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Parting tool chatter

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goldstar31

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I have the same 3/32" blade inserted in 1973. The front IS wearing and is repeated reground-- and because it slopes is getting very near to being unable to cut 2" diameter stock.

It's Euclid. for those who missed his propositions at school missed a very valuable contributor. How sad!
But then he only worked in 2D:D
 

johwen

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Yes 1. put a small top groove in the blade to collapse the chip so that it does not drag in the groove. 2. make sure the blade is at right angles to the work. 3. make sure that cutting edge is square to the blade otherwise the too can drift sideways in the groove and if it is a deep cut can drag in the groove. 4. use a quality cutting oil on the blade. 5. if it is a deep cut in larger diameter work take a second cut opening up the groove. These are my tips for successfully Parting. If chatter is still a problem try using a narrower blade. Happy parting and stay well.
John
 

Steamchick

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Hi Dazz, I have experienced a similar effect with worn twist drills. The "Old-and-trusted" and many-times re-sharpened drill simply binds when used for a deep hole, where most of the previous drilling - and wear - has been on shallow holes. A micrometer can barely detect the wear, but it is significant and"destroys" any chance of a precise drilling when it starts the "screaming" as un-worn flank tries to ream the holes where the worn drill has left a fraction of a thou of metal. - Time to replace the drill bit! (I worked out the 3/8th in drill bit was bought around 1980! It now has a bit of tape telling me how deep I can safely drill without binding!).
K
 

BaronJ

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What you state makes perfect sense- in theory. In practice I’ve never experienced this, nor have I ever read about it in any of the lathe “bibles”. I suspect that any wear on the sides of the blade is so minuscule it is more than compensated for by the fact the blade gets shorter as it is sharpened.
I must admit that I've never experienced this phenomenon !
All but one of my parting blades have parallel sides. I would have thought that if your theory was correct, then I would have run into difficulty long before now.

As said in the quote above, any microscopic wear on the side of the blade would be removed when it was sharpened.

I did a test by swiping a red marker pen across each side of the tip of the blade, the marker only got wiped very slightly on the chuck side, but I put that down to grinding the cutting edge slightly off square or the blade being not absolutely vertical.
 

BaronJ

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Hi Dazz, I have experienced a similar effect with worn twist drills. The "Old-and-trusted" and many-times re-sharpened drill simply binds when used for a deep hole, where most of the previous drilling - and wear - has been on shallow holes. A micrometer can barely detect the wear, but it is significant and"destroys" any chance of a precise drilling when it starts the "screaming" as un-worn flank tries to ream the holes where the worn drill has left a fraction of a thou of metal. - Time to replace the drill bit! (I worked out the 3/8th in drill bit was bought around 1980! It now has a bit of tape telling me how deep I can safely drill without binding!).
K
Hi Ken,

I've noticed that, particularly on older drills that don't have ground flutes and some cheap Indian drills that I should have avoided !

The effect is worse with drills that I've reground 4 facet. Having the lips very slightly unequal stops the binding because the hole is a fraction larger than the drill.

Of course this also assumes that the drill isn't bent, or that the drill is blunt and enough pressure is used to force cutting and causing the drill to bend whilst drilling, which will cause the drill to wander off in a deeper hole.
 

goldstar31

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As the 'bibles' have been quoted, I've forgotten TWO. Well, I'm 90 and have success in parting off.
Suffice to say that I've written about it more than enough.
The origin of the one by G H Thomas is merely a development of a very successful model engineer who wrote under his own name and and with a Dr Norman Hallows as Duplex. Bradley wrote a trilogy on the Myford lathes but prior to this wrote a definitive book on tools for the lathe and shaping machine as well one on the Drilling Machine, the Shaping Machine itself. His book on grinding machines preceded everything. Fairly impressive, but turn the clock back to 1948. I was running a Technical Library in the Royal Air Force( Oh Yes, it's a non commissioned fitter's job- and I certainly was an aircraft hand general duties - the lowest of the low) and out of my miserable pay bought Leonard Sparey's The Amateurs Lathe.
Yes the rear tool post with the sloping inverted was- and I still have it- is in there.
It is still a recommended read whilst his 'engines' are built and copied yet.

Postulate if you must but 'it was ALL THERE then
 

dazz

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What you state makes perfect sense- in theory. In practice I’ve never experienced this, nor have I ever read about it in any of the lathe “bibles”. I suspect that any wear on the sides of the blade is so miniscule it is more than compensated for by the fact the blade gets shorter as it is sharpened.
Hi
It is a practical problem. I have experienced this with HSS blades.
I avoid the problem by using carbide tooling.

