Needle Rotational Position
Let’s get in the weeds…
Why would a needle at 5:30/6:30 pick up when one at 6:00 won’t?
In every Longarm Forum there are lots of questions and suggestions about changing needle position to enable great stitch quality. In addition to my HQ training tech training I also completed APQS Maintenance Training and was able to get perspective from another manufacturer on needle position - similar to HQ - 6:00 is preferred and "should" work if hook/needle is timed properly, but a minor rotation to 5:30 or 6:30 might enable stitch formation if timing has slipped a bit, thread is slightly different than what was previously working (tri-lobal vs round for example), or there is abnormal pressure on the thread path/bobbin area from lint, a burr, or some other gremlin.
As a primer - longarm timing has two or more alignment factors (as opposed to most if not all domestic machines or even your car engine which only has one variable) - the hook has to be in the correct rotational position at the correct time in relation to the needle scarf, and as will be shown below the hook and needle need to be in proper position from the front-to-rear of the hook shaft so there is appropriate alignment for thread pickup.
So... why would needle position affect pickup - the scarf is the scarf - right? Let's go to some magnified photos:
The first photo shows a hook (on the right) and needle scarf (on the left) in correctly timed position to allow the thread to be picked off the scarf by the hook - you will note that the top and bottom as well as the sides (only one shown) are rounded, smooth, and chamfered to minimize any thread shredding - remember at 2500 SPM the stitch-formation magic happens more than 40 times a second - not much room or time for error.
The second photo shows the scarf area of the needle - in this case a Groz-Becker 16 - where you can see the scarf bends away from the center line of the needle and is also a little thinner.
The third photo shows the needle scarf in what looks like pincers but is actually the external measurement sides of a digital vernier caliper - fancy name for a measuring device for small stuff...now let's see what the caliper tells us.
The fourth photo shows the thickness of the scarf at 6:00 - 0.77mm - a little thicker than a business card - now here is where it gets interesting…
The fifth photo is with the needle at 5:30 (would be the same as 6:30), and the thickness has increased to 0.97mm - so the scarf area is not round but somewhat oval and with just a small movement there is more than 25% more thickness in play at the hook/needle interface.
The sixth photo shows the needle at 5:00 where the thickness has increased to 1.05mm, about 25 or 36% thicker!
So now we know why a slightly mis-timed hook/needle may work when the needle is slightly rotated from 6:00 - the scarf is thicker and therefore could overcome a slight gap from front-to-rear for needle/hook contact, and/or a slight rotational error where the hook is arriving a bit earlier or later than expected.
As a recent example of how precise timing needs to be, yesterday I re-timed a Forte that had "enjoyed" a collision between the needle and a pin on the quilt. When the event occurred a Handi Quilter educator happened to be there, but no amount of needle rotating would allow the bobbin thread pickup to occur. At first glance I did not see anything wrong - for sure the scarf-to-hook alignment front/rear was OK, but after getting out the magnifying camera it verified the hook, instead of being at 12:00 for the thread pickup, as at ~12:10 - so when the needle came up with the thread the hook was late for the "date" and went home without a partner. A minor rotational correction and the hook and needle are now dancing with enthusiasm!
To conclude - a 5:30 or 6:30 needle position is a work-around and proper timing should be re-established as soon as possible - and hopefully the details shared here can take some of the mystery out of this tactic.
Do you have questions on this topic or a suggestion for another one you are interested in?