Precious Metal Job Shop

A San Diego Job Shop Specializes In Machining Gold, Silver and Platinum

by C. H. Bush, Editor
photos by John Semonish, Staff Photographer

Take any of the really difficult-to-machine materials such as platinum, gold, silver, titanium, MP35N or 303 stainless steel. Write a part spec that calls for a pin that has four diameters, the largest of which is .020", the smallest .010". Now drill a .011"-diameter hole in one location. Add a .009"-diameter crosshole. Finally put in some .010" slots, part off, deburr and inspect.

Do all of the above with tolerances of .0002" and you’ll have a good idea of the daily routine at San Diego, CA’s Johnson Matthey, Inc.

“We have many dedicated employees producing parts like that in the hundreds of thousands, mainly for customers manufacturing implantable medical devices,” says Johnson Matthey machining manager Glen Crews. “We machine all the materials mentioned, but the bulk of our work is done on some form of platinum, like pure platinum, platinum-iridium, platinum-tungsten, and platinum-nickel. I guess two things really set us apart from most job shops; one is our ability to micro-machine very small parts and our experience machining platinum, which is one of the most difficult metals to machine.”

Getting Started In Precious Metals

Overview of the Johnson Matthey Medical job shop, showing a wide variety of Citizen screw machines at work. In the foreground is Johnson Matthey medical products R&D machinist Vesko Jojic working with a Citizen Cincom M20.

“Actually, we weren’t a job shop that moved into machining precious metals. We were a precious metals supplier that moved into machining the materials we supply,” Crews explains. “Johnson Matthey is a 150-year-old international corporation headquartered in London, England. Our business was founded as a platinum precious-metal trading company. Over the years the company has grown to include a number of divisions that manufacture products primarily out of platinum or platinum-group metals.”

The San Diego operation is just a very small piece of Johnson Matthey’s worldwide operations, according to Crews. “In San Diego our biggest output goes into heart pace makers and electrophysiology products like heart stems and implantable pacemakers,” he says. “We got into machining such products about eighteen years ago when we were supplying platinum rod stock to a couple of companies who were making parts for pacemakers. One day a customer back in Pennsylvania asked us to supply them with finished parts instead of raw platinum stock. Johnson Matthey agreed and over time the business grew. They finally moved everything to our San Diego facility.”

Tiny Size Creates Big Challenges

According to Crews, most of his shop’s machining challenges come, not from complex part geometry, but from the very small size of the parts they produce and the types of materials they machine.

Glen Crews (standing), Michael Stone (left, seated) and Vesko Jojic discuss the best approach to holding and machining a .075" dia. part with a .015" dia. hole among its features.

“Usually the geometry of the parts we make is pretty basic,” he says. “The challenge is the size, because when you’re working in the dimensions we do, tooling is the key. Almost anyone can write programs to cut our geometries, but when you take it down to a part that is less than twenty thousandths in diameter and you still want precision, you’re in a different world altogether.”With micro-machining every little detail matters, Crews reports. “One of the things I learned early on in this business is you have to sweat the details,” he says. “With parts our size, everything in your machine has to be set perfectly. Your tool settings have to be exactly precise. If you don’t center your tools exacly right, you won’t be able to make the part.”

Virtually all of the parts produced by Johnson Matthey are made from stock that falls within a range of 1/8" diameter down to .085" diameter. As a result, Crews feels that making parts in the quarter-inch size range would be easy.

“You get parts up to a quarter inch and you have this nice big range of tolerance,” he says. “You can slap your tools in the machine, push the button and it’s easy. You can set a tool in a couple of minutes, but in our case the parts we make frequently are smaller than the specified tolerances, so things like tool setting, general machine set up and material conditioning are very critical. If you get a platinum or other type of rod that’s a little out of round, you’re not going to hold tolerances.”

Tooling Challenge

When sizes move down to the micro category, tooling needs change drastically, too, according to Crews.

Crews came to Johnson Matthey in 1992 because the company needed someone experienced in both Swiss screw machining and tooling. Crews had spent his entire career prior to joining Johnson Matthey working with his father machining miniature parts on CAM-style Tornos Bechler screw machines.

