( o o o o o o o o o o o o o o o o o o o o ) The Metal Construction Set FAQ Slanted Toward Robotics Enthusiasts Rather Than Collectors Covering Meccano/Erector, Exacto, Temsi, and Marklin Metall By Jeff Duntemann KG7JF jeffd@coriolis.com (c) 1995 by Jeff Duntemann. All rights reserved. May be distributed and reposted freely provided no changes are made to the document. I do maintain this document and request any and all changes, corrections, additions, suggestions, and so on be sent to me at jeffd@coriolis.com. I will dutifully incorporate them into the next update. This file last updated 6/27/95 ____________________________________________________________ ( o o o o o o o o o o o o o o o o o o o o ) * What is Meccano? Meccano was probably the first metal construction toy to reach the mass market. It was developed in Liverpool by a British toymaker named Frank Hornby around the turn of the century. Hornby founded Meccano Limited, which also manufactured toy trains (Hornby Dublo) toy vehicles (Dinky Toys) and many other types of toys over the years. Hornby’s formula of a relatively small number of general-purpose metal parts like girders, brackets, pulleys, shafts, and gears was widely imitated, most notably by Gilbert, which created the familiar Erector Sets that were discovered under virtually every American Christmas tree during the 1950’s. Meccano Limited ceased manufacturing operations in the UK in 1980, however, but a French firm kept the name alive and now manufactures Meccano sets for the world market. In the U.S., Meccano of France now owns the trademark "Erector" and manufactures "Erector" sets for sale in the States. These Meccano-built "Erector" sets are *not* compatible with the old Gilbert Erector sets, but are simply relabeled Meccano products. The parts are completely identical. Several other firms manufacture metal construction sets that are compatible to some degree with Meccano. What incompatibilities exist are mostly due to English/metric measurement conflicts. Although considered toys, metal construction sets like Meccano present opportunities to robotics crazies who do not have access to machine shop tools, or who simply don’t have the mechanical skill to machine their own small parts for robotics experiments. Both sets and spare parts are available mail-order in the U.S., Europe, and South America. * What is the "Meccano Standard"? Any construction set depends on there being a set of standard dimensions that all the various parts adhere to. All the bolt holes must be of the same size, and holes in girders must have the same spacing, and so on. To be compatible with Meccano parts, another manufacturer must adhere to the same standards as Meccano uses. * What are the Meccano standard hole and shaft sizes? Meccano bolt holes on parts manufactured today (in France, a metric nation) spec at 4.1mm. The holes used to be bigger. Parts made in the Thirties have holes that clear a #16 drill but not a #15, so they were about 0.178". Today’s parts have holes that *barely* clear a #19 drill bit, which makes them almost exactly 0.166" (it’s a real tight fit, especially on painted parts.) When holes are arranged in a linear run, (as for girders, plates, and so on) they are 0.5" on centers. To turn freely within 0.166" bolt holes, the shafts must be a little smaller, and mike out at 0.1603" on my Sunday-only mike, giving about 0.005" play. The shaft diameter is thus almost precisely 4mm, and if you can find metric drill rod 4mm works beautifully. Almost as good is #20 drill rod (0.161") which is available at Industrial Pipe and Steel. 5/32" rod will clear holes and hubs, but at 0.156" it’s a pretty sloppy fit and I don’t recommend it for anything other than simple models, and certainly not for robotics. * What is the size of the standard Meccano screws? Meccano screw threads are 32 per inch, and mike out at about 0.152" across the threads. This is just a bit smaller than your standard hardware store 8-32 NC (National Coarse) machine screw, which is supposed to be .164" across the threads. However, a spot check of my bolt drawers shows none that big; most come in at 0.158" to 0.162", with the bulk of them about 0.159". So it’s close. 