Cylinder Drain Cock (November 2015 - December 2015)
Whilst the tapering attachment is set up to match the taper reamer it makes sense to make the drain cocks...
Both of these valves present the smallest and most fiddly challenge to date! The dimensions are tiny and the drawings are rubbish! These parts were started by taking all the available information and dimensions from the drawings and transposing them into a set of working drawings that the parts can be made from. It was found that a lot of dimensions were left to the builder's imagination and if the given information was used in totality then the valves would not end up looking anything like the sketch in the drawings!
The valve bodies and spindles were made PB102 bronze as it felt more stable to machine when working in this scale. The bodies were the first to be made and consisted of various turning (freehand and tooled) and milling operations to achieve the hexagonal features and profiled outer surface. The tapered hole was again completed on the mill using the taper reamer already made. However, the reamer was only just small enough (another reason for making this reamer no less than 2mm at the pointy end) so in fact the finished taper was slightly larger than specified.
Whilst the tapering attachment is set up to match the taper reamer it makes sense to make the drain cocks...
Both of these valves present the smallest and most fiddly challenge to date! The dimensions are tiny and the drawings are rubbish! These parts were started by taking all the available information and dimensions from the drawings and transposing them into a set of working drawings that the parts can be made from. It was found that a lot of dimensions were left to the builder's imagination and if the given information was used in totality then the valves would not end up looking anything like the sketch in the drawings!
The valve bodies and spindles were made PB102 bronze as it felt more stable to machine when working in this scale. The bodies were the first to be made and consisted of various turning (freehand and tooled) and milling operations to achieve the hexagonal features and profiled outer surface. The tapered hole was again completed on the mill using the taper reamer already made. However, the reamer was only just small enough (another reason for making this reamer no less than 2mm at the pointy end) so in fact the finished taper was slightly larger than specified.
The 5BA lower thread was a challenge to complete as the drawing specifies less 2mm of it! In sufficient care was taken on the first body and the thread was completely stripped of as the die nut met the spherical feature. This was very disappointing, however the seconds and third bodies turned out better through practice(!), the 5BA thread was also increased in length to increase practicality.
The spindle, grinding and washer was completed using the same method described before however, on a much smaller scale! The upper features of the spindle was completed on the 4th axis and parted off the stock using the a semi circular cutting path.
The groove in the upper section [to take drive from drain cock handle] was a challenge as the part was so small to hold. A number of ‘vice’ based solutions were tried to no avail, then finally the part was literally superglued to the top of the vice! The groove was again cut using a Dremel disc in the mill, taking very light cuts! Then the glue was broken using a little heat.
The spindle, grinding and washer was completed using the same method described before however, on a much smaller scale! The upper features of the spindle was completed on the 4th axis and parted off the stock using the a semi circular cutting path.
The groove in the upper section [to take drive from drain cock handle] was a challenge as the part was so small to hold. A number of ‘vice’ based solutions were tried to no avail, then finally the part was literally superglued to the top of the vice! The groove was again cut using a Dremel disc in the mill, taking very light cuts! Then the glue was broken using a little heat.
The drawings omit all reference and detail regarding the retaining nuts for all the steam fittings, so these are again down to the builders imagination. The drawings do suggest that the steam pipes should have a 60deg collet silver soldered on the ends ‘before turning’, suggesting that post soldering the pipe needs to be chucked and the 'collect' cleaned up. In practice, this is mega difficult and not a great mechanical solution. So the decision was made redesign all the steam fittings to incorporate brass collets machined to fit inside the threads of the retaining nut; interface with the 60 deg cone on the valves and slip over the pipe, so the pipes can be silver soldered to the collet. This method also allowed the solder to be applied away from the sealing face of the union, thus (hopefully) making a better steam joint.
The retaining nuts and brass collets were made for the drain cock in this manner, however on a mega small scale!
The retaining nuts and brass collets were made for the drain cock in this manner, however on a mega small scale!