Platen hardness and type imperfections

With a spare platen salvaged from a wrecked Nr. 5 it was possible to try a variation of platen hardness. The Underwood Nr.5 already had its platen professionally re-covered a few years ago with relatively soft rubber - too soft for typewriter use really, but chosen anyways and types fine. The salvaged platen still had relatively good rubber, properly hard yet resilient. The newly-covered soft platen probably is around Shore 85 and the hard salvaged platen likely Shore 95 or thereabouts.

To start with, a few lines were typed on the machine with its soft rubber and a regular new ribbon; the type widely sold with a relatively coarse weave. (Though not quite as bad as the ribbons sold today for adding machines and/or cash registers - those are coarse and heavily inked too.)

Swapping in the hard-rubber platen and comparing the same lines, it becomes visible that the soft rubber cushions the impact and thus also blurs the type. The hard rubber creates a blacker and crisper imprint. The sound of the typing also is noticably crisper with a hard platen; more a sharp tick than a thud. The overall sound-levels are not all that different, more a change in character of the sound rather than a change in loudness.

The harder platen is less forgiving for any alignment issues of the type. Where the misaligned 'L' typeslug still prints the whole character on the soft platen (the type digs deeper into the rubber / the rubber accomodates the error), the hard platen only prints the top of the character. 

Swapping out the ribbon for a better one with proper inking and a fine weave, this perhaps makes the characters still a bit more crisp. Alignment issues of course show up very clearly too. That's the third test-paragraph on the test-sheet (no backing sheet).

Some forming and re-attaching of the 'L' slug mostly corrected its angle towards the platen, in the fourth test-paragraph it prints better. Not evenly, but at least a complete character. It is still too high and slanted to the left, but correcting that requires specialist bending and/or peening tools for typewriter repair (which we do not have).

From this brief dabbling, optimal hardness for a typewriter platen is probably at least Shore 90. If accepting a more blurry imprint, then a softer platen of less than Shore 90 (but likely (much) harder than Shore 80) can make a machine more forgiving for misaligment and change the sound a little.

(Comparing also with a cork platen; the cork definitely is on the softer end of the scale. Not quite as blurred as the soft-rubber, but certainly less crisp than a proper hard-rubber platen. This was a very hard cork platen, likely dating from the 1940s, and not comparable to cork-sheets available today from craft stores. The plus-side of cork for a platen is of course that it does not harden over time the way that natural rubber can do and will have made sense e.g. when rubber was hard to come by (England in the 1940s); but there is a trade-off with print quality.)

Net outcome, an Underwood 5 that types very decently; with a choice between crisp writing with sharp/loud typing sound and a slightly less crisp with more of a thud/loud typing sound. Swapping platens on an Underwood 5 is not quite as tool-less and easy as on some machines, but with a single screwdriver can be done in a few minutes.

-and also extra understanding of platen hardness and its effect on typing quality.

March 2026 safari - A single Swiss machine from Chemnitz

This morning's visit to the local thrift store, shiny chrome and gloss black amongst the bric-a-brac!

Viewing a bit closer, a Continental Standard in very nice condition - with an extra carriage attachment. Probably for typing cards?

With a QWERTZ keyboard and in French 'MAJUSCULES' on the shift keys.

Its origin is clear from the dealer label; this machine was sold in Lausanne, Switzerland.

Patents on the back (missing / screw-holes for optional tabulator parts?).

Its serial number 477466 dates this Continental to 1931. 

Over irs 95 years it travelled from Chemnitz via Lausanne all the way over to Friesland, now for sale on a table in a local thrift store - and recorded for The Database too :)

Marchant Pony continued tweaks and fixes

The old, battered Marchant Pony is not yet a very good calculator, but improving.

It is looking better than it did originally - and does very stylishly have matching woodgrain handle and baseboard.

To make it still better -or at least nicer- continued tweaking and fixing of the machine. 

The pinwheel drum of the 1920 machine was also completely taken apart, all parts cleaned and re-assembled. This drum does not have a date scratched in, but a stamped number - A977.

Unknown what these codes mean. Similar numbers are found on the check-dials frame, on the carriage and on the carriage-rail, etc. These could be job or order numbers, or quite possibly employee numbers.