8-32 screws clear the standard Meccano bolt hole with ease, and may be substituted for the more expensive Meccano screws. I’ve purchased 1/4" 8-32 brass screws at hamfests for two dollars a pound, and a pound is an enormous number of screws. Modern Meccano screws have an allen-socket head with a 3mm socket. Older Meccano screws have what is called a "cheese head" design, with a screw head shaped roughly like a round of Edam cheese with a screwdriver slot. Older Meccano screws were brass; the newer ones are zinc-plated steel, like most hardware store nuts and bolts. I much prefer the allen-head screws, as they can be perched on the end of an allen wrench and worked into tight spots where fingers don’t quite reach. Metric hex keys are available at larger hardware stores; my favorite has a plastic- coated T-handle and works *very* well. Some Meccano parts come with setscrews having a metric allen head 2mm in size. I keep the 2mm and 3mm T-handle keys with my Meccano parts, and that’s all I need. * Will 8-32NC set screws work in Meccano hubs? No! Meccano screws are slightly smaller in diameter than 8-32, and while the thread pitch is the same, the hubs are tapped a little too small to accept 8-32NC set screws. (The tap drill for the one standard Meccano thread is given as 3.25mm. Meccano is made in France now, which is metric.) It is possible to re-tap a Meccano hub to 8-32, but is has to be done *very* carefully to avoid breaking the tap off in a part that may be worth a lot more than the tap. (Meccano gears, in particular, can be very expensive.) Meccano setscrews are readily available from American mail-order sources, which I list later in this FAQ. * What are Meccano parts made of? Nearly all Meccano parts are steel or brass. There is virtually no aluminum in the line. In recent years some plastic parts have appeared, primarily realistic wheels, transparent plates for windshields, and other small oddments. Some gears are now made in plastic to reduce their considerable cost, but equivalent gears are in every case available in brass. There is a separate line of plastic parts called Meccano Junior, targeted at small children and intended to price-compete with Lego, but I won’t discuss these further here. * How thick are the girders, plates, etc? Recent-build Meccano parts are stamped from several different thicknesses of steel. Perforated strips are 0.041" thick. Flat and angle girders are 0.033" thick. Larger flat plates are 0.026" thick, and about .001" of that is paint. Remarkably enough, the older girders I have (from as far back as the early Thirties) were thinner and obviously not as strong. Flat plates made by Exacto (an Argentine firm making Meccano- compatible spare parts; see below) are .043" thick and substantially stiffer than the Meccano-made parts. Rigidity is sometimes a problem in robotics work, and I have more and more been requesting Exacto parts, simply because they’re thicker and more rigid. * What sort of finish do the girders and plates have? Finish on Meccano parts has varied a lot over the years. The girders I have from the 1930’s are "black steel," unpainted and not plated. They’re handsome in their way but they will rust in damp climates, as I’ve discovered. Until 1964 Meccano parts were an ebullient Christmas-y red and green, red for the plates and green for the girders. In 1964 the color scheme was changed to bright nickel plate for the girders and yellow for the plates, to make Meccano models of cranes and construction equipment look more like "real life.". Some parts were given blue or black painted finishes, and other oddball color schemes were used here and there over the years. The yellow-and-silver color scheme is used to this day by Meccano of France. Temsi and Marklin Metall, (two Meccano-compatible construction set manufacturers; see below) however, retain the red and green finish used by Meccano until 1964. And Exacto (another Meccano-compatible manufacturer) girders are a rather handsome battleship gray, while their plates are a bright Meccano yellow. One problem with the painted finishes is that they chip and scratch very easily, and after a few go-rounds your parts will look very "lived in." This may or may not matter, but given the price to be paid for the parts, many builders use a plastic washer under bolt heads and ahead of the nuts to keep bolt-to- paint contact to a minimum. This works well and the washers are tolerably inexpensive, but it makes construction considerably trickier, especially in tight spots. The zinc plated girders get blotchy after some handling. One advantage to zinc in certain circumstances is that the girders can be soldered to, with a hefty iron. This can really help when you need a good electrical ground. * What gear sizes and pitches are available? There is one mainstream Meccano