# Boring To Seat A Ball Bearing



## prasad (May 14, 2016)

I have a task where I have to cut a few holes or bore to seat a ball bearings. The part is aluminum bar, nearly 36 inches long and therefore this work can not be done on my 9x19 Grizzly G4000 lathe. The other machine I have my mini-mill. I have tried test cuts using my milling cutters. I ran into two problems. 
1. I don't have milling cutter of the right diameter to suit the bearing diameter. 
2. The surface finish I got when I plunged the end mill into aluminum was not smooth like I would get if I had cut this bore on a lathe. 
Would a new end mill of the same diameter as the ball bearing work? 
How to get better surface finish? 

I will buy new end mill cutter(s) if there is a solution to my problem. Seeking your advice, 

Thank you
Prasad
Eastern PA


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## Ulma Doctor (May 14, 2016)

you may wish to drill/mill slightly undersize and ream the hole to desired dimension.
both operations could be done with a hand held drill if the bores are not relatively large


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## JimDawson (May 14, 2016)

Ulma Doctor said:


> you may wish to drill/mill slightly undersize and ream the hole to desired dimension.
> both operations could be done with a hand held drill if the bores are not relatively large


:+1:


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## Wreck™Wreck (May 14, 2016)

Is the ball a fluid seal?


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## Tony Wells (May 14, 2016)

A common terminology issue that needs to be clarified. Is this a single ball, or a ball bearing assembly with an inner and outer race and individual balls with a cage?


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## RJSakowski (May 14, 2016)

Dimensions and tolerance requirements would help.  Also, the function of the ball as that will affect the process used.  Are you machining the end of the bar?  Round stock, flat?

I would not trust an end mill to cut a hole to nominal size.  An undersized hole and boring bar to finish would be a better choice.


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## Mark_f (May 14, 2016)

I would use a boring head in the mill to bore to size.


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## prasad (May 14, 2016)

Ulma Doctor said:


> you may wish to drill/mill slightly undersize and ream the hole to desired dimension.
> both operations could be done with a hand held drill if the bores are not relatively large



Thanks. I should have given this info in my original question - the bearing is type 6202. I am not sure if I can use a handheld drill to drill a 35 mm hole about 11 mm deep. 

Prasad


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## prasad (May 14, 2016)

Wreck™Wreck said:


> Is the ball a fluid seal?


The ball bearing is a standard variety - type 6202ZZ

Thanks
Prasad


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## Tony Wells (May 14, 2016)

I think you can safely forget using an end mill to plunge a proper size hole for a press fit in your application. A reamer that size will be rather expensive and pretty long. And as always, there are pre-ream conditions that must be met to achieve the results you need. 

The proper thing, IMO, is what others have suggested. That is a boring head. Drilled holes are seldom placed accurately in terms of assemblies where ball bearing supported components are used in the first place, even if you could somehow hit the size. Center drill or spot drill, then drill under size, then bore to finish size and on location. That's the most common approach. There are some crude, but effective, tricks to using a fly cutter to bore a precise hole that you might want to look at if you do not have a boring head.

But first, I think I'd forget using an end mill for this.


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## Wreck™Wreck (May 14, 2016)

prasad said:


> The ball bearing is a standard variety - type 6202ZZ
> 
> Thanks
> My mistake as I thought that you were using a single ball, bore it or ream it, the ZZ means metal shields on both sides.


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## Andre (May 14, 2016)

For reference, 6262 bearings are 35mm in diameter. 

Can you tilt your mill head sideways, clamp the bar to the table horizontally (supporting the other end that's off the table) and machine it like you would on a horizontal boring mill?


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## prasad (May 14, 2016)

Tony Wells said:


> I think you can safely forget using an end mill to plunge a proper size hole for a press fit in your application. A reamer that size will be rather expensive and pretty long. And as always, there are pre-ream conditions that must be met to achieve the results you need.
> 
> The proper thing, IMO, is what others have suggested. That is a boring head. Drilled holes are seldom placed accurately in terms of assemblies where ball bearing supported components are used in the first place, even if you could somehow hit the size. Center drill or spot drill, then drill under size, then bore to finish size and on location. That's the most common approach. There are some crude, but effective, tricks to using a fly cutter to bore a precise hole that you might want to look at if you do not have a boring head.
> 
> But first, I think I'd forget using an end mill for this.




