Check spring range of motion

[Dave4]

The best explanation I can find of check spring function is from the Navy manual:  The check spring prevents the needle from stabbing into it's own thread by keeping tension on the thread until the needle tip buries into the material.  Just when the needle eye reaches the goods, the check spring should land on it's stop, thereby relieving tension on the thread just as the takeup lever begins its down stroke.  

If my observations are correct, the check spring should not enter the game again until after the hook has carried the captured upper thread more than half way across the bobbin face on its journey to becoming a lockstitch.

Once the thread has crossed the bobbin case face, the check spring should again take a load as the rising takeup lever pulls each knot tight.

If the only movement you see in your check spring is smooth up and down sweeps synchronized with the needle and takeup action, it's probably functioning correctly.  

However, if you see the check spring making little jerking spasms at the start of each takeup lift, what you are seeing is tension loads on the thread at the very moment that the thread is trying to cross the face of the bobbin case.  It shouldn't do this.  Possible solutions: advance your check spring stop to reduce the range of motion of the check spring so that the thread has time to get past the halfway point of the bobbin case face before the check spring actually picks up any load.  Or, slightly advance the hook timing relative to arm shaft timing so that the hook has time to bring the thread more than halfway round the bobbin case face before the takeup lever begins to pull the thread up.  Or optimally, adjust both.  

Check spring range of motion is determined by where you set the stop and by the relative position of the thread guides adjacent to the check assembly.   

Check spring tension is determined by how much preload you set into the spring according to the adjustment procedure for your machine.  

Assuming all of the above is correct, I guess I'm finally getting to my own questions.  :-)

1 - My understanding is that you only need enough check spring tension to keep slack out of the thread during the check spring duty cycle (about half of every stitch).  This means that check spring tension just needs to be pleasantly firm, not snappy taut.  Is this correct?  What effect does too much check spring preload have?  What problems does it cause?  Are there any rules of thumb setting check spring tension differently according to thread weight used or thickness of material sewn?  

2 - I have recently been playing with check spring settings on a handful of household machines plus a 31-15 and 206RB.  If I try to set these machines up so that the check spring lands on the stop when the needle eye hits the goods, and so that the check spring isn't trying to introduce tension before the thread has made it around the bobbin case face, I invariably end up with a stop setting that results in only a tiny range of motion for the check spring.  Like a quarter inch total, or maybe 3/8" max.  I must have it set in my head that the check spring should moving in a sweeping arc, not a small blip.    

On rural roads, most oncoming drivers wave as you pass each other.  Some lift their whole arm and do a nice big wave.  Some barely lift a finger off the wheel (stingy wave).  

My sewing machines all now have really stingy check spring waves.  Is this normal?  

[gottaknow]

Once you get the stop set to ensure the thread is still taught as the needle enters the material, the torsion of the spring should corespond with the needle thread tension. The tighter your needle tension, the more check spring torsion. Sometimes you can find a happy place and it will accommodate different tensions. I don't set my hook timing to make the check spring happy, I set it to compliment the hook timing and thread tension required to make the best stitch possible. I always encourage people to experiment with check spring setting to see the cause and effects. 

Regards, Eric

[Dave4]

 

11 hours ago, gottaknow said:

 

Once you get the stop set to ensure the thread is still taught as the needle enters the material, the torsion of the spring should corespond with the needle thread tension. The tighter your needle tension, the more check spring torsion. Sometimes you can find a happy place and it will accommodate different tensions.

 

Thanks Eric.  This gives me a better starting point.  

[alexitbe]

So as the needle enters the leather there should be no tension on the thread from the check spring or can it remain until the needle starts its upward cycle? Mine is doing the latter.

 

I am having difficulties with a glove sewing machine... I wasn't until I removed the check-spring assembly to clean...

 

My problem is that the check-spring or something is pulling the leather away from the sewing surface right at the top of the needle cycle as it sets the stitch..  And thus pulling the bottom thread through... I have reduced the check spring torsion to quite low....

 

Cheers

Alex

 

[alexitbe]

It seem as our own dear Uwe has done a video...Whilst there is no mention of what constitutes too much torque/tension he does clarify the stop position... and that is as it enters the fabric

 

 

Thanks Uwe!

