Cobra class 4: 346 bonded polyester thread? Help!

[DieselTech]

Guys & gals I have a Cobra class 4 & it was set up for 277 thread & sewed fine. 

I need to sew some rear flank billets for a saddle. The billets are 9mm thick that I need to sew. Which they will be 2 layers. They will be constructed using 5mm veg tan saddle skirting & 4mm Latigo, both Hermann Oak. 

Ok. So here we go: I swapped the thread over to lubricated 346 bonded polyester thread, both on top & in the bobbin. #25 Schmetz D point needle.

So when I 1st started sewing, it kept picking up the leather when the needle was coming up. So I increased the presser foot tension, by 20 turns in. 

So now it no longer picks the leather up when the needle is on the up stroke, but at 1st it kept breaking my top thread. 

So I re-threaded it 3 times before it stop breaking my top thread. 

So now I got it sew thru 2 layers of 6mm saddle skirting, but it made lot of squeaking as the needle came back up thru the leather. 

So my question is: Why did it keep snapping my top thread at the beginning of sewing? Was it because my thread is 8-10years old? (Thread was in zip lock bags stored in the dark) if that matters on its age?

Or because of the #25 needle is too small & I should go to a #26 needle? 

Should I be running a lube pot? Only running my machine at 200 rpm. 

Thanks. Any help or pointers will be greatly appreciated. 

[DieselTech]

Also I forgot to mention, I am using @Patrick1 #25 throat plate & feed dog. 

Also would switching to a different needle point change anything. Like go to a #25 S point leather needle? 

Thanks. 

[CdK]

Did you adjust thread tension after going to the thicker thread and needle? I had similar trouble and solved it by reducing the top and bottom tensioning.

[DieselTech]

19 minutes ago, CdK said:

Did you adjust thread tension after going to the thicker thread and needle? I had similar trouble and solved it by reducing the top and bottom tensioning.

No I have not touched the thread tension since switching to 346 poly thread.  But I will mention that when I was using 277 thread I had to tighten/increase bobbin tension by 1 full turn on the bobbin thread tension to get it to even the stitches out. 

Should I decrease my bobbin tension by 1 full turn back. This will put the bobbin tension back to how the machine was shipped to me. 

Thanks.  

[DieselTech]

Ok. I cut 2 pieces of the actual leather I will be sewing. Looks Ok to me. I think my feed dog height might be a touch high. Or I need to back the presser foot tension off a bit. I'm not sure, I'll have to do some more practice/testing. 

[Constabulary]

Playing with top and bottom thread tension and adjusting foot pressure is part of the sewing game when sewing different thicknesses or using different thread / needle sizes. You have to practice this.

You just need as much foot pressure that the materials is not lifted by the rising needle.

To me the needle holes look fairly large but I have not used D point needles. My preferred needle is the S point needle for having a straight seam look.

[DieselTech]

10 minutes ago, Constabulary said:

Playing with top and bottom thread tension and adjusting foot pressure is part of the sewing game when sewing different thicknesses or using different thread / needle sizes. You have to practice this.

You just need as much foot pressure that the materials is not lifted by the rising needle.

To me the needle holes look fairly large but I have not used D point needles. My preferred needle is the S point needle for having a straight seam look.

Thanks. Yeah I am going to switch to a S point needle in the morning. Then start playing with my presser foot pressure too. I think it needs backed off a bit now or I need to lower my feed dog height a touch. 

I guess it all part of the game, plus I haven't had my Cobra class 4 out & sewing in probably 4 months or longer. 

Thanks. 

[DieselTech]

Ok I switched to a #24 S point needle & backed off my presser foot presser by 2 turns. 

The 2nd stitch line in from the edge of the leather is the # 24 S point needle. 

I think I could get away with a # 24 S point needle with the lubricated polyester 346 thread. 

I'll continue to decrease my presser foot pressure, until the presser feet tracks go away or at least try. 

