Sunday, 1 January 2017

Automatic Slag Dumper

Want to see it in more detail?
Click on any of the photographs to enlarge!

The truck starts to tip as it reaches the top of the slope
In 1948 when this model first appeared as model 4.20, it was a far more innocent time. The title of this model would not have raised an eyebrow, as it may do today. To confirm what we are referring to here the Cambridge Dictionary gives the meaning of 'slag' as: "Waste material produced when coal is dug from the ground or a substance produced by mixing chemicals with metal that has been heated until it is liquid in order to remove unwanted substances from it." If you are not familiar with the contemporary slang use of the word, I am not going into it here - look it up!

Now we have cleared that up, the reason I am mentioning it here is that I have just built a version of the model for the 2016 Christmas Challenge that has just finished on the Spanner II list. The challenge is run each year with a different set of rules. This year the requirement was to produce an improved version of a manual model without detracting to far from the look of the original. The full rules can be found HERE, and all the entries are collected together in one gallery HERE on the NZ Meccano website.

Model as illustrated in the 1948 set no.4 manual
This simple model's main feature is the action of the tipper wagon that automatically tips its load as it reaches the top of the ramp. Most of the 'improvements' to the model have been made by redesigning the truck. The chassis and tipping mechanism are all new. and the four 1 inch pulleys have been replaced with small flanged wheels. The shape and dimensions of the tipping body have been retained.

The modified tipper truck
The automatic tipping is achieved by the tightening of a short length of cord (arrowed in the picture below) that is attached to the front edge of the tipper at one end and to the cross-tie of the track at the other. The cord used is Ralph's String, fine. It is available in cut lengths HERE.

The body starts to tip as the truck approaches the top of the slope

At the top of the slope, the cord that propels the truck up and down the slope, runs around a ½ inch Pulley that is held in place using rod connectors slid onto a 3 inch rod. These also retain the rod within the rails negating the need to use spring clips or collars to prevent the rod from sliding out of position, as arrowed on the right-hand side of the picture above.

The tipper body is fully raised as the truck reaches the top of the slope
 Although keeping its original dimensions the winding house is modified by using angle girders at the corners and some bracing is added under the redesigned roof which is attached to the tops of the girders using hinges. the shallow pitch of the roof is achieved by using the relatively new narrow obtuse bracket that is set at only 22½º as opposed to the usual 45º of its standard width cousin. Two flanged base plates, joined with 5½ inch Perforated Strips were used to make the floor, onto which the winding gear, built pretty much as the original model, is attached.

The modified winding house
The original instructions made good use of cord to make driving bands. I was never a fan of this as a kid, but in recent years I have made good use of it. In this model the crank has a 1 inch pulley attached to the far end that is used to drive the 3 inch Pulley via a loop of cord. it works very well, even negotiating the knot with ease. The cord that propels the truck up and down the track is wound around the other 3 inch Pulley a full turn before being attached to a spring under the modified truck.

The truck returns to the bottom of the ramp to collect another load
The modifications made to this model have been mainly cosmetic, apart from redesigning the tipper mechanism to be more prototypical. The finished model is rather pleasing and it has only taken me about fifty-five years to get around to building it. If it was not for the Christmas Challenge, it would probably still be waiting to get built.


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