Dazz
 

goldstar31

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Hi
That is not what I mean. Flank wear tapers the blade width. Close to the cutting edge, the blade wears narrow. Moving back from the cutting edge, the blade is wider (not worn). The result is a fine wedge that jambs in the cut slot.

Dazz
I'm pretty sure of what BaronB has- and what standard he is capable of grinding to. He designed his own home brewed tool and cutter grinder. I have a Quorn which is capable of some very fancy grinds both in HSS and - with a CBN or diamond wheel, it can happily tackle the differences in angles--- and being able to precisely 'round off' the two cutting edges in lathe tools. The Quorn user's group has been going great guns on this topic.
So with a sort of return to what passes for eyesight, might I ask what or how the many correspondents have tackled the problems which have given them the experience to advise.

Me? In the dim and distant past I was not only a person who was making/modifying resins and - you will have to laugh- a shareholder in a failed local grinding machine manufacturer 😆

Over to others- thank you

Norman
 

stackerjack

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Hi Norman, Guys,

Well the only commercial parting blades that I have are 3/16 and 2 mm both 1/2" or 12 mm wide. The only other parting blade that I have used is 25 thou and 6 mm wide. Though in the past I've used Stanley knife blades and hack saw blades all with some success.

As far as insert parting tips are concerned, I've seen them used but I've never used one.

When you get around to chip breakers and changing angles, I've always used two or three degrees of top rake and 7 degrees of front rake. I've not altered them for years.

Best move I made for parting off was a rear tool post.
I bought some nice inserted parting tool bits. The first time I used one it flew out of it's holder, and I haven't seen it since.
 

stackerjack

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I agree with Dazz on the parting tools being tapered. Lots of books advise this method. However, when you buy a new parting tool it it always parallel. I find the thinner the blade, the better.
Jack
 

goldstar31

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I agree with Dazz on the parting tools being tapered. Lots of books advise this method. However, when you buy a new parting tool it it always parallel. I find the thinner the blade, the better.
Jack
According to 'Sparey', his tapers were 2 degrees on each flank. Mathematically, one loses a great deal of metal in subsequent re-sharpening. The next question is how does one grind two degrees?
Yes, I CAN do it but as I have the tools to do it- some bought, some I made but how does a beginner achieve it- with limited facilities? Really that is what the forum members ask-- and we try to answer.
As a sort of follow up, Sparey for one senior expert in such matters describes EIGHT standard lathe tools- including one to part off and not including boring tools.
His quoted angles were 5, 55,7,12,30, 2, 45 degrees and rounded noses of 1/16"th and 1/8"th!
The book, I must repeat is or was 'the Amateurs Lathe'

I made a comment but haven't dared print it
N
 

ajoeiam

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A "parting" shot:
"Slowly solowly.... Speed kills!"
Dunno about that - - - - especially in parting faster gets you far better chip control the smaller the diameter - - - its that last 1/8" of cutting that's such a pita!
Been more than once I stopped the machine before the cut was done - - - - it seemed safer to just break off the part!
 

Steamchick

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Mathematically, the theory says that the metal is at zero speed when you get to the centre of the parting cut. So (I think) a continuing cut will always reach some point where the metal is too slow to cut properly, and the torque required more than the tiny stem can resist, so it always breaks the last smidgen anyway.
When u you say you go faster to improve chipping, are you referring to rotational speed or feed? Maybe it's the cutting angles on my tools, but I don't get chip problems. I do cut a bit then back-off for cooling, for a second every few seconds, but that's because I cut dry most times. I'm retired so slowly occupies my time better than rushing breaking and remaking bits.
Enjoy making swarf! However you do it.
K
 

goldstar31

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As far as theory is concerned, I have passed that and for more years than I wish to recall, I CAN PART OFF SUCCESSFULLY.
The only possible problem which could arise is that the part - parted off will nip between centres.
None of these 'taking endless bites of the cherry' and that plunge cutting and starting a new cut and all sorts of variations which would baffle . Paganini. My set up is designed to part off TWO whole inches in diameter- and that's it. Enough to say that I have another lathe-- and have the casting to make another satisfactory parting tool. All That I have to do is put a sub plate under the thing and chew a few millimetres off the casting 'foot'
 

