What RPM for slow pace?

[Leatherguy123]

Trying to buy the right size pulley. What rpm should I aim for to get a nice slow stich. Like 1 stich per second slow...

[kgg]

5 hours ago, Leatherguy123 said:

Trying to buy the right size pulley. What rpm should I aim for to get a nice slow stich.

To be accurate on the speed reduction this is a little more complicated then just throwing a pulley on either the motor or the hand-wheel. Factors like:

i) Motor type (clutch motor or servo motor, brush or brushless)

ii) Motor pulley size (typical size are 2" or 3")

iii) Motor startup speed as some don't start spinning below certain speed setting on the speed controller when under load

iv) Type and style of the pulley (3L,4L,etc)

Reducing the speed can be accomplished by just installing a larger hand-wheel but there are physical limits to the diameter and balance of the new hand-wheel that may come into play. Typically just changing the motor from a clutch type to a servo motor will give much greater low speed control. If that isn't quite enough speed control then generally a speed reducer pulley setup is installed under the table between the drive motor and the hand-wheel pulley. Typically installing a 3:1 speed reducer that commonly consists of a 6 inch large V-belt pulley and a smaller 2 inch V-belt pulley either as individual pulleys placed on a common shaft or are manufactured as a 2 step V-belt pulley is installed. 

If you want to build your own reducer setup a good place to start is using a pulley calculator to determine the sizes and combination like www.blocklayer.com/pulley-belt

What type of motor are you using on what sewing machine?

kgg

 

Edited May 13, 2023 by kgg

[Wizcrafts]

8 hours ago, Leatherguy123 said:

Trying to buy the right size pulley. What rpm should I aim for to get a nice slow stich. Like 1 stich per second slow...

You left out a few important details, like the following.

1. The make and model of the sewing machine
2. The type of motor. If clutch, does the clutch engage smoothly, or with a sudden jerk then off to the races? If servo, what kind: digital with a readout screen, or analog with a knob?
3. The diameter of the pulley currently on the motor

I have a lot of industrial sewing machines. One has a clutch motor, while the others have servo motors with knobs to limit the top speed. The servo motors all have very small pulleys, like 2 inches or less. However, my different machines have varying pulleys on the balance wheels.One that I use a lot for repairs and custom jobs has a small machine pulley; about 3 inches or so. The servo motor has a 45mm pulley and I still have to turn the knob almost all the way down to sew 1 stitch per second, feathering the pedal. It will not sew that speed with the pedal down. For that I would need to add a speed reducer. Those are usually either 2:1 or 3:1. On the machines equipped with a reducer, I can usually floor it and sew 1 stitch per second.

Note, that analog servo motors (with a speed knob) may not have enough torque to turn over the machine at the slowest setting. You have to give it a little more speed to overcome the resistance and the leather. If you have a reducer between the motor and machine, you can increase the speed setting to get into a better torque range and feather the pedal to get very slow speeds. On my Cowboy CB4500, it has a motor with a 50mm pulley, a 3:1 reducer, and a huge machine pulley. The total reduction is 9:1. I can dial up the speed knob on the motor and easily feather the floor pedal to sew at watching grass grow speeds! I mean like 1 stitch in 1 minute! I use this technique to place the needle exactly where I want it to hit at corners or the end of a precise stitch line.

I hope this helps.

[Leatherguy123]

It's a Consew 225, with the stock clutch motor. I put a 1" pulley on the motor and a 10" pulley on the machine. It gets the machine down to 175 rpms from my calcs. Which is definatly slow enough (for anyone else searching for this), but would like to get it even slower. 10" is about the limit for my table, there is very little rubbing on the table from the belt, which I had to grind the table down about 1/4" to eliminate the rubbing.

I'm thinking a servo motor is the way to go, just wasn't planning on spending that much, but it's looking like it might be worth it.

The 10" pulley does allow me to sew by hand just taking the belt off and spinning the wheel with my finger. I don't mind doing this for small passes, but anything longer then about 24" and you start to feel it.

Thanks for the input!

[dikman]

For sewing leather a servo is the only way to go (unless you are very experienced at using a clutch motor). 

I learned this the hard way!