Screw cutting problem

[John ReeseParticipant @johnreese12848]

JasonB' photos are n excellent description of how to set the compound slide for threading right hand threads cutting toward the headstock. For left hand threads and internal threads the compound slide must oriented differently. My rule of thumb is set the compound parallel with the trailing edge of the tool then move it about 1/2* toward perpendicular with the work. That works when feeding with the compound (flank feed). When feeding with the cross slide (plunge feed) the orientation of the tailstock is irrelevant.

[Clive FosterParticipant @clivefoster55965]

As has been said, in normal lathe use the primary advantage of setting the topslide at an angle is to generate clearance between the top and cross slide handles or topslide and tailstock depending on whether its at 90° to the bed or parallel to it. Small amchines tend to be cramped.

A secondary advantage is that it reduces the possibility of error should the topslide not be exactly at 90° or parallel if using it to apply a cut. Getting it dead right and ensuring its always dead right can be a pain. Especially on smaller machines with only the basic equipment that home shop guy/gal budget can stretch to.

Odds are that any such cut will be done mid job with no chance to verify settings. Often the last cut that has to be spot on to make the job just right too!

Setting at 90° to the bed always seems a bad idea to me because tool in feed cutting forces need to be applied via both cross slide and topslide screws. Which generally are fairly slender and not exceptionally stiff on our (usually) smaller lathes. Unless the topslide is locked solid. But most lathes don't have provision for that without disturbing gib adjustments.

With two screws in the way you have two lots of backlash clearance floating around so if the cut goes into "judder in and out" mode it can be twice as bad. No nice when parting off decides to go wrong.

When screwcutting the big advantage of setting the topslide at an angle is that you can use the Zero-2-Zero method which is by far the easiest to set-up and implement. Forget the American insistence on setting at exactly 30° which requires maths to calculate feed and, along with the lantern tool post, provides further proof that our colonial cousins are not quite bright when it comes to lathes. The Zero-to-Zero method lets you set the topslide at any sensible angle, mine lives at 25° which does Whitworth, American and Metric just fine, because the lathe actually does the infeed calculations for you.

When using Zero-2-Zero you initially touch the tool tip to the job and set both top and cross slide dials to zero then move the tool clear of the end of the job and feed the cross slide forward by the depth of the thread you wish to cut. Straight out of the book usually. Re-set the cross slide dial to zero and pull back the topslide to gain clearance. Make the cuts with the cross slide set to zero and apply feed with the topslide. When both dials are at zero and all spring cuts are worked out you have cut what you set.

Which probably doesn't actually fit as, in the home shop, the minor diameter tends to come out too large.

Generally our home ground tools aren't exactly the correct tip shape and when using factory carbide or chaser tooling we don't have the correct infeed data to generate a thread right first time. Understanding the clearances involved and their interaction with tip shapes from the usual "lots of triangles" picture in the Zeus or other reference book is hard. Easy enough to add a bit of extra feed to the cross slide, shaving things down until they do fit. If the cross slide zero is altered to refect this any subsequent threads will fit perfectly.

Organised folk will make a note of the extra feed needed for chasers et al. I've had my Johannesson / SKF chasers for 20 years and not got round to it.

Biggest disadvantage of Zero-2-Zero is that it needs a slightly larger run out groove at the end of the thread. 1 1/2 pitches minimum rather than 1. But who is that accurate at dropping the halfnut.

Hardcore manual machinists consider single tooth clutches and Ainjest attachments cheating.

Clive

[Ramon WilsonParticipant @ramonwilson3]

Hello Phillip,

Over the years I have screw cut many items on my S7 without using the compound slide.

This is permanently set at 15 degrees for normal turning for no other reason than to give clearance to the tail stock. I only change this position if the specific turning warrants it so it remains at 15 degrees for screw cutting too but of course is not used to apply a cut. You can see the corner of the compound slide still at that angle in this image.

The image is from the build of an Atomatic 5cc diesel which required several parts to be screwcut – L&R/H all done as above which can be seen in this view of the parts.

