The in-situ platinum polishing attachment for the Cad 4 diffractometer.

This is perhaps among the coolest, but alas unrequited mechanisms that I tried to build. While a Senior at U of I, a very strange combination of things fell into place. One, the School of Chemical Science's x-ray lab had an old Enraf-Nonius Cad 4 Diffractometer laying around. Second, a professor was looking for a way to accurately surface platinum. Third, I was looking for a job. Enter a project far too complex for a single undergrad to have even a remotely fighting chance of getting done and working: Using an x-ray diffractometer to orient crystalline platinum in such a way that one particular crystalline face can be polished to a finish good enough to do surface chemistry on. Wow! Look at all the stuff that I don't have a clue about- diffractometers, crystalline platinum, and grinding, all in one wholly impossible thing. At this point I was still in my 'oh, no problem' sort of mindset. In my overzealous imagination it all made perfect sense. All I needed to do was repair a 20 year old Enraf Nonius Cad 4 diffraction machine missing unknown parts and untested in almost a decade, design and build a custom floating head polishing system, find or build a control system for it, learn how to mount, orient, and operate the whole mess, and then teach someone else how to use it. Undergrad project? You betcha. The amazing thing is that it almost worked.

Spare Cad4 parts Step 1: Repair the Cad 4
The Enraf Nonius Cad 4 is an x-ray diffraction machine based on kappa (as opposed to four circle) geometry. This particular geometry allows the orientation of an object anywhere in 3D spherical space without having the sample totally enclosed by a circle. The benefit of this is that the top of the machine is totally open, allowing room for me to get a grinding attachment in. The problem was it had not been used in over a decade, and was missing parts. Enter the pickup truck and a couple of trips driving around the midwest to pick up other university's old destined-for-garbage Cad 4 bits. This photo shows an assortment of parts that I got from Northwestern, some of which ended up going into our Cad 4. The actual goniometer itself, in the upper right of the picture, is extremely heavy, probably on the order of 400 lbs or so. Scott and I would roll it around the lab on dowels, or else drag it on carpets, since we could not pick it up. The main bit missing was the HV tank, a gentle term for what essentially amounts to a pole transformer in a rectangular box. The repairs made to this machine includes the following: The HV tank, numerous other repairs to the x-ray generator, including rebuilding the autotransformer, replacing some connectors, re-doing the safety circuits, replacing the x-ray tube itself, rebuilding a flow switch and re-plumbing the cooling circuits.

The Cad 4 had a PDP-11 inside it to make it work, which is the card cage at the front of the picture. This needing nothing more than a good scrubbing to make it work again. I also had to spend some time with Scott Wilson, the lab's director, rooting around in the optimistically termed 'archives' to find the software for this thing, which originally ran on a VAX. Fortunately, we didn't have to set up the VAX to run this system, as at one point he had paid for the upgrade to PC-based software, and now we had a DOS application to talk to the diffractometer. It took my several months to get this going, including finding spare parts, getting cooling hoses installed, and driving around. While I was doing this I was also a full time student, and designing the rest of this thing as well.

The Cad4 with the grinder attached Step 2: Design the polishing head
This was the last project I did without the aid of CAD software. I designed this all up in Geoworks, making drawings using the vector-based drawing package included. I really miss Geoworks, by the way. It was a wonderfully obvious and easy to use piece of software. The part I designed is basically anything shiny aluminum in the photo above. The theory was that the polishing wheel itself (Brass wheel on the right) was floating on springs on linear bearings to the drive motor (black cylinder on right), which could be drive up and down on its cross member to change the applied force. The up and down motion was driven by a ball screw by the motor parallel to the ground, while the oscillating back and forth motion of the head was driven by the vertical mounted motor.

The School of Chemical Sciences machine shop did all the machining and helped me out a lot with the drawings for this. I needed to learn all about ball screws, worm gears, thrust bearings, motor controls, machining tolerances, and talking to machinists to make this work. The grinding equipment came together quite nicely. I had the benefit of having several other old diffractometers lying around to offer up parts.

The control rack from behind Step 3: Build the control rack
This rack contains the controller for the Cad 4, as well as the drives for the stepper motors used in the polishing attachment. The rack came from what was once part of Scott's VAX 11/750. At top is the DC speed control for the polishing motor, which was one of the only new things bought for this project which was not part of the machining. Next down are two stepper drive card cages, which came from a broken 4-circle diffractometer Scott had in his archives. Next down is the Cad 4 control cage and its associated wiring. The bottom of the rack had the original DEC branded power distribution board, which was nice to have.

