Now You Can Finish Your Boiler For The Beginner's Locomotive

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Now You Can Finish Your Boiler For The Beginner's Locomotive

by Cliff Blackstaffe

Victoria Society of Model Engineers

The Miniature Locomotive, July-August 1954

You can now lay out the tube holes on the tube sheet former plate for the firebox end. They are 1/2 inch centers horizontally and 7/16 inch centers vertically. There are eighteen tubes in all, 3/8 inch O.D. and standard commercial IMperial tube is used.

Now the question of superheaters is bound to come up so I'll tell of what I've seen. We have a 4-4-0 3-1/2 inch gauge engine with fifteen 3/8 inch tubes and cylinders 1-1/8 inch by 1-3/4 inch. She is non-superheated but can run like a deere with not only a dry EX but a clear one. Her grate is 2 inch by 6 inch though deeper than our 0-4-0. She'll do 1/2 a mile regularly on one firing so what more do you want.

This engine is designed to run on almost any coal because it's no trick to clean the tubes after every run as I've had to do myself when on certain inferior coals. Now feature an efficient superheater getting full of tarry muck after one run. No, if you can't keep a superheater clean you're better off without it, as then you'll get more draft. Dear old Curly will object to this but I think one run on our coal would cause him to stretch a point here and I'm not claiming superheaters are no good.

Drill the steel former plate 3/8 inch and place it in the firebox tube plate and this in turn centered up in the smokebox tube plate with a 1/4 inch scrap of plate under it clamp down on the drill table and drill as many holes as possible. Then hold with another clamp and removing the first one drill the rest of the holes. You'll now have good clean holes in both plates. Cut your tubes off to 6-1/16 inch long and chucking each end face off a skim and remove burrs.

Now swell three tubes with a drift or tapper punch until they are a tight fit in the smokebox plate. Drive them through about 1/16 inch one in each corner of a triangle. Fit the firebox plate onto these well in to hold them projecting 1/16 inch into the firebox. Now stand the works on end resting on the tubes projecting through the smokebox plate on a flat surface where your going to braze. Drop in all the rest of the tubes which will now rest on the surface below and hence stick through evenly above. Paint all around with wet flux and braze as before being very careful every tube is done all around. Reverse and do the other end.

The hole for the throttle is drilled 5/8 inch on the vertical center line at 11/16 inch from the top of the tube plate; also two 1/4 inch holes for the ongdritudinal stays. Clean up the joints.

The tube nest can now be set on the combustion chamber end and when on; a rule should be laid along each side and the top of the firebox to ensure the tubes are parallel. When right, three 7/64 inch holes should be drilled through the flange into the combusion chamber. One each side at the top and one at the bottom. Tap these 1/8 inch by 40 and screw in bits of threaded copper wire. This is to be sure the thing dont' go out of place on heating. Now with it standing on its nose, flux around the joint, and getting things hot enough to flow again, start it on side and flow right around. Then a touch over the screwed wires for good luck.

You may as well lay out all the stays on the shell and drill them 3/32 inch for now, until they're swdged in.

The smoke box tube plate may need easing until it goes through the shell from the rear when the fire box can be shoved into place. Put a bit of 1/4 inch square stock, copper prefered, but brass will do, the full length along each side. These will need notching to clear the throat plate flange and drill 1/8 inch at each end for temporary bolts. See that the firebox is evenly spaced all around and do likewise on the other side.

You can now cut the fire hole in the backhead. Now shove the backhead into the shell until its up against the firebox end and scribe the door hole on it. The stay holes can now be drilled through into the firebox and as they all enter radially no trouble should ensue. Remove fire box and swedge the holes into counter sinks by the little male and female punch and die shown. These are made from 3/8 inch drill rod and left soft so the punch pilot won't break off. Take a square bar of iron say 1 inch to 1-1/2 inch square and about a foot long and drill a shallow 3/8 inch hole near one end into which the die or punch may be set. Grip this solidly in the vise put the shell over it with a stay hole in line then insert the punch pilot through the shell into the die and hit it squarely with a hammer. A nice conical counter-sink will be formed without thinning the plate. This method leaves the stays flush both ouside so lagging plates will fit snug and smooth inside to be easily cleaned of soot. Do the firebox holes likewise only put the punch into the bar and drive the die onto it. Cut the fire door hole in the door sheet. Cut the firehole ring out of 1/4 inch sheet brass or copper prefered. Rivet this onto the firebox with two rivets countersunk into the ring. When the backhead is put in for the last time two more copper wire rivets can be put through the whole works holding it for brazing.

The hole for the throttle in the back head is 3/4 inch diameter but note it is drilled 3/16 inch off center to the fireman's side and you'll notice also that the block carrying the throttle rod gland is eccentrically drilled. This is to avoid a solid piece of metal into which the trottle fulcrum is screwed.

