Chipping Workpieces At Headstock

So this begs the question... if HSS is, perhaps, the key solution, is there a preferred choice for best results (best at maintaining an edge)?

Are there presharped HSS inserts by chance?
 
Can you dig up a hss toolbit from somewhere and freehand grind it? If you have a way to hold it you can grind a drill bit to make a cutter or even an endmill.

If you can, you may be able to grind one of your inserts dead sharp, just make sure you grind your clearances.
 
Another thing you can try is to start at the ends and work towards the center. That will provide more the material more support while cutting. Also, I'm not sure you want a sharp pointed tool. More like a round nose with a positive or neutral rake may be may be better.
 
What is the remaining thickness of the plastic at the insert end?

I have seen stuff crack when there isn't enough material left to stand up to the compressive pressure of the centers OR sometimes the pressure of the glue overcomes the material it is bonded in or to. The glue builds pressure against the two diameters and swells upon setting.

Can you turn the diameter up to the insert then rechuck it so only the insert end sticks out and machine that end and, if needed, blend it in with emery?
 
Cut blanks, drill hole, light sand tube , paint, let dry, I use 10 min epoxy ,dental wax tube ends, make sure tube has full glue coverage inside drilled blank, let dry 2 hrs
The ends of said tubes / acrylic must be square, I use a pilot counterbore, mount with correct bushings for that pen type on each end of tube , should use a pen mandrel with bushings , you are probably useing square pen blanks and turning them round " interrupted cuts" I tried carbide for about 2seconds , not sharp enough ,use hhs ground honed sharp, turner chisels are best , when your close to final size take light cuts with sharp tool and sand to bushing diameter 320-400-600, polish with micro mesh, done
Hope this helps
 
Carbide inserts are really not good for this type of turning. I am a pen turner myself, but have not done much on the metal lathe. Either a brazed on carbide sharpened to a point, then very lightly 'bumped' to radius the edge, or a HSS blank done the same way will make much easier work of this. You may also try feeding from head stock to tail stock direction, not so much on finish pass, but in roughing go close to the end, then come off and reverse direction.
 
I have had similar effects occur when turning brittle plastic materials in the past, POM (Delrin) for example.


Picture what is happening as the tool nears the end where it will run off of the part, the tool is making the part very slightly smaller in diameter via tool pressure. Not just from the material being removed, it is actually deforming the material.
This works fine at the beginning of the cut for several reasons, it also works well during most of the rest of the cut because the material is constrained by itself on either side of the cutting zone, when the tool point reaches the end where the material is constrained on only one side it will return to its original diameter if in doing so it contacts the tool it may cause a chip. One thing to try is putting a small chamfer on the part at the head stock end, also try a tool with a very high back relief and virtually 0 nose radius,

Good Luck
 
Or... you could grind that end with a dremel and a small sanding drum. Stick a boring bar in your tool post for a rest to guide the dremel.
 
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