The History of Single Point Diamond Turning Part 1 with Dr. Jeff Roblee

In this video ASPE Fellow, Dr. Jeff Roblee, talks about the early days of diamond turning starting with the precursor company to Precitech - Pneumo Precision. Pneumo Precision was started in Keene, NH in 1962. Pneumo Precision was known for making the type of precision stages needed for single point diamond turning machines. Jeff talks about the early days of diamond turning at Lawrence Livermore National Labs, Carl Zeiss, and Polaroid and how diamond turning enabled unique and new optical designs. 

Transcript:

Savannah: Hi, I’m Savannah Jones and today we're speaking with Jeff Roblee, Divisional Vice President of technology at Precitech in New Hampshire. Let's talk about Precitech and the solutions you're providing for your customers.

Jeff: Precitech started out as Pneumo Precision back in the 60s already. It's a predecessor company, and it was a Pneumo Precision split off over the time since the 60s. It went through several different ownerships. The original founder of Pneumo Precision was a fellow named Don Bramm, and after his non-compete expired, he started Precitech and both Pneumo Precision and Precitech were famous for making their bearings and their bearing rotary stages. Precision motion. They're very linear stages. And one of the biggest needs for precision motion is in manufacturing of optics by means of diamond machining. And diamond tools really have a magical property with certain materials, particularly non-ferrous metals, but also different plastic and synthetic materials where you can create an optical surface wherever you place the diamond tool relative to the work piece and you get an optical finish that doesn't require any polishing from direct machining. That's very unlike traditional optics, where you grind and polish glass, for instance.

Savannah: And why is that important?

Jeff: So you can make better and better optics, the better and better you can position the tool relative to the work piece, because wherever that tool is, that's where the surface is going to be generated on the surface. And so that's driven the precision of our ability to position the tool. So Precitech is all about in the end, taking the pieces originally developed at Pneumo Precision and at Precitech for precision motion control to actually position a diamond tool and also positioning a work piece that's spinning at high speed, very accurately and bringing the two together machining material off at the end of a finished optic, which doesn't require any polishing at all.

And also the beauty of diamond turning is that you have a range of different tool shapes. And you can make very structured surfaces and odd surfaces that you couldn't do by traditional optics manufacturing. And I would say the advent of diamond turning drove the acceptance of asymmetric optics. Before then when I started my career in the late seventies, it was pretty unusual for people to design aspherical optics. With the advent of diamond turning, we can diamond turn an asphere just as easily as a spherical optic, and then we can actually, we've gone beyond that now to do more and more complex shapes. So we've focused on taking these building blocks, Precitech. Historically, before my time in the sixties, even a precision motion control and applied it to making optics. And that's our primary focus today. And we have offshoots in the Sterling product line for making ophthalmic lenses using the same fundamental positioning of a tool with respect to the work piece.

Savannah: Jeff, you've been involved with diamond turning since the early development of LLNL, which you mentioned earlier. What would you say are some of the challenges your customers working on advanced applications are facing in manufacturing optics using single point diamond turning?

Jeff: The advent of, as I was talking earlier, the proper name now is single point diamond turning as opposed to multiple point diamond tools like grinding tools. We actually have a precision, a fabricated single crystal diamond. It's a gem quality diamond that's used to create the surfaces and to cut these nonferrous materials on our machines. And the early research into this dated back to Philips in the Netherlands in the late 40’s and 50’s, because they could precision shape diamond crystals, you know, close proximity to Amsterdam and Antwerp helped with that. And the diamond industry there.

One of the first pioneers of using diamond tools on a machine tool to make precision artifacts, not necessarily optics was Lawrence Livermore National Laboratory, and I was fortunate to have done my summer internship as an undergraduate in 1977 is when I started my relationship there. Livermore started with single point diamond turning already back in the mid-sixties, I'd say. And so I was fortunate enough to start my career with some of the very early pioneers in the United States in this technology. And we've taken it from there. And I have to say, I stayed at Livermore through 1990. I spent some time at Carl Zeiss in Germany, also doing diamond turning, then moved on to Polaroid in Cambridge, also doing diamond turning and optics manufacturing.

