Why is this guys mini lathe parting off so well?

[Mick B1Participant @mickb1]

Whether or not a rear toolpost is worth making or obtaining depends on how much parting-off you really need to do and how much of a fetish you're prepared to make of it. If you're making several tens of something from bar stock it's worth having and may even be worth making.

If you generally part-off half-a-dozen or so times a week, and you have to do your milling in the lathe for the time being, the location is better used for a vertical slide – and you resolve your parting problems well enough so they don't get in the way of what you want to do.

There can be problem materials for parting, but with those you usually find that parting's only another aspect of the misery you'll meet in other kinds of op too.

If the tool's sharp, square to the spindle axis, on-centre, as close as practical to the chuck, and the right width and protrusion for the work, it shouldn't be so stressed as to nod the toolpost or flex the compound, even in a tiny lathe. Those movements in the vid were a clear sign that other things were wrong.

[Neil WyattModerator @neilwyatt]

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Neil

[Neil WyattModerator @neilwyatt]

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[Philip AParticipant @philipa30666]

Posted by Vic on 22/10/2020 11:05:02:

The best parting tools I’ve used on my mini lathe are the HSS chip breaker type.

**LINK**

I've seen these mentioned, why are they not more popular?

[Philip AParticipant @philipa30666]

Posted by SillyOldDuffer on 22/10/2020 09:28:49:

What sort of steel are you working with Philip? Mild-steel formulated for enhanced machinability (EN1A, even better En1APb) is significantly friendlier than ordinary structural mild-steel (EN3). Many other steels don't machine well and some are vile. Beware of unknown scrap! Better for beginners to buy a machineable steel rather than get into a disappointing muddle with one of the awkward squad. Difficult metals can be tackled later.

Dave

I bought some steel from the local stockholders as it was dirt cheap. I've just looked up the EN1A steel, though one problem will be that it can't be zinc plated once machined due to the lead content (according to Google).

[Philip AParticipant @philipa30666]

Posted by Ron Laden on 22/10/2020 14:06:15:

I think one of the failings of the small mini lathes is the lack of rigidity of the tool mount/compound slide through to the cross slide, you can see in the video the amount of flex at the tool post.

My CJ18 mini lathe was a bit of a nightmare when parting off, it depended on the job it was sort of ok with not too heavy or deep cuts in aluminium but parting steel was always a problem.

I went down the rear tool post route which transformed it and made parting off a pleasure to do, it did mean however making a heavier duty cast iron cross slide with T slots and a 50mm square steel tool post for the parting tool. Obviously a fairly serious mod but it did cure the parting problems and to some degree improved general turning having a heavier cross slide bed.

Picture below of the original cross slide and the heavier version, not a 5 minute mod but it was worth the effort.

Ron

Edited By Ron Laden on 22/10/2020 14:20:20

Did you make the new cross slide? Does it also use gibs with bolts to tighten it up?

[Philip AParticipant @philipa30666]

Posted by JasonB on 22/10/2020 12:58:20:

The only thing more worrying is how much trouble the OP must be having to feel that the cut in the video is so good!

Phillip exactly which of the parting blades did you get from ARC?

This is the parting tool that Arc recommended: https://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Lathe-Turning-Tools/8mm-Parting-Off-Tool-with-Parting-Blade

[Philip AParticipant @philipa30666]

Thank you for all the friendly replies. I can't answer every post but will be trying out all the tips and advice and I'll let you know what happens.

[Andy_GParticipant @andy_g]

Posted by Philip Antoniou on 22/10/2020 07:08:55:

I've ordered some taper bearings and upgrade gib strips as I've read that these help with parting off.

 

As another fairly inexperienced mini lathe owner, I'd say don't rush into changing things (especially spindle bearings) – there may well be bigger improvements to be made through set-up and technique.

In addition to all the advice above, I'd say to run the spindle as slowly as you sensibly can (maybe 150RPM or less), at least to start with. My lathe has a brushless motor (no high/low gear) which might make this easier.

Check your compound slide for play (grab the toolpost and rock it across the direction of slide travel and look closely at the joint between the two halves of the slide for signs of movement.

[The main issue with my compound slide was that the gib strip was rocking as load came on the toolpost, allowing the slide to lift. The problem (in my case, and I suspect many others) was that the gib adjustment screws were acting too far back from the sliding face of the gib for it to be stable (the gib is too thick for its height). This was compounded by the shape of the adjusting screw tips and recesses in the gib.]

