5" gauge Britannia (a builder's diary)

[trainman]

Hi Steve,

How did you secure the axle in the fixture exactly?

Grub screw?

Thanks,

Paul

[springcrocus]

If you look carefully at the second picture you will just make out the M5 grubscrew. I set it to one side to take advantage of the increased material thickness, a 3/4" dia shaft through a 1" square doesn't leave a lot of meat in the middle section.

Steve

[springcrocus]

The crank pins and end caps were made from various offcuts of mild steel and are straightforward machining operations in the lathe. The most important part is getting the diameters accurate and concentric so the 3/8" diameters for press-fitting into the wheels and the bearing diameters were turned in a single operation prior to parting off. Each of the pins was then held in the 3-jaw self-centering chuck for any subsequent operations.



There are two pairs and two individual pins that go to make up the set although they all have a common locating dia. The nearside rear crankpin differs from the offside because the speedometer bracket bolts to it. I'm nearly ready to assemble the wheelsets.

Thanks for looking in

Steve

[springcrocus]

To finish the driving and coupled wheels, they need the holes for the crank pins made, the pins inserted and the keyways cut into the bore. I also need to cut some keys from some 1/8" square keysteel, usually EN5 or EN6, which I just ordered. The latter is not to drawing but is how i've chosen to quarter (and retain the setting of) the wheelsets.

The position of the crank pins needs to be very accurate across all six wheels and I have, therefore, chosen to use a drill jig for this purpose. The jig is just a piece of 1.1/4" x 1/4" flat bar drilled and reamed 1/4" dia to take the locating peg at the hub end, drilled and reamed 1/8" dia at the crank-throw position and drilled and reamed to take another pin to locate between the spokes.



Using the jig, the crankpin holes were first drilled 1/8", then drilled 23/64" with a drill that I had modified for cast iron, and finally reamed 3/8".
The next job was to make the keyway bush with an alignment slot and a bush with a similar alignment slot to fit the crankpin holes. The two bushes were turned from some suitable mild steel and a 3/16" alignment slot milled into both. These need to be a good fit to the alignment bar to ensure that the keyway position is consistent across all six wheels.



This is what Ed what referring to in his post at the top of this page



The keyways were cut using three passes of my home-made keyway broach (covered in a separate thread HERE) just using my simple, lightweight drill press....



.... and here's the first wheel completed ready to have the pins pushed in and then pressed onto the shafts. As one can see, I've taken the opportunity to clean them up in the shotblaster.



Thanks for looking in

Steve

[Deleted]

lovely work Steve and a great explanation of your process, I also intend to cut keyways and it's always good to see how others broached the subject...pun fully intended...

Pete

[jma1009]

hi steve,

very interesting as always. if you need some very accurate 1/8" square steel ive got a few lengths somewhere in case your keyway steel isnt up to spec and has rounded edges.

cheers,
julian

[springcrocus]

Today I made the keys for the main wheels, pressed in the crank pins and then pressed the wheelsets together. Everything was about half a thou interference fit and is unlikely to come apart in use. The only modifications I had to make was to thin the axlebox covers down a little because of fouling the back of the wheels.









Sorry about the poor picture quality, this new camera seems to be a piece of junk but I will have a play with the settings and see if I can get it to take better pictures.

The rods will have to wait a while, I will try and cover the pony truck next, followed by the front bogie.

Thanks for looking in

Steve

[rogsteam1959]

Hi Steve,
some questions.
Are you married, are you working...
No need to answer;-)
It's nice to see your engine growing. The tempo is like its your main job.
Michael

[springcrocus]

Aug 9, 2015 20:29:22 GMT rogsteam1959 said:

Hi Steve,
some questions.
Are you married, are you working...
No need to answer;-)
It's nice to see your engine growing. The tempo is like its your main job.
Michael

I will , though! Yes to both, and I am just one amongst many of you who's spouse is also their best friend. It counts for a lot.

Mind you, Brownie points have to be earned and assistance in the garden sometimes takes priority.

Steve

[runner42]

Hi Steve,

great work it will be a magnificent locomotive. I have a question on the wheel castings, it shows that the counterweight is not dead opposite the crankpin but offset, what is the reason for this? I assume that it is a modification to optimise the balancing of the driving and driven wheels under dynamic conditions.

Brian

 

[springcrocus]

Aug 10, 2015 8:28:47 GMT runner42 said:

... the counterweight is not dead opposite the crankpin but offset, what is the reason for this?

Brian

 

Like you, I have noticed the asymetric positioning of the balance weights but have no idea why they should be as they are. Photos of Britannia and Oliver Cromwell also show that it is not handed. By this, I mean that the balance weight is leading on one side of the axle and trailing on the other side. There must be someone out there who knows what's going on.

Steve

[Deleted]

hi Steve

this may help a little... 5at.co.uk/index.php/definitions/terrms-and-definitions/hammer-blow-2.html i found this some time ago and found it most interesting...i don't know if all balance weights are offset but they certainly are on Gresley pacific's.

Pete

[springcrocus]

The pony truck horns are made up as left-hand and right-hand assemblies and include the front and rear horn plates, the horn blocks, horn stays, spring anchor blocks and spring guard amongst others. The only castings used in this part are the horn blocks and the horn stays which are made of gunmetal, all the rest is fabricated.

I started by splitting the castings into the four horn blocks and machined these all over in the milling machine, all very straightforward work with the flycutter. The base of the horns were drilled and tapped 4BA and the holes in the sides to enable the riveting together of the assembly were marked out and drilled 1/16". The horn stays only need the mating surface machined and this was flycut in the same manner although I also cleaned up the side faces and the bolting face. These were then marked out and the 4BA clearance holes drilled.



