Insert parting tool chewed up :-(

[Flynth]

So I was happily parting away with my 25mm MGEHR 2525-3 parting tool running 92rpm with 90mm stock(about 3.5in), using cross power feed at 1 thou per rev, squirting oil into the groove every few seconds. The whole piece is about an inch long. It's held in a 3 jaw chuck through very thin aluminium shims on 8mm (1/3 of an inch) of its length, then there is a 2mm wide, 3mm high shoulder to prevent the part migrating into the chuck on heavy drilling, about 15mm (0.6in) of slightly smaller diameter (86mm, or 3.4in)is sticking out in front of the shoulder. There is a 48mm (almost 2in) threaded hole through the piece. I'm cutting right in front f the shoulder so 2mm (80 thou) from the chuck.

When about 20mm (2/3rds of an inch) in BOOM and my work piece is jammed stopped, the spindle is stopped and the 3ph motor is buzzing loudly.

I hit the stop switch in under a second. Then I assess the damage. I see the part is kinked in the 3jaw. I loosen it. I move the carriage right with the part now permanently attached to the front of the tool and I rotate the spindle by hand, then repeat in gear... It feels fine... It was very lucky...

Then I try to start the motor and all I hear is a loud buzz, so I stop it straight away and I discover one of three phase fuses has blown. I replace it and the motor works fine. Great.

Then I look at my part. I move it back and forth by hand and eventually I manage to free it. But the bottom-front of the Mgehr2525 insert tool is gone :-(

Also the insert pieces are jammed in the groove in way I can't remove them. So there is no way I'm band sawing this.

Eventually I chucked the part and I faced off what was before the chuck side until I got to within 10 thou of the parting groove. Then I cut from the inside hole out and a 10 thou thick disk of material fell off. It seems I was within few mm of parting all the way when it happened.

Then I removed all the big chunks of the insert. I ground off any gouges that could have had insert pieces in and I faced the part. It was saved.

Now, I have a Mgehr tool with the front half of its bottom jaw missing :-( I can put an insert in, but last quarter of a inch (6mm) is unsupported. Clearly I can't use it like that. Option one is to buy a new tool (they're not that expensive) or try fixing it. I know which option I'll choose. I'll try to build that edge back up by tig welding and filing it to shape. The question now is what filler to use. Mild steel will surely not be strong enough. I'm leaning towards using stainless filler, but I worry it will increase a chance of the tool "grabbing" in future. What do you think?

As for lessons learned... I really have no idea. I've used this parting tool about 4 times before on similar diameter and same material with the same oil lubrication. Perhaps I was a second late in oiling? I didn't think that would matter. The tool was on center (checked with a height gauge) and parallel (set before the cut). The only thing I can think of is that the piece must have slipped in one of the Jaws, it kinked and a side grabbed, then it was a chain reaction.

The morale of the story is, don't part unless you're having full length of 3-jaw jaws holding the part. It doesn't matter how secure the part feels in the chuck.

 

[682bear]

I agree... the part likely shifted in the chuck. 8mm is not a lot to hold on to. It would be fine for turning, but parting applies a lot more pressure to the work.

-Bear

 

[MrWhoopee]

Agree that there was not enough grip in the chuck. It's also hard to get lube down to the cutting edge in a deep groove.

I gave up buying inserted parting tools for my employees. Every oops resulted in a trashed holder. It just got too expensive. I use inserts for everything except parting.

 

[Winegrower]

In my experience, power feed works fine initially but when the diameter gets small, say 0.25" or so, disasters can strike. I now increase the speed significantly and the cut works pretty well.

 

[Aukai]

If you can set up the tool to cut upside down it will pull the tool out of the cut under load, not into it. Back upside down normal rotation, front upside down reverse rotation. I think I have that right...

 

[Flynth]

Agree that there was not enough grip in the chuck. It's also hard to get lube down to the cutting edge in a deep groove.

I gave up buying inserted parting tools for my employees. Every oops resulted in a trashed holder. It just got too expensive. I use inserts for everything except parting.

Are you using hss for parting? Which tool? What width of the tool, and what stick out? Do you follow any hard rules, like "don't part diameters over 1.5x your spindle bore" etc? (I heard this in a youtube video, probably if I followed it, it would have been fine.) also, please say if you're parting "largish" diameters like 4in etc (and in which lathe).

