing are "supposed" to be on the spindle.
When you look at the quill you will see that from the upper surface of the lower ball bearing to the upper shoulder of the quill is a length of 238mm. This is a difference of 9mm. longer and it will make the upper ball bearing lay on the quills shoulder and not on the spindels shoulder, the lower side of the upper bearing will be about 9mm. above the shoulder of the spindle. And the ball bearing will have 13mm. of its surface to rest on the spindle surface not on it's full 16mm.race. The adding mikey did with the 2mm. thick spacer is on it's place..... It seem to me that the upper bearing should have had a larger surface of the race to rest on, to short/bad engineering?


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## Ludvigsen (Mar 8, 2019)

If anybody want a copy of the drawing, mail me and I send you one. I have checked the number several times and i get to the same result every time, so I guess they are fairly good. I had to make the drawing due to the numbers did not seem to add up, but with the drawing i scale 1:2 I got the picture and could see how the relation was between the quill bearing and the spindle. I got my FAG bearings at a price of 4325bath it's 135$ US from FAG supplyer her in thailand, but one thing I like to ask, shuldent you need the same quality/precision on the drive sleeve bearings also but you only radial?

BRG's
Knut


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## mikey (Mar 8, 2019)

Knut, I admit that I'm not clear on what you're trying to say with your numbers. Could you clarify?

As for the radial bearings on the drive sleeve, they do not sustain any axial load. They only need to constrain the radial loads at the spindle at the top. Therefore, radial bearings are sufficient and a normal accuracy class is fine. Deep groove bearings can sustain heavy axial and radial loads anyway so they are a very good choice for the drive sleeve.


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## Ludvigsen (Mar 9, 2019)

Hi mikey

the numbers I'm talking about are  the dimensions of the quill and the spindle. I was working late last night so I see the the drawing contain an error but the dimensions are all right. The error is the drawing around the upper bearing, on the drawing the upper bearing is resting on the shoulder of the spindle but in real life it's lying 9mm. above it and resting on the shoulder of the quill. I am going to make a new drawing.
as I said, the reason I made the drawing is to get an understanding of where the ball bearings position on the shaft and the quill, before I start to assemble it, so nothing gets *****d up.

Thank you for the information on the sleeve bearings .

BRG's knut


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## mikey (Mar 9, 2019)

The placement of the bearings is defined by the shoulder on the lower end of the spindle itself (that one fits into the lower end of the quill and stops at a shoulder inside the quill) and the shoulder at the upper end of the quill. The replacement FAG bearings are each 1mm thinner than the stock bearings so a 2mm or thicker shim is required to allow the bearing preload to be set properly. The distance between the bearings is what it is on your machine but their limits, the shoulders, are what determines their positions.


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## Ludvigsen (Mar 9, 2019)

Hi Mikey

Thats exactly what I wanted to see. that was the intention with making the drawing, to give me a visualization of the relation between the quill and the spindle.

 I thought it (the upper bearing) should rest on the upper shoulder on the spindle. but I was surprised to see that only 13mm. of the 16mm. race of the upper ball bearing was touching the area  of 30mm. diameter surface. About 3mm of the ball bearing is above it. when the outer diameter is resting on the shoulder of the quill.

The 30mm. diameter for the upper ball bearing is 22mm. long so the ball bearing is 9mm. above the shoulder of the spindle and then the ball bearings race is 16mm wide, so it seem to me that this area on the spindle on my mill is 3mm. short. 9mm. +16mm.=25mm and I only have 22mm. I dont know if this is the same on all RF31's or if it realy make any difference, these figures are checked and rechecked several times but I get to the same measurements every time. One thing is sure and that is that it should not be any problem to press the bearings on the spindle or the quill. But one thing I think now is that I need to measure the gap between the nut and the upper ball bearing before I complete lock the spindle bearings.

I bought my mill new a year ago, and did not start use it for more than about a week ago, after a couple of cut it came intolerable noise from the quill area, I thought that the bearing was dried and that's the reason for the noise. But no the grease was fine so there is something else that caused the bearing(s) to break down I can't tell. I just have to wait till I get the new bearings and see how it all aligned and measure it to see if everything is all-right and then I am thinking about the 2mm. spacer the preset pressure, god knows what that is supposed to be? "only to be tight enough to hold it in place?

