Coupling different diameter shaft

[MarkyMark]

My motors have a 3mm shaft.  I wish to connect them to pickup rollers which have either a 7mm or 8mm shaft.

I've searched everything I can think of to connect them with no luck.  It all boils down to me getting a solid shaft and drilling a hole but I have neither the equipment or skill to drill it centred and straight enough to be effective.

Are there any off-the-shelf solutions?

Thanks in advance,

Mark

[bdeuell]

would these work for your application?

http://www.lynxmotion.com/p-242-mounting-hub-3mm-pair.aspx

[MarkyMark]

Thank you but unfortunately not as the screw holes are much wider than the 7mm shaft it needs to attach to.

[bdeuell]

does the roller have a 7mm shaft protruding or 7mm hole?

can you load a picture or drawing of the two parts you want to connect?

[MarkyMark]

http://img.weiku.com/a/000/385/high_quality_paper_pickup_roller_for_HP_Laser_Jet_9000_9040_9050_RF5_3403_000_6300_2.JPG

It had a 7mm hole. Not identical but similar to link above.

[CJAlbertson]

Fill the 7mm hole on the roller with epoxy then after it sets up drill a smaller 3mm hole through the epoxy.  "JB Weld" or some similar brand of epoxy  is very strong.

If you can't drill a 3mm hole them place a 3mm dowel (coated with some kind of wax, perhaps from a candle)  in the epoxy while it is setting up then pull the dowel.

The key to both drilling and setting in the dowel is making an accurate jig.  use wood, metal, bricks or whatever to hold everything in perfect alignment setting up the jig is the hardest part.

If you are going to do this kind of work a lot it is worth investing in a small top top drill press and a small drill press vice.  Cost less them $100 total at Harbor Freight.

[bdeuell]

Building your own adapter will have varying degrees of success based on your skill/craftsmanship, tools available, and precision required. The construction methods described above are all valid. You also might be able to find a piece of tube to make a spacer out of with minimal machining.

I did a little more searching for a shaft coupler but the significant size difference in your shafts makes finding an off the shelf solution challenging (without connecting several adapters together). So time to think a little more creatively...

I found the following 3mm shaft coupler with a 8mm OD.
http://www.technobotsonline.com/inline-coupling-3mm-to-3mm.html
Im sure you could find other similar products if this exact one doesn't fit the bill.

Be warned that while the OD is listed as 8mm it is likely not very precise and may require a little modification (sanding or shimming) to fit nicely in a 8mm bore. Also a coupler such as this does not contain any features to attach a wheel to the outside but you could probably glue it. An epoxy with roughened surfaces would probably work well.

[MarkyMark]

Yeah I don't trust my skills!  Link looks promising.