Need Help With New Cowboy 3500

[buffalobill plus Ed D]

Are you running a regular leather feed dog?...or one of those specialized plates (slotted or holster plate) ?

[JS22]

The regular that came with the machine.

[Wizcrafts]

A pendulum always swings farther at the bottom, than higher up its shaft. Most modern sewing machines, including all of the 205 and 441 type machines, work on the pendulum needlebar principle. They pivot at the top, in an arc that is by nature longer at the bottom than up the bar. Once the needle penetrates all of the leather layers and begins to move them, the distance higher up must be shorter than if there were only a couple of layers to move. It may not be what you wanted to hear, but it is backed up by science.

Most upholstery class machines don't sew over 3/8" of anything, so the stitch length variance is less noticeable (but present). That is no longer the case when you move up to 3/4 inch. You must lengthen the stitch length adjuster to compensate for the variation when changing from 1/4" to 3/4".

Here are possible workarounds that you might be want to try out, in the hopes of getting the least variation in stitch length from thin to thick leather.

1. First, make sure that the feed dog is set to its highest position as it moves the work. It can only go so high before it makes contact with the underside of the throat plate.
2. Next, try backing off the top pressure on the pressor feet. You can only back off so far before the leather raises with the ascending needle and thread. Your machine doesn't have individual springs for the inside and outside feet, so one upper pressure adjustment serves both feet.
3. Try going up or down one needle size. A thicker needle won't flex as much as a thinner one, but requires more pressure to hold the leather down. A thinner needle penetrates the leather easier, but the knots may not be pulled up as easily.
4. Reduce the top and bobbin spring tensions equally. Less top and bottom tension makes it easier for the mechanism to feed the thick material.
5. Spray or wipe silicon or Teflon lube on the throat plate under the leather to reduce friction on the bottom.

There are sewing machines that don't exhibit the change in stitch length with changes in thickness. I own such a machine (ULS), but it is not for the faint-hearted. Such machines have what is known as square drive. This is not found in most sewing machines, as it is more complicated and expensive to implement than a pivoting pendulum needlebar. Square drive machines sell for more used than you paid for your new CB3500.

Edited March 10, 2011 by Wizcrafts

[catskin]

Thank you WIZ.

That does explain why my old fossil of an Adler with just bottom feed and jump foot is more consistant in stitch length regardless of how much is under the foot. It is because the feed dog moves the material the same distance regardless of how thick it is. I do understand now why this is as it is on the needle feed machine. And that it isn't just this make of machine that does it.

Edited March 10, 2011 by catskin

[Wizcrafts]

My friend's Cobra Class 4 does the same thing. We set it to the stitch length we need for various thicknesses. We also change stitch length for effect. It is not set in stone.

I can tell you with certainty that if you remove the regular throat plate and feed dog, and replace them with the slotted plate, that you will lose about 25% or more of the set stitch length in forward, and maybe more in reverse. That was my finding a few weeks ago when I tried that. I think a teflon strip taped onto the throat plate might help reduce the loss of stitch length from friction with the slotted plate.

I think that perhaps my recommendation about loosening both top and bottom thread tensions will help al lot when sewing tall leather loads. With less bobbin pressure a smaller needle size could be used and would still be able to pull the knots well up into the layers. The smaller needle exhibits less friction going in and out of the leather. With less friction on the way up, the top pressure spring can be backed off, making it easier for the machine to feed stitches of any length.