Question about turning to square shoulders.

[Nelson_2008]

Hello,

Maybe someone can advise me on the best way to accomplish the following?

I have a round, 6" long piece of 2" OD, 1.5" ID UHMW polyethylene tube, and I want to turn down the diameter of the central 4" length of it by 0.040", but I want the two inside shoulders formed to be basically square.

Should I first plunge-cut the ends of the turned-down-section with a grooving tool, and then finish the rest with, say, a type "E" tool, or is there a better way to do this? (Also, I was planning on having the tubing mounted on an expanding mandrel for this operation). Thanks.

Regards,
Nelson_2008

[neilw20]

You are only taking a small amount off.
A grooving or parting off tool will cut sideways as long you don't overload it.
If doing any quantity, I would suggest carbide as plastic stuff destroys HSS very quickly and you will loose the sharp edge.

[Nelson_2008]

Thanks for the reply.

At first the tubing was a little oversized and out-of-round, and when I went to turn it down a little to make it concentric, I first tried a c2 carbide insert...with terrible results. I then put a HSS insert in the tool, and it worked much better.

In any case, my problem now is that, as a newbie, I just don't know what technique to use to turn down the middle 4 inches slightly, while creating square inside shoulders.

[neilw20]

The carbide must be VERY sharp. Even if you have to sharpen an insert. They usually have some small radii.
Put a mandrel up the middle, as you probably find it very wobbly and unstable.
If the mandrel goes all the way through, the chuck won't distort material where it is clamped. The other end can run in a live center.
Turning it un supported will give poor results.
If the speed is too high melting will start to occur as the stuff is not a good conductor of heat.

[Nelson_2008]

Ok, assuming that the work is solidly supported by the mandrel, and that carbide vs. HSS is not an issue, is there any other practical way to do it besides using the cutoff/grooving tool to cut sideways? Thanks.

[Superman]

You could use a 35° R/H tool for turning towards the chuck, and then use a L/H tool of the same for the little bit leftover turning towards the tailstock

you may have good success using Aluminium tips - these are honed, sharp and uncoated