Axle Boxes and Side Rods for the Beginner's Locomotive
An 0-4-0 Switcher of Simple Design in 3/4 inch Scale
The Miniature Locomotive, March-April 1953
The next thing we want is the axle boxes. These are fabricated from 3/4 inch square brass bar. Chuck in the four jaw, set running truly, face. Set up a parting tool and turn down the end to 5/8 inch diameter for 3/16 inch length. Note the cross slide index setting and leaving a 1/4 inch wide square portion run the parting tool in to the same index setting. Move the carriage ahead another 1/16 inch and part off. Repeat four times. Now cut out eight rectangles of 1/16 inch brass plate 3/4 inch by one inch. Tin them and sweat together. Chuck in the four jaw and drill and bore to 5/8 inch until the axle boxes will enter. Heat and separate. Tin the faces of the axle boxes and slipping a side plate on each side of the axlebox heat up until the solder flows, pressing the sandwich up tight until cool. As a precaution 1/16 inch riets or 1/16 inch brass welding rod can be flush riveted into each corner. Dress up as needed to slide freely in the frame slots with a little side play but snug front to back way. The bosses go inside. Mark each one and its opening so it can be replaced in the same slot at future time. Now it is essential that the axles be parallel and square across the frames so we'll make a jig in which to bore the axleboxes so that if in error one error will be common to all and so be canceled out. The jig is a piece of 1/4 inch steel plate with a slot same size as the frame slot so the box fits in. . By pushing all the slack one way you can see how much you are out on the spacing of the holes and which way they are out. Suppose you are nearly 1/32 inch out; in the conventional way the rods would be ruined but here we just make the bushings of bronze or brass (provided it's of a short grained metal) with the hole about 1/64 inch off center. Push in the rod with the offset in the direction to correct error. Ease the end of the next bush so it will enter easily 1/16 inch into the rod and place it on the dummy axle spigot. With the other end of the side rod mounted on the other dummy axle and holding the rod against the end of the bush turn the same till the eased down end will enter the rod. Start the bush in at this place. Try the rod Now set the engine frame upside down on the bench and take out one of the axle boxes on the far side; i.e., the projecting boss is facing you. Take out this box and drop it into the jig without turning it over. Now set it in the four jaw with the boss outwards, one jaw passing the axle box into the jig and the other three jaws holding the jig. Center the axlebox by setting the boss to run true and the jig not to wobble then proceed to center, drill 31/64 inch and ream 1/2 inch. If you are a real beginner and have not acquired reamers or have not the ready cash then bore with fine cuts till a bit of 1/2 inch cold rolled steel will just turn freely in it. The main thing is not to give up building an engine because you don't have the fancy tools specified in many instructions. They are nice if you have them but certainly not essential to success. Having that axle box bored, slacken the jaw over the box and take it out of the jig replacing it in the slot it came from and put the other one from the same side in the jig and do likewise. Now when you come to the other side of the engine put them in the jig with boss toward the chuck. By this means every axle hole will be bated and errors will never show up. Drill through the keeper plates spotting the axle boxes and finally drill and tap 3/16 by 32 for the spring studs.
The springs for an automatic spark advance as used on almost all present day cars seem just about the right size for this weight of engine and only need stretching with a screwdriver. Drill a countersunk oil hole in the top of the axle boxes.
Now, strange as you may think, the coupling rods are needed in my way of building an engine so get a strip of steel large enough, chaulk one side and hold against the axleboxes and scribe the holes through the boxes. IN the center of this circle deeply center punch. Drill and ream 3/8 inch for bushings. Mark out the profile of the rod and saw and file to shape. A usual way to file round bosses on each end is to make two buttons of steel the diameter of the boss with a 1/16 inch spigot turned to fit the rod hole. These are case hardened and used by placing one each side of the rod with spigot in the hole clamping the lot in the vise. You now apply the file until it skids off the hardened steel and you are down to size. By setting correctly in the vise it is surprising the combinations of button and vise jaw you can arrange to prevent filing too deep where you don't intend to. Those who have milling machines won't need me to tell you how to run them.
Experienced builders may wonder why I haven't stressed the extreme importance of getting the rod center exactly the same as the axle center. Well, beginners at machine work often can't work that accurately so I've attacked it from the other end, that is to make a way of escape. So, take two pieces of 1/2 inch cold rolled steel about four inches long (you'll use them for axles later) and turn a 1/4 inch diameter pilot about 1/4 inch long on one end of each. Slip these through the axleboxes and try the rods on these. By pushing all the slack one way you can see how much you are out on the spacing of the holes and which way they are out. Suppose you are nearly 1/32 inch out; in the conventional way the rods would be ruined but here we just make the bushing of bronze or brass (provided it's of a short grained metal) with the hole about 1/64 inch off center. Pus in the rod with the offset in the direction to correct error. Ease the end of the next bush so it will enter easily 1/16 inch into the rod and place it on the dummy axle spigot. With the other end of the side rod mounted on the other dummy axle and holding the rod against the end of the bush turn the same till the eased down end will enter the rod. Start the bush in at this place. Try the rod on the dummy axles again. The axles should turn freely in the axleboxes and in the side rods and proves you have eccentricity of the bush far enoug around to correct the error that had at first existed. Mark which side this rod is for and turning the axles end for end fit up the other side. You now have a perfect set of coupling rods. I can see the advanced machinist raising his eye brows at this method, but I can guarantee beginners, that set up side rods, wheels and axle boxes to my method, that they will get wheels to roll around without tight spots or slack in the side rods.