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Parts 27-27d: Spur Gears

Many people consider gear wheels to be an integral part of the Meccano system, but in fact they were surprisingly thin on the ground. The first gear wheel was introduced in 1902, but a choice of gear ratios wasn't available until 1915, with further gears in 1924 and 1931. Throughout the period of UK production, most gears were limited to the 10-outfit, with only one in outfits less than number 9.  For this reason, the separate "Gears Outfit" introduced in 1949 was a popular addition to the system.

27	Gear wheel, 1¼'', 50 teeth	1902	-	5	5	4	N°9
27a	Gear wheel, 1½'', 57 teeth	1915	-	8	7	6	N°5	56 teeth until 1921
27b	Gear wheel, 3½'', 133 teeth	1924	-	1	2	1	N°10
27c	Gear wheel, 2½'', 95 teeth	1931	-	n/a	0	1	N°10
27d	Gear wheel, 1 5/8'', 60 teeth	1954	-	n/a	n/a	1	N°10

The parts

Gear wheels in the Meccano system are cut approximately to 38dp (diametrical pitch).  That is, they have 38 teeth for each inch of their pitch diameter.  Pitch diameter is the effective size of a gear wheel taken where the teeth are designed to mesh (the teeth themselves extend inside and outside this theoretical size).  Obviously, Meccano gears are intended to be mounted at half-inch spacing in the standard Meccano holes. This half-inch spacing gives us our 19-tooth multiple (half of 38dp).  The 19-tooth pinion mates with itself at ½'' spacing, 19-tooth pinion and 57-tooth gears mate at 1'' centres, the 19-tooth and 95-tooth at 1½'' centres, the 19-tooth and 133-tooth at 2'' centres.

Some Meccano gears aren't quite right for this system, though.  The 15, 25, 50, and 60-tooth gears are actually made at 37½dp, meaning that they don't quite match up with the other gears in the system properly.  The 25 and 50-tooth gears mate at 1'' centres, but there should be 76 teeth (not 75) if they were made to the same specification as the other gears above.  In practice, this isn't too much of an issue because of the tolerances involved, and because matching the two different 'families' of gears requires non-standard hole spacing anyway.

Further reading on the design of Meccano gears can be found here,   and an extremely comprehensive description by Alan Wenbourne is here.  

Chronological variations

There are a huge number of variations in the early gears.  Holes, finishes, and thicknesses all changed regularly and it's almost impossible to date most of them.  The most significant one, however, is the shape of the teeth.

Prior to about 1912, the teeth have a strange elongated form.  From 1912 onwards, the teeth have a more 'correct' involute shape.  You can see the difference from the photo to the right, showing early (top) and later (bottom) forms.  Gears don't mesh well if these two types are mixed.

Ed Barclay has pointed out an interesting change to the yellow plastic gears of the late 1970s.  A number of these have longer bosses (see top example in the photo to the left).  These are the earliest types, manufactured at Binns Road, where the gear is stamped Meccano England.

Later gears with the same stamping, then with the bar (French, where the word "England" has been removed from the mould), and black gears all appear to have shorter bosses.  There are only a small number of parts stamped "England" with short bosses – it is possible even that these are old stocks from the UK but with bosses added in France.

The 'long boss' version is approximately 14mm (0.55''), the 'short boss' version is the same length as brass pinions, at 12.7mm (0.5'' exactly).

The same applies to parts 27a, 27c, 27d, and 28.  While this is a minor change, it is one that is worth knowing about for the builder, as you can choose to use a shorter or longer-bossed gear depending on the space available.  Oscar Felgueiras, the expert on modern Meccano, takes up the story:

Variations and oddities

Whether we can call all of the early variations of the gears true "variants" is debatable.  Some of them are very unusual and only very small numbers of them exist.  One of the most elusive is the four-hole part 27a (which we don't yet have a picture of for the table below), but Ed Barclay helpfully spotted a stray one in model 319 "Pit Head Gear" of the 1922 Meccano Book Number 1.  A scan is shown here.  The part thus dates from before 1922 (and from the quality of the photograph I would suggest it was not one of the last models to be included in this manual).  However, there is also a later non-quartered 3'' pulley (part 19b) in the model, dating it from no earlier than about 1919/1920.  This kind of detective work is about as good as we can get, but remember that the photograph could easily have been of a model built from an old set of parts.  Many of the models and diagrams in this particular manual go back well over a decade, and include tongue-keyed gears!

Dealer spare parts boxes

Individual part numbers

Part numbers for the parts on this page are as follows:    Unique part numbers
For identification, each variation has been given a suffix to the main Meccano part number. These suffixes consist of a two-character code for the colour, and if there are many variations, a further number and sometimes letter code to identify each variation. See the bottom of the 'Parts' page for further details.

You don't need to worry what the codes are, just click on any one for a photograph.

The button above turns on and off the display of DMS numbers (where they are known). The DMS (Development of the Meccano System, Hauton and Hindemarsh) published in 1972 and added to in 75 and 82, suggested part numbers for every variation of every Meccano part. These numbers aren't perfect, but they are recognised and also referenced in the EMP (Encyclopedia of Meccano Parts, Don Blakeborough).

