Retractable top slide or cross slide?

[Ian Owen NZParticipant @ianowennz]

I am considering adding a retractable top slide or cross slide to a Taiwanese belt drive lathe I purchased.

Along with a couple of other additions.

The Taiwanese lathe were a bit “course” on the feed so I am considering changing the carriage feed to an electric motor feed instead of the geared feed, I’ve seen a couple of examples of that but neither had a “clutch” mechanism in the case of trouble.

A while ago I came across a write up about a reversing clutch for the leadscrew that was designed for the Warco BH600 lathe, from memory it was designed by Graham Meek. This would be a great addition for threading along with either the retracting top slide or a retracting cross slide.

The Hardinge HLV used the reversing leadscrew and a retracting top slide, while the Schaublin 125 used a retracting cross slide, and they both used electric motor feed for the carriage and cross slide feeds. I like the way the Shaublin drive was executed but need to determine how the “clutch” worked to see if I can duplicate it.

I know there are a set of plans for the Myford 7 retractable top slide, are there any plans for a retracting cross slide?

Where would one locate the drawings for the Warco BH600 reversing leadscrew?

Thanks

Ian

[Clive FosterParticipant @clivefoster55965]

I prefer the retracting cross slide as I use the “zero-2-zero” angular infeed method of screw cutting which is inherently suited to a retracting cross slide. Always felt teh retracting top slide idea was a bit cumbersome and somewhat limited.

Many ways of doing a retracting cross slide. Probably the simplest is the screw set threading stop clamped to the cross slide ways as per SouthBend and Boxford. Stop body sets how far back the slide comes on retraction, screw sets for far forward it goes for the cut. Obviously limited to jobs that can be done by putting the cut on via the top slide, hence “threading stop”, but its way simple.

I like the system fitted to my P&W Model B 12 x 30. Basically the cross slide dial and feed screw thrust bearings carrier connects to the slide proper via a short, very coarse, male thread. Turning the whole boss through 90° gives plenty of movement to clear any normal thread depth. Form memory approaching 1/4″. Bound to be two start thread. But it’s big lathe. Probably rather less movement would do on a smaller machine so a single start thread could work. In principle easily made. Needs some form of lock to hold the moving boss in the forward position for normal work.

The P&W also has provision for a threaded rod on the cross-slide to act as a forward travel stop using a pair of setting nuts. Essentially same idea as the SouthBend threading stop but operate over the full cross slide travel range. handy if you have number of components to do.

I’ll take some pictures tomorrow.

Clive

[BazyleParticipant @bazyle]

The drawings for the Meek design for the BH600 were on a website that looked like a plain text newsletter. A quick google found this pdf from 2012.
https://modelengineeringwebsite.com/Screw-cutting_clutch_3_files/Metric%20BH600%20.pdf

There is also a cross slide retraction design for a 12×24 style lathe somewhere on the web. As far as I remember it was similar to other designs with the saddle ‘fixed’ bearings put into a tube that could then be moved back by a lever.. Some Holbrooke lathes had this built in with, I think, a way of rotating the feedscrew back one turn and returning without losing its place.

[DC31kParticipant @dc31k]

In one sense, all top and cross slides are retractable, simply by turning the handle. Thus, to achieve quick retract, nothing special is required, only a good hand.

The challenge is not retracting the slide at the end of the cut, but easy and repeatable re-positioning it at the start of the next cut. In other words, putting it back where it was without looking at the dial.

If you have that more general principle in mind, you will not constrain your thoughts by having a specific mechanism in mind (e.g. lever-operated retraction).

You probably know that there were also retracting toolholders produced. Tripan is one example (https://groups.io/g/schaublin/topic/tripan_retractable_threading/111625433)

I mention this specifically in conjunction with the cross slide as the Monarch 10EE might provide inspiration. It has a mechanism on the cross slide (something like an infeed stop) that allows repeatable resetting. It is, in principle, the same as that described for the Holbrook above.