Alex

[Gregg From Keystone Sewing]

This information at the one minute mark...is impossible to find.  The only place I remember reading this is, actually in the 111W manual.  None of any of the modern manuals for many machines that use the same tension go into this in the owners or even engineers manuals, yet the thread controller stop is a critical setting.

[Wizcrafts]

Not yet mentioned is the purpose of the screw in the little curved slot on the front of the check spring assembly, over the shaft and nut. This lets you fine tune how much slack thread is sent to the bobbin and shuttle; aka: the throw. Turning it all the way clockwise feeds more thread on the downstroke and around the bobbin case. Turning it counterclockwise feeds less thread to the shuttle. If your threads is snapping a bit as the thread goes around the shuttle, try adjusting the throw using the set screw.

[dikman]

Thanks Wiz, I had been curious about that screw.

[alexitbe]

13 hours ago, Wizcrafts said:

Not yet mentioned is the purpose of the screw in the little curved slot on the front of the check spring assembly, over the shaft and nut. This lets you fine tune how much slack thread is sent to the bobbin and shuttle; aka: the throw. Turning it all the way clockwise feeds more thread on the downstroke and around the bobbin case. Turning it counterclockwise feeds less thread to the shuttle. If your threads is snapping a bit as the thread goes around the shuttle, try adjusting the throw using the set screw.

Wizcraft, is that screw P or Q on the figure shown above?  Is it finely adjusting the position of the spring stop?

Thanks

Alex

 

[Constabulary]

I think Wiz means #25 in the below picture

[alexitbe]

Thanks Constab....

 

So if it is screw 25 it must means changing the stop position?

 

 

[Constabulary]

The 25 screw is just for fixing the position of the disc #24 - I have the screw centered in the oval slot (so it is shown in the manual) - never had an issue with this position. Other tension units - f.i. Pfaff  145 and the like - do not have this screw. The disc at Pfaff tension units is held in position by just a pin so its not adjustable. So on Singer type tension units you "could" adjust the position of where the thread pops over the hook tip when threading the machine but being honest I never thought of changing this position or playing with it. If I had to change the travel of the regulating spring I´d do it on the curved piece #27 (on either Pfaff and Singer). But maybe there is an explanation for the slot in the disc 24 - yet I have not figured its purpose but that does no mean anything.

[Wizcrafts]

I have a long body Singer walking foot machine that has been retro-fitted with a Juki LU hook. Despite being as timed as it can be, top to bottom shafts, the top thread still tends to snap on the way around the bobbin and shuttle. I am able to alleviate this by rotating disk #24 to the right, after loosening screw #25. The far right position feeds more slack thread into the shuttle and compensates for the much larger diameter hook that was over-stressing the thread.

Unmodified machines rarely need to have the disk moved from dead center in the slot. But, one can use this adjustment to fine tune how much slack thread is fed to the shuttle on the downstroke.

[alexitbe]

Thank you everyone... I see that I am going to have to have a close look at one of my old machines and see what difference rotating disk 24 makes...  I think the spring rests on it and thus that is why I thought it changed the stop position of the spring... However, now I am not sure...

 

Cheers

Alex

[Constabulary]

curved piece #27 is where the spring rests on. It is mounted with 1 screw (Singer manual picture screw "P") - loosen the screw and you can adjust the spring travel

[ke6cvh]

This is an amazing thread that I appreciate very much for it' s information.  I can see these tension assemblies for the Singer 111w through Consew 206RB on eBay for just under 10 US dollars.  I am planning to install one of these on a cheap Chinese leather patcher (we actually have 4 different types with one of them being a clone of a Singer 29k72, one being the tiny one people many times buy, one being a heavy hitter rc32-3a taking up to nm250 and max 3.5cm thick/min essentially zero thick, one being a post bed rc32-2a with same bobbin as the large version of the 29k patchers).  I see lots of people on this facebook group for patchers install aftermarket tension assemblies but they are always removing the check spring.  The 29k72 clone has a leaf spring on the take up lever that is adjustable but my suspicion is that it is a crude and inferior version of a check spring.  The other three low cost patchers only have a spring on the take up lever.  My suspicion is that everyone who is experiencing stitches with upper loops occasionally are having one of two issues.  One is the known issue of allowing the hand crank to go backwards even a tiny amount during a cycle.  The other likely is a crude or completely missing check spring assembly.  We are installing diy pulley reducers and 750 w BLDC motors with a total reduction of around 6:1 in speed.  We want good control not so much the power available from the motor as we'll be sewing very slow on them.  With the pulley reduction and servo the backwards motion is a non issue.  I prefer Bob's brushed DC motors but these do have an advantage in that there is no brake pads.  If I'm going slow anyways I don't think I need the brake pads anyways (and the motors were easily available with same pulley shaft as clutch motors allowing me to change to different sizes).  My suspicion is that this information, coupled with the assembly same as one in Uwe's video and discussion will vastly improve quality of stitching (when properly adjusted).  Best regards and many thanks for contributors on this thread, Mike

