At last I'm back in the workshop. It seems an age since I did any metalwork. I had to stop to make yet another doll's house (the 6th!!) So many grand daughters.

However, I've made a start on the frames. There seem to be a lot of holes to drill which is not easy as the length needs supporting. I began with the buffer beams and the angle brackets. These I drilled on the mill using the DRO which gives an accuracy to 0.2 of a mm. When it came to riveting them to the beams, I turned two spacers at 6.2mm thick so that the gap created was a fairly tight fit on the frames. Even this could have been a bit wider. If I'd made it 6mm, I've found that this proves to be too tight and the frames almost impossible to push between. It's probably because the angle pieces aren't perfect right angles. I used 3/16" rivets to the beams and 6mm bolts to the frames.

While this has been going on, I've spent some time on the design aspect and decided to use needle roller bearings instead of the usual cast iron blocks. Fairly expensive, but solves the problem of getting to them for lubrication. More of this when I get to that stage.

I've made a start on the horns and suspension. I've begun with the centre axle. The problem is, because the wheels are on the outside of the frame, there is little space for the firebox. This centre axle goes right across the centre of the firebox and so there are complications with the ashpan. I'm trying to keep the intrusion into the space as small as possible by making the suspension unit as narrow as I can. The largest intrusion being the diameter of the springs, so these are as close to the horns as I can get them. I am making one complete unit first to see if it works OK before I begin to mass produce all the individual parts. I've riveted the horns on with countersunk rivets to avoid contact with the springs. The top of the angle going across, has to be within certain limits as the boiler will sit on top of this. Likewise, I've riveted the cross piece with countersunk 3/16" rivets. I would have used bolts, but the nuts would have fouled the suspension action.

Notice I've a block in between the two angles. This is accurately machined to width and when in place, holds the angles in the right place as the block fits in the frame opening. I have found in the past, that no matter how you clamp them in place, they can still slip a small amount when you drill and when riveting. This seems to work for me. The inside edge of the cutout in the frame is part of the surface which comes against the axle boxes.

The completed unit shows how the set up works. The adjusting nuts will be easily located from underneath when the time comes to set up the springing. At the moment, it requires a considerable effort to move it against the two springs. The brass guides also act as spring locators. I had to make the cross bar 8mm thick so that there was no chance of bending under driving conditions which might have produced sudden shocks to the system. The weakest part being caused by the hole and thread for the centre bar. Because of this I've welded them in deep countersinks after screwing in place. This arrangement means that there is only 10mm of movement available before it hits the bottom of the boiler firebox. However, that should be quite enough providing I set it up so that when stationary, it is on the stop. All I have to do now is make five more just like it!

Although I've spent a long time in the workshop, there doesn't seem to be much achieved. I've been working on the suspension, and I calculated that I drilled 1682 holes, made 224 different pieces and put in 206 rivets! This has included the bogie suspension which is a smaller version of the main system. I've still not made the axle boxes,
I've also been working on the swivel and side springing of the bogie. The full size version is a massive affair and I've decided to make a substantial job of this. The stretcher in the main frame is 12mm thick and bolted into through the frame to hold it in place. I felt this wasn't thick enough as a support for the king pin's side load and any twisting. Not wishing to add any great weight by using a steel block, I welded a piece of box section being 25x50x3 with a welded seam. This is very strong and gives a support for the pin of 37mm instead of just 12. Although the mig welder does quite a reasonable job from the appearance point of view, I've used body filler, not from any aesthetic reason since it won't be seen, but to fill in any irregularities which might hold water and therefore rust as welding is prone to this.

The problem of how much side movement to allow arose, and that I wasn't sure how to calculate this. So the way I've got round it is by having a sliding block resting on two stretchers. In theory, the block can move the entire width of the bogie but this will be controlled by the springs and two adjustable stops. These being able to be adjusted from outside the bogie frame. The block is made of cast iron, which works well against the steel stretchers.
The king pin is also substantial being 12mm diameter with a centre portion of 18mm. This allows the nyloc nut in the main frame to be clamped hard up and swivelling takes place in the sliding cast iron block.
The two stretchers are well over the top and in my drawings are about half the width, but I made use of the materials to hand as they are only 155mm long and so I found them in the offcut box.

20 October 2005

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