[More Coffee]

I'm flirting with the idea of putting a power cross feed on my 9x20 bench lathe.
I think a stepper motor would offer more fluid control of the cutting tool.In the end for finer control, the motor will be run at a 4:1 ratio to the cross slide wheel
I would like to put together a system that's variable speed, forward/reverse with a normally off switch.
no microcontrollers or computer interface.. analog manual control through a switch and potentiometer only
So im doing a little research.. Nema 17 motor.
I'm looking at a motor that's rated at 5.32 Kg holding torque and operates 12v..

Does a stepper motor's holding torque represent its shaft torque.
Any recommendations for a simple circuit? Or an avaliable control and power supply?
Everything Im finding requires an interface with some other gadget.

Im very new,and :cheers:Thanks for listening.

[doorknob]

The holding torque will be greater than the torque when the motor is turning, and the torque when turning will decrease as the speed increases.

I am not sure that I understand how you plan to use the motor. Are you going to drive the Z axis only? Are you going to turn a leadscrew with a half-nut, or drive a handwheel (through a belt or directly)?

My guess is that 5.32 Kg means 5.32 Kg-cm. If I have done the conversion correctly, that's about 70 oz-in, which is much less torque (by a factor of four or more) than the motors that I usually see people use in CNC conversions of small lathes.

The control box that you are describing has some features in common with what is typically called a "manual pulse generator" or MPG (although MPGs are typically used to jog an axis rather than continuously drive the axis, and many of the ready-built ones are based on microcontrollers and are designed to plug into a computer instead of for sending the step pulses directly to a stepper driver).

What you want also has features in common with what is usually called an "indexer" (but again, those designs are generally built around microcontrollers). For example, there is a thread on cnczone.com that describes the construction of an indexer designed to drive a stepper-motorized rotary table.

It should be possible for you to build an analog pulse generator to do the job for you, but offhand I don't remember having seen such a circuit specifically for this application. You may be able to use something as simple as a 555 timer circuit followed by a pulse shaper/buffer stage to do what you want.

If you can calculate the range of rpm that you want to drive the leadscrew at, and you're going to use a standard 200 step-per-revolution motor, and you select a drive and a stepping (or microstepping) mode, then you can work out the range of step pulse repetition rates that your pulse generator will need to provide, and then find a suitable circuit based on those parameters.

[More Coffee]

I am not sure that I understand how you plan to use the motor. Are you going to drive the Z axis only? Are you going to turn a lead screw with a half-nut, or drive a handwheel (through a belt or directly)?

Hi and thanks.
I guess its Z axis?? the cross slide..not the compound rest.sorry this is new to me.
I'm going to drive the handwheel.A manufactured one that will also act as the sheave for the belt.My plan is to reduce the hand wheel 4:1 to the motor.
With a belt,,This well also allow more torque to the lead screw,but it will also slow the feed down.
I cant find a max rpm ..what i did find, one motor turns 300 rpm @12v that's roughly 75rpm on the lead screw ,which is more than fast enough for what I want ,I rarely run my lathe more than 400rpm spindle speed.

Possibly just an over center spring tensioner to engage the feed when i need it.Or just set the motor up like an alternator on a simple screw type bracket. on the apron.

So If I can find a system that offer's 280 oz/in torque as you imply on the motor shaft,
That will comfortably and easily deliver 300rpm at that torque range assuming 75 rpm max. is the fastest i want the lead screw to turn.

That runs on 12 volt,(preferably, but if needed it can be more)

I can step away from variable speed ,,if its easier, to just have two or three predetermined motor speeds.or stepping modes. as long as I can control the direction of the feed on a normally off,-----> on/off/on toggle switch.

Thanks for taking the time to respond ,
Clear as mud .

[doorknob]

Figuring out the maximum rpm that you can drive the motor at depends on many factors, including the characteristics of the driver that you are using and the voltage that you are applying to the motors. In general, if you want to achieve better torque at higher speeds, then you will probably need more than 12 volts to do that.

It's probably worthwhile to look for guidance from people who have already done CNC lathe conversions (I hope to do one with my small desktop lathe, but haven't done it yet).

[More Coffee]

I dont need high speed ,low rpm with good torque@ 24 volt if need be, I can build up 32V but its just as easy to purchase a power supply to run the system.


It's probably worthwhile to look for guidance from people who have already done CNC lathe conversions

where to ..sorry ..I thought I was in the right spot ,,wheres a mod when a guy needs one..LOL..

[Al_The_Man]

I would like to put together a system that's variable speed, forward/reverse with a normally off switch.
no microcontrollers or computer interface.. analog manual control through a switch and potentiometer only

[B]
I'm going to drive the handwheel.A manufactured one that will also act as the sheave for the belt.My plan is to reduce the hand wheel 4:1 to the motor.
With a belt,,This well also allow more torque to the lead screw,but it will also slow the feed down.

I can step away from variable speed ,,if its easier, to just have two or three predetermined motor speeds.or stepping modes. as long as I can control the direction of the feed on a normally off,-----> on/off/on toggle switch.

:

I guess its a question of deciding what you want? so far your desires are a bit conflicting.
As already covered, if you want simple hand wheel control, the typical MPG puts out 100p/rev this could drive a step/dir amp directly but does not give any flexibility and relies on manual feedrate, a simple logic IC circuit could provide multiply or divide, but still manual.
If automatic indexing, 2 or 3 predetermined feed rates would be a bit restrictive, I would think?
The simplest automatic feedrate requires some logic, and although you expressed you don't want to go with microcontroller, I would be surprised if there was not a design out there based around a PicMicro or other controller that makes it simple and flexible.
Incidentally there are suppliers of Microchips that will pre-program them if you have the hex code from a design, if you want to avoid the cost of programmer etc. and just want to put it together.
Al.

