DC Motor shaft coupler

I need to connect a DC motor to a square shaft (pictured below).

The problem: The Gearhead motor shaft is semi circular with a small flat piece. The shaft is a square face. How can I make this work?

I need to demo this working on Thursday, all info is appreciated.

drinking straw + epoxy

;D

I forgot to mention that this is a high torque motor and the load is heavy.

If you don't have machining facilities, file the end of the square shaft as round as you can get it and use a 'lovejoy coupling' (Google it). They can easily handle a fair amount of misalignment.

If you don't have machining facilities, file the end of the square shaft as round as you can get it and use a 'lovejoy coupling' (Google it).

I second this. File the end round, then couple it. To file it round, chuck the square rod into a drill (this might be difficult with a three-jaw chuck, you might have to get fancy), turn on the drill, then apply the file (be very careful, hold the file in both hands, wear gloves, and goggles!).

Alternatives to the "lovejoy coupling" (though depending on the torque, might not work):

  1. Rubber hose with pipe clamps on each end (you could try this without even filing!).

  2. Use thermo-plastic (polymorph) to make a custom "coupler" between the shafts.

  3. Drill holes through the shafts perpendicular to their axis, then use an over-sized (larger than both shafts) bit of small diameter pipe. Drill holes in a similar way, but orient them 90 degrees opposite to each other (so that if you passed pins thru them, and looked thru the pipe, you would see them crossing each other in a "plus" + sign). Pass pins thru them and the shafts, and you would end up with an el-cheapo form of a "universal joint" that would allow for some misalignment.

:)

DIY couplings probably have shaft alignment issues. I've seen shafts in toys using tightly wound springs which may be helpful in dealing with alignment. How different are the shaft diameters? Round shafts with no flat spots for set screws or interference fits may be hard to grip.

I used the spiral shaft coupler and an Oldham shaft coupler in this project:- http://www.thebox.myzen.co.uk/Hardware/CNC_Conversion.html