Parting with power cross feed

[Robin GrahamParticipant @robingraham42208]

I seem to have had a charmed life with parting. It's obviously one of the more bum-clenching operations for us home enginering types, but somehow I have got away with it without the need for rear toolposts or whatever, and without breaking anything. Until today – when my Glanze tool sort of exploded about half an inch into a bit of 2 inch ali bar. I was trying power feed at 0.05mm / rev , 200 rpm. I'll go back to hand feeding when you can feel when things are going wrong – it was just an experiment, but my question is – why did this happen? Was my feed/speed crazy?

Regards, Rob

[Robin GrahamParticipant @robingraham42208]

[Ady1Participant @ady1]

Anything can go wrong with parting off, absolutely anything

And when it does, it all goes bang

[MWParticipant @mw27036]

Perhaps the tip is protruding a wee bit much from it's slot, i had a few go bang til i finally sent it home in there, if it's one of those ones that need to be pushed in, use a plastic faced (soft like nylon/acetal) mallet (but not a copper faced lest it will chip). 

Michael W

Edited By Michael Walters on 30/06/2016 02:07:00

[Gary WoodingParticipant @garywooding25363]

Ali is terrible stuff to part. It tends to build-up on the tip of the parting tool which then cannot cut any more – resulting in a bang. If you hand feed you will feel the point when this build-up happens and can stop in order to remove the build-up. Power feed just keeps on pushing, and you now know the result.

[Bob Brown 1Participant @bobbrown1]

Ali has a habit of sticking to the tool tip, were you using a coolant?

[KettrinboyParticipant @kettrinboy]

Aluminium is not quite as user friendly as you might think for parting off , the softer grades especially need coolant or thin oil when parting off bigger dia stock as cut dry you can start to get a built up edge on the tip and then it will struggle and probably break or jam up in the cut.

regards Geoff

Edited By Kettrinboy on 30/06/2016 07:30:56

[Anonymous]

Posted by Robin Graham on 30/06/2016 00:50:26:

Was my feed/speed crazy?

Yes, but in the wrong direction. I find that my insert parting tool chatters at anything under 0.1mm/rev feedrate. Above that it is fine. I use flood coolant for parting on everything other than brass or cast iron.

This groove was machined under power feed at a few hundred rpm and 0.1mm/rev:

Andrew

[Robin GrahamParticipant @robingraham42208]

OK, thanks, all makes sense now – it must have been build up on the tip. I wasn't using flood coolant (the bit I was making was to repair the suds pump, so not possible), just squirting WD40 into the groove occasionally. When I started the cut the swarf was coming off in a continuous strip, but just before the big bang (and it was quite big – not just a broken tip, it ripped the jaws off the tool) the swarf stream started breaking up, which I guess was indicative of of an imminent jam. I'll make sure the next insert is well rammed home, thanks for that tip tip Michael W.

Back to winding by hand – not really much of a hardship!

Robin

[MWParticipant @mw27036]

Yes you can't go wrong with a judicious slosh of your chosen product of oil when parting.

I reason that if the tip has a little bit of over hang from it's body, the bar itself, as it is spinning is able to gain enough leverage to snap the end off under strain, if any of it is exposed, being brittle as it is hard, it's easy to see how this could happen. Once i made sure it was fully secured sure enough it started working again. I couldn't even get half way into a bar without a snap before i made this check.

Spinning anti-clock wise and a tool being fed from the from side, the forces are always trying to pull the tool under. 

Michael W

Edited By Michael Walters on 30/06/2016 22:28:40

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