The tender is of the eight wheel design with a water pick up chute.
The frames have been water cut to obtain the profile and the first job is to drill all the various holes which I do by mounting the frames paired together on the mill bed with a sacrificial plate underneath to accept the drill bit going right through.
As the mill table movement is not sufficient on the X axis the frames have to be moved along the table to finish drilling the last set of holes for the rear axle and drag bar.
With all the holes drilled and deburred the next job is the horn blocks.
These are castings and they are cast as a pair end to end.
Looking at the webs and offering up against the drilled holes in the frame it looks as if the outer webs are going to interfere with the holes as they are too thick and near the end of the block.
Before tackling that potential problem the blocks need to be machined. The first machining task is to make a flat reference side from which to work. I chose the axle box side as this was the easiest as the block could be clamped in the vice suported on a parallel, the block outer edge being on the parallel. This had the advantage of ensuring the machine face was parallel with outer edge. The blocks were machined in their cast pair configuration.
One of the problems of trying to grip shallow items high up in the vice jaws is the effect of the moving jaw tipping due to small amounts of play in the moving jaw. This means that trying to machine a second side square with the firest is almost impossible.
So having got a reference surface the next job was to machine the surface that bolts to the frame. The web that bolts to the frame is dimensioned at 5/32″ thick. To machine this face I chose to mount the hornblock on the mill bed on a parallel by the use of clamps. The machining would be done using the side of the milling cutter and would produce a square face.
Whilst the clamping area was quite small is was very effective and the cut depths were very concervative to avoid loading the work piece too much and risking it moving. Also the cutter was new and sharp.
After taking the photo and machining the first hornblock I changed the set up by putting a fixed fence at right angles to the table against which the hornblocks where clamped. This made the setting up of the horn blocks quicker.
With the two faces machined the casting was sawn in two to produce the individual blocks. This showed up a minor problem in that the casting was not long enough to take the saw cut and end up with the correct length.
The next problem to be identified was the alignment of the drilled holes in the frames with the gaps between the webs on the casting.
With the casting set at the correct height from the top of the frame it can be seen in the photo above that the centre lines of the holes do not fit nicely with the gaps beteen the webs.
The horn blocks are riveted to the frames with 1/8″ RH rivets and there is not enough room for the heads in every case. In order to find out exactly where the holes would come in rlation to the webs I jig drilled the holes from the frame.
To do this I used a 3/4″ spacing block that fits into the frame and a couple of jewellers clamps to hold the block in position. Withe holes drilled it was clear that the webs would have to be machined to allow the rivets to fit.
Block in place with temporary bolts.
The next difficulty was that the head of the rivet snap does not fit cleanly on the rivet head as there is insufficient clearance despit grinding the snap head down as far as I dare without weakening the edges. The net result is the rivet heads are not nice but disfigured.
To get the other block in place and ensure it was parallel I used the spacer again and clamped it all together to jig drill the holes.
So that was the first axle box horn blocks done and the method of doing it was OK but the end result in respect of rivet head finish leaves a lot to be desired. I now have to think about the other 15 to be done!
One and a half frames done, but I am really struggling with fitting the horn blocks due to the poor castings plust the mis match of dimensioned holes with the casting ribs. I know not which is to be blamed, but I suspect the casting and possibly the pattern maker. Jig drilling the horn blocks from the frames alway gets one and sometimes two holes right up against a rib and invariable when that happens the drill breaks on break through as it gets pushed over and jams. I have gone through half a dozen 1/8″ drills so far!
Having managed to fit all the horn blocks I turn my attention to the spring hangers.
Here I find another minefield as the hangers come as a cast stick of six and the castings are quite frankly close on rubbish. I will just have to get the best I can out of them and hopefully they will all be of a similar size and shape.
I machined a reference face by holding the stick in the mill vice first.
The stich was then turned over to mill the other face flat.
Having checked that the two faces were at 90 degrees to each other the inside faces were milled by clamping the stick to the mill table with a clamp at either end then adding a clamp in the centre and removing and end clamp to complete the cutting.
This process gave me the required thickness of the hanger.
Tyhe next task was drilling the holes. This is where the casting problems really showed up as the centre of a hanger as determined by its base width was not necessarily the centre compared to the apex. So a lot of juggling around to get the best compromise possible was necessary.
As a consequence some of the holes are nearer the edges than others.
However finally 16 were produced and fitting them is underway.
Front and rear beams
The front and rear beams are made from 40mm x 40mm x 4mm bright steel angle. This has to be machined down to size for the depth of the front beam and the ends cut at an angle. Once done it is then drilled and the slot for the drag bar milled out.
There are holes to be drilled in the top of the beam but these will be done when the tender floor plate is in position.
