Drawing 15 - Valves, Ejectors and Pipework
(Marked as drg No. 21 at bottom right)
1. Smokebox Ejector    
The drawings offer a somewhat sparse version of an ejector but we have to start somewhere. However, scaling from the drawing the 9/16" width is actually 1/2" which is par for the course with these rubbish drawings. I made a block to the dimensions given from an offcut of 1" dia brass bar just to get the ball rolling. I decided to try and make something a little closer to prototype and printed this picture from a blow-up of a Nigel Fraser Ker picture. I've milled out the basic shape and drilled and tapped holes to suit based purely on the visual aspect of the ejector.
Contrary to the drawing, the pipe flange at the bottom of the ejector is triangular, not square, and was made from some brass hexagon material. After turning on the lathe, the triangular shape was milled and the picture to the left shows how easy it is to make a triangle from hex bar - just index round two flats at a time. This was then returned to the lathe and parted off. The flange that connects the smokebox pipe to the ejector body was made in similar fashion, although the square section was created in the vertical mode instead. After finding the centre, it's simply a case of winding round at the same x-y reading, just plus or minus to suit. The central hole is for a 6BA screw to clamp it to the body. The flange holes are 10BA.
After this, it was a case of nibble a little off here, a little off there and generally keep removing material to leave a similar shape to the photo. There are no dimensions, everything just done visually. Once the various screws were in it started to look more the part. The bit to the side was made next but, not knowing anything about ejectors, I've no idea of what to call it! The front end was turned first, taken to the mill for the flats and flange holes to be machined, then returned to the lathe for parting off. The M6 thread is to screw the next piece of pipe to.
To finish the ejector, I bought an 8mm brass elbow from Screwfix for 2.09 (part no 78141 if anyone else wants to get one), cut the threads off and linished the smokebox shape on one end, flat on the other. A short length of 1/4" bar made the joining pipe, a piece of hex material for the left-hand nut and the crenellated nut was made from some 7/16" dia bar. A 1/16" dia end mill formed the crenells, of which I made eight by indexing round forty five degrees at a time. The base of the ejector was shaped on the linisher and finished using emery cloth on the smokebox to get the radius correct.
The mounting holes were drilled 10BA clear and the smokebox drilled and tapped to suit. All the parts are just press-fitted together and there is also a plug wedged into the other part of the elbow, tapped 6BA to allow a screw to come though from the smokebox to fix it. The various sections of pipe will be cut later, possibly substituting solid bar depending on how easy they bend. Meanwhile, here is the assembly finished, although I will probably spend some idle moments rounding a few more edges and filing away some more material before it finally gets painted.
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