Fitting independent fine feeds to ML7 lathe

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Fitting independent fine feeds to ML7 lathe

This topic has 23 replies, 16 voices, and was last updated 23 October 2017 at 18:27 by Enough!.

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15 October 2017 at 21:40 #13065
Martin Dowing
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@martindowing58466
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15 October 2017 at 21:40 #321652
Martin Dowing
Participant
@martindowing58466
From time to time I am doing various upgrades to my ML7.

Of course the best upgrade would be to buy Hardinge lathe but lets see what can be done on machine which I already have.

I found it very inconvenient to meddle with changewheels while going from turning to screwcutting and vice versa. On the other hand I do not mind at all to rearrange gears for different screwcutting operations, as long as fine feeds are always available.

S/C gearbox is usual solution for this type of issues, but it is also carrying its own troubles (limited number of pitches, troubles while going from imperial to metric and vice versa etc). This gearbox also cost about thousand pounds on ebay and there are better ways how to spend these money.

My idea is to fit some sort of drive on tailstock end of machine.

Very slow motion motors with planetary gearbox (which allows gearing ratio in range of 200:1 or so are sold as nice compact units. Such motors coupled with frequency modulators could provide very convenient means of such arrangement, eg providing fine feeds. Unit could be integrated with modified bracket for tailstock bearing of a leadscrew (holes for mounting usual bracket would be used to house discussed assembly and there is a chance that they would be sufficient for the task).

Did anyone attempted with success something like this?

What power motor should have to provide adequate torque, assuming 200:1 gearing ratio via planetary gearbox. Lets assume that my ML7 is expected to make up to 1/4 inch @ 4thou/rev cut in MS. How much power such geared motor would need? 50W enough? It is important to get this power right – will provide for idiotproving as well, in case of crash assembly will just stop without causing unforeseen destruction here or there. A clutch would also be needed to disengage this drive at any moment during normal turning and also during screwcutting.

Did anyone think about such solutions?

Any othe Idea, how to resolve this fine feed problem?

Martin
15 October 2017 at 23:17 #321666
Clive Foster
Participant
@clivefoster55965
Maybe simpler to put the motor at the headstock end on some sort of pivoting mount so a gear on the motor shaft could be bought into mesh with the one on the end of the feed screw. Obviously the banjo carrying the normal screw cutting gears needs to be taken out of engagement with the drive from the spindle but I imagine you normally do that anyway except when screw cutting or power feeding. I'd use a nylon gear in expectations of a quieter drive than as steel one.

Pretty sure I've seen at least a picture and possible write up of a device along these lines. Windscreen wiper motors are said to work adequately on bench top milling machine power feeds so might be up to this job too. Maybe hunt down a 24 V lorry or coach size one.

Or put the device at the tailstock end. Not too difficult to extend the leadscrew with a plain shaft so a gear can be mounted.

Clive.
16 October 2017 at 00:00 #321671
ega
Participant
@ega
Lots about this in Martin Cleeve's Screwcutting in the Lathe (WPS3).
16 October 2017 at 00:00 #321672
Nick Hulme
Participant
@nickhulme30114
I like the idea of a drive coupled to the carriage hand-wheel using the rack for power feed reducing wear on the lead screw.

I'm in the process of designing mine but it will use a Stepper Motor, Stepper Drive, Pulse Generator (available specifically for driving Stepper Drives) and PSU. I haven't finalised the coupling method yet, current two options are –

1. Worm and Wheel with the worm on the stepper shaft, the worm wheel on the carriage hand wheel and the stepper mounted on a pivoting plate allowing engagement of the gears.

2. Toothed belt and pulley drive with a clutch (possibly Dog) on the stepper shaft.

I like the idea of being able to add in switches/sensors to cut the feed at a pre-set point for repeated cuts to a line.

– Nick
16 October 2017 at 00:07 #321674
duncan webster 1
Participant
@duncanwebster1
Posted by Nick Hulme on 16/10/2017 00:00:36:

I like the idea of a drive coupled to the carriage hand-wheel using the rack for power feed reducing wear on the lead screw.

I'm in the process of designing mine but it will use a Stepper Motor, Stepper Drive, Pulse Generator (available specifically for driving Stepper Drives) and PSU. I haven't finalised the coupling method yet, current two options are –

1. Worm and Wheel with the worm on the stepper shaft, the worm wheel on the carriage hand wheel and the stepper mounted on a pivoting plate allowing engagement of the gears.

