This weekend I’m upgrading the site to one of Laughing Squid‘s Cloud Hosting plans.
You may notice some weirdness with the blog and forums as the new DNS records propagate and I fix minor migration issues.
The good news is, if you can see this post, you’re looking at the new site!
Welcome to Part 3 of the Diamond Chop Saw build. In this installment I’m going to focus on the construction of the mechanical aspects of the saw structure, motor attachment, vacuum chuck, and splash guard. This is a picture-heavy entry…
After thinking for a while about how to build the saw, I decided that it would be best to have the blade move only in the vertical axis, and the workpiece move horizontally in two axes. This led to the overall machine design which consists of a vertical column with pivoting cutting head assembly, and a workpiece holder that has two axes of horizontal motion.
Completed Dicing Saw
I wanted to ensure the motor and blade had a rigid, heavy mounting structure to reduce effects of vibration and flex on cutting performance. I decided to mount the motor using the original mounting flange from the hard drive enclosure since it was nicely machined to match the motor flange. I used a hacksaw to cut out the shape roughly to size, then straightened up the edges and machined a mounting recess on my milling machine. The L-shaped piece of aluminum is 1/2 inch thick which gives lots of weight and provides sufficient thickness for mounting the bearing while preventing motion orthogonal to the bearing axis.
Cutting Head Assembly
Another view of the cutting head assembly. In the upper left hand corner is the pivot bearing. The bearing is held in place with a set screw that goes through the L-shaped aluminum piece. Along the bottom edge of the black hard drive enclosure portion I attached a strip of white LEDs to help light the work area. RTV Siliconeis used to seal the electrical contacts from water that migt not be caught by the splash shield. At the lower left hand corner of the aluminum plate is a rounded off screw. The cutting depth adjustment micrometer pushes against this rounded off screw. Pushing against the aluminum would be less accurate (aluminum would become unevenly worn).
Cutting head assembly (rear view)
At the top of the column on either side is a hole for the screws that hold the pivot bearing (also from a hard drive) in place. Luckily the one I used has 4-40 threaded holes on either side. A screw on each column holds the bearing in place, and then the rest of the column assembly and adjustment plate are attached resulting in a good alignment of the column to the bearing.
Pivot bearing/column mounting detail
Controlling the depth of the cut is critical, as my cuts will be as small as 5 thousandths of an inch deep! I mounted a micrometer head to a plate on the back of the column which controls the height of the cutting head assembly.
Rear view of the column and depth adjustment control
Now for a little detail on the vacuum chuck… The chuck is made from two 1/4 inch plates of aluminum. The top surface has a shallow set of trenches cut to distribute the suction across the bottom surface of the glass plate used for holding parts. The lower plate has a deep trench cut in it to distribute the suction to the three small holes drilled on the top plate. The whole thing is held together with screws and sealed with silicone. I made a set of hose barbs (one is pictured below) so that I can use 1/8 inch vinyl tubing to connect to my vacuum pump. The barbs were made by turning down 10-32 stainless steel screws on my lathe.
Lower half of vacuum chuck with custom-made hose barb
The last major component of the saw is the splash guard. This actually took a fair amount of effort to make, as I broke pieces more than once and had to start over. Essentially it is a two-piece design with a thick piece screwed to the cutting head assembly, and a thinner piece which screws onto the first. I used a heat gun to soften the plastic and carefully mold it to the shape of the face plates. I then glued the curved section and the outer face plate together using epoxy and while not very pretty, it holds together well.
Splash guard on the saw
This weekend I am attending the European hacker conference Hacking at Random. HAR takes place every four years at a former socialist youth-camp about an hour away from Amsterdam in the beautiful Netherlands.
Rather than fly directly to HAR, my wife and I decided to make a larger vacation out of our trip, and we have been busy touring Europe for over a week now. We still have over a week left, so expect slow updates until I return and have a chance to catch up!
10, 20, and 5 mil thick alumina substrates with 50 ohm transmission lines
In part 1 I gave an overview of what this project is all about. In this part I will describe the basics of the machine and some of the reasons I made the design choices I did. To start with, I wanted to do this on as small a budget as possible. The main project for which this machine serves ends up being a real money pit, so I have to budget accordingly. Hence the use of hard drive parts and scrap metal. Total spent so far is about $60.
