This is a model of the early Stockton and Darlington railway Chaldron wagon. It is based on the images of a wagon in the The National Railway Museum at Shildon catalogue number: 1979-7005

This is dated there as 1835-1845. It is similar to a wagon dated 1826 catalogue number 1975–7054 which is not in such good condition.

The model has been designed purely based on the images and the very brief description give in the link above. It is therefore unlikely to be particularly accurate and future changes may occur.
The wagon has been designed with non-rotating axles made of 2mm silver steel or stainless steel (I used stainless). One axle can pivot to provide compensation. The wheel each have a MR52ZZ bearing embedded to provide free running.
Currently I've provided only a wheel with round rod spokes although the images of the actual wagon show different wheel on the the two axles for some reason. The wheel profiles are to the Gauge 1 society fine scale standard but still look oversize compared to the original which have tiny flanges.
Updates:
01/11/2024:
Modified wheels to allow 2 bearings per wheel. This should improve any wobble caused by a single bearing.
Changed the split underframe location to avoid cutting the door fixing pins.
Provided an underframe top section without the chains which are difficult to print on an fdm printer.
Added drain holes on split underframe sections so that they can be printed on the base of a resin printer