Parting a sintered bronze bearing FAIL (initially)

[Surprman]

I'm making a wobble plate engine (Elmer's Engines). I needed some bronze bearings and I picked up a couple at Lowes. They were a bit longer than I needed, but figured I could part them easily enough on the lathe. My first attempts were less than successful. The bearings deformed in the chuck and with the light pressure required, they came loose while I was turning them which I learned does nothing for the bearing function or aesthetics. I ended up buying a couple new ones and building a mandrill to do the job. It worked pretty good. (I used a slower spindle speed and a carbide threading tool to do the parting. The photos uploaded in reverse from what I planned. The first photo is of the status of the engine so far.

Rick

 

[ogberi]

Use a razor sharp HSS parting tool for that. Your setup relies on compression force from the nut to keep the bushing from spinning on the mandrel. When it gets thin, it'll tend to spin and grab, probably as you've seen. I'd grab the bushing in the 3 jaw chuck to part it off, then deburr it by hand. The parting cut isn't critical to the concentricity of the part, so you should be okay. You can always pass a reamer through the part afterwards to clean up the ID.

I'm a firm believer in sharp HSS. If it'll peel off an alarmingly large hunk of thumbnail without effort, it's about halfway sharp enough.

Just remember to use a pencil or scrap of wood to put in the bore of the parted-off piece, lest it whing off when parted to the land of Lost Parts somewhere under the lathe. The parted workpiece drops off nice as pie onto the end of the pencil when parting.

 

[Surprman]

Use a razor sharp HSS parting tool for that. Your setup relies on compression force from the nut to keep the bushing from spinning on the mandrel. When it gets thin, it'll tend to spin and grab, probably as you've seen. I'd grab the bushing in the 3 jaw chuck to part it off, then deburr it by hand. The parting cut isn't critical to the concentricity of the part, so you should be okay. You can always pass a reamer through the part afterwards to clean up the ID.

I'm a firm believer in sharp HSS. If it'll peel off an alarmingly large hunk of thumbnail without effort, it's about halfway sharp enough.

Just remember to use a pencil or scrap of wood to put in the bore of the parted-off piece, lest it whing off when parted to the land of Lost Parts somewhere under the lathe. The parted workpiece drops off nice as pie onto the end of the pencil when parting.

Actually , it was chucking it in the three jaw using a sharp HSS tool that caused the problems. The mandrill worked out much better (it did spin at the end, but by then with the pointed threading tool it was pretty much cut through already - there was a bit of debuting to do.

 

[Ulma Doctor]

if you can run you lathe in reverse, do so and invert the parting tool in the toolholder and re-find center.
the bushings will cut a lot better due to the cutting forces pushing the tool away from the work rather than trying to pull the parting tool into the work in the same manner as forward rotation.
if you have not tried it, please do it will help immensely.
it will work for other hard to part materials as well.
i hope the information is helpful to someone...
mike)

 

[Surprman]

if you can run you lathe in reverse, do so and invert the parting tool in the toolholder and re-find center.
the bushings will cut a lot better due to the cutting forces pushing the tool away from the work rather than trying to pull the parting tool into the work in the same manner as forward rotation.
if you have not tried it, please do it will help immensely.
it will work for other hard to part materials as well.
i hope the information is helpful to someone...
mike)

Thanks Mike. I have some parting left to do on this project and I had read before that inverting the tool and running in reverse can make things easier. I'll try it out.
Rick

 

[Terrywerm]

One other trick is to make a short shaft about the length of the bushing, and a snug fit inside the bushing. The shaft can be steel or aluminum, your choice, just use whatever is handy from your scrap box. Put the shaft in the bushing, then chuck the whole thing up in the three jaw. The shaft will provide support for the bushing when the jaws clamp down on it, and you will then be able to part off the bushing without the bushing being deformed, yet hold it tight enough to part it off.

I will echo previous comments about using a HSS parting tool, but make sure it is good and sharp. Stone or diamond hone the cutting edge a bit after grinding it too, you will be surprised at the difference this can make.

 

[Dataporter]

I usually saw those dudes off and then face the end off.
I chuck them up in a 5C collet in one of those square 5C holder blocks, and clamp that in the band saw vise.
Trying to part them and they just want to spin in the chuck or collet.
Next time I have to part something, I'm going to try the tool upside down, lathe in reverse trick as suggested by Mike the Ulma Doctor. There is a youtube video I saw on this and forgot about it.

BTW your engine looks cool!

Dave

 

[gheumann]

Ulma Doctor wrote "if you can run you lathe in reverse, do so and invert the parting tool in the toolholder and re-find center.
the bushings will cut a lot better due to the cutting forces pushing the tool away from the work rather than trying to pull the parting tool into the work in the same manner as forward rotation."

I've heard this before but I don't understand it. My mental picture: If the tool is too high (forward, normal tool orientation) or too low (reverse, upside down tool) then as force bends the tool in the direction of the cut, the cut becomes deeper and the tool can dig in. This is bad. But if the tool is properly at dead center height to begin with, it can only be "bent" to a lighter cut. Seems to me the physics are identical in either case.

Can you elaborate?

 

[Dataporter]

Hopefully my crude drawing and the picture of it are worth a thousand words...

Best Regards

Dave

 

[gheumann]

Thanks! I see the point. Still unless cutting very large diameter material, or having a really crappy tool holder, the "falling away" of the surface being cut in either direction as the tool deflects is likely to be a far greater influence and should more than compensate. I still believe most parting problems can be traced to the reasons I gave above.