Parting tool chatter

[mcostello]

I use a front mounted upside down insert parting tool. No where to put a rear tool. The insert tool curls the chip very good, the chip falls down out of harms way. If the tool does jam it is pushed up as I have a BXA quick change tool post. Best of both worlds.

 

[goldstar31]

I use a front mounted upside down insert parting tool. No where to put a rear tool. The insert tool curls the chip very good, the chip falls down out of harms way. If the tool does jam it is pushed up as I have a BXA quick change tool post. Best of both worlds.

And Geo H Thomas writing in his Model Engineers Workshop spends 16 pages of drawings and print on the very subject of a rear mounted tool. This , I have recommended on NUMEROUS occasions--HERE.
Again, Thomas and I share the same problematic lathe that precludes the suggestion of running a lathe with a threaded spindle BACKWARDS.

I Made a GHT version -many years ago for my Myford-- with great success and and absence of 'unusual' variations. Hemingwaykits( no connection) sells kits for the 7 inch lathe and another for larger machines.

I still have an un-machined casting and new drawings etc

 

[Richard Hed]

I use a front mounted upside down insert parting tool. No where to put a rear tool. The insert tool curls the chip very good, the chip falls down out of harms way. If the tool does jam it is pushed up as I have a BXA quick change tool post. Best of both worlds.

I've been paying attention to this thread, and I have a shi*ty little Enco that this upside down on the back side method probably would have helpt me immensely. However, now I have a new lathe that is rigid, solid, heavy and strong. I have been parting off from the front, not long cuts, but still cuts the Enco could not have made with comfort, and these are cutting like a hot sword thru . . . . well, I can't thimpfk of a metaphor. But I haven't had a bit of trouble so far. If I needs deeper cuts, I use the bandsaw. Someday, however, I will probably needs to do a deep cut with the lathe and then I might experience nasty chatter with an extended blade.

 

[goldstar31]

As I have already intimated, the little GHT is purposely designed to part a piece of 2" diameter of mild steel.

What more is there? well surprising, the Late Martin Cleeve in his hints to beginners in Model Engineer, described how he parted off 3" diameter Mild steel. It was on a part Myford ML7 because he couldn't afford a whole one-- and a mechanical hacksaw. We live and some of us learn.

 

[goldstar31]

Perhaps the topic should be:-

'How to sharpen and then hone a hss lathe tool'. and then
the Past master's one of------'How to do it all on a parting tool'
and then----- Oh no-- How to make a Quorn tool grinder

Wasser Qurn thing- mista? Like, you know all those funny ball handles that look like shaking hands with an octopus. LOL Tellus, tellus

 

[jackary]

What about this "vertical" parting tool arrangement. The topslide has been wound back just enough to enable the parting tool holder to rest solidly on the cross slide, preventing any downward deflection due to the normal cantilever extension on both a front or rear mounted parting tool. The topslide on this screenshot can lock the upper slide to the lower slide for the full slideway length using an oval gib arrangement. The parting tool shown can be HSS or a carbide insert just slightly wider than the mounting.
Alan

 

[goldstar31]

Myford to whom al shall pay due obeisance , toothbrushes at the slop, kitbags will not be worn and so on, produced a parting tool which cut from both sides of the lathe bed.

Joy upon joy-- and then they went bankrupt

Hoowz zat for a memory?

 

[Steamchick]

The tool post n tool are mounted on the cross-slide on the saddle, so fewer sliding joints between the axis of the lathe and tool. So stiffer, less clearances for relative movement,man less chatter,
k2

 

[BaronJ]

What about this "vertical" parting tool arrangement. The topslide has been wound back just enough to enable the parting tool holder to rest solidly on the cross slide, preventing any downward deflection due to the normal cantilever extension on both a front or rear mounted parting tool. The topslide on this screenshot can lock the upper slide to the lower slide for the full slideway length using an oval gib arrangement. The parting tool shown can be HSS or a carbide insert just slightly wider than the mounting.
Alan

Hi Alan,

That looks reminiscent of the sort of method used on auto or CNC tool changers.

