View Full Version : Bearing Pockets

02-24-2006, 01:58 PM
Howdy All!!
I'm new here but I've been lurking for a while.

I need to bore a 1-3/8" bearing pocket 3/8" deep in 1/2" AL plate.

What is the right way to do this, I have a Small Milling Machine. I don't have cnc capability and the parts are to long for a rotary table ( which I don't have ether).

I have done this using a hole saw, then mill away the inside of the hole.

I'm new to Machining so any help is appreciated.

Sandy H
02-24-2006, 02:25 PM
Unless I am misunderstanding the question, you'd use a boring head. I used to own a mill/drill and it was fine with the boring head. I didn't like the import boring bars, though. I'd look for something a little more robust on sale if I could do that part again.

I now have an old Bport and a year or so ago used a boring head with those same junk boring bars to do a set of 'connecting rods' for a friend's press brake. They were about 2" dia x 1" deep in mild steel.

I'd say you rough the hole out and then go after it that way. There may even be boring bars that are made to cut through without roughing out, but I've never really ever noticed.


Alistair Hosie
02-24-2006, 04:02 PM
With aluminium you could use a router with a tungsten bit and a home made trammell I did this opn my router table when cutting out the hole for the router bits to come through.Alistair ps take your time and set it up all ok first

02-24-2006, 06:25 PM
There are lots of ways to make holes that aren't fussy, but for a bearing bore, you'll want a boring head. A bearing bore that size will likely want a tolerance of less than .001". Too big and the bearing will fall out or spin, too small and you won't get it in...or if you do it will run tight. You'll need a 1-2 mic and a telescoping gage to measure the diameter. Practice on a piece of scrap if you haven't done bearing bores...measure very carefully...when you think it's "dead nuts" try pressing in the bearing. It should be a very light press fit.

02-24-2006, 07:02 PM
Thanks for the Responses,

If I understand the proper use of a Boring Bar, I would nee to make a hole first, then gradulally increase the Dia until I get the hole size I need, Is that correct?

Sandy, How do you rough out the hole?

02-24-2006, 07:17 PM
<font face="Verdana, Arial" size="2">Originally posted by Hawkeye:
Thanks for the Responses,

Sandy, How do you rough out the hole?
Thanks </font>
Use a center cutting endmill to start, or flat bottom a big drill bit.

02-24-2006, 10:20 PM
Yes, rough the "hole" first. A 1-1/4" end mill would work fine, after drilling a center hole. Or you could layout the hole by center punching the location, then scribing the circle with a pair of dividers...then take whatever end mill is handy and and mill close to the scribed line. Always helps to drill a start hole in the center...end mills really don't like to be used as a drill :-)

One question...is there no through hole in the pocket?

02-24-2006, 11:11 PM
I don't know what happened here, I just lost my entire reply with one errant push of a button. Sometimes I hate this thing.
Anyway, here goes again. If you don't have a boring head, you can do the job with a set of fly cutters. It will be tedious, but by making small adjustments to the position of the bit, you can enlarge a bore with successive downfeeds. You will need to have a minimum size hole to start with, and will probably need to change flycutters as the diameter of the bore gets too large for the previous flycutter. When you approach final size, you'll have to get creative when making the minute adjustments to the cutter's position in the flycutter's body. One way to do this is to lower the cutter so it's touching the wall of the bore (power off), then move the table over some, then return it to within a few thou of the previous position, then loosen the cutter and slide it to touch for the new positoin, tighten, raise the quill, return the table to the first position, then make the next cut. Tedious, but it lets you make a micro adjustment to the position of the cutting edge without needing a boring head. If you're careful to adjust the table each time, taking play into account, you can return the position of the workpiece precisely, and the x or y dials have allowed you to make known adjustments to the cutting edge position. Of course, you need to remember that for each thou you move the cutter out, you're increasing the bore diameter by two thou.
When the desired bore size in very near, you can make a micro adjustment without moving the table and setting it back again. To do this, just lower the cutter again so it's touching the previous diameter (power off of course) then loosen the cutter, use some finger pressure to force the cutting edge a tad into the material, tighten, raise the quill, power on and bore again. However much you moved the cutter outwards is how much it takes off next time it cuts. It wouldn't hurt to practise a bit before the full size bore is reached, to get a feel of this way of micro adjusting a flycutter.
You will need a way of precisely measuring the bore without removing the workpiece from the mill, so think about how you'll do this before committing the material and your time. Sometimes there won't be room to get a measuring device of some sort in there.
Make sure you have enough room to mount the largest flycutter that will be needed for the job without having to reposition the head. If you have a round column mill, and need to maintain the axis alignment, this applies.
Also, when the final diameter cuts are being taken, make the quill a little tighter so it doesn't tend to give you an oval shaped hole.
If you're concerned with making a nice flat bottm in the pocket, it helps to grind the cutter's bottom edge to be nearly parallel to the table. That way the cutter itself will tell you when the depth of the bore for each succesive cut has reached the same position as the last cut. You can't rely on a downfeed dial to tell you this because as you move the cutter out each time, it will also lower a bit.
If you really want a nice way to bore pockets for bearings, you'd want to use an adjustable-on-the-fly boring head with settable stops. Took me a day and a half to make one, but man it's nice, and a lot cheaper than buying one. I hope to get some time away from my current project to take pics of it and post them. Soon.

02-25-2006, 08:32 AM
Thanks All!!!

I think I can get it done!!

I was hoping there was something like a fostner bit that I could buy cheaply and use, but I guess not.

Big dipper, your correct, No thru-hole.

Thanks All!!

John Stevenson
02-25-2006, 09:56 AM
Couple of points.
You need to slightly recess the centre say 1" diameter so the inner race isn't rubbing on the bottom of the hole.
Second point, if the design permits it drill two 3/16" holes, opposite each other, right thru just inside the 1-3/8" Ø bore for a pin punch to knock the bearing out if needed later.

I spent two hours on Friday grinding an outer race from a closed bearing housing with a tiny die grinder because the designers hadn't thought about removing a race that had collapsed.
No heat or welding allowed on this machine.

John S.

02-25-2006, 12:15 PM
Roughing out the hole with a endmill and a rotary table will get you close and cut down on the 'boring' time.