Parting off

[Peter Simpson 3Participant @petersimpson3]

Hi all,

I have just been asked to make a part

Final dimensions are as follows

BMS 34mm diameter 2.8mm thick with a M10 x 1.0 hole through the centre Basically a large washer. I tried drilling and tapping the central hole, then attempted to parts off over length. Using various parting off tools I could not part off “slices” as the parting off tool just kept grabbing half way through the cut. Any ideas how to proceed ?

[Andrew CrowParticipant @andrewcrow91475]

Hi Peter, I think a bit more information would be needed ie machine being used, type of parting tool, front or rear tool post, spindle speed, coolant/lubricant being used etc

Andy

[HollowpointParticipant @hollowpoint]

My guess is that your parting tool isn’t dead square to the face of the chuck. If you go in at an angle it will almost certainly grab.

[JAParticipant @ja]

There are a lot of things that can go wrong parting off. Try or correct:

1. Is the tool the correct height?
2. Try a rear tool post.
3. Always cut or move the tool away from the work.
4. Remove swarf frequently
5. Use slow speed.
6. I consider 12mm, radial, a deep parting off cut. Do the first 4mm, remove the tool and move half a tool width away from finishing face. Then cut the next 4mm. Return the tool to its first position and do the next 4mm. And so on.

JA

[Roderick JenkinsParticipant @roderickjenkins93242]

I suggest you use a parting blade with a carbide insert.  The insert is wider than the blade and gives clearance to the supporting blade.  Another suggestion is to be bold with both spindle speed and feed rate.

Rod

[JasonBModerator @jasonb]

I take it you did not buy the bandsaw you were asking about previously. If you did lop it off with that and then face to width.

As per first reply without knowing the lathe and setup it is hard to offer advice.

You also mention “sliceS” do you have a lot of material sticking out the chuck to make multiple parts?

[Grindstone CowboyParticipant @grindstonecowboy]

The usual, and very good, advice is to have the tool on exact centre height. However, I’ve found – possibly due to a bit of flex in my setup due to wear – having it a fraction higher than centre helps. Not a lot, of course, maybe up to 5 thou.

Rob

[Roderick JenkinsParticipant @roderickjenkins93242]

Here’s video parting 32mm diam. EN3 using a 2mm insert from ArcEuro of blessed memory

I used to rely on my rear toolpost but have learnt that parting is largely a matter of confidence.  I still use the rear toolpost but mostly for convenience.

Rod

[JasonBModerator @jasonb]

I also like the 2.2mm wide GTN-2 inserts, this is a bit of 30mm EN3 on an Amadeal 210E lathe, nicer swarf than Rods😉😉

 

Same tool on the Warco 280 cutting a 1.5mm slice off a 70mm diameter iron casting

[Julie AnnParticipant @julieann]

The swarf shown by JasonB looks a bit odd. I would have expected a parting off insert to form the swarf into a curved shape of narrower width than the insert. Thus reducing the risk of jamming. This is the steel swarf I get from my 3mm insert parting off blade:

Another factor rarely mentioned is feedrate. With parting off inserts I never go lower than 0.1mm per rev, otherwise the insert chatters. I always part off using power crossfeed.

Julie

[Howard LewisParticipant @howardlewis46836]

The rules for parting off are:

Slower than normal turning or facing.

Part off as close to the chuck as possible.

Minimal overhang of the parting tool.  You need to have everything as rigid as possible.

The face of parting blade should be perpendicular to the lathe axis. (A parting blade ground at an angle will produce swarf that is wider than the groove, and likely to jam)

This where the raplaceable carbide tips score. They generally have a central groove, so that the tool mproduces two harrow streams of swarf, which curl minwards and are unlikely to jam in the groove.

Keep a slow steady feed, DON’T rush, but don’t let the tool rub! (This means that you need to have the basic skill of providing a steady feed of the tool, whatever task you are underaking on the lathe). If in dounbt, go slow!

If you can arrange a steady, if only a drip feed, supply of lubricant (Soluble or mineral oil) this will help. Machine brass and copper alloys dry, lubricate ferrous materials, but not cast iron.

If you can fit (make?) a rear toolpost, an inverted parting tool in it will improve matters (The swarf falls away, so less likely to jam)

Needless to say, the parting tool needs to be sharp (I do not use top rake; and am now so brave /over confident that I often part off under power cross feed of about 0.002″ per rev wihich leaves hands free to apply lubrication.

This is my take; others may use other methods, but H T H

Howard

 

[JasonBModerator @jasonb]

If I blow the image up I can see some fold lines where the edge has been turned in. Likely the finer feed I was using on the less powerful and less rigid machine combined with having to feed one handed and no power feed has an effect on how the swarf is shaped.

It curls more on the Warco with it’s power feed but that won’t take a 0.1mm feed unless the diameter is quite small but on that sort of diameter I’m more than likely to use a 1mm wide insert.

[JasonBModerator @jasonb]

I just braved the hot workshop, hopefully this not very good photo will show th edufference feed rate can make.

