Quick and Dirty X2 Mill feed

[klank]

(Moderator, please excuse me if this topic should be added to the on-going one started by Darren on May8 - please move or remove my post if its in the wrong place).

I need a power feed on the X axis of my Sieg X2 for no more good reason than "arthritis" in my wrists.

There is an excellent thread topic (Darren - May8) a bit further down the board on a mill power feed with a load of advice re. electronics and designs of the mechanical linkage between motor and table leadscrew.
As a newbie, as far as the machining work is concerned, I do not think I have the skills to make some of the necessary "clutch/gear" components accurately enough, so I have been pondering a simpler "basic" solution.

The "ox-cart" type feed wheel on the X axis of the mill table needs a helluva lot of turning to get from one end of its travel to the other and its becoming too painful to tolerate.
I just need a motor feed to get the X axis "in the ball-park" and then go to manual operation. Possibly, milling under power might be useful, but this is not my prime consideration.
I have read a number of threads on this good site and others where a WW motor is usefully employed, but obviously some type of "clutch" mechanism is necessary if manual feeding is required in the operation.
I was fortunate in obtaining a selection of 12V motors from a Ford Fiesta when it was scrapped after our last bout of snow down here (my No. 1 son wrecked his wheels in an ungritted lane!).
My first thought was to utilise either the radiator fan motor or the car heater motor. Both of them would not need any form of "clutch" as there is no reduction worm/pinion to prevent manual operation with the motor connected to the X leadscrew.
I have a good 30amp p.s.u. with volt/ammeters from my ham radio gear and so did some quick tests with it. Both motors would start with the ammeter kicking to around 5 amps and then settle down to spin freely at about 1 amp. They are both quite powerful and would do the job easily, but the physical mounting of them presented problems and also they ran quite fast if uncontrolled.
I discarded the heater/blower motor - nicely as it ran, mounting it would be difficult - the unprotected brushes are at the output shaft end and are fully "open" eg. - to flying swarf/suds and what have you
Motor control is no problem - I have a three pwm controllers from previous electronic projects, but at low revs., the radiator fan motor did not sound too happy so I discarded this.
The tailgate wwm has a mechanical linkage internally to give to-and-fro movement on the output shaft which could be removed but the casing would need re-drilling and a new output shaft fitted - so I discarded this one.
The main wwm looked the best bet.
Fortuitously, my old Dad's motorised 12V bath hoist became surplus to his needs and so I plundered its guts to see what might be worth having.
It is powered by a nice little Bosch wwm type of affair that was easy to remove. This turns over quite slowly at 15V and responds well to a pwm controller - right down to a slow crawl. The output shaft has a flat machined on it.





Motor control has been covered so well in other posts - all I can add is I am using the controller suggested by Websterz in the May8 thread'
http://www.electronickits.com/kit/complete/motor/k166.htm
In the UK - available from:-
http://www.quasarelectronics.com/3166v2-bidirectional-dc-motor-speed-controller-5-32vdc-10a.htm
This is a surprisingly elegant design and very efficient - "H" configuration of 4 power Mosfets - means no need for a reversing switch (must be rated at at least 5 amps) and easy control by a single pot. left, off or right in the event of "exciting problems" when in use. Carries 5 amps easily and can be used up to 10amps if some of the circuit board tracks are "beefed up" with tinned copper wire.
I built one into an old 18v minidrill case I had, using a scrap transformer.





I have put some dimensions in the following if they are of use to any other X2 owners.
My Sieg X2 mill has a slot ready cut in the end of the X axis leadscrew (I don't know if this is standard with all the similar "clones"). the shaft is circa. 12mm dia. with the slot 4.5mm wide for about 30mm. (I measured these without stripping the whole thing down - so might be a slightly out).



I made a shaft to connect with the slotted end from 12mm steel bar, milling the tongue 4.4mm, 30mm long.
Length of bar to suit needs - mine is 140mm.
Took a 45mm length of 20mm dia. steel bar and bored it 12mm - to a nice slide fit over the tongue.
Fitted this with 10mm projecting proud of the tongue with a cross drilled bronze pin at the other (inboard of the tongue) end.



I machined down the rest of the length to (arbitrary) 10.5mm.

I had a piece of 6mm black steel plate, 150mm x 100mm - which I used to replace the "end" plate on the mill table (held by two M5 screws). These appear to be on 72mm centres, 21.5mm down from the top face of the table.
To allow for the leadscrew not turning exactly true with the shaft added (mine described a bit of a circle at the outboard end when engaged with the slot), I drilled the mounting holes oversize at 7mm to allow for some "adjustment" - see later.
The hardest bit was spotting the point where the shaft would pierce the new endplate. I measured this as accurately as possible - exactly dead centre between the mounting holes and 38mm down vertically.
I machined a substantial bush from a bit of gunmetal bar I had blagged from a scrapyard - 15mm length of 28mm dia.
Bored to a running fit over the 10.5mm length of what will be the "input" shaft.
I made the bush a very tight fit in a 14mm hole bored in the end plate.



