Cross slide lifts when parting off

[mickParticipant @mick65121]

Have you tried increasing the top rake angle to assist the swarf to curl, as it sounds like a tool problem. speed is far too slow for a 20mm bar, try at least doubling it and hand feed in, this gives you time to react to any change in the tool cutting behaviour. I know it sounds wrong but Increasing feed and speed will quite often cure machining problems. Minium tool overhang, only enough unsupported blade to cut through, the blade must be completely parrallel to the chuck, part as close to the chuck as possible, if you have a live back centre use a pressure pad to help absorb any vibration, plenty of coolent delivered via a hand held oil can. If the tool still dips I think I might resort to a hacksaw

[Donald WittmannParticipant @donaldwittmann92536]

Martin B.

If you have the scope of adjustment as regards tool height you could try inverting the parting tool and running the lathe in reverse [ok with bolted on or Camlok chucks] also for en1a steel you should try using the inserts that have a positive cutting geometry they are usually uncoated and very sharp with very low cutting forces. The type specified for non ferrous metals, a good grade will last you long enough on en1

also when parting off the worst thing you can do is approach the task with trepidation parting off calls for a fairly heavy feed and constant cutting. NEVER use a tailstock centre when parting off or the problems you are having just now will be the least of them.

Also for Ø20mm you should up your speed to about 250-300 rpm and flood coolant.

Donald.

[Martin BrundellParticipant @martinbrundell]

UPDATE:

 

Thanks to all for your suggestions and help – I’ve cracked it!!! (well you cracked it)

 

Took the crossslide off cleaned up and re-seated, upped the speed to 250rpm – this alone helped, it worked 50% better after that but still flexing slightly.

 

I then reduced the tool overhang and made sure the toolpost was more central. 75% better.

 

Then I inverted the parting tool, reversed the chuck rotation – 85% better

 

Then I dug out my carbide tipped parting tool (3mm tip) that I have never been able to use because it chattered like a bugger, inverted. PERFECT – went through it like butter!!!

 

Thanks again for all your help – I am a happy bunny again!

 

PS has anyone got a turning speed chart for EN1A – 303 free cutting stainless etc in RPM??? All I can find is metres or feet and I can’t find out how to translate.

 

Again thanks, it really is much appreciated

 

[JasonBModerator @jasonb]

This is a reasonable table in easy to work out RPM, use it as a basis as each machine will be a bit different depending on its power and rigidity.

 

http://homepage.ntlworld.com/alanet.marshall1/WS-page/table-page/tables.htm

 

One thing I didn’t add was that I tend to use the lathe with the topslide about 3″ in from the front of the cross slide, this keeps more of the slide engaged in the dovetail and saves exposing the screw when turning small diameters.

 

J

Edited By JasonB on 03/05/2011 18:23:29

[Martin BrundellParticipant @martinbrundell]

Brilliant Jason – thank you

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