Erector set part numbers "GS" & "GU" eccentric (loop)

BGHansen

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Back with another reproduction Erector set part project. This is one is actually two parts that worked together: The p/n “GS” eccentric and “GU” eccentric loop. First, the obligatory history lesson. . .

A. C. Gilbert started selling the Erector set in 1913. He had different stories as to how the idea came to him; he was a man who didn’t let the truth stand in the way of a good story! One version is he was at a department store in Toronto in 1912 trying to sell magic sets from his company (then called the Mysto Manufacturing Company). While waiting to see the store’s buyer, he noticed that there was one partial shelf of magic-related toys. There was also an elaborate display of Frank Hornby’s Meccano building sets taking up many shelves and a lot of traffic at those shelves! Gilbert could see the handwriting on the wall regarding producing only magic sets; it was a very limited market. He bought a Meccano set, returned to New Haven, CT and worked on a similar toy which evolved into the Erector set.

Meccano was sold in department stores alongside Gilbert’s Erector sets. In 1928, he bought the rights to produce Meccano in the United States from British Meccano. The agreement was that as long as Gilbert produced a product with “Meccano” in the title, British Meccano would not distribute or manufacture toys in the US. I suspect that once Gilbert and his engineers looked over what Meccano’s construction toy offered (advertised as “Real Engineering in Miniature”), they concluded that Meccano was FAR superior to their sets. Gilbert sold “American Meccano” sets alongside his Erector sets starting in 1929.


Couple of manual pages from Gilbert's American Meccano sets. The Meccano system was FAR superior to anything Erector had to offer
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Gilbert’s bread and butter was the Erector set, I suspect to more level the playing field with his American Meccano line, they created a number of pieces collectively called “the Mechanical Wonders” parts. These parts demonstrated different forms of motion and machine control: cams, levers, helical gears, eccentrics, etc. Yup, finally getting to the point! The “GS” eccentric and “GU” eccentric loop were a couple of the Mechanical Wonders parts.


A manual page showing the GS/GU in use
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First, the “GS” eccentric. Gilbert included a p/n “P7” pulley in all of their Erector sets. It was made by putting two “pie tins” together with a 5/16” diameter brass hub peened over on the back side to lock the two plates together. The “GS” eccentric was one of the “pie tins” with a hub installed 1/4” off center. I made a die set from CRS on the lathe to form the pie tins.


Didn't show the lathe work, but the dies were turned there. Set a brass blank between the two and mash away.
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I rough cut blanks from 0.020” brass and mashed it between the dies on a 20-ton press. I made a second set of similar dies with the OD cut to the final diameter of the pie tins. The rough blanks were stacked 4-6 deep between these two dies on the lathe and the final OD was cut. One of those dies had a ¼” hole drilled through for transfer punching in the hub location. Process there was to set a “pie tin” between the dies, transfer punch the ¼” offset position, then hand punch the 9/32” hub hole with a Roper Whitney No. 5 hand punch.


Made a 2nd set of dies, or a holding fixture to turn the rough blanks to size on the lathe. One die had a transfer punch hole in place for marking the off-center hub hole.
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The hubs are turned from 5/16” brass on the lathe. I have a centering jig for the #20 axle hole so I can skip the center drilling step. After drilling the center hole, a shoulder is cut with a parting tool. I swap to a chamfer tool to thin the material at the perimeter of the hub for peening. I also used an already made (the hubs are common on Erector parts) hardened drill jig for knocking in a 6-32 tap drill hole. The 6-32 tap drill hole and 6-32 tap are run with hand drills. The 6-32 drill jig was made to the overall length of the hub; helps to quickly position the parting tool. I clean the nib off the parted hubs with a Scotchbrite wheel.


Turning the brass hubs: center hole, shoulder, chamfer, drill fixture for a 6-32 tap hole, power tap and part.
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I use this holding tool with a center knock-out to take the nubs off the end.
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The hubs are attached to the “pie tins” using a steel ball and hammer to peen over the back side of the hub. The plastic block in the picture has a short pin in it to hold the hub in place. Set the pie tin over the hub, set the steel ball on top and whack it with a 2-lb. hammer.


Hubs are peened to a disk with a steel ball
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On to the “GU” eccentric loop. These were made from 5/32” stock (standard Erector set axle size). The axle was bent into a loop and set between two of the “GS” eccentrics. A 1” long straight leg extended from the loop. The “GU” was a bit loose to the “GS’s”, so when the GS’s rotated, the GU would slip letting the 1” straight leg reciprocate back & forth ½”.


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This one took a little development work but came out nicely. Two things needed to be developed: the overall length of the rod and the diameter of the circular mandrel. The ID was something like 1.1”, I started with a mandrel of that size. Bent the 1” straight length and pinned it in place. Wrapped the 5/32” rod around the mandrel and measure the ID at something like 1.2”. I turned a new mandrel to 1” which after some spring-back gave me the correct ID. Once I got the ID set, I fiddled with the length AFTER the 1” bend was made so the rod ended just short of a complete circle.


Start with a 90 deg. bend leaving an ~1" leg. Leg goes into a pin to hold the end. Then a couple of dowel pins are set in place to hold the axle.
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After the mandrel is set in place, a bending lever is bolted to the fixture through the mandrel. Then walk the pry bar around the loop. Pull the pin on the left of the 90 deg. bend at the end to complete the circle.
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Couple of prototypes as I was developing the length of the blank (these are short)
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Probably more than a lifetime's supply! I repurposed a grill which happened to be the perfect diameter stock.
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So why are there 3 sets of holes for pins, axles, etc. in the fixture plate. Oops! One set was for the initial mandrel to determine the spring back. The mandrel shrunk in size, which I should have accounted for in the hole locations for the stop pins used during bending, but I didn’t. . . This resulted in a tear-drop shape at the straight leg. Hence, the 3rd set of holes.

And in the “it’s better to be lucky than good” department, we had a microwave crap out. The never-used grille was destined for the trash. It ended up being 5/32” stainless rod stock, out came the bolt cutters!

These have been selling pretty well at $30 a set. Yeah, I won’t quit my day job, but that’s a nice thing about being comfortably retired!

Thanks for looking, Bruce
 
What captures the circular rod? Are two of them mounted back to back?
 
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