Very slow sewing machine motor operation.

[mikeincousa]

I am brand new to this forum. I am a very rusty electronic experimenter.

Needing to slow down a sewing machine for better control I built a little jig.

The jig limits the travel of the foot peddle to a point where I need to turn the hand-wheel to get it started.

From there it does not sound like the motor is straining and it produces solid stitches.

My first question.

Will prolonged operation at this level hurt the motor in the long run?

 

[KJ6EAD]

Only if you stall it a lot. The bigger problem will be the excessive heating in the resistive pedal which will probably lead to the element failing. The obviously most desirable solution would be a different drive ratio but that's complicated by the fact that the motor pulley is usually quite small already and the machine pulley has a built-in clutch. Possibly, you could mount a dual pulley idler between the motor and machine to adjust the ratio.

 

[mikeincousa]

KJ6EAD. de KA9TTY.
This is an inexpensive home sewing machine. I have not had any reason to look a the drive mechanism. Would the modification you suggest be possible? Could you point me to a drawing?

 

[Bluejets]

Like so........

 

[Rapidrob]

For what it is worth, Harbor Freight sells a motor speed controller that is dial controlled. It slows the motor down but keeps the current up to allow the motor to not overheat. I think it is rated for 15 amps?.
It has a 115 VAC receptacle built into it. You plug in the sewing machine,"floor the foot pedal" set the speed knob, and use it as you'd normally would but it is running slower as you need it.
I use it on an 1/8 HP high speed precision drill press and it works very well. It's under 20 bucks on sale/coupon.

 

[Bluejets]

Standard triac phase angle controller....nothing special.
Heating of the motor at low speeds will still apply.
As for keeping the current up...water is an analogy for electricity.i.e. more current does not assist cooling.

 

[CDRIVE]

Do you need to preserve the max RPM of the motor? If not you may be able to replace the motor with a Gear Motor. You will loose the top sewing speed you now have but gain very good slow speed operation with plenty of torque.

Chris

 

[CDRIVE]

Like so........

Yup, the intermediate (pulley + shaft + bearings) assembly is called a "Jack Shaft".

Chris