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I have a motor with a 4mm shaft. I've purchased a propeller that's designed to fit a 1/2 inch shaft. How can I securely couple the two?

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    $\begingroup$ Have you asked yourself if attaching something designed for a 1/2 inch shaft with all the weight and strength requirements that implies is a sensible thing to attach to a motor with a 4mm shaft, with all the (lack of) strength which that implies? $\endgroup$ – TimWescott May 9 at 16:13
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If the motor speed matches the speed range needed for the prop, then make an adapter with relevant locking screws or equivalent, balanced as necessary.

something like :

enter image description here

Source https://shaft-collars-couplings.staffordmfg.com/viewitems/shaft-adapter-couplings/shaft-adapter-couplings---step-up-type-with-keyway

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  • $\begingroup$ Can you be a little more specific? I'm kind of a neophyte here. $\endgroup$ – Megalonychidae May 9 at 12:12
  • $\begingroup$ @Megalonychidae see update $\endgroup$ – Solar Mike May 9 at 12:24
  • $\begingroup$ Perfect! Thank you very, very much. $\endgroup$ – Megalonychidae May 9 at 18:06
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Following on from Solar Mike's answer, I'm not sure you'll be able to find something off-the-shelf with the diameters you have (mix of imperial and metric units), so you may need to get something custom made instead. I have sketched the following (not knowing what shaft lengths you had, I made a few assumptions - adjust to suit your needs):

enter image description here

The outer diameter is 1/2 inch, while the ID is 4mm. I have toleranced it as H7 hole so that it's a snug fit on the 4mm shaft. The adapter is secured onto the 4mm shaft with 2 M3 grub screws at 90 degrees, you can also use Loctite 638 if you want to be sure. I have added a 1mm chamfer on the end of the shaft adapter.

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  • $\begingroup$ Good job, plus 1. $\endgroup$ – Solar Mike May 9 at 18:07
  • $\begingroup$ Beautiful sketches, do you mind if I ask what software you used? $\endgroup$ – Megalonychidae May 9 at 18:08
  • $\begingroup$ Thanks. I used Autodesk Inventor. $\endgroup$ – am304 May 9 at 18:28
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Use gears, mechanical losses will only be 1 % and that's negligible.

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