2. Toothed belt and pulley drive with a clutch (possibly Dog) on the stepper shaft.

I like the idea of being able to add in switches/sensors to cut the feed at a pre-set point for repeated cuts to a line.

– Nick

If you use the toothed belt you probably don't need a clutch, when you want to hand feed just de-energise the motor and it will wind round freely
16 October 2017 at 05:04 #321680
Hopper
Participant
@hopper
There have been a number of articles in Model Engineer's Workshop in recent years on fitting fine feed motor to Myfords. You could look it up in the online index here **LINK**

Most seem to use a car windscreen wiper motor and gearbox assembly, with a cheap 12 volt DC variable output power supply bought online.

I have an old battery drill in my scrap box that one day I plan to get around to converting to a fine feed motor. I figure you could use the original trigger with an eccentric shaft to vary the RPM, and probably run it from a 12 volt battery charger or power supply. The drill has a two or three stage planetary reduction gearbox so rpm can go right down slow, while keeping the motor revving enough to have sufficient power.

On my other lathe (Drummond) I fitted a toothed belt and pair of pulleys where the revers tumbler usually goes. This drops fine feed by half and makes it more useable. But has to be taken off every time I want to do screwcutting. Hence, the interest in a drill motor on the other end of the leadscrew.
16 October 2017 at 09:29 #321700
Martin Kyte
Participant
@martinkyte99762
Hi Martin

There was a mod published to add a stepper to the rear of the tailstock end of the bed driving a toothed belt onto a pulley which replaced the hadwheel. The mod also encorporated thrust bearings on the feedscrew bearing support.

I got all the hardware done but never got around to the stepper drive. (Being an electronics engineer I fell into the cobblers children go barefoot problem). My idea was as you sugest to provide dialable feed control for normal turning but I also was planning a fixed distance feed and return for turning to a shoulder. This would have doubled as an auto feed for clock wheel cutting.

It all got shelved when I bought a graduated carriage handwheel and upgraded to a S7 with a gearbox. I may still go with it as I still have all the bits purely so that I can synchronise feed with headstock dividing and end up with an automatic wheel cutter.

I will try and find the mod, but don't hold your breath.

regards Martin
16 October 2017 at 09:43 #321703
Douglas Johnston
Participant
@douglasjohnston98463
I have fitted a stepper motor feed to the tailstock end of my Myford Speed 10 lathe. As has been pointed out a direct drive coupling from the motor to the leadscrew is fine since the leadscrew can be turned from either end quite easily when the stepper motor is not energised.

I also added a very useful feature which automatically stops the carriage at any point. This was done by an adjustable stop using a microswitch. When the microswitch is triggered it disables the stepper motor driver and the carriage stops instantly. This makes boring blind holes and turning up to a set point so much easier.

It has been mentioned before on other threads that turning an unenergised stepper motor runs the risk of producing back emfs which could damage the motor driver, and I did worry about that, but I have had my system running for a few years without any trouble.

Doug
16 October 2017 at 11:04 #321719
Martin Kyte
Participant
@martinkyte99762
OK, so the bearing mod is here.

**LINK**

regards Martin
16 October 2017 at 21:08 #321836
Robbo
Participant
@robbo
An article on a leadscrew power feed using the ubiquitous windscreen wiper motor driving the tailstock end of the screw was in MEW Nos 225 and 226
16 October 2017 at 21:31 #321843
Neil Wyatt
Moderator
@neilwyatt
Posted by Martin Dowing on 15/10/2017 21:40:19:

50W enough? I

Vastly more than enough. Apparently walking takes 60 watts and winding a leadscrew handwheel is a lot less energetic!

Neil
16 October 2017 at 22:21 #321856
Martin Dowing
Participant
@martindowing58466
Many thanks for feedback up to date. It seems that issue is an interesting one.

@Clive Foster, I would prefer tailstock location. Seems neater. Alteration at headstock could easily hamper smooth changing of changewheels for screwcutting. If done on tailstock, I would replace leadscrew handwheel with an appropriate toothed pulley or gear, coupled to motor by toothed belt or something alike. Would try to make it as compact as possible.

