I got back from France on Monday evening and found my room FULL of parcels! For the past 2 months I have been designing new lens formulas and housings for them to go into. Whilst doing this I made decisions about materials and general dimensions for the optics, interchangeable barrels, mounts etc, so that I could order the materials in ahead of me arriving back in the UK. Among the things I had delivered were 4 tubes of aluminium, 3 different clear plastic rods, camera mounts for Canon and Nikon, a rod of Nylon, and some other bits and bobs. I turned up to my old school once again (Altincham Grammar School for Boys) at half 8 the next morning to make use of their manufacturing workshops and get the prototyping rolling! (Thanks for the school support in letting me use the equipment again!)
The aim for the week is to make working prototypes of the 2 selected lens designs, the 90mm F/2 and the 50mm F/2.8. There is so much to do, so much to consider, and so much to work out how to manufacture using the equipment available to me that it is really easy to get lost in it all. So to begin with, I decided to get myself back into the swing of things by following my manufacturing list that I made while I was still in France. It covered the making of all the non CNC parts.
To start with, as you can see in the images above, I started off by cutting down my lens mounts. I had one Canon EF mount left over from the last round of prototyping, but because I am making multiple mount I had bought in new ones from the same company. Much to my surprise, the new ones which arrived were different! Much more compact and short. As part of the design I had to turn down the diameter to 63.5mm (so that the mount covers the entire EF mounting ring on the body of the camera) as well as spinning off the front thread (these mounts are actually reverse ring adapters). The original mount was a good couple of millimeters taller than the new one, so I decided to save this for the 90mm lens. Seeing as I have two of the new type of mount, I saved them for the 50mm lenses (because I plan on making two copies).
The next step having modified the mount was to cut some outer barrels. There is a slight variance in barrel size between the Canon and the Nikon versions (due to Nikon having a 2.5mm longer flange distance). However, the reverse ring adapters that I am modifying have different heights also, and so as it happens the 2.5mm difference is swallowed up by it. Therefore the barrel lengths for both versions are the same. It was a simple case of cutting off a length of bought to fit aluminium tubing, and trimming it down to size on the lathe until it fits and mount and protrudes the correct amount from the camera.
With that done, I moved onto cutting the inner barrels. To make my life much easier, I designed the barrels so that I could make use of particular stock material sizes. So, in this case, I bought in 60mm diameter 3mm wall aluminium tube for the outer barrel, and 60mm diameter 5mm wall aluminium tube for the inner. This meant that I could cut a step into the 5mm wall and simply slide it into the 60x3mm outer barel tube without having to modify it.
I think I'm going to keep the barrels plain, ie not paint them. I think they look good as they are! I am saving all the finishing processes till the very end just before assembly, to ensure everything is flawless just before finally putting everything together. I will give all the aluminium parts a rough buffing, to give a dull shine. It won't be like a mirror, more like a brushed aluminium look.
With the easy bits done and 3/4 of the day gone, I was unable to avoid turning to the CNC for any longer. Here's the thing. Making these prototypes is tricky, but feasible. However, there are unknown risk factors which could make it MORE tricky than I would like. The main risk factor was the CNC lathe and whether it would be able to cut concave surfaces. Let's cut to the chase, after checking the machines software by running one of my pre-prepared DXF surface curvature files through it, I discovered the answer was no. Using the software control package which automaticly converts DXF profiles into machine G-codes, it is not possible to do what I want. Disheartening news, even if it was half expected. It makes a simple job of running a file on a CNC machine into a very difficult problem with a number of possible solutions. With it being near to the end of the day, I decided to leave it to be solved later on in the week. Instead I started to cut the first optic of the 50mm optical assembly, which is double convex and poses no problem for the machine and my tooling.
We're stretching the limits of this machine. It's a training cnc lathe, designed to get students or new engineering employees upto speed on CNC machining. We're running the chuck wide open on it's limits to hold the optics (upto 50mm diam, but stepped down to 30 for the chuck to hold) and collets. Cutting an oversized peice like this is not a problem, but parting off just isn't possible with the machines tools, so the part has to be taken out and parted off on a manual lathe before being placed back into the CNC in reverse for the back surface to be cut.
In the first day, as you can see, I got a lot done. I leaving to go home though, I wasn't happy. The fact that the control software couldn't program the machine to cut the surfaces I needed was a looming headache which I knew would slow down the prototyping process and make everything I want to do much more difficult. Without an immediate solution, I thought about it and left it to discuss with Garry the technician the next day.
