Trouble with my Sabel

[Anonymous]

Posted by Martin Connelly on 06/05/2020 15:09:17:

If using a full form threading insert what rpm would you think would be needed to get blue chips off an M12 thread and how fast would the carriage be travelling?

Full form threading inserts are subtly different to normal inserts in that they don't tend to have chip breakers and have sharp edges. So you don't need to run them in quite the same way as standard turning inserts. Here's a M16 thread screwcut in EN16T:

Turning speed was 40rpm as it is a metric thread on an imperial lathe, so I had to disengage the tool manually rather than rely on the high speed threading unit. If it had been an equivalent imperial thread I'd have been cutting at 180rpm.

Andrew

[Dave HalfordParticipant @davehalford22513]

Posted by Jim Beagley on 06/05/2020 11:36:47:

Hi all and thanks for the feedback.

@Dave Halford – I will take a good look at the cross slide as I think thats where most of the adjustment is required. Is there a good resource to help me with possible scraping, or will I just destroy it if I give it a go myself?

@Andrew Johnson – I thought the finish was odd too, but Dave Halford thinks its OK – good old internet The finish is worse when using the apron to turn down the diameter. Maybe its just the crap steel. It seems to dig little chips out, but I thought that was from vibration.

My added problem I guess is that I dont really know what speeds and feed i'm using or should be using – again the web is a minefield. My drill has a handy chart next to the pulleys – cant I get the same for turning?

Thanks so much for all your time – its appreciated and I really hope to get better at this.
Jim

Jim,

I used an old file ground like a wood chisel ( no teeth), a straight edge and feeler gauges I didn't expect, nor try to get it perfect, just better. Most scraping info talks about using blue and a known flat surface, try and get one into a dovetail !!

Dave Halford said it was typical mild steel finish as in 'I've had that, it's what you get with steel that doesn't turn well. Junk like that does turn worse length wise, it's best kept for sacrificial spacers, adapter plates for mounting chucks or something that needs welding like wheel rims. You were blaming the lathe which is not at fault.

Chatter is noisy hence the name

Every chart I've seen has been unsuitably fast, assumes you have 5hp and flood coolant. In other words they are all industrial. All you can really say is if you are getting blue chips off HSS on steel slow down. At least you can't blow a motor board if you push the Sabel too hard

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