BAYKO - Manufacturing Detail

The purpose of this section is to discuss some of the alternative BAYKO manufacturing details, and what approach was applied to which part, primarily for the plastic parts.
Animated GIF asking the question Cut Drill or Pin?
I am not an expert in plastics manufacturing, but I've a lot of experience in manufacturing, with the performance improvement analytical skills on which my career was based, which I think can help me analyse the basic approaches used to manufacture the various BAYKO parts.
The first thing to understand is that we are not dealing with one-off, bespoke manufacture, we are talking a mass production operation, of what were intended to be a range of small, low-price items - BAYKO - remember, sometimes hundreds of them were included in a single set.
To achieve that, Plimpton, and subsequently MECCANO, would have wanted to keep each manufacturing operation as simple as possible…
…and, if anything more intricate couldn't be avoided, to use the simplest, proven technologies available at the time.

Simple Moulding

Top and Bottom moulding surfaces of two Side Bricks
Firstly, to illustrate the simplicity, I'll start with Side Bricks. Though they didn't appear until over half-way through BAYKO's life and look rather intricate, they were amongst the easiest BAYKO parts to produce.
Side Bricks can be manufactured very simply using a two-piece mould : -
The top moulding surface of the Side Brick has the brick pattern detailing and the mid-way groove.
The bottom moulding surface of the Side Brick has the end detailing, Rod Groove, etc.
Neither the top and bottom [the long sides of the moulding] nor the edges [the two short edges] have any moulding detail whatsoever to contend with, so all four moulding edges are flat - the two part mould is achievable.
Side Bricks are the only BAYKO bricks ever made which were so simple, though Crazy Paving and the MECCANO era were similarly simple, all the others have at least one of two issues to contend with : -
Spans with Rod Grooves, Rod Holes and Ejection Pin Marks
Rod Holes through them - wholly or partially.
Rod Grooves on two edges.
I'm confident that the flat plate used at the short end of the Side Bricks and also on End Bricks and the equivalent edging of Corner and Full Corner Bricks were all designed specifically to side-step the Rod Groove manufacturing issue.
To me, this is where things start to get interesting…
…let's look at how BAYKO manufacturing addressed these two issues.
Just for the record, before we move on, Chimneys, Crazy Paving, Display Shelves, Domes, Gables, Pinnacle Roofs, Side Windows and all large roof pieces could also be made using simple two-piece moulds…
…all other plastic BAYKO parts had to overcome these problems, so how did they go about it?

Rod Grooves

Image showing the key details of standard 1950s Bricks

Pre-war red Half Brick showing a web of plastic where the pin hasn't located correctly.
Rod Grooves are a problem because, to create them, the plastic has to be recessed at that point, so the mould, or part of it, has to stick out proud of its main surface. This has the unfortunate side effect of preventing easy release of the finished parts when the mould is opened…
…the mould and the part are locked together.
There are two ways round this problem : -
1 ► Use two movable pins for the Rod Grooves, creating a four part mould.
The pre-war red Half Brick [below, right] was evidently made in this way, and clearly shows the consequences of getting it wrong… over dose of material has meant that the mould hasn't closed properly, and you can clearly see, at the left hand side of the rod groove, that the pin left a gap which the plastic has filled with a narrow webbing - click anywhere on the image to see a larger version.
When Plimpton switched to polystyrene, in the mid 1950s, and for MECCANO era production, it's a fair bet that Rod Grooves were again created in this way.
It is possible, even probable, that larger, more valuable parts, generally with much smaller production volume, such as Windows, Doors and Arches may have used this four part mould approach right from day one.
BAYKO Brick with Rod Grooves on all four edges
2 ► Grind the Rod Grooves out, as a secondary operation, after moulding.
Creating an additional processing stage sounds inefficient, but it would be relatively easy to create a jig to hold a batch of bricks from the mould, allowing them to be presented to a grinder which could cut the Rod Groove(s)…
…and this could, theoretically, have been done “free” by the mould operator whilst waiting for the next batch to be processed, though cleaning off any flashing would have made this unlikely.
Several Bricks exist which have Rod Grooves on three edges and even, like Robin Throp's example [left, above], on all four edges, very much pointing to this approach…
…and also suggesting that bricks may have been ground one edge at a time.
All the bricks I've seen, with this manufacturing fault, are from the peak production period in the early and mid 1950s, strongly suggesting that grinding was the chosen process during this period.

