RGB - Corona Special Colors

Special Coronas!

The Corona Special's in color - the three Special variants with a plain color all-over made from 1928 to 1930. The finish was then changed to colored panels on black.

Red, Green and Blue - in a row:

And un-folded opened up, ready to type:

The red one was by far the hardest to find. The Database has too few entries to be able to say much statistically, but judging from the number of galleries the red indeed seems the rarest color.

These colored Corona Specials were probably mostly sold to US consumers - most specimens have US keyboard layouts. They are relatively rare outside of the US. Regardless of region; the colors did make a relatively low-cost and by then somewhat outdated typewriter more attractive.

That makes this here blue machine a bit more special - it has an export, international keyboard. The other two have an American keyboard and will have originally been sold in the US, but this blue machine was exported and purchased around 1930 by a Dutch consumer. Perhaps a Corona Special was not the greatest writing machine that could be bought in 1930, but relatively afforable it did come in a very nice color - good choice! :-)

Timing - Marchant XL

The de-rusted Marchant XL mechanism is together again (for the umpteenth time ;-) and now looks to be timed correctly. After a few tries the taking apart and re-assembling becomes easier. For the XL the interconnections between the various sub-mechanisms is unfortunately so that to e.g. change one gearing tooth, the whole drum, carriage and carriage race have to come off. And then also at least one side-wall must come off. And to remove (and replace) the carriage race the carriage-indexing rod has to be snuggled-in at the same time same as the counter-slider - these cannot be done later, it all has to come together at the same time. After dojng this a few times, it all starts to make sense and doable :)

The machine assembled without its main covers (and much cleaner than it was!):

The more interesting and tricky bits are better viewed from the back of the machine. Fortunately the large pot-metal carry-drum of the counter was relatively fine. These can swell and then foul the rest of the mechanism, so had expected to have to re-manufacture this. Fortunately this specimen is still fine, blockages were not due to this drum. Instead for example the main drum-axle was simply rusted firmly stuck inside its right-bearing - hadn't seen that before!
 

The counter carry-drum, the reversing gears, the counting-vane, the carriage interlock and of course the main-drum have one correct meshing. To get this right seemed a bit daunting, but fortunately the machine contains hints on the correct meshing.

To start with, there is one notch on the carry-drum that must line up with a vane on the direction-switch rod. It's at the very left when looking at the back of the machine:

This gets the carry-drum correctly oriented. Then the gear-train that comes off the main drum also rotates the carriage interlock. This interlock can be seen from the front; a cut-out that permits the carriage to move when the machine is at rest-position. That correctly orients the main-drum driving gear-train.

Then a tricky bit is fitting the direction reversing gear that also drives the carry-drum. It has again one (1) correct orientation. This connects the carry-drum and carriage interlock - if both are still correct after meshing this sliding gear, then it is mounted right. This gear has a few narrowed, tapered teeth to enable the sliding-over between gears - this sliding/switching will only work when things are mounted exactly right:

The little counting tooth (front) is fitted onto its rod with the vane pointing down. 

 

Another tricky bit is engaging the counting-slider rod with the carriage. Slide the carriage in to almost its left-most position and then push the slider rack to engage the transfer gear. After a few tries this usually works out - easily checked because the counting vane must smartly hit only a counting wheel gear when the carriage is in a locked position. 

The counter reversing switch and its sliding gear mechanism is very finicky - it needs the main crank to be just right when locked in rest position - some tweaking/pressing home was needed of the tapered pin.

The main drum orientation is relatively easy - the cut-out of the full-turn gear must point up.

All this being done, so far the machine works all correct. It calculates fine and adds, subtracts, multiplies and divides. One remaining function however that still does not work is the overflow bell - after dealing with the timing, that should be a doddle to fix. (Right?)