I usually coat the part with a felt tip pen and scratch the surface with the tool to check the pitch then depending on material and depth of thread required take at least a 10 to twenty thou cut reducing as the depth increases and taking spring cut passes at stages without putting a cut on – I have no aids other than the cross slide movement so speeds are a bit slow to prevent mishaps if working to a shoulder. One tip I was shown at work many years ago was on that last cut or so if the gauge/mating part won't quite go on is to make a cut on the same setting but apply a very slight drag on the saddle handwheel by hand – this will give a scrape to the rear face of the thread without digging in. An acquired skill but one worth trying to master – try it out with plenty of material to go first!

BTW – Shouldn't that 29.5 degrees in your image be 27 .5 Jason

Regards – Tug

Edited By Ramon Wilson on 17/03/2022 09:58:30

[Anonymous]

Posted by Clive Foster on 17/03/2022 09:53:16:

Hardcore manual machinists consider single tooth clutches and Ainjest attachments cheating.

More fool them, but they probably also regard the electric motor as an invention of the devil.

Andrew

[Douglas JohnstonParticipant @douglasjohnston98463]

When it comes to screwcutting I think the set over technique is beneficial when using a small lathe. I have a Myford Speed 10 lathe and almost always use the top slide set over and the lathe seems happier this way. Chunkier lathes probably don't benefit to the same extent.

Doug

[John HaineParticipant @johnhaine32865]

As has been pointed out you don't need to angle the topslide, just move it to the left slightly for each cut by an amount calculated to give the same effective angle.

[HopperParticipant @hopper]

Posted by Andrew Johnston on 17/03/2022 11:38:23:

Posted by Clive Foster on 17/03/2022 09:53:16:

Hardcore manual machinists consider single tooth clutches and Ainjest attachments cheating.

More fool them, but they probably also regard the electric motor as an invention of the devil.

Andrew

Funny you should say that… I was just reading a 1929 ME article on making a small sensitive drilling attachment for the lathe tailstock. The author T Dyer describes drilling a tiny #75 hole in an injector "by foot power and no broken drills.

"The writer prefers foot power for small delicate jobs, as one's foot seems to work in unison with one's mind, and sort of senses trouble before it actually comes along, which is more than can be said for a countershaft."

[phillip burbankParticipant @phillipburbank45787]

I was using.g the setting over of the compound slide as that was the way that I was taught to screw cut when I wasvan apprentice

( 50 yrs ago). The smallest lathe that we used was a Colchester Student which seemed huge to a 15yr old lad who had never used a lathe before,and compared to the Myford that I now own it was.

Everyone has given me lots to think about on this topic and I will try out most of the suggestions forwarded.

When Hopper came back to me very early on in the discussion he answered a question that I hadn't even given any thought to

I.E. not being able to set the compound slide over to 30 degrees from square onto the axis. I have forgotten a great deal that I did when an apprentice, but wasn't a machine apprentice anyway but a fitter.

I have just had a thought aswell and it's 55yrs not 50yrs as I first said.

[HopperParticipant @hopper]

Posted by Ramon Wilson on 17/03/2022 09:55:15:

Hello Phillip,

Over the years I have screw cut many items on my S7 without using the compound slide.

This is permanently set at 15 degrees for normal turning for no other reason than to give clearance to the tail stock. I only change this position if the specific turning warrants it so it remains at 15 degrees for screw cutting too but of course is not used to apply a cut. You can see the corner of the compound slide still at that angle in this image.

The image is from the build of an Atomatic 5cc diesel which required several parts to be screwcut – L&R/H all done as above which can be seen in this view of the parts.

I usually coat the part with a felt tip pen and scratch the surface with the tool to check the pitch then depending on material and depth of thread required take at least a 10 to twenty thou cut reducing as the depth increases and taking spring cut passes at stages without putting a cut on – I have no aids other than the cross slide movement so speeds are a bit slow to prevent mishaps if working to a shoulder. One tip I was shown at work many years ago was on that last cut or so if the gauge/mating part won't quite go on is to make a cut on the same setting but apply a very slight drag on the saddle handwheel by hand – this will give a scrape to the rear face of the thread without digging in. An acquired skill but one worth trying to master – try it out with plenty of material to go first!

