Parting off and general HSS tool sharpness

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jim:
i gave up trying to part off until i tried a rear tool post!

DaveH:
Ross,

Parting off is one of these perennial things.

Ask 10 guys "How to part off" and you will get 20 different answers. So what is one to do, - keep trying (when you feel like it) eventually you'll hit on a way that will suit you and your particular set of circumstances. :thumbup:

In the meanwhile just cut it off with a hack saw.

Enjoy it and have fun :D

:beer:
DaveH

John Swift:
Hi Ross ,

the parting tooling your photo is only is roughly shaped and needs sharpening
as it is it has a zero top rake that's OK for brass but needs to be reground for steel or aluminium
to give you a positive rake , also it looks a little too wide

while at school in the 70's , parting off tools usually broke before I could cut one part off

years later while making some electrical repairs to an EMI-MEC "plug board" automatic capstan lathe
watching them part off every few minutes , I realised why I broke so many parting off tools on the Myford lathes

first a 2.5 to 3 mm wide parting tool is too wide !! for small lathes - they are under powered and not ridged enough
you need to part off as close to the chuck as possible .

once you start you need to keep going , the feed rate needs to be constant , no stopping halfway through

I've recently re learned the art on a smaller version of your lathe ( machine mart CL300M)
first time I tried ,the tool deflected downwards, as it metal bar climbed onto the tool-,,,,,crunch !!
you could see the toolpost move ,due to the play in the slides !!

I replaced the gibbs on the top slides with brass ones from to reduce the play ,the originals didn't fit too well ,

( with no milling machine I took the easy way out and bought them from Arc Euro Trade )

I reground the parting off tool so its now about 2 mm wide and the top rake about 3 degrees ( angle needs to suit the material)
the tool will get thinner as the cutting edge is resharpened

my second attempt with the correctly fitting gibs was successfull :D

as other have said its very important the tool is at the correct height

one problem with aluminium is it friction welds its self to the tool

with practice , you will know by the sound from the tool when its cutting correctly

John

SKIPRAT:
Ross

What a can of worms to open up on Christmas Eve "Parting Off" there are many theories on the "Black Art" concerning parting off you will however if you persevere get it right and look back on the problems you had and say it was not that difficult.I will first outline a few requirements for successfull parting off 1/ machine rigidity such as Gib's correctly adjusted spindle bearings ,mass of machine 2/horsepower available 3/ tool sharp and on centre 4/correct speed and constant feed of tool into material 5/ adopt a technique that suits you and your machine 6/ make sure the saddle is locked or restrained. the tool needs to be as narrow as possible as it takes a lot more force to push a wider tool into the material and on a smaller lathe you only have a limited amount of horsepower.also do not have the material too far out of the chuck rule of thumb no more than 3 diameters you will get the hang of it in the end .

Cheers Paul

S. Heslop:

--- Quote from: DaveH on December 24, 2011, 12:07:57 PM ---Ross,

Parting off is one of these perennial things.

Ask 10 guys "How to part off" and you will get 20 different answers. So what is one to do, - keep trying (when you feel like it) eventually you'll hit on a way that will suit you and your particular set of circumstances. :thumbup:

In the meanwhile just cut it off with a hack saw.

Enjoy it and have fun :D

:beer:
DaveH

--- End quote ---

This is great advice.

I wish I just started grinding any old tool bits from the get-go, instead of spending far too long reading about it in books and online. All the experts online scared me to death, with anecdotes and facts on how if I was just a degree off in my rake angle, I was almost certain to gouge the tool into the metal and blow my motor. It didn't help that the values they'd then give almost always conflicted with everyone else's.

Oh also is your lathe set in forwards and not reverse? It's kinda embarrasing to admit, but when I first tried grinding parting bits I ruined two good blanks before realising I'd somehow set my lathe in reverse.

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