Machining out the ID on 24 bearings

[cathead]

There are not a lot of machinists out in this country and I got a call the other day from a fellow
who wanted the ID of 24 bearings machined out to a slip on fit. With some trepidation, I took
on the job. Bearing material is notoriously hard and these bearings had little to hold on to(about 3/8 inch)
to hold in the lathe chuck. I used a carbide triangular carbide in a heavy boring bar. It required a lot
of pressure to get the cutter to cut even with a small surface area on the tool. I ended up using
a piece of cold roll as a go/nogo as trying to machine off a specified amount according to the dials was useless.
Anyway, it's done and I have the rest of the day to do something else.

I did try a grinding stone using a die grinder on the tool post but boring them out with the carbide boring bar was the way to go.

And there they are, all 24 of them with a slip on fit. The box of bearings weighs about 60 pounds.

 

[MrWhoopee]

I believe that type bearing should be a slip fit as received, hence the set-screws. What size were they to start and when finished?

 

[cathead]

Slightly less than 1.25 inches. They may have press fitted on but I didn't try it since they wanted a slip fit. They said to
take out 10 thousandths but to do that was virtually impossible accurately as bearing material is very hard of course.

 

[rwm]

Tough project. Let us know how the customer likes them. What do you think the tolerance is?

 

[cathead]

Tough project. Let us know how the customer likes them. What do you think the tolerance is?

I didn't get out the caliper, just made cuts until my go-nogo test shaft fitted in nicely. My thought is that they were
happy to find someone who would attempt the job and I suspect I was not the first person they asked...
I went and looked over the application and could see that the work would be acceptable such as it is.

 

[cathead]

Tough project. Let us know how the customer likes them. What do you think the tolerance is?

Well, they paid me more than I was thinking the job was worth so have big gobs of money hanging out of my pockets now.
They were very happy with the job and speed it was undertaken so all is well here.

 

[Mini Cooper S]

I put a small negative rake on the edge of my cutting tool when machining hard materials, works like a charm.

 

[rwm]

I always thought negative rake was for soft materials like copper? Why/how does that work for hard turning?
Robert

 

[Mini Cooper S]

I always thought negative rake was for soft materials like copper? Why/how does that work for hard turning?
Robert

Back in the 70's an old machinist took a bandsaw blade, and with a hand grinder, put negative rake on the teeth of half the blade. I thought he was nuts. He then took a bar of hard Ampco bronze and started cutting a piece off of it. The unmodified part of the blade would not touch the hard Ampco but the modified section cut through like a hot knife through butter! He told me that the same thing works for turning hard materials.
I don't know the physics of it, but I've used that trick many times since and taught it to many others after that.
Richard

 

[Mini Cooper S]

Well, they paid me more than I was thinking the job was worth so have big gobs of money hanging out of my pockets now.
They were very happy with the job and speed it was undertaken so all is well here.

We can help you spend that money!