The bush is thick enough to take the shaft "wobble" when slotted into the leadscrew and smooth everything out - helps eliminate backlash on this screw too!
The shaft can be pushed into engagement, but with the extra length of the collar, it can be pulled out with the end of the collar meeting the endplate and turning smoothly without engaging in the slotted end of the leadscrew - my "clutch mechanism". It moves in and out with a smooth clack each time - most satisfying.





All that is left is for me to fit the end of the motor output shaft to the end of the input shaft, hook up to the psu/controller and test.
Will post this later.

[Bernd]

Nice mod klank. No problem with starting your own thread on how you did it. Keeps the confusion down if you post something like this in a new thread. People won't have to search through a single thread to find an answer.

And the mod looks quite simple so far.

Keep up the good work.

Bernd

[Brass_Machine]

I agree with Bernd on all accounts. Looking good and keep it coming!

Eric

[John Hill]

Good work Klank!

The thought did cross my mind when I got to the bit "I just need a motor feed to get the X axis "in the ball-park" and then go to manual operation"  that a battery screw driver with some sort of crank on the end would make an easy and convenient "knob/wheel" turner.

[Darren]

Very nice, very nice indeed.

I really like your "clutch" method. Should be a joy to use.

I've seen those power supplies before, and nice they are too. I have one reservation, well two really.

I have heard that finding the center off can be fiddly. Easy to put the motor into reverse by accident. Is this true?
Second, to reverse the motor you loose the "sweet" speed setting and have to find it again every time you change direction.

Though if you are not going to mill under power then this won't be an issue.

Sorry I didn't mean to cloud things, just speaking aloud 

[CrewCab]

First class write up Klank, as is Darren's so imho they compliment each other by addressing the requirements from a slightly different view point 

Good on ya both 

CC

[klank]

Thank you Gentle men for the encouraging and kind remarks.

I too was a little concerned about the "controlability in a crisis" - as Darren quite rightly remarked.
I bench tested this "H" type kit motor control unit on the Bosch motor and was agreeably pleased.
There is a pronounced "dead-spot" at the middle of the pot's rotation. Provided whatever control knob you use has an easy to see mark, or pointer tip on it (and the knob is mounted with the middle of its travel at exactly 12o'clock), it is fairly quick, positive and obvious to stop the motor. As you approach the centre spot, the speed drops off rapidly, so inadvertantly over controling the pot. beyond 12 o'clock shouldn't result in too much trouble as it takes quite a fair turn to start movement and pick up speed in the other direction. 
I may change the style of my control "knob" to a pointer type one.
This particular Bosch motor runs fairly slowly at "full power" anyway (probably wound for a hoist type application), which should be an advantage in a situation where things get a bit hairy by mistake.
The pot can be turned down to make the motor barely turn over (like one rev in 2 seconds) with no apparent overheating or distress and the ammeter rock steady. I tried to grip the output shaft at this low speed but couldn't check it at all, and still the ammeter barely moved. Very torquey.


I hadn't thought about re-finding the "sweet spot" after stopping - good point. I suppose a simple calibrated dial behind the knob/pointer might help.

There could be a problem though, if the motor is directly switch reversed WITHOUT STOPPING IT FIRST (if you try to keep that sweet spot setting).
I will try and explain - although I am not an electronics expert by any means and please tell me if I am talking rubbish, or this point has been covered and resolved elsewhere:-

Previous to this "H" (kit) controller, I had made one on veroboard, using a simple single chip quad op-amp (rather than a 555 timer) to provide the variable pulses to a single power mosfet. (Used a simple circuit recipe found on the net).
The problem was finding a dpdt. reversing switch rated at 10 amps (to be safe) in order to change motor direction. I tried a relay with a small panel dpdt switch, but life was getting too complicated with the extra wiring and space needed, and instead used a chunky dpdt. "stomp switch" from an old guitar effects unit I had made for one of my sons (in their garage - thrash - band era). I linked the output to a pair of resistor protected led's, back to back (red/green) so as to give a visual indication and avoid confusion over which way the motor was running.
All worked fine, but the Bosch motor quietly screamed with the pulses (?windings/resonance?) at some frequencies.
Not a problem I think. No overheating or anything bad - just a bit weird to hear.
In the "power out" part of the circuit, I had fitted a hefty Schottky diode to protect the Mosfet.
I tested this circuit on the bench, with an ammeter on the power - in - line from my trusty 13v 30amp psu.

I tried the stomp switch first after stopping the motor - no problems, the amps stayed well below 3 or so on restart in the opposite direction as power was fed in, even with loading the output shaft.
I then tried hitting (!) the stomp switch with the motor running at speed (keeping the "sweet spot" setting on the power control pot.). The needle on the ammeter jumped to over 10amps and the schottky diode got somewhat hot under the collar (I had mounted it on a heat sink with the mosfet).
Not good.

