Stitch length maxes out too early

[cumberlandharp]

Hey guys,

TL;DR version:  My stitch length maxes out at 6/spi. I have another identical machine that can achieve close to 4/spi, so I know I can get the stitches longer, but the stitch length regulator is already maxed out. Looking for advice on what I need to look at to regain the full stitch-length spectrum. Details below.

Longtime lurker, first-time poster. A couple of years ago, I took over the management of our sewing department at work due to the retirement of a longtime employee. I have learned over time to do basic maintenance and adjustment of our machines. However, I have one machine right now that is repeatedly giving me issues and I'm at a loss for what to do. I do have a sewing machine repairman who has been very helpful to me over these years and has taught me a lot, but he is having health problems right now and is unavailable. So I'm turning to you guys for any suggestions I can get.

The machine in question is a Consew 339RB-1. It's a double-needle, walking foot machine with reverse stitching. I have two of them in operation, which is very helpful for side-by-side comparisons, but I still haven't figured out what is going on. My problems started about a month ago when the operator popped the safety clutch. I reset the clutch, timed the needles, and all seemed well for a couple of days. Then the clutch popped again, but this time the timing belt broke. So I replaced the timing belt and went about looking for what else might be going on. During this process, I have timed the needles, tightened up the play in the safety clutch, adjusted the needle bar height, adjusted the feed dog height, taken apart the stitch length regulator for de-gumming, adjusted the hook to needle clearance, and adjusted the reverse stitching to match the forward stitching (I am just listing everything I have touched on this machine, even if irrelevant to the question at-hand, just so you know where my hands and tools have been). After all of this, the machine sews pretty well; no thread breaks and very few skipped stitches, which is a great improvement. However, I cannot adjust my stitches to be any longer than they are right now, which is about 6/spi. I can adjust them down to 0, but it seems to me that the stitch length regulator pegs out too soon and I can't achieve the default maximum stitch length. I know that they can be longer because I have another machine that is identical to this one that is set to 4/spi with a bit of room to go even bigger. Plus, before the operator initially tripped the safety clutch, I could adjust the stitch length up and down without any issues.

My suspicion is that during the timing belt replacement I did something incorrectly, but it's hard to know what it is considering the machine is sewing nicely. I'd appreciate any leads or suggestions anyone might have regarding what I need to check or adjust next. I don't know if there's any other information you guys need, so just ask if you need further details about the machine or what I've adjusted so far. I have used the search function here and checked out every relevant post I could find, but my issue persists. TIA.

[Uwe]

Have you checked the stop screws that limit the reverse lever movement? They can be used to limit stitch length. The bracket may have rotated on the shaft, inadvertently changing the stop limits. Or perhaps you changed the stops when balancing forward and reverse, which can results in a shorter overall stitch length. 

The Consew 339 is really a re-badged Seiko LSW-8BL. The pictures below are from the Seiko parts list and my Seiko LSW-8BL.

Also verify that the stitch length eccentric itself has the full range of motion. The eccentric movement sometimes binds in a certain position before the pin that moves inside the spiral groove reaches the end of that channel. The two parts rotate against each other as you change stitch length. It should give about 4/5 of a full rotation during adjustment. This is hard to observe since the whole thing rotates as you change stitch length. I took two pictures of the the stitch length eccentric in both extreme positions on my Seiko as a reference. Check if the notch in the right disk lines up the same way in your machine when you dial in stitch length "0" and maximum stitch length. On my machine the two discs rotate about 4/5 of a full rotation against each other. Other machines have a different spiral track disc design, so they may offer more or less of rotation. 

Here's an annotated graphic from the Seiko LCW-8BL parts list that shows the spiral track and the pin that runs inside it. You can see the end points of the spiral track. 

I separated the eccentric discs on my machine just to illustrate the spiral track mentioned above. You don't have to take this apart to verify range of motion. I just did to see the actual spiral track on my machine and how the end points of that track align with the limits of the stitch length adjustment. 

 

Edited June 18, 2018 by Uwe

[chrisash]

Wow, what a great reply to a post

Great work Uwe

[Evo160K]

That's impressive Uwe.