However it doesn't get you away from the play in the cross slide.

 

[goldstar31]

However it doesn't get you away from the play in the cross slide.

Theoretically, a normal and a larger cross sectional area should be more of a problem than a very much thinner parting tool blade. The only serious concern is a thin blade being damaged or broken by swarf binding. IMHO, this is why a very experienced professional machine shop OWNER ground a kerf on the thicker bit of the parting tool, angled it all at 7 degrees to minimise 'having to grind another kerf' and then created a 12 degree and male vee shaped cutting edge.

But no John, people seem incapable or unwilling to follow logic and get their money out but rely on some far less able - perhaps nobody, as their mentor in a correspondence course.

I'm going on,

Norman

 

[fcheslop]

I now use chip breaker blades as they are cheap enough and long lasting and it saves this lazy beggar having to grind them up
https://www.chronos.ltd.uk/product/...-mm-wide-x-80-mm-long-m-35-hss-with-5-cobalt/

 

[bikr7549]

I have been frustrated by the cut off operation, but recently it has all changed for the better. I came across an idea for a tool holder and tool alignment on the lathe that has made this operation a dream! A YouTube video on the holder and one on cut off tool alignment are below, and I cannot believe how easy this has become. Aligning things so that there is minimal torque on the tool might have helped operations without making the new holder, but I decided to try it with the new holder (and a narrower T type blade). In retrospect I bet much of my troubles were due to the tool holder (a quick change type) being off to the side-now the tool holder sits close to the center of the rest. I don't think he mentions why he has the compound adjusted to be perpendicular to the lathe axis, but I did this as well. Check it out. The holder was pretty easy to build, maybe 4 hours of work-I used my new Harbor Freight 4x6 saw to make the clamping slit, and it worked like a charm-I am pretty happy with that saw so far.

 

[bikr7549]

Here is a top view of my new holder.

 

[SmithDoor]

It is used for products work for speeding up work.
The only time I have used back cutoff .
But you do need to a lot of parts and do setup right.
Since most my work is 1 to 5 parts and a fast change tool post is faster.

Dave

What are the benefits (or disadvantages) of rear, upside down mounting of the cutter for parting off?

 

[goldstar31]

It is used for products work for speeding up work.
The only time I have used back cutoff .
But you do need to a lot of parts and do setup right.
Since most my work is 1 to 5 parts and a fast change tool post is faster.

Dave

Of course this is NOT home workshop! Having to 'Work' takes away whatever we we have in this limited existence
My thoughts on a mere 36 years of retirement were, on reflection, not long enough.
So back to GHT and I had a quick look at the alternative drawings-- and note that a Mr Riley alltered the GHT turret to one parting blade and-- another lathe tool.
Somewhere else, and a long time ago, the rear turret was further modified to take things like boring tools.
From where I sit, this parting off thing- which is merely at the making washer stage, has to advance and not only slice rectangular and irregular material but go on to such things as making tee slots around the periphery of a rotary table or- in my case on the Quorn T&C, a continuous angle cut to add limits or stops.
As some say, it's all go!

The old site was that of a Chris Heapy, Sadly, very little seems to be left

Nornan

 

[Apprentice707]

I may have missed it, but I don't think Bikr7549 locked the carriage before he made the cuts. This is always a good idea since it gives even more rigidity. I use a rear tool post with a Ganze insert cutter which serves me well, just have to remember to check the tool height from time to time.