When I first thought about how to cut these little pieces of ceramic, it seemed that there were a few elements that would be tricky on a budget. First thing I did was try and figure out how commercial dicing saws work. Certainly Intel and others have figured out a good way to slice ‘em and dice ‘em a long time ago… And they did.
Tricky thing #1: Holding the substrate while it is being cut.
After a wafer full of chips is finished being made, it is mounted onto a wide stretchy tape, creatively named “dicing tape.” The tape is pulled over a frame and then the wafer placed on top. Next the taped wafer goes into the dicing machine where it is cut by an insanely fast spinning diamond encrusted blade of blingy wafer death.
To keep the wafer from heating up (chips generally don’t like heat) water is sprayed at the cutting surface. This also helps to wash away crud generated by cutting and to prolong blade life. Once the wafer has been diced into individual chips, the tape is exposed to UV light or heat. The adhesive on the tape is made to become less sticky when exposed, and at this point the chips can be easily removed with tweezers, or an automated pick-and-place machine.
My first thought was to try and get some of this tape and use it in the same manner, but for smaller pieces. Then someone at work told me about something far more cool, with a far better name, something called Crystalbond! Crystalbond is essentially a mounting adhesive designed for exactly what I want to do. You simply heat it up, it becomes liquid, place the part in the puddle, and then do nothing until it cools off and then solidly holds your part. I managed to find 5 lifetime’s supply on eBay for dirt cheap, but several other places sell it. Anyway after the parts are cut you wash it away with acetone and you are left with clean diced parts.
Tubes of Crystalbond mounting adhesive
Okay, so the part can be held, but I didn’t want to have to glue a part to my machine every time I wanted to cut something. So instead of gluing the part to the machine I decided to glue the part to small pieces of glass which are a convenient carrier and can be used with my hotplatethat I built for my wire bonder.
Hotplate for thermosonic wedge bonding
So now I’ve got a piece of easy to handle glass, with one or more substrates to dice which has to be mounted to the machine. I could use tape, a temporary adhesive, or clamps, but why? I just put together a digitally controlled vacuum pump for some composites work, so why not make a vacuum chuck? And even better, I mounted it to a precision X-Y dovetail slide that I purchased on eBay for cheap. Now I can easily position the glass, reposition if necessary, and make measured cuts my moving the X-Y stage and measuring at the same time with a runout gauge. This allows me to make cuts that are accurate to 0.001 inches.
X-Y positioner I bought off eBay
A note here regarding XY stages… I chose specifically a dovetail style positioner because unlike the more common linear bearing style slides, a dovetail slide has static loading. The benefit is that there is a much greater resistance to vibration and since I am grinding, I want as solid a mount as possible.
Tricky Thing #2: The Blade
This is really a compound Tricky Thing, a combination of finding the blade, holding it, and spinning it. First a little background on dicing saws and blades…
Wafer dicing used to be done (and still is, especially in research situations) with a diamond scribe, basically a pencil with a diamond at the end. A small scratch is made along the crystal plane of the wafer and then carefully bent until a long, very straight crack is made through the wafer.
The same can be done with alumina substrates, although since it is not a mono-crystalline structure, the crack won’t be as straight or as predictable. Scribe dicing is a relatively labor intensive task and chip manufacturers HATE labor, but even more than that they REALLY HATE any time that an actual person touches a wafer.
Wafer dicing today is usually done with a very thin diamond abrasive blade that grinds away the metal or semiconductor until a cut is made. It is nearly identical to the way you might cut tiles when doing a counter top in your kitchen but on a much smaller scale. When cutting tile, if the blade wobbles a bit or is not centered perfectly, you are not likely to notice. With the alumina substrates I’m working with, the pieces are 20-40 times thinner. This implies that any vibration, wobble, or eccentricity errors can cause problems.
Commercial wafer dicing machines use high speed motors that are carefully balanced and rather than using ball bearings, employ costly air bearings. These are essentially out of reach for hobbyists and really not necessary. What is necessary though is a way to hold and spin the blade accurately. Dicing blades are thin, and the thickest ones I could find on eBay were 300 um wide. At 4.6 inches in diameter, a a very large inner diameter, they are also hard to accurately mount on a typical spindle like that found on a Dremel tool.
