reamer question

Turn to a press fit, maybe a few thou under and press them in - if you overshoot use Loctite bearing retainer

Save your money on the reamer :)

Andrew

I would say in that size a couple of thou would be a heavy press fit and could cause issues with the bearing internal clearance leading to issues (hot running) depending on the service conditions. You should be able to look up the recommended housing dimensions on the SKF site and likely other bearing makers sites.

Would a boring head fitted with a carbide tool be suitable? Once set it should hold its dimensions.

That is a great idea that will use in the future when presented with a similar problem. Richard

Should, and probably would - but how do I prepare the hole? If it's with a boring bar - then I'd need two boring bars.

Peter Fairbrother

A drill?

I suppose I could start with a drill, but the bottom of the hole is flat. A drill then an end mill possibly, but I reckon I'd still need to go over the bottom with a boring bar.

Also, it might be some months before I finish cutting the seats (they go in several different parts and I expect it will take some time to finish developing the pumps they are part of), and I wouldn't want to tie up a boring head for that long.

So back to my original question, does anybody know, is a reamer accurate enough to provide a defined fit?

ta

Peter Fairbrother

As you need a flat bottom, wouldn't you be better to use a slot drill rather than an end mill to achieve the full depth and then finish to size with a boring bar?

Alan

Reamers into blind bore are always a problem, as the end of the reamer will be slightly tapered

Andrew

Reamers can be very accurate. I just reamed about 300 oil bearing sintered bronze bushings to .7505-.7507. Once I got the speed and feed right I had no problems. But the first few were a little oversize because the reamer wasn't exactly centered in the lathe. My mistake in setting up. The end of the reamer will have a chamfer so any bearing you press into the hole must have a corner radius large enough that it doesn't interfere with the undersized diameter at the biottom of the hole. Reamers can also chatter. Straight flute reamers are more prone to chattering. If I had to do 20 blind bores to fit a ball bearing I would bore them. The bores could be roughed and the bottoms flattened. Then they could all go back into the machine for the sizing cut, with the boring bar never being moved once the size is established. This means feeding the boring bar in and out with the bar cutting both directions. The reason I was reaming the bronze bushings was because I needed a short cycle time, which was 5 seconds per pair. Boring would have taken much longer. And the job is a repeat job, so the setup is paid for over very many parts. Eric

Why must the bottom of the hole be flat? Why not go deeper and fit the bearing using a hold-off/spacer ring if necessary?

I never worked out which was which, slot drill vs end mill. There will be central holes in the pockets for the shafts in I think all cases, so does it matter?

Peter Fairbrother

In exotic materials like you use. I would in production go

1/ 21.5 drill 2/ 21.8 flat bottomed drill or slot drill. 3/ david brown floating reamer to size.

Job could be done in either lathe or mill.

David brown reamers are adjustable and can be dressed with only as much chamfer as you can allow, they will work up to a square face. . They are very expensive but come up on ebay frequently. In practice once set and locked they will hold tenths with no problems.

Regards Colin

Note to self.The word locked is important got one set and passed by inspection 24 componants latter had 2 pass final inspection and 22 rejects.

In that case, provided the diameter of the central hole is larger than the area uncut by the end mill, then probably not. A traditional slot drill has 2 flutes (cutting edges) and cuts across the centre of the hole so can be plunged into the material whereas an end mill has 4 flutes but is not centre cutting. I'm not sure if the 2 wider flutes on a slot drill are better at stopping swarf from interfering with clean cutting than the 4 narrower flutes of an end mill. Probably the best compromise is a modern 3 flute end mill in carbide eg from JB Cutting Tools.

Alan