[Futterama]

Hi forum,

I have a general metalworking question.

How is a hole for a ball bearing created in a thick aluminium plate without a CNC machine? The ball bearing should be press-fit into the hole.

Let's say the bearing outer diameter is 8mm. The hole should then be a bit smaller to make the bearing fit tight in the hole. So it's not possible just to use a 8mm endmill on a milling machine, the bearing will fit, but it will easily pop out.

I know it will be easy if the part that the bearing should be mounted in was round, you could use a lathe to create a hole of the exact dimensions. But when it is a big plate that cannot be mounted in a lathe, then how is it done?

I know this is a CNC forum, I guess it wouldn't be a problem to mill a round hole using a CNC mill, but I don't have access to a CNC machine, so how is it done with "normal" machines (lathe/mill).

Thanks.

[CNCRim]

Do the old fashion way, drill hole close to want you want then file it by hand to the size you want.

[fatal-exception]

You would drill a pilot hole then finish to size with a boring head.

Paul

[Oldmanandhistoy]

Hi,

Can you use a bearing block; will save you a world of trouble?

John

[Futterama]

You would drill a pilot hole then finish to size with a boring head.

Paul

Oh, some kind of adjustable end mill type of thing. Do they come in small sizes too?

[ee_t]

Oh, some kind of adjustable end mill type of thing. Do they come in small sizes too?

Do you see the one being held in the bottom of the picture, it looks to be quite small .

Or you can drill and ream.

[Futterama]

Do you see the one being held in the bottom of the picture, it looks to be quite small .

Yeah, but it seems that it should be attached to the big one in the middle and I need it to fit a mini mill.

I found the danish word for the tool and will now look for one that will fit my mini mill. Thanks for the replies!

[Oldmanandhistoy]

Hi,

Can you use a bearing block; will save you a world of trouble?

John

Sorry didn’t realise you had a manual mill.:stickpoke

In that case I would defiantly go with drill and finish with an adjustable boring head (how I do it). The adjustable boring head with care will give very good control of the tolerance (fit) of the bearing.

Don’t forget to research the necessary fit from the bearing manufactures specifications.

Good luck,
John

[BobWarfield]

Depending on the side of the plate, a lathe will also do a very accurate job with a boring bar. It's effectively the same operation as with a boring head on a mill, except you're spinning the plate in the lathe chuck instead of a boring head.

Be careful that the press fit is not so tight as to damage the bearing. They're more delicate than you'd think.

Cheers,

BW

[shanon]

this is very tricking the right size hole may not really be the answer. Depending on this situation I would worry about too small, too large, and because its in alum. the wearability when the bearing fails. My suggestion would be to first mill out a square or rectangle recess in alum. plate to allow for a bearing cover to be drilled, tapped, and then attached flush with the face of the alum plate. this will allow more tolerance on the actual bearing hole aswell as easier replacement of ware bearings.

[Futterama]

Again thanks for the answers.

My application it not VERY critical, and I wanted to use cheap china bearings because of the price and because the bearings may need to be replaced often due to operation in very dusty conditions - that's why the bearing price is a bit critical.
The cheap bearing I have access to have VERY much internal tolerance - so much that I can move/tilt the inner part of the bearing with my fingers.

shanon, I have thought about the plate thing, but it's too much work I think.
I would like you to further explain what you mean by this: "Depending on this situation I would worry about too small, too large, and because its in alum. the wearability when the bearing fails."
Do you mean that the hole in alum. wound "wear" when replacing the bearing? So after a number of bearing replacements, the press fit will no longer be "press fit" but only "fit"?

[shanon]

I was referring to thickness of alum. plate, clearance between alum. plate and any thing else. You may be able to attach bearing cover w/o milling recess. perhaps w/ thru holes and bolts??. Exactly what will you do if hole does ware?? and if hole is tight enough to press in cold but not under some operation heat or stress. something to take into consideration..

[roninB4]

Do the old fashion way, drill hole close to want you want then file it by hand to the size you want.

That was either meant as a joke or from someone that has no idea what a bearing fit is. The guy is asking for help so go sit down.