BTW – Shouldn't that 29.5 degrees in your image be 27 .5 Jason

Regards – Tug

Edited By Ramon Wilson on 17/03/2022 09:58:30

Beautiful work Ramon. I am in awe. And great tip about dragging on the handwheel to clean up the trailing flank. Much less faff than winding the topslide back past the backlash and then back a thou or two before the 0 mark. YOu learn something new on this forum every day.

[JasonBModerator @jasonb]

The staged photo was taken some years ago for a member who was chewing up an attempt at a metric thread, would not have wanted to confuse them more with those old imperial angles

One of the main reasons I keep my topslide set parallel (by dti) is that the carriage handwheel is not that sensitive and the divisions on the wheel are 0.020" each so not so easy to put on a cut of known amount. So the topslide handwheel scale gets used for measured cuts, setting the length of say a spigot or spacing out cooling fins on aircooled cylinders, Oh and tapers too.

Clearance does not seem to be much of a problem and if it does get a bit tight I have the extended Dickson holders or more often these days use a DCMT insert which gives all the reach needed.

J

PS Ramon, any progress on the compound or does the time of year mean gardening and flying have now taken over

[robjon44Participant @robjon44]

I have to agree with Andrew Johnston's comment above about people who insist on living in the past where slavishly adhering to ancient practices on the off chance someone might award you some brownie points is a complete loser, there is no real way to shift some peoples mind set out of the single furrow they insist on ploughing. Having served an apprenticeship as a skilled manual turner from 1960 I moved up through the ranks of automatic lathe setter & eventually Programmer Setter Operator of CNC lathes the size of a Transit van, all along the way this mind set was evident, even though change gears, flat belt drives & putting chalk marks on the moving parts had been consigned to the dustbin of history. One day, not long before he retired my dear old dad who had served his apprenticeship as a Fitter/ Turner prior to WW2 & was now the Chief Planning Engineer of the company where we both worked was in the machine shop, he looked through the armoured glass window where it was all happening & said "bloody hell boy, I wish we'd had all this in 1938" So I can keep internal & external CCTV cameras, 3D graphics when running simulations of new programs & my own personal favourite Iris Recognition then, if that doesn't keep meddlers out nothing else will.

Bob H

[Ramon WilsonParticipant @ramonwilson3]

Posted by robjon44 on 17/03/2022 13:55:35:

I have to agree with Andrew Johnston's comment above about people who insist on living in the past where slavishly adhering to ancient practices on the off chance someone might award you some brownie points is a complete loser, there is no real way to shift some peoples mind set out of the single furrow they insist on ploughing. Having served an apprenticeship as a skilled manual turner from 1960 I moved up through the ranks of automatic lathe setter & eventually Programmer Setter Operator of CNC lathes the size of a Transit van, all along the way this mind set was evident, even though change gears, flat belt drives & putting chalk marks on the moving parts had been consigned to the dustbin of history. One day, not long before he retired my dear old dad who had served his apprenticeship as a Fitter/ Turner prior to WW2 & was now the Chief Planning Engineer of the company where we both worked was in the machine shop, he looked through the armoured glass window where it was all happening & said "bloody hell boy, I wish we'd had all this in 1938" So I can keep internal & external CCTV cameras, 3D graphics when running simulations of new programs & my own personal favourite Iris Recognition then, if that doesn't keep meddlers out nothing else will.

Bob H

Well yes I guess I do live in the past where conventional machining is concerned – on basic kit found in the home workshop. I too have had my time on transit van sized Haas machining centres but when I step into my workshop with my Super 7 that has served me well and the post war Linley Milling machine the same then reality strikes home and I use practices that suit the kit and the skill level required for the job.

I've always tried to help people on here who are beginners or are struggling to achieve something by giving an example to go by. Never thought I'd be considered a 'Medlar' nor that I might be seen as attempting to score brownie points but there you go – something I guess I'll have to live with

Thanks for the comments Hopper – just for interest all done on my S7 and Linley mill and from solid – no castings were harmed in the making. A full build log is here if you are interested. Oops there I go again, looking for brownie points – bugger.

Jason – some progress has been made – basic assembly all okay and all cast finished. Control Line currently has the upper hand over and yes some serious developments in the garden too but hope to be back on it in the Autumm. Hope you are keeping well

Regards – Ramon

[Anonymous]

Posted by Ramon Wilson on 17/03/2022 14:25:58:

…be considered a 'Medlar'…

Nothing wrong with medlars, got one in the garden. They look horrible after bletting, but taste lovely.

Andrew

[Neil LickfoldParticipant @neillickfold44316]

It is common to drag your hand on the hand wheel of the saddle at the start of all the passes, especially on older lathes with plenty of back lash everywhere. Also to nip up the top slide to reduce it from moving, unless doing the angled topslide way, or the Hardinge way as I call it. There are many ways to skin a cat as they say, and nothing like experience. We are very fortunate for the likes of Ramon who have gone out of their way to record and keep such a great build log of not only how it's done, but shows the equipment it is done on. Now days we are spoilt for choices to learn, and youtube I find has some great things, but there is also some rather nasties their as well. If you never know anything about engineering, I always think some of the old books and booklets are always a great starting place, then move onto where ever for the knowledge. Apprenticeships are no longer what they used to be that is for sure and most it seems are just too keen on the newer ways than learning the old skills. A simple example is making a thread cutting tool, either internal or external.

[Tony Pratt 1Participant @tonypratt1]

Posted by Clive Foster on 17/03/2022 09:53:16:

Hardcore manual machinists consider single tooth clutches and Ainjest attachments cheating.

Clive

Clive, where did that 'pearl of wisdom' come from?

Tony

[Ramon WilsonParticipant @ramonwilson3]

Inverted 'commers' Andrew but point made never the less

Tug

[Clive FosterParticipant @clivefoster55965]

Posted by Tony Pratt 1 on 17/03/2022 15:01:18:

Posted by Clive Foster on 17/03/2022 09:53:16:

Hardcore manual machinists consider single tooth clutches and Ainjest attachments cheating.

Clive

Clive, where did that 'pearl of wisdom' come from?

Tony

Merely an attack of creativity I'm afraid.

My Pratt & Whitney has a single tooth clutch and my Smart & Brown 1024 will get one, or a functional equivalent thereof, if I ever manage to figure out an elegant method of fitting.

Jasons need for fine longitudinal feed is indeed the best justification for setting a topslide parallel to the bed.

I'm impressed that he generally doesn't have any issues with cross slide to tailstock interference. On a small lathe avoiding that sort of problem needs very careful detail design and dimensioning.

Hafta say I've never driven a lathe that didn't have at least potential issues there. Even the stubby topslide on my P&W with its gear driven screw and raised, angled, handle / dial assembly manages to have issues. Which really surprised me once mid job. Had to resort to an extended toolholder. I loathe the things due to constitutional distrust of anything forcing the tooltip to divine its support at considerable distance.

When it comes to short longitudinal feeds I prefer to rely on a bedstop to give positive end position rather than a dial. Must be well over 30 years since I last used a machine without a micrometer bed stop or at least a solid one set with the aid of a near freebie "gash" set of gauge blocks that no longer wring so can't say I recall what it was like to do without.

Lots to be said for the modern DRO scale on the bed if you don't have a longitudinal feed dial. My S&B has an excellent and accurate one so I'm in no rush to go electronic. I did hear of someone who had successfully fitted a small retracting tape measure to the tailstock side of his saddle and found it effective for approximate work. Presumably one of those tiny pound shop bargain things so clearyl attractive to the fiscally challenged (AKA normal) home shop person.

Clive

[HopperParticipant @hopper]

Posted by Ramon Wilson on 17/03/2022 14:25:58:

Thanks for the comments Hopper – just for interest all done on my S7 and Linley mill and from solid – no castings were harmed in the making. A full build log is here if you are interested. Oops there I go again, looking for brownie points – bugger.

All brownie points fully deserved. Thanks for the link. Awesome work. And a beautiful little engine design.

