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 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!

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!