spur gear pitch size: 12 teeth to the inch. A large number of gear wheels and pinions is available >from either Meccano or Exacto (see below) and are all compatible. Gear wheels may be had with 45, 50, 55, 57, 60, 65, 95, 133, and 152 teeth. These gear wheels have a 1/16" face. A 38 tooth gear wheel is available with a 1/4" face. Pinions are available with 10, 11, 15, 19, 20, 22, 25, and 30 teeth. Most pinions have a 1/4" face but a few may also be had with a 1/2" or 3/4" face. Two sizes of crown (contrate) gears are available to mesh with the pinions, 25 and 50 tooth. A 1/2" diameter single-cut worm is available. Two sizes of bevel gears are available: A 26-tooth gear that works in pairs, and a two-gear set that must act together, with a small gear of 16 teeth and a larger gear of 48 teeth. There is a linear rack on the same pitch, 6 1/4" (160mm) long. Helical gears are available, with a 35-tooth helical gear and two sizes of helical pinions: 12 and 14-tooth. The helical pinions are available in both right and left hand orientations, both of which mate with the larger helical gear. There is a sprocket system with chain and sprockets, with 14, 18, 28, 36, and 56 tooth sprockets available. Exacto makes a pinion that mates somewhat gamely with the sprocket wheels, and more importantly, the 3 1/2" ball roller bearing assembly, which has sprocket teeth around its rim. * What other useful mechanism elements are available? There is a ratchet wheel and pawl set, the pawl available both with a hub and without. Meccano includes a two-part dog clutch in brass. There is a brass universal coupling. A shaft with a keyway running its full length is available, as well as special setscrews with a key stud that allows gears to be driven with the key shaft while running along its length, as in a change gear box. Threaded rod is available in several sizes to 12 1/2", and a coupling is available to match threaded rod to plain shaft. The threaded rod can act as a lead screw because most Meccano hubs and couplings have setscrew holes at 180 degrees, threaded together so that a threaded rod can run freely through them. (It’s a s..l..o..w lead screw, however, at 32 threads per inch...) * How are Meccano parts identified? Each unique Meccano part has a unique part number. These run >from 1 up into the several hundreds. There are also alphabetic suffixes in some numbers; for example, part 1 is a 12 1/2"" flat girder, and part 1a is a 9 1/2" flat girder. This was done to allow later additions to the parts line to have numbers within a single block of related parts. * Are the Gilbert-built Erector parts compatible with Meccano? Not really. Gilbert Erector isn’t that interesting these days except to toy collectors. Although the parts were roughly the same size and used similar sized holes and shafts, there were niggling differences that made certain combinations impossible. Gilbert parts were generally not painted and rusted very easily, the gears were very coarse, and the girders were thin and not especially strong. Many parts were made of aluminum. All in all, compared to Meccano, the old Erector comes off looking more than a little shabby. * What is Exacto? A small manufacturer in Argentina began making Meccano-compatible parts (but not sets) under license from Meccano for the Spanish- speaking market many years ago. Today, most are exported to English-speaking countries. These are called Exacto (no relation to the American tool company) and in some respects are even more interesting than Meccano to robotics enthusiasts. (They are available mail-order in the U.S; see the distributors listing at the end of this FAQ.) In addition to manufacturing parts identical to or better than Meccano’s, Exacto has expanded the line with a bewildering array of additional parts designed to be dimension-compatible with existing Meccano parts. They are extremely well-made and are very popular with adult hobbyists who can afford to import them. Of interest to robotics experimenters are Exacto’s broad line of gears that far exceeds Meccano’s: Exacto makes 14 different pinions, 10 different gear wheels, a left and right hand worm, two sizes of contrate (crown) gears, three sizes of bevel gears, both right and left hand helical gear pairs, internal gears, and several (large) sizes of "toothed discs" which are basically hubless gears. (Hubs may be bolted onto them.) Exacto also manufactures Meccano-compatible shafts in very polished, very rigid stainless steel. Perhaps Exacto’s most significant