What is the difference between a normal and heavy-duty sewing machine?

Do I need a heavy-duty model?

If we take a sewing machine engineer's point of view, or look at the question from an expert stitchers eyes. There are three selections to what can be classed as a heavy-duty model!

• First is an industrial model, with oil bath, clutch motor and heavy-weight stands, often noisy, and ugly looking.
  They are not really suitable for in home use.
   
• Second, Not a professional model, but very nearly their! If you're looking for a robust, proper heavy-duty machine capable of continually handling projects like home furnishings, heavy curtains, horse blankets, quilts, we recommend choosing a strong, reliable brand with models featuring a metal chassis and sewing bed, with industrial heritage and powerful DC motor. They are heavyweight, have a rotary hook, and use bearings in place of bushes!
  Best suited to a dedicated sewing space, in your sewing room.
  
  Consider options like the Janome 1600P or 6700P, Brother PQ1600S, Juki TL2200, or Bernette B08.
   
• Thirdly, is the heavy-duty by name model, some of which are very good stitches, and reliable models, like the Singer HD series, and selected Janome, Necchi, Pfaff models.
  They are very well engineered with powerful DC motors, and can sew many thicknesses of denim.
  The drive belt has teeth and will not slip when the stitching gets tough. 
  This section are heavy-weight examples, but are a little tougher than others at the same price levels
  
  Perfect choice for occasional heavy stitching tasks: HD4423, 6335D, HD6605c, HD6805c, Q123A, Select 4.2, 423s, HD2200, Strong & Tough HF37