Sewing Machine

I've been sewing today.  There were a number of tasks that need to be done including some alterations some additions and making two old table cloths and two parts of the thermal curtain for  for my workshop.  My sewing machine looks good and I have plenty of good materials to work with however every now and then the sewing machine forgets to do a chain stitch and begins to knit.  This makes me tired because I have to take out the bobbin and then undo the tangles and look for the possible cause.  Even so I am grateful to have a sewing machine because many of the things that I accomplish with it couldn't be done otherwise without tedious handsewing.