Rod Holes

Many BAYKO parts have Rod Holes in them either to support the rods - Arches, Bases, French Windows, Garage Doors, Shop Windows and Spans - or to be supported by the rod(s) - Corner, Curved, End and Full Corner Bricks plus Bay Window Covers, Canopies, Pillars, Pinnacle Platforms, Roof Ends, Wall Capping and Curved and Opening Windows.
Here again there are two possible alternatives : -
White Curved Window, with the mis-aligned drilling mark clearly visible towards the bottom of the central panel
1 ► Use pins for the Rod Holes, creating a potentially multi-part mould.
2 ► Drill the Rod Holes as a secondary operation on the moulded parts.
The alternatives are similar to those for Rod Grooves, but the solutions chosen are slightly different and again some were adjusted over time.
Drilling was a proven, reliable and reasonably accurate technology, long before plastic moulding was ever thought of, so is likely to be the front runner, at least in the early production days.
It's worth noting, however, that drilling wasn't the perfect solution as can be seen from the image [right - click on it for a larger image] of a mis-drilled white Curved Window - just look at the bottom of the central panel.
I'm sorry if I appear to be using “damaged” or poor quality parts as examples, but it's only the mistakes that really demonstrate what was happening.
Clear evidence of drilling - 3 abortive drill holes
There is also clear evidence available that Wall Capping was also drilled…
…the image [left - click on it to show a larger image], shown courtesy of Andy Harris, has three rogue drill marks clearly visible, showing it was drilled - though whether before or after the 9-hole Capping was cut down to make a 3-hole and a 6-hole Wall Capping is less easy to deduce…
…either way being perfectly feasible.
Wall Capping could have been produced using fixed pins in a two-part mould, so drilling must have been seen as simpler and / or cheaper.
The only other question would be how many holes were drilled at one go.  There are two leading candidates; nine, with 6 and 3-Hole Wall Capping being created by a subsequent cut; three, meaning careful alignment would be needed, but the drilling/cutting sequence becomes impossible to deduce.  My vote is for three holes to be drilled by a triple-headed drill - it would be cheaper to make, but required more operator action, however, given that the total number made was comparatively small, this latter issue was probably seen as being less significant.
There is further evidence to support drilling [below, right] with Robin Throp's 'Oak' Arch…
…which clearly shows drill marks, well off the vertical, where there should be two neat holes to support two rods - click anywhere on the image to see a larger version.
Another example of poor quality control by Plimpton I'm afraid…
Robin Throps Oak Arch with clear Drill Damage
…but we shouldn't be too precious - there aren't that many!
Looking at this quality issue with an historical perspective, apart from the fact that it's nice to have the rarities generated, it's also invaluable when trying to work out exactly how the various BAYKO parts were actually made.
With some BAYKO parts the story is mixed - a look at the selection [left, below] should show you what I mean…
A mix of drilled and pinned BAYKO parts
…the orange Bay Window Cover [shown courtesy of Robin Throp], pre-war remember, shows all the signs of having been drilled, and having picked up an extra hole…
…the two red parts, however, were clearly made using fixed moulding pins.
I can say this with confidence because, if you look at where the holes should be, there is a very thin film of plastic covering them.
This happens when the mould hasn't closed fully, perhaps because of a slightly heavy-handed weighing of ingredients.  This then allowed a thin gap to appear between the end of the pins and the base of the mould into which the plastic has run.
This would appear to be conclusive proof of a shift, with the initial decision to drill being superceded by the introduction of fixed moulding pins.
I feel confident in asserting that the 'optional' hole in the top of the Domes was created by a pin, or something similar.  This was done in such a way that, if you want a hole, you have to make it yourself, through the deliberately very thin plastic at that point, coupled with a reinforcing 'ring' underneath were clearly intended to help.  The mould includes a reinforcing ring around this hole, on the underside, to prevent the hole spreading out of control.
The situation is quite a bit more complicated when we come to consider how the pre-war Full Corner Bricks were manufactured.
The number of moulding variations [e.g. bottom right of image - right] which were created in such a relatively short period of time, testifies to the production problems experienced with them, as does the relatively high damage rate you find in job lots of pre-war BAYKO.
Full Corner Bricks one showing the extra holes
The final, and by far the longest lived, version of BAYKO Full Corner Bricks [top left of image - right] all have two 'extra' partial holes, both top and bottom [click anywhere on the image to see a larger version]…
…were these produced by moulding pins [or perhaps even by pre-drilling] in order to create a supporting “jig” which could then be used to generate improved accuracy in drilling the difficult central Rod Hole?
I can't prove it, of course, but the holes certainly seem to have no structural or modelling purpose at all, and going to the expense of adding pins to the mould would have been an expensive luxury if they serve no purpose whatsoever!
Finally, in this section, I'd like to consider Bases. Once Plimpton changed to the smaller, Type 1B Bases, I believe they were made using a 2-part mould, incorporating fixed pins for the Rod Holes, right from the start. The evidence for this scant - a complete lack of Bases with drill damage. It is possible that the earlier large Bases may have been drilled, after all we know that many of the photographs in the early manuals used drilled wooden blocks in place of Bases. Either way, creating the Rod Holes may well have contributed to the well documented early manufacturing issues with these Bases.
Again I can't prove it, but I believe that Spans were also manufactured using a two-part mould incorporating fixed pins to create the Rod Holes and fixed protrusions to create the Rod Grooves. Like Bases, Roofs and early Roof Ends, Spans also had ejection pins to help remove them from the mould.