The cabling to make it all get along Step 4: Wire the system together
This photo shows the rack where it lived during part of the development process. That laptop sitting there is another piece of surplus equipment, on which I did most of the mechanical design. That 386 and I have a lot of good memories. Have I mentioned how much I miss Geoworks Ensemble? The thing ran snappy quick on this 386.

At the left of the rack is the HV tank. Good heavens this thing was heavy. So heavy that it actually would sink into the tile if left in one place for too long. Getting this into the bottom of the Cad 4 was an interesting exercise in simple machines. The HV tank has two eyelets on the top, and we used a combination of 2x4s, metal rods, and little rollers to get it moved into place. Much levity was had rolling this thing around the floor. Helping Scott move heavy, fragile, and potentially very expensive equipment around his lab using ramps and levers is a very positive memory for both my brother and I.

Programming development equipment. I.e. some old crusty laptops. Step 5: Write some software so the thing actually does something
Here are my two vintage laptops. The left is my trusty 386, and the right was a 486. I'm just using the right hand laptop as a serial terminal in this photo. The drives for the stepper motors had an RS-232 port on them, and I needed to write a simple piece of software to make the motors do their thing in the proper order. This was a simple GW Basic program I ripped out in one night, featuring such simple commands as home, up, down, polish, and stop. When running the system, the left laptop talks to the stepper controllers, and the right runs the Cad 4.

Dust collection equipment. Basically a used, brokendown shop vac. Step 6: Solve other problems not necessarily considered when I set out
I overlooked dust collection in this. I figured that the surface I was polishing was going to be so small, who cares? However, it turns out that whenever you polish something the edges of the sample get rounded due to how the cut material gets distributed. To minimize this I chose to encase the sample in hard transparent epoxy using a mold and a custom head in the goniostat. This increased the surface area exposed to the polishing surface, but also created more dust. The nozzle of the collimeter on the Cad 4 is very small and quite fragile, and besides, it is not a good idea to have platinum and epoxy dust blowing around inside your x-ray equipment. Enter the dust collection system. The vacuum cleaner came from the physics dock, the same place where the projector came from. They had a huge pile of them, presumably at one point used to demonstrate something cool like hover crafts. Then I got some fine filter material (think good quality allergen furnace filters), rolled them into cones, and shoved them into the PVC tube. The dust from the polishing would be quite fine, and the vacuums were free, so it made more sense than buying a new shop vac.

The wheel and a test sample in place in the goniometer head Step 7: See how everything fits.
This photo shows the polishing wheel at top, over the goniometer head with the sample at the tip of the stick. At right is the dust collection nozzle, and in the foreground is the microscope used to optically orient the sample. The stick in the head in this photo is just a piece of metal at the right height to check the clearances on everything. This actually worked out quite nicely in making the tip of that stick shiny. The plastic bag at the back is covering the collimater and the photomultiplier tube assembly.

The whole system, as it was almost completed. Step 8: See it work
Here's the system largely complete, but before we installed the X-ray tube. There are spare tubes standing at the right of the Cad 4's enclosure. The two laptops are at the right, the control rack is full of it's goodness, and the thing is actually working. I believe this photo was taken at the same time as the previous photo was. The next test done on this was with x-rays that we actually used to orient a sample.

Step 9: Heartbreak
Just as I was moving into final stages of testing with this, I had to leave for Australia. I made some efforts to find one of my friends to keep working on this, but that didn't work out. The sponsor of this project, Dr. Andrzej Wieckowski, also tried hard to find a grad student to take over the project, but to no avail. Eventually the lab space that the Cad 4 was in needed to be used for a new machine, and this whole machine was scrapped, minus the grinding bits, which are somewhere around the University of Illinois. The problems requiring solving when I left were grinding, epoxy and polishing related. I designed a new counterweight suspension arm to better control the pressure, and was doing research into low-friction gas bearings. The epoxy and polishing related issues I learned a great deal more about while doing Solar Car stuff in Australia. I returned from Australia for my super-senior year, and made efforts at getting back into this project. Unfortunately, the project had floundered while I was away, and I was unable to complete it. I did, however, successfully repair the Cad 4, use it to orient test samples, and polish stainless steel sticks. Unfortunately, it never did surface platinum for surface chemistry.