How are bearing holes machined in aluminum?

[norco kid]

My dad has a small metal mill and lathe and I'm interested in trying to make some small RC parts. My question is how are holes machined for bearings so precisely? I know that simply making a hole with a drill press of the same diameter bit leaves too much slop in the part. The bearing drops into the hole instead of having a bit of resistance like the aluminum RC parts you can buy. My dad is suggesting that the part should be held in the lathe and to use a boring bar to precisely enlarge the hole. That seems a bit awkward to me if the part is not cylindrical (for example a motor mount plate for 1/8 buggy)

[Duuuuuuuude]

The old man is right, they are bored.

For irregular shaped parts it'd be easier to do in the mill, but you'd need to buy a boring head.

If you decide to go for it, make a lot of practice runs. It is a fine line between a good fitting part and a sloppy fitting part.

[mikemcE]

Or a cnc mill


Hang up and Drive

[EddieO]

On a manual, some are bored, some reamed....depends on the size of the hole typically.

On a CNC, while boring heads and reamers are used, a lot is just done with an endmill. Again, depends on the hole.

You could do it on the lathe, but have fun holding most parts....especially if you need to do multiples and want them to be the same.

Later EddieO

[norco kid]

Thanks guys! It looks like a boring head for the mill would be the way to go. I am thinking of holes for center diff bearings (motor mount) that are typically 16mm OD. Don't know if I'll get the boring head as it's quite expensive. Might try out a 16mm reamer first and see if that is adequate.

[DrewHammer]

Drill really close to final size and ream with the appropriate reamer. Good boaring heads are expensive. Reamers are much more affordable.

[Hydrocarbon92]

Your dad is probably half-right, although this method isn't ideal. For low production they chuck up a boring bar offset into a vertical mill, or use an adjustable boring bar, then plunge it into an existing thru-hole. The part is fixed while the tool bit spins.

Most parts you see will be done several dozen at a time, so it's done different. They drill the small thru-hole, then use a end mill a little wider than half the final hole's width then move in a circle around the edge. If there's no step they'll just do the same w/o the initial thru-hole. A reamer is more expensive & has less uses than a small end mill, and most CNC's can get holes precise enough for most bearings with an end mill.

[FRIZZLEFRY]

For a straight up size like 16mm your best bet is a reamer. Drill your hole .020" under and then ream. Experiment with RPM and feed rate to get your desired fit.

In a manual or CNC machine a reamer will give the best, fastest, and most repeatable results.

[wings_of_fire]

Originally Posted by norco kid

Thanks guys! It looks like a boring head for the mill would be the way to go. I am thinking of holes for center diff bearings (motor mount) that are typically 16mm OD. Don't know if I'll get the boring head as it's quite expensive. Might try out a 16mm reamer first and see if that is adequate.

Reaming is the right way to go. For a 16mm od bearing, you can use a 16mm reamer with H7 tolerance class.
Assuming your bearing has an exact od of 16mm +- 0 microns, A 16mm H7 reamer will give you a hole size anywhere between 16 to 16. 018mm (18 microns allowance ) provided you ream it right. You will need diesel or some special reaming oil to do the job.

[chino63]

It's probably wrong and not advised as I'm no machinist but I still have all my fingers. I've used my mill and the correct size end mills to make 4mm to 11mm bearing pockets. Make sure your end mill is a center cutting end mill though. I've done it many times without issue, just be careful. Remember, if it doesn't sound right, smell right, look right or feel right, it probably isn't.

[Etype R]

Not to sharp on manual machining, I am lazy and much prefer CNC. But the reamers I have seen and used are not made for blind holes. Are there reamers designed for cutting flat against a shoulder? I have used boring heads before, and they work great once dialed in.

On my CNC mill i just circle interpolate the bearing pockets.