Needle hook distance

[Gymnast]

This is what I think happen to the hook needle distance when you change needle size:

This sketch is only based a few measurements on some household sewing machine needles. I also got some input from a guy knowing a bit about the needle systems before it was common to make them with a scarf. I have not been able to find more detailed information about how a definition of a needle system might define this. So I hope someone here may know more about this.

If you adjust the needle hook distance to a minimum with a large needle and make use of the needle scarf, and you later on change needle size in the machine to a small needle, that you might have the hook hitting the needle. I guess you need a rotating hook in order to get the hook close to the bottom of the scarf, because you need the point part of the hook to be at some distance when the scarf have moved upwards.

[kgg]

 

6 hours ago, Gymnast said:

I have not been able to find more detailed information about how a definition of a needle system might define this.

I would assume the stroke, type of sewing (leather or fabric) and the thickness of the material would be major factors in selecting the needle system. Too long or short a needle would cause the hook to miss properly picking up the thread. The thicker and tougher the material would require a larger diameter needle to prevent the needle from bending, deflecting or strikes. To allow for proper needle to hook clearance I think most sewing machine manufactures give a clearance range to best accommodate needle sizes within a needle system that the machine was designed to sew. Like the Juki DNU-1541S needle to hook clearance is range from 0.02mm to 0.05mm. Being able to fine tune the clearance could be a real benefit if you were only using one size of thread and needle with a certain type and thickness stuff. The problem is if you change the needle size you could get strikes or skipped stitches.

For domestic machines I think a bigger problem would be if you set the hook clearance for a needle with a scarf and then changed to a needle without a scarf as the hook would always hit the needle shaft where the hook thinks the scarf should have been. Going the other way probably would be a problem.

 

kgg

[Gymnast]

Juki DNU-1541S have got a rotating hook. When you adjust the clearance that close, is it then to the bottom of the scarf of the needle? I just think that the hook needs to have a geometry, so the needle do not hit the hook further back, when it moves up.

I got four domestic machines 66k and 201k. For both of them, you cannot adjust the needle hook distance without making very serious modifications. It means that they most likely have got the factory setting of distance.
When these machines was designed, they were most likely designed for the 705 needle system without any scarf. I do not think, that you can get this needle system any more, and they were mostly replaced by 130/705H, that is used today, and these needles all got a scarf. 

I measured the distance to the bottom of the scarf of a Schmetz 130/705H, 18/110 universal needle. The dept of the scarf is 0.25 mm.

Singer 66k von 1910 - 0.45 mm
Singer 66k von 1930 - 0.4 mm
Singer 201k von 1950 - 0.5 mm
Singer 201k von 1954 - 0.5 mm

So the needle hook distance outside the scarf or to the old system would be 0.15 mm to 0.25 mm. So I do not think these machine will ever hit a needle.

I have measured the scarf dept of a 10/70 needle to be 0.1 mm and a 22/140 needle to be 0.4 mm.

But you do have other kinds household machines, that got the possibility to adjust the needle-hook distance, and then of cause you can get into problems.

[Nmgunguy]

Have you considered making your comparison based from the centerline of the needle?  In the needle systems that I have experience with, the point of the needle, the needle O.D., and the needle shaft are all concentric.  The distance from the hook point to the centerline of the needle bar does not change when you change needle sizes unless you make an adjustment.  To me, this means the the potential differences in scarf-to-hook clearance comes from the differences between the centerline of the needle and the bottom of the scarf.  In my experience(very limited mind you…), this difference is less between needle sizes within the same needle system as the larger needles also have deeper scarfs.  To my limited understanding, this leads me to believe that the change in hook clearance may not be linear with the change in needle diameter.

I am very interested to learn more about this dynamic so if someone sees my perspective as incorrect, please feel free to add to my education!

[Gymnast]

I think we all are in for some education here 

I have tried to look in a German book by Wilhelm Renters from 1957, and I took a copy of one side below. It seems to me, that you are right. There is a lot of needle systems, so I guess we cannot be sure. But Renters explains, that the flat shank needles (typically for household machines) are as I described in my drawing above. But the round shank needles got the center with the point of the needle in center of the shank.

Nmgunguy, if you state what needle system your machine use, I guess somebody can answer your question.

[Nmgunguy]

Gymnast, I have zero experience with household machines which use flat shank needle systems so thanks for that information!  Your description applied to a “flat” needle system makes sense to me.

My experience with sewing machines is within the 794 and 135-16 needle systems in a CB4500, CB3200, and Singer 111-155 machines. I also have a old Union Lockstitch(hook and awl) machine which I have somewhat restored.  That was a massive learning experience for sure, it is a beast of a machine!

[Gymnast]

Nmgunguy, So based on your experience and the Renters Book, it may look like the sketch below, when you change needle size on a sewing machine using round shank needles, that is used on industrial sewing machines:

If you adjust hook needle distance here to a smaller needle and change to a larger needle, you might encounter problems. It will also depend on the moving geometry. You got a risk, that the needle at eye below the scarf may hit the hook, when needle moves upwards. It depends on the hook geometry and how fast it go past the needle.

Edited February 1, 2022 by Gymnast

[Wyowally]

I guess I'm not real concerned with scarf vs. no-scarf differences of 1/4 of a millimeter. I try to discover the adjustment procedure for each machine. I choose the needle I want to use and try it out, maybe watch the action and relationship hook to needle. I have not measured that gap in 4 or 5 years.  I do use a tiny LED light and get where I can see things. I get the needle close without touching. It works. BTW, I helped a lady with a commercial long-arm quilting setup. That manufacturer in their own tuning videos, want the hook to just contact the needle so it makes a tick sound!  Works for them, and it means to me that the hook just bumping isn't necessarily a bad thing.  Nice info to know, but I will never use it.

