Milling power feed

[ChrisBParticipant @chrisb35596]

Hello, I'm growing tired of turning the wheel to traverse the table on my milling machine so I thought a power feed would be a nice treat. However, buying one off the shelf is going to be expensive, the DIY route would most probably be cheaper but I'm not exactly the best person to figure out electrics (unless I have some serious help!)

My mill is a WM18, going through the forum and online I was people have successfully built their own power feed for this machine, but most of the times the details are not there such as the harware you'll need and wiring (what connects to where)

From what I could gather, stepper motors are mostly used with some sort of controler to control speed and direction.

Can someone kindly help me out to determine what I would need and how to connect the wiring together please?

Thanks

Chris

[ChrisBParticipant @chrisb35596]

help figure out what I need

[Brian OldfordParticipant @brianoldford70365]

 

 

Edited By Brian Oldford on 23/09/2018 19:35:25

[Michael GilliganParticipant @michaelgilligan61133]

Chris,

I think you nicely represent the target audience for the video that I linked in this recent thread: **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=137671&p=1

MichaelG.

.

Edit: Closely followed by this one:

https://www.model-engineer.co.uk/forums/postings.asp?th=137731&p=1

Edited By Michael Gilligan on 23/09/2018 19:49:30

[ChrisBParticipant @chrisb35596]

Thanks for the links Michael, the first video although interesting lost me half way through when he started mentioning mosfet and codes.

The video in the second link by myfordboy is more like it, so I should be fine with the items listed in the description. The problem is what he connected to where.

Edited By ChrisB on 23/09/2018 20:16:39

[John ReeseParticipant @johnreese12848]

Myfordboy had a great you tube video on this. He even posted a shopping list.

[dcostaParticipant @dcosta]

Hello Chris,

I am building a new power feed for my milling machine.
The items I am using are as follows:
– An Arduino Uno (Amazon: £ 6.95).
– A 12 volt 6Amperes power supply (Ebay: £ 17.60)
– A stepper motor similar to that used by Mr Myfordboy acquired years ago in the ArcEurotrade, double shaft (£ 84.00). Remember you need a powerfull engine!
– A TB6560 driver (Amazon: £ 5.19).
– One 10kOhm potentiometer

My motor is already running very well.
The connections are very simple.
If you want I can draw the schema and post it and a small video of the set.

Best regards
Dias Costa

[Enough!Participant @enough]

Re using a stepper motor: bear in mind that you *will* still want to move the table manually – perhaps more than you might think. If the stepper is permanently connected, this means the stepper puts a considerable drag load on the leadscrew and I can attest that it feels awful. In addition, back-driving the stepper means it acts as a generator and I was left in no doubt on another (stepper) forum that it was a bad-thing-to-do. My suggestion of simply opening the winding connection with a switch was pooh-poohed too.

Not being, by any means, an expert on stepper technology, I couldn't say but I believe I have severely weakened a stepper in another situation by driving the shaft manually.

[john fletcher 1Participant @johnfletcher1]

My simple totally unsophisticated milling machine power cross feed consists of an up/down car window motor, these motors are designed to rotate in both directions unlike some windscreen wiper motors. I used some gears from a discarded photo copier and made a dog clutch so that I can still use the hand wheel.For speed control I used a small circuit published in Model Engineer 21st September 1990 and inserted a small push to give rapid travers. So, by my reckoning its worked without failure for 27 years and all the electronic components we were pre-used. Total cost less than £5. John

Dias Costa I'm also interested in your video and circuit details please let me know when and where they/it will be available.,

[Ian HewsonParticipant @ianhewson99641]

Hi

Check out my thread of last week stepper motor speed control and connections, it shows how I fitted x control to my mill using Myfordboys guide and connections, works a treat!

The wiring diagrams and driver settings are opened at the end of Myfordboys video by clicking on the down button and going on to his blogspot.

Whilst scrap components will work, you have to first source them, and then hope they are ok.

Car scrapyards in this day and age are not the source they were in my younger days and there is a lot to be said for buying new components on the net

Ian

[Douglas JohnstonParticipant @douglasjohnston98463]

A good solution when using direct drive steppers is to incorporate a simple clutch between the motor and leadscrew. I did this with mine and it works well. Another good idea is to use the enable input of the stepper driver to eliminate any drive current from the motor when it is not in use. This makes manual movement much easier even when the clutch (if fitted ) is engaged.