Bolt the lathe down to something (with care to avoid distorting it) – this helped a lot with mine – see here

 

I might have gone a bit OTT with truing up the base, but it does help a lot. My parting at the end is still a bit hesitant, because I was expecting bad things to happen, but I've parted off 42mm dia free cutting steel and 80mm aluminium since without any problems. I do use a decent parting tool in the original 'lantern' toolpost for parting anything tougher than (say 20mm diameter) brass or aluminium.

Edited By Andy Gray 3 on 22/10/2020 20:12:33

Edited By Andy Gray 3 on 22/10/2020 20:13:31

[Andy_GParticipant @andy_g]

Posted by Philip Antoniou on 22/10/2020 19:55:36:

This is the parting tool that Arc recommended: https://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Lathe-Turning-Tools/8mm-Parting-Off-Tool-with-Parting-Blade

I have something very similar, and don't find it very useful – I do use it on a quick change toolpost for small diameter brass / ali or for cutting grooves.

I found this type much less touchy and more useful:

https://www.rdgtools.co.uk/acatalog/SMALL-PRO-PARTING-SYSTEM–9MM-SHANK–1729.html

[Andy CarlsonParticipant @andycarlson18141]

Posted by Philip Antoniou on 22/10/2020 19:55:36:

This is the parting tool that Arc recommended: https://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Lathe-Turning-Tools/8mm-Parting-Off-Tool-with-Parting-Blade

I havent got the Arc Euro one but it's important to check that the blade is being held properly upright with this type of holder. If it's leaning over by just a few degrees that will mean that the clearance angle on one side is not doing its job and that side can rub. I needed to use some shim to make sure my blade was properly vertical.

[Andy StopfordParticipant @andystopford50521]

[The main issue with my compound slide was that the gib strip was rocking as load came on the toolpost, allowing the slide to lift. The problem (in my case, and I suspect many others) was that the gib adjustment screws were acting too far back from the sliding face of the gib for it to be stable (the gib is too thick for its height). This was compounded by the shape of the adjusting screw tips and recesses in the gib.]

You can also check this by trying to lift the topslide from underneath the dial end – you may find an alarming amount of play.

On my mini-lathe this was due to the cross slide gib being completely the wrong shape in cross section, and not deep enough to fill the space in which it was supposed to work. I made a new one from brass – quite fiddly due to the difficulty of actually gripping the thing – if you're a beginner, you might want to leave doing this for a while.

To be getting on with, if your gib strip is like this I reckon you could probably make it work a lot better by shimming it against the underside of the cross slide – an old beer can is a useful source of aluminium shims. Try to fill the gap at the top as much as possible short of making it jam.

[Ron LadenParticipant @ronladen17547]

Posted by Philip Antoniou on 22/10/2020 19:53:46:

Posted by Ron Laden on 22/10/2020 14:06:15:

I think one of the failings of the small mini lathes is the lack of rigidity of the tool mount/compound slide through to the cross slide, you can see in the video the amount of flex at the tool post.

My CJ18 mini lathe was a bit of a nightmare when parting off, it depended on the job it was sort of ok with not too heavy or deep cuts in aluminium but parting steel was always a problem.

I went down the rear tool post route which transformed it and made parting off a pleasure to do, it did mean however making a heavier duty cast iron cross slide with T slots and a 50mm square steel tool post for the parting tool. Obviously a fairly serious mod but it did cure the parting problems and to some degree improved general turning having a heavier cross slide bed.

Picture below of the original cross slide and the heavier version, not a 5 minute mod but it was worth the effort.

Ron

Edited By Ron Laden on 22/10/2020 14:20:20

Did you make the new cross slide? Does it also use gibs with bolts to tighten it up?

Philip, yes I did make the heavier duty cross slide but like I said it is quite a serious mod, picture below of finished item. You need a sizeable chunk of cast iron, a T slot cutter and a dove tail cutter, and a mill. Yes the cross slide is gib mounted with adjusting screws but I increased the screws from 3 to 5.

Before getting in to any serious mods and I am not suggesting for one minute that you make a new cross slide, I did but I wanted a rear tool post and T slots. Have you tried inverting the parting tool and running the lathe in reverse, quite a few people seem to get better results in parting this way on the mini lathe.

[Philip AParticipant @philipa30666]

Posted by Ron Laden on 23/10/2020 08:14:33:

Posted by Philip Antoniou on 22/10/2020 19:53:46:

Posted by Ron Laden on 22/10/2020 14:06:15:

I think one of the failings of the small mini lathes is the lack of rigidity of the tool mount/compound slide through to the cross slide, you can see in the video the amount of flex at the tool post.

