How Can I Safely Extend the Shaft of My Motor for Encoder Installation?

[vinayak Joshi]

Hi,

I have this motor with me,
http://www.etonm.com/products_detail/&productId=46.html

What I want to do is mount an encoder at the back side of the output shaft of the gearbox. I am trying to figure out how to extend the motor shaft in the rear side. The encoder I am fitting will be optical, and as such will not put any load on the gearbox shaft.I thought of drilling a hole into the shaft's back-side, but then realized, that it may cause the shaft to expand making it press fit into the bearing. Now for obvious reasons, I don't want that to happen.

The second idea i though of was to stick a metallic part to the back side of the shaft with a metal adhesive. But my friends told be that's a bad idea, as the adhesive will come off if the motor experiences vibrations, which in my application it will.

Please help.

Thanks for the reply.

 

[berkeman]

Hi,

I have this motor with me,
http://www.etonm.com/products_detail/&productId=46.html

What I want to do is mount an encoder at the back side of the output shaft of the gearbox. I am trying to figure out how to extend the motor shaft in the rear side. The encoder I am fitting will be optical, and as such will not put any load on the gearbox shaft.I thought of drilling a hole into the shaft's back-side, but then realized, that it may cause the shaft to expand making it press fit into the bearing. Now for obvious reasons, I don't want that to happen.

The second idea i though of was to stick a metallic part to the back side of the shaft with a metal adhesive. But my friends told be that's a bad idea, as the adhesive will come off if the motor experiences vibrations, which in my application it will.

Please help.

Thanks for the reply.

Welcome to the PF.

From your link, it's hard to see what part of what shaft you are asking about. Could you upload a picture that shown the shaft more clearly? If you can find a *.JPG image of it, you can use the little picture icon thing above the edit window to link to the picture. Otherwise, if you have an image of it on your computer, you can use the UPLOAD button at the bottom right to upload the image or PDF.

 

[Mech_Engineer]

It looks to me like the OP wants to attach an encoder to the "stub" shaft at the back of the motor opposite the gearbox.

I'd say your "best" bet is probably to drill a hole in the shaft, but you might be able to bond something to it. Even with vibration its possible to choose a durable adhesive (like a high-strength epoxy) that could tolerate the vibration. But, you would not be able to disassemble the motor for servicing after bonding.

 

[vinayak Joshi]

@berkeman: I don't actually have the motor in hand. Still waiting for the delivery. I have taken the picture from online and highlighted the back side of the motor shaft with a red color circle. What you see there, is an 8 mm shaft at the center, then there is a 2mm thickness (OD-ID) bearing, and then an extruded part of the gearbox casing.
What I need is some way to extend the 8mm shaft. I have also uploaded a photo of what the front of the gearbox looks like, so that no-one gets confused. As per what I am rotating with the help of the motor, I have no way of mounting an encoder on the front side. So the back side is where I need the encoder.

@Mech_Engineer: As I Mentioned earlier, I don't want to endup spoiling the bearing, while drilling. I think there is a reason to believe, that the shaft might expand slightly If I drill it. Now if there is a way to absolutely avoid that, I am all ears.

 

[256bits]

What if you slot the shaft along a diameter, and then you can add a matching shaft of desired length and width with the end machined to fit nicely into the slot. Slot can be part of an arc and you might be able to do that carefully with a dremel tool. Just make sure the fit is just tight enough so that backlash is eliminated and alignment of the extension does not cause problems when assembled. Or that the bearing surface is disturbed one either the shaft or mating surface.

 

[berkeman]

What resolution do you need from your encoder? You might just be able to glue an optical pattern to the short end of the shaft and use a fine retroreflector to read the pulses as the shaft turns.

Also, how come you can't do something with the long end of the shaft instead? What are you attaching to the long end? Is it that you want the motor speed monitored and not the geared-down speed?

 

[CWatters]

+1 to that. Just watch you don't get paint of glue in the bearing.

I reckon you could carefully drill and tap a thread up to say M3 in the 8mm shaft. Use a lathe to centre the hole? Take it apart first.

You might also find that the gear inside is a press fit on the shaft - might be possible to push the gear along the shaft so that a bit more sticks out the back.