Anycase, the 1920 pinwheel parts were placed back into the 1920 machine, using the shaft of the 1919 pinwheel. The 1920 dials were in slightly better condition than the 1919 drum and also (surprisingly) there are several minor design-differences. The donor-machine 1919 drum worked fine, but re-fitting the 1920 dials keeps machine 70049 a little more 'original'. 

Oddly, the 1920 dials fit the 1919 shaft fine, but the 1919 dials do not fit on the 1920 shaft; not quite fitting the key. Another indication that dimensions bach then at Marchant were 'inexact' or perhaps per-batch is that the washer that goes next to the clearing-arm is matched to fit the specific drum-element, like a shim.

The washer thickness is matched to its specific drum-element - in above image shows the different thickness of the washers of the two machines. There must have been a lot of test-fitting and machining of parts to fit in the Marchant factory.

Images of other Marchant Pony calculators online suggested that the grey, thick felt that was still with one of the machines is likely original. The holes for the screws are sloppily cut out, but that may have been done later. This thick felt thus cleaned and placed under the machine instead of the new green sheet.

The donor-machine came with ill-fitting hex-bolts: M6 with an 8.8 strength-marking, they are probably items from the 1960s. The target-machine's original American-thread screws were present, but badly mangled and bent. With a lot of filing, they now do at least fit the thread in the machine base and hold it secure.

These Marchant calculators' baseboards sit on very distinctive rubber feet. These are nailed in place, using four nails per foot. The feet on the donor baseboard were rather damaged, but dimensions could be taken from the surviving parts and a quick CAD model created to make new 3D printed feet in TPU rubber.

The old feet then removed and the new feet hammered into place with similar black nails.

Now not on original feet, but the machine has a less 'gnawed' look and a proper grip again - plus rubber-parts are reasonable items to be replaced at a refurbishment.

Several Pony calculators seen online have a small paper 'notice'  pasted on the baseboard. This baseplate indeed showed signs that something had been glued to it, vague remnants/damage in the lacquer on the front-left corner: probably this specimen also originally had its Six Dont's notice.

This lists of Six Dont's for the user was recreated using images of surviving (bits) of these that can be found online.

The surviving specimens are all very brown - unclear if this is from aging, or if they were brown originally. Unsure of what would be a good color, a range of brownish hues were tried.

Pasted to the baseboard with a starch-based glue - it may yet be replaced with a darker brown. (Starch: warm water should weaken/remove the glue, i.e. reversible.)

This old, battered Marchant Pony is perhaps not a very good calculator, but a great item. It now does work, but not as smooth to operate or reliable as it once would have been. It's a great object for tinkering and this re-building using a donor-machine too gives a lot of fascinating insights into the workings and the manufacture of these calculators, made well over a century ago.

It is a great historic technological item!

Glossy Adler Favorit 2 portable (with extra weight)

This glossy Adler Favorit 2 typewriter was bought from another collector, already some time ago. It was not working, some linkages loose and a very wobbly carriage, so first kept safe in its case. There is some damage to the decals, but the paint remains incredibly shiny - a wonderful glossy black. Last week had a go a repairing this glossy machine, to make it type as nice as it looks.

Several repairs indeed made the Adler mostly functional again. 

Linkages are not too hard, but re-adjusting carriage bearing races on these is hard by-design. Pinning screwed parts in place is great, until some parts get bent and need re-adjusting. The escapement also needed fixing; the trip-points of spacebar and universal-bar were not agreeing.

It is overall a bit of a mystery how this machine got damaged. Cosmetically it is fine, but somehow 3 mm thick steel of the carriage got bent out of shape. E.g. the escapement bracket is bent, but the bell with its tiny mounting-screw are pristine. Must have had a very 'lucky' fall.

A puzzling design choice of these Favorit's is the routing of keylevers to their keys; the A and the Z keys trade places along the way down from the comb-plate. On the right-side of the keyboard the IJ and the 'accent grave'  keys play slalom around the 'accent aigu' key.

Don't think there is a strong need for that, but it does look fancy complex.

Another puzzling item was a strip of metal (zinc?) glued to the inside of the top cover, with a sticky-plaster to keep it all in-place.