innovation for serious robotics experimenters is a second, larger 5/16" shaft size and compatible parts for use in applications where the Meccano 4mm shaft simply isn’t big enough. A 5/16" shaft of 2" length is available with a high-precision 4mm bore all the way through, so that you can have the thin shaft turning freely inside the thick one. Exacto girders and plates are generally thicker and stiffer than equivalent Meccano parts, and I recommend using them for robot frames or anything that must carry a lot of weight. * What is Temsi? Temsi is a metal construction set manufactured in the Netherlands, and is basically metric Meccano. The smaller parts are very similar; however, the larger parts do not align completely with English-measure Meccano parts. * What is Marklin Metall? Marklin is a German manufacturer best known for expensive electric trains. The firm also makes a construction set toy called Marklin Metall. It is mostly compatible with Meccano, and whereas there is not the breadth of parts available, the parts in the line are more precisely made than Meccano’s and the girders are stamped from significantly thicker steel. The dimensions seem to be English-based, so even the longer parts will mesh with standard Meccano. Alone of all the metal construction set manufacturers, Marklin at one point manufactured a "theme set" devoted to a single model: a simple robotic arm. (Robot Kit 1007.) I have this kit and am very pleased with it; however, it was fearsomely expensive and is no longer made. On the other hand, there is nothing in the Marklin arm that cannot be duplicated with ordinary Meccano parts. * What complete Meccano sets are available? Meccano and Erector are mostly thought of in terms of sets that include a selection of parts, a little bin of nuts and bolts, and an instruction manual showing how to build various models. The sets are mostly slanted toward children in terms of the models presented in the manuals. Meccano and Meccano/Erector sets are numbered, with the larger numbers indicating the largest sets. At their peak of popularity in the 1950s there were 12 separate levels of sets, from 00 (which were almost useless and sold mostly as kid bait, to get the twerps agitating for something larger) to 0, and then from 1 to 10. The 00 and 0 sets have not been made since the late 60’s. The progression of complexity of the models in the manuals went up smoothly through set #9. Then there was an awesome gulf to the #10 set, which had more than twice the parts of #9, and models of tremendous size and complexity. It was plain that the #10 set was meant for adults. Several years ago, Meccano ceased to manufacture sets past #6. Collectors are quickly snapping up the larger sets, and prices have begun rising. An unused #10 set now routinely sells for over $2500US. Used sets of all vintages are still available, but you have to look for them, and they are not cheap unless they are heavily damaged from rust or missing most of their parts. * What are the Meccano upgrade sets? In the old days, each set from 00 to 9 had a companion upgrade set numbered with an "a" prefix (3a, 7a, etc.) that converted that set to the next highest set. I received a #6 set for Christmas 1959, and for Christmas 1960 I received a #6a set, which converted my #6 to a #7. This system still prevails, although they are now called "complementary sets" and have a "C" prefix rather than the "a" suffix. * How appropriate are Meccano sets for robotics work? Not very. Meccano sets are keyed to prepubescent boys making cranes, trucks, tanks, and things like that. No single set is ever likely to have enough "stuff" in it to enable the enthusiast to piece together a reasonable robot arm or chassis--and you’ll be paying for realistic steering wheels, windshields, and other specific gimcracks of zero usefulness. Get yourself a set to become familiar with the *idea* of Meccano; build the silly truck and tank models, and decide whether it feels like something you could *think* in, from an engineering perspective. The owner of Exacto calls his business "miniature engineering," and there’s a lot of truth to that. Once you become familiar with the parts system, buy *only* the parts you need for a given project through the mail-order dealers listed at the end of this FAQ. That’s what I do. * What motors are available for Meccano work? Motors were a sticking point for me; the motors available from the set and parts manufacturers seem awfully small and weak for their price ($64!) and I