My CJ18 mini lathe was a bit of a nightmare when parting off, it depended on the job it was sort of ok with not too heavy or deep cuts in aluminium but parting steel was always a problem.

I went down the rear tool post route which transformed it and made parting off a pleasure to do, it did mean however making a heavier duty cast iron cross slide with T slots and a 50mm square steel tool post for the parting tool. Obviously a fairly serious mod but it did cure the parting problems and to some degree improved general turning having a heavier cross slide bed.

Picture below of the original cross slide and the heavier version, not a 5 minute mod but it was worth the effort.

Ron

Edited By Ron Laden on 22/10/2020 14:20:20

Did you make the new cross slide? Does it also use gibs with bolts to tighten it up?

Philip, yes I did make the heavier duty cross slide but like I said it is quite a serious mod, picture below of finished item. You need a sizeable chunk of cast iron, a T slot cutter and a dove tail cutter, and a mill. Yes the cross slide is gib mounted with adjusting screws but I increased the screws from 3 to 5.

Before getting in to any serious mods and I am not suggesting for one minute that you make a new cross slide, I did but I wanted a rear tool post and T slots. Have you tried inverting the parting tool and running the lathe in reverse, quite a few people seem to get better results in parting this way on the mini lathe.

I was asking more out of curiosity, that is too much of a mod for me, though I'll consider the rear toolpost for a later date.

I just shimmed the gibs on the underside of the carriage as they were riding on the edge of the ways. I used shim washers instead of cutting strips of shim that most people use, seems rigid. Fitted the Arceurotrade brass gibs; one has made an improvement, letting me tighten up the gib more while still letting the side move. But the other gib is the wrong size and just jams the movement.

I'll probably fit the taper bearings as I have them now, but need to make a special nut to hold the back of the main shaft for the puller. That's a 30mm part so will see if I can part that off or if I have to resort to a hacksaw.

[LainchyParticipant @lainchy]

I personally use an arc 3/32 parting blade and it's fine on my Chester DB7….as long as it's sharp, and set at the correct height. I tried with 1/16, and it was too flexible – it wondered off easily, even on brass.

[Alan JacksonParticipant @alanjackson47790]

Here is my version for a parting tool. The cutting tool is in compression, avoiding the flexure due to the conventional cantilevered parting tool

Alan

[Lee RogersParticipant @leerogers95060]

My Drummond Admiralty B type is not the most rigid machine so I avoid insert tooling and anything else that might upset it. However it's party trick is a Glanze parting insert tool and powered crossfeed . Consistent feed and a free hand to keep the cutting oil flowing does the trick.

[Philip AParticipant @philipa30666]

Posted by Ron Laden on 23/10/2020 08:14:33:

Posted by Philip Antoniou on 22/10/2020 19:53:46:

Posted by Ron Laden on 22/10/2020 14:06:15:

I think one of the failings of the small mini lathes is the lack of rigidity of the tool mount/compound slide through to the cross slide, you can see in the video the amount of flex at the tool post.

My CJ18 mini lathe was a bit of a nightmare when parting off, it depended on the job it was sort of ok with not too heavy or deep cuts in aluminium but parting steel was always a problem.

I went down the rear tool post route which transformed it and made parting off a pleasure to do, it did mean however making a heavier duty cast iron cross slide with T slots and a 50mm square steel tool post for the parting tool. Obviously a fairly serious mod but it did cure the parting problems and to some degree improved general turning having a heavier cross slide bed.

Picture below of the original cross slide and the heavier version, not a 5 minute mod but it was worth the effort.

Ron

Edited By Ron Laden on 22/10/2020 14:20:20

Did you make the new cross slide? Does it also use gibs with bolts to tighten it up?

Philip, yes I did make the heavier duty cross slide but like I said it is quite a serious mod, picture below of finished item. You need a sizeable chunk of cast iron, a T slot cutter and a dove tail cutter, and a mill. Yes the cross slide is gib mounted with adjusting screws but I increased the screws from 3 to 5.

Before getting in to any serious mods and I am not suggesting for one minute that you make a new cross slide, I did but I wanted a rear tool post and T slots. Have you tried inverting the parting tool and running the lathe in reverse, quite a few people seem to get better results in parting this way on the mini lathe.

One question though Ron, I would have thought that most of the play in the slides is due to the gib moving/rotating and not due to the steel flexing, so I'm surprised that increasing the size of the slide is a major upgrade. Am I missing something?

