This is the story about how and why
The basic principle for the construction of this model was to make a model as realistic as possible which outer functions would all be identical to the real model.
The only concession was the electric cable for steering.
Several inner functions have been solved differently from the original, for example electromotors instead of diesels.
All speeds of the various functions had a maximum permissible deviation of 5% compared to the original: this in order to get the most realistic operation possible.
The specific gravity of the materials used had to equal the original as much as possible; this meant that steel was nearly the only component, so that the gross weight of the crane was finally the best approximation possible.
The latter was necessary to obtain a realistic balance in the machine, so that the maximum lifting capacity on scale also became possible (this is 100 US tons = 90 metric tons = 90000 kg divided by 15 to the third power = 26,5 kg maximum lifting capacity with the shortest boom configuration at 83°.)
This plan succeeded completely and the model has also passed the maximum load test successfully.
The model is operated by means of an external control panel with a cable and a connector that is plugged in the crane.
It is situated behind a sliding door of the crane and when the model isn’t being used the door can be closed so that a beautiful static model is standing there.
Drawings weren’t available so all dimensions were obtained by measuring the original machine itself and from leaflets and the crane manual.
Everything was then converted into drawings.
The entire construction took place in a period of 12 years in which about five months a year (the winter months) were spent working on the model.
Based on circa 12,5 hours a week I spent 3000 hours constructing the crane.
Almost two man-years indeed and this is a very cautious estimation.
I chose this crane model because I think it is a very beautiful crane that also represents a very important period in crane history, namely that of the big mechanical American crawler cranes.
The model can be built up in a lot of configurations and it was used in many variations in the Netherlands, where I live.
Various functions:
* Slewing to the left and right continuously variable
* Topping of the mainboom continuously variable
* Forward and backward moving of left and right crawler continuously variable
* Lifting of left and right winch drum in two turning directions continuously variable, during which they also reach the single pull of 14 t (= 4 kg).
* Telescoping A-frame for transport configuration that can lift and lower for the independent putting down or picking up the ballast.
* Crawler frames removable for transport configuration.
* Assembly and disassembly and change of boom length happen in exactly the same way as with the original machine and self-disassembly of the crawler frames and putting down and picking up of the ballast is possible too.
Additional accessories yet to be made for various other configurations:
* orange peel grab
* 2 additional 40ft boom sections for the maximal length of 200ft = 60 m = 4 m in 1:15 scale
* 2 additional 20 ft jib sections for the maximal jib length of 80 ft = 24 m = 1,6 m in 1:15 scale
When I started working on the construction of this model I had no idea of the time it would be going to take nor of the number of problems that I would face, but I enjoyed it very much and it took me to places where I would never have gone otherwise.
I would like to thank the crane drivers and dealers that helped me in any way and especially Dirk.
Now that the project is almost finished it is time to think about a new project.
I still don’t know what it is going to be but it will probably be another American crane but then of a quite different type and scale.
It hardly needs saying that I am a fan of everything that involves American cranes.
So if you have something or if you know something special about this subject or if you want to ask something, please contact me by email:
eef7260@yahoo.com
Eef
Some facts :
American 7260 crawler crane scale model 1:15
Make: American hoist & derrick company St. Paul Minnesota
Type: 7260 100 US t (old model with narrow cab)
Ballast: Type S-S = basic casting + 6 parts extra casting + one centre
overlayer + one rh + one lh overlayer
Track plate: width 50 inch = 85 mm 1:15 scale
Mainboom: type 59S
1x 20ft inner section = 40 cm in 1:15 scale
1x 20 ft tapered outer base = 40 cm in 1:15 scale
1 x 40 ft section = 80 cm in 1:15 scale
1x 20 ft section = 40 cm in 1:15 scale
1 x 10 ft section = 20 cm in 1:15 scale
1x hammerhead
This results in a boom length of 110 ft with the hammerhead = 33,5 m = 2,25 m in 1:15 scale
1 x 20 ft tapered tip = 20 cm in 1:15 scale
This results in a boom length of 130 ft with the tapered tip = 39,5 m = 2,64 m in 1:15 scale
Jib: type no9 hl
1 x 20 ft inner base = 40 cm in 1:15 scale
1 x 20 ft tip = 40 cm in 1:15 scale
1 x 10 ft section = 20 cm in 1:15 scale (under construction)
Hook blocks
1 x 15-t McKissick overhaul ball
1 x 35-t McKissick single sheave hook block
1 x 100-t McKissick 5 sheaves hook block
Additional accessories :
* Wire guide
* Wrecking ball
* Dragline bucket
* tagline winder
* dredging grab