The beams are held in place by BMS angle 20mm x 20mm x4mm that bolt to the frames. When I ordered the material for the beams I failed to check the delivered items and when I came to make the angle brackets I found they were 5mm thick. This gave me a minor problem later on when drilling the holes as the outer holes on the beam now came very close to the inside edge of the bracket meaning that the fixing was going to be a problem.
In making the brakets the drawing calls for four, two for the front and two for the rear beam. However the front and rear beam fixing holes on the frame are not the same so just as well I noted that before drilling them.
The brackets were jig drilled from the frames and also jig drilled from the beams.
The fixing of the brackets to the front beam is shown as a countersunk rivet. As mentioned above with the holes coming close to the inner edge of the bracket a rivet snap could not be used, but there was just enough room for a 5 BA reduced nut with one face thinned so I decided to use 5 BA c/s screws as the fixing.
The fixing to the frame is 5 of 4BA into tapped holes of the bracket. Two of the fixings are c/s the other three hex headed.
The temporary fitted front drag beam
The rear buffer beam is attached to the frames in a similar manner to the front drag beam. However the holes are different for fixing the angle bracket to the frame.
Jig drilling the angle bracket fixing holes
Here the drawing shows the problem of the foul of the bracket/frame and buffer boss and rod
Angle brackets temporary in place – note the recess for the bbuffer stock
The fixing of the buffer beam to the angle brackets is by 5BA c/s screws. Now a problem arises.
The distance between the inside edge of the frames is 6 3/8″. The distance between the centre lines of the bufferes is 6″. The buffer stock is recessed into the buffer beam and angle bracket by a 7/16″ dia boss and the buffer rod is 1/4″ dia. This results in the boss fouling the frame and there being no room for a retaining nut on the buffer rod. This means the angle bracket has to be relieved to give room for a nut with one side machined very thin to clear the frame.
The relief machined in the angle bracket to accept the buffer rod nut
The buffer stock is machine from 1 1/4″ square BMS. It is first reduced to the overall measurement of 1 3/16″ square then using a self centering four jaw chuck turned down to the profile and drilled and bored out for the buffer.
The work is then turned around in the chuck to machine the boss.
To get the buffer stock to fit in the recess of the buffer beam a flat has to be filed on the boss to coincide with the inner edge of the frame. The buffer stock is jig drilled from the buffer beam for 8 BA fixing screws.
The buffers are the same as the loco front buffers, 1 7/16″ OD with a 1/2″ stub to slide into the head stock. The first task is to turn down the stock material to give the 1/2″ by 11/16″ stub. This is then drilled and tapped 1/4″ x32 ME by 1/2″ deep. It is then turned around in the chuck and the rear of the buffer turned at 10 degrees and the out side diameter finished to size.
Machining the 10 degree rear taper.
The curved fron face of the buffer is machined following a fixed guide mounted on the lathe bed with a follower mounted on the cross slide. The tool and follower are both on the same vertical center line.
Initially the face is rough turned to approximately the right width and then the follower has to be adjusted so that when the tool is on the outer edge of the buffer at the correct width the follower is in contact with the face of the template. the top slide can then be turned in and the topslide will move back as the follower pushes against the template.
The buffer has a 1/4″ OD rod screwed into it 2″ long. The other end of the rod I reduced to 3/16″ and threaded 2 BA to accept a reduced 2 BA nut. This I found cleared the frame just nicely when all assembled but has enough back and fore movement in the relieved bracket to enable the buffer to spring in and out and not be able to come completely out.
The assembled buffer beam
The buffer stock was jig drilled from the buffer beam for the four 8 BA fixings.
The front beam drag box is a silver soldered assembly of a top and bottom plate with 1/4 ” spacers at the sides.
It is bolted to the drag beam with reduced head 4 BA set screws.
The holes for the pin will be drilled when the tender floor is fitted.
There are four angle brackets fitted to the frames to support the tender floor. Thses are seen in the photo below.
All the holes to fix the tender floor to these brackets and the front and rear beams will be drilled with the floor clamped in position at some future time.
Axle bearing boxes
The axle bearing boxes are one piece castings and more casting problems were evident due to mould slip so the dummy cover fixings do not line up and the bosses are going to be difficult to get centred.
The first maching task is to turn the top boss that takes the spring buckle. This was done by using the four jaw chuck and getting the boss to run as true as possible. It is not dimensioned on the drawing but is readily established as being 7/16″ in diameter. The height and bore details are dimensioned.
The second maching task is to clean up the two sides. This was done by holding the work by the boss in the three jaw chuck in the dividing head. Knowing the centreline distance to the base and using a height gauge the side surface could be machined accurately to be exactly 1/2″ above the centre line.
Having done one side the dividing head is rotated 20 turns to do the other side.
The job is then returned to the lathe to clean up the bottom face so it measures the corerct distance from the top face.
