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Best practice to machine a cylindrical elongated hole on a turning center


Aug 19, 2016

A 3 axis turning machine Doosan Puma 300M is to be used for machining this cylindrical hole. Its radius is 2.5 mm, so I used a 5 mm solid Carbide end mill (Kennametal brand) as live tool. My method is a zig zag move:
(0.5 mm each pass as ramp)

G01 Z-0.5 H70 F0.02
Z-1 H-70
Z-17 H-70

But this method takes a long time. What is the best way to machine it? (Best depth of cut, Feed...)

Material: 1.4122 (ASTM 431)


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Radial slot. How many live tool heads do you have? I would be tempted to at least pre drill and then full width slot with a carbide roughing end mill, or rough it out with a drill. I have zero experience with 431 SS though.
I would drill both ends to depth with a 4.5mm drill. Then slot with a 2fl 4mm at what ever step down your live tooling can handle, then do a full periphery clean up path with the same or a 4fl 4mm, because slotting will leave a shoddy looking sidewall. At least with lathe live tooling. You'll have to be careful doing the final plunge at the bottom as you'll have about a 1.2 to 1.4mm drill tip material left there.

You don't say how deep the slot is, but if your current method is leaving a nice clean wall, even being slow it might win out against my suggestion speed wise. Wouldn't know until I tried it. All sort of depends on your lathes live tool slotting capabilities in that material.
@bigjon61 , @13engines
Thank you for your suggestions. I can use maximum 3 stations for live tools. In my first experience 431 SS is not a hard material to machine.

The slot depth is 16 mm. And a clean wall is important for me.

After your suggestions, what I'm going to try, is roughing it out with a 4.7 drill and then use a 4.5 mm solid carbide end mill with 3 mm step down.

Any idea for speed and feed?