12Volt DC Electric Motor Controlled Powerfeed

[snub]

My Craftex Lathe/Mill combo has a power feed for the table, but if I want to use this feature with the mill, I have to have the lathe turning. And that is not safe as well as a large power consumer ( 3/4 horse motors). Also, it is time consuming to  disengage for a fast return to my starting point.  Thirdly, I buggered someting when using the power feed. Ran the table past the point of no return. Must have screwed up some gears. So I decided to build an electric motor controlled power feed. The motor is geared down to about 100 RPM.  The rheostat is actually a Pulse Width Modulated (PWM) controller. It controlls the motor speed from zero to full. I also have a second switch that bypasses the PWM , giving me full speed return.

In case you are wondering about my choice of motor, pulleys and belts. I got them for free.

The motor and pulleys:



I love this bycicle speedometer. Got it from an E-Bay vendor for $8.00. It reads directly in RPM if you want, no need for fancy wheel diameter calculations.











And the wiring. Wish I had started with a bigger box.



The schematics:

[Brass_Machine]

Very nice. Like the bike speedo!

Eric

[John Swift]

Hi Snub,

thats the way to do it

using a ready built speed control and counter makes it easy for any one to build

                    John


 ps     the only thing I would look in to is some form of interlock so
         both switches can't be on at the same time

[John Swift]

Hi Snub

just a thought

two possible control circuits

depending on if you can verify that on your controller

1, the positive supply and positive motor outputs are linked

2,  the the control transistor controls the current from the negative motor terminal to the  negative supply
 
 you can short circuit the negative terminals for maximum motor speed


otherwise use the first circuit 

(I first intended to use a  biased switch that latched in only one on position for
the speed control but large toggle switches were silly prices (£14 + vat!) hence the jog button)



 John

[andyf]

Snub, I'm not trying to hijack your thread, but I'm very slowly working towards a power feed on my old mill, incorporating limit switches and motor braking, which I can't resist showing now I've seen John's post . The idea is to have one switch (SW2a in the pic below) to turn to the left to sent the table to the left and to the right to send the table right, and another switch (SW1) to set it either to move slowly left and fast right, or slowly right and fast left. I have "breadboarded" it, and to my surprise, it seems to work OK.

I don't think there's room for a relay in your box, though!

Andy

Edit: Last line of second paragraph in the caption below should read: "...under raw 12v if SW2a is set to the right."

[John Swift]

Hi Andy

a  4 pole 3 position switch is used on sieg C3  minilathes as the forword / reverse switch  ( eg  Machinemart CL300M )

the limit switches are a  good safeguard

Im not sure of UK prices but little machine shop lists it as item 1335 @ $11.95

       John

[andyf]

Hi John,

Good point about the mini-lathe switch. Mine was a 2A at 250 VAC, 5A at 125 VAC one which these people http://www.fephydraulics.co.uk/Directional-Control-Valves-contact_us.html were, for some weird reason, advertising on Ebay for around a fiver.

I'm hoping the limit switches will have enough consistency to stop the table in the same place on repeated cuts. Hence the need for motor braking. Though, looking at Snub's photo, my gearmotor is fleapower compared to his, it runs at over 15,000 rpm flat out. The gearing is 148:1 so at that speed the output shaft is doing around 100 rpm. Despite its relatively small mass, the speed of the armature means that the output shaft overuns by a full revolution if the motor is simply disconnected without any braking, which wouldn't help repeatability much when driving a 10 tpi feedscrew. Only once I've finished and fitted the power drive will I know if the braking will be reliable enough.

Andy