Parting Off Help --

M

mneblett

Registered
Registered
Joined
Nov 17, 2019
Messages
13
Hi -- I'm slowly getting up to speed with my new PM 1030 lathe, having spent quite a bit of time leveling, aligning, etc. and making a couple projects.

Of the things I've done on the lathe, parting off is the one thing I've definitely not mastered -- I get shallow conical surfaces on the two sides of the part.

My set-up and things I've done:

Practicing by cutting off the end of a 1" 6061 bar.
1/16 x1/2" cutoff blade in a cut-off blade AXA holder.
Just enough stick-out to reach the center of the work.
Blade tip precisely centered (triple-checked).
Blade tip ground perfectly square.
Blade adjusted to be perfectly square to the previously-faced end of the work.
Plenty of cutting oil (drenched).
Rpm ~600.
Slow advance of the blade into the cut, with frequent oil application.
Bar is sticking out of the 3-jaw ~1".

So, what am I missing? Is the 1/16" blade too thin for this task?

Thanks for any suggestions!

Mark
 
With the blade mounted, try using a dial indicator to double check the blade square to the work from front to back.
 
  • Like
Reactions: Z2V
AGCB97 said:
Until now I've had trouble parting (100 year old lathe!) and mostly just used the bandsaw. Saw this vid, which was referenced above and ordered the tool and some inserts. Made a adjustable support plate (surface ground) that rests on the bed and an adjustable rod that slides along it that supports the tool at the clamping point. Works great and I'll be parting off in the lathe from now on!
Thanks for your interest
Aaron

View attachment 326184 View attachment 326185 View attachment 326186
Click to expand...
 
When you say the blade tip is ground perfectly square, do you mean side to side or top to bottom? Or both? You want to grind a little vertical relief angle on the front of the tool, 5 degrees or so, to make sure it cuts and doesn’t just push on the work. Especially important when the part gets down to the last little small diameter. Theoretically it shouldn’t matter, but it does.

You don’t mention locking the carriage in your routine like francist mentioned. Not locking it can cause conical faces due to minute carriage movement during the cut, caused by cutting forces and/or your hand turning the cross slide handwheel.

Tom
 
Lock carriage and increase motor speed as you get deeper into the cut.
 
Thank you everyone for the help.

The carriage is locked. The blade tip is square (parallel to the rotation axis). The front of the blade was ground on a grinding wheel to put a slight curve on the front to create clearance.

I'll try the dial indicator next.
 
I normally part off @ 200 rpm. Also hand feed in constantly with enough pressure to create a curled chip similar to a record, as per Tom Lipton. As you go deeper you may have to back out to clear some curls from the cut.
 
You must log in or register to reply here.
Back
Top