I did some background reading and although I do not fully understand it, changing the direction of output of the motor without stopping it first can be BAD!! - Unless the circuitry can withstand the extra amps/heat - even momentarily, and your protection diode has to be good, or you can blow the mosfet and then full power runs straight into the motor - which could be quite exciting if machining at the time. Something to do with ?back emf and inductance as the armature fields collapse/change direction? if the motor polarity is reversed suddenly whilst running at speed.

Maybe someone out there knows more about this.

Anyway, since it seemed good practice to stop the motor before changing polarity (from what I had read), I felt that the "H" type drive and single pot control would be a much better and possibly safer solution - the motor automatically having to be stopped as the pot passes through 12 o'clock, no amp. jump, no heat. It does mean, in either case though, that the "sweet spot setting" cannot be retained at the time of switch over.
If I have got this wrong, please do say so.


John, I think there is a thread re. using a scrapped cordless drill (with the pistol grip sawn off) to directly power the X leadscrew on the MECH forum (I think) - can't find it at present.

Will post a bit more tomorrow if I can couple the motor to the shaft and tidy up the loose ends.

Respects and best wishes.

[Darren]

Oops yes, reversing a motor without stopping it can cause some problems, mostly I think because if the motor is still turning without power input then it becomes a generator. (EMF) Then you go and whack voltage in the opposite direction = lots of stress.

I did think about a pulse circuit for mine, but they are not good with inductive loads unless the motor is designed for it. Basically the windings do a dance to the pulses, ie they move. This is not good as the winding insulation won't take long to wear through.

That's as I understand it...?

Glad to hear the voltage knob has a positive center 

For the reverse switch I used a DPDT center off type.

 

[klank]

Thanks Darren,

Now I'm being stupid - yes of course, so simple - with a dpdt/centre off switch, no problemo - you switch off automatically as you reverse, just allow a second or so in the "off" position.
 
I didn't have a toggle switch rated for 10amps - a bit 'spensive to buy new, so used what I had. Got a dead spot in the middle of my brain!

All of my motors are DC magnetic - not field coils - hence (generally) seem o.k. with pwm control?
I suppose cheapo motors only have enamel insulation on the armature windings, but the better ones have some kind of ?epoxy? to stop the wires moving.
I have used that kind of (pulse) control for many years on "Dremel" type low voltage kit and my old model railway.
A (very) few railway motors sang a bit - but generally the motor control was excellent.

[sbwhart]

Hi Klank

Very well done  you're clutch system is similar to what I'm intending to do when I fit power feed to my X3, I have difficulties with the elctronicy parts but I have gleaned a bit of understanding from these threads, so keep them comming.

Have fun

Stew

[klank]

A bit more on "centre off" pots - Circlip suggested finding a pot with a centre detent - similar to those on audio amps for tone control/balance. Trouble is I think most of those are Log pots - a Lin pot is needed in this application.
Maybe there is one listed somewhere - 100k (I think) is the right value.

[Darren]

Umm, you might have a job finding one of those esp a lin one.

My amps are "pure" so never used one,

Where to look,

Farnels
CPC
Maplin
Rapid
Cricklewood

There are others, peeps please add to the list.....

[Darren]

RS
Farnels
CPC
Maplin
Rapid
Cricklewood

[Darren]

Over the pond but it seems they are available

http://www.guitarpartsdepot.com/100K-100K_Pot_Linear_Center_Click.html

Now to find one on this side 

[klank]

Just to finish this off:-

I cut to length, drilled and counter bored the "input" shaft for the motor shaft/flatted end, cross drilled and tapped M4 for a couple of grub screws to catch the flat on the motor shaft and fitted it up.





To stop the motor "kicking" when under power I fitted a length of M6 studding to one of the mounting lugs and drilled the end plate to match for a free sliding fit.
To prevent the motor pulling out of the shaft when dis-engaging, a couple of M6 nuts, thread-locked at the right place on the stud seem to do the trick.

Engaged


Disengaged


I admit this is all very simple and very crude compared to the lovely projects shown on the other thread, but it will do for my needs.

In case of using suds, I appreciate the motor is (probably) not water-proofed - I can either cover it in a plastic bag, or it is really quick and easy to pull off - just undo the grubscrews and unscrew the stud form underneath.

I am not 100% happy with the present pwm motor control - as Darren pointed out, the centre-off position can be hard to spot if in a hurry. A centre detent pot would do very well here - but none of the usual suppliers stock one over here. Motor control and slow speed is excellent however.

If anybody wants a selection of ex-car 12v motors (including wwm's) I would be delighted to pass them on to a good home.

[Darren]

It works dunit, that's all that's required 

I have been looking for that center pot for you in the UK but I just can't seem to find one....