carriage feed motor

[12bolts]

I am looking at fitting an electric motor to my carriage for auto feed fo the saddle and cross slide.
I am NOT going to use it for threading.
It is a Hercus (sb 9 clone). As I dont have the worm and wheel for this machine I am thinking if I fit the gear that runs from the worm wheel (normally driven by the leadscrew) and drives a plain spur gear to connect to the saddle/cross driven gears with a small, (probably mains) electric motor and some sort of speed controller, I will hopefully have a nice, compact, infinately variable, simple reversing auto feed.
The mains wiring is straight forward for me, (but happy to go low voltage if thats easierer/betterer).
The nuts and bolts I can do, (jerry building stuff is my middle name), I am just not all that clued up on variable speed drives or what I need to adapt existing motors to do what I want. It doesnt want to be too big as it will be mounted on the apron front where the clutch would normally be and this is limited radially by the carriage handwheel and feed levers. Obviously it can protrude towards the operator, but limiting this would be desireable also.
I am thinking that I will only be needing 0-20 'ish rpm on the motor output shaft

Cheers Phil

 

[Hawkeye]

Phil,

You'll find direction and speed easiest to control with a DC gearmotor. The more the gearhead slows the motor down (still above your design speed), the easier it will be to control it to your satisfaction.

Google Pulse Width Modulation circuits and see what comes up. There are lots of web sites that will explain what it is and how to build the circuits.

Basically, the circuit sends your full DC voltage to the motor, but cuts it up into a variable pulse width. For a given cycle time (a constant) the voltage is turned on for a shorter or longer time, expressed as duty cycle. A 10% duty cycle will turn the motor a lot slower than an 80% duty cycle. Since the motor gets full voltage whenever it is on, the torque is better than if you were slowing the motor down by lowering the voltage.

Direction in DC motors is reversed, of course, by simply reversing the polarity to the motor - easily done with a double-pole, double-throw (DPDT) switch.

One thing to watch with whatever circuit you use is to make sure the output transistor(s) are sized for somewhat more than the maximum current drawn by the motor you will be using, ideally, the locked-rotor current.

 

[jumps4]

could you fit a wiper motor in there they are at 90 degrees and most are about 60:1 ratio
I'll look around here tomorrow i had a motor like a wiper motor only more powerful it was for a wheelchair lift
but they may have tossed it when we cleaned up, I know it probably would of had the power and it had a metal worm gear
if i find it i'll post a pic if you think it will work you can have it for what ever it costs to ship.
if i cant find it, another really strong small dc motor is from an electric boat trailer winch, but you cant have mine thats how i move heavy things into my shop.
steve

 

[12bolts]

Thanks Jumps, I hadnt thought of a 12 v car part.....

Hawkeye, I will look into this. Would having the motor run quite slowly under possibly high loads for extended time lead to overheating do you think?

Cheers Phil

 

[12bolts]

One thing to watch with whatever circuit you use is to make sure the output transistor(s) are sized for somewhat more than the maximum current drawn by the motor you will be using, ideally, the locked-rotor current.

Mike, given that you have my lathe, (so to speak) would you like to hazard a guess at what sort of max torque I might need, and what sort of current draw there would be? (worst case scenario)

Cheers Phil

 

[8ntsane]

Phil
A wiper motor could be a option. Some have 3 speeds, and can be run continous with out over heating. Local scrap yards would be full of them. Many wiper motors have been used on mill power feeds. I guess it depends on the work load you want to impose on it.

Trailer winch, wouldnt be a good choice, they are to be used intermittantly at best.

Another option would be a stepper motor but with this method, the cost maybe higher than you want to spend. With many options out there, you probably need to have the other option of gearing it for your speed use.

 

[Rbeckett]

Ford window lift motors are also very simple to control and can be run at varying speeds too. Just a thought for a 90 turn in your drive configuration.
Bob

 

[jumps4]

wheel chair lift motor would get hot probably
how hard is this going to be to move while cutting
how about a pic of where it has to fit with a few measurements
steve

 

[ScrapMetal]

Thanks Jumps, I hadnt thought of a 12 v car part.....

Hawkeye, I will look into this. Would having the motor run quite slowly under possibly high loads for extended time lead to overheating do you think?

Cheers Phil

If you are looking at 12V car motors you have another option, the motors that move the adjustable seats back and forth.

These brand-spanking new 12VDC motors are made to move automobile seats but are willing to change. They spin at approx 190 rpm, draw 1.5A no load, and stall at approx 25A. Threaded shaft is at a right angle and is 4-1/8" x 7/16". Shaft thread is non-standard, so treat it as a smooth shaft and mount pulley or gear with a setscrew. Measures 5-5/8" x 2-1/2" x 2-1/2" overall, not counting the shaft, and has power terminals opposite the gearbox with (2) 1/4" mounting holes opposite the shaft.

40588 CAR SEAT MOTOR

$14.75 EACH

http://www.sciplus.com/category.cfm/subsection/18


You should be able to find these locally from a salvage yard or such.

Hope that helps,

-Ron

 

[Hawkeye]

The automotive motors do heat up, but I haven't had one fail. I made a 'portable' motor unit that could be used to drive X or Y on my mini-mill or crossfeed on my former mini-lathe. Has a switch in the motor unit that turns it on in forward or reverse. It was powered by a PWM unit I built, which contained a large-ish transformer and a bridge rectifier, as well as a potentiometer to adjust speed. Not sure if it was a window or a seat motor.

It worked really well for the mini and did okay for a while after I got the ZX-25 mill/drill. The output transistor finally packed it in on a heavy feed and I haven't gotten around to fixing it. That's why I recommend making sure the output can handle more than the locked-rotor current of your motor.