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 additions and subtraction and were manually actuated. The later ones, like my 1956 STW 10, were electrically driven and featured 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 packed 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 a combination of cunning and forceful persuasion (read: hammer and pliers). Then some adjustments were completely off. But I revived it bit by bit progressively. See several videos below. That I did not have documentation did not help either, but I have still found some, scanned it and also made it available 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 the 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 found an old fellow that still sold some copies of the manuals. The copies were expensive, incomplete and of limited quality, but the that's the best I have found. 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, mostly out of context. You have no idea 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 which is not a copy. It is a very nice users' manual, and teaches you how to operate the machine. I follow the examples in this manual in my demonstration video.

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 the 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 Nye 140B oil. It is expensive but it's the only oil that I have found effective, and I have tried many. It has been a very effective method 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 actuate it back and forth by force. Progressively it will free up. But if parts are stuck hard, like in my case, it’s 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 works great at first, but once you have used it, you must immediately get rid of it with alcohol, simple green, or better, taking the mechanism entirely apart. Even a trace leftover will contaminate the oil,form a sticky goop over time, and clog everything back fairly quickly.

Finally, the one and only sure way to truly restore machine is to take the machine completely apart. Then clean the parts individually in ultrasound with alcohol. But 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, and choose to take apart, use Nye or WD-40 depending on the case. The more you can take apart the better.

Now if you take things apart, another difficulty arises: timing, which is the relative positions of gears and levers. You must make sure you understand and can adjust the timing when you put it back together, which 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 one is one of my most popular videos. It shows a division by zero on the Friden, which produces intersting 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 I made for the National Geographic. And zero divided by zero as a bonus.

Friden STW 10 Repair Videos

This is a full video of the restoration, from the start when it is completely frozen, to when I get it mostly working.

This video shows a multiplication repair I had to do before it 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 earlier manually operated Friden H8, which I did with summer interns at the computer history museum.

The Friden calculator makes music!

We repair a carry propagation fault that we never knew we had.