I am a beginner with mechanics, so I might go the idiot way to figure it out. so with this, no offense meant Mikey the information you gave in the description of disassembly and assembly is good, but I just need to go this way to assure myself and I like making these drawings , and I'm not of english origin (Norwegian berserk) so it's take some time to formulate and use the right terminology, both English and mechanical. 

knut


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## mikey (Mar 9, 2019)

No offense taken, Knut. Once you get in there and see how it all lines up I think you'll see what I mean.


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## Ludvigsen (Mar 10, 2019)

so, I have continued "working" on my spindle and the quill and tried to turn the nut down the shaft and I could turn the nut all the way down over the groove above the locking nut has "no stop". So how to know how much I need to tighten the nut, how big torque, should I just tighten it easily and lock it? and it's more, when looking at the lower bearing: it's lying on the lower part of the spindle this part has a diameter of 62 millimeter and that mean that this surface are covering both inner and outer part of the bearing!! i should make a spacer here as only work as a spacer for the inner part of the bearing of 40mm  don't you think? here is the link to FAG's lower bearing https://medias.schaeffler.com/medias/en!hp.ec.br.pr/72..-B-2RS*7207-B-XL-2RS-TVP . where d2 is say 45mm. so 40mm x 1mm. spacer should be good for compensating and correcting for should be good and take a one millimeter thickness disk, when I am looking at Mikey's spindle I can see that it's different from mine, as you can see on this updated drawing :


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## Techee (Feb 20, 2020)

Mikey & Canuck75, thank you for this thread.

A question for both of you;

How are the bearings performing in both of your mills?

I have a Central Machinery, Chinese,  Grizzly G0705 copy that I bought new from a guy that never used it.  I stole it for $500.

 I am surprised at how good the  quality is, but I am looking at doing this bearing replacement.

Thanks guys!


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## mikey (Feb 20, 2020)

Mine is basically unchanged since I did this bearing replacement - still accurate, temp hasn't changed so preload is stable and there have been zero issues. If you do change the spindle bearings, I would also change the drive sleeve bearings while you're in there. It makes a big difference and will reduce wear on the spindle bearings.


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## Techee (Feb 20, 2020)

Thanks Mikey.

Do you have drive sleeve bearing recommendations?


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## mikey (Feb 20, 2020)

Yup, here you go.


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## Techee (Feb 22, 2020)

No attachment visible


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## mikey (Feb 22, 2020)

See the highlighted/blue text in the post above yours? That's a hyperlink to the article with bearing info.


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## Techee (Feb 23, 2020)

Thanks Mike!

Jack


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## DavidR8 (Mar 9, 2020)

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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## mikey (Mar 9, 2020)

If you can get them for that price, I would do it. P5 bearings usually aren't that cheap.


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## DavidR8 (Mar 9, 2020)

@mikey Ordered!


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## DavidR8 (Mar 26, 2020)

My bearings arrived today!
Maybe I'll swap them out before I put the table back on for my DRO install.


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## mikey (Mar 26, 2020)

Keep us posted, Dave.


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## DavidR8 (Mar 26, 2020)

mikey said:


> Keep us posted, Dave.


Mike can you confirm that the bearings have different inside and outside diameters?


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## mikey (Mar 26, 2020)

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.


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## Old96er (Apr 6, 2021)

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...
> 
> View attachment 316232



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.


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## DavidR8 (Apr 6, 2021)

@Old96er This is where I got mine.





						Homepage
					






					www.bdiexpress.com


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## Old96er (Apr 8, 2021)

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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## djs1234567 (Jun 14, 2021)

mikey said:


> ​​​​​​View attachment 132814​
> 
> 
> 
> ...


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


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## samasher (Nov 11, 2021)

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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## Canuck75 (Nov 12, 2021)

Techee said:


> Mikey & Canuck75, thank you for this thread.
> 
> A question for both of you;
> 
> ...


Techee, sorry about the time delay but have just looked back at this thread. Like Mikey, I too am very pleased with the double sealed angular bearings. No issues whatsoever since install. If I run the mill at 3000 RPM I can feel the spindle warming up after about 20 minutes, but the spindle still rotates freely so isn't "tightening up" thus indicating too much preload. It's great not to have to think about greasing those bearings. Great investment.


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