[Gymnast]

After studying the subject a little more, I have also become more relaxed in relation to this subject. Sometimes I have seen strong warnings in some sewing machine forums, but I have never personally experienced major problems with this. But it has sometimes been difficult to completely decipher instructions on adjustment, where e.g. is already quite some slack for a CB shuttle hook - typically 0.3 mm.

It is also my experience that these "CB shuttle hooks" with a little slack in outer positions might be able to hit the needle, but that it usually does not cause problems.

When sewing Jersey, I have experienced lost stitches, and after an adjustment, it has solved the problem. And it has so often been the case that the machine had been incorrectly adjusted. Here I have not always been aware of the extent to which it could mean something for other needle sizes. Now I know a little bit about that. I have not usually seen the big differences with a change of 0.1 mm. However, an incorrect adjustment to about 0.4 mm too much distance will be apparent when sewing jersey.

Due to the normal geometry of double-rotating "hook", those machines can probably be adjustable to a slightly closer distance.

[Wyowally]

Almost every service manual I have shows very precise measurements for these settings. Some of the manufacturers made up some special tools and spacers, and they don't instruct us on anything except using those tools. I haven't been a jersey sewing person, more like Cordura and canvas for me. What I have seen when checking timing on the machines brought to me is needle eye-to-hook point being off. Sometimes that is hook rotation, but more often it is needle height. If the owner confesses about needle strikes or breakage I really suspect needle height.  The little screws used to hold the needle bar in place are pretty wimpy on many machines - enough so I speculate about them being intentionally weak to help prevent damage from needle strikes.

[Wizcrafts]

I want to point out an observation I've made over my decades of sewing. Unless the bobbin and top tensions are very light (think thin cotton thread), the needle often gets pulled slightly to the left at pick-off time. So, if the hook in that machine is set so it barely makes contact with an unthreaded needle, it will probably not make contact with the threaded needle as it sews material and gets pulled to the left. This fails if the tensions are so low that the needle isn't deflected by the thread. This puts the hook and needle in peril. Further, thicker thread will tend to pull the needle more than thinner thread..

I prefer to adjust the check spring for a big enough thread loop so that the hook never needs to be in contact with the needle to pick it off. I purposely bend the deflector shield if necessary to prevent the hook from contacting the needle.

[Nmgunguy]

So I ran a few “tests” on my 4500 to see what the impact of this hook-to-scarf delta had in my application and came to some really interesting conclusions that are somewhat different than what I had expected.   To start, I choose the largest needle I had(27/250) and adjusted the hook-to-scarf clearance to 0.5mm.  I have never really measured this setting before, only adjusted by “eye” but the 0.5mm seemed to be a much larger gap than normal for me.  With the stitch length at the maximum, I had no missed stitches in forward or reverse.  So then I changed to the smallest needle I have(22/140), swapped out thread both top and bottom and tested again.  This time, I had no missed stitches in forward, but I did have one missed stitch in reverse.  I’m not sure if this had any relation to the larger gap, or my not so great handling of the material

For test two, I put the scarf to hook back to “normal” for me and shortened the needle bar height by 0.5mm (raising the needle eye in relation to the hook point) and repeated the tests above.  This time it was very obvious that the adjustments were off as it missed nearly all of the stitches in both directions!

This tells me that for this particular scenario,  the relationship of the hook point to the needle eye was more critical for the hook to catch the loop than the distance from the hook point to scarf.  From a logical perspective, I can’t imagine that this would be the same for every machine as most of the machines that I am familiar with form a loop that is taller than it is wide.  This makes me think there is more tolerance in the height relationship than there is the width.  There are also so many other influences on the size of the loop that it is hard for me to know exactly which has the most effect.

In normal operation for me with both the 4500 and the 3200, I regularly switch between needle sizes without any adjustments other than tension and seldom have any issues.  Thank goodness for such a versatile platform! 

 

Anyway, very interesting topic for me and another great learning experience!  Thanks for all the input!

 

Now to put all the adjustments back so it can run……

[Gymnast]

I agree, that the normal timing adjustments of needle bar height and timing of hook is important. I just think these adjustments are well defined, because the same needle system got the same distance between needle but and upper edge of the needle eye when needle size is changed. I have had a harder time finding information about needles systems and the dept of the scarf and some of the geometry here, when you change needle size. So this is why I decided to discuss this in forum. 

I do not have a CB 3200 or 4500, but I have seen videos of them. They have got an oscillating hook and Uwe have made a nice video about it:

 

According to Uwe, the play of the shuttle hook regarding distance to needle needs to be low and I guess it means below 0.1 mm. The distance is adjusted by having more rings (race back) to be replaced behind the shuttle, and the rings got different thicknesses. Uwe comments about the orientation of the race back, that can influence reverse stitching.

Nmgunguy, did you adjust the distance by replacing the ring or did you do it in some other way?

I got a Bernina household sewing machine with a oscillating CB-shuttle hook. It have got a quite high play of about 0.3 mm regarding distance to the needle. For this machine I see the lowest distance when the needle go down and pass the hook while doing so. The lowest distance is determined by the part of the needle outside the scarf and near the needle eye. Perhaps you will se the same with this much larger machine, because it is also an oscillating hook machine.