“I learned to program the CAMs, which has been a big help,” he says, “but my most important experience was learning about the kinds of tooling needed for machining small parts. If you don’t know tooling, you won’t have much success doing micro-machining.”

Crews points to the usually simple process of drilling as an example.

“Drilling at our dimensions is very difficult because there’s a limited selection of tools available,” he explains. “To make matters worse, most of our parts are not sized for standard-sized drills, so a lot of our drills have to be special made. Even so, our tolerances are very tight and our customers aren’t flexible in their requirements.”

Just finding suppliers for tooling suitable for micro-machining of platinum is a real problem, Crews says.

“First of all, you really can’t go to the big tooling manufacturers, because their research is aimed at creating tooling for larger-size machining, which is where the volume is,” he says. “If we go into a normal tooling supplier and ask for tooling that has a zero tool-nose radius, they look at us like we’re nuts. Yet, that’s what our customers demand and what we have to deliver. A Swiss-tool adapter for a regular diamond-shaped cutting tool just doesn’t do it for our kind of work. We use Swiss tools, which have a 90-degree shape. We solved our problem in two ways. One, we found a few companies who make the kinds of tools we need; second, we learned to make or grind our own tools when necessary.”

Developed Special Techniques

As in any specialized field, there are certain tricks of the trade that professionals learn in order to make their lives easier. In the case of micro-machining, two of the tricks Crews has learned are to produce miniature parts requiring virtually no deburring and to “part off” in a way that prevents the tiny parts from getting lost in the chips.

“Our customers want good parts without burrs,” he says, “and deburring a part you can’t see with the naked eye is an expensive proposition, so we have developed machining techniques that virtually eliminate the need for deburring. Ditto the problem of part separation. Trying to separate parts you can’t see from a pile of chips is tedius, time consuming and very costly. We’re able to part off without losing parts in the chips, which helps us be much more efficient.”

Equipping For Micro-Machining

If tooling is crucial to achieving high quality results in micro-machining, so, too, is having the right equipment, according to Crews.

“Before Johnson Matthey moved their job shop operation from Pennsylvania they already had elected to use Citizen CNC screw machines for production,” Crews says. “When operations moved to San Diego and I came on board, I had the opportunity to change the type of equipment we were using, but after going to some trade shows and looking into availability, I concluded we were well served to stick with Citizen. At the moment I believe we’re their largest customer on the west coast.”

Michael Stone, associate engineer R&D, checks the pick-off location of a part on one of Johnson Matthey’s new Cincom C16 screw machines.

Johnson Matthey will not divulge just how many Citizen screw machines they operate, but Crews says they operate almost every model the company makes that can handle their product size range.

“We have L10s, L16s, B12s, M20s, E16Js, L20s and some of the new C16s,” Crews says. “They’re all good and do a fine job, but my favorite, frankly, is the new C16. It’s a great machine for a lot of reasons, especially for our kind of work.”

What makes them so great for Crews?

“It’s the way they’re designed,” he says. “It looks to me like the designers were machinists themselves. With micro-machining there’s a lot of touch and feel and hand skills involved.With these C16s you have a lot of room to put your face in there with an eye loop and see what your tooling is doing. We think they’re one of the best machines ever made for micro-machining.”

Crews stayed with the Citizen machines for a number of other reasons, too, he reports.

“For one thing, we like the way they’re programmed,” he says. “Citizen has functions that make them easy to program. They have some macros for standard operations that really speed up programming. They also make tool setting easy and have multi-line programming and there’s front and back sides because of the sub spindle. Another thing I like is the commonality between models. They try to keep the same basic programming structure throughout all their models. For instance, we have one 1988 model and the programming on that corresponds almost exactly to the programming on the new L20s. That makes learning and training much easier. Of course, it goes without saying that they have the high precision needed to meet our tolerances, plus so far, after nearly twenty years, they’ve proven to be very reliable.”

A Smaller Future

Where does Crews see micro-machining headed in the future? “Smaller and smaller,” he says. “Our customers are demanding high-precision parts that seem to get smaller every year. Right now the C16 is doing a great job for us on really small parts, but we really don’t know where the future is headed. Basically, all I can say is smaller.”