Thank you Tony, 

I understand Boring Head is what need. I don't have one. I will order one from LMS. Appreciate your help. 

Prasad


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## prasad (May 14, 2016)

What do you mean by single ball? Sorry, I have much to learn..


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## prasad (May 14, 2016)

mark_f said:


> I would use a boring head in the mill to bore to size.


Thanks, ordering a boring head next


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## Tony Wells (May 14, 2016)

Ball bearings can be bought one at a time. Think "BB", as in "BB Gun" from the toy section. They shoot small, round projectiles. Although hardly precise "ball bearings", the concept is shared in that the main object is a single sphere that is the projectile. 
There are a few uses for individual balls where there is also a need for precision, so the suppliers of ball bearing assemblies make available individual balls. One example that pops into mind is building/rebuilding a precision ball nut/screw. Clearances there are critical, and to make allowance for variations in the actual screws and nuts, precision balls with small but precise variations are made so they can be selectively assembled to yield the best quality movements.


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## Andre (May 14, 2016)

1/2-5/8" bearing balls (that are accurate, measure them!) are great to use on your surface gauge to measure squareness.

EDIT: I believe I had posted this in another thread, not sure how it ended up here. Sorry for the off topic post.


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## Wreck™Wreck (May 15, 2016)

prasad said:


> What do you mean by single ball? Sorry, I have much to learn..


Many hydraulic devices use balls a valves where a seat is created for the ball to seal.
Like so


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## RJSakowski (May 15, 2016)

If you are not looking for a tight seal but wish to locate or secure the bearing, here is a process the I have used.  I select and end mill smaller than the diameter but as close to the final size as I can.  I then bore the primary hole.  Then I offset the end mill by 1/2 the difference in the X direction.  I repeat the process in the -X direction and in the plus and minus Y direction.  If the difference in diameters is small, this is usually sufficient.  For greater differences, I will make four additional cuts on 45º diagonals.  The offsets for these cuts are .7071 x 1/2 the difference in the diameters in both X and Y directions. 



As an example, if you are cutting a 1.005" counterbore and have a 1" end mill, 1/2 the difference in diameters would be .0025".  If the coordinates of the center of the bore are 0,0, the four auxiliary positions would be (.0025,0); (-.0025,0); (0,.0025); and (0, -.0025).  If you want to get closer, the four additional positions are (.0018), (.0018); (.0018, -.0018); (-.0018, -.0018); and (-.0018, .0018).  This process would give you a minimum clearance diameter of 1.0035" for the four auxiliary positions and 1.0046" for the eight auxiliary positions.



The offsets can be increased slightly to get the proper fit.  If a precision fit is desired, it would prudent to turn a set of precision test pins slightly undersized to determine the progress.


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## Smithdoor (May 15, 2016)

Please post a drawing or photo
I have machined  hundreds of thousand ball bearing seats. Most had to be with in ± 0.000,2 [0.005mm] of the diameter of the ball bearing.
I do not think a mill cutter will work that well.

Dave


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## Wreck™Wreck (May 26, 2016)

For those that like ball turning, 1 1/2" diameter ball seat through a 1 1/16" hole.
2 aluminum parts bolted together with a 3/4" hole produced with a reamer in a mill.
Indicated the hole in a 4-jaw chuck using stepped soft jaws after having milled the steps in a Bridgeport knee mill, this is by far the fastest way to put thin parts in a 4-jaw.




Used a 1/8" wide full radius internal groove tool for the inside work, chips were a problem as they could not get out. Used .002 feed and a 20% percent step over in order to make the chips as thin as possible, took less then 15 Min. for each part and the finish was excellent.




I  made the male parts last week. 1/4" round insert tool, 750 RPM's, .030 DOC, .010 feed for roughing and ,004 DOC and .005 feed for finishing


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