Question For Cobra Owners

[Cobra Steve]

Van Dutch, remove the shuttle hook and make sure there is no thread caught in the race assembly. Steve

[VanDutch]

Van Dutch, remove the shuttle hook and make sure there is no thread caught in the race assembly. Steve

Thanks Steve.. I will do that.. Appreciate your help.

Will let you know the outcome.

BTW I love the machine.

cheers

[Cobra Steve]

Thanks good buddy!

[VanDutch]

Van Dutch, remove the shuttle hook and make sure there is no thread caught in the race assembly. Steve

Steve.. checked the shuttle..all clean. Also double checked the belts and pulleys.. All tight.

[muzzleblast]

Frans, I think I share your same problem with my new C4 and am also looking for a solution.

When stitching through two layers of hard, 10/12 ounce veg tan, with 346/277 and a 25 needle, very slowly, the machine has to be hand wheeled because there is not enough torque at very slow speed to drive the needle through. Increasing the RPM setting is actually counter productive, because I am needing to run the machine very slowly, smoothly and precisely to land my stitches. Going through hard, Barge glued, double 16 ounce in a straight line at top speed is actually very easy. But, that is not the issue. (And yes, belts and pulleys are tight.)

If anyone has any thoughts or suggestions it would be appreciated.

[Wizcrafts]

VanDutch;

Try placing the stitch lever in the zero position; not moving the feed dog forward or backward. Then rotate the flywheel as before and see if the binding stops happening. If so, a clamping screw or bolt may be loose on the stitch length/direction crank arm. This can be checked from the large round cover plate on the right front and back of the head. I have heard of cases where the one accessed from the back shook loose and made it difficult to balance forward and reverse stitches. It could also halt the machine if one of these bolts backs out too far.

[Northmount]

Hi Tom.. I have worked a lots with Servos/Stepper motors on CNC machines and the feature of these motors is that they have Max torque at any RPM range. They don't use inertia like an induction motor

There is a big difference between servos and steppers on CNC machines and those used on sewing machines. My statement was intended for anybody but a CNC user. I normally say "most motors", but neglected to do so this time. Other motors such as used for traction motors don't fit the general statement either, but no one here would draw such a comparison, so I would usually be safe with such a generalization.

For your sewing machine servo, 600 W, 0.83 HP, its torque does fall off at low speed. I don't have as heavy a machine as your Cobra, and have a servo with 3:1 gear reducer followed by a 6:1 reduction pulley set. It can go really slow and punch through 3/8" of leather right from the start, and not run away because I had to give it too much juice to get started. Of course my top end speed is much reduced too, but that is the way I want it. I don't need high speed production.

There are quite a few threads here about servo motors, pulley reducers, etc. that you can peruse and see what others have experienced and done.

Tom

[VanDutch]

There is a big difference between servos and steppers on CNC machines and those used on sewing machines. My statement was intended for anybody but a CNC user. I normally say "most motors", but neglected to do so this time. Other motors such as used for traction motors don't fit the general statement either, but no one here would draw such a comparison, so I would usually be safe with such a generalization.

For your sewing machine servo, 600 W, 0.83 HP, its torque does fall off at low speed. I don't have as heavy a machine as your Cobra, and have a servo with 3:1 gear reducer followed by a 6:1 reduction pulley set. It can go really slow and punch through 3/8" of leather right from the start, and not run away because I had to give it too much juice to get started. Of course my top end speed is much reduced too, but that is the way I want it. I don't need high speed production.

There are quite a few threads here about servo motors, pulley reducers, etc. that you can peruse and see what others have experienced and done.

Tom

Tom.

I am talking about small servos & steppers that are used on CNC machines. Motors that are only $100-$200 each. some of these motors are only 6x4inch and they drive 500lb gantry's with minimal gearing.

Tom, your gearing is much higher at 18:1. From my understanding the cobra's with the speed reducer only get 9:1.

[Northmount]

Tom.

I am talking about small servos & steppers that are used on CNC machines. Motors that are only $100-$200 each. some of these motors are only 6x4inch and they drive 500lb gantry's with minimal gearing.

Tom, your gearing is much higher at 18:1. From my understanding the cobra's with the speed reducer only get 9:1.

So what's the coefficient of friction for your 500 lb gantry? FF = mu * N I'm sure that it is properly mounted, aligned, supported with bearings such that you could move it easily with your little finger (with all cables or rack and pinion removed). Try pushing a needle through the leather with your pinky. That's why you bought the sewing machine. Anyway, enough said.

Tom

[VanDutch]

Whilst we are on the subject of servos, here is a torque curve of a servo motor. Servos actually lose torque at higher RPM. Totally opposite to an induction motor.