Timing series part 6: The others
Two things I touched on but didn’t explore in detail are feed dog timing and how the timing on a shuttle bobbin works (Vibrating shuttle or transverse shuttles, also known as bullet and boat shuttles)
Feed dog timing is very straight forward – The feed dogs move the fabric. In order to do that effectively, the needle must be clear of the fabric before they start to move it.
The general idea is that the dogs are lowering as the needle is lowering and moving forward. As the needle rises, the dogs start to rise. As the needle clears the fabric, they start their backward motion to pull the fabric the equivalent of one stitch back.
Usually the only time that feed dog timing needs to be addressed is after parts are replaced. In most cases, feed dog timing is controlled in a relatively non-adjustable way on a Vintage machine. If there is adjustment, it’s in the form of a set screw or a nut and bolt that you loosen then adjust the dogs and retighten. Following the feed dog motion under the machine will show you where the adjustment is.
On a newer machine, the feed dog timing is often managed by a second set of gears on that main shaft at the bottom of your machine. There’s one gear on that main shaft, and a second gear on a parallel shaft that drives the feed dogs. These gears are often plastic, and can break. When they do, the feed dogs stop moving and they come out of time with the machine. Once the gears are replaced, the feed dog timing needs to be reset.
On these newer machines, (note: this assumes that the gears have been changed already. Changing the gears is out of scope for this series.) you would:
- Loosen the set screws on the gear on the auxilairy shaft or on the main shaft so it can turn. One is fine, no need to do both. Typically I find the longer “worm” gear to be easier to manipulate in this case.
- Slide that gear on its shaft to clear the other gear.
- Turn the auxilairy shaft until the feed dogs are at their lowest and farthest forward point when the needle is about to start its ascent.
- Once this is set, slide the gear back to mesh with the other one
- Tighten all of the set screws.
Shuttle sewing machines, how they make a stitch:
As you can see in the image above (again, I found this image on the Internet, if you own the rights to it, and object to my use of it, please contact me via email and I will remove it. I claim no rights to it.), the premise of “timing” on a shuttle system is basically the same as I discussed in the first part of this timing series.
- When forming a stitch, the threaded needle goes down, through the fabric into the hook area. While in descent, the thread is fairly tight against both sides of the needle. This is the purpose of the “grooves” above the thread on a sewing machine needle . They let the thread lie into the needle, and lower the friction and resistance the thread would cause trying to travel through the fabric. It’s aerodynamics for sewing machines.
- As the needle starts to travel back upwards, the thread “puckers” a little, forming a small loop under the fabric.
- This is where the shuttle based sewing machines differ from the hook based machines. In the bobbin area, instead of a hook carrying the thread around the bobbin and bobbin case, the shuttle’s carrier sends the shuttle through the loop of thread. The way the shuttle carrier is designed, the thread can go around the shuttle, and not hang up on the carrier. Once the shuttle is through, the needle thread is pulled tight and the stitch is completed, forming the “knot” I mentioned in the previous timing post. It’s rather ingenious. 🙂 Once again, tension, both top and bottom determine where the knot sits in relation to your fabric.
- Once the needle clears the fabric, the feed dogs carry the fabric back the length of one full stitch.
I hope I’ve cleared up any outstanding questions you might have, and that this series has demystified timing. It’s something that a person with a good fitting screwdriver and a little patience can tackle easily. Please let me know below if you have any other questions, or even just how you made out with this series.