How to improve Central Bobbin Class 15 Shuttle Hook on Sewing Machine

This video shows an improvement to a central bobbin or class 15 shuttle hook. Before the improvement, the maximum thread size was V69 for the Singer 237. Afterwards it was able to handle a V138 thread (Serafil 20). For all sewing machines, that use such a shuttle hook, the improvement reduce thread friction for any thread size and will make the sewing machine sew better. List of contents 0:00 Intro 0:17 Removal of shuttle hook 0:32 Identification of sewing problem 0:56 Hard point in sewing cycle 2:13 Thread U-turn friction at hook needs to be low 2:34 Sharp edges at thread U-turn 2:56 How to grind and smoothen the U-turn 3:20 The same kind of shuttle hook is used in a huge number of sewing machines 3:30 End I used strips of strong sandpaper to grind the edge. Emerald canvas should be better. First grit 220 was used and afterwards grit 2000. You may finish it by some polishing by a polyester cord soaked in scouring cream. In order to service the housing of the shuttle hook, you may link these Indonesian videos:    • Sewing Machine heavy to Operate | मशीन भार...   and    • SHUTTLEHOOK BASIC KNOWLEDGE & TROBLESHOOT ...  . And this is about replacement of shuttle driver spring:    • धागा बार बार तूट रहा है | Thread Continuou...  . Please "like" this video, if you find this information useful. You will probably find other tips for your sewing machine on my YouTube channel. Leave a question and a comment as you like.