A lot has been said about the wisdom of manually turning a stepper due to the back emf produced possibly damaging the driver, but I have been doing it for years with no problem so I think modern stepper drivers have sufficient protection for this.

Doug

[mechman48Participant @mechman48]

Hi Chris, have a look at…

**LINK**

**LINK**

George.

[ChrisBParticipant @chrisb35596]

Thanks for all the replies, all have been helpful. I think I'll go for the Myfordboy setup – it seems simple enough for me to follow, worst part looks the wiring, but I now I found the schematic ( thanks Ian ) I probably will pull it off.

Regarding manually turning the table with a stepper motor directly connected – I was thinking that when there is no input to the motor it would be free to turn, no? I would want to avoid clutches and couplings etc, that's why I'm not considering geared motors.

[Tim StevensParticipant @timstevens64731]

If you are nervous about switching stuff on and off by electronics, you might consider using a simple toggle switch each side of the table, fixed in the slot where the end stops go. Then all you need is to put the switches in the right positions, and switch on – when it gets to the 'end', click, and it stops. Next step might be to use an on-on switch so that automatically the traverse is reversed. Etc. Nothing complicated, and when it does not do what you expect, you do not need a degree to work out where you went wrong. And if you drive your feeds via toothed belts it is easy to arrange a dog clutch to disconnect for manual feed, and you have the safety feature of a stripped belt when the irresistible force meets a sold lump of cast iron. And plain DC motors are a lot cheaper than steppers.

Mine works OK for me. Tim

[Ian HewsonParticipant @ianhewson99641]

Take a look at the pic”s in my album using a simple sliding flexible coupling as a drive.

Using the circuit with the driver connected as in Myfordboys circuit the hand wheel drives as normal with no drag, but if you want to disconnect it is a straightforward job.

[Mark P.Participant @markp]

I second Tims idea of using a DC motor, I used a windscreen wiper motor and toorhed belts when I motorised mine.It worked well.
Mark P.

[SillyOldDufferModerator @sillyoldduffer]

Posted by ChrisB on 24/09/2018 16:09:09:

…

Regarding manually turning the table with a stepper motor directly connected – I was thinking that when there is no input to the motor it would be free to turn, no? …

Free to turn with no input? No, afraid not. When you turn steppers they do work and generate. I doubt they make enough volts to damage a driver if turned manually at hand speed but I haven't tried it.  Don't blame me if it does!

There's a noticable rather than strong resistance to turning the shaft with the motor disconnected. Being multi-pole devices the resistence to turning has a gritty feel to it. If I expected to move the table a lot by hand I would consider fitting a simple dog-clutch.

An advantage of a stepper motor rather than ordinary types is the controller can (usually!) jog and/or move the motor slowly in very small steps. Hand operation might not be necessary.

Dave

 

Edited By SillyOldDuffer on 24/09/2018 19:53:50

[Ian HewsonParticipant @ianhewson99641]

As stated in my last post, the handwheel turns smoothly with no drag, trying to turn a stepper shaft by hand will feel notchy, but not in practice on my mill.

Ian

[I.M. OUTAHEREParticipant @i-m-outahere]

I tested a spare nema 17 stepper and with nothing connected it turned freely but if i put a jumper wire across the pins for each coil creating a closed loop or really two separate closed loops the resistance was substanially more .

I know that with my 3D printer when the power is switched on the motors lock – possibly the driver is supplying some current through the coils to cause a braking effect , if i turn the power off i can move the steppers easily .

I'm guessing you will be using an arduino to supply a variable frequency square wave to a stepper driver or possibly one of those cheap pulse generators from China ? so if you wire it up so the main power switch is also the activation switch ( power is supplied to the Arduino which boots up and starts supplying the square wave and power is also supplied to the stepper driver with this switch ) you have a separate potentiometer or rotary encoder to set the pulse frequency ( travel speed ) and a forward / reverse toggle switch . You could also use a pushbutton nvr set up to activate the unit and add limit switches to shut it off at a set point but i have never used the limit switches on my power feed so don't think they are really necessary .

I have also heard that a driver can be damaged by turning the stepper over with no power supplied but as SOD also mentioned the voltages would never get high enough besides that there should be protection diodes in circuit to stop the voltage spikes created by the coils in normal use , i have zipped my build table of my 3D printer back and forth all over the place and fast enough to generate enough power to light up the lcd screen even though there was no power connected and it hasn't failed yet ! I think this rubbish came about because of cheap dodgy drivers that were around a few years back and i think they have improved a bit over recent years .