You can work out how most things function by studying the exploded diagrams in the manual. Most available Schaublin manuals are available on the anglo-swiss tools website. There is also a Schaublin io group where someone would know how the clutch works. The Monarch system could be seen in the manuals on the vintagemachinery website. A P&W manual might also be there as well as the Southbend one. I am not sure where you would see a Holbrook manual.

[Neil LickfoldParticipant @neillickfold44316]

What I like with the retractable top slide, like the Hardinge one, is they work very well even on internal threads. Its just reversed. Then keep applying the cut on the cross slide.

When thread cutting, I like the top slide at the angle that allows for the tool to retract without wiping the sides. So 30 deg for metric and UN thread forms, and 27.5 deg for Whitworth 55 deg forms. Depending on how your topslide is graduated, it could be 60deg mark or 62.5 deg marks, on a S7 for example.

I set the topslide flush with the end casting. So is either wound back for external threads, then wound back to Zero set for the next cut, or is wound In for the Internal threads and wound back out to Zero for the next cut. Preparing the run out or exit area is also important. Sometimes that is not so easy to achieve so retracting as it nears the end can work well too. Just takes time to learn the coordination required to achieve this.

It is not as nice as using the snap tap systems or any of the other ones that have an auto retract system for external or internal threading. But is cheaper and does work well.

Adding a VFD with micro switch stops works really well for me.

Neil

[Neil Lickfold]

On Neil Lickfold Said:

.. …Adding a VFD with micro switch stops works really well for me… ..

 

Neil

It’d be interesting to see your set-up for that, but fully understand there are always better things to be doing in the workshop than taking pictures for the curious.. 😊

[JasonBModerator @jasonb]

If you are thinking of fitting an ELS then why not fit a two axis one. Then it will retract and put on the next cut for you as well as retracting in the same place every pass.

[Neil LickfoldParticipant @neillickfold44316]

I used to have some pics, that got lost from a failed phone chip and then a failed hard drive. They were on the old ME sight but got lost in the new merger.

All I could find is this old youtube video cutting a M14x1.5 pitch thread with everything set at Zero. Not how I normally cut threads. It was to show a friend the use of the 2 limit switch stops. The LH limit switch is not easy to see in the video. But does show the deceleration and it only starting in reverse. missing is putting on  the cut etc.

The micro switches are just held in place using little magnetic DTI holders, as they have a micro adjustment on them.

Neil

 

 

[Bazyle]

On Bazyle Said:

The drawings for the Meek design for the BH600 were on a website that looked like a plain text newsletter. A quick google found this pdf from 2012.
https://modelengineeringwebsite.com/Screw-cutting_clutch_3_files/Metric%20BH600%20.pdf

There is also a cross slide retraction design for a 12×24 style lathe somewhere on the web. As far as I remember it was similar to other designs with the saddle ‘fixed’ bearings put into a tube that could then be moved back by a lever.. Some Holbrooke lathes had this built in with, I think, a way of rotating the feedscrew back one turn and returning without losing its place.

Bazyle, thank you so much for the drawings, has anyone actually built and fitted this to the BH600?

While I haven’t actually got a “Warco” lathe I do have one of the generic Taiwanese lathes made by Wey YII Corp which is still making lathes and sold as Microweily.

If I understand correctly the advantage of the screw cutting clutch is you can keep the spindle rotating and the leadscrew changes direction, with the outcome that the carriage reverses until it trips the rod and starts feeding in the correct direction again. This is done automatically so great for threading metric on an imperial lathe or imperial on a metric lathe.

The advantage of the retracting cross slide or top slide is you can use any threading tool, carbide or hss, both internal and external. I have read about the Hardinge HLV & Schaublin 125 retracting feature but wasn’t aware that Southbend, Holbrooke and others had something similar to this feature. I will see if I can find any info about them.

The disadvantage of the retracting tool holder like the Tipan, Ifanger and Multifix is you are mostly limited to their tooling/blades, which may not have what you want available.

 

Thank you everyone for the replies I found a manual in French and German for the Schaublin 125, while they give a schematic drawing it doesn’t give an exploded view or a list of parts, not like the Hardinge.

[Clive FosterParticipant @clivefoster55965]

As as been said previously the important part of the retraction system is that it goes back to the same place each time.