have not used them. Meccano made a number of fairly gutsy motors in the past, but they are no longer made and collectors prize them. The solution I’ve found is to scour the surplus market for DC or stepper motors having a 3/16" shaft. Meccano gears and couplings are bored for a 4mm shaft, but that’s a close undersize to 3/16", and you can drill and/or ream a 3/16" bore in any of the standard Meccano parts. (Obviously, if you can find European-build motors with 4mm shafts on the surplus market, you’re in hog heaven.) Keep in mind that drilling out the parts makes them useless on Meccano shafts, so you’ll want to choose one gear or coupling (a universal coupling is available, albeit somewhat pricey) and make that the standard power takeoff >from the motor in question. I’ve bought a couple of Pittman DC gearhead motors at surplus for $10 or $15 that run at about 250-300 RPM and have loads of torque. Their mounting holes were weirdly spaced, so I had to modify a standard 1 1/2" X 3" Exacto flat plate with additional holes, but that done, the motor bolts to assemblies through the flat plate and works very well in a Meccano context. I’m still tinkering with stepper motors in a Meccano context, but there’s no reason not to use them if you have the controller. I intend to create a Basic Stamp controller, and will update this FAQ with more information once I get it working. In the meantime, one of the very best sources for all manner of robotics stuff is Herbach and Rademan, and a quick scan of their current catalog shows a number of compact motors with 3/16" shafts. No robotics freak should be without this catalog: Herbach & Rademan 18 Canal Street PO Box 122 Bristol PA 19007-0122 800-848-8001 (orders only) 215-788-5583 (office) 215-788-9577 (FAX) I’ve also bought suitable motors from this firm: C and H Sales Company 2176 E. Colorado Boulevard Pasadena CA 91107 213-681-4925 818-796-2628 818-796-4875 FAX It’s a good, thick catalog to have, full of switches, relays, fans, air fittings, etc. in addition to pages of motors. Another similar catalog is this one: Surplus Center 1015 West "O" Street PO Box 82209 Lincoln NE 68501-2209 402-474-4055 402-474-5198 FAX 800-488-3407 Their motors run large, and they have a strong emphasis on hydraulics, but well worth having. And a thin but often useful one, with odd motors, relays, and other oddments: Brigar Electronics 7-9 Alice Street Binghampton NY 13904 607-723-3111 607-723-5202 FAX * What is MECCANO MAGAZINE? A publisher in England produced a "boys’ hobby magazine" under license to Meccano Limited for many years--something like 1916 to 1981. I’ve only seen the publication through five years of its life: 1960-1965. It covered lots more than Meccano construction; in fact, Meccano construction was a pretty small part of it. The rest was coverage of other Meccano Limited toy products, which in the Sixties was quite a lineup and included model trains, an architectural model building set called Bayko, diecast car/truck models called Dinky Toys, and--gasp!--Play Dough. The balance was material of general interest to preteen boys: Trains/trucks/ships/aircraft, space travel, electronics, stamp collecting, photography, and so on. Because there was typically only two or three short construction articles on Meccano in each issue, I consider them of mostly historical interest today. Even in the issues I still have, there is almost nothing of interest to the robotics experimenter. * Has much been published in terms of robotics-related models? Not really. In the Erector/Meccano world, "robot" generally means "mechanical man," in the sense that they used to appear in 40’s and 50’s schlock Saturday morning adventure movies--clanking bipeds with gears visible through windows in their middles. Meccano Special Model Leaflet #27 is typical, and while clever, it’s not what most of us consider robotics. One publication, however, is *very* compelling: the *Rhino Charged Robotic Arm* which is Canadian Special Model Number 4, published by *The Canadian Meccanoman’s Newsletter.