Diagram depicting blade mounting: Part A shows the original platter and spacer configuration, Part B shows the modifications I made, Part C shows the blade mounted.
All of these issues led me to use a hard drive motor and platters to spin and hold the blade. Hard drives have very long service lives and need bearings of the highest precision. The mounting of the platters is also done in a precise way, as any imbalance would shorten the bearing lifetime and result in undesirable operation.
To make a long story short, I removed (and reused) the spacer ring between the two platters of a hard drive, and reduced the radius of one platter to 3.5″, the inner diameter of the blade. You can see in the picture that the two platters are stacked and there’s a nice surface for gluing the blade down. Machining the platter down was not easy with my tiny lathe, and it ended up being out of round by perhaps 10 mils. It works to roughly locate the blade, but I will need to tack the blade down, measure, adjust, and finally glue into place. 10 mils out of round is really bad because the thickest substrate I’m working with is 10 mils thick. That means that one part of the blade would never actually do any cutting!
Blade test fitted to the saw.
Tricky Thing #3: Driving the motor
This seemed to be slightly daunting at first. Hard disk motors are typically some kind of brushless motor and require special circuitry to run. I imagined that I would have to build a circuit, or use a motor speed control from a radio controlled plane, etc. It turns out though that the main circuit board in the hard drive I’m using is dumb enough that even though it has had the equivalent of a frontal lobotomy, it just keeps doing it’s job. A couple other hard drives I tore apart did not do this.
Motor Control Box
The box in the picture above shows the hard drive main circuit board and below that, a 12v/5v switching power supply. It’s pretty basic and at the flip of the switch on the front panel, the DC supply is connected to the motor driver and voila, the motor spins up.
Schematic Diagram for the Motor Control Box
A little over a year ago, I became an Uncle.
This is my nephew, Harrison, doing what he does best – being cute.
For his first birthday, Harrison’s Mom wanted to give him something really special. Not just an ordinary toy for a one year old, but something strange and wonderful, tactile, interactive, unique. Thus was born the idea of an “electric box”, an electronic contraption full of switches, lights, buttons, knobs, levers, and sounds.
An elite task force was assembled to create this special gift, codenamed “Harrison’s Box”. The team consisted of Grandpa, the Woodworker, Jeff (alias mightyohm) the Engineer, and Kylie, the Project Manager.
Upon defining the project, we immediately jumped into phase one, Procrastination. Deliverables were met, and as the birthday loomed closer, we eased into phase two, Git ‘er’ Done.
Supplies and materials were ordered, wood chips started flying, and soldering irons blazed. A short time later, the front panel was realized:
Harrison’s box consists of (clockwise from the upper left):
Almost all of the electronic components, including the arcade buttons and joystick, were sourced from All Electronics. A few odds and ends came from my junkbox.
The wiring is point to point – zipties and hot glue keep all of the individual wires in place. Here’s a shot of the wiring for the pushbuttons and the joystick.
The buzzer consists of the guts of a cheap bicycle buzzer and a single C cell battery to power it. Some creative wiring allows a pushbutton elsewhere on the panel to control the buzzer.
I salvaged a few high brightness red LEDs from a surplus automotive taillight assembly I picked up at Weird Stuff a few years ago. A 5 Watt power resistor I had in my junkbox limits the current to the LEDs to a bright but not blinding level.
The whole box (with the exception of the buzzer, as noted above) is powered by a pair of AA batteries.
Finally, the big day arrived, and it was time to present Harrison (and Mom) with his gift:
Initially the Box was met with some skepticism. Perhaps Harrison was dwelling on the simple question: Toy or thermonuclear device? Understandably, there were very cautious button pushes at first.
Moments later, knobs were being turned, switches switched, buttons pushed, and Harrison had learned how to use the joystick. Look out Steve Wiebe!
The front panel mounts to a small stand that conceals and protects the wiring while also giving Harrison something to hold onto while operating the Box.
I’m happy to report that Harrison’s Box was a success.
Check out more pictures of the box on flickr.
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