Everywhere I went, I was a customer of Precitech. And in fact, Lawrence Livermore National lab is part of the Department of Energy. And they had actually got funding in the 1979, 1980 to do technology transfer to private industry. Because from the department, it was still part of the Navy. Because at that time anybody that wanted to diamond turn anything they had to home build a machine. So we were doing custom made home built machines at Livermore. There's a few of the other early pioneers Union Carbide, even Zeiss in Germany. Polaroid in the early 70s was making home built diamond turning machines. There was no place you could go and buy one. There was no commercial market for that. And so my colleagues at Livermore starting in ’79 or’80 did this, had this program called the machine tool technology transfer program, where they worked with private industry to transfer the technology developed at Livermore. Through that time, private industry to make commercially available diamond turning machines. And one of the companies they worked with was Pneumo Precision and that was the predecessor to Precitech. And so the first diamond turning machines that Pneumo Precision made and sold were to Lawrence Livermore National laboratory. There was a collaboration already going back to Pneumo Precision and all these places I worked, I was either a customer of Pneumo Precision or Precitech. And so it became kind of a no brainer to finally join Precitech in 2002 is when I started here. Because I had been working with them for decades and it was involved in some of the first machines that Pneumo Precision made for the diamond turning market.

Savannah: Let's hear more about those early days.

Jeff: The early days, it was purely two axis machining, making it axi-symmetric surfaces, surface of revolution. So aspheres, as we call it. Finally, Fresnel optics. And that was the main Forte of what we were doing at Livermore also. Then I got involved in this project called the large optics diamond turning machine project and it's a very large special purpose lathe for chemical laser optics and is still considered the most accurate lathe ever built of that size 1.65 meter swing. We developed a fast tool servo for that. It was one of the first fast tool servos. And at that time it was a very short travel, only 2 and 1/2 microns and it was intended to correct for repeatable errors in the lathe, not to create unique shapes to it. But in the end, after we finished the optics on LDTM it was part of Air Force weapons lab program. We started experimenting, making freeform surfaces on that same lathe, using fast tool servos and also controlled motion of the z-axis as a function of angle the spindle, so xzc turning or some people call it slow tool servo turning. So in the early days of that, we were able to make wave front correctors as one of the first applications. Another one of the the first applications for freeform surfaces at Livermore was to simulate turbulence in the atmosphere. So like a wave front corrector for lasers propagating through the atmosphere and those were quite successful and took a lot of time and a very expensive machine. Even in my time at Zeiss, we would occasionally do three axis turning. We have two linear axes, an x and z-axis, the axial radial axis of motion. But you might combine it with a rotary axis the B axis that could just keep the tool pointed normal to the surface in a lot of the early diamond turning machines. In fact, DTM 1 and 2 at Livermore had a B axis to do tool normal machining, and that was because you couldn't get good quality diamonds. So one of the largest error sources was the waviness on the edge of the diamond. So if you always use the same point in the diamond that eliminated that error source. As diamonds got better there was less need for that and it kind of went away. But during my time at Zeiss, we were doing some of the first refractive lenses for infrared optics, for instance, kinoforms, and direct machining of diffractive structures on top of a refractive surface in germanium, these are transmissible lenses in the infrared. We were doing some of the first diffractive lenses for infrared there during my time there in the early 90s.

Savannah Jones: As you mentioned, you've been in the industry in one form or another since the 70s and worked with many companies, and eventually you made your way to Polaroid in the 90s.

