Turns out the machinists were using acrylic, rather than polycarb. I explicitly asked for poly-carb, but they wanted to see if it would work with acrylic since they didn't have any suitable polycarb lying about.
8-ball, what was going on was that as the tubes were being machined down, the ends of the tubes would chip away, leaving a tubeless piece. This is exactly what I feared would happen if acrylic was used. Acrylic is quite a deal more brittle than polycarb and doesn't handle vibrational stresses that well. It'll just crack if you try to cut it too fine. The tubes have 0.20mm wall thickness while being cut, and the acrylic was just falling away as a result of the cutting action acting on so thin of a thickness.
The 0.20mm wall thickness is actually about the same that is on the current Cascade, for which the wall thickness varies between 0.20-0.30mm with the hexagonal shape of the tubes when being cut. They then get drilled out to around 0.10mm thickness at the thinnest bits, so I know that polycarb is capable of being machined to such levels.
The thing is now that they've been set back with the acrylic they are reluctant to re-try with polycarb. LOL - I always tell the machinists that it's my job to push them to levels that they never knew they could achieve, and the sales rep for the NC mill continues to be impressed at the levels being pushed, so I find myself (again) in the situation of trying to convince them that they can do it. They'll come around with a bit of pursuading. I seem to go through this with them every time I ask for something new.
|