[Michael Cooper 5Participant @michaelcooper5]

When cutting threads the basic set up should go something like set the compound slide to half inclusive angle.Set dial on compound to zero.If possible turn a root diameter at either the start or exit of the thread using cross slide.When the root diameter is achieved set cross slide to zero.Clear tool from work by backing off just enough using compound slide.Select RPM and touch on work using only the compound slide.Wind down the bed till your of your work.Set your first cut on compound and and chose a number on your chaser dial and engage.At end of each pass(remember to disengage) clear work using cross slide and wind down bed past the work to the beginning.Wind in cross slide to zero , put cut on compound slide and engage on same number.Repeat until compound reads zero.I would set up like jasonB as it cleans up trailing face nice.

[JasonBModerator @jasonb]

If you do turn a section to the root diameter do consider the form of the tool being used before you do. A full form insert, a partial form insert or a home ground HSS tool will not all have the correct radius on the end so may need to go in deeper than the root diameter.

[HopperParticipant @hopper]

Posted by Michael Cooper 5 on 17/03/2022 22:29:56:

When cutting threads the basic set up should go something like set the compound slide to half inclusive angle.Set dial on compound to zero.If possible turn a root diameter at either the start or exit of the thread using cross slide.When the root diameter is achieved set cross slide to zero.Clear tool from work by backing off just enough using compound slide.Select RPM and touch on work using only the compound slide.Wind down the bed till your of your work.Set your first cut on compound and and chose a number on your chaser dial and engage.At end of each pass(remember to disengage) clear work using cross slide and wind down bed past the work to the beginning.Wind in cross slide to zero , put cut on compound slide and engage on same number.Repeat until compound reads zero.I would set up like jasonB as it cleans up trailing face nice.

Well, that's one way of doing it, out of many as discussed above. I think maybe there are as many ways as there are machinists!

Unfortunately the OP's lathe, an ML7, does not allow you to rotate the topslide to half the thread angle. It is limited at 45 degrees from the lathe axis so can't make it to the required 61 degrees or so. So he is limited to either straight plunge cutting or the common method used in industry of advancing the non-angled top slide by half the amount of infeed.

[HopperParticipant @hopper]

Posted by JasonB on 18/03/2022 07:01:23:

If you do turn a section to the root diameter do consider the form of the tool being used before you do. A full form insert, a partial form insert or a home ground HSS tool will not all have the correct radius on the end so may need to go in deeper than the root diameter.

Yes I have almost always found screwcutting to be a "fit and try" effort the final five thou or so, for this reason. One advantage of the method keeping the toplside set parallel to the lathe axis is if/when you get to full thread depth (or what you calculate to be full thread depth) and your sample nut will still not fit on your thread being machined, or goes on but is a bit tight, you can take a skim along each flank of the thread to clean it up without adding thread depth. This will often then allow the nut to screw on beautifully. With the angled topslide, you don't have this option and have to keep on adding depth of cut until the side flanks clear the flanks in the nut. Probably more relevant on larger threads than smaller, which are easier to do with a die anyway.

[KEITH BEAUMONTParticipant @keithbeaumont45476]

Ramon, That is a lovely set of parts for your Atomatic 5cc Diesel. I am not familier with this design. Are drawings available or is it another of your re-design projects?

Keith

[Ramon WilsonParticipant @ramonwilson3]

Hello Keith – how are you? Still beavering away I hope.

I was smitten by the Atomatic '4' as soon as I saw Les Stones version on Model Engine News. The drawings I did for mine were pre CAD (for me) and simple pencil on paper. Ron Chernich was going to re draw them in CAD for MEN and a set were sent to him. Sadly his illness got the better of him before he was able to do so.

There was an Atomatic '5' as well so drew it out without the need for scaling

I still have the original drawings I did so if you would like them I can either copy you a set or take some images of them – unfortunately I am now not able to scan them to send digitally.

Regards – Tug

[Anonymous]

Posted by Ramon Wilson on 17/03/2022 16:46:28:

Inverted 'commers' Andrew….

I was picking up on the spelling rather than punctuation, but also thought the thread could do with a little levity.

Andrew

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