Multi-Mould Parts

In mid-1959, not long before the MECCANO takeover, Plimpton introduced the Garage [or Opening] Doors [left]. This was their first venture into muli-mould parts…
French Windows
The original green Garage Doors
…in this case requiring four separate parts…
…the left and right hand [opening] Doors; the white brickwork panel; and the green Door Frame, the later being the only part not made with a two part mould - because of the need for Rod Grooves.
The complete Garage Doors unit was then assembled with the top brick panel being glued into position, to secure the free-moving doors, and create the finished article.
MECCANO continued [Garage Doors] and then added to this type of manufacture with the launch, in August 1962, of the French Windows [right] - again made from four parts, in exactly the same way.
I suppose that you could also argue that the complete Dormer Roof Unit fits into this category, though, personally, I regard that as a pre-packed sub-assembly, not least because the three parts remained separate - intentionally!


The Shop [or Picture] Window, launched at the same time as the French Windows, was a little less complicated. The Rod Holes were, almost certainly, created using retractable moulding pins, which was routine technology by that date.
Shop [or Display] Window
However, there is one unique feature of this part…
…the yellow window frame [clearly visible, right] was achieved by the simple expedient of painting over the red plastic…
…as I said at the beginning, simple, proven technology!
Thanks to Gary Birch for the 3 images above.


This information came directly from a gentleman who used to work in the Gibraltar Row factory - at an age when noticing women was definitely on the agenda!!!
Plastic moulding was almost notorious for the quality control pressures it created.  The biggest single issue was, undoubtedly, flashing.  This is nothing to do with dirty old men and raincoats.  The flashing, or flash, is the name for the little tags, flakes or lumps of plastic on the edges of parts, basically the result of leakage at the joints within the mould.
The solution, very labour intensive, was to employ women [predominantly] to sit either side of a long, continuously running, sanding belt.  Touching the 'offending bit' of the BAYKO part on the belt was sufficient to smooth off the excess plastic.
Health and Safety standards were noticeably lower in those days, and, by the end of her shift, you could tell what colour parts she'd been working with, because she would be covered in coloured plastic dust!  Apparently this lead to politically dubious references to “the coloured girls”!
This flashing issue is slightly more significant than you might think.  Even in expert hands, flash removal could leave a visible mark on occasions.  Moulds were almost certainly designed with this in mind, ensuring that the vulnerable areas of the finished part were as inconspicuous as possible, thus minimising wastage.

Other 'Holy' Parts

A classic piece of badly drilled Floor, shown courtesy of Robin Throp
Sorry about that!
Lastly, let's consider the non-plastic parts, namely Floors and Tie Bars : -
Floors, including Binding Strips and occasional Tie-Bars, were made from PAXOLIN, or something very similar, i.e., Resin Bonded Paper, which was supplied in sheet form. These were probably supplied to Plimpton, pre-cut to size, [this would be a core competency of the supplier] at least in the case of Floors. The holes in Floors must have been drilled, almost certainly several sheets at a time for greater efficiency - though not always greater accuracy! [Left, shown courtesy of Robin Throp.]
Tie-Bars were stamped out on a fly press - near neighbour Frank Hornby had been stamping out model railway carriages, and other parts, from tin-plate sheets for several thousand years by the time BAYKO's Tie-Bars emerged in 1938, but that's not the whole story…
…sufficient numbers of badly produced Tie-Bars have survived to support the theory that the stamped outline and inner holes happened in different stages, with the Rod Hole alignment sometimes not all it should be…
A sample of different types of Square Tie Bars showing two unstamped blank examples
…were the two extra large holes punched as an alignment aid?
The Rod Holes may, initially at least, have been drilled out - though a lack of 'burrs' suggests not - with the extra holes being for alignment, then again this could equally apply to a secondary punching stage, and later Ties were certainly punched.
The blank Corner Tie-Bars strongly support the two stage process argument - two of those shown here [right] have clearly missed stage two!
Thanks to Gary Birch and Robin Throp for their contributions to the discussions on the Tie-Bars section.

Cock Ups

No manufacturing operation is perfect and the life of BAYKO very much pre-dated the modern quality culture. That's not to say BAYKO was a low quality product, far from it, but some errors did slip through the quality inspection net - as some of the examples above have already shown. Personally I'm very grateful for these - it makes it much easier to work out what should have happened!
Different sized Domes
The white Dome [left] is clearly smaller than the red Dome, shown courtesy of Robin Throp - this is easier to see if you click on the image to launch a larger copy. The red Dome is a clear example of a moulding error, and has other distorted features underneath, in this case probably caused by inaccurate measurement of the materials [possibly a double dosing] which has caused the mould to fail to close properly.
Many of us are familiar with the multi groove error on standard Bricks…
2 pre-war Side Steps, both with 4 Rod Grooves
…much less common is the same problem with other BAYKO parts.
In the example [right] you can see two pre-war Side Steps which have the same issue - rod grooves on all four edges of the brick section - which may well have been allowed through the quality net because the parts are perfectly usable…
…oops - if I'm not careful, I'll end up on the conspiracy theorists' side of the fence rather than the cock up theorists' side!!!
If you have any other examples of BAYKO cock ups then I'd love to here from you and hope you can photograph them for inclusion on the site…
Well, that's it, a fair amount of educated guesswork, but supported by an increasing volume of evidence in most cases. If you want to support or counter any of the arguments above, or provide additional information then I'd love to hear from you…
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Latest update - August 11, 2022
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