[ChrisBParticipant @chrisb35596]

Took the plunge, and ordered a 1 axis nema 23 cnc kit and a 24v 4.5A power supply from stepperonline – should have the parts next week. The pulse generator ordered from ebay – China, that will take a while I guess.

Next I need to order a pair timing gears and a belt, any suggestions what I should go for size wise and if both should be the same size?

[Ian HewsonParticipant @ianhewson99641]

Hi Chris

Dont know what size gears you need, but just a heads up on the circuit that is shown from Myfordboy, the switch will need the unused connection on the on off side of it connecting to the other opposite end connector on the same side, or the motor will only run in one direction as the feed to the relay will not operate.

Hope this makes sense to you.

By the way the controller is on the bay from a UK supplier and arrives in a week, mine f rom China took ages, but I bought a spare and converted it as per Myfordboys design as I found I did not know in which dir ection the table would start with my push button design.

Ian

[ChrisBParticipant @chrisb35596]

A couple of weeks ago I received all the parts I needed for the power feed project on the WM18, and after looking at different type of setups for this type of mill I finally decided on the way to go.

Rather than timing belts and gears, I went for a direct stepper motor to lead screw drive. In between the leadscrew and the motor I put a friction clutch which is manually operated on or off. The reason I opted for a friction clutch rather than a dog clutch is that the friction clutch will slip if there is an overload situation (such as hitting the end stops) that way I can also make without limit switches. The other reason for the clutch is to decouple the motor if I need to move the table manually – after someone mentioned you could damage the electronics if you turn the stepper motor manually.

I have already machined all parts required for the project and so far it seems it will work…next step is sorting out the electronics – I'm completely useless when it comes to wires and circuits, luckily for me my brother can handle that.

My aim for the electronics control is to take the supply directly from the mill control box in such a way that when I press the emergency stop button on the control box I will kill both mill and powerfeed. Then I want the powerfeed to operate on two speed ranges, a slow speed for actual milling feed and a high speed range for fast table traverse. Will see how that goes, my brother says it's doable.

Will post some photos of the progress so far in the coming days.

[Joseph Noci 1Participant @josephnoci1]

ChrisB

No need to worry about damaging the drive electronics when manually turning the stepper – You will not generate anywhere near enough back-emf ( compared to the driver itself driving the stepper) to damage anything. In any event, all half decent drivers have individual protection diodes, or diode as part of the drive FET's that will prevent damage.

However, many drivers feed the back-emf as well as any switching spikes back in to the main stepper supply line, so what often happens while manually rotating the stepper is that when that 'back-fed' voltage is seen by the driver to be in the driver operating voltage range, the transistor or FET bridge that drives the stepper windings has the lower drivers turned on – That with the upper protection diode gives a conduction path for the stepper winding current while turning, ie, is shorts out one or both windings, and suddenly the stepper becomes very hard to turn! Your friction clutch may not help in that situation..

I would dispense with the friction clutch and all its mechanics – Fit the stepper and apply a voltage to the driver that is JUST enough to to the table feed reliably, ie, no stalls on the way – increase that voltage by 10% and leave it at that. The stepper torque will be sufficient to drive the feed acceptably, and will simply stall when hitting the end stop, with no more drama than your friction clutch. Steppers may be stalled with no consideration – they suffer naught, neither do the drivers. May simple stepper mechanisims zero the axis by driving into an end stop, stalling and retracting – all at acceptable torque of course.

Not sure what size steppers you have – for example, if NEMA-23, I would feed with 20 to 25 volts in your application..

Joe

[John HaineParticipant @johnhaine32865]

Just in support of Joe, don't get too worried about driving a stepper against the end stop. They make an 'orrible noise but generally suffer no harm. Guess how I know? I've got 5 of them on various axes and all have been driven into the end stop at some point.

[Ian HewsonParticipant @ianhewson99641]

 

 

Why not just fit a flexible coupling from the stepper motor to the drive shaft, and limit switches to the dc power unit?

Fitted them to my mill and they work fine, 2 x 16amp momentary push button switches and a cnc flex coupling from the bay for £11-00.

Enough power from the nema 23 motor to wind up the coupling without the limit switches, don’t ask how I know.

Edited By Ian Hewson on 11/11/2018 22:22:00

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