[Constabulary]

Foot pressure if often overlooked and folks keep it high when the last project required high foot pressure. Guess how I know (different machine though). I sew thick leather only now and then and I always do some tests before I start the project. Speaking of thread tension - a leather worker I know even has different hooks for different size thread and has marked the hooks with the specific thread size but he is using linen thread from one manufacturer only - no poly and no nylon.

To me the needle holes still look fairly large - or not?

[DieselTech]

5 minutes ago, Constabulary said:

Foot pressure if often overlooked and folks keep it high when the last project required high foot pressure. Guess how I know (different machine though). I sew thick leather only now and then and I always do some tests before I start the project. Speaking of thread tension - a leather worker I know even has different hooks for different size thread and has marked the hooks with the specific thread size but he is using linen thread from one manufacturer only - no poly and no nylon.

To me the needle holes still look fairly large - or not?

Let me ask this? Cause I don't know. Can your thread tension be soo tight it causes your needle holes to elongate from high thread tension? Causing the stitch/needle holes to appear/be enlarged?

Lmao last time I used this machine I sewed 2 layers of 5oz Conceria Walpier Buttero with 277 thread. 

The time before that I sewed 2 layers of 2oz Conceria Walpier Dollaro with 138 thread & a #23 throat plate & feed dog. 

[Constabulary]

Good question. I think it depends on how soft the material is.

I have sewn some leather handles with linen thread a while ago. This is how it looks. Thread size unknown (old wooden spool) but I used a 280 / 28 needle. The holes are pretty well filled with the thread. Material is 10-11mm thick.

[Constabulary]

sorry - it was a 250 / 27 needle I just checked.

Edited October 21, 2024 by Constabulary

[DieselTech]

14 minutes ago, Constabulary said:

Good question. I think it depends on how soft the material is.

I have sewn some leather handles with linen thread a while ago. This is how it looks. Thread size unknown (old wooden spool) but I used a 280 / 28 needle. The holes are pretty well filled with the thread. Material is 10-11mm thick.

Ok. Thanks for sharing that. The other thing I was wondering if maybe my stitch length is too close together & it is stretching the leather between the stitch holes.

I will play around some more. Lmao I bought 2 full sides of leather just to make 2 rear flank billets, soo I got some practice leather. 

Just hate that it's Hermann Oak sides I'm practicing on. 

[Constabulary]

buy some leather scraps for testing. I never bought a hide. I just buy scraps. Often good enough for what I do.

[RockyAussie]

Quite a few changes I would think are needed. First when you do thicker thread it often needs the bobbin backed to be looser. Try at least a 1/4 anticlockwise turn.(remember the lock screw needs to be loosened first) The needle should be size 26 for that thread and the s point or LR should look better than the d or tri points. If the needle is too small for the thread you will be getting flagging a lot more because the knot is having a hard time getting up in too small a hole. Lubricating the thread with some machine oil running through some foam can help as it transfers to the needle and makes it slip through better which includes making it easier to pull the knot up. The foot pressure marks would be better if the back foot were the double one that goes on both sides but the narrow set may not be the best in this application anyway. One tip I will offer is get a sample piece ready of the thickness you are wanting to stitch and keep backing of the foot pressure until the job starts to lift then take it down 2 or 3 turns. If You need to run the left foot only then you could do as I have done and tig weld a wider base to it as shown in the pictures.The wider base reduces marks by a lot.

[kgg]

7 hours ago, DieselTech said:

Ok. So here we go: I swapped the thread over to lubricated 346 bonded polyester thread, both on top & in the bobbin. #25 Schmetz D point needle.

A #25 needle is good for V277 but for V346 a #26 would be the choice ( Needle / Thread Chart: https://www.tolindsewmach.com/thread-chart.html  )

7 hours ago, DieselTech said:

So when I 1st started sewing, it kept picking up the leather when the needle was coming up. So I increased the presser foot tension, by 20 turns in. 

Probably to small a hole created by needle for V346 polyester.

