In the last article I promised to continue with some machining examples including the cylinders. I’m also going to try and demonstrate how versatile my lathe (ELATHE 613) and milling machines (EMILGH/130 and 045) are if they are set up correctly and, of course, used correctly.
The cylinder assembly
The cylinder assembly is one of the more complex systems on these locomotives. It consists of the pistons and rings, the cylinders, a common valve chest, with floating valves, drain cocks and not to mention all the drilled ports and machined valve slots. Material selection is also a major concern with the bulk of the material being cast iron; the high wearing components were manufactured from phosphor bronze and the shafts and rods stainless steel. In the picture below you can see the assembly and the sliding valve. The sliding valve consists of a buckle with the valve fitting in the middle allowing free movement within the buckle but with no rattle.
The valve ports were machined using a mini drilling/ milling machine (EMILGH/130) one of the first machines I bought a good number of years ago. The advantage of the variable speed came in handy with the small cutter required for the slotting. Unfortunately these smaller milling machines don’t come with the same slots on the side of the table for stops like the larger machines. This was overcome by bolting a piece of square bar to the table and a fixed square to the carriage. Milled square clamps to suit the square bar worked well as guides when machining the valve ports. The swivel head made light work of the holes connecting these slots to the piston chamber.
When you mill on any milling machine it is a necessity to use a collet. Milling using a drill chuck is looking for trouble, simply because the chuck jaws will never line up with the end mill flutes essentially resulting in unbalanced forces. A collet solves this by distributing the clamping.
Even though I get a very good finish from my machines I still lap all mating and sliding surfaces using 600 grit water paper on a piece of flat glass. If the mating surfaces stick together with a small amount of light oil or water then I know it will seal nicely.
I’ve had a few interesting discussions with some of my colleagues about the best obtainable accuracy in a home workshop. I maintain that it is possible to machine within a few microns with these machines. Most engineers will dispute this vehemently but hear me out. If your machine an assembly in the same workshop using consistent measuring instruments, and you can check the fit as you go, how could you possibly be more than a few microns out? Of course I’m not speaking about a specific micron that can be reproduced in another temperature controlled workshop, I’m talking about achieving fits better than industry but the matching components need to be made in the same home workshop. A good example is the piston in the cylinder. It needs to be steam tight with no rattle, but it needs to move freely along the full length of the cylinder; easily achievable.
This is where most people go wrong; they buy a new lathe and bolt it down onto an imperfectly flat surface resulting in distortion of the lathe bed. The slightest amount of twist in the lathe bed will result in taper cuts and the accuracy of machined components will be poor. If the tool tip height is not on the centreline or in a poor condition; rubbing instead of cutting, will result in an inaccurate, poor surface. Slender components set too far from the chuck will cause the tool to push the part away resulting in loss of accuracy. The dial gauges need to be checked that they don’t rub losing the datum point when taking consecutive cuts. The list goes on and on, but I think you get the point.
Some tips on tips
I make extensive use of the tips supplied by Adendorff, and I personally have the 10 and 12mm indexable cutting tool set. I have found the golden tips work well with stainless steels and any other tough material, or intermittent cuts. I use the grey tips for general cutting but I try to avoid any shock loading as they seem to be more brittle than the golden tips. When I cut brass or any other material that requires a zero rake I just flip the tip around and use the bottom with no chip breaker. All the used and chipped tips are kept and generally find their way brazed onto some special once off tool or boring bar. A green bench grinding wheel comes in handy for sharpening or shaping the tips. For thread cutting I prefer to use HSS with 10%Co, it is far more forgiving in manual lathes than tipped tools.
Machining small and complicated components
Specific to this loco, here are some of the more complicated and smaller components I’ve machined. I’m not going into the specifics of how I did them, but the pictures speak volumes of what these home workshop machines are capable of.
The frame and valve gear comes to life
With the cylinders and valve gear machined and assembled it’s time to see how it runs on air…
In the next article I’ll share some welding techniques I used on the boiler and the tender water tank, as well as some heat treatment techniques useful if you ever need to make thread taps or piston rings. Then to close off the series the final article will be on painting and lining (and there’s just lining everywhere!) the loco as well as comparing some of the detailing to the full scale loco.