The holes for the longitudinal stays in the backhead are drilled 3/32 inch and taper punch is driven through with the plate resting over about a 3/8 inch hole so the metal will be extruded into the boiler until a hole 13/64 inch is produced. Tap this with a 1/4 inch by 20 U.S.S. and the two 1/2 inch bronze welding rod stays are screwed through until flush with the outside of the backhead. This will be later brazed flush.

Now shove the firebox back into the shell and try the back head in place. Adjust the inner nuts on the stays at the smokebox end until the nuts hold the backhead up against the fire door ring and the curve of the backhead flange is sitting about 1/8 inch or 3/16 inch proud of the shell sheet. This is a very prominent feature of all boilers and adds neatness to a miniature. When right, drill the other two rivet holes through backhead door ring and door sheet and rivet up. Tighten the two outside front end nuts and remove the whole assembly until we'lve fitted the throttle tube or dye pipe. Set the shell on the banch and scribe a center line down it's back on which to set the fittings so they don't look like you've broken rule G.

Now starting from the back end of the shell 5/8 inch forward center punch and drill 1/2 inch for the auxiliary steam connection. At 3-13/16 inch from back edge drill another 1/2 inch hole for the dry pipe stand pipe. 9/16 inch forward of this is the center of the dome and in a 1-1/2 inch circle drill about 10 or 12 holes 3/16 inch diameter to let the steam enter the dome but keeping the splashes down and the shell is not locally weakened by the large hole otherwise used. At 7-7/8 inch drill a 3/8 inch hole for the feed inlet flange. And at about 1-1/4 inch back from the front end of the shell another 3/8 inch hole to take the socket of the bell bracket flange. A 3/8 inch hole can be drilled at each side of the firebox to take the flowdown and washout plugs or two blow downs if you like.

We now need to make the dry pipe and throttle gland block, etc, as this must be put in before the tube assembly can be put in the shell for keeps. The front end piece is turned down 7/8 inch bronze rod. Face, center drill 23/64 inch and ream 3/8 inch. Leaving 1/2 inch length full diameter run in parting tool until you've reduce it down to 5/8 inch diameter. Turn along for 3/4 inch and part off. Now make the throttle seat from the same 7/8 inch stock. Face center, drill 3/16 inch for 1/2 inch deep. Turn down 1/8 inch length of it to a spigot fit in the 3/8 inch reamed hole and face joint surface flat. Take a light scrape off the valve seat with a tool set to approximately 45 degrees. Part over all. Drill a 1/4 inch cross hole to break into the 3/16 inch steam way into which the 1/4 inch copper steam pipe to cylinder will be brazed. Now drill three 9/64 unch holes around the rim missing the steam way out. Put the two parts of the throttle together spot the holes, drill 7/64 inch and tap number 6-32. Under the dome there is a block of any scrap of old brass as its on a TEE. It is drilled 3/8 inch right through and cross drilled 21/64 inch and tap 1/8 inch pipe thread for the stand pipe to the dome.

The throttle gland block is 3/4 inch diameter and setting it over in the four jaw so it is 3/8 inch eccentric, face, center, drill 1/8 inch for 1-1/2 inch deep. Open out with a 1/4 inch drill for 3/8 inch deep. For the packing box. Part off 1-3/8 inch over all. REverse in chuck using the shank of the 1/8 inch drill in the hole to center up to and drill 3/8 inch for 7/8 inch deep.

Now look at the back head drawing and you'll see the way it has to go, i.e., heavy side on the left. On the top in this position file a flat to provide a flat surface to start the drill on and locate the center of it in relation to the hole in shell allowing the back to stand 1/16 inch pround of the backhead. Drill and tap 1/8 inch pipe thread. Screw in a nipple to get the line up and, using this as vertical, scribe a horizontal line across the end cutting the center of the throttle rod hole and a vertical line ditto on which to drill the gland holes 3/8 inch over to the left drill 7/64 inch and tap number 6 for the throttle fulcrum to screw in. Now turn the gland from 9/16 inch brass having a 1/4 inch diameter spigot 1/4 inch long and drilling 1/8 inch for throttle rod. While some full size locos have round gland flanges, I rpefer the oval ones so as you've had practice on the cylinder glands, do likewise. Drill the stud holes 5/64 inch place gland in box and set it vertical by the scribed line, spot, drill and tap 0-80. You may feel these are awfully small but they're still over scale and strong enough with ordinary care. The studs and nuts should be all brass as there is no oil here and drips of water will rust up steel studs and nuts all to easy. Don't fit stud until brazed in.

Cut off two pieces of 3/8 inch copper tube 2-1/2 inch and 7 inch long for the dry pipe. If it fits loosely in the 3/8 inch holes swell it a little so it will hold where put and proceed to set it all up in place so the TEE piece comes in line under the 1/2 inch hole under the auxiliary steam stand pipe will line up with the hole in the shell for it. Set the front end flange around so steam outlet hole from throttle is horizontal