[Gymnast]

On 1/2/2017 at 6:54 AM, gottaknow said:

Once you get the stop set to ensure the thread is still taught as the needle enters the material, the torsion of the spring should corespond with the needle thread tension. The tighter your needle tension, the more check spring torsion. Sometimes you can find a happy place and it will accommodate different tensions. I don't set my hook timing to make the check spring happy, I set it to compliment the hook timing and thread tension required to make the best stitch possible. I always encourage people to experiment with check spring setting to see the cause and effects. 

Regards, Eric

I hope that is in order to start this thread again, because I did not find other general threads about this issue of check spring stroke adjustment.

I agree with Dave4 regarding how books and most people will tell you to adjust the stroke. But I do find Erics comment interesting. I like to make two questions about it:

1) What can the problems be, that is caused by too little a check spring stroke?
And I have seen these answers:
- Needle can hit own thread
- You can get thread tangled

2) What can the problems be, that is caused by too large a check spring stroke?
And I have seen these answers:
- If the check spring pulls the thread when loop below fabric is formed to be catched, you risk that you got too little a loop
- A bit higher thread tension for the hook at parts of the way it pulls the thread down.

I guess this means, that you want the check spring to be at resting position, when the needle start to rise from lowest position.

I think the setting may be changed, so you have a larger stroke when you use thin fabric and short stitched (little use of upper thread each stitch). And when you use more upper thread each stitch, you man need shorter stroke.

I tried to experiment with a Household Pfaff 30 machine, and it do not think to care about this stroke setting. It will work anyway:

 

Edited July 24, 2021 by Gymnast

[Wizcrafts]

6 hours ago, Gymnast said:

I hope that is in order to start this thread again, because I did not find other general threads about this issue of check spring stroke adjustment.

I have learned to adjust the check spring tension and stroke according to the type of material and thread I am using. My most common combination is #92 (T90) bonded nylon thread, top and bottom, with a #19 (120) needle, into about 1/8 inch of leather, plus or minus.

On my long arm machine, the top tension is fairly high most of the time. This is because I upgraded the tension spring to a heavy duty type. ;-)

By running not too loose tensions I get tight stitches on the top and bottom of the work. (Aside: there are exceptions where I back off the top and bobbin tensions).

I find that with this machine, which has been upgraded to use a Juki U hook and take-up lever, The top thread tends to snap as it passes around the hook. I can offset this by feeding a little more thread during the downstroke by playing with the check spring stopper and its position in the curved slot. It only takes a minute or two to find this setting and it makes it so much smoother to sew. Shortening the throw of the spring causes the top thread to be more slack on as the take-up lever starts down. The position of the screw in the slot in the disks fine tunes this. A standard factory setup usually has the screw in the dead center of the disks.

Rotating the disks to the left increases the slack thread tension and vice versa.

As for the travel, I always ensure that the spring holds the top thread taut until the needle fully goes through all layers. I NEVER let it continue holding the thread to BDC! That is asking for skipped stitches. The needle thread should have a little slack at BDC which increases as it moves up 3/32 inch to form a good loop for pickoff time. I have literally seen loops disappear on the upstroke when the check spring throw is too long. It is easy to watch this process on a shoe patcher.

All of this is my opinion, based upon my own findings with my own sewing machines. Your results may vary.

[Wyowally]

Not sure if this is related, if not, apologies! My Singer 111w155 has a check spring that bounces twice while the arm is on the upstroke. First bounce is just a blip, then the second is more pronounced, right when the arm is close to finishing going up, check spring is pulled about max, and the upper thread has cleared the case opener finger. I have cleaned and checked the bobbin case tab, the opening for the tab in the needle plate, and the thread opening in the feed dogs. It is like something is snagging or adding tension to the upper thread. From my description, is there a check spring adjustment that may be out of whack? 

