Friden STW 10

The Friden calculators were very popular professional calculators in the US in the 1940's and 1950's. They were impressively large and fast, and built like tanks. The early ones like the 1941 Friden H8 (see video below) featured only addition and subtraction and were manually actuated. You would do multiplication and division in several addtion or substraction steps, following a simple algorithm. The later ones, like my 1956 STW 10, were electrically driven and featured automated multiplication and division. The last mechanical model, the SRW 10, had a square root function! Finally, in 1962, Friden introduced one of the earliest transistorized electronic calculators, the EC-130, and then in 1964 the EC-132 which added a square root function.

The Friden company was founded in 1934 during the great depression by Swedish immigrant Carl Friden, and operated near San Francisco in San Leandro, California. It became the city's largest employer. Unfortunately, after a long successful and inventive stretch under its visionary founder, it all went downhill fast when it was purchased in 1965 by the German company Singer, which was unable to capitalize on Friden's early lead in electronic calculators.

I bought my Friden STW 10 on eBay and it arrived intact (a rare thing for such heavy items from eBay). Although it was in good shape cosmetically, it was in horrible shape mechanically. The restoration was very arduous: most of my machine was frozen solid, necessitating finding the faults one by one and unlocking things manually using forceful persuasion (read: hammer and pliers). Then some adjustments were completely off. But I progressively revived it, bit by bit, as you can see in the videos below. That I did not have documentation at the time did not help either! Fortunately, I have found some since then, scanned it, and also made it available for download below.

Friden Calculator Video Playlist

Friden STW 10 Beauty Shot by Kevin Twomey

The inside of the machine is spectacular, and San Francisco based photographer Kevin Twomey made a beautiful picture of my STW 10 innards after the restoration.

Friden STW 10 by Kevin Twomey

Friden Documentation

There was just about nothing available on the net when I started repairing my Friden. Fortunately, after the restoration, I discovered an old fellow that still sold some copies of the manuals. The copies were expensive, incomplete, and of poor scan quality, but the that's the best I have found so far. Unfortunately he since passed away, so you can't even "buy" the copies anymore. So I have taken the liberty to scan whatever I had, and posted it below.

One of the most interesting document is the Friden W Line Mechanical Operations. This document tries to explain how everything works, and would have been invaluable if I had it at the start of the restoration.

The Disassembly Manual shows you how to take the major assemblies apart, including the backplate, which is not obvious at all.

Next is the Service Manual, which is the ultimate guide to adjustments and mechanisms, but very hard to follow. It assumes that you are a trained technician, already very familiar with the machine. It only shows small portions of the mechanisms on over 100 pages, out of context. It is not shown where they are located in the machine, and the cryptic naming is often the only clue you have about what they do. But with some persistence and close machine observation, I was able to figure out most of it.

The Friden STW Instruction Manual is the only original manual I own. It is a very nice users' manual, and teaches you how to operate the machine. I go through the manual and try the examples in this demonstration video, including doing the complicated square root algorithm at the end.

Restoration Tips

A good tool to have is a hand crank. If you want to make one yourself, know that the thread at the end of the crank is 1/4-28.

I am often asked for tips on how to restore a Friden. There are probably much more qualified people than me to answer these questions, but here is my answer to one of my viewers:

The Friden is the most difficult calculator or mechanical restoration I have done so far. Previous experience with restoring a mechanical clock, typewriter or a smaller calculator will definitely come in handy.

The simplest way to clean machines that are still in relatively good shape is to remove the motor, which is quite easy, and bathe the whole thing in Simple Green overnight. But that will only dissolve away stuff that’s still fairly liquid. My next favorite method for stuff that's stuck, but still moves under some moderate force, is using Nye 140B oil. It is expensive, but it's the only oil that I have found to be effective in this situation (and I have tried many). It is able to dissolve old, almost solid residue, and replace it with new oil in one fell swoop. Put some Nye oil around the articulation of the sluggish or stuck part, and try to force it to move, back and forth. Progressively it will free up. However, if parts are stuck hard, like in my case, it’s even more difficult. You might have to resort to using lots of force and WD-40, which I recommend avoiding as much as possible. WD-40 might be the only thing that will help you get the parts unstuck without breaking them, but once you have used it, you must immediately get rid of it. Clean with an alcohol wash, in Simple Green, or better, take the mechanism entirely apart. Even a tiny leftover trace of WD-40 will contaminate the oil, transform it into sticky goop over time, and clog everything back again.

Finally, the one and only way to fully restore a machine is to take it completely apart. Then clean the parts individually in ultrasound with alcohol. However, in the case of a machine of the complexity of the Friden, this is excessively difficult and risky. So in practice, you will find it more practical to identify which individual parts or sub-assemblies are stuck or malfunctioning, and take apart as much as you safely can, and use Nye oil (or, God forbid, WD-40) on the rest. The more you can take apart the better.

Now, if you take things apart, another major difficulty arises: timing. Timing refers is the relative rest positions of gears and levers when you reassemble the mechanism. You must make sure you understand and can adjust the timing when you put it back together, or it just won't work even though the parts are mounted correctly. Figuring out timing can be pretty hard unless you have the service manuals. Fortunately, I have since found them, scanned and uploaded them on my web site.

With that, your chances of success should be much higher than mine.

Good luck!

Friden Calculator Demonstration Videos

This is a full demonstration of the repaired Friden STW 10. It's way more capable than you'd think. At the end, I even calculate a square root.

This short video is one of my most popular videos. It shows a division by zero on the Friden, which produces interesting results.

The end of this video has great clip from the film "The Apartment", which shows a floor full of Fridens, typical of a large bank, accounting or insurance company installation.

Mechanical calculator music anyone? Hear the Friden play the Friden March.

The Friden March is simply 5551155511 divided by 1.

This video also has some really nice beauty shots of the machine, which I made for the National Geographic. And even zero divided by zero as a bonus.

Friden STW 10 Repair Videos

This is a the main video about the restoration, from the start when it was hopelessly frozen, to when I get it mostly working.

This video shows a multiplication repair I had to do before the Friden was filmed for a Japanese documentary. The documentary was about the contribution of NASA women engineers. Katherine Johnson famously used this very Friden model to compute orbits of the Mercury missions.

This video shows the repair and demo of an early, manually operated Friden H8, which I did with summer interns at the Computer History Museum.

This video shows the repair of a carry propagation fault that we discovered fairly late.