In the meantime, started sprucing up the covers. Cleaning and polishing of the decimal markers and brightening the wonderful nameplates. The large nameplate on the back of the machine polished up quite well and the dark green fond came back too :-)

The extending segment drum - Marchant XL

The drum of the XL is very different in mechanism as well as construction from that of a pinwheel calculator; instead of castings with lots of channels with sliding pins, the drum is built up entirely of stampings. Unfortunately these were blackened steel, so vulnerable to rust. After a lot of oil and working (forcing) some parts, it all started to move. (Fortunate because much is riveted together.)

The drum with all the segments visible in retracted state.

And the drum with the segments extended, teeth out:

This is the early version of the extending segment with sliding geared-sectors. I.e. the segments have a long stem that slides in- and out between studs/pillars. After about 1930 the design was modified with the segments hinged. The segments then rotate around one pillar - making them probably much lighter to actuate. (This lighter-actuation probably also enabled Marchant to do away with the main crank-handle pull-out lock later. The early XL's need to hard lock the setting-dials right when the drum starts rotating. A lighter, later-actuating mechanism could make do with only the hard-lock that kicks in around 5 or 10 degrees into the turn. Then only a detent to 'feel' the rest position is enough for the main crank - easier to use.)

An overall benefit of the extending segment mechanism is that the levers can remain stationary (and can thus have a large grip), and also that the teeth can be properly shaped as involute gear. I.e. driving the register should be much smoother/quieter than with pinwheel pins.

(Yet another benefit, probably the aspect that was the most important for the Marchant company, was that it unlocks the ability to do keyboard-setting of the drum. Actuation is light enough to make that possible - and in the early 1920s Marchant really needed an answer to Monroe's fast keyboard-setting for number entry.)

For now, this particular drum seems functional again and mounted back in the machine it correctly added 5 to the expected position on the carriage register.

There's no revolution counting yet, that whole timing challenge is to come. So best to take the machine apart again:

This XL is one wonderful puzzle! An ingeneous mechanism with history behind it too to discover :)

Replacement platen knob for Corona 3, late model, typewriter

To replace a missing platen knob on a late 1920s Corona folding typewriter, a simple 3D model to print a replacement. The early folding Corona's have a more 'chubby' platen knob, this is a model for the thinner, 30-rib pattern used from the late 1920's on, as e.g. on the Special models.

Printing it simply with the stem-down and using supports will get a one-piece print with the scarring from the supports on the rear-face of the knob. This face is not really visible when mounted on the typewriter.

Thread tapped in a plastic part is not really strong enough to take the force needed for a set-screw. As solution a slot is included in the stem to take a steel hex-nut. Press a regular M2 nut in the slot in the stem. A short M2 screw then as set-screw.

The forces now needed are minimal anyways - this screw only needs to prevent the knob from sliding off the platen rod. The flat of the hole already prevents any slipping of the knob on the rod.

With matte black hobby paint (water-based acrylic), several layers and some very light sanding and rubbing, the layer-stepping of the print is hidden. In below picture, a printed reproduction is next to a genuine original knob.

In the side-view it is of course easier to tell the reproduction from the original.

Fitted onto a ~1930 Corona typewriter, it is functional and looks the part.

The 3D model is available for download on Printables.

Replacement ribbon-spool clip from battery-strip

Many 1920-ies typewriters use a steel clip to clamp the ribbon to the stem of a spool. For example both the Remington Portable and the Corona folding typewriters use such a clip. This clip can however be missing - surpisingly often this was broken or lost.

Using nickel battery strip it is however fairly easy to make a functional replacement. For example here with 8 mm wide and 0.2 mm thick nickeled steel strip. This is widely available as battery connector strip. At 0.2 mm it can even be cut with (old!) scissors. Snip off a length and then file away any sharp edges.

With small pliers and e.g. the stem of a screwdriver as anvil to bend around, a new clip can be bent in shape. The 0.2 mm mild steel strip is still springy and strong enough to firmly clamp a ribbon to the spool.

With a 1 meter length of strip (at a very reasonable price), that's a lot of replacement clips :)