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Making single-point Threading easier on a Mini-Lathe

Electronic Leadscrew Fitting to an EMCO Mini-Lathe

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Joseph Noci 126/03/2017 16:14:14
628 forum posts
875 photos

Hi All,

This is a 'lengthy' posting, so am forced to split into many...

SO- post-1

The Main Panel:

main panel selection setup_0844.jpg

The Sub-Panel:

sub panel - start threading_0855.jpg

I had previously posted in this Forum on the start of this project and have progress quite a ways. I thought it better to start a new thread (!) though, since things did change a lot along the way!

The aim of this was to create a simple Electronic threading aid using a small microprocessor reading a spindle encoder wheel, and driving a stepper motor attached to the main lead screw. The encoder provides 4096 edges on two quadrature channels, and an index pulse , per rotation. The 4096 pulses are 'divided' down, using a DDA computation, to give the required Stepper pulse rate, taking into account the chosen thread pitch, leadscrew pitch and stepper to leadscrew drive pulley ratios. The single index pulse is used to synchronise the start of the stepper pulse ( and movement) to the lathe spindle, so that the thread always starts in the same place each threading run.

The process is :

Select thread ( Imperial or metric) and pitch required on the main panel.

Move the tool to a thread start point around 1 or 2 thread pitches away from the thread start. ( allows for leadscrew/half nut backlash takeup). Press THREAD_START BUTTON. Use the jog wheel or joystick to move the carriage and tool to the thread end point. Press the THREAD_END Button.

On the sub Panel, press DONE-REWIND, and the carriage and tool moves to the thread start point. Press Start Thread. Put on cut, and start Spindle.

Once the index pulse is seen, the stepper drives the tool along the cut till thread end, and stops spindle and stepper. Retract tool, press DONE-REWIND and the tool goes back to the starts. Put on cut and repeat till done...Works for RH and LH threads, up to 6mm pitch on my lathe.

The Spindle motor is fitted with a VFD that is programmed to stop the spindle within 150milliseconds in threading mode, below 300RPM max. The MicroP controls the VFD as well for FWD, REV, stop with brake or without, etc. The rapid stop allows threading to take place without worrying about stopping the spidle before the thread end, or pulling the tool out at just the right time - fewer clean underpants required. - I have threaded a 2mm thread at 350 RPM up to a shoulder with Disdain...

Auto-feed also is implemented, and can feed FWD and REV obviously.

This 'ELS' cannot do pseudo CNC stuff that the others seem to do - that over-complicates the use of a basic Lathe in my opinion - GO CNC if you want that! This does threading VERY well, and Auto Feed as well.

Next Post (2)

Joseph Noci 126/03/2017 16:30:57
628 forum posts
875 photos

And now POST - 2....

Here are some pics of the fiiting to the Lathe.

The lathe is in the process of re-furbishment and will be stripped for new leadscrews, nuts, bearings, etc, as well as new full-cover Swarf guards and a DRO - the DRO may be the subject or a new post..

The 'original' Lathe:

lathe before els fit-801.jpg

Modifying the housings for new electronics:

cable entry housing_812.jpg

Wiring the Electronics in:

Uses a NUCLEO (Semi-Arduino compatible) STM 32bit process module and code all in C. Processor runs at 124MHz

>>wiring - nucleo_832.jpg>>

Next up, a 1mm pitch Thread cut, and then a 2.5mm Pitch.


Joseph Noci 126/03/2017 16:35:55
628 forum posts
875 photos

And then Post-3 :

Some pics of cutting a 1mm pitch thread

Main Panel setup for 1mm Metric Pitch

>>main panel selection setup_0844.jpg>>

Set the Thread Start Point:

set start point_0862.jpg

Press START POINT on main Panel and then move carriage to end point and Press END-POINT

Then press DONE REWIND on Sub Panel

Tool now at start of thread. Press THREAD START, and spindle on:

sub panel - start threading_0855.jpg


Cut proceeds to thread end point:

tool at thread end_0853.jpg

Retract tool and press DONE-REWIND:

sub-panel - done-rewind_0854.jpg

Tool goes back to start, and we repeat:

Thread some more:

>>threading again_0858.jpg>>

and then we are done:

threading complete_0859.jpg

POST 4 Next - a 2.5mm pitch Thread>>

Joseph Noci 126/03/2017 16:42:24
628 forum posts
875 photos

POST-4 - Cutting a 2.5mm Thread.

