Attaching Shaft to Plastic Gear Without Shaft and Screw Hole

[Mande Mandiri]

How to attach shaft to plastic bevel gear without keyway and screw hole? I fear that drilling a screw hole and using set screws are not suitable for plastic gears. Below are the plastic gears I'm planning to use.

 

[mfgenggear]

Mande Mandiri
with out seeing the gearbox design many here are probably hesitant to answer.
one suggestion would be make a shaft with a shoulder to locate right hand face (eng dwg) slight press through hole.
a taped hole at the end of shaft , then a cap with a clearance hole or thread at end of shaft to tighten and lock in place.
to prevent the gears from slipping , cut key slot in id.

 

[Compositepro]

Broach a square hole to fit a square shaft end. It would be best to mold the square hole with the gear, if possible.

 

[spigor]

I've seen this in many plastic gear designs, that a groove is cut through in the back face of a bevel gear, to create a dog clutch with two dogs. Since your bore is 8 mm, this groove should be e.g. 6 mm wide. Here's an image, but with many dogs:

https://www.diva-portal.org/smash/get/diva2:634202/FULLTEXT01.pdf

page 7

 

[dvd]

based on duty-cycle of gear drive and build up of heat in the gearbox sump, thermal expansion of the plastic gears could lose interference fit with steel shaft and become loose.

A threaded insert in the gear hub would allow a setscrew to be installed.

 

[Tmoose]

Is that a "stock" gear for KHK ?
The m90 material looks to be an industry standard.

https://www.polyplastics.com/Gidb/GradeListSelectGradeAction.do?id=1771&_LOCALE=ENGLISH

"Possesses good mechanical & snap-fit properties and thermal stability."


Once you have the gearbox design stuff mfgenggear suggested KHK should be able to tell you what to make it out of.

I like spigor's drive dog idea.

A steel sleeve on the 20 mm Ø hub and pressing the gear onto a splined or knurled shaft might be pretty secure.

How to glue it -

https://www.permabond.com/materials_bonded/how-to-bond-acetal/

 

[Pud]

The material spec says POM (polyoxide methylene) aka known as trade name 'Delrin' (Du Pont name)


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[mfgenggear]

sketch

 

[juergenwt]

STRAIGHT knurl on dia 8 shaft and maybe M4 screw in front. Press on knurl.

 

[TheTick]

Cross-hole and roll pin

 

[aMengel]

For bevel gears like this you definitely need a shoulder to locate the gear axially on the shaft, as this gear type is very sensitive to correct positioning.
You also need to centre the gear accurately on the shaft, so a section of the hole there needs to be a close fit with the shaft (transition fit is ok).

Now, for transfer of torque, the most commonly used (and best) way is to use a spline.
If the gear needs only to transfer small loads, a spline on the shaft and a slight interference with the plastic gear's hole is ok. But if you have more torque to transfer, you need a mating spline in that hole.
Internal splines can be broached quite easily.. if you have the broaching tool for that particular spline. Ø8 is a normal diameter for shafts, so it should be easy to find fitting spline tools for shaft and gear.

have fun