Pictures of the P&W system as promised.

Normal turning set up, note the stop on the main dial collar engaging with the stop on the slide assembly.

Retracted

Approximately 90° rotation giving approaching 0.2 inches retraction, less at first due to backlash. So the quick screw is 2.5 TPI. I reckon anything up to around 3/4 of a turn is acceptable with this form of retractor. So 5 TPI (ish) would be fine on a smaller machine.

The stop on the collar is now out of sight having rotated away from the stop on the slide assembly.

Square headed bolt on the slide assembly locks the retraction device, Square headed bolt on the feed system collar locks the feed screw preventing inadvertent alteration of the feed setting when retracting.

The threaded rod for the stop adjustments can also be seen. There is a locking device on the moving part of the ross slide that can be released to pull out or push in the rod to roughly set things. Add a locked pair of nuts as appropriate to make the settings by contacting the casting around the hole. Normally teh rod is left fully retracted to keep it put of the way.

A single tooth dog clutch retains feed position on disengagement and re-engagement but you still have to do retraction manually before reversing. The P&W has a big lever on the carriage to select feed direction and adjustable stops to set disengagement position in both directions. Frankly I never use the tailstock end stop. Easier to just haul the lever when the tool is clear. The P&W is a bit idiosyncratic in that teh whole operating philosophy is built around the single tooth clutch.

The SouthBend device is a simple add on stop, not a built in feature.

CVA use a simple lever on top of the cross slide assembly operating a cam so no chance of inadvertent feed adjustment as can happen with the quick thread.

Hafta say that on my other lathe, S&B 1024, I simply make all the cuts with the cross slide at zero so a swift half turn does teh retraction bit just fine. Of course cuts have to go via the top slide. But that’s inherent to the zero-2-zero screw cutting method.

Clive

[JasonB]

On JasonB Said:

If you are thinking of fitting an ELS then why not fit a two axis one. Then it will retract and put on the next cut for you as well as retracting in the same place every pass.

If doing that just fit full CNC and be done with it.  In this day and age, if you are fitting self-act feed which needs to reverse, cut to a defined point and stop, etc, a stepper motor drive is the obvious way to do it.

[Ian Owen NZ]

On Ian Owen NZ Said:

 

Bazyle, thank you so much for the drawings, has anyone actually built and fitted this to the BH600?

I designed the BH600 unit for Graham Howe which he fitted to his machine. I also believe Anthony Mount fitted one to his lathe.

As a general rule for any published screwcutting clutch design, these have been made, fitted, and tested.

Regards

Gray,

 

[Graham Meek]

On Graham Meek Said:

On Ian Owen NZ Said:

 

Bazyle, thank you so much for the drawings, has anyone actually built and fitted this to the BH600?

I designed the BH600 unit for Graham Howe which he fitted to his machine. I also believe Anthony Mount fitted one to his lathe.

As a general rule for any published screwcutting clutch design, these have been made, fitted, and tested.

Regards

Gray,

 

Gray, thanks for the design

Was the building and fitting of the reversing clutch for the BH600 ever featured in a magazine?

This is one project that I want to build and fit to my Taiwanese belt drive lathe.

This in combination with a quick retract cross or top slide would make internal and external threading quicker and easier.

I don’t want to create a hybrid cnc/manual lathe which is why I’m looking for mechanical systems to assist in threading.

Regards

Ian

[Graham MeekParticipant @grahammeek88282]

Hi Ian,

Graham Howe wrote the article up on the Model Engineering Website, link below.

One thing with constructing something mechanical is that the parts are all in the scrap-bin or material stores. Nothing heeds to be bought-in and you are always in control of what is happening.

For what it is worth I prefer the retracting topslide, but Jim Schroder in the USA has designed and published a retracting cross-slide attachment for his Grizzly version of this lathe, (sister magazine to Home Shop Machinist). There are a couple of videos on this and his screw cutting attachment. The latter was published in the Home Shop Machinist.

https://modelengineeringwebsite.com/Screw_cutting_clutch.html

Regards

Gray,

[Graham Meek]

On Graham Meek Said:

Hi Ian,

Graham Howe wrote the article up on the Model Engineering Website, link below.

