Stitch length changing

[keithski122]

I use a juki 563 for auto upholstery and have noticed that I have a nice big stitch when sewing a thin vinyl but at the same setting using thicker materials the stitch shortens.Pressure foot height is nearly at max and machine feeds ok as far as I know.Is this normal or is something wrong?

[Wizcrafts]

It's the pendulum effect that shortens the stitch length at higher distances above the feed dog. The needlebar pivots at the top of the machine. The greater the distance to the work, the longer the stitches and vice versa.

[JLSleather]

[keithski122]

Many thanks, nice to know that the machine is normal. 8mm stitch on thin vinyl, 3 thicknesses of leather 6mm foam and 3mm foam and the stitch drops to about 6mm.

[mixmkr]

That seems to be a drastic reduction.  I'm not experiencing that amount on my 562.  Just the wacky tension changes!

[MADMAX22]

Could be the foam when that thick combined with everything else is a little harder to feed which doesnt help the stitch length (depending if you have smooth or toothed feed dog and feet) combined with the effect pointed out above. 

[Uwe]

A variety of factors may affect stitch length as material thickness changes.The pendulum effect by itself accounts for less than 0.5mm of the 2mm you're losing.

Sometimes the feed dog movement isn't quite right and it only manifests itself with thick material. If the feed dog descends too early or rises too late, it may affect stitch length. With thin material it may be less noticeable since the material gets pressed into the throat plate opening to make contact with the feed dog even if it's a little off. If there's significant drag or friction at one or both ends of the material feed movement, it will affect stitch length.

Ideally, the inner presser foot arrives at the material at the same time as the tip of the needle. If it's far off, it may affect stitch length. That inner presser foot timing may also need to be adjusted a little if you sew very different material thicknesses.

How squishy or stretchy the material is also plays a role.

A little high school geometry math (or a CAD program) will let you figure out what the pendulum effect itself may contribute to the theoretical change in stitch length. It contributes surprisingly little, actually.

On a 562 class the needle bar pendulum is roughly 9" long. If the needle "swings" an 8mm (0.315") stitch length at the throat plate level, it will swing a 7.54mm (0.297") stitch length at 12.7mm (1/2") above the throat plate. So theoretically the pendulum effect accounts for less than 0.5mm in shorter stitch length if your material is 1/2" thick. 

This image is a screenshot of the very bottom of the pendulum in my CAD program, showing the two stitch length measurements at throat plate level and 1/2" above:

 

 

Edited March 24, 2017 by Uwe

[mixmkr]

Additionally although very slight, the reduction in length due to the "pendulum'  effect would increase with larger stitch settings, versus shorter stitch lengths, as the material thickness increases..  Probably to the point, the naked eye would have difficulty actually seeing it.  As the pendulum movement stays more vertical, the effect diminishes.

As I mentioned, in my 562, I've gone from 2-3 layers of canvas and "crawled over" a mondo seam of 10 layeres, and the stitch length wasn't noticeably altered.
 

Edited March 24, 2017 by mixmkr

[mixmkr]

watch at the 2:20 mark where the thickness varies, in this Sailrite demo vid.  The stitch length is not noticeably changed.

 

[Gregg From Keystone Sewing]

CLICK HERE for the LU-563 book, it's on our website for download.  On owners manual page 11, check out part # 14, and adjust the wing nut so that it up as high as it can go, or climb, for heavy materials.  Also, check the tension like people said, so that it is a balanced stitch.

Also, see attached image for Juki LU-1500 Series.  I think this fits in perfectly into the content of this thread, and helps explain a lot.  As far as getting into feed mechanisms on sewing machines can get you.  

Edited March 24, 2017 by Gregg From Keystone Sewing

[shoepatcher]

I would also check the to see if the feeding is the same on the inner and outer presser foot.  Sometimes, one foot is slight off, i.e. one foot rises higher than the other which can make a difference in stitch length.

glenn