Shape of thread U-turn on shuttle

[Gymnast]

I just like to share a kind of modification I have done on a Singer 237 domestic machine. With this machine I try to make sew with V138 polyester thread, and it fails (of cause). The upper thread gets damaged when I try to sew more than 5 stitches, and then the thread jam or break. So I tried to figure out why. The Singer 237 have got an oscillating shuttle, and it is a zig-zag machine. The Pictures below illustrade the modification:

The modification fixed the problem, and now it is able to sew with V138 serafil 20 polyester thread. Of cause I need to increase thread tension of the machine for this to happen as well, and the machine may wear down quick. Before the modification, the shape of this U-turn was rectangular with quite sharp edges. I suppose these original edges will be all right with thinner thread and lower tread tension. However I cannot be sure, if this could be a fabrication error.

I have looked at some similar new shuttles for sale on internet, and I think they some of them have got quite sharp edges as well, when I look at Pictures of them:

https://www.searspartsdirect.com/product/1i5kk8lux0-0020-385/id-532096007

https://picclick.com/Shuttle-Hook-For-Singer-Butterfly-Flying-Man-Old-153009787971.html#&gid=1&pid=5

https://www.amazon.com/SINGER-Sewing-Machine-Shuttle-Hook/dp/B008MM42UM

Has this area of the shuttles of industrial sewing machines for leather the same kind of issues?

Perhaps you should expect some Wear on these surfaces as well.
 

Edited August 17, 2019 by Gymnast

[Gymnast]

I just looked a bit more into this subject, and perhaps this is a more general problem. I think this Singer Class 15 shuttle is used at many sewing machines. I have looked at pictures of these shuttles on internet, and I think all of them are not that rounded at these edges, as I should like them to be. Some are quite sharp.

I am not sure if you will consider the Sailrite or Rex sewing machines as industrial sewing machines. They do have a combined feed. But i think you would expect them to sew up to a V138 thread. When I look at this video from Sailrite, these edges are somewhat more rounded than many other class 15 shuttles, I looked at from internet. But I would not be satisfied with this. I rounded these edges to some higher radius than the shuttle I see in the Sailrite video. I cannot say how much is needed. But If I had a machine like this, I would look into that.

The driver is a bit different on this Ultrafeed than my Singer 237. The 237 have a flad spring attached to the inside of the driver. The Ultrafeed have not got this spring.

To do the job I used some abrasive cord like this: https://www.gesswein.com/p-2867-abrasive-cord-and-tape.aspx 

To polish the surface I soaked some Ø2 mm polyester cord into some scouring cream I use for cleaning.

 

 

[kgg]

18 hours ago, Gymnast said:

I am not sure if you will consider the Sailrite or Rex sewing machines as industrial sewing machines. They do have a combined feed. But i think you would expect them to sew up to a V138 thread.

The Sailrite portable LSZ-1 are rated up to a #22 needle (135 x16 or 135 x17) needle which should take a V138 thread but further looking at specs it is rated only to V92. The Tandy Craftool® Pro Stitch Master® Sewing Machine has the same thread and needle specs. The only one that I know that will handle V138 in that class of sewing machine is the Reliable Barracuda. I wouldn't consider or class any of the portable walking foot sewing machines as industrial. They do have their place and can to decent work but.

I think the machining quality of the hook is going to be dependant on the actual manufacturer (brand name vs clone) (German vs Japanese vs Taiwanese vs Chinese).

kgg

[Gymnast]

Thanks kgg for clarifying this subject and the specifications for this class of portable machines using the class 15 shuttle. My point is, that some of these machines actually might be able to handle a thicker thread and materials if this thread U-turn area of the shuttle are better rounded.

When sewing heavy materials very slowly, I have noticed, that the required torque to drive the sewing machine vary a lot during a sewing cycle. Maximum torque is required when the needle eye passes the heavy fabric in upwards direction. At this point the shuttle (some people call this the hook) pulls the upper thread downwards at high speed. And a high friction force is added to the thread passing at both sides of the needle in the "narrow" hole in the fabric. Sometimes the machine is forced to a complete stop at this point. So I am sure, that the thread tension in this part of the sewing cycle can be very high. Therefore I think that the smooth passing of the thread at this U-turn should be of interest, if you sew with thicker thread and heavier fabrics.

