Friden Flexowriter - Hardware

Hardware

As a cutting edge device of their time, Flexowriters, especially some of the specialized types like typesetters, were quite costly. They were made with extreme durability. There were porous bronze bearings, many hardened steel parts, very strong springs, and a substantial AC motor to move all the parts. Most parts are made of heavy gauge steel. The housing and most removable covers were die castings. While the final Singer models did make some use of plastics, even they are quite heavy compared to other electric typewriters of their time. As a result the platen carriage is very heavy, and when the "Carriage return" key is pressed, the carriage moves with about 20 pounds of force and enough momentum to injure a careless operator. If used only as manual typewriters, and properly maintained, Flexowriters might last a century. When reproducing form letters from punched tape, the enormous energy input to the device made watching it a somewhat frightening experience. It also produced enormous noise.

Towards the bottom of the unit there is a large rubber roller ("power roll") that rotates continuously at a few hundred rpm. It provides power for typing as well as power-operated backspace, type basket shift, and power for engaging (and probably disengaging) the carriage return clutch.

Referring to the photo of the cam assembly (often simply called a cam; it was not meant to be disassembled), the holes in the side plates at the lower left are for the assembly's pivot rod, which is fixed to the frame. At the extreme upper left is part of a disconnectable pivot that pulls down on the typing linkage. When installed, down is to the right in the photo, so to speak.

Referring again to the part at the upper left, the mating part has a threaded mounting for adjusting cam clearance from the power roll. The irregular "roundish" part, lower right center, is the cam, itself. It rotates in the frame while in contact with the power roll. The surface of the cam in contact with the power roll had grooves for better grip. As the radius at the contact patch increases, the frame rotates clockwise to pull down on the linkage to type the character.

This particular cam assembly has a cam that rotates a full turn for each operation; it might operate the backspace, basket shift, or carriage-return clutch disengage mechanism. Cams for typing characters rotated only half a turn, the halves of course being identical.

Below the cam in this photo (hidden) is a spring-loaded lever that pushes against a pin on the cam. On the upper edge of the cam, as shown, is a little projection that engages the release lever, which is at the lowest part of the image; it's an irregular shape.

When a key is pressed down, it moves the release lever and unlatches the cam for that letter; the spring-loaded lever pressing on the pin rotates the cam until it engages the power roll. As the cam continues to turn, increasing radius rotates the cam's frame slightly (clockwise in the photo) to operate the typing linkage for that character.

As the cam continues to rotate, the spring-loaded lever pushes on the pin to move it toward home position, but if the key is still down, the cam (now out of contact with the power roll) stalls because the projection on the cam catches on another part of the release lever. The cam stalls until the key is released. When released, the lever catches the projection so the cam is now in home position. This is like a simple clock escapement, and prevents repeated typing. (The "key-down" anti-repeat stop can be removed, so that fast repetitive typing can be done, but this change is difficult to undo.)

Carriage return was done by a non-stretch very durable textile tape attached to the platen advance mechanism at the left of the carriage. For a return, the tape wound up on a small reel operated from the drive system through a clutch. A cam engaged the clutch; it was disengaged by the left margin stop, perhaps directly, perhaps via another cam. (Info. needed here!) A light-torque spring kept the return tape wound on the reel.

The basic mechanism looks just like an IBM electric typewriter from the late 1940s. In fact, some Flexowriter parts are identical in fit and function to the early IBM electric typewriters (those with rotary carriage escapements, a gear-driven power roll, and a governor-controlled variable speed "universal" (wound-rotor/commutator) motor.)

The early IBM rotary-escapement proportional-spacing typewriters (three wheel rotary escapement, spur gear differentials) had code bars to control the amount of carriage movement for the current character. They were operated by the cams. However, the Flexowriter's mechanical encoder was a very different and far more rugged design, although still operated by the cams.

Flexowriters (at least those prior to 1969) do not have transistors; electrical control operations were done with telephone-style (E-Class) relays, and troubleshooting often involved problems with the timing on the relays. Another reader has also found that the timing settings of the various leaf switches (such as in the tape reader) are also important.

The screws used in the Flexowriter were unique, having large flat heads with a very narrow screwdriver slot and a unique thread size and pitch. This may have been a conscious decision. Another reader found that standard 4-40UNC threads appear to fit some of the cover-attachments; internally, the headless set-screws require fluted Bristol keys, which are not commonly available in Great Britain.

There is a holder for a large roll of paper tape on the back of the unit, with tape feeding around to a punch on the left side, toward the rear. The tape reader is on the same side, toward the front, and is essentially identical to the reader shown on the front of the square housing in the photo of the auxiliary reader. The right side of a Flexowriter has a large (~1") connector for hooking the unit up to computers and other equipment. Depending on the model, this connector may be wired in many different ways.

At various times and in various configurations, flexos came with 5, 6, 7 or 8 channel paper tape reader/punches, could have several auxiliary paper tape units attached, and could also attach to IBM punched card equipment.