Coupling

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.

Bob on

Here is the first RepRap part that HydraRaptor has milled :-



It is the extruder barrel clamp as shown in the previous post. As you can see it is dimensionally correct to two decimal places! It's not a fluke, the height is bob on 45.00mm as well. I have been getting pretty good accuracy with my previous milling attempts but this is astonishing.

I used a smaller end mill (2.22mm) in a collet chuck which is more accurate than the three jaw chuck I used before. The plastic is a sheet of 9mm Delrin or Acetal which I used because I read somewhere that it was a good plastic for machining. It did machine well but all the edges were left with a thin burr. This was fairly easy to remove with a fingernail.

This is not the latest version of the RepRap design but I decided it would fit my machine better. I added two more mounting holes and changed the central hole diameter to match my PTFE barrel which is 12mm rather than 10 or 16mm in the original design. The central slot is 2.5mm rather than 2mm because my bit was too big. Obviously I will have to drill the horizontal hole for the clamping bolt with a drill press.

Here is an edited video of it being made, it took around 20 minutes to make the part :-



And here is an amusing out-take if you listen to the sound :-



So having achieved perfection on this first part, things can only get worse when I attempt to make the rest of the extruder.

End of play

You may recall that I said my replacement spindle motor, AKA Minicraft drill, had a bit of end play due to the bearing moving. This evening I made some shim washers by milling a thin piece of hard plastic that I got from the inside of a PC power supply. They are 11mm diameter with a 8.5mm hole and about 0.2mm thick. They were a bit ragged round the edges due to the plastic burring quite badly but it didn't really matter. I made three but two were enough to stop the bearing moving.



This is what the inside of the drill looks like. I added the capacitor myself to keep the radiated emissions from the cable to a minimum.



The result was very pleasing and I now have a working milling machine again. My next job will be to mill an FDM extruder. I plan to start with the clamp as this looks the easiest part.




Obviously I will have to modify it a bit. For example I can't do sharp internal right angles due to the tool's radius.