Jeff Roblee: All the time I was at Zeiss we just did axi-symmetric surfaces that whether they're aspheres or diffractives. Finally, we started doing some freeform surfaces at Polaroid and the first commercial use of a true freeform surface was in the SX-70 camera which predated me and my time at Polaroid when I joined them in 1994. Back in the 80s it was a very successful camera and they had a special focusing lens that was represented by Fifth order polynomial. And they did that by raster grinding and a lot of polishing in steel. Now with the diamond tool, that was the only technology at the time, so they measured and polished. It could take weeks and weeks to converge on this crazy shape. That kind of surface, a more general freeform surface, the needs for that have been growing in recent years. In fact, the time I joined Precitech in 2002, we were wanting to do more odd, freeform shapes more quickly, and there's a whole class of them like these focusing lenses called Quintix or some kind of Alvarez lenses for focusing.

Savannah Jones: Let's explore that more. The beginning of freeform shapes and some of their uses.

Jeff Roblee: It’s an extra degree of freedom for an optical designer and really designing non axi-symmetric surfaces generally for freeform surfaces. The design tools for optical designers weren't there in the 90s. Polaroid did a lot of their own development in the 80s on it, but you couldn't buy commercial optical design software, so you didn’t see many demands because people didn't know how to design them into it. But once they got some of the tools for designing it, they had these freeform surfaces. They had no axis of symmetry. Now it's by definition relaxed some of the design parameters. So that they could either improve the performance of an instrument or an optical system or make it more compact. That was important for Polaroid cameras because they had to be very lightweight and compact and image across a large piece of instant film. As you fold optics, you have to correct for the image distortion and the best way to do that was with freeform optics. So at the time I joined around the time I joined Precitech in 2002, we'd been looking at freeform surfaces that are close to being axi-symmetric but deviate a bit. Toric lenses might be an example where you have astigmatism, power in one direction different than the other direction. And there you can use a fast tool servo which Precitech and Pneumo Precision actually started the first commercial applications of fast tool servos for direct lathing of contact lenses using fast tool servo in the mid 90s. And this allows very rapid production of non axi-symmetric surfaces by rapidly positioning the tool as a function of angle. But also if you don’t need the longer travel and the expense of a fast tool servo, you can use the main z-axis of the machine. And we were calling that slow tool servo. I don't really like the name because the slides are still moving pretty fast. So I like to call it xzc turning because it’s three axis turning, you can create a whole class of freeform surfaces that are close to axi-symmetric. So it depends on the excursion. We've done some mild toric surfaces up to 2000 RPM using the z axis, moving in and out twice per revolution.

Savannah Jones: So now it sounds like the processes are getting simpler and more streamlined.

Jeff Roblee: So that was just starting to catch on when I started here in 2002. Now that brought the cost down for making molds or optics directly for mild freeform surfaces. By almost an order of magnitude because you could just do it on a normal turning machine just using the extra axis, the c axis, just the rotary axis of the work piece. Or I would tell people anything you could do with xzc turning, you could do with a fast tool servo so long as you stay within the travel limits of the fast tool servo, but you can do a 10 to 15 times the speed. So it's a speed thing. There's another class of freeform surfaces where you can't use xzc turning one rotary axes and 2 linear axes. The more general case is using three linear axes x, y, z and and again, starting in about just before I joined Precitech in the late nineties, Precitech started coming out with a machine with a vertical linear axis and two horizontal axes. There you can position a spinning tool we call that fly cutting. The diamond tool spinning, a single crystal single point tool, but spinning. Then you can move that over the surface and create very arbitrary, freeform surfaces like one application is an F-theta lens which is used to focus for laser printing or laser scanning. But if you want to take a spinning laser and focus it on a piece of paper to write or scan on, it requires a lens to take that sweeping laser beam and focus it down to a tight spot on a piece of paper. And that's called an F theta lens. It's a very crazy, freeform shape. Large changes of shape. And the only way to do that was with freeforms. You can do that by xzc turning. And so it's applications like that. Early days of projection television helps with some crazy freeform surfaces. We couldn't do it by spinning the workpiece. You had to do it in 3 linear axes. There's two classes of freeform surfaces I like to talk about, and Precitech does both, and we've been advancing those a lot in the last 20 years since I joined Precitech.