Sunday, 1 July 2007


Well in my last post I said things could only get worse and they did! I picked the extruder motor coupler to make next as it looked easy. Ironically the first thing I did was to destroy my z-axis motor coupler by getting the vacuum pipe trapped underneath the drill. It's amazing how much torque a decent stepper motor can deliver. Fortunately I had another stronger coupling lying around.

The only problem was that the hole for the shaft was only 6mm and my shafts were 1/4 inch. Luckily I posses one reamer and it happens to be 1/4 inch. I didn't even know it was a reamer until a friend told me it was recently. I thought up to then it was a milling bit. It got a bit toasted the other day when I used it to cut MDF at 30000 RPM. Still it worked on aluminium like a dream with some paraffin lubricant and my drill set to its slowest speed.

The machine is a lot noisier with the thicker coupling so perhaps a rubber one would be better.

The next disaster was that I dropped my camera on the floor and broke the USB connector so I had no way to get the pictures off it. Surface mount connectors are a nightmare. They make production cheaper but they are just too fragile for external connections. It broke off the PCB and all the pins came out. I managed to solder it back on and press the pins back in, hence these photos.

Milling the coupler was tricky because the small milling bit I used to keep the corner radii small has limited reach because its shaft is 0.3mm bigger than its head.

The coupler is 16mm deep so I had to step the outside out 0.2mm half way down. Similarly the inside slot had to step in. It made the programming complicated because in order to step out part way down you need to have opened up the gap to the scrap above. I.e. you have to cut a sort of stepped V shaped trench needing three passes.

The final result came out OK

It couples the motor which has a round shaft with two flats to a hexagonal nut. Here it is attached to the motor :-

I have made a start on the polymer pump halves but they have curved upper surfaces requiring a ball end mill and true 3D milling so a bit more programming is required.


  1. Hi :)
    I am a graduate school student in Korea. I need broken coupler picture because I will present my study in May. so If you don't mind, I want to use your broken coupler picture. It is not a commercial present. and I will surely show the source of the picture.

  2. Hello, I am a graduate school student in Korea.
    I need broken mechanical coupling picture in order to quote in my master graduation thesis. My thesis is about magnetic coupling. So if it's okay, I want to use this picture. Also, with your permission, I will definitely indicate your blog's URL as reference.