How to cut a bearing block ?

[ringram2077]

What is the method to make a simple bearing block manually, eg. no CNC ? Let's say you need two bearings, one on each side of a piece of 1" aluminum with a 1/2" hole through and the bearing pockets on each side to hold .875 OD x 1/4" bearings. I have already tried this and made pretty much a mess. Also since bearings are usually a little under sized the pockets might need to be a tad smaller for a tight fit. If there is a thread on this I could find it.

Thanks

[JDenyer232]

Rotary table.

[handlewanker]

Hi ringram, by bearing block I take it you mean for a ball race housing.

If you know how to use a micrometer and telescopic gauges then it's just a matter of drilling and boring to a "size for size fit", that is the bore of the housing should be the same diameter as the outside diam of the bearing, which will give you a LIGHT press fit.

Getting the bore to size is a matter of "walking up to it", first you drill to leave about 2 mm undersize, then you use a boring bar in the lathe to bore out the hole by taking small cuts and CHECKING with the tele gauge until you get to the size you want.
Easier done than described.

The usual rule of thumb for press fits is .001" per inch of diam.

That is, you make the housing smaller by .001" for every inch of diam of the bearing.

This will give you a definite press fit, but for a lighter fit then use the size for size fitting.

If you're a newbie to lathe work, then it takes a bit of practice getting the feel of the telescopic gauge when measuring the bore.
Ian.

[ringram2077]

Rotary Table, hmmm I think I see how that could be used maybe in conjunction with a vertical mill to cut a circle pocket.

Using a lathe would require that I attach the rectangular stock to the chuck somehow. I have a 3 jaw chuck so that wouldn't work for me. Is there a way to do that with a 3 jaw check ?

Thanks

[Andre' B]

On a lathe you would/could clamp the part to a face plate. I think every lathe comes with a face plate, most never get used.

On a mill use a boring head.

Lock the X, Y slides.

Drill the 1/2 hole a bit small.

Switch to the boring head and bore the 1/2 hole to size. Functionally this hole may not need to be round and smooth but it makes the second side easier.

Now bore the counter bore for the bearing on the first side.

Flip the part over.

Now using a test indicator pick up the 1/2 hole, it depends on what the part does but I would guess you want less then 0.0005" TIR, zero is even better.

Lock the X, Y slides.

Put the boring head back in and bore the C-bore for the second bearing.

[ringram2077]

Andre
What type of boring head could bore holes of this size? I thought they would not bore this small.

Richard

[cam1]

Hi:
Refer to the bearing manufacturers engineering section in the catalogues for correct Housing to bearing outer race Fits.Every catalogue has this section. The rule of thumb for .001 interference/inch dia is for permanent shrink fits, not for bearings. Generally line for line fits or -.0001 to -.0002 inch will result in reasonable fit for steady loads.

regards

[Andre' B]

Originally Posted by ringram2077 Andre What type of boring head could bore holes of this size? I thought they would not bore this small. Richard

That mostly depends on the bar that you put in the boring head.
You can get bars for inserts that will fit in a 0.190" hole and solid carbide bars down to about any size you want.

But even the sets that come with the cheap 2 and 3 inch heads will get down to around 5/16 or so.
http://www.use-enco.com/CGI/INPDFF?PMPAGE=216&PMCTLG=00

[ringram2077]

OK thanks. Now I see how the boring head works. I have one on order and will attempt to redo my previous screwup. I really appreciate the responses to my thread. I will be back in a while and let you know how my experience with a boring head comes out.

Richard

[handlewanker]

Hi, I would say that if anyone could design an airship out of lead and make it fly then there would be a hundred engineers that would have the expertise to do it.

By this I mean that it is not the way to go, making airships out of lead that is, and just because a clever engineer can do it doesn't make it right.

So with the job in hand, having bored the first hole in the square block to depth with a boring head in the mill and NOT being able to face the bearing seat at the bottom, you are left with a face that has a number of grooves left by the tool point as it comes to depth.

You cannot face the bottom of the bore with a boring head, this requires a boring and facing type head that moves the slide out as the head rotates.

In a lathe it is just a matter of facing the bottom of the bore to get the bore and face square to each other with the same boring bar.

The fun begins when you turn the job around to do the second side and try to get the two bores in line and concentric.

For ball races they MUST be concentric and square to each other, otherwise they self destruct in a very short while.

However it is much simpler to bore the hole right through in one operation, thus ensuring that the two ends are DEAD in line with each other.

Depending on how much retention is required in the housing to ensure that the bearings stay pressed in will decide how much press fit is applied, which would/could make a shoulder for the bearings to press up to uneccessary.

The shoulder that the bearing is pressed against make it very difficult to get concentricity with two bores and faces at the ends of a bearing block, even if you have a rough bore to clock up to, on the other side when you turn over.

The solution is to use circlips to make bearing seats if required or locktite a sleeve in the bore between the bearings to space the bearing outer races apart.

Boring a hole in the lathe for bearings requires that the lathe headstock is ABSOLUTELY DEAD TRUE, otherwise you will get a tapered bore, and the longer the distance between the bearings means you get a hole that is either too tight at the far end or too loose.

Boring to size in the mill with a boring head will ensure that the hole is round and dead parallel, which is what you want to achieve, but NOT with the two shoulders in the bore necessitating that the block be turned over to do the other side, this is just not the way to do it.

Concentricity will be very difficult to achieve, even for an experienced person.

That is why it is better to bore right through in one hit, and worry about retaining shoulders after, either grooving for circlips or locktiting a sleeve etc.

If you haven't got a four jaw chuck, get one. It's like having a suit of clothes and the pants are missing otherwise.
Ian.

[ringram2077]

After purchasing a boring head and boring bits for the mill I realized your point about the shoulders for the bearings. Seems like there would be a boring tool for the head that would allow you to square up the shoulders.

Your other point about boring straight through makes sense and I can see how you could loktite a sleeve in the the hole the support the two bearings. But you see all these cnc builds where the bearing blocks are machined with shoulders. Guess there is a lot more to this hobby than meets the eye.

What is a circlip ? Never heard of that ?

[cam1]

A circlip is a C shaped ring that can be either inserted into an internal groove(using snap ring pliers), or an external surface (like a shaft) to prevent parts from moving. It is slightly compressed, and then slid into the bore, where it snaps into a groove. To install one on an internal bore, you would first cut a recess in the bore the width of the circlip X the OD of the circlip (a general statement). The Machinery Handbook would have the correct groove dimensions for most common circlips. This operation is usually performed on the lathe, with a boring tool, or grooving tool.

regards