Pushing the 3D limits for production
It is important to understand what we can do reliably, and what will inevitably cause quality control problems due to pushing the limits of our process. This applies to conventional engine turning as much as to CAD CAM work, but the necessity is to be more cautious with production work because mistakes in design can be very expensive in production.
This sample ball pen body was cut successfully, but we decided to modify the design for the production version to leave the bottom 10mm uncut.
Had we put it into production in the illustrated format, we would have had a significant reject rate from streaks appearing near the narrow bottom end of the tube, at the point where the last few cuts were executed by the machine.
The engine turning in this case is a conventional barley pattern, to match a well known luxury Swiss watch brand, with stripes of zigzag lines.
One of the great advantages of CAD CAM engine turning in this example was that the pattern is able to retain it's geometric integrity right to the narrow tip of the pen. If the pen had been cut with conventional machinery, the opposed zig zag or wavey lines that make up the barley pattern would have overlapped and looked unsightly, but careful manipulation of the tool path to decrease the amplitude of the waves near the narrow bottom end of the tube retained the geometric accuracy of the design even on such a 3D surface.
Sometimes a new pattern just doesn't turn out as well as we require.
One that didn't work. We rejected this experimental sample design because an unexpected raggedness occurred in the boundary between the fine basket work in the diamond shapes and the barley background.
Our standards, and those of our customers, are very high and we will not put a bad design into production.
This tube was another earlier sample for the pen above, also rejected. We found that the border between the two pattern areas looked untidy, as is visible in this image. Sometimes it is possible to resolve such issues, but in this instance we had already shown more than one alternative design and the customer simply selected one of those without actually seeing this one.
We needed to find a way with this product to safely finish the barley engine turning without any risk of a visible streak on the last cut. So we produced these ideas to find a way to finish the design reliably.
The problem was resolved and went into production sililar to the image above. Several thousand pens were produced in both Ball, Roller-ball and Fountain pen configurations.