Steamchick

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Hi Goldstar. Good. I'm glad to hear that so many of us are capable of this particular operation. But (in my case) - I don't understand what I am doing well enough to know why it is easy for me and not for others? Maybe I am wrong in what I am doing, and would get better results from following others' advice, but this thread seems to cloud the issue with many saying that they have done "everything" and fail to be happy with the results. The only thing I have really spotted is that many seem obsessed with speed of parting-off, whereas I was taught (in the 1960s) to "slow down boy!". A bit slower often produces better results than "forcing" cuts to their limit.
So all I have been doing is throwing my pennorth of experience into the pond, hoping someone will find and use the treasure one day.
Sorry if I upset you? - Not my intention.
K
 

goldstar31

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Ken
Thanks for the explanation and if I am a bit critical of things, I apologise as a crusty old ninety year old- who certainly wasn't an engineer😀
I realise that model engineering is really an insignificant part of a real world.
As far as eradicating the myth of difficulties in parting off, I spent £30 or so and the cost of a couple of blades-- in 1973. I passed the aged manual to a member here after buying a clearer one. I still have the rear tool and bought a spare blade as replacement was imminent.
So arithmetically( I took top marks in Cost Accountancy:D, long before I retired for longer than I ever worked) I don't think that lost in time and in expence in the pursuit of a hobby. If you think about it, the cost -- so far- is piffling on an annual basis.

Putting it into a simpler understanding- I paid out less in almost half a century LESS than a bottle of cheap whisky- which was gone in a night

Norman
 

Steamchick

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Hmmm. Maybe I was over-reacting a bit as well... Sorry Norman.
I don't want to "compete" with that, but I made a rear tool post from a scrap off-cut from a sash weight (HORRIBLE steel - possibly ex-Battleship armour? - A lot of which went into the melting pot after the First World War?), and a simple tool post from a rectangular block of iron, with a High-speed steel tool ground to suit a traditional parting tool shape.... Cost = piffling (but who cares?), and it is arranged with a clamp such that if there is an overload, the tool post "slips" and releases the cut. It isn't the stiffest mount, but works fine for me... But maybe my crude version with a "slow and careful" cut doesn't suit everyone's style? As I am not designing tooling for high volume production it matters not a jot to me, as long as I am happy with the activity and results are good enough for my models.
But I do like to learn from all the expert machinists that write on this website.
Incidentally, as I just grind tools "by hand and eye" - the various tool angles are wherever I happened to hold the part against the grinding wheel, rather than anything exact or calculated. (after 50 years it seems natural). But my tools look a lot like the sketches in such books as "the Amateur's Lathe". I'm sure I had something like it, but I passed on my books to a friend who inherited a lathe and had zero training or background in "workshop tool and machining practice"... When I forget what I am doing I won't need to refer to the old text books, but till then.... this website is interesting.
Thanks,
K
 

goldstar31

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Well we've digressed somewhat but parting off has been flogged and flogged not just now but several times earlier and sadly - got nowhere really.

So let's deal with Three similar problems and attempt to find WORKABLE answers?

The First is 'your window weight in cast iron'. i agree with every word and suggest that you nget rid of the sand-- from where your German battleship settled in the sand in 1917 in Scapa Flo.
First heat it up red hot- perhaps on the barbecue and leave it overnight to get rid of the hardened 'skin' with some of the sand attached/embedded.
Then dunk it in what you can get- battery acid, drain cleaner or vinegar, the remain of the pickle jar or any cheap acid-- even your vomit. I jest not- all will work:p
Then hitting the right angle from a perhaps 6 inch grinder. Let's say that you want a 7 degree angle?

Multiply the 6 inches by 7 degrees and multiply it by a secret constant of 0.0088. and you get 0.369 and call it thousands of an inch. The nearest usable figure is 0.333" or a third of an inch. If you build up a wooden/plywood 'grinding table' to be that third of an inch from the centre of the wheel--- you have a grinding angle of 7 Degrees. It's taken me longer to type it than do it. It's what the 'greats' tell you but put it oion a list to hide how simple it all is :p

And now - between phoning a 'girl friend' and accepting an offer to quaff a whole bottle of Scotch with a mate- I hit trouble with a cheap and not very nice 4 jaw SC chuck which I finally wanted to use.
Everytime she walks she wobbles--- moving pictures. So what to do? Well, Martin Cleeve,authour of Screwcutting in the Lathe and Professor Dennis H Chaddock author and designer of the Quorn tool and cutter grinder came up wit a solution without buying a GripTru chuck. So far, I stripped the chuck off the Myford backplate and did a facing cut of the plate including the register-- and put it together. The wobble was gone but the jaes were a gnat's cock out. So far so good- a man on a motor bike would never see it.
But these two worthies got closer to 'concentricity' so my next job-- assuming that I will be sober tomorrow, is to remove a bit of the register on the backplate so that the chuck with its 4 bolts could move if altered. So I'm going to overbore the holes in the chuck-- so that a chuck is just tight enough o be clocked to run true- with the judicious application of a hammer.
OK if the jaws are still out a bit, I did mention the use of va Bosch POF 45 wood router.

As they say, meanwhile back on the ranch. Hope this all helps

Norman
 

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