[cumberlandharp]

Thanks Uwe, this is great information. I haven't checked those stop screws you mentioned, so I will do that and report back.

[cumberlandharp]

After inspecting the areas that you mentioned, Uwe, I was unable to find anything amiss. My stop screws are still set up the same way as the other machine I have; both the machines behave the same way in that regard with a normal range of motion for the reverse lever.

Also, my stitch length eccentric looks just like yours and rotates from the same zero to the same maximum as the one you photographed.

Could there be anything else involved with the reverse linkage that could be causing this? I did take that apart when swapping out the timing belt. I wonder if something else could have been reassembled incorrectly. 

[DonInReno]

Uwe, I have no real interest in this machine yet once again it's impossible to look away with such a great description, great visuals, and an actual picture of your machine. Very nice.

[Uwe]

Lots of things can be re-assembled incorrectly.

Since you have twin machines and one of them works as it should, your best bet may be to put them side-by-side and very carefully compare every last bit of hardware involved in the stitch length and reverse mechanisms. How far does a part move? In what position does it start and stop to move? Things that appear the same at first glance often turn out to be not quite the same upon careful inspection. Finding or noticing that one thing that's off is a key skill in sewing machine repair and adjustment.

Many mechanisms that translate partial rotary motion to linear motion need to be "centered" to work as designed and provide the correct range of motion, both linear or rotary. The stitch length and reverse mechanism does this rotary-to-linear movement translation in four or five different places in sequence (the reverse lever rotates a shaft which moves an arm that in turn rotates another shaft, and so on.) Some of these linkages are adjustable and if they're not properly "centered" they may not provide the correct linear or rotary motion. Whatever movement the reverse lever makes when you push it down needs to produce a precise 180˚ rotary movement somewhere else in the reverse mechanism. 

I'd also check the feed mechanism, especially since you changed the timing belt. If the feed timing is off, it may not transport the material as far as it should, or the needle may penetrate the material after it already started moving towards the back (or before it reaches the front.) 

Make some stitches in stiff paper to get a good needle hole distance measurement. I made a stitch length gauge some time ago for a video (https://www.youtube.com/watch?v=iiaaT1npYrQ). You can download the PDF file and print it out yourself: http://docs.uwe.net/SLG.pdf 

 

Edited June 19, 2018 by Uwe

[cumberlandharp]

Thanks again Uwe for your replies. As you suggested, I think my best course of action is to compare the movement and mechanics of my machines side by side. I’ve already been doing that, but I’ve only really been concentrating on the more likely culprits in the linkages. I believe more scrutiny is in order for the tertiary parts. I will follow up with the results of my troubleshooting. If I get it corrected, I will be sure to update this thread for future patrons of the search function. 

Readers, if there are any other suggestions for me, I would greatly appreciate any and all input. 

[cumberlandharp]

So here I am, one year later, and this machine is still having issues with stitch length. I'm looking for any ideas as to things I can adjust to affect the stitch length.

 

The only update I have is that I have discovered that I can "cheat" my way into getting longer forward stitches if I adjust the stop screws affecting the forward and reverse travel to be unbalanced. This will give me longer forward stitches, but it makes the reverse stitching shorter, of course. This does tell me, however, that longer stitches are possible – I just can't figure out how to tap into them.

 

Any and all suggestions for things to adjust are welcome.

[Gregg From Keystone Sewing]

Make sure that the crank clamp with the limit screws is set correctly to give both the possibility of a 4mm SPI in both forward and reverse.  It could be set so that the crank is going to give for example 6mm in one direction and 2mm in the other, if that makes sense.

 

 

[cumberlandharp]

5 minutes ago, Gregg From Keystone Sewing said:

Make sure that the crank clamp with the limit screws is set correctly to give both the possibility of a 4mm SPI in both forward and reverse.  It could be set so that the crank is going to give for example 6mm in one direction and 2mm in the other, if that makes sense.

 

 

Gregg,

Thank you for that. When I mentioned above that I could "cheat" my way to longer forward stitches, that's what I was referring to – that I was moving that clamp on purpose to allow more bias to the front stitches. If I balance that area to produce identical forward/reverse stitch lengths, I end up back at 6/spi in both directions.