@ega, he says, he did it but no details are disclosed.

@Nick Hulme, Saving leadscrew this way will be offset by frequent need to replace handwheel pinion gears.

I would rather install telescopic springs as swarf guards on my leadscrew, if objection is to reduce wear. Nevertheless idea is interesting, it didn't come to my mind while analyzing problem.

@Hopper, Search results from your link do not deliver any output. Maybe I do not know yet how to use it correctly.

Planetary gearbox with normal motor seems to be a good way forward, but clutch is a necessity as such gearbox is not "reversible". During screwcutting it could be damaged.

@Martin Kyte, thanks for reference to mod, but my leadscrew is still 5/8 inch (machine is from Dec.1968), so the kit sold would not be suitable and it still would need to be altered to incorporate motor drive.

Interestingly I had ideas about incorporating thrust bearing on leadscrew of my ML 7, particularly because it will be replaced with new one which I am free to modify. Sometime ago I had a daft engineering idea with modifying screw press with thrust bearing. Press got damaged.

By profession I am chemist and I am not well versed in electronics beyond basic concepts, albeit I have designed and made simple few V @ 300A DC power supply based on 6 diode rectifier of 3 phase input. I went for 3 phase version to get rid of problems with 10F or so "smoothing" capacitor which would be needed otherwise, at 50Hz at least. This machine and dangerous buzzing sound it produces as well as diameters of wiring there is causing fear in my wife but it is useful also for other things. Nevertheless I would have considerable difficulty with programming controller of driver of stepping motor.

Anyway, don't you worry that stepper motor will jerk, possibly adding to chatter during turning? I understand that so called microstepping is only applicable to a very low power stepper motors.

@Douglas Johnston, Regarding automatic carriage stop, I am now testing very similar device, but this one trips relay in 3 phase power supply in my main motor. Inertia of 3 phase motor, pulleys and a chuck spoils a fun at open speeds, though my stop has buffering spring incorporated and system will work without causing damage to machine. For screwcutting to shoulder or screwcutting of blind holes on backgears it works well.

Btw, congratulatios. You have made device discussed here. Did you notice any problems related to jerking by stepper motor? How much power or torque your stepper motor gives?

Martin
16 October 2017 at 23:10 #321862
Enough!
Participant
@enough
Stepper-Drive on my ML7 leadscrew. Part of my ELS but could be driven independently by suitable electronics.
17 October 2017 at 05:42 #321877
Niels Abildgaard
Participant
@nielsabildgaard33719
There is a video somewhere here

**LINK**
17 October 2017 at 07:00 #321880
Joseph Noci 1
Participant
@josephnoci1
Did the Full Monty on my Maximat V10 – About to do it on my brand new EMCOMAT 14D.

I have posted pics of the full ELS/Autofeed conversion on the V10 – have NO idea at all how to link to those posts in this page – one of those website mysteries…

My stepper is mounted as in Bandersnatch's post, on the right side, driving the leadscrew via a toothed belt.

The steppers do not jerk if you use the correct size stepper and driver for the load. Microstepping works very well, on ANY size stepper – does not bring improved accuracy of angular position but does allow smooth acceleration and helps to avoid any mechanical resonance. Problem is that for example, 1/2 step has 1/2 the holding torque of full step so size the motor accordingly.

A Berkshire fellow has implemented my design fully as well – he may do a post soon…

There are many pics in my album on the stuff. None are really a DIY recipe, but give some idea.

My implementation does full autofeed variable from 0.05mm/sec to 10mm/sec and cuts any thread from 0.1mm to 7mm pitch in 0.1mm increments, and 5TPI to 60TPI in 0.1 increments. Stops tool automatically at the end of thread as well!

I recommend trying to implement something based on a stepper -NO more gears and changing gears and thinking about ratios, and noise..

Implementations using wiper motors or the like can work for autofeed, but really need motor speed feedback to control the speed properly. Open loop speed implementation notoriously give varying feed speeds during the cut, depending on the cutting loads, carriage friction on the bed at different carriage positions, and so on.

If the stepper size and stepper driver are chosen well, there are no missed steps, no changes in feed speed, and it works well.

If only autofeed is desired, a simple variable pulse generator ( NE555 type for example – Easily found on Banggood, etc) and direction toggle switch can feed the stepper driver connected to the stepper.