[Martin ConnellyParticipant @martinconnelly55370]

NDIY hinted at the Z axis overhang early on (Parting off outboard of the centre line of the cross slide and/or top slide is inviting more flex in the machine.). This is how far towards the cutting tip is towards the chuck beyond the carriage support point for the cross slide. In the video by the OP this is clearly a major error in the setup. One of the things rear tool post parting systems do is effectively reduce this overhang to zero. I suspect that a dedicated mounting for a parting blade that mounts directly to the cross slide at the front will have no z axis overhang and so remove one of the potential errors in set up. Parting requires everything to be set up correctly, any error will be punished. My starting point for setting up for parting is to move the carriage under the point of parting off (or as near as I can get it) before anything else. Neil's photo with chatter marks looks like it may have some z axis overhang.

Martin C

[Andy_GParticipant @andy_g]

Posted by Philip Antoniou on 23/10/2020 09:35:29:

I just shimmed the gibs on the underside of the carriage as they were riding on the edge of the ways. I used shim washers instead of cutting strips of shim that most people use, seems rigid. Fitted the Arceurotrade brass gibs; one has made an improvement, letting me tighten up the gib more while still letting the side move. But the other gib is the wrong size and just jams the movement.

Be slightly careful with the shimming – it cures a symptom rather than the cause. The gib shouldn't bear on the bottom of the slide (or the top). If it does, it is either not being held properly by the adjustment screws, or is rotating slightly, which forces the lower corner into the bottom of the slide.

In an ideal world, the pressure on the gib should be at right angles to the sliding face – it isn't on the mini lathe (and many other designs, too) so there is a tendency for the gib to be pushed downwards as the adjustments are snugged up. There needs to be enough engagement of the adjustment screw tips to stop this. Also, as the gibs are so narrow, the point of action for the adjusting screws needs to be close to the sliding face to reduce the tendency of the gib to rotate, not on the back of the gib as is the default.

After trying several internet solutions without making a huge difference, the thing that sorted mine was to depen the recesses in the gib to take the tips of the dog-point adjustment screws. These need to be angled to match the adjustment screws, not flat to the gib strip itself. I managed to do this by clamping the gib to the slide itself (with the hole location overhanging) and drilling them deeper. I also had to add clearance to prevent the threaded part of the adjusting screws fouling the gib. I managed this with a 4mm end mill in a drill press. (A bit hairy, but worked OK).

[egaParticipant @ega]

It sounds as though mini lathe gibs would benefit from being dowelled, a procedure that has been covered here and is very well described by GHT in his Workshop Manual.

Edited By ega on 23/10/2020 14:15:13

[Neil WyattModerator @neilwyatt]

Posted by Andy Gray 3 on 23/10/2020 12:43:27:

After trying several internet solutions without making a huge difference, the thing that sorted mine was to depen the recesses in the gib to take the tips of the dog-point adjustment screws.

The gib on mine was fine, but when I made a t-slotted cross slide and a gib for it, I had to do exactly this.

[Ron LadenParticipant @ronladen17547]

Posted by Philip Antoniou on 23/10/2020 11:33:43:

Posted by Ron Laden on 23/10/2020 08:14:33:

Posted by Philip Antoniou on 22/10/2020 19:53:46:

Posted by Ron Laden on 22/10/2020 14:06:15:

I think one of the failings of the small mini lathes is the lack of rigidity of the tool mount/compound slide through to the cross slide, you can see in the video the amount of flex at the tool post.

My CJ18 mini lathe was a bit of a nightmare when parting off, it depended on the job it was sort of ok with not too heavy or deep cuts in aluminium but parting steel was always a problem.

I went down the rear tool post route which transformed it and made parting off a pleasure to do, it did mean however making a heavier duty cast iron cross slide with T slots and a 50mm square steel tool post for the parting tool. Obviously a fairly serious mod but it did cure the parting problems and to some degree improved general turning having a heavier cross slide bed.

Picture below of the original cross slide and the heavier version, not a 5 minute mod but it was worth the effort.

Ron

Edited By Ron Laden on 22/10/2020 14:20:20

Did you make the new cross slide? Does it also use gibs with bolts to tighten it up?

Philip, yes I did make the heavier duty cross slide but like I said it is quite a serious mod, picture below of finished item. You need a sizeable chunk of cast iron, a T slot cutter and a dove tail cutter, and a mill. Yes the cross slide is gib mounted with adjusting screws but I increased the screws from 3 to 5.