Shows nicely the rapid stop at thread end - no over-run.

The threading process works very well - Start 1 thread pitch away from start, stops right on the entered thread end point, no-over run, clean underpants all the way, even at 300RPM / 4mm pitch thread...

Main Panel Setup again for 2.5mm Pitch, and set start and end points:

threading 2.5mm pitch setup_0861.jpg

The Start Threading:

End point reached with rapid stop.

>>end point reached - rapid stop_0864.jpg>>

Mark the stop point:

mark end point_0866.jpg

And repeat after putting on more cut:

threading stops on the spot_0868.jpg

Threading stops om the spot!

Now finish threading:

>>threading put on cut_0867.jpg>>

Final Cut:

Always stops on the spot!

>>final cut_0872.jpg>>

I made a video, but the motion from one button to another and to the tool tip, and the thread start and end - makes me ill !!!!!

All worked well, so now I must make all the swarf guards, fit the DRO, modify the cabinet for drawers and doors, and strip, Paint, fit new parts, and reassemble neatly..maybe I will post that lot as well...>>


Neil Wyatt26/03/2017 16:51:01
17698 forum posts
697 photos
77 articles

Wonderful execution Joseph, and a fantastic case.


John Stevenson26/03/2017 16:56:19
5068 forum posts
3 photos
I question whether stopping spindle and stepper will not chip the cutter in steel?
Nylon is very forgiving but it would be an easy job to pre-machine a run off groove.

Edited By John Stevenson on 26/03/2017 16:57:06

Joseph Noci 126/03/2017 17:16:10
628 forum posts
875 photos

Hi John,

Yep, catered for as well - Two ways in fact. Just did not post all the nuances as it gets boring for folk...

If you make a run-out grove, just set the end point in the middle of the groove, and that's where the tool will stop moving. A second mode is that I can disable the spindle stop at the same time the tool stops - That way the threading tip cuts its own runout groove when the tool stops - except the groove is a V instead of the usual flat bottom - maybe not good maybe from a stress point of view, but can be cleaned up into a flat bottomed V very quickly - better than a flat bottomed, straight sided groove...Now I'm babbling...


SillyOldDuffer26/03/2017 20:13:55
5607 forum posts
1153 photos

Like it!


Benny Avelin26/03/2017 22:43:56
80 forum posts
86 photos

Fantastic looking stuff! I have been thinking about something like this myself, but it seemed like a big project. I am impressed by your execution on this.

Michael Gilligan26/03/2017 23:07:45
15434 forum posts
666 photos

Fabulous job, Joseph ... Thanks for showing it.

I hope Neil might persuade you to write it up fully for MEW.


David Taylor26/03/2017 23:14:25
128 forum posts
39 photos

Great project!

Given you're controlling the carriage movement you could do multiple start threads by cutting one thread completely and then making an adjustment to the carriage start position to cut the next part of the thread.

John Stevenson27/03/2017 00:53:07
5068 forum posts
3 photos
Posted by Joseph Noci 1 on 26/03/2017 16:42:24:

I made a video, but the motion from one button to another and to the tool tip, and the thread start and end - makes me ill !!!!!


I do so wish some of the other posters on here will take heed of Joe's words.

To say that a lot of the members here can make such marvelous models and jobs the fact that the tripod was invented at least 400 years ago seems to escape them.

Niels Abildgaard27/03/2017 07:05:18
268 forum posts
96 photos

I want one for my Boxford.

I do not thread more than 20 .30 times a Year but the gearbox noise from normal cutting feed makes me crazy.