One thing with constructing something mechanical is that the parts are all in the scrap-bin or material stores. Nothing heeds to be bought-in and you are always in control of what is happening.

For what it is worth I prefer the retracting topslide, but Jim Schroder in the USA has designed and published a retracting cross-slide attachment for his Grizzly version of this lathe, (sister magazine to Home Shop Machinist). There are a couple of videos on this and his screw cutting attachment. The latter was published in the Home Shop Machinist.

https://modelengineeringwebsite.com/Screw_cutting_clutch.html

Regards

Gray,

Hi Gray,

Thank you for the link.

Do you know which issues of Home Shop Machinist the articles about the retracting cross slide and his screw cutting attachment are in?

Regards

Ian

[Ian Owen NZ]

On Ian Owen NZ Said:

Do you know which issues of Home Shop Machinist the articles about the retracting cross slide and his screw cutting attachment are in?

Is it not listed in the online index to the magazine at https://homeshopmachinist.net/resources/article-index/ ?

[Howard LewisParticipant @howardlewis46836]

If you have a BH600, or one of its look alikes, to reverse the Leadscrew, or the Feed, relative to the chuck, you need only need to use the Tumbler Reverse!

A screwcutting clutch is another matter, and will operate irrespective of the direction in which the Leadscrew is rotating.

There are several designs of retractable tool holders, for screwcutting: Martin Cleeve, G H Thomas etc, and probably Tubal Cain or Radford as well.

Which is it that you desire?

Howard

[Nigel Graham 2Participant @nigelgraham2]

Interesting discussion!

I enhanced my Myford ML7 by fitting an early-pattern gearbox, making then new, shorter leadscrew it uses so as to keep the original as a spare, and this certainly makes both normal turning and screw-cutting much more efficient.

However, this thread (!) is about attachments to retract the tool at predetermined points.

 

Can we approach screw-cutting and plain turning the other way, though – by stopping the saddle travel?

 

The basic approach is an ajustable stop-bar and trigger on the clasp-nut control to stop the traverse at the inner end of the thread, and I believe such mechanisms have been published for lathes like the Myford and Drummond.

That looks after the thread length but still relies on the thread-dial indicator (TDI), low spindle speed and deft operation by an alert operator.

SO….

Has anyone looked at prinicple of the Ainjest (patented) attachment, to design something similar for the Myford or similar-size lathes? The original Ainjest attachment was for lathes of around 5″ to 9″ centre-height; and enables rapid screw-cutting for higher production rates.

The Ainjest does not retract the tool – the operator has to do that, with due care if using the half-angle method to allow for the advance this creates. Instead, the adjusted end-stop trips the traverse at the thread end; and for the next cut, finds its own, repeating engagement-point.

It does not use the lathe’s own half-nuts. It has its own. The lathe’s own clasp-nut stays serenely at rest, open.

The turner simply retracts the cross-slide, winds the saddle back, sets the next depth, presses the operating lever and lets the machine do the rest. Its advantage is allowing screw-cutting at the normal turning-speed for the work, and relieving the operator of having to follow the TDI’s counting.

I assume the attachment has something like an internal “TDI” that sets the repeated engagement on the same “number”, to close its half-nuts. The turner presses the operating-lever down, and the device closes the nut as soon as it is ready. Since the lathe can be run fast the operator would probably not notice any delay. The lever seems self-locking but not so it cannot be disengaged if necessary.

The Ainjest unit has another control, with four positions: I could not determine its function from the information I managed to find, but guess it allows either multi-start threads, or pitches normally dictated by specific even/odd/same TDI numbers.

 

It would be an interesting challenge but not insurmountable. Not knowing what is actually inside the Ainjest, the key to the repeatabality may be the internal “TDI” rotor having, e.g., a step or notch to admit the clasp-nut link. One such pass-point would equate to using the same number all the time on a conventional TDI.

[DC31k]

On DC31k Said:

On Ian Owen NZ Said:

Do you know which issues of Home Shop Machinist the articles about the retracting cross slide and his screw cutting attachment are in?