I still have inserts for this tool so I'll attempt to fix it. It was going very well... Until it wasn't :-/

Once I fix it I intend to use it only for fairly shallow grooves(no deeper than a 3mm insert length) and then finish parting with a bandsaw.

I never had any luck parting with hss, except that one time when I really wanted to part on the Chinese mini lathe and I turned the chuck by hand, using the key, all the way.

I have a "big" lathe too, that's the one that chewed that tool. Last time I tried HSS on it I decided to give those thin hss parting blanks a try.(3x10mm or 0.120 x 0.4 in) I ground the angles. I relieved a little bit of material behind the cutting edge too. I set it up in a 4 way tool post with a stickout of about 50mm(2in). I wanted to part aluminium, about 100mm (4in) in diameter. I used wd40 to lubricate. I fed it by hand at a fairly slow rate and rpm of around 120. This time the blank was held very securely. You can imagine how it went. It parted about 20mm in and the tool must have flexed, or my hand feeding was uneven. The hss tool broke in half. The spindle didn't even notice. The part did move in the jaws a little too despite being held all the way.

I read all the theory, so I realise now I probably had a floppy parting tool, but that gave me a general dislike for hss parting. I know now a wider tool would help, but then with increased width there is more force and we're back to square one.

So I would love to hear about the details if people successfully use hss tools parting steel (and aluminium) that is pretty thick (4in) on fairly small lathes (my lathe is 18in swing 40in bed, it was originally 3.5kW,but the previous owner put a 7kW motor in).

In my experience, power feed works fine initially but when the diameter gets small, say 0.25" or so, disasters can strike. I now increase the speed significantly and the cut works pretty well.

Good to know, I never tried to part that far with this tool as its not long enough on the diameters I used it.

If you can set up the tool to cut upside down it will pull the tool out of the cut under load, not into it. Back upside down normal rotation, front upside down reverse rotation. I think I have that right...

That's a good tip, but my lathe has no T-nut table on top of support, like I saw some lathes do. To present the tool from the back I would need to wind the cross feed all the way there and it doesn't go that far... (or use a boring bar arrangement).

 

[rodm1]

I've had these problems will keep an eye on this.

 

[GeneT45]

I think it was a combination of a low fixed-speed feed and the small grasp on the work. I almost never use power feed when parting, though I would if I had continuously variable speed on my lathe. You pretty much have to increase your feed as the diameter gets small or it will rub... ...then grab. If the setup is rigid you might survive the grab, but if it's not... Best to avoid the grab in any case and I was advised to listen to the cut - and that works well for me.

Small needle oilers are great for getting fluid down in the cut if you're parting deep.

GsT

 

[Flynth]

I think it was a combination of a low fixed-speed feed and the small grasp on the work. I almost never use power feed when parting, though I would if I had continuously variable speed on my lathe. You pretty much have to increase your feed as the diameter gets small or it will rub... ...then grab. If the setup is rigid you might survive the grab, but if it's not... Best to avoid the grab in any case and I was advised to listen to the cut - and that works well for me.

Small needle oilers are great for getting fluid down in the cut if you're parting deep.

GsT

I never had much luck feeding by hand. That power feed on the lowest setting (1 thou per rev) is what allowed me to part (mostly) successfully at all.

Please be aware my 90mm (almost 4in) part had a 48mm(~2in) hole in the middle. So it isn't a case of the diameter getting really small.

I was making a large washer like nut for a surface grinder wheel hub. This was my second one. The previous one parted fine. The previous one was held by approximately 10mm so only 2mm more. This one when failed had about 4mm to go, so it was very close to succeeding. Perhaps I was just lucky with the previous one?

When feeding by hand I never manage to get nice even chip, I always got no chip, then heavy chip and so on. The power feed on this lowest setting results in a chip that is tinfoil thin.

I wonder if chips not being evacuated fast enough had something to do with it.

 

[Aukai]

I don't remember if you were using a new tip or not, but I have had this problem after parting either several times, or after something hard, and the insert may have dulled, also you may have hit a hard spot in the material, along with what has been stated above.