Please go comercial.

I can handle the stepper motor -leadscrew and have VFD already


Joseph Noci 127/03/2017 07:11:58
628 forum posts
875 photos

John, yes , a sea-sick video is not pleasant, but I fear your dig re the tripod is a little glibly over-simplified perhaps? I have a few tripods and nowhere to place them for this video - it turns into a major nether Pain ->>

The camera needs to pan from the top left panel to show jogging and thread pitch selections, thread start and end point selections, and between each the view must move to the tool tip at start point, then at end point then move the view to the sub panel ( lower left) to show the rewind and then watch the tool rewinding and the the start threading button and spindle on, the back to the tool and watch the threading and the quick stop, etc, etc...The operator is in the way of the camera when viewing the tool and if the camera is overhead the tool it can't see the control panels, and the like...Just describing it makes me ill...

It is not an issue of keep the camera still when viewing the specific panel or area of interest - my tripod did that fine, but it is the panning from view to view that is nauseating!

>I also tried making separate videos - do just the main panel, then the sub panel then the tool movement and cutting, with a tripod and the camera not moving. Then I tried editing the bunch into one and attempted to get the sequencing correct. After three or four attempts, because the choreography was not always nicely sequential, and the gaps or jumps looked silly, I gave up...The panning still was to much..>

Panels and buttons and tool tip all over the place - from top left to bottom left to mid right overhead and back again...

panels in place.jpg

mechman4827/03/2017 09:13:57
2626 forum posts
407 photos

Super set up Joe & well done, but you lost me after...

...'The aim of this was to create a simple Electronic threading aid using a small microprocessor reading a spindle encoder wheel, and driving a stepper motor attached to the main lead screw. The encoder provides 4096 edges on two quadrature channels, and an index pulse , per rotation. The 4096 pulses are 'divided' down, using a DDA computation, to give the required Stepper pulse rate, taking into account the chosen thread pitch, leadscrew pitch and stepper to leadscrew drive pulley ratios'...

At this point in time I'm quite happy to manage 1 single start thread in the 5 years I've had my machines, & can't remember cutting another thread in the past 30 years, apart from my apprenticeship 50 years ago... never the less superb write up.


Joseph Noci 127/03/2017 15:50:37
628 forum posts
875 photos

Hi Mechman - Sorry, the intent was not to sound clever...just kind of what came out of my head.

Basically all this thingy is , is an electronic implementation of the very neat single point mechanical Dog Clutch that has done the rounds on this web site, among others. The index pulse from the encoder wheel is exactly the electronic equivalent of that single point in the clutch. The 'Quadrature pulses' ( 4096 pulse per chuck revolution) are then simply coupled to the stepper driving the leadscrew, in a ratio to give the required thread pitch, as would be performed by your lathes mechanical gear box or Gear Change set. And Bob's your uncle...


Raymond Anderson27/03/2017 18:07:02
767 forum posts
152 photos

Excellent piece of gear, Would like to see a full write up in MEW, would be worth buying a copy just for that alone.

Great stuff.

Martin Connelly29/03/2017 11:16:51
1188 forum posts
142 photos

Regarding the rapid camera panning and splicing video segments together, would a split screen or an inset window be a good option. The software you used may have this as an option. It seems a good way of showing what a control panel is doing in other videos I have seen.

Martin C

Joseph Noci 129/03/2017 12:16:52
628 forum posts
875 photos

Martin, that is a very good idea. For me the problem that sort of stuff does not come naturally , and so it becomes a whole new mission and process to learn - I have not seen any such option on my (rudimentary) video software either, so a new bit of software to buy and learn...

Not sure it brings much more interest to these sorts of postings anyway.

But still a good idea!


Leslie Higgins21/07/2019 16:36:17
1 forum posts

Really excellent job did you use an arduino mega. I would really to have your setup on my lathe as changing gears is a pain and I have cant cut left hand threads or feed so is there any chance you could share the scrip/sketch and schematic I would be prepared to pay

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