[Gymnast]

On ‎8‎/‎19‎/‎2019 at 4:48 AM, kgg said:

I think the machining quality of the hook is going to be dependant on the actual manufacturer (brand name vs clone) (German vs Japanese vs Taiwanese vs Chinese). 

Recently I inherited a Bernina 910 machine. I do like a Singer 201 a lot. But sometimes I read and hear reviews of a Singer 201 to be the most silent and smooth sewing machine ever made. Well, when you have tried a Bernina, the Singer 201 sounds like turning on the blender. But hopefully I will never have to buy spare parts for the Bernina, because they seem very expensive. The Bernina 910 have got a shuttle hook. I took two pictures of it side by side with the modified Singer 237 shuttle:

When I look at the machining of the thread U-turn area, I think the Bernina is made quite well, as should be expected from a Swiss product.

Many of the dimensions are very close, and I can use the class 15 bobbin in the Bernina.  I can also put in the Bernina shuttle into the Singer 237, and it seems to fit, but it is NOT the same:

The thicknesses of the flanges are very different, so the race gate will not hold on to the shuttle as it should when interchanged. With the Bernina shuttle in the Singer 237, at some point the needle hits the shuttle.

Would you consider the Bernina shuttle a Class 15 shuttle?

Edited August 24, 2019 by Gymnast

[kgg]

I maybe wrong but I would consider the Bernina 910 hook as being a class 15 based on the bobbin needed is a class 15. The bobbins for the Bernina are probably slightly different in height/diameter and shape when compared to those of the Singers you mentioned.

kgg

[Gymnast]

10 hours ago, kgg said:

The bobbins for the Bernina are probably slightly different in height/diameter and shape when compared to those of the Singers you mentioned.

You are right.

According to this list, the bobbins are the same:

https://www.thethreadexchange.com/miva/merchant.mvc?Screen=CTGY&Category_Code=sewing-machine-bobbin-style-info 

The overall dimensions from data on the internet seems to be 11.8 x 20.6 mm.

However, when I measure on the bobbins that came with the machines, I do see other differences. The inner diameter to the axle is different, the Berninas are 6.0 mm. The others are 6.3 mm. On the Bernina bobbins the tube forming this inner diameter extents more out from the surfaces of the spool. When you sew with low lower thread tension, such small differences can make a difference.

[Gymnast]

I have tried to make a small video about the modification of this class 15 shuttle hook. It got no more information than already given above in text above, but I suppose the message get better clarified: https://youtu.be/80WASgbKIX4

And then I continue my reputation on being a nerd on measurements and numbers:

After the modification above, I tried to make a measurement set-up to give some figures related to the thread friction in the shuttle area. It looks like this:

One end of a thread is attached to a digital dynamometer with no movement and the thread goes down through the needle plate and around the hook. This end simulate the thread attached to the previous stitch. The other thread end is attached to a moving spring dynamometer and it simulates the thread comming down the needle grove through the needle eye and to the hook. When I advance the machine and the hook, you see the indicator of the spring dynamometer move down, and you can measure the two thread tensions. No needle was used.

The thread length was adjusted, so the position of the hook at measurement corresponds to a needle eye position of about 3 mm above the needle plate. The difference in the two thread tensions indicate how much friction is applied by the hook thread U-turn, but also some other friction. Furthermore I measured the torque on the flywheel by removing the belt and by use of another dynamometer.

I tried this test set-up on three vintage domestic machines, and got these results:

I am sure, that the improvement in grinding the edges of the class 15 shuttle hook could have been measured this way. So the figures above is only after the modification.

I did also try the measurements with thinner thread, and then the thread frictions became less significant.

[kgg]

I did enjoy your youtube videos.

kgg

[dikman]

11 hours ago, Gymnast said:

And then I continue my reputation on being a nerd on measurements and numbers: