New Way to Measure and Visualize Hook Timing

[friquant]

Hook timing...what a drag!

You remove some parts, insert a brand new needle, then get out the calipers and measure a tiny rise of the needle bar past bottom dead center. Afterwards, if the machine does not sew well, you repeat the process and hope for better results. 

That's why I'm going to start measuring hook timing another way---at least on my vertical hook-shaft machines. I'm going to start measuring degrees of hook rotation.

 

Protractor

I'll set up my axes like this:

• 0 degrees: when the hook shoulder is farthest from the user
• 90 degrees: when the hook shoulder reaches the apex of the hook's journey around the bobbin

I'll print this protractor and tape it to the machine bed. Note the origin/center of the protractor is at the center of the hook/bobbin.

Note in the photo above, the white top thread is stretched between the throat plate hole and what I've been calling the hook "shoulder". 

I'll rotate the hand wheel to where the take-up lever is at is lowest point. 

Then I'll take a measurement of the hook angle from the center of the hook to the hook shoulder. (I chose the hook shoulder because it is the part that actually drags the thread around the bobbin, and it is easy to see from the top.) If you click into this image you can see that the edge of the ruler/square crosses the center of the hook and crosses the hook shoulder where the bit of white thread is peeking out. Note this photo shows a 39 degree measurement.

 

What This Measurement Style Provides:

1. Easy to measure hook timing without removing anything but the bobbin cover plate
2. Easy to visualize where the hook is in its cycle in relation to where the thread take-up lever is in its cycle
3. Easy to make generalizations (I hope) about certain hook timing angles producing certain behavior/symptoms across lots of different machines
4. The timing angle is the same regardless of what stitch length is selected
5. The larger the timing angle, the more advanced the hook timing. (Note with the old/conventional measurement system, larger numbers mean the hook timing is less advanced.)

Background / Theory:

The hook's job is to grab the top thread and drag it around the bobbin. As the hook shoulder rounds the apex of its path (goes around the right-most edge of the bobbin), that is the farthest that the thread gets dragged through the needle before the thread take-up lever pulls the thread back the other way. The hook shoulder going around the right-most edge of the bobbin must coincide roughly with the thread take-up lever being at its lowest  point, otherwise the thread will be tight and the hand wheel hard to turn as the hook drags the thread round the bobbin.

Some Data Points and Corresponding Behavior
I was working on dialing in the timing on an old Singer, and to learn the machine better (and develop my skills) I was purposefully doing it without referring to a manual. Here are the timing angles on the left, and a description of the corresponding behavior on the right.

• 2°      Top thread tight and grabby as it rounds bobbin
• 13°     Top thread tight and grabby as it rounds bobbin
• 20°     Top thread tight and grabby as it rounds bobbin
• 44°     Most of rounding bobbin is easy...but snags just a bit on the hump by the bobbin tension spring
• 46°     Easy to round bobbin. Good clearance between nearly-formed loop and hook
• 51°      Easy to round bobbin. Minimal clearance between nearly-formed loop and hook
• 70°     Very easy to round bobbin. Negative clearance between nearly-formed loop and hook. (The hook stabs into the nearly-formed loop and jams the machine.)

In this round of measurements, the 46 degree setting was my favorite. (I did not get more measurements between 30 degrees and 44 degrees because I was having trouble getting the worm gear slid into position.)

Making Generalizations

By trying out various timing angles, I was able to observe certain behaviors and put them on my mental map of what causes those behaviors. (And can hopefully fix some of the tendencies from the "70°" row that I've been having on a different machine!)

Hope this is useful to someone wanting to understand not just how to set hook timing by the book, but how to react to certain (mis)behaviours, and possibly how to design a sewing machine 😀
 

Edited 16 hours ago by friquant

[CowboyBob]

The easiest way to check the hook timing on this type of machine is if you drew an imaginary line from the center of the bobbncase to the center of the front needleplate screw the point of the hook should be directly under it when the needlebar is all the way down.

[AlZilla]

14 minutes ago, CowboyBob said:

The easiest way to check the hook timing on this type of machine is if you drew an imaginary line from the center of the bobbncase to the center of the front needleplate screw the point of the hook should be directly under it when the needlebar is all the way down.

Where is that "Like" button? 

Thinking about it, a person could do this on any machine they work on regularly, just set an easily seen mark on the bed of the machine. 

Thank you for that.