Parting Off Blues

[Mick HenshallParticipant @mickhenshall99321]

My best parting tool is made from the old fashioned carbon steel, have quite a few carbon steel tools and actually like them, mostly hss for me though, do not like inserts of any description apart from cost and to me bewildering choice my lathe has a top speed of 450 rpm so doesn't run fast enough, I machine small diameters at this speed,or lower, and get a perfectly acceptable finish using hand feed

Mick

[SillyOldDufferModerator @sillyoldduffer]

Posted by Neil Wyatt on 14/12/2017 16:21:04:

Should be possible to get uncoated parting tips for Al.

…

Neil

They certainly exist but – so far – I've not found a UK source of GTN-3 inserts for Aluminium. GTN-2 yes; GTN-3 for Stainless Steel yes; GTN-3 general purpose yes; GTN-3 'unsuitable for Aluminium' yes. What I want, no. Well not yet anyway!

They are available in the US and hence a little expensive to import. I haven't tried ebay or banggood yet, so the Interweb may not have failed completely! I notice a number of tool sellers hide information inside their catalogues such that Google doesn't find individual parts. As I didn't have time to read through pages of inserts, it's likely I've missed a UK seller.

Dave

[Ian S CParticipant @iansc]

Mick, I see you use carbon steel for parting tools, my first parting tool was a modified piece of a broken 12" x 1" flexi back power hacksaw blade with the teeth ground off, this saw me through the first couple of years of using a lathe, and if I want a thin blade I still use it. With the teeth ground off it still has a little bit of HSS and this cuts well, you must have the cutting edge square to the blade, and the blade square to the work or it will wander off and jamb up.

Ian S C

[Mick HenshallParticipant @mickhenshall99321]

Yep Ian  I have some parters made from m/c hacksaw blades its what my Gramps used although I have not tried one yet, I did like the recent post where someone used a slitting saw,might try that later long as I can clear swarf, I think firm but not heavy handed on feed is the order of the day, perhaps grinding every other tooth out on the saw would help

Mick

[Mick HenshallParticipant @mickhenshall99321]

Yep Ian  I have some parters made from m/c hacksaw blades its what my Gramps used although I have not tried one yet, I did like the recent post where someone used a slitting saw,might try that later long as I can clear swarf, I think firm but not heavy handed on feed is the order of the day, perhaps grinding every other tooth out on the saw would help

Mick

[SillyOldDufferModerator @sillyoldduffer]

I've had a most useful phone call from Ketan Swali who knows this type of blade well. He highlighted the importance of maintaining a steady feed and proper lubrication when using them. They're intended for use in a CNC machine rather than being manually driven.

CNC machines cut at high speed, properly lubricated, with a steady feed-rate. I confess my hand parting-off feed-rate is erratic. And bumping and rubbing are both bad news, particularly with Aluminium. I'm sure I could be more consistent with practice

Ketan's advice fitted well with my practical experience. Next time I'll be setting up a coolant drip-feed and parting off under power at high speed. While nervous about the result I'm convinced that fortune favours the brave when using carbide! This beginner must become a man of iron in both senses.

Despite this being an apparent tail of woe, I've had much more success with a blade type holder and insert than any other method I've tried. It has long reach, is easy to set-up, cuts like fury, and – ahem – takes a fair amount of abuse. In comparison I think HSS is more tolerant of mistakes, even though I've broken a few of them too. HSS blades work well at slower speeds but only if kept sharp with correct rake and applied gently. I also have a conventional chip insert parting holder: it doesn't seem to cut as easily as the blade type and has limited reach. Never broken one though!

None of the parting tools work properly unless the whole set-up is rigid. Cut close to the chuck; tight slides; locked saddle; rear-tool posts etc. – it all helps.

Dave

[choochoo_balooParticipant @choochoo_baloo]

Posted by Vic on 13/12/2017 23:06:20:

Posted by choochoo_baloo on 13/12/2017 20:59:57:

Dave, I was told recently by machining researchers at major engineering research centre (in other words it's on very good authority!) that indexable tip tools are actually overkill for virtually all amateur lathes.

I think many on here would actually agree with this but that’s not to say insert tooling can’t be used to good effect on small Lathes.

Whilst industrial inserts really don’t work very well on small machines there are lots of inserts now available that are aimed at the home user. I particularly like using the polished carbide inserts on my modest 8” Lathe. Time and time again though new users asking for advice are here are directed to using HSS tooling before trying anything else.

Sadly some have chosen to miss read what you’ve said and even resorted to making stupid petty comments as usual.

Yeah thanks Vic. I was just trying to be helpful.

Neil, for the record these industrial/academic researchers are improving methods across all machining scales. I hope other hobbyists will take direct over circumstantial evidence.

[John ReeseParticipant @johnreese12848]

A few observations:

If the insert doesn't seat fully in the blade the height of the tip will become lower as the insert pushes back in the blade. I have seen tools made to properly seat the inserts. It was a bar with 2 pins protruding. One pin engaged the hole in the blade. The other pin would bear end of the insert. It was used to lever the insert into place.

On a deep parting cut it is difficult to get lubricant to tip of the tool. Lube is essential to prevent chip welding to the insert. It also keeps the chips from welding to the sides of the cut.

I have found it useful to cut as deep as I can without difficulty. Then I offset the tool and cut the groove wider. That prevents chips binding in the kerf. After that I can resume cutting from the bottom of the kerf.

I have both carbide insert parting tools and HSS parting tools. On aluminum I prefer the HSS because I can get a dead sharp edge and I can grind in back rake.

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