7 hours ago, DieselTech said:

Why did it keep snapping my top thread at the beginning of sewing? Was it because my thread is 8-10years old? (Thread was in zip lock bags stored in the dark) if that matters on its age?

I would first change to a #26 needle like @RockyAussie suggested, readjust the presser foot tension and give it a try. Also check and see if there are any burrs in the top thread path like a guide, the eye of the needle, presser foot, feed dog etc. If it works great if not then change to a new spool of thread.

kgg

[Patrick1]

Did you ever lubricate the presser foot bar inside the cover since you purchased the machine? It will stick or not move as freely giving a false pressure adjustment so you end up over compensating the pressure. The presser foot you are using spreads the pressure lengthwise vs widthwise as in @RockyAussiewelded foot.

[DieselTech]

3 hours ago, RockyAussie said:

Quite a few changes I would think are needed. First when you do thicker thread it often needs the bobbin backed to be looser. Try at least a 1/4 anticlockwise turn.(remember the lock screw needs to be loosened first) The needle should be size 26 for that thread and the s point or LR should look better than the d or tri points. If the needle is too small for the thread you will be getting flagging a lot more because the knot is having a hard time getting up in too small a hole. Lubricating the thread with some machine oil running through some foam can help as it transfers to the needle and makes it slip through better which includes making it easier to pull the knot up. The foot pressure marks would be better if the back foot were the double one that goes on both sides but the narrow set may not be the best in this application anyway. One tip I will offer is get a sample piece ready of the thickness you are wanting to stitch and keep backing of the foot pressure until the job starts to lift then take it down 2 or 3 turns. If You need to run the left foot only then you could do as I have done and tig weld a wider base to it as shown in the pictures.The wider base reduces marks by a lot.

 

2 hours ago, kgg said:

A #25 needle is good for V277 but for V346 a #26 would be the choice ( Needle / Thread Chart: https://www.tolindsewmach.com/thread-chart.html  )

Probably to small a hole created by needle for V346 polyester.

I would first change to a #26 needle like @RockyAussie suggested, readjust the presser foot tension and give it a try. Also check and see if there are any burrs in the top thread path like a guide, the eye of the needle, presser foot, feed dog etc. If it works great if not then change to a new spool of thread.

kgg

 

1 hour ago, Patrick1 said:

Did you ever lubricate the presser foot bar inside the cover since you purchased the machine? It will stick or not move as freely giving a false pressure adjustment so you end up over compensating the pressure. The presser foot you are using spreads the pressure lengthwise vs widthwise as in @RockyAussiewelded foot.

Thanks everybody. You all gave me a lot of things to try & play around with today. 

I would think the #25 needle I was using is big enough. That 346 lubricated poly thread falls thru the needle eye like throwing a hot dog down a hallway. 

Ok I'll try adjusting presser foot pressure & changing my presser feet out. Also I will order some #26 needles. 

Also if I go to a # 26 needle can I still use @Patrick1 #25 throat plate & #25 feed dog? Or does that need changed out as well?

Thanks.

Edited October 21, 2024 by DieselTech

[Patrick1]

1 hour ago, DieselTech said:

 

 

Thanks everybody. You all gave me a lot of things to try & play around with today. 

I would think the #25 needle I was using is big enough. That 346 lubricated poly thread falls thru the needle eye like throwing a hot dog down a hallway. 

Ok I'll try adjusting presser foot pressure & changing my presser feet out. Also I will order some #26 needles. 

Also if I go to a # 26 needle can I still use @Patrick1 #25 throat plate & #25 feed dog? Or does that need changed out as well?

Thanks.

Should work but not guaranteeing it. The feed dog slot is .106 and shorter than the stock dog so not sure how a thicker thread will sew. 

[Wizcrafts]

6 hours ago, DieselTech said:

The other thing I was wondering if maybe my stitch length is too close together & it is stretching the leather between the stitch holes.

