Bottom Stitch Issues

[FHL FERG]

I have a new to me Cobra Class 4, I messaged Steve but I figure he's pretty buried up getting things together to go to the boot and saddle show in Wichita Falls Tx this weekend.

I'm having issues with the bobbin thread stitches. They don't look as clean as the top, like the top thread isn't pulling up enough. So I figure the top thread needs an increase in tension. Is there a method other than trial an error to adjust the tension for different thicknesses of leather? How do I check the bobbin thread tension? By that I mean, is there a standard setting it should be at.

The other issue is my feed dog leaving marks in my leather. I have adjusted the nut and spring bolt all the way out, but it still marks on as little as 6oz of leather. Is there another adjustment I'm missing?

[Wizcrafts]

Try reducing the tension on the bobbin spring. This will loosen the bottom thread making it easier for the take-up system to pull the knots up.

Also, if the knots don't pull well up into the bottom layer, try using the next size of needle.

Tracks from the presser feet are a part of life in the 441 world, where very heavy springs are needed to hold down thick or dense leather. I suspect that that most of our dealers have softer pressure springs laying around.

[FHL FERG]

Thanks Wiz. When you say the next size needle, do you mean bigger or smaller? Also, since we're talking needles, I forgot to ask why the hole the needle makes look so sloppy on the bottom side. If that doesn't make since, I will post a pic shortly. Thanks, Ferg

Edited October 2, 2013 by FHL FERG

[FHL FERG]

[Wizcrafts]

By next size needle, I meant up. This pokes a wider hole that makes it easier for the take-up lever to pull the lockstitch knots into the leather.

The photos show a combination of tension and pressure issues. Try these options:

1. Reduce the top thread tension to bring the knots down a bit.
   
2. Or, go down one needle size, for tighter holes.
   
3. Or, tighten the tension spring on the bobbin case.
   
4. Make sure that the thread is feeding under the bobbin tension spring! It can sometimes slip out and free-feed. Reverse the direction of the bobbin if this happens, so it feeds backwards into the diagonal slot in the case.
   

If you got the flat, narrow-slotted plate with your machine, you can try using it without the huge feed dog and see if this improves the bottom appearance (it does on my CB4500). Here's how.

1. Do this with the needle up and power off.
   
2. Remove the shuttle cover, remove the two shuttle screws and carefully pull out the entire assembly, making sure that the shuttle and bobbin case don't fall onto the floor.
   
3. With the shuttle out, rotate the hand wheel until you have a direct line of access to the flat slot in the big screw that secures the feed dog. Use a strong, wide blade screwdriver to unscrew that screw. You may need to tap on it with a mallet to loosen the screw threads, which may have blue Locktite on them.
   
4. With the big screw removed, pull and wiggle the feed dog until it comes out of the movable block to which it is attached. Remove it completely.
   
5. Using long and short, or right-angle flat blade screwdrivers, remove the two screws securing the throat plate.
   
6. Remove the throat plate completely.
   
7. Clean away any thread or leather fragments.
   
8. Install the flat, slotted throat plate and apply the screws loosely to hold it onto the top of the arm, while allowing it to be moved right or left.
   
9. Slowly lower the needle until it is just above the slot in the plate.
   
10. Position the plate so the needle is centered right and left, than lock down the two screws.
    

[Wizcrafts]

Keep in mind that there must be some tension of the bobbin thread, or the bottom stitching will not lay straight, or inline, or tight to the leather.

Also, leather point needles come in different configurations. The most common ones for type 794 are D, P and S point. Different dealers stock different types. For instance, Bob Kovar sold me some #25 diamond (D) point needles that sew in a straight line and cause the thread to lay on top of the leather. The usual type S needles cause the stitches to sink into the holes on the front and back, reducing the apparent stitch length (to the eye). Type P produce a jagged stitch line on top of the leather.

But, I think you'll find that these different needle shapes also produce different results on the bottom. Experiment young Jedi!

[FHL FERG]

Thank you Master, I will heed your advice and continue to focus on the needed adjustments as I focus on using the force.

[Reds Leather]

Just wondering if your work started looking any better on the bottom? I have the same issue with my new machine. I know a little bit about machines and have slightly started messing withe the tensions. If your work is looking any better, please post a picture and what you did!

Thanks!

[ec2121]

i'm kinda having the same issue, but only when i back stitch over the previous stitches to finish it up. the knots on those stitches don't pull up and it looks really bad on the back...

thanks..

[Reds Leather]

Anyone have any more advice on this? Im going to try needle size to start with. Im pretty sure i can figure this out.

[Yanni]

I think Wizcrafts has said it all.

We make leather bags here in England and the tension is something you set depending on thickness and hardness of leather.

You might have thin leathers but very dry so you need more tension for the needle to get back up etc.

As previously said on the post, most issues are generally related to top tension of the thread.

If too high and the stitch is filling the holes on the top side of leather, then reduce the tension until they disappear but make sure the stitch is not coming from off the back.

Also, make sure the bobbin spring is doing its job and the bottom thread is not too lose, check also tension on bobbin winder..

On older SInger/Seiko flat bed machines, there is a little metal pin behind the tension roller that usually gets stuck in one place and needs oiling or replacing.

This can also be a cause.

In our factory we've got a PFAFF 335 for closing backs(3-4 layers of 1.4-1.8mm leather) and another one for sewing around pockets(2 layers of leather) etc.

The one that is used for pockets has less tension than the one used for closing the bags.

We use 130 size needle as we sew mainly rucksacks. If I see missing stitches and tension problems on harder leather, usually a 140 needle cures that.

This is all UK sizes...we use Schmetz needles type S, although for a more decorative stitch I would use LR type.

Edited November 21, 2013 by Yanni

[Cobra Steve]

Hello. To me, this looks like a needle/thread problem. I see needle holes that appear to be larger than the kno,t which allows the knot to travel up and down in the hole looking like a tension problem. In the instruction book there is a needle and thread reference guide that will tell you what size thread and needle to use for different applications and thicknesses. It is not written in stone because there are so many variances in leather, but it is a good starting point. Also when back tacking, make sure that the needle comes up 1/4 to 3/8 of an inch before you start your back tack. If you are using 346 thread on top, then you cannot use 346 in the bobbin (you must use 1 size smaller), unless you are not back tacking. The reason for this is in every hole that the needle punches there are 4 strands of thread and 1 knot, when you back tack in the same holles then you have 8 strands of thread and 2 knots and all of that thread will not fit in the hole, so always remember to use 1 size smaller in the bobbin when using 346 thread on top. Steve

[ec2121]

thanks Steve... i change the top thread to 277 with a #25 needle and bottom 206 and really helped alot. i do notice that with thicker leather the stitches look better. i've been working with two pieces of 4oz leather...maybe my consew 2050 works best with thicker leather???