Diamond turning - Lens machining

[gkan]

Hi,

We have been flirting with the idea of making a large collimator lens for a flood exposure system. Now, I realize that I am probably going to fail miserably and that this is a black art etc but still, I want to give it a go. So, my plan is to try optical grade PMMA first and BK7 after that, machine the shape and then work with diamond pastes to get the surface needed. I have a couple of questions though:

1. Where does one get diamond turning tools?
2. Is the diamond tool suitable for PMMA?
3. Since PMMA is very soft, is there another tool material I could use that is very sharp but cheaper than diamond tools? Would aluminum cutters work?
4. What kind of lubricant does one use with diamond pastes? A mold maker told me I should use water or ethanol when moving to very small grit. Hoes anyone heard about this? Doesn't ethanol attack PMMA?


Thanks in advance!

George

 

[MikeHalloran]

1. Polycrystalline diamond cutters are available from the usual cutting tool sources. I've been under the impression that single crystal diamond cutters are used in machining mirrors.
2. The process I'm remotely aware of uses diamond tools to machine copper mirrors, with the workpiece rotating on an air bearing spindle. I would guess the diamond could cut PMMA, but more ordinary tools can also cut it.
3. Ordinary "High Speed Steel" cutters work on PMMA just fine.
Aluminum would be unsatisfactory.
4. I don't know about ethanol. I have used kerosene as coolant for PMMA with good results and no crazing or cracking.

I don't know why you think you need diamond past to deal with PMMA.
Toothpaste works fine, as do lots of common polishing agents.

Why don't you try designing your lens as you like it, and let your favorite machinist take a crack at it? A radius cutter in a manual lathe plus a little polishing can make a pretty decent lens, unless you need aspherics.


Mike Halloran
Pembroke Pines, FL, USA