The box is rechucked to do the axle bore but first the axle centre has to be found and centre popped. The box is set on its top on the mill table so the top boss falls into the mill table slot. Then using a height gauge the centre line can be marked on the axle boss according to the as drawn dimensions. The box is then turned on its side and again the centre line can can be scribed with the height gauge.
This shows up how far the casting is out as the centre of the boss is way off the cast centre.
With the box chucked in the four jaw using a wriggler in the centre pop the box can be centred so the centre pop runs true.
The face can now be turned so it is the correct dimension from the cast front of the box. Fortunately that leaves enough spare metal so the as cast boss can be turned off and the 1/16″ deep boss machined in place.
Once that is done the axle bore is drilled and reamed 7/16″ for 1 1/8″ deep.
The box is returned once more to the mill to machine the side slots.
The box is mounted on parallels in the vice and the a 7/16″ bar is put in the axle hole. This bar provides the datum for the slot dimension away from the centre line.
Having established the relevent surface datums to slot is milled.
With one side done the box is turned over and the other side machined establishing the datums is a similar manner.
All that remains is then to clean up the as cast cover.
With two axle boxes done an axle was made turned between centres as the axle will not go down the bore of the lathe headstock. The 5/8″ diam bar was first held in the chuck and a centre put in, turned around and the other end centred as well. This means the 5/8″ bar will not be truly symetrical about the centre line as the length extending from the chuck does not rotate true at the far end into which the centre drill is drilling. However when between centres the turned ends for the wheel bore and axle box bore will be true.
Having turned one end to the correct dimensions the axle is turned around and the other end rough turned having marked off the approximate point of the 4 11/16″ back to back measurement. Once a resonable shoulder is achieved the axle is removed from the centres and the back to back length measured to establish how much has to be turned away to acieve the correct back to back measurement. With this knowledge the axle is returned between centres and the second end finished to length and diameters.
With the axle fitted into both axle boxes will they freely slide into their hornblocks? ……. Yes…. a result!
Interestingly the as drawn distance between the axle boxes is 3/16″ longer than the length of the axle over the wheels giving a 3/16″ “slop” side to side. Yet the middle pair of axle boxes have their inside boss removed so increasing the side to side movemeny by 1/8″ overall. I checked this against my A4 tender and that too has the side to side allowance although I did not check if the middle pair was greater.
I have aslo now checked a couple of other loco’s built by club members and their “slop” is minimal so I guess its down to either the builders or as drawn choice. I will leave mine as they are.
All four axles and their boxes are now done.
There is more work to be done on the axle boxes namely the finishing off of the as cast cover. The problem here is that the two pips either side of the cover which form the area where the fixing bolts would be located do not line up. They are offset due to the pattern/mould slip mentioned earlier.
If you look at the photo above carefully you can see my scribed line of the centres of the fixing lugs, the right hand one being higher than the left. I am still in thinking mode about what to do.
So…. having thought ……. use the CNC to profile the cover, which is what I am now doing.
As the axle boxes are all slightly different in dimensions due to getting them machined out of the under sized castings each one has to be individually profiled, fortunately it does not take long to draw and the CNC operation is about 2 hrs with a very small cut of 10 thou. with a 1/8 end mill running at the max speed of the mill of 2000 rpm. Just another seven to do ……
The lugs have to be 1/8″ radius so both can be aligned. I will have to wait and see if that is OK for all axleboxes.
So, all axle boxes were OK with 1/8″ lugs and have now been finished.
In the picture above can be seen the dummy cover fixing bolts which are 10 BA.
The next job is to make the axle box keeps. These are held in place by the tapped holes just above the axle box in the picture above. (The tender frame is upside down at the moment).
The keeps are simply 1/4″ x 1/8″ bar with two holes for the fixings. As I did not have any stock material of that size I used a slitting saw to cut the keeps from 7/16″ x 1/4″ flat bar that I had.
With eight keeps cut they were stacked together for drilling as can be seen in the photo below.
As the jewellers clamps are wider than the keeps there is a piece of scrap material (the bit sticking up) to pack out the keeps in the vice.
Next on the job list was to drill the sole plate. I bought the 16g brass cut to size so it was clamped to the frames in place so that all the holes that went through the frames would line up when drilled.
I did the drilling on the mill table and the clamping arrangement is as shown below.
The frames were aligned parallel with the table and there are clamps at the right hand end both clamping the sole plate to the frames and then the frames to the mill table.. On the left another clamp to hold the sole plate to the frames and then the two large clamps holding the frames down on the table. This clamping arrangement had to changed four times as the frames were too large for the drilling to be done all in one setting and the frames moved to get the required holes to be drilled under the quill.
With all the holes drilled the sole plate was marked out for where the wheel splashers go.