# Parting Off (Again)



## Ken I (Aug 31, 2021)

This may be an old trick but its new to me.

My hobby lathe does not have coolant and trying to dribble in HP cutting oil whilst parting off it tends to throw it out before it does anything useful.

How to deliver coolant to the cutting edge ? Then it dawned on me to use a syringe :-





Delivered where its most needed and allowed me to go all the way in without any binding.

Parted off - warts and all.




I advanced the cross slide with my left hand while delivering (Rocol) cutting fluid with my right. I am a southpaw - maybe that helps.

The needle is cut off and blunted so I don't hurt myself with it.

The whole cut only used about 1.5cc of oil so its less messy as well.

This is the first time I ever tried this and I was so pleased with the result, I thought I'd share the tip.

Regards,  Ken


----------



## Lloyd-ss (Aug 31, 2021)

I have that same HSS parting tool and would never think about plunging it that deep. With your idea, maybe I will now.
Thx, Lloyd


----------



## Ken I (Sep 1, 2021)

Lloyd, that's a 3/32" PO blade into 30mm dia. chewing gum grade extruded aluminium bar - just for scale.  4mm drilled hole on centre.

I did have to back just a bit up once rather sharpish due to me not keeping the lube flowing (trying to take photos at the same time) - you can hear it developing in time to react to it - my fault.

The second part off went flawlessly  with no working it sideways whatsoever - just the one plunge cut.

This horrible gummy grade of aluminium would normally be a sod to part off.

Regards,  Ken


----------



## Thommo (Sep 2, 2021)

Ken I said:


> This may be an old trick but its new to me.
> 
> My hobby lathe does not have coolant and trying to dribble in HP cutting oil whilst parting off it tends to throw it out before it does anything useful.
> 
> ...


----------



## L98fiero (Sep 2, 2021)

Ken I said:


> This may be an old trick but its new to me.
> 
> My hobby lathe does not have coolant and trying to dribble in HP cutting oil whilst parting off it tends to throw it out before it does anything useful.
> 
> ...


I just use a half inch chip brush with tapping fluid or a dark cutting oil, a little messier but uses little oil and it's quick.


----------



## Thommo (Sep 2, 2021)

I placed this post earlier but it seems to have mixed in with Ken I’s post. I was always taught that kerosine is the best cutting fluid for aluminium. You don’t need a lot of it, but it always results in a beautiful finish, but that is assuming that you have a sharp cutting tool and the correct spindle speed and cutting rate.


----------



## Ken I (Nov 27, 2021)

I finally bought myself a better part off blade holder vis :-




This holds the blade such that you do no need to grind on any top rake (rake angle provided by the holder itself) and only need to resharpen the front clearance face from time to time.
This not only extends the useful blade life and saves re-sharpening time but it also allows you to leave the upper bevel intact to act as a chip breaker.

Thus yet a further improvement in part-off performance by narrowing the chip to prevent binding as in the photos below :-




Top Left - Vertical View of the PO blade.
Top Right - Off Vertical down the front clearance angle (note you can still have a front relief angle to get a pip-free part off.
Bottom Left - Chip width is 2.30mm while using a 2.38 (3/32") blade.
Bottom Right - Close-up of chip - you can see how the bevel deforms the chip to make it narrower.

Since the blade in this configuration has no effective side relief, you do have to get it dead square.

Regards, Ken


----------



## SmithDoor (Nov 27, 2021)

I have used that type for 40 years works great. 
Sometimes on a few material you will need a greater rake angle

Dave 



Ken I said:


> I finally bought myself a better part off blade holder vis :-
> View attachment 131380
> 
> This holds the blade such that you do no need to grind on any top rake (rake angle provided by the holder itself) and only need to resharpen the front clearance face from time to time.
> ...


----------