* This is a 2/3 scale model of a real commercial robotic arm, and includes all six axes plus grasp. The model is about 3’ high and probably weighs well over a hundred pounds. The main shoulder bearing is a 4" ball bearing riding on 35 steel balls, and the gearing is complex, to say the least. And although this would be a beautiful item to have in your lab, my guess is that it would take over a couple of months of loose moments to assemble, and (alas) the parts probably come to over $3000, much of which is in the gears alone. The model, however, is a beautiful example of what can be done with Erector/Meccano parts in a robotics context. * What do Meccano parts cost? Akkkh--there’s the rub. This stuff is pretty expensive. Here’s some of the spare parts prices from a recent mail-order catalog: 12 1/2" angle girder $2.63 Brass worm gear $5.92 30-tooth brass bevel gear $9.68 Universal joint $14.26 In reality, these prices aren’t bad if you compare the gear prices to stock gear catalogs; the problem is that most of us buy our gears from surplus for fifty cents each. The girders seem expensive, but you have to factor in the cost of your own time and effort drilling accurate holes in similar stock. There is a tremendous advantage in having "standardized parts," besides. If a chassis prototype you spent 50 hours fabricating just doesn’t pan out, you dismantle it and re-use the parts, rather than toss the whole mess in the corner for spiders to live in. Assuming you don’t butcher a part customizing it somehow, the parts last forever; I still use the girders my father played with as a boy in the early 1930’s, rust or no rust. * Where may Meccano sets and parts be bought? Sets can be had in most large hobby shops, especially right before Christmas. Spare parts must be ordered through the mail. I have dealt with two different mail-order dealers, and one chap local to me who has a store here in Scottsdale, Arizona that should be seen if you’re ever in the area. The real World General Headquarters for Meccano nuts is in England, near London, where Geoffrey Maxwell-Wright runs M. W. Models. Mr. Wright has an astonishing collection of old and new Meccano stuff, including back issues of Meccano Magazine going back fifty years. Importing things from England is slow and costly, but if you’re really going to go nuts for this stuff, you should contact him for his lists: M. W. Models Geoffrey Maxwell-Wright 4 Greys Road Henley-On-Thames Oxfordshire ENGLAND RG9 1RY +44-491-572436 +44-491-571175 24-hour FAX Of course, if you’re ever in England I’ve heard his shop is a must-see. The two American mail-order dealers I’ve dealt with are these: Valley Erector Sales Joel Perlin Roy C. Zuehlke Metal Construction Toy Specialist PO Box 2184 1111 Acapulco Street Rogers AR 72757 Oxnard CA 93035 501-636-4312 805-985-5498 501-621-5452 FAX 805-963-4668 FAX Both of these guys have been *very* courteous and helpful to me. Their product lines are very similar, and the major difference seems to be that Joel Perlin carries more obsolete parts and leans more toward collectors. In addition to Meccano, both carry the excellent Exacto line of Meccano-compatible parts. Their prices on new material are very similar. BTW, *please* don’t harrass them for the cost of this stuff. It’s pretty expensive >from a Toys-R-Us perspective, and to keep it in perspective you have to factor in the value of your time otherwise spent banging out non-reusable one-off robot parts in your garage. If you’re ever in Scottsdale, Arizona (adjoining Phoenix on the east) go to McCormack Railroad Park, at Indian Bend and Scottsdale Roads. Inside the park is Gerry’s Trains and Tools, which (in addition to a large selection of model trains) carries complete Meccano sets and some spare parts. Gerry’s Trains and Tools 7337 E. Indian Bend Road (McCormick Railroad Park) Scottsdale AZ 85250 * Are there any American clubs devoted to Meccano? The only U.S. club I’ve heard of is this one: Southern California Meccano and Erector Club PO Box 7653 Porter Ranch Station Northridge CA 91327-7653 Joel Perlin is connected with this club. I don’t belong and can’t tell you much about it, though I get the impression most of its members are collectors rather than technologists. * What other Meccano contacts are there? There are a few I’ve gathered but never followed up on, and here, in no particular order, are other people and organizations you might contact in connection with Meccano. The Canadian Meccanoman’s Newsletter 2681 Third Avenue East Owen Sound ON N4K 2M5 An excellent newsletter, and they publish large model construction pamphlets, including a superb one on a working scale model of a Rhino robot arm. (Canadian Special Model #4.) Your Toybox 3648 Rochester Road Troy MI 48083 313-689-2060 Mainly exports Meccano materials to Canada. Lou Boselli 19 Payson Road Cornwall-on-Hudson New York NY 12520 914-534-2863 Dealer of Meccano parts and sets. He is Meccano’s official representative in the US.