Can a guy not catch a break?! Day 8 was a total disaster. Honestly i'd have achieved more had I stayed at home in bed. Nothing worked, everything went wrong, it was the biggest waste of a day ever. Okay, so I've got that out of my system now, lets explain why.
So the previous day I had encountered problems with cutting tight radii concave surfaces using the boring tool. With no other tool available no way of knowing if the machine could be configured to use a different tool, and no technical support available in school for a couple of days, I had to think outside of the box to come up with a solution for cutting the concave faces.
In the code that I wrote, the hollowing processes cuts out the majority of the material and leaves steps that can be chamfered down to for the final curve. The CNC actually managed to cut all the steps out without colliding with the face. Therefore, most of the material was actually hollowed out. This led me to think that if I could cut a billet with a positive version of the negative surface curvature, then I could use it with abrasive papers to smooth down the steps to get the final form!
With plenty of nylon left over I cut a short billet. I went onto Solidworks and made a positive of the concave profile, and allowed the CNC control software to generate it's own G code form an exported DXF automatically. I then went ahead and cut the part.
Me and nylon have a mixed relationship. Today nylon was being argumentative and didn't want to co-operate. As a man I have no control over this, and so I simply let it pass and tried to fix everything up after she'd finished moaning.
Honestly look at her, swarf wrapped tightly around the entire machine, what is her problem today?
After calming her down, she went back to normal. The cut was good and the finish was adequate. The surface was -0.25mm off of the radii to allow for abrasive paper to be glued onto it.
As you can see I then had a roughed out negative profile and a finished positive plug. I super-glued a strip of sand paper to it and mounted it in the tailstock of a manual lathe.
Slowly I inched the positive closer and close to the negative and gently let it start abrassing the steps in the acrylic away.
It didn't work :@ Oh and not only that, I dropped my camera as I went to explain why it didin't work to someone. Thank god for UV filters! It landed lens first and went pinggggggggg, but only the UV filter smashed. The damage to the lens was minimal. Nothing like dropping your camera to further piss you off though!
So back to the problem. The method I was using caused an error I really wasn't expecting. It caused internal stress fracturing. Now usually you don't see this in plastic, because most people don't usually use clear plastic where you can see inside. But through the side of the acrylic billet it was obvious. Pressure has been created on the centre steps and had caused the fracturing, which look like blades sticking up inside the plastic. Obviously this isn't acceptable, it'd be more than obvious when looking through the lens. So that's that idea out of the window. With no way of cutting tight concave surfaces, I was out of ideas.
So, with that having failed, I decided to carry on with all the other bits I was still able to do. There aren't many element with shallow concave radii, but there are some, so I got to work coding them. One of them was on a polycarb element. I hadn't cut any polycarb by that point, so it was all going to be new to me. I was hoping it would cut the same as acrylic, but come on, that'd just be too easy wouldn't it.
After coding and cutting a billet and mounting it and running the machine, this is the result. F**king useless! Whats with that blob in the middle? And why is the surface so frosted? The material didn't cut anywhere near as nicely as the acrylic, and it was so difficult to polish that I just gave up. It just wasn't going to go my way. With not much time left, I grabbed a piece of aluminium and did one of the last jobs I knew couldn't go wrong; I cut the inner barrel for the 90.2 lens.
Well atleast that didn't go wrong. After an entire day I had made no real progress. The stress of the week and growing prospect that the lenses might not even be able to be cut with the resources I have available to me meant that I might actually just be wasting my time. Not a good position to be in after nearly 2 working weeks and not long to go until I had to return to France.
