Friday, October 23, 2020

Faber 1/54 (and how to take care of your slide rule)

 The number is on the box.

Again a fine and solid instrument made by A.W. Faber Castell. Around 1935 they moved from the 3-digit type-numbers to a 'slash'-code system and that year also introduced a 'Darmstadt' slide rule as the 1/54.

This slide rule was a bit yellow with ageing and also seized-up, but otherwise fine. Complete with no damage, chips or worn spots and still straight as a rule. The date-codes stamped in the wood of the base at either end of the slide rule show it was manufactured in Germany in May 1941. Date-codes '41' at left, '5' at the right end. (There's also a 'D' stamped in the left end-face of the rule, meaning unknown so far.)

Brief instructions on the back (label 'K8d'), and at both ends a transparent celluloid section with the gauge-lines for the Log-Log scales on the back of the tongue. The goniometric scales have been moved to the front edge of the scale and the linear scale to the far edge. At the spot where there'd be a linear scale on a 'conventional' Rietz, there is the Pythogarean scale P - ergo a 'System Darmstadt' slide rule.

Even inside the well, there is a cm-scale extension. Every surface serves a purpose. This also means there is a complex 3-sided cursor. This is constructed from aluminium brackets holding Plexiglas plates. (It is a German slide rule, so Plexiglas, in English this'd be called Perspex and in North America Lucite.)

The slide rule was a lucky find on a German auction-site - the instruction booklet to go with it was also sourced from Germany (albeit much less of a bargain...).

Much like wanting to have the vintage items functional, there is some satisfaction in completing an item with the correct paperwork - to come a bit closer to experiencing the product as it would have been purchased originally. This booklet is reasonably correct for this rule - second printing, dated February 1945. Had not expected that by that time there would still be materials for the printing (with colours) of a slide rule instruction manual. Perhaps deemed important - but I'd think the situation had become rather dire in Germany by then. (This particular rule is more likely to have had a first printing of this edition of the booklet, d.00001 was from April 1941 - but to hold out for a first printing 'd be pushing things a bit too far perhaps.)

The illustrations match the slide rule, these are definitely the instructions to study :)

The text is of course thoroughly informative, exact and precise. Likely because I'm not a native-speaker of German, but this made its sudden use of the word 'ungeheuer' unexpected. (Bottom paragraph of the page 11.)

The scale R is indeed 'enormously' useful, but as non-native reader I read it as 'monstrously' useful - 'Ungeheuer' as noun also means 'monster'. To a native speaker the phrase very likely would not be remarkable at all, but it made me smile :)

There are extensive instructions with examples on how to get the best use out of this precision instrument. Very importantly, it also contains a paragraph on the maintenance of the slide-rule. The "How should one treat his Castell slide rule?" paragraph.

Obviously one should keep it out of direct sunlight and not expose it to large variations in temperature or humidity. For cleaning the scales, the celluloid surface can be wiped with petroleum or white spirit. (Never with alcohol! This dissolves the celluloid - indeed it does, rather rapidly too.)

An alternative method given for cleaning the celluloid scales is a soft eraser - that is excellent advice and it worked wonders on the old, yellowed surface. The white stripe across the rule in the picture below shows the effect of only a brief application of the eraser - with some time spent going over all surfaces the whole sliderule becomes much cleaner again.

Further advice is to apply a little vaseline to the sliding surfaces of the tongue. This does indeed help to revive a long dried-out rule. In this case it also needed a little (little!) talcum to reduce the stick-slip effect that remained, but vaseline is I think generally good advice for a wooden slide rule.

Again a functional instrument! Obsolete of course, but fascinatingly ingenious and it will be entertaining to discover from the instructions how to work it.

Monday, October 12, 2020

Faber 375

The number is on the box.

A fine and very solid instrument, made by A.W. Faber.