No idea if all (or any other) Favorit's have this. Maybe a later modification by an owner / service - perhaps to dampen noise of a 'singing' top-plate?

After repairs, adjusting and some cleaning, the Adler favorit 2 typewriter writes fairly well. Even though the platen is uncomfortably hard, with a new ribbon the print-quality is not bad at all.

The serial number 610,385 is quite late for a pre-war Adler machine. This places manufacture at the very end of 1940 (actually, this means it is not a pre-war machine). Sold likely early '41.

The dealer decal shows it was sold in Amsterdam by Moolhuijsen.

This firm dealing in kantoormachines (office machines) was established in I think 1925 and today still is in the business of selling office equipment in Amsterdam. Today not typewriters, but mostly digital printers.

Like all Adler thrust-action machines experienced so far, this machine is very snappy - when clean these mechanisms are very light and fast machines to type with. And glossy - this one is very glossy too!

Sticky keys on the Royalite 120

Guest post by owner of Royal Royalite 120 - that does have a few sticky keys :)

Straight-line mechanism (in Meccano, with a little mystery)

With a wonderfully descriptive title, the 1924 Dutch edition of Meccano Book 1 contains a straight-line mechanism; 'a device to convert a circular motion into a rectilinear motion'.

In English with a more abbreviated title, this same model here also in a 1930 instruction book; 'geometrical apparatus'.

The manual ascribes the mechanism to M. Pierre Th. Dufour who, it is stated, designed this as part of his thesis work for Doctor at the University of Paris. It is also explained that that point C will move in a straight line, perpendicular to line through F and E.

This Meccano model first appears in 1918, so Monsieur Dufour's thesis will likely have been around 1917 (indeed it probably was).

The illustration still shows the long 3/4" version of the double-angle brackets part nr. 11 that was updated in 1917 by the half-inch version. The illustration is made from a photographed model that was thus likely made in the model room in 1917 or perhaps early 1918.

Now reproduced in nickel Meccano also using long, pre-1918 double-angle brackets:

Some minor modifications were made to the illustrated model. A few hinge-points were changed to use round pins instead of screws - these give less play. The mechanism does work, but Meccano still has noticable play on the joints; so point C has a few mm leeway from the straight. It does work, but is more of a straight-ish line mechanism perhaps.

This straight-line mechanism is known as the Peaucellier mechanism of 1864, rather than the Dufour mechanism of 1917. For example, it is shown here in the chapter on straight-line mechanisms in the book 'Ingenious Mechanisms for Designers and Inventors':

It is also known as the Peaucellier-Lipkin linkage or the Peaucellier Inversor.

The Meccano model is indeed the Peaucellier linkage, showing the same point having the linear motion. One difference however is the extra linkages GHK of the Meccano model which seem entirely unneccesary. These links play no role at all in the straight motion, as was already noted in a description of this model in number 39 of the Meccanoman's Journal of July 1975:

This does raise a question; why would Meccano Ltd. in 1918 show this mechanism as a design of M. Dufour and why the extra superfluous linkages? 

Reflecting on the alleged creator; it would be highly unlikely for M. Dufour or the Faculty of Science in Paris to not be aware of the Peaucellier mechanism. It is much more likely that M. Dufour simply used the mechanism as part of his work. Considering this, it is then possible that Meccano Ltd. enthusastically created this model, unawares of it being a Peaucellier Inversor. It is also very much possible that M. Dufour expanded on the Peaucellier Inversor - that would perhaps account for the linkages GHK.

Toying a bit with the mechanism (it really is fascinating); could it be that M. Dufour expanded the mechanism with a point H? It (almost?) makes a straight-line motion parallel with C. Or perhaps its deflection from line EF is of interest, relative to the deflection of point C? And that in writing the description, Meccano did not realise and/or omitted the addition that M. Dufour made to the Peaucellier linkage?

Astonishingly, today it is possible to identify the proibable thesis that this mechanism was created for. Monsieur Pierre Th. Dufour most probably was a Swiss student, who after studying in Lausanne obtained a degree at the Paris University's Faculty of Science in June 1917. His thesis is stored in several university libraries - its content has however not (yet) been digitized. Al least, a digitized version could not readily be found.