Joe
17 October 2017 at 10:07 #321905
Douglas Johnston
Participant
@douglasjohnston98463
As Joseph has said steppers should not produce a jerking motion and my set up is very smooth in operation over the whole speed range. I experimented to get the best microstepping setting on the driver board to ensure I did not get any resonance effects through the speed range.

I used a Nema 23 motor with a torque of 2Nm which had a step angle of 1.8 degrees or 200 steps per revolution. The microstepping of course increases the number of steps per revolution. I have found that this size of motor works very well for my smaller lathe but might not be big enough for a larger lathe.

Doug
17 October 2017 at 11:32 #321917
not done it yet
Participant
@notdoneityet
5Where has the post by Douglas Johnston (@10:07) gone?!?
22 October 2017 at 12:43 #322806
OuBallie
Participant
@ouballie
Bandersnatch,

Would appreciate details of stepper and pulleys please as I may have to do something similar on the BH600G.

Thanks.

Geoff – If anyone in the past had told me I would be wearing long johns, they would have got an earful!
23 October 2017 at 01:54 #322949
Enough!
Participant
@enough
Posted by OuBallie on 22/10/2017 12:43:42:

Would appreciate details of stepper and pulleys please as I may have to do something similar on the BH600G.

Hi Geoff,

The stepper is NEMA-23. I originally had a relatively small motor in there ~150-200 oz.in I think. It ran OK for some time but then started missing steps so I swapped it for a larger one. ~300 oz.in or so I think. (It's kind of buried and I don't want to take it apart). It turned out later that my carriage alignment had gone off and that was probably the main cause of the missed steps – but I think it's more comfortable with the larger motor anyway.

The motor is mounted in a length of 2.5" square (outside) thin-walled steel tube, suitably cut away where it counts and fitted with a plate to mount the motor at one end and a blank plate at the other. This reasonably seals the motor from swarf. It's mounted to existing tapped holes on the rear of the ML7 (along with my home-brew splash shield).

The motor pulley is 12 tooth and the leadscrew pulley is 25 tooth for ~2:1 ratio. I determined this by the Skyward-method (I looked up at the ceiling and said "What's a good ratio? Oh yeah 2:1 ought to be OK".) In fact, anything around 2 or 4:1 ought to be fine. I used XL037 series belts/pulleys for the good reason that that's what I had around ….. except the belt which depends on the particular geometry and you'd have to work yours out for yourself. My centre to centre distance is about 5-1/4" and the belt I used is this

Hope it helps.

PS I was wearing long-johns as quite a young man. Shovelling snow in January in Ontario you tend to be a lot less picky.
23 October 2017 at 11:07 #323014
OuBallie
Participant
@ouballie
Thanks Bandersnatch.

Geoff – Recovering from the 'battle' 5 year old & I had yesterday
23 October 2017 at 11:46 #323033
Tim Stevens
Participant
@timstevens64731
The toothed belt idea seems eminently sensible, but I wonder why a stepper motor is preferred over an 'ordinary' one? I would suggest two minor alternatives for the drive –

1. use a round belt as used on sewing machines etc. this would slip and screech if the drive was stalled.

2. use a pivoted jockey pulley on the tight side of the belt, and add a microswitch to switch off if the belt went really tight.

Both ideas are to avoid problems when you forget to disconnect the fine feed. Having some slack in the drive with a jockey pulley also makes it easy to slip the belt off when you want to cut threads.

Regards, Tim
23 October 2017 at 12:03 #323038
Martin Kyte
Participant
@martinkyte99762
"why a stepper motor is preferred over an 'ordinary' one?"

One thing springs to mind. Doing the thing with a stepper does open the possibilities of semi or full CNC as future development. By semi I mean electronic saddle stops or maybe auto feed/return for clock wheel cutting.

But if fine feed is all you reqire then alternatives are as you say feasible.

regards Martin
23 October 2017 at 18:27 #323113
Enough!
Participant
@enough
Posted by Tim Stevens on 23/10/2017 11:46:20:

The toothed belt idea seems eminently sensible, but I wonder why a stepper motor is preferred over an 'ordinary' one?

If you're referring to my setup, Tim, my earlier post explains that this is part of my ELS system (not simply an independent drive for the leadscrew) hence the stepper.
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