Motech MT-1704HSM168RE shaft without flat section

  • Hi all,

    As I upgrade my printer to have a Duet, I also purchased a couple stepper motors from E3D, the Motech MT-1704HSM168RE, however I just noticed that the shaft is fully round and doesn't have a flat part for the pulley screw to apply pressure on.

    Now I'm worried that in fast prints it might slip inside the pulley.

    Is my worry exaggerated or should I grab my Dremel and flat a bit a side of the shaft?


  • Moderator

    @Ralms My experience is that you don't need a flat on the shaft. Normally, if you use a proper set screw, which usually have a small cup or point on the end, this should raise a burr on the shaft that stops it moving. Make sure you tighten it sufficiently, and use threadlock if necessary; if it's not tight enough, it'll move whether you have a flat or not. A flat may also mask the pulley slipping, as it will always move back and forth between two positions. On a round shaft it will more likely just slip, making it obvious where the problem is.

    There's an argument to be made that a set screw on a round shaft can cope with more torque than a set screw on a flat; it's further from the centre of rotation than a set screw on a flat shaft. Also, a set screw on a flat shaft is more unsupported laterally unless the pulley has a D shape shaft hole (ie a cast or printed pulley, which adds to the grip). Just make sure that your set screw is long enough to engage the full thread of the pulley.

    If you really want to file or Dremel a flat, use Blutak/Plasticine/putty to cover the gap between the motor shaft and motor body; you don't want metal filings going into your motor.


  • Moderator

    I've got the same motor and I dremmeled a flat. I clamped it to a table and used electrical tape to protect the innards. Took all of 5 minutes., which was worth it to me to guarantee no slipping on the shaft. Though droftarts makes some points I hadn't considered at all.

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