Is it not listed in the online index to the magazine at https://homeshopmachinist.net/resources/article-index/ ?

Thank you for the link, it took a bit of searching, I used Jim Schroeder with no results, cross slide still no results, retracting still zip, next screw threading nothing by Mr Schroeder but did find Gray Meeks article for the clutch article for the Myford, so I searched for Schroeder and found the reference to the Threading clutch for the Grizzly G0602.

But no reference to an article regarding the retractable cross slide, which is the article I’m looking for.

I did find this reference to it on the internet though

A cross slide retractor for my TH54 | The Hobby-Machinist

I have the plans for the reversing clutch for my lathe which is similar to the Warco BH600, thanks Bazyle & Gray.

 

Regards

Ian

[Nigel Graham 2]

On Nigel Graham 2 Said:

Interesting discussion!

I enhanced my Myford ML7 by fitting an early-pattern gearbox, making then new, shorter leadscrew it uses so as to keep the original as a spare, and this certainly makes both normal turning and screw-cutting much more efficient.

However, this thread (!) is about attachments to retract the tool at predetermined points.

 

Can we approach screw-cutting and plain turning the other way, though – by stopping the saddle travel?

 

The basic approach is an ajustable stop-bar and trigger on the clasp-nut control to stop the traverse at the inner end of the thread, and I believe such mechanisms have been published for lathes like the Myford and Drummond.

That looks after the thread length but still relies on the thread-dial indicator (TDI), low spindle speed and deft operation by an alert operator.

SO….

Has anyone looked at prinicple of the Ainjest (patented) attachment, to design something similar for the Myford or similar-size lathes? The original Ainjest attachment was for lathes of around 5″ to 9″ centre-height; and enables rapid screw-cutting for higher production rates.

The Ainjest does not retract the tool – the operator has to do that, with due care if using the half-angle method to allow for the advance this creates. Instead, the adjusted end-stop trips the traverse at the thread end; and for the next cut, finds its own, repeating engagement-point.

It does not use the lathe’s own half-nuts. It has its own. The lathe’s own clasp-nut stays serenely at rest, open.

The turner simply retracts the cross-slide, winds the saddle back, sets the next depth, presses the operating lever and lets the machine do the rest. Its advantage is allowing screw-cutting at the normal turning-speed for the work, and relieving the operator of having to follow the TDI’s counting.

I assume the attachment has something like an internal “TDI” that sets the repeated engagement on the same “number”, to close its half-nuts. The turner presses the operating-lever down, and the device closes the nut as soon as it is ready. Since the lathe can be run fast the operator would probably not notice any delay. The lever seems self-locking but not so it cannot be disengaged if necessary.

The Ainjest unit has another control, with four positions: I could not determine its function from the information I managed to find, but guess it allows either multi-start threads, or pitches normally dictated by specific even/odd/same TDI numbers.

 

It would be an interesting challenge but not insurmountable. Not knowing what is actually inside the Ainjest, the key to the repeatabality may be the internal “TDI” rotor having, e.g., a step or notch to admit the clasp-nut link. One such pass-point would equate to using the same number all the time on a conventional TDI.

I agree a very interesting discussion.

I have never seen a Ainjest threading attachment in person, and not sure if there are any here in New Zealand, but have seen them on Ebay occasionally, usually advertised as from a Colchester or a Harrison. They are certainly a marvel of engineering and, designed for production threading.

There are a number of interesting solutions that people have come up with to aid them in their situations and they obviously work for them.

The generic Taiwanese belt drive lathe has been found to be a good lathe, just with a few deficiencies/issues (I don’t think any lathe is perfect, well none that I have found to be readily available). My solution is to address some of the deficiencies/issues the belt drive lathe has and make the lathe easier to use for threading both metric and imperial and both external and internal threading.

This is where the reversing clutch comes in and the retractable top slide or cross slide also is an advantage. I have the drawings for the reversing clutch and at present I am looking at the differences between the retractable top slide vs the retractable cross slide. One withdraws the cutting tool at 1/2 the included angle of the thread and the other withdraws the tool straight out from the thread.