This sliderule was seized-up, but otherwise undamaged. No chips or worn spots and nearly completely straight still, but the tongue was held very tight - nearly unmovable. Even the cardboard box is still in good shape. The instrument needed only a little light cleaning to be very presentable. The tongue being 'stuck' made it 'unusable' however. It is obsolete of course and not for actual use, but I do like the 'analog collectable objects' to be as functional and working as possible.

Loosening the five (5!) adjustment screws that control the 'grip' of the stock would yield a gap between tongue and stock (i.e. much too loose) and still the tongue was barely movable (i.e. much too tight). Somehow the sliding surfaces of the parts had become roughened to 'grip' with even the lightest clamping force. Having tried a few remedies, what finally brought the friction back to usable levels was applying a very little vaseline. (This was actually the method advised by Danish manufacturer Diwa for their sliderules.)

Like most continental sliderules, it has the Rietz arrangement of scales - the scales are not marked, but follow the conventional arrangement. Being an older sliderule, it hasn't got the inverse C scale.

Instead of the more usual mahogany, this sliderule is made of Swiss pearwood. This makes it relatively light in colour and surprisingly heavy. In comparison, a Keuffel & Esser Polyphase sliderule weighs about 57 grammes, this Faber sliderule weighs 113 grammes. Though the Polyphase is admittely slightly smaller, both have a 25cm scale and offer the same functions and accuracy.

The datecode on this sliderule is a simple '1' on the right and a '9' on the left - these should be for month and year (in the 1920-ies). From the information in the Sliderulemuseum, this would mean this Faber 375 sliderule was manufactured in September 1921 or January 1929. The German patent 365673 listed in the well was issued in April 1922. The sliderule does have the patent's construction - so it will be January '29.

Whichever exact year, it was made during the Interbellum for export to The Netherlands. The table with conversions and constants is in Dutch. The seller was able to share that it was owned (and probably purchased new) by a teacher in a technical college. Probably well cared for and little used.

The A.W. Faber or Faber-Castell company is still in business. What's more - until very recently at least you could still purchase a new (NOS) sliderule from them online. Since last year however, this article seems to have been taken offline...

No need to buy a new one though. This instrument is still in good shape - obsolete of course, but very usable :)

Friday, October 9, 2020

New brushes for the E6 motor

Putting the E6 motor together again with the fixed parts, it unfortunately still did not work. It seized up and the current draw was too high as well - tripping the circuit breaker used to protect the battery. (That circuit breaker is an original ~1937 Meccano item made exactly for this purpose - 'Retro Tech Holland' here :-)

Measuring the windings of the armature and the stator suggested these were all as they should be - in the 1 Ohm range. Comparing with another E6 motor of similar vintage, showed that the main difference was the resistance of the brushes. This motor has copper-filled brushes with very low resistance, unsure if those are original or later replacements. 

Additionally the brushes are very worn, short enough to tilt and wedge themselves between holder and commutator. Even though the armature rotated freely, when powered the brushes seemed to wedge and lock-up the armature - totally blocking the motor.

Buying new brushes for such a motor is a bit of a challenge, not a common size today. Unexpectedly, there is a ready supply of graphite rods sold as electrode! Sourcing a couple of graphite electrodes of nominally 5 mm diameter was easy enough and surprisingly affordable. The rods are "almost round" and closer to 5.2 mm, but readily ground down to about 4.8 mm (3/16" probably). Then sawing off two lengths of almost 10 mm (3/8" seemed right) and adding a slot gave reproduction electrodes. ('Repro Tech Holland'...)

With the new graphite brushes, the motor again runs - starting up fine without tripping the circuit breaker. With hardly any arcing/sparking too.

To give the motor a test-run - bring it into use again - it was built into a simple crane model out a 1928 instructions booklet.

It still needs some adjusting, as one direction runs smoother than the other. This is not unexpected, probably needs further tweaking of the positions of the brush holders relative to the motor-axle and of course some running-in of the brushes.

How well the graphite electrode brushes will stand up to wear remains to be seen of course, but for now they will do. 

So, the happy outcome is that this wrecked 87 year old E6 motor is again 'up and running' :)