Metal lathe - parting tool problems

[Harry Bloomfield]

I'm trying to use a blade type parting tool, in my lathe, I've tried various techniques, such as altering the speed of cut, moving the back and forth, to provide it some clearance, but regardless, I always get the same problem.....

Every few seconds, once a mm or two into the cut, the blade seems to bind really tightly, before clearing itself and carrying on. The bind is so tight, it pulls the blade down a little, and showers the area with cuttings. I'm obviously doing something wrong, but what?

I'm presently making myself, a brass stand for my razor, I've made a drilled post, as the main part of the stand, I'm just making some brass disks, to fit on the base - 3mm thick, and struggling to part them.

 

[Old Salt]

Is the parting tool tapered towards the post to give you clearance?

 

[Harry Bloomfield]

Is the parting tool tapered towards the post to give you clearance?

The blade is wider at the upper edge, the at the bottom.

This type of thing.. https://www.rdgtools.co.uk/acatalog/Parting_Sytems__High_Speed_.html

 

[Old Salt]

That’s fancy! I’m old school - it needs to be tapered top to bottom and front to back. My drawing is exaggerated but you get the idea. It needs to have clearance on all sides as it progresses in the parting operation.

Alternatively you could part it off in stages, progressing in steps like a sideways pyramid.

 

[Harry Bloomfield]

Front to back, is flat/parallel, exactly as it was bought. The jamming in the sides of the slot, was what I assumed was happening, which was why I tried moving it a fraction, side to side, as it cut, but it still didn't help. The blades is so thin anyway, there is little material available to thin it down to a wedge.

 

[Old Salt]

So part it off using steps. Start away from the finished parting off point and take a cut, rewind to surface, advance a couple of mm or thou if working in imperial, take second cut, wind out, advance, take third cut etc. you will only need a small clearance.

Alternatively what about maching the back away before parting off.

 

[Old Salt]

Check out this guy

 

[Burnerman]

Do check that the parting tool is exactly at centre height......too low and the tool digs in, too high and it rubs.
The heavier duty the parting tool is, the better!
A good flow of coolant helps too.
John

 

[Harry Bloomfield]

I'll have to try that method next time, thanks - the little job's done now.

 

[Burnerman]

I didn’t used to grind mine square.....just a slight angle of a degree or two off the axis.
Maybe that has been covered here, and a little pip would be left on the main bar.
Parting off is always a difficult procedure - I’ve lost count of how many tools I’ve snapped!
John

 

[Harry Bloomfield]

Maybe that has been covered here, and a little pip would be left on the main bar.

Yes, I'm getting that.