You do have to be careful to not sew too short stitches when using an S point needle. It slices inline and can weaken the stitch line if the holes are too close. OTOH, diamond/tri points punch a shorter hole and the thread stays on top of the leather, as opposed to being almost buried by the S points. So, I try to stay above 7 to the inch with S points.

[Wizcrafts]

3 hours ago, Patrick1 said:

Did you ever lubricate the presser foot bar inside the cover since you purchased the machine? It will stick or not move as freely giving a false pressure adjustment so you end up over compensating the pressure.

This is an important, often overlooked issue for most sewing machines, but especially the 441 clones. I have a long-time buddy who bought a Cobra Class 4. After a few years the presser and alternating foot bars started getting stuck in the up position. He added more foot pressure to get them to drop, marking the leather even worse. He had me come over to troubleshoot it and I unthreaded the machine and removed the front cover plate. IIt was dry inside and there were scoring marks visible. I removed the presser bar and pulled it through Emory cloth to get the marks off. After putting it back together, I oiled every moving part. The machine worked perfectly afterward. So, remove the front cover and oil every crank and rod that moves against or through something.

[DieselTech]

3 hours ago, Patrick1 said:

Did you ever lubricate the presser foot bar inside the cover since you purchased the machine? It will stick or not move as freely giving a false pressure adjustment so you end up over compensating the pressure. The presser foot you are using spreads the pressure lengthwise vs widthwise as in @RockyAussiewelded foot.

 

22 minutes ago, Wizcrafts said:

This is an important, often overlooked issue for most sewing machines, but especially the 441 clones. I have a long-time buddy who bought a Cobra Class 4. After a few years the presser and alternating foot bars started getting stuck in the up position. He added more foot pressure to get them to drop, marking the leather even worse. He had me come over to troubleshoot it and I unthreaded the machine and removed the front cover plate. IIt was dry inside and there were scoring marks visible. I removed the presser bar and pulled it through Emory cloth to get the marks off. After putting it back together, I oiled every moving part. The machine worked perfectly afterward. So, remove the front cover and oil every crank and rod that moves against or through something.

Yes I think this is what happened to me. I think the needle bar & presser foot bar were stuck in the up posisition or stuck in general from sitting soo long & collecting dust. 

I have since then backed the presser foot pressure off by 10 full turns out. Now it is not marking the leather up as bad. I Think my presser foot pressure is still a bit high. 

I will find a video on removing the said plate you 2 are referencing & lubricate things. 

The tolerances must be real tight on the needle bar shaft & the pressure foot shaft. 

Thanks. I'm getting ready to make a couple more practice runs. Soo I will report back. 

[DieselTech]

Soo I went ahead & removed the side/front plate, whatever you wanna call it. 

But does Cobra/Leather Machine Co. even mention all the oil holes under that cover in their oil maintenance schedule. I should of took some pictures. 

But there must be like 7-9 more oil holes/spots to oil the linkage & bars under the cover. Point taken for sure now. 

Ok I'll run a piece of leather thru in a bit & post results. 

[DieselTech]

Ok. So I removed side/front plate & lubed everything. 

Then I went & glued up exactly what I would be using for the rear flank billets. 

I then switched to a #25 S point needle. I increased stitch length to exactly 5 stitches per inch. 

I adjusted my presser foot pressure to 6 full turns out, from where I originally had the machine before putting it away. 

I think I could decrease my presser foot pressure some more. 

Also how do you guys fudge a stitch? When coming around to your original start point? 

Wether you need to fudge a shorter/ or longer stitch to meet in the original needle hole you started at? 

Thanks. 

[kgg]

5 hours ago, DieselTech said:

I would think the #25 needle I was using is big enough. That 346 lubricated poly thread falls thru the needle eye like throwing a hot dog down a hallway. 

The question: The V346 may slide nicely through the eye of the needle but... is the hole made by the needle large enough to allow for the V346 (top and bobbin) from being caught by the leather as this would become more critical as the thickness of the item being sewn due to more surface area that could act as a catching point???

kgg