Description	from	27	27a	27b	27c	27d
Feather key fixing, short boss, no holes	02	.mm
Feather and tongue key fixing, no holes	??	.mm1
Tongue key fixing, two holes in face	??	.mm2
Tongue key fixing, two holes, 1911 short boss	11	.mm3
Tongue key fixing, no holes, 1911 short boss	??	.mm3a
Tongue key fixing, no holes, 1911 full-sized boss	11	.mm4
Old teeth², no holes, 1911 boss single-tapped	12	.br1
New teeth², no holes, patent boss single-tapped	12	.br5
Two holes, patent boss single-tapped 50/56t	12		.br1
Thick steel face, nickel plated, patent boss 50/56t †¹	15	.ni	.ni
Very thin steel face, nickel plated, flush boss 56t †	16		.ni1
Very thin steel face, nickel plated, two holes 56t	??		.ni2
Thin steel, nickel plated, two holes 56t	??		.ni2a
Thin steel, nickel plated, no holes, offset teeth 56t	??		.ni3
Thin steel, steel boss nickel plated, no holes, 56t	??		.ni4
Thin steel, brass boss nickel plated, no holes, 56t	??		.ni5
Six holes, patent boss single-tapped 56t	??		.br2
Thicker face, turned from solid brass, no holes	??	.br2
Steel disc, nickel plated, single-tapped ½'' boss	24			.ni
Eight holes, patent boss single-tapped 57t	??		.br5
Brass disc and standard boss, 50/57t single-tapped	27	.br3	.br3
Brass disc and standard boss, double-tapped	28	.br4	.br4
Steel disc, nickel plated, double-tapped	28			.ni1	.ni
Steel disc, bronze finished, double-tapped	30			.xx	.xx
Steel disc, gold finished, double-tapped	34			.go	.go
Steel disc, brass plated, double-tapped	34			.br	.br
Steel disc, painted red, double-tapped	37			.re	.re
Brass disc, post-war stamping	46	.br	.br			.br
Steel disc, painted black, double-tapped	50			.bk	.bk
Steel disc, blackened (Korean) †	51		.bs
Steel disc, painted gloss black, double-tapped	72			.bk1	.bk1
Steel disc, painted dark yellow	79			.dy	.dy
Yellow plastic ''Meccano England'', long brass pummel	79		.ye2		.ye2	.ye2
Yellow plastic ''Meccano England'', short brass pummel	79		.ye		.ye	.ye
Yellow plastic ''Meccano'' and bar, short brass pummel	81		.ye1		.ye1	.ye1
Black plastic ''Meccano'' and bar, short brass pummel	94		.bk
		ALL	ALL	ALL	ALL	ALL

Notes:
¹ In this list, 'very thin' means around the same thickness as a short Meccano strip or thinner, 'thin' means just under the standard later gear thickness, just under twice as thick as a strip, and 'thick' is an unusually thick gear, almost three times as thick as a Meccano strip.  Where thickness is not mentioned, the standard thickness of a gear is around twice as thick as a strip.
² Prior to 1912, all gears had old-style teeth, longer and thinner.  All gears after this change had correctly shaped involute teeth.

Please send us pictures of missing parts! Hints and tips for pictures
Take a picture of the part in very good light, preferably on a plain yellow background, without a flash but with a tripod.
Ideally, trim the picture to about 150 pixels per inch of the Meccano part (unless the part is particularly big or small), save it as a reasonably good quality jpg file with a filename of exactly the part number, for example 19b.ni1.jpg, and email it to us by clicking on 'Contact us' at the top of the page. Thanks!

• A greyed-out box shows that no part exists for that colour combination.
• Part number codes with a green background have an attached picture of the part, just click once on the code to show a photograph of that part in a separate window.
• Parts marked "†" were temporary or economy parts, or existed only within specific themed outfits. The previous part continued throughout or afterwards.

Further information

Total number of messages on this page: 27.  This is page 1 of 5.   

bob t      (at 6:59pm, Sun 1st Aug, 21)

Wibert, Meccano engineering drawing shown on Meccano-index website says 27d drawing was dated 13th September 1953.

Wilbert Swinkels      (at 3:46pm, Sun 1st Aug, 21)

The article mentions part nr 27d, a 60t gear. Two introduction dates are mentioned: 1946 and 1954. Which one is correct?

Peter Ellis      (at 2:45pm, Wed 24th Jun, 20)

I have just discovered a part 27 with 51 teeth it was playing havoc with the timing on a model i am working on.

Brian Maunder      (at 10:08pm, Wed 17th Jan, 18)

On ebay at the moment is a 59-tooth gear stamped meccano, presumbly a factory error

Nick Smith      (at 5:21pm, Sat 5th Apr, 14)

I have examples of Matt Brass 27 and 27a, the latter almost certainly from an extension set S, which also had 21 & 22 in Matt brass

Keith Stanley      (at 5:19am, Sat 6th Apr, 13)

I have a nice example of both the bronze plated and nickel plated 27c, but I'm put off sending pictures given the negative comments appearing here concerning the response (or lack of it) which others have received. I am also frankly amazed at the attempt here to define "thick" and "thin". Whatever happened to the Micrometer and Standard Wire Gauge? Don't they have these in New Zealand? There's a lack of technical discipline here which eats in to the credibility of the whole site. Sorry but someone has to say it!!

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