Elmer

Elmer's Mine Engine

The first part to be made was the cylinder. A bit more to this one than the other models I've done so far. I decided to take this process a step at a time to show how it is made.

The cylinder is made from 1" square stock. I chose to use brass. The print looks like this.

The print shows the bore is offset 1/32" off center in one direction. To get that it's chucked up in a 4-jaw and indicated "0" to two sides 180 degrees apart, and +.030 and -.030" to the sides 90 degrees off. The first end is turned to the 15/16 diameter shown back 1/4"

To keep the ends concentric I replaced the 4 jaw with a 3 jaw chuck and turned the piece around chucking on the already turned end. I did run an indicator up one of the flat sides to be sure it was square in the jaws.

The opposite end was then turned and center drilled. The bore finishes at .500" so I drilled through at 15/32" leaving .015" per side for finish boring.

It's all mill work from there. The sides are milled as the print specifies

The mini mill cuts the brass easily taking .060 at a time as the video above shows. After that it's ground, sanded and polished to it's finished shape.

The cylinder heads are turned from 1" brass stock.

They're turned complete, then parted off the bar.

After drilling and tapping all the holes in the cylinder and heads I made the piston rod guide. When I was at the hobby shop to buy ANOTHER 2-56 tap, I saw these little 2-56 socket head screws.

I bought all he had. They do look good in this partial assembly of the cylinder.

Next I built the steam chest. It starts out as a 1-1/4 X 5/8" X1/4" block of aluminum.

The ends are turned round in a 4-jaw chuck. I drilled the hole for the steam valve rod, clearance hole and tapped the end for the packing nut before taking it out of the chuck. The rest is mill work. The center is milled out and 4 holes are drilled in the corners for clearance on the 2-56 bolts that will attach it to the cylinder. I've seen other's models with clear covers on the steam chest to show the valve, and decided to try that on this model. I think it turned out OK.

These pictures also show the finished table. It's made from 1/8" thick aluminum.

The next item on the list was the valve rocker assembly

Making the levers was a little involved. There may be a better way, but this is how I did them.

First I turned a disk the proper diameter from a piece of brass stock and parted it off, allowing about .020" on the thickness. The disk was then chucked up and the faces dusted parallel. After that the 3/32 and 1/16" holes were laid out and drilled. It was then chucked up is a 4-jaw lining up to the 3/32 hole, and the face was turned back 1/16" to the diameter of the raised boss.

Using scribed lines as a guide it was roughly cut to shape on the band saw, then ground to the finished shape. Then back to the mini-mill to be drilled and tapped for a 2-56 set screw. Soldering a 1/16 x 3/16" pin into the 1/16" hole finished it. The rocker shaft was made from a flat link and a piece of brass turned to 3/32" The rocker bearing block was nothing special, so I won't document it's machining. The final assembly looks like this.

Next step was making the valve links and cross heads for both the valve and the cylinder. The cylinder crosshead started out as a piece of 1/4" square brass stock. The second picture shows the finished cross heads.

Next item was the piston and rod.

Both parts are made from brass stock. The piston is drilled and tapped for the rod to thread into, and the opposite end of the rod is threaded for the nuts that will secure it to the cross head.

That brings us to this point.

The top end of the engine is done.

I finally found some 1/2" thick aluminum stock to make the base.

That involves a few steps.

First it's cut to rough size allowing stock for finish machining. The bottom piece of the base is 1/4" thick, so that part had to have 1/4" milled off of it. I used a homemade flycutter shown in the third picture. The last picture shows the three pieces milled to size, drilled and tapped for assembly. The edges of the two 1/2" thick plates get beveled, but I will do that later.

The plans call for the bearings to be made of aluminum with bronze bushing for the crankshaft to run in. I decided to make them completely of bronze since I have a good bit of it in the stock box.

The two pieces are cut off my stock bar and milled to their overall dimensions. They are then milled to shape and mounted to the base for drilling. They are drilled assembled to ensure the bores will be in line.

The next parts were the columns and connecting rod.

The columns are pretty basic. Just 1/4" brass rod turned on one end and threaded to screw into the tapped holes of the base. The opposite ends are drilled and tapped for socket head 6-32 bolts that will mount the table to the top of them. The connecting rod was as much fabrication as machining. The cross member is one piece machined from 1/4" square brass. The rest of it is separate parts soldered together. Keeping it square and maintaining the center distance between the crankshaft eye and the piston cross head eyes took some jig work.

With the base plates beveled and all the parts finished to this point assembled we're at this point.

The crankshaft was next on the list. It is two parts. The crank end is brass and the shaft will be steel to better run in the bronze bearings. Making the crank is another multiple step deal.

First the major O.D. is turned and the bore is drilled. It's then parted off allowing .020" on the thickness. Then it's turned around and chucked up grabbing it on the 3/32 hub, and the back face it turned true to bring it to the proper thickness. After that the crank pin hole is drilled and tapped. Then the profile is milled to shape. A little polishing up and the crank is done. Now the shaft.

The shaft was first chucked up short and the end was turned for .004" press fit in the crank, and center drilled. It was then pulled out and a live center was used to turn the length of it for .002" clearance in the bearings. Once that was finished it was parted off to length and it was pressed into the crank to complete the part.

Most of the screws and nuts for this engine are purchased, but the crank pin is special to the design.

It's turned for .002" clearance in the connecting rod end, threaded to match the thread in the crankshaft crank and slot is cut for a screwdriver.

It took some adjusting of lengths diameters and clearances to get the assembly to turn freely, but it all came together. This picture is of the crankshaft installed on the engine.

The eccentric that will operate the valve is to be 5/8 O.D. with a 7/16" offset fit machined for a .050" throw. First it is tuned to the 5/8" and drilled 1/4" for clearance on the crankshaft.

I read somewhere that a throw can be machined in a 3 jaw chuck by shimming one jaw. The formula is: Offset = 2/3 Shim Thickness To get my .050" I need a shim of .075" I happened to have some 1mm thick brass that is .039" thick. Two pieces stacked would be .078" I chucked the piece up with the shims and checked it with an indicator. Perfect .100" total run out. .050" throw with no indicating!