Parting Off Blues

I've used indexable parting and grooving tools to much success in the past, although the nib does wear.

The carbide tips still cut, although I think a lot of the apprehension around carbide has come from the dodgy geometry of the old cheap brazed tools that come in the sets.

Some of the boring tool ones have ridiculous geometry that's well and truly past the centre line for e.g, Even for Industrial machine it would be rubbing like hell. 

Having said that, I have got some old industrial brazed shank ones that are very smooth, sharp and well made.

Michael W

Edited By Michael-w on 14/12/2017 14:44:26

Should be possible to get uncoated parting tips for Al.

The uncoated carbide end mills work like a dream on aluminium alloys.

Neil

In answer to Colin Brannigan,

**LINK**

the blue book was "Greer and Howell". My copy, bought in 1968 for the City & Guilds 393 course, was a small hardbound book. I have a later version, "Mechanical Engineering Craft Studies," printed 1978, the first of two parts by the same authors for the CGLI 200 course, with a third part by Greer. This book is slimmer but A4 sized, with thin card covers. I think the 500 course came later than this.

As Mick B1 indicated in his answer, Chapman came in three volumes.

Nostalgically,

Bill

Hi chaps, it might be appropriate to point out that all coated grades of throw away tips have a radius over the edges, otherwise when the coatings were applied a sharp edge would push through, to see the difference one only has to fondle the exaggerated angles & ground all round with razor sharp edges displayed by tips for fine finishing on Aluminium, no coatings there then.

Where parting tools are concerned & I speak here from personal experience, when confronted with a component that calls for a flat parting off face after parting through hexagonal EN24T, to obtain an uncoated tip we would merely get a used tip out of our private collection, put it in a holder made from a short piece of part off blade attached to a small block of metal then show it to a diamond wheel, both sides, front & a tichy little chamfer on both corners no more than say 0.015", the work of one minute, problem solved. We used this technique for many years & sad as it may seem even kept records of their performance due to the mild form of OCD we suffered from, note that I can't speak for other brands but Mr. Sandviks part off blades would accept 2 adjacent sizes ie 3 & 4mm would fit the same blade, this came in useful if called upon to cut an O- ring groove in a face where a draughtsman had dreamt that it would it would be a suitable embellishment, look that one up in a dictionary as I just did, its description is bang on!

I will now shuffle off & post the last few christmas cards & let you chaps get on with some workshop time.

cheers Bob H

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

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

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

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

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

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

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.

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.