[Wizcrafts]

4 hours ago, Wyowally said:

Not sure if this is related, if not, apologies! My Singer 111w155 has a check spring that bounces twice while the arm is on the upstroke. First bounce is just a blip, then the second is more pronounced, right when the arm is close to finishing going up, check spring is pulled about max, and the upper thread has cleared the case opener finger. I have cleaned and checked the bobbin case tab, the opening for the tab in the needle plate, and the thread opening in the feed dogs. It is like something is snagging or adding tension to the upper thread. From my description, is there a check spring adjustment that may be out of whack? 

Your needle/hook timing is probably retarded. The hook should arrive at least 1/16" above the eye after the needle lifts 3/32" above BDC. I time mine a little higher up in the scarf. Until I did the top thread made a snapping sound going around the hook and the check spring double or triple stroked. Advancing the timing can cure this.

Once you time the machine properly your check spring adjustments will be more effective.

[Wyowally]

Thanks  Wiz!   I'll try what you suggest about timing. With mine although I think I've done it all correctly,  the needle bar/needle clamp will bump against the the presser feet when lifted manually. When I think I've got the needle 3/32" above bottom it does this. One other oddball thing - with the hook I've got, just about the time I get the checkspring jerk, the opening in the bobbin case hits the gap in the shuttle/hook and there's a little jump there, too. Don't know it they/re related. I'll keep playing and studying Uwe's videos.

[Uwe]

When I adjust machines I make sure the check spring engages a little to put some tension on the top thread when it’s about to get pulled through the gap between the bobbin case tab and the throat plate cutout. This will look a like secondary little jump of the check spring as it goes through the stitch cycle. 

This kind of contradicts the statement @Dave4 made in the original post at the top of this topic that stated:

“If my observations are correct, the check spring should not enter the game again until after the hook has carried the captured upper thread more than half way across the bobbin face on its journey to becoming a lockstitch.”

If the thread is too slack at the moment it gets pulled around the far side of the bobbin case, then it may not slip though the gap before it closes up again. This could cause a potential snag and loops.

I don’t have a separate video about it but I sorta-kinda mention it in the Juki LS-341 stitch cycle video at the 1:30 mark

 

 

Edited August 4, 2021 by Uwe

[Gymnast]

7 hours ago, Uwe said:

If the thread is too slack at the moment it gets pulled around the far side of the bobbin case, then it may not slip though the gap before it closes up again. This could cause a potential snag and loops.

@UweI looked at your video and noticed your comment, that the check spring should only engage a bit at this position in sewing cycle. After thinking a bit about that, I would guess, that it should depend on the thickness of the fabric. With higher thickness of fabric, you got more thread use and then more pull of the check spring should be expected at that point. Can you agree to that?

Edit: I am not so sure about this. I guess some trial or analysis in more detail is needed.

Edited August 4, 2021 by Gymnast

[Wyowally]

10 hours ago, Uwe said:

When I adjust machines I make sure the check spring engages a little to put some tension on the top thread when it’s about to get pulled through the gap between the bobbin case tab and the throat plate cutout. This will look a like secondary little jump of the check spring as it goes through the stitch cycle. 

This kind of contradicts the statement @Dave4 made in the original post at the top of this topic that stated:

“If my observations are correct, the check spring should not enter the game again until after the hook has carried the captured upper thread more than half way across the bobbin face on its journey to becoming a lockstitch.”

If the thread is too slack at the moment it gets pulled around the far side of the bobbin case, then it may not slip though the gap before it closes up again. This could cause a potential snag and loops.

I don’t have a separate video about it but I sorta-kinda mention it in the Juki LS-341 stitch cycle video at the 1:30 mark

 

 

Uwe, thanks again. Mine is snagging a little right at 2:25 in your video, like it is catching on the gib plate or something related.

[Wizcrafts]

Just now, Wyowally said:

Uwe, thanks again. Mine is snagging a little right at 2:25 in your video, like it is catching on the gib plate or something related.

Try advancing the hook a couple degrees. Also, loosen the set screw in the check spring disks and rotate them clockwise to the right of center. You might also have to back off the round nut on the shaft. I change my check spring centering often so I leave the set screw a little loose in the slot and loosen/tighten the round nut when I want to readjust the position in the slot. This setting gives more or less slack thread to the hook. I rarely change the bottom stop bracket once it is dialed in.