The cylinder castings

These are the cylinder castings that came with the set of locomotive parts.

(They are 90mm long and and have an out side diameter of 66mm. The finished bore is 40mm).

It is the first time for me that I’ll incorporate cast iron cylinders, all my previous locomotives are fitted with bronze cylinders. 

The boring of cylinder, with only light cuts. The set-up in the chuck is far from desirable.

This cast iron is of a good quality (no hard spots) and machining in the lathe was done with carbide cutting tools.  Although they are large, they could be clamped in the 3 jaw chuck. This made turning a straight forward job.

During manufacturing of the cylinders there is not much difference with bronze, but the usageof cast iron cylinders on the finished locomotive will be different. This material depends on good lubrication with first grade quality steam oil. Otherwise rust will set in quite quickly. Also all the condensated water has to be removed via the drain cocks after the run I'm told.

Honing the bore with honing stones

After boring out the cylinder to the correct diameter (in this case 40mm, which is small for a 7.25” locomotive) anautomotive honing tool was bought and used for finishing the bore to a smooth surface.
I’ll be using Teflon piston rings of the same design as used in the Mona, Dacre and Didcot. In these locomotives they proofed to be successful and never needed any maintenance yet.

A smooth finish is obtainable

The cylinder port face on the original Prussian T3 (for which these castings are intended)  has an inclined angle. In my design this will not be incorporated, so the shaping machine was put in action to remove the surplus of material. The shaper leaves the port face with a very flat surface. The machining marks, left by the tool, are all parallel and in straight lines. 

This will be near to perfect to take up a small oil film, on which the valve can glide. The slide valve it self will also be machined in the shaper, but the set up will be arranged so that the grooves left by the cutting tool will be 90 degrees to the ones in the port face. I’ve used this method before with the other locomotives and the slide valves and port faces still look very good after years of service.  

  

The cylinders partly finished, with the covers in front. These were made by Wolfgang years ago and can be used without any problems.  

Cutting of the steam ports. They are 4 mm and 8 mm wide and were cut with a small 3.5mm cutter. You'll see no chips in the picture, because I've used a vacuum cleaner to remove them after every cut. This way I kept a clear view on the process and the chips would not clog up the relative deep ports during the cutting process.

Set-up for drilling the steamports

The exact angle was diterment  in Solidworks, before drilling!

A lot of holes

The steamports, avoiding the tapped holes.

The light beam shows the exact match of the holes.

Opening out the steamports at the cylinder ends.

Providing clearance in the cylinder covers.

The steam passages.

The cylinder cover.

The portface with steam and exhaust ports.

Fabrication of the steam chest from solid bar.

Drilling and tapping the holes for taking up the steam chest

Bronze valves

The piston rod and gland

Both glands on the covers

The pistons whit the grove for the Teflon piston rings

The Teflon U-shaped ring. This was turned from solid Teflon and sits with a side play of 0.2mm in the grove of the piston. In the depth there is a clearance of approx. 0.4 mm.

 They have a sliding fit in the cylinder bore. Expansion due to heat and steam will press them further against the bore; but they also have the possibility to buckle the thin 'legs' of the U shape, if the expansion would be to much so that they wouldn't fit in the grove in the piston.

When the engine is in steam, steam pressure  will also get under the ring and will press the ring against the cylinder bore.   I have these types of rings successful in service in my 3½" gauge and 5" gauge locomotives for many years now. 

The bronze piston in position.

The brown stuff is copper grease, which is used when screwing the studs in the cylinder.   Hopefully the studs are removable from the cylinder; even after many years of service.  

   

       

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The axle boxes, horn blocks and springs.

  
   

The axle boxes are the so called split type. The upper bearing is made from bronze, the lower part from brass and the axle box from mild steel. Of course everything could be made of bronze, but I had no material available in this size. One could ask if the split bearing type is necessary, but I would like to able to remove the bearings, without removing the wheels from the axle. I must state that I’ve this type of axle boxes on the “Mona” (3.5” gauge) and “Didcot” (5” gauge) as well………and I had never to remove the boxes jet.

Due to the relative small wheel diameter (138mm) there is not much ground clearance for the spring hangers. If I would use the same design as with the Mona and Didcot, there is a possibility that in case of a derailment (not uncommon on 7.25” gauge ground level track I’m told) that these spring hangers would get seriously damaged.

I could have made a design with the springs on top, but that would coincide with the boiler.
 So I’ve drew up a system on which the springs are positioned inside the frame beside the axle box. The springs are fixed between a bar on top of the horn blocks and one bar below.

Milling of the horn blocks from square brass bar.

This construction is quite strong and the lower bar acts like some kind of skid plate in case of a derailment. 

For the necessary oiling of the axles, each axle box has a milled recess on the top, which has a drilled hole that is in connection with the bearing below. 

Tribology theory taught me that it is unwise to feed the oil to the axle on the top. There is a hydrodynamic lubrication: This form of lubrication occurs more or less naturally in properly finished, sized, and lubricated holes and shafts. Essentially, rotation of the journal causes it to drag lubricant into a wedged-shaped channel generating a load-carrying pressure. The lubricant in this wedge creates sufficient pressure to keep the journal riding on the oil film. This form of lubrication is generally preferred because it is simple and dependable.
An oil feed hole on top would partly destroy this build up of pressure. So why use it anyway? There is a quite simple explanation, I found in a reprint of an old German locomotive handbook. 
Indeed the oil film build up of pressure is not as good as it could have been, so most of the wear of the bearing would take place on the top………just were you want it. The locomotive “would sink deeper in the bearings” and that is easy compensated by the springs. The wear over the horizontal line of the bearing however will be less, because the oil film is there not interrupted by an oil feeding hole. And exactly on that position are, on a steam locomotive, the greatest forces due to the movement of the driving rod and movement it translates from the piston to the frame. 

    
The manufacturing of the axle box is a straight forward milling job.

The boring of the hole for the axle was done in the lathe. The set up for machining this hole was done in the 4-jaw-chuck. To get the hole exactly in the middle, a small pilot hole was first drilled in the milling machine (with the aid of an edge-finder this is precise and quick). Once the job is transferred to the lathe, a fixed centre point is put in the pilot hole and the centre is supported with the tail stock. A dial test indicator is put on the centre, and by adjusting the jaws the reading of the indicator can be set to zero.

The hole for the axle is on this loco 22.04 mm. First the hole is drilled up to a diameter of 20 mm. The last 2 mmare turned with a boring tool. Reaming is also possible, but I didn’t had a parallel reamer in this size and find that the lathe boring tool gives a better and more controled finish.

On top of the axle box I’ve made a small lid, which can be opened and closed with the tip of the spout of an oil can, which conveniently fits through the spokes of the wheels from the outside. The lid should prevent to get dirt and grid in the oil reservoir, which is always around when driving on ground level track. The lower part of the axle box has a milled groove, in which a piece of felt will be fitted. This should make sure that, even in the event that the oil reservoir is running empty, a small quantity of oil will keep the bearing lubricated.

A simple set-up for pressing the hinges of the oil cover.

The mild steel plate is only 0.75mm thickness and is cut from the housing of a dvd-rom player

All the parts ready for assembly.