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Polymorph NEMA17 CNC Stepper Motor Coupling

Joins a 5mm shaft with an 8mm lead screw
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Introduction

Couplings are expensive, but tubing and Shapelock (Polymorph) is cheap.  This is a cheap way to build a coupling between a 5mm stepper and an M8 screw.  When I tried this I did not expect the Polymorph to stick to the tubing.  It does stick, which makes this a pretty good coupling.

 

Materials

NEMA17_Polymorph01.jpg

Figure 1: You'll need Polymorph (<5 grams) and tubing that will fit tightly over your lead screw.  I used tube with 6mm inner diameter for an M8 (8mm) screw.  You'll also need one of your motors to mold the plastic.

Procedure

 NEMA17_Polymorph02.jpg

Figure 2: Drop the Shapelock in the water and wait for it to become tranparent.

NEMA17_Polymorph03.jpg

NEMA17_Polymorph04.jpg

Figure 4: Remove the plastic from the water when it is transparent (see-through)

NEMA17_Polymorph05.jpg

Figure 5: Pull off a small piece of Polymorph

NEMA17_Polymorph06.jpg

Figure 6:  Roll the polymorph into a cylinder slightly smaller than the tubing, and insert the Polymorph into the tubing.

 NEMA17_Polymorph07.jpg

 Figure 7: Do not insert the Polymorph too far into the tube -- just a centimeter or two.  Use your fingers to pinch the tube, and then push the Polymorph into the tube until it is full.

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Figure 9: Pinch off the extra Polymorph.

NEMA17_Polymorph10.jpg

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 Figure 11: The tube is ready to go on the motor, but it has cooled down.  We'll want it as soft as possible so it makes a good strong coupler, so we'll put it back in the water.

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 NEMA17_Polymorph14.jpg

Figure 14: It's ready to go on the motor.

NEMA17_Polymorph15.jpg

Figure 15: Center the motor shaft in the tube as best you can and push it in a little.

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Figure 16: Pinch the tube to keep the Polymorph from sliding too easily into the tube, and push the motor shaft into the tube.  The coupling tube may get a little bigger where the polymorph and motor were forced in, and that is okay.

NEMA17_Polymorph17.jpg

 Figure 17: It is done! The Polymorph is still hot and needs to harden, so leave it on the motor until it turns white.

NEMA17_Polymorph18.jpg

 Figure 18: When the Polymorph hardens and turns white, you can pull the motor from the new coupling.  In this figure you can see the impression of the motor shaft.  The top side is flat.

NEMA17_Polymorph19.jpg

Figure 19: Now you can put the coupling on the motor and lead screw and use it on your CNC machine.

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Nice one....

.... the neat idea with this is that the Polymorph makes a good bond to the plastic tubing.

Containing the Poly in the tube compresses onto the contact surfaces (or splines on the shaft) too...cool.

In fact polyMorph leeches onto most plastics in general....

.... the added effect is that your motor coupling can bend  - good for driving motors on a suspension system.

Its worth tagging your workshop under polymorph as interest is picking up with this amazing material.