(If deeply curious, a copy is available online from an antique books seller.)

Its title "Les perspectives-reliefs : nouveau procédé permettant de les obtenir par simple transposition automatique en projection oblique des formes du terrain représentées sur les cartes hypsométriques" does however give clues what it is about. It is about methods to apply transformations from oblique projections to obtain depth/altitude maps in geography (hypsometry). Linkages seem a logical tool to use for such an undertaking.

Pierre Dufour probably used Meccano to prototype various mechanisms. Maybe he corresponded with Meccano (France?) on the subject, or his work was picked-up on by Meccano.

Ergo - the model as described in the Meccano instructions is actually the Peaucellier mechanism. M. Dufour is likely to have made modifications to obtain specific properties. The superfluous linkages shown, but not described, in the Meccano instructions may be such a Dufour-modification, but its meaning for now unclear.

Perhaps after reading his full thesis the meaning of linkage GHK would become clear. 

Until then - it is anyhow an intriguing mechanism (and remains a bit of a puzzle mystery :)

The Burroughs Portable ribbon spools; the 7/16" keyhole type

The common Burroughs Portable adding listing machine that was introduced in 1925 uses a narrow, 7/16" ribbon. The spools are also narrow, small-diameter and have a Burroughs-specific keyhole driving hole/slot.

This spool was not created for the Portable line, but it was a carry-over from the Class 3 machines. The Burroughs Class 3 machines in turn are originally the Pike adding machines made by the Pike Adding Machine Company of 1904. 

(Above image from bss1250's video on a Class 3 machine.)

The Pike company started around 1904, their machine was perhaps first sold commercially around 1906. These Pike full-keyboard adding-listing machines were probably selling well enough for Burroughs to notice. By 1909 Burroughs had taken control of Pike; in industry press it is reported late 1909 that the sales of the Pike company are now controlled by Burroughs.

In January 1910 a new model, the Pike Visible is announced. The 7/16" ribbon and keyhole spool may have its origins in this ~1909 Visible design-effort, but probably it dates right back to the original Pike design of ~1904.

The Burroughs Pike Visible Model production starts as/when the Pike operation is moved from their orginal Orange, NJ factory to a new-built factory in Detroit. The stated plan at the time is to make 7000 machines a year in the new, expanded facilities. That would account for a quarter of Burroughs output for 1912. By volume, that is - by value it would be a lot less, the Pike was at the lower end of the Burroughs machines price-range.

The Burroughs Visible is included in the company naming system as their Class 3 machine and continues until it is superseded by the more modern and modular design of the Portable (Class 8 and 9 machines). Judging by the number of these 'Pike Visible' machines still turning up today on classifieds and auction sites, it really did sell in large numbers. 

The Portable of 1925 sold in even larger numbers over ~40 years. It kept the Pike's spool and ribbon; keeping the 7/16" ribbon with the keyhole spools in production for more than half a century!

When Burroughs introduces a typewriter for office work in the '30s, they however conform to the 'industry expectations' and use a regular half-inch ribbon. The original Class 1 and 2 machines used a very wide ribbon, so for a time there were (at least) three different sizes of ribbons sold by Burroughs for their machines.

In the 1950s, the Pike spools are used in the Rooy portable typewriter. An astonishingly thin 'ultraportable' typewriter; a design where 1/16th of an inch saving would be relevant. The smaller diameter of the spool would help as well. 

(Above image shows keyhole spool on this Rooy on The Typewriterdatabase.)

Using the Burroughs adding machine ribbon and spool design meant that availability was not an issue; the Burroughs Portable was in production until the 1960s (as P-Series machines) and the enormous installed base of machines meant that replacement spools and ribbons were widely available. Rooy thus could get the benefit of a 'custom' smaller size part without having to support an own proprietary format.

(Above on the site of Ribbons Unlimited)

And even today these keyhole spools with narrow ribbon are still available! Not just the narrow ribbon, but even complete with appropriate spools. Stocks won't last, but there may still be a lot of these floating around. As a business-only item not very visible to the general public, but the keyhole spool will have been fairly common. 

A succesful design, like the Portable itself :)