1″ EN1A, 250rpm, GTN-1 Insert.

On the right was a fine power fee dof 0.00075″ on the left the feed was double at 0.0015″ which has not only been folded far more but also broke up into smaller pieces.

I would expect a heavier lathe like Julie’s to fold the swarf even more

[John HaineParticipant @johnhaine32865]

I am amazed just how often this topic comes up – an annual event?  I know this site is hungry for content but surely there must be a case for posting a permalink to an edited summary of the best advice?

[Howard Lewis]

On Howard Lewis Said:

…over confident …

 

Like the man in the cartoon which appeared in ME many years ago!

[MacolmParticipant @macolm]

One thing to be aware of is the possibility a four way or QC tool post may seem to be securely clamped by the centre bolt, but have low clamping force round the periphery. In operations subject to shock loads such as parting, it may deflect, resonate or allow dig in.

My Bantam came with an OEM Gibraltar tool post, but this proved unsatisfactory for parting off. The clue was that when its fixing bolt was tightened, the top slide became slightly stiff – it distorted the top slide, so presumably did not achieve full area contact. I simply no longer use it, having done nothing about this. A low cost four way tool post proved little better for parting off, though fine for normal turning – it had a flat surface in contact with the top slide.

I eventually bought an AXA (wedge) QC tool post, which appears to be well designed for rigidity. It did need a 5mm thick spacer to set the optimum height, and I made this circular (and have never got round to squaring off the periphery), but I relieved both top and bottom faces by about 0.03mm (just over a thou). This is plenty to ensure high contact pressure around the periphery. The proof is that parting off is now easy and undramatic. The QC kit also came with a T slot clamping bar the same length as the tool post, and this increases considerably the stiffness of clamping surface.

 

 

[Howard LewisParticipant @howardlewis46836]

EGA,

Not too over confident; dig ins are very rare with a HSS blade. (Saying that is asking for trouble, despite a rigid rear toolpost)

They were more frequent when the HSS parting tool was angled to leave no pip on the workpiece, beacause of the swarf being wider than the groove and therefore likely to jam.

Am a firm believer in a slow steady feed (Which is what my PCF gives) I’m lucky to have that facility, otherwise the need for the skill to provide a slow steady hand feed.

The carbide inserts make life easier by folding both sides of the swarf inwards, reducing the risk of jams.

Howard

[egaParticipant @ega]

Howard:

No dig(in) intended, of course. I turned up the B Terry Aspin cartoon and, in fact, it was nonchalance rather than confidence:

https://www.homemodelenginemachinist.com/threads/one-of-my-farthers-cartoons-b-terry-aspin-chuck.31508/

[John Haine]

On John Haine Said:

I am amazed just how often this topic comes up – an annual event?  I know this site is hungry for content but surely there must be a case for posting a permalink to an edited summary of the best advice?

but who decides what is “best advice” and what is bad advice

[Howard LewisParticipant @howardlewis46836]

The advice given is usually what works for the one posting. They hope that their experience, which works for them, will be of benefit to the enquirer.

What works on one particular machine/tooling/operator set up may not successfully read across to another different one.

Many find a rear toolpost beneficial, others are able to part off, without problems using just the front toolpost.

You don’t find out until you try

Horses for courses

Howard

[martin haysom]

On martin haysom Said:

On John Haine Said:

I am amazed just how often this topic comes up – an annual event?  I know this site is hungry for content but surely there must be a case for posting a permalink to an edited summary of the best advice?

but who decides what is “best advice” and what is bad advice

As Howard says the “best advice” needs to be tailored to the specific enquiry, hence the early posts asking the OP for more details but as so often happens people ask and then don’t come back to their thread.

 

For example using Julie’s 3mm wide tool with a 0.1mm feed would be good advice for someone with a M300, Colchester Student, or similar but it is bad advice if the person only has a Unimat 3, which will just grind to a halt. Likewise no use telling a U3 user to make and use a rear tool post when the cross silde is only a 50mm square with a single slot offset to the front as you can’t get behind the work.

[Chris CrewParticipant @chriscrew66644]

For what it’s worth, and I have said it all before,  inverted tool set just above centre height in a rear tool post. I use the old fashioned Eclipse parting blade type. Copious coolant,  preferably pumped on not dabbed on, slower speed and continuous feed (l usually feed in by hand) and once the tool cuts,  keep it cutting. I have parted noggins big enough for Myford backplates like this, although admittedly on a Colchester Student which is a very rigid machine but the modus operandi works for me.

[duncan webster 1Participant @duncanwebster1]

The eclipse blades  had taper top and bottom to fit their holder. Can you still get them, I’ve tried and failed

[JasonBModerator @jasonb]

MSC Direct have them in 5 different widths

[JasonB]

On JasonB Said:

… but as so often happens people ask and then don’t come back to their thread. …

 

I expect I’ve been guilty of this. It might help if the option for an email notification of responses were on by default.

 

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