Mini-lathe - first commercial job!

Part of the deal to get the larger lathe feed gears printed was that the owner of Regenerate3D, James, needed some aluminium parts machined for a radio controlled glider. The bit he needed was an adaptor to go between a motor shaft and a printed propeller. I agreed to make the bits to his drawing and we corresponded for a few days refining his design.

One of the most interesting bits of machining anything is working out the best sequence of operations and I'll show you what I did here but I can't pretend it was the best sequence!

The first step was to cut a chunk of 1" 6021 round bar, face one end in the lathe and reduce it a little so that it would go further into the chuck. I then turned it around to machine the other end to something close to the finished state:

Next step was a face knurl, which I had never done before. I used an existing wheel and made a little holder for it with a bit of 10 mm round bar. The washers are there to prevent the wheel contacting the work. The issue is to get the knurl close in to the centre means you cannot have anything protruding beyond the wheel - so there is no room for a nut or screw head to retain the knurling wheel.

I was very pleased with how it came out, and turned the work around to finish the other end to the same standard. At this point I still had a half millimetre oversized on the journal that would carry the propeller.

I replaced the chuck with the ER25 collet to hold the work whilst I parted it off - this was a mistake, because there was not enough length available to hold the work in the collet to withstand the parting off loads. I should have sawn them in two. Fortunately I hadn't taken any of the diameters down to size and I was able to remove the scuff marks caused by the work moving in the collet. 

Once I had the two bits separated, I could drill the holes for the grub screws. There's a chamfer behind that flange which is out of shot here and I made sure that the holes were drilled and tapped before I formed that chamfer, to give me enough room to hold the part for drilling.



This is the 3D printed propeller that will be used to launch the glider into the sky:



Here is the rear view. You can see the chamfer that I was talking about earlier:



The propeller is actually in two parts - there is an M8 nut hidden inside which retains the prop to the aluminium adapter.