GH Thomas designed the retracting topslide for the Myford and I’ve looked at the drawings for this, now I’m trying to find the drawings for the retracting cross slide, so I can evaluate that solution and see which solution would be best for me to build.

Regards

Ian

 

[DC31k]

On DC31k Said:

In one sense, all top and cross slides are retractable, simply by turning the handle. Thus, to achieve quick retract, nothing special is required, only a good hand.

The challenge is not retracting the slide at the end of the cut, but easy and repeatable re-positioning it at the start of the next cut. In other words, putting it back where it was without looking at the dial.

If you have that more general principle in mind, you will not constrain your thoughts by having a specific mechanism in mind (e.g. lever-operated retraction).

You probably know that there were also retracting toolholders produced. Tripan is one example (https://groups.io/g/schaublin/topic/tripan_retractable_threading/111625433)

I mention this specifically in conjunction with the cross slide as the Monarch 10EE might provide inspiration. It has a mechanism on the cross slide (something like an infeed stop) that allows repeatable resetting. It is, in principle, the same as that described for the Holbrook above.

You can work out how most things function by studying the exploded diagrams in the manual. Most available Schaublin manuals are available on the anglo-swiss tools website. There is also a Schaublin io group where someone would know how the clutch works. The Monarch system could be seen in the manuals on the vintagemachinery website. A P&W manual might also be there as well as the Southbend one. I am not sure where you would see a Holbrook manual.

“The challenge is not retracting the slide at the end of the cut, but easy and repeatable re-positioning it at the start of the next cut. In other words, putting it back where it was without looking at the dial”

Without using the screwcutting reference dial, the easiest return to zero is to stop the spindle, leave the half-nut engaged – reverse the spindle to beyond the start of the the thread being cut, put a new cut on with the cross slide, and carry on with the next cut, with the spindle in forward rotation?

 

[howardb]

On howardb Said:

On DC31k Said:

In one sense, all top and cross slides are retractable, simply by turning the handle. Thus, to achieve quick retract, nothing special is required, only a good hand.

The challenge is not retracting the slide at the end of the cut, but easy and repeatable re-positioning it at the start of the next cut. In other words, putting it back where it was without looking at the dial.

If you have that more general principle in mind, you will not constrain your thoughts by having a specific mechanism in mind (e.g. lever-operated retraction).

You probably know that there were also retracting toolholders produced. Tripan is one example (https://groups.io/g/schaublin/topic/tripan_retractable_threading/111625433)

I mention this specifically in conjunction with the cross slide as the Monarch 10EE might provide inspiration. It has a mechanism on the cross slide (something like an infeed stop) that allows repeatable resetting. It is, in principle, the same as that described for the Holbrook above.

You can work out how most things function by studying the exploded diagrams in the manual. Most available Schaublin manuals are available on the anglo-swiss tools website. There is also a Schaublin io group where someone would know how the clutch works. The Monarch system could be seen in the manuals on the vintagemachinery website. A P&W manual might also be there as well as the Southbend one. I am not sure where you would see a Holbrook manual.

“The challenge is not retracting the slide at the end of the cut, but easy and repeatable re-positioning it at the start of the next cut. In other words, putting it back where it was without looking at the dial”

Without using the screwcutting reference dial, the easiest return to zero is to stop the spindle, leave the half-nut engaged – reverse the spindle to beyond the start of the the thread being cut, put a new cut on with the cross slide, and carry on with the next cut, with the spindle in forward rotation?

 

Hi Howard,

The repositioning from the end of the cut to the start is done by the reversing clutch, without having to stop the spindle.

I believe Gray designed the reversing clutch, originally for the Myford, based on the principle that Hardinge used for the HLV lathe.

With the Hardinge you could set the limits for the carriage and the carriage would take a cut then stop, move the lever and the carriage would reverse and stop, dial on the next cut and move the lever and start the process all over again. This was all done without stopping the spindle, and the built in retractable top slide meant you didn’t have to wind a handle to withdraw the cutting tool, the top slide did this and returned the tool to the correct position to apply the next cut.