 

[Steamchick]

Hi Guys,
A lot of clever stuff here, and I don't doubt that you all make it work somehow.
But just a note on parting using the toolpost mounted directly on the cross-slide behind the work-piece, the workpiece rotated "normally" and the tool upside-down. This is so that the forces through the saddle onto the bed are exactly the same (rotational torque) as "normal cutting", so you are using all the sliding surfaces on the bed as designed to resist that torque. You are NOT transmitting torque through the rotatable longitudinal top slide, which adds extra potential slack to the chain of torque transmission. And if your quick-change toolpost doesn't act as stiff as a directly mounted tool, then pit it on the shelf and directly mount the tool near tool centre. For precision machining you need the stiffest set-up possible, but for light machining you can get away with hand-held tools (It is called Graving).
Also, if you run the lathe backwards with an upside down tool in the regular toolpost, you are actually putting the stresses at saddle-to-bed and between top-slide and cross-slide all on the gib-strips - I.E. the "adjustable" parts of the slides. This is not doing you any favours in a situation when the blade chatters. The lathe was designed to work best one-way, so when highly stressed - as in parting and anything that takes a lot of torque, it is better to use it that way.
I am not saying don't work backwards, standing on your head or with eyes wide shut, but it is better to work "forwards", standing upright and with eyes wide open.
Just do what you like doing and enjoy it.
We are only here to advise BEST PRACTICE, not smack your hands like teachers. (I sometimes break the rules myself - because I am lazy, or find it works well enough for the job I am doing - I am just a normal human that does that sort of thing, but I wouldn't advise you copy my bad practices!).
Enjoy,
K2

 

[Steamchick]

What about this "vertical" parting tool arrangement. The topslide has been wound back just enough to enable the parting tool holder to rest solidly on the cross slide, preventing any downward deflection due to the normal cantilever extension on both a front or rear mounted parting tool. The topslide on this screenshot can lock the upper slide to the lower slide for the full slideway length using an oval gib arrangement. The parting tool shown can be HSS or a carbide insert just slightly wider than the mounting.
Alan

Great. This is doing the same thing as a rear mounted toolpost - attaching the tool to the cross-slide and eliminating the twisting motion on the top-slide gibs.
I like the rear mounted tool-post, as I don't have to set anything up every time I part-off (almost every job I make from stock bar).
Remember, if the parting tool isn't EXACTLY square to the rotational axis of the workpiece there will be unwanted side forces on the blade (the cut face will be tapered or curved, not flat and true). Also a blade with any taper in any direction will cause side thrust at the cutting edge that will cause more problems than I want to consider. Goldstar is clever and can grind near perfect symmetrical shapes on the ends of his tools (from what I can glean here), but with hand grinding I would not attempt it - because of the side-thrusts that can ruin a job. Often Parting is the last operation, so you don't want to waste all the work done previously (and possibly your only bit of metal that size!).
Set right, cut once, cut right! (always Check, check, and check again.).
And ENJOY your HOME MACHINING.
K2

 

[SmithDoor]

My experience comes from manufacturing starting 1960's. Including setting up turret lathes an screw machines. Setting up Gisholt #5L , J&L #4 , B&O #3 , B&S #2 and Truab screw machines

Dave

Of course this is NOT home workshop! Having to 'Work' takes away whatever we we have in this limited existence
My thoughts on a mere 36 years of retirement were, on reflection, not long enough.
So back to GHT and I had a quick look at the alternative drawings-- and note that a Mr Riley alltered the GHT turret to one parting blade and-- another lathe tool.
Somewhere else, and a long time ago, the rear turret was further modified to take things like boring tools.
From where I sit, this parting off thing- which is merely at the making washer stage, has to advance and not only slice rectangular and irregular material but go on to such things as making tee slots around the periphery of a rotary table or- in my case on the Quorn T&C, a continuous angle cut to add limits or stops.
As some say, it's all go!

The old site was that of a Chris Heapy, Sadly, very little seems to be left

Nornan

 

[jackary]

Baronj wrote,

"That looks reminiscent of the sort of method used on auto or CNC tool changers.

However it doesn't get you away from the play in the cross slide. "

I agree with you Baronj but the main point of the vertical parting tool is it avoids the horizontal cantilever distance from the parting tool mounting point to the cutting tip. This horizontal distance is present in both front or rear parting tool set ups and this exaggerates any defficiences at the mounting point base or as you say cross or topslide. The vertical parting tool has solid metal support from the tip to the top of the cross slide.

Alan