Friday, April 14, 2023

Making new ribbon shields for the Hammond typewriter

The Hammond typewriter uses two wear-items; the impression strip and the ribbon shield. These two items were originally sold at modest cost by the Hammond Typewriter Company. Today, with the information from the online world, it is possible to make replacements at home with relatively simple means. The most tricky of the two items is probably the ribbon shield. This is a thin metal part that guides the ribbon and prevents adjacent characters on the shuttle from also making a smudgy imprint.

From pictures of surviving originals found online, measuring a Hammond machine and the informative drawings in the Hammond Folding manual on The Classic Typewriter Page, it is possible to reconstruct the dimensions of a ribbon shield for the Hammond Multiplex typewriter, or a Hammond 12.

The making of a new shield as documented on In Mechanica Antiqua inspired to want to make a new shield. The video of Haelschear's Haven on making shields showed the great idea of using thin (~ 0.1 mm) aluminum sheet from a (cheap, disposable) tray that made it much more achievable.

After some experimenting, the following method worked well to create new ribbon shields:

Making the shield-blank

Tracing the user-manual images, combined with dimensions of the machine and knowing that it should guide a 7/16" (~11 mm) ribbon, a cutting outline was drafted. Extra helper-lines were added for lining up the scalpel/chisel/tool when cutting the small angled details.

For the Multiplex shield, simply do not cut-out the lower aperture to create the one-color version.

The above Hammond No. 12 shield pattern is for wire ribbon-clips instead of fold-over sheet. (Note that the printing position of the No. 12 is nicely in the middle of the ribbon. This does however mean that the vibrator must be lifted quite a long way, to still enable visible typing. Strange, that.)

This shield outline is printed (using the reference length bars for size) on a sticker-sheet, for pasting to the aluminum.

In case the outline is printed on regular paper, a glue-stick to paste it to the aluminum sheet also works fine.

To cut the details and especially the rounded shapes, a set of very cheap, small wood-working chisels comes in very handy. These allow cleanly cutting or punching the rounded corners and sharp inner-corners. The aluminum can also be cut with scissors. After the corners and details are punched with the chisels, it is then relatively straightforward to cut out the blank with scissors.

This then results in the flat shield 'blanks', as shown below for the two-color Multiplex version.

Using a hard, smooth tool (e.g. handle of a hobby-scalpel) any burrs or curled edges of the aluminum are flattened and made smooth.

Folding the shield

To consistently and cleanly shape the shield, a guide was designed. The parts for this guide are also printed on the sticker-sheet and glued to thick card, again using the reference dimensions for correct size. The base is glued to 2 mm card and the spacers on 1 mm card. The prongs are lengths of wood coffee-stirrer sticks (~5 mm by 1 mm).

The lines on the shield-blank help in aligning it relative to the prongs of the folding-guide. With a flat helper-tool (i.e. a bit of card) and pressing down on the blank with a finger to keep it in-place, the ends are folded up over the prongs. With fingers then folded over completely and smoothed to the surface of the shield.

Using a bit of scrap card or aluminum, cyanoacrylate glue is applied underneath the flap that now 'floats' over the shield. This flap is then pressed down flat onto the shield, using a length of stick or thick card (best not do this with fingers, glue can be squeezed out - do not get superglue on fingers!).

Making the ribbon clips

The wire clips as used on the Multiplex guides are relatively easy to replicate. These can be made from ~1 mm soft-steel wire as sold in DIY and hardware stores. First straighten a length in the 'standard' way by stretching and twisting using a dril, a straight ~ 50 cm length makes a lot of clips :)

The bending can be done 'free-form' with pliers using the user-manual picture as guide, but it is easier to use a simple jig or mandrel. Making the jig from metal would be best, however here the jig was glued-up from the same coffee-stirrer sticks used on the folding-guide and then strengthened with some cyanoacrylate. A simple flat shape of ~1mm thick and just over ~11 mm high is all that is needed. The extra vertical slat is for conveniently aligning the straight upright length and the line is for consistently replicating width.

The shape of the clips is simpler than it looks at first sight, a basic fold-around of the ribbon-width. Change winding directions for left and right versions. The formed clips can be slid off the jig and then cut off at the short leg. If needed, the bends can be tightened a little with pliers and the ends can be rounded with droplet of glue.

Using this jig, it is fairly easy to quickly make several identical ribbon clips.

Fixing the ribbon clips to the shield

For mounting the ribbon clips, another tool was quickly made. This guide helps positioning the clips in the correct position on the guide and keeps the upright of the clip distanced from the shield.

The guide parts were printed on paper and glued to card (using reference dimensions for size). Again, 2 mm card for the base and 1 mm for the spacer and support. The lines on shield and guide help aligning and positioning the clips. A left and a right ribbon-clip are then placed on the positions indicated on the guide.

The clips are fixed in-place by letting a drop of cyanoacrylate ('runny', low viscosity) run against and under the clip.

Letting them set for half a minute or so, they are then firmly attached to the shield - at any rate, easily strong enough for normal handling and guiding of a ribbon. With the clips added; the new shields are complete and functional.

Finishing the ribbon shield

To finish a new ribbon shield, it is painted. This hides the paper with guidelines and paint also infuses the paper to make it stiffer and more durable.

Choice of color of course - also tried silver, but flat black worked well. To make it look nice (and help visibility), the printing-point position indicator can be picked-out in a contrasting color, e.g. red.

Mounting the ribbon shield on the typewriter, adjusting

The ribbon shield can be pressed down over the prongs of the vibrator fork, all the way down. The prongs of the fork should hold the shield under a light tension, pulling it taut. The ribbon can be passed through the gully at the prongs and through the ribbon-clips.

The vertical position should be so that the typed line is still (just-about) visible in the resting position and the top aperture in the shield aligns with the type in the raised, printing position. The shield can be slid up on the prongs if needed, to make it 'underline' the typed line. To make sure the shield is lifted with its top aperture to the typing position, the pusher-rod that lifts the vibrator fork (at arrow) can be taken out and length-adjusted as needed.

In case the shield and its aperture does not align horizontally with the type, then loosening the two screws that hold the fork (circled) allows a slight tweaking of the horizontal position. Note that when a bi-chrome adapter is fitted to the typewriter, the fork may snag when too much to the right and not drop back reliably.

Result - a glut of ribbon shields

With this method, it turns out to be fairly easy to make reproduction Hammond ribbon shields. Enough to get the Hammond Multiplex a functional shield and spares to last it for decades to come.
(A PDF with the pattern and the guides on an A4 for printing can be downloaded here.)
Made possible by the multiple online resources of the wider Typosphere :-)


  1. Really excellent-looking work!
    There is also good advice on this topic from Jim Petroski in ETCetera no. 127.