For a bearing fit there's likely a fairly close tolerance for a proper fit on the bearing. The manufacturer will have the best info if it's a good bearing. When it's not a good bearing then make it a light press fit of .0005-.0007 per inch of diameter undersize is a general rule you can use. As the interference fit numbers go up the more difficult it is to press the bearing in. Pressing in bearings can ruin the bearings if you press the balls/taper rollers against the inner/outer races. A proper bushing is required to avoid this.

Making a hole in a plate should be done with an adjustable boring head. A single point cutting tool will yield the best accuracy for what you're doing here. Use a drill, hole-saw, end mill, trepanner, etc. to make the hole .06 or so undersize. Use the adjustable boring head (I've even used fly cutters on occasion) to achieve the final size.

Shanon is right about the hole wearing out if you replace the bearing often. This is why pressing the bearing in/out is rather critical because material will be pushed out every time you replace the bearing. Aluminum will wear much faster than steel. Keeping the bearing perpendicular to the bore will lessen the effect when replacing the bearing but it will still become loose in the hole after a few bearing replacements. You may want to try putting in a shouldered bushing that can be replaced when the bearing becomes too loose. It's easier to replace a shouldered bushing than the entire plate. Hope this helped.

[Futterama]

roninB4, by shouldered bushing, you mean something to hold the bearing with a pressfit but easily replaced on the plate, right?

I might just use that solution - I can make the bushing on the lathe e.g. in steel and then I don't need to purchase a boring head - I haven't found any place to buy one yet, but they look like a rather expensive tool for the hobbyist.
Also I can avoid a hole through the plate for bearing replacement when the bushing holding the bearing can be bolted flush on the plate.

Again, thanks for all the answers, this is a great forum :-)

[roninB4]

A shouldered bushing would go all the way through the plate, the shoulder holds the bushing in place on the plate. If you want to do a flush mount then that's fine too, it's about what's easiest for you to make and when it's time to replace the bearing what's easiest to replace. What's also important is the use of the bearing that holds the spindle. If the spindle is high speed/high load then the alignment will be important. Any misalignment will produce vibration, accelerated wear, or both. I'm gathering that since you're using a cheap bearing that this isn't much of an issue for you. If you can get a grease fitting in there an open bearing that's greased may last longer than a cheap sealed bearing. If you can't use the flush mount then go ahead and pop a large enough hole for the shouldered bushing (that holds the bearing) and just locate/lock it in place with 3-4 SHCS, toe clamps (like they do with die set bushings), or 2 dowel pins with 2 SHCS. The choice is only limited by your imagination, you can even create a hole with the plate clamped to a rotary table. Hope this helped.

[Futterama]

roninB4, do you have a picture as an example of the shouldered bushing, because I'm not completely sure how it looks like.

This is what I'm thinking:

[grg12]

I might just use that solution - I can make the bushing on the lathe e.g. in steel and then I don't need to purchase a boring head - I haven't found any place to buy one yet, but they look like a rather expensive tool for the hobbyist.

Build one - it's a nice project for a hobbyist
This one is really small - designed for Proxxons BFW40/E (6mm shaft).
There: http://members.chello.at/grzegorz12/...f/bohrkopf.rar you can find prject in Alibre format.
Gregor

[tobyaxis]

Build one - it's a nice project for a hobbyist
This one is really small - designed for Proxxons BFW40/E (6mm shaft).
There: http://members.chello.at/grzegorz12/...f/bohrkopf.rar you can find prject in Alibre format.
Gregor

Actually it is a great project for an Apprentice Machinist as well. It teaches the Basics of Milling, Turning, and Producing an Assembly Product.

Very nice boring head!

[Futterama]

Build one - it's a nice project for a hobbyist

I would if I had the time. But making a complex tool like this to finish my current project is just not what I want - this will only delay my current project further, and I really would like to finish my project as soon as possible - it has been going on for far too long already.

Also I think the "shouldered bushing" would be the best solution to avoid the wear on the hole in the aluminum plate when replacing the bearing.

[tobyaxis]

Buy a TreePan Tool. They are as cheap as Fly Cutters and work very well. The only problem is that a Bearing Bore needs to have a fine surface finish and a close tolerance for Press Fit somewhere around .0005 U/S.

You can take a short cut and pay for it in functionality or do it right the first time and get years of dependability.

The choice is yours, but it is not a good idea to go half way or cut corners.