This is the process I am trying to duplicate without having to start, stop, reverse and start the spindle for each cut.

 

Regards

Ian

[JasonBModerator @jasonb]

You probably need to decide which way you like to cut threads first, as that is what will determine if you need a retracting top or cross slide. I tend to keep my topslide parallel to the lathe axis and put on the cut with the cross slide. Our Ainjest owning forum member also does it that way so a retracting cross slide would be of no use. Your larger lathe should be upto using the cross slide to put on a decent cut rather than the angled method often preferred by those with smaller lathes.

[JasonB]

On JasonB Said:

You probably need to decide which way you like to cut threads first, as that is what will determine if you need a retracting top or cross slide. I tend to keep my topslide parallel to the lathe axis and put on the cut with the cross slide. Our Ainjest owning forum member also does it that way so a retracting cross slide would be of no use. Your larger lathe should be upto using the cross slide to put on a decent cut rather than the angled method often preferred by those with smaller lathes.

Jason, your thoughts regarding the lathes ability to infeed with the cross slide correspond with my thoughts and is the way I am leaning.

The ability to thread at faster speeds using the reversing clutch and the retracting cross or topslide should also produce a better finish using carbide.

I would like to see a Ainjest in action, can the Ainjest do metric and imperial on an imperial lathe?

[Clive FosterParticipant @clivefoster55965]

Ian

I’m unsure as to where the myth, alluded to by Jason, of screw cutting via angular in-feed of the topside being purely a small lathe thing originated. Obviously it keeps the handles and dials of the two slides out of their mutual way. On small machines it can be disproportionally difficult to read the cross slide dial when the top slide is in line with the cross slide. On my old SouthBend 9 inch machines the top slide dial was almost directly above the cross slide one when so set which was less than wonderful with the small dials.

However, if the forums are to be believed, angular in-feed from the top slide has always been pretty common practice in the USA. Probably helped by the depth feed maths being much easier for US standard 60° threads than for the British 55° equivalent, let alone the 47.5 BA breed. For British threads straight in feed is clearly easier and the chip crowding inherent to cutting on both sides just has to be accepted. Although at typical single point thread cutting depths the small chip means crowding is generally not a major issue.

I adopted the zero-2-zero angular in-feed method on my first screw cutting job after reading it described by George Thomas as the “star turners method” at his works and have never looked back.

If you have adjustable dials this method uses the lathe to directly calculate the in-feed needed for any approximate, slightly less than half thread angle setting of the top slide so making things vastly easier. So much so that it completely dispelled any lingering doubts as to whether making a single tooth dog clutch system as per Graham Meeks excellent design was really worth the effort for the amount of screw cutting I do. Having a Coventry die head with lots of chasers helps.

Zero-2-zero requires only the ability to accurately feed in the thread depth and set the dials to zero with the lathe stationary coupled with repeatably performing sufficient manual cross slide retraction to clear the thread followed by its accurate return to zero for the next pass.

Simples!

Personal taste whether you drop the half nut and exploit the thread dial for native threads or use machine reversal to return on both native and non native threads.

From the screw cutting perspective the prime virtue of the single tooth clutch is its ability to preserve the angular relationship between spindle (work) and feed when re-engaging any arbitrary period after dis-engaging. In both directions. Albeit with a shift between forward and reverse directions corresponding to the width of the clutch dog aperture plus any backlash. Obviously it has to be in the right place in the drive train, so follow Grahams instructions. You (probably) can’t use tumbler reverse.

My Pratt & Whitney Model B 12 x 30 was clearly designed from the outset around the single tooth dog clutch giving considerable virtues in normal operation once you’ve made the necessary mindset adjustment. Most especially so given that the “B” dates from the era of screw engaged feed clutches rather than modern flip a lever types. Having gotten used to the “B” I reckon the single tooth clutch as a screw cutting aid is, for me at least, is at best marginal whilst having it integrated as part of the operating system is highly desirable. I often regret the morphological impossibility of converting my other lathe, a Smart & Brown 1024 VSL and a superb machine in its own right, to the integrated dog clutch system.

Clive

 

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