Before getting in to any serious mods and I am not suggesting for one minute that you make a new cross slide, I did but I wanted a rear tool post and T slots. Have you tried inverting the parting tool and running the lathe in reverse, quite a few people seem to get better results in parting this way on the mini lathe.

One question though Ron, I would have thought that most of the play in the slides is due to the gib moving/rotating and not due to the steel flexing, so I'm surprised that increasing the size of the slide is a major upgrade. Am I missing something?

Philip when I said the heavier duty cross slide is a fairly serious upgrade what I meant is it is not a five minute job its quite a bit of machining to turn a large lump of cast iron into a cross slide with the T slots, dovetails and the stepped hole mount for the compound. The main reason I went down this path was wanting a rear tool post and T slots, there is not the space or more importantly the meat to achieve this on the smaller standard cross slide the lathe comes with.

I dont agree that the play in the slides is the only cause of flex in the mini lathe, others may disagree but the mini lathe lacks rigidity, thats just a fact. I,m not knocking the mini lathe I wouldnt do that as mine got me started and I managed to do some nice work on it. I would argue that you can fit good quality gibs correctly adjusted to eliminate any play but that wont cure the lack of rigidity, it will help but it wont cure it and yes the metal will flex as I know from experience.

I stalled my mini lathe whilst parting off (twice) and the second time broke the plastic high/low gears in the head, when it happened the amount of movement through the tool post/top slide was scary even though the top slide gib was very well adjusted and set up.

Ron

[Philip AParticipant @philipa30666]

Posted by Andy Gray 3 on 23/10/2020 12:43:27:

Posted by Philip Antoniou on 23/10/2020 09:35:29:

I just shimmed the gibs on the underside of the carriage as they were riding on the edge of the ways. I used shim washers instead of cutting strips of shim that most people use, seems rigid. Fitted the Arceurotrade brass gibs; one has made an improvement, letting me tighten up the gib more while still letting the side move. But the other gib is the wrong size and just jams the movement.

Be slightly careful with the shimming – it cures a symptom rather than the cause. The gib shouldn't bear on the bottom of the slide (or the top). If it does, it is either not being held properly by the adjustment screws, or is rotating slightly, which forces the lower corner into the bottom of the slide.

In an ideal world, the pressure on the gib should be at right angles to the sliding face – it isn't on the mini lathe (and many other designs, too) so there is a tendency for the gib to be pushed downwards as the adjustments are snugged up. There needs to be enough engagement of the adjustment screw tips to stop this. Also, as the gibs are so narrow, the point of action for the adjusting screws needs to be close to the sliding face to reduce the tendency of the gib to rotate, not on the back of the gib as is the default.

After trying several internet solutions without making a huge difference, the thing that sorted mine was to depen the recesses in the gib to take the tips of the dog-point adjustment screws. These need to be angled to match the adjustment screws, not flat to the gib strip itself. I managed to do this by clamping the gib to the slide itself (with the hole location overhanging) and drilling them deeper. I also had to add clearance to prevent the threaded part of the adjusting screws fouling the gib. I managed this with a 4mm end mill in a drill press. (A bit hairy, but worked OK).

Hi Andy, I was actually talking about the gibs that hold the carriage down (pic below), which were riding on the edge of the underside of the ways. I used shim washers to get those horizontal, and was wondering why others are using more awkward shim strips:

But you are right about the slide gibs, the grub screws are forcing them to rotate, it doesn't look right at all, but seems to be working as there's no play now. I'll probably do something better once I can afford to buy a milling machine:

[Philip AParticipant @philipa30666]

I haven't done much to test all the parting tips you've given me yet. Mainly because the Arc parting tool has the blade on the wrong side so it's not possible to part less than 16mm away from the chuck which is way further than the 1/4 – 1/2" you're recommending.

I've ordered a sample of EN1A steel to see if my problem is that I'm working with the wrong material. I was wrong to say that EN1A can't be zinc plated, it's only the leaded EN1A-Pb which can't be plated.

Would you be able to explain whether the top side of the parting blade needs to be horizontal or at an angle? The parting tools shown on the mini-lathe.com website show blades which have a horizontal top side:

However the Arc tool and many other tools and websites recommend that there is an angle. The arc tool achieves this by having a half moon ground into the top side:

I think practically speaking a parting tool with a horizontal blade would be more convinient because if used with a quick change tool post it's height would only ever need to be set once.

[Author]

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