Brakes Part 4-Pull rods

On to the pull rods, I began with the 'U' shaped ends which slide over the beams and are then secured with the remaining pins. These are the same width and thickness as the links shown in the last entry but these are doubled over and thus why I called them 'U' shaped. There are two sizes, small which connect to the beam behind and long which slide over the beam in front and then connect to their relevant compensators. The rods themselves are of 2 different lengths plus the leading pull rods which are different altogether.  I'll cover all of these parts when we get to them, for now I'll concentrate on the 'U's'.

The first picture shows the parts cut oversize and centre drilled ready for heating and folding. The rods themselves are 1/8 dia, I have drilled smaller holes for now as these holes will distort when folding. Differing from the drawing a little, I plan to drill/tap these holes 5BA and thread the rods to match, this will allow me some adjustment to the lengths to unsure the rods work properly, I will silver solder them after. With the holes drilled I then drilled a cross hole into some steel bar that's  slightly larger than 1/8 to use as a jig for forming the 'U', the same drill was then bonded into the bar to act as a pin. Thus this gave me  a method of ensuring the bend is in the middle of each 'U'. As can be seen, we need 4 long and 6 short 'U' shaped ends.

Next job was to heat each to a cherry red, slide onto the pin and form around the bar. I used forceps to hold each piece, only heating the middle section around the hole. I then checked that the 'U' was square to itself, IE both parts were inline with each other.

Each end was then removed from the jig, slid over a length of 1/8 flat bar and squeezed tightly in the vice.

I then needed to drill the holes for the pins that secure the rods to the beams, to keep the two 'wings' apart a short length of 1/8 bar was cut and wedged into the part. I had deliberately cut these over length so that I could drill the holes without having to drill through anything in between and also to do the final shaping at the end, more on that in a minute. here's one of the short ends ready for cross drilling No. 30.

I then clamped a stop to the machine vice and set the distance from the end to the hole. There are two measurements, for the sort as seen in this next picture it's 1/2", for the longer ends it's 1 1/2". Of course, the center was also clocked.

This resulted in these 10 part finished 'U's...still very rough at this stage.

Now, as with the links the middle section is also reduced, although in this case there is only one end with a hole to the reduced part goes right the the folded end. This may look a bit precarious but it worked out very well, as mentioned before I had cut the steel over-length, it's at this stage that I used that extra metal to hold each 'U' securely for me to be able to reduce the end, machining both top and bottom wings in one go. I did the longer parts first, if there was going to be any issues it would happen with these, there was none, no movement whatsoever while machining. Note the screw, this had two functions, first it held the wings together, I used a suitable nut as a 1/8th spacer, it also showed me that the part was held level in the vice as I could use the thread as a visual guide that the part was being held upright. The smaller tongue is 60 thou narrower that the end.

This got me to this stage...

next job was to profile the end boss, before returning to the rotary table I first removed most of the tails that were used to hold the parts for the previous machining operation.

Then to the rotary table to round off the ends...

After a general clean up the center holes were opened up for a 5BA tap, I forgot to take a picture showing all of the parts, only remembered to take this one showing a few of them after making a start on assembling the rods. As mentioned earlier I have deviated from the drawings and threaded the ends of the 1/8th  rods 5 BA to give me some adjustment during final assembly. The chances of all the components going together and working without being adjustable just isn't going to happen, well not in my minds eye at least. This way I can assemble all the parts and adjust the rods for the best operation of the brakes. I have added a 5 BA nut to each rod to lock against the 'U' shaped end once happy with said adjustment.

Lastly for these parts a couple of pictures to show them fitted to the chassis, to do this I used the lifting rig and worked on the model from underneath, made life much easier.

One from an angle...note that the brakes have been fully engaged with the wheels to help get all the parts equally spaced, that is, the rods are the length that they need to be.

And lastly directly from underneath, nothing is secured yet, with the pins being loose for now. Once happy with the fine tuning I'll fit the various washers and split pins required to make the brakes tight and free to operate.

The next entry will hopefully show the brakes completed and also tested. I need to make the leading pull rods (nearly done) the adjuster and the shaft pull rods, after that everything needs to be taken apart again for painting. Once that is done and they are refitted I best take a look at the steam sander pipework as they need some fine tuning of their own to stop them fouling the brakes. So guys, for those following in building 'Doncaster' do the brakes first...:)