[More Coffee]

Yes your very right it is a bit conflicting..Because im just that dumb when it comes to a stepper motor..Ive never used anything outside a servo tester in the realm of PWM..In fact I initially thought I could integrate that circuit into a driver to command the motor..

I'm trying not to be a leach..:nono:

If I could get pointed to a MPG schematic ,,or where to purchase one ..that would at least let me mess with some of the steppers i have in the junk drawer..for trial and error....As I get a better grip I can be a little more direct in what a may need help with in the future..

Thanks

[Mad Welder]

..........I cant find a max rpm ..what i did find, one motor turns 300 rpm @12v that's roughly 75rpm on the lead screw ,which is more than fast enough for what I want ,I rarely run my lathe more than 400rpm spindle speed........................So If I can find a system that offer's 280 oz/in torque as you imply on the motor shaft,
That will comfortably and easily deliver 300rpm ..........................I can step away from variable speed ,,if its easier, to just have two or three predetermined motor speeds.or stepping modes. as long as I can control the direction of the feed on a normally off,-----> on/off/on toggle switch.......

Hi there more coffee I’m not an electrical guru far from it actually but I wonder if you are misunderstanding the difference between an electrically driven motor (i.e. your lathe chuck’s rotation motor) and a stepper motor!!!

Am I correct in my understanding from what you posted is you were looking for a simple way to automate/ mechanize your Z axis movement while you looked on and manually altered the Z axis speed/rotation direction to give a more uniform turned finish?

If I misunderstood your post forget my analysis and listen to what doorknob has to say as you won’t go wrong…



And it does get kinda confusing so in as simplistic a way as possible……. basically your lathe motor spins when plugged in through what ever it's wired configuration, you turn on the switch it spins.

But a stepper motor depending on wiring configuration will yield a given torque, but only when it receives its signals (i.e. its step and direction) from a stepper driver and the stepper driver also has to receive its electrical pulses from a controller. Therefore three different pieces of hardware required as opposed to your basic motor mentioned above.
So you don’t really look for max rpm in a Stepper motor but a term given as “steps per inch/millimetre” i.e. how many steps will the Stepper Motor require to rotate the shaft to give your required linear movement length and also the speed to travel that linear length……..

The Stepper Motor also takes its power supply from the Stepper Driver, therefore not any old driver will suffice either, the driver has to have the ability to output the specific required amperage to supply the Stepper Motor.


I hope this will be of help……
:cheers:

[Al_The_Man]

This one sold on ebay for $59.00 150707810307.
You can use a cheap 100p/rev encoder for the same thing, just that in Hand wheel form it comes with the operator and has a tactile indent for every pulse.
Al.

[UUU]

An alternative approach - one that I have on the X-axis of a manual mill to provide variable speed power feed. Uses a three phase motor (1/8 HP) driven from a VFD. This is geared down a lot more than 4:1.

In my case I have two 3-position switches and a potentiometer. One switch is left-off-right to control which way the table moves.

The second switch is speed - high, medium and low. The high is the max speed for rapids, and the low is the lowest that the setup will reliably go, for crawling. Then the middle speed is anywhere in between, controlled by the potentiometer.

Simple and reliable.

[Mad Welder]

an addition to my previous post as Al_The_Man had posted while I was typing
now he IS an electrical guru


:cheers:

[More Coffee]

Thanks guy's.

Yes ..really all i want to do is mechanise my cross feed for a uniform finish when facing or parting off..
And yes i haven't a clue on stepper motor function.
I understand amperage and torque can lead to a lot of magic smoke..I also understand that voltage may be correct but the wattage is wrong and that can lead to magic smoke..Ive blown up my share and look to the left or right and Ive blown up that person's share to..Raise your hand if you've had your lips and eyelids burnt from capacitor oil:cheers:

As I understand it Al..the link you posted is basically a remote for the cross feed..and one indent on the dial is one indent on the motor..which translates into XXXX movement on the crossfeed..
That has its place and actually would be quite useful..for picking of thousandths of an inch.It is very interesting..
Would there be away to override it to just feed through? like as I've finally been able to convey for a smooth uniform facing or parting operation..

Sorry guys ..but I don't normally ask for help until Ive at least blown up a few hundred dollars worth of gear .. ,At that point its safe to say the guy is serious about doing something.

[More Coffee]

I just thought of something.

Isn't a MPG like the volume control on some of these audio amplifiers..they turn continuously, and have an indent feel..:idea:

[More Coffee]

LNS Technologies Electronic Kits

Unipolar Stepper Motor Driver Kit

Now that looks all the part ,and its a stand alone system ..

More over I can use the limit switch mode ,and have an on/off/on switch on the console to override the limit switches..

Seems really simple ,5amps of current ..should be able to push a motor needed to move the cross slide around..Ive lots of heat sinks if needed..

Any comments?

[James Newton]

Wouldn't it be best to figure out how much power it will take to move the load you are moving, at the speed you would like it to move, and then find a driver that can manage that power and THEN find a motor that can handle that power?

More info at:
techref.massmind.org/techref/io/steppers.htm#Estimating

[Mad Welder]

........Yes ..really all i want to do is mechanise my cross feed for a uniform finish when facing or parting off.....

Here's another link to check out for information and have a look around the site it might be a good starting point CNC Conversion plans


Good luck.....:cheers:

[Mad Welder]

......More info at:
techref.massmind.org/techref/io/steppers.htm#Estimating

Thanks for the link James :cheers: