Drawing 5 - Bogie
1. Bogie Frames    
I made the front bogie assembly many years ago but there are still some bits needed to finish it. The two side frames were marked out and then cut to shape, using hand tools only, before co-ordinate drilling all the holes using the Bridgport with its DRO. There were also quite a few components that had to be made and rivetted to each side prior to rivetting the two end stretchers including the horns, the guard irons, the lower spring supports and the pressure brackets.
The inner horn blocks needed to be cut away to clear the equaliser bars but I didn't remove enough metal before assembly, hence the saw marks on the sides. One of those situations where I wish I had used rivet-headed screws instead or rivets, they could have been dismantled and worked on further. The main centre bogie stretchers, which are also the guides for the sliding block, were also made at this time but I had chosen to fix these using screws instead of rivets.
2. Kingpin    
The kingpin was made from some 7/8" diameter mild steel just held in the 3-jaw chuck and the pivot end turned down to 1/2" dia by 1.3/4" long followed by reducing the front to 1/4" dia and threading 1/4" BSF. I didn't form the two tapers at this point as I wanted to chuck on this diameter to turn and thread the opposite end. After the second end was done, I reversed the work once more, holding on the short length of 3/8" dia and machined a slight taper from the front to the half-way mark using ther compound slide set at about two degrees. Then I set it over the other way and ran from the middle to the shoulder, finishing off with some emery cloth to blend it all in. I wasn't bothered about concentricity for this, nor are the sizes overly critical - a couple of thou under nominal seemed about right. The dull black finish is the phosphate finish that I had applied at the time.
3. Sliding Block    
Next I had to make the sliding block which fits between the centre stretchers and drops over the kingpin. There is a gunmetal casting available for this but I had a lump of bronze available so used this instead. This was made many years ago but my notes remind me that I first faced up the billet in the lathe and drilled the hole 7/16" diameter. Then I turned the billet round, faced the opposite end to length (1.1/8") and then bored and reamed the 1/2" hole to size. I then loaded the block to a 1/2" diameter mandrel held in a 4th axis chuck on the table of the bridgeport and machined all the sides, finishing off by putting the spring retaining reccesses in with a 3/8" dia slot drill. The photo does show one difference from the drawing, the four tapped holes in the bottom of the block that I will explain once the bogie is fully assembled.
4. Axle Boxes and Axles    
I have made the axleboxes in the same matter as for the pony truck (page 6) so wont cover the same ground again and, likewise, the axlebox covers. As before, I have dispensed with the oiling holes as I am using sealed-for-life bearings. If they fail in service, it's no big deal to press the wheels off and replace the bearings. The axles were turned from some 5/8" dia EN8DM. I roughed them out first just holding in the 3-jaw chuck and leaving about fifteen thou on the diameters but getting the 3.543" length bang on size. The bearing journal length of 0.572" is not actually that important as long as it is not over length. This is because the wheels are pressed on with spacer collars between the bearing and the wheel to set the back-to-back distance between wheels. .
Second op was to hold on the bearing journal using some brass shim to protect the surface and turning the opposite end diameters using a rotating centre to keep things running true. The bearing diameter was machined as a light press fit and the wheel journal with a half- to one thou interference fit which will be tweaked later if needed, depends on how the reamer cuts. Once machined, I assembled both axles into their respective axleboxes and then checked the width across the bogie horns. This turned out to be a bit oversize so I then mounted the bogie to the table of the new mill, pushing the rear horns up to a pair of tee-slot packers and clamping as shown.
Then the tee-slot packers were removed and the horns to the rear given a light skim with a long-series endmill. I then came round to the front horns and dressed those to the correct dimension. Final job for the moment was to start polishing the horn block faces for a nice sliding fit of each assembly although I will probably need to ease these down to a light rattle fit later on but they will do for now. Apart from making the spacer collars and pressing on the wheels, all I need to do now is fit the axle keeps below the horn blocks.
5. Equaliser Bar    
The bogie suspension comprises a single leaf spring each side with an equaliser bar rather than independant suspension to the four wheels. At this stage, I am following the drawing and using the dummy spring castings with the hidden coil springs but I will replace them later with properly-constructed springs even though they are almost entirely hidden within the equaliser bar. The supplied castings are aluminium and I think that there will be a weak spot at the point where the spring support bars screw in and they may well break in service. They're junk but will do for now while I get further along the build. The centre section was just cleaned up in the mill to get some square faces to work with and then the holes drilled. The spring support bars were made at the same time, just threading some 3/16" diameter mild steel with 2BA
I marked out the four equaliser bar side plates on some 16 swg mild steel and then cut out the shapes with hacksaw, stitch drilling and carbide burrs although I deliberately made them longer to accomodate the bends at each end. Then I made the four spacer blocks from some 1/2" square mild steel which I drilled and then parted off in the lathe. Also made, from some 5/16" square mild steel, were the four spherical pressure pads. The radius was formed with a form tool and each one then parted off. I drilled all the holes in the side plates and the spacer blocks to take the rivets and then changed my mind, deciding instead to use 8BA countersunk screws rather than rivets, so all the holes were modified to suit, deep countersinks being formed in the side plates and 8BA tapped holes in the blocks.
The next job was to bend the offsets into the ends of the side plates and, since the step-over is only 3/32", this was done freehand in the bench vice. They were adjusted until, when assembled, they gripped the 5/16" square shanks of the pressure pads which were then positioned over the centre-line of the axlebox and clamped in place. Then the cross-hole for the rivet was drilled and the pressure pads riveted into place. Getting everything placed correctly was the most fiddly and difficult part of this job. Finally, the spring support bars were screwed into the dummy springs, assembled into the equaliser bar and the coil springs with their retaining nuts fitted.
6. Assembly    
In this picture, all the various parts have been assembled and set into place followed by lowering the axle onto the springs and bolting the keeper plates into position. I have used a 2-part epoxy adhesive to fix the pressure pad cups to the axleboxes but they should be captive now. I have set MDF packing pieces between the axleboxes and the top of the horns to set the simulated ride height and I now need to adjust the guard irons for height because they are fouling the rail at present.