I made the front and rear horn plates out of 16swg mild steel sheet and have added extra fixing points for a bit more robustness. Because I am using the front casting, I have also drilled holes for screwing the backplates to it. The spring anchor blocks are just a couple of lumps of brass milled to size and their top and bottom plates made from some 16swg brass sheet. All the rivet holes are drilled 1/16" and the home-made rivets are just some 1/16" dia brass bar cut to length.



Assembly has been a bit tricky because of the need to get the horn blocks in the right place and keep everything square. The holes on all of the parts were marked out and centre-popped with extreme care and then drilled 1/16". To make life easier, I decided to solder the spring anchor blocks and the respective top and bottom plates together.



For this, I used solder paint and then riveted the parts together, using a 4.8mm drill shank in the spring pin hole to aid alignment. Once riveted, the drill was removed and the assembly heated until the solder flowed and finally left to cool for a while.



Next I riveted the axlebox guard, just a piece of 3/16" brass angle, to the top of the front plate. Although not on the drawing, I added an 8BA hole in the back of the spring anchor blocks and a corresponding countersunk hole in the backplate so that I could also bolt them together and then riveted the front plate, backplate and spring anchor block assembly together.



The final job on this sub-assembly was to rivet the horn blocks into place. A couple of the holes needed clearing with the 1/16" drill so a rivet was pushed through the top part and the horn stays bolted on to help keep position prior to running the drill through the other three holes. Then all the rivets were hammered up and the whole lot treated to a bit of filing. I also need to dress the horns to suit the axle boxes because, during marking out, I deliberately set the horns to be a few thou tight.



There are still the springs and their fittings along with the spring guard to make to complete these parts.

Thanks for looking in.

Steve

[springcrocus]

The pony truck can be fully fabricated but there is a cast iron casting available to make the front part which I have chosen to use. There is very little machining on this but it does need filing or milling to the correct width to allow the back horn plates to be affixed.



The hole for the pivot bush was marked out 5.9/16" from the flat back face of the casting but the side-to-side position was just judged by eye. This was then drilled using a 3/8" dia drill followed by a 3/4" diameter drill, although the drawing calls for 7/8". There is also the pivot bush to be made and I have made this from 1.1/8" dia brass, turning the O/D to a touch over 3/4" diameter for a press fit into the casting and then drilling and reaming a 1/2" hole through the middle prior to parting off. This was then pressed into casting.



The side faces where the back horn plates bolt to were machined on the lathe by mounting the frame as shown in the photo below, once this way up then up and over for the other side. To align the casting, I just loaded a length of bar to the 3-jaw chuck and offered the casting up to it before clamping.



Then the casting and horn plates were set up on a variety of packing to get them aligned and the holes were spotted through from the horn plates prior to drilling and tapping 8BA. I shall use countersunk screws to fix the horn plates to the front frame.The final section that needs attention is the cutout where the centre brace fits to and this was left for the moment as I will file it to depth after I have made the centre bracing bar.

Thanks for looking in.

Steve

[springcrocus]

The rear section of the pony truck is fabricated from 16swg brass sheet and forms a hollow box section. The top plate carries the pressure plates which allows the truck to move laterally and the inside of the box section carries the return spring bar which is used to return the truck to a central position.

I have chosen to make mine differently to the drawing and made two side and end pieces, a top plate and a bottom plate. I have also made the centering bar bushes more like the actual rather than what has been drawn.

After cutting the two strips of brass that form the sides and ends, I marked out and drilled and tapped all the 10BA holes in the ends before bending to right-angles. These were then dressed for length and soldered together to form the section shown below.



The top and bottom plates were also finished to size with the slots drilled and filed to size, the bottom plate having the longer slot. I have soldered the top plate into position but have left the lower plate for now because I need access to the inside for the cetering pin. I also made the centering bushes with their more authentic shape, just a bit of simple turning followed by milling the shape of the base and drilling the four 10BA bolt holes and the spring return bar to fit them which I have modified to suit.



The other part I have made is the centre support which bridges the axle and is fabricated from 16swg brass sheet, soldered and riveted together.



It isn't exactly to drawing but is close enough as it will never be seen once the loco is assembled. The ends have been milled to get them parallel...



...and I have drilled and tapped two 10BA holes in the back end and four 10BA holes in the front end to allow for fixing to the rear beam and the front casting.



The front casting has also been filed to size and the 10BA clearance holes put in.



More on this later, thanks for looking in.

Steve

[donashton]

I was just idling my way through page 9, enjoying the good work and answers to problems, when I came across a query. I went for my drawings to find a driving wheel and checked out that a keyway usually sits on the side of most of the metal. Did you have a drawing which told you where the key should go?
Hope I'm not upsetting an apple cart.
Don.

[springcrocus]

Aug 29, 2015 17:09:52 GMT donashton said:

I was just idling my way through page 9, enjoying the good work and answers to problems, when I came across a query. I went for my drawings to find a driving wheel and checked out that a keyway usually sits on the side of most of the metal. Did you have a drawing which told you where the key should go?
Hope I'm not upsetting an apple cart.
Don.

Not at all, Don. Since keyways were not part of Perrier's design, nor played any part on the original, it doesn't matter where I put them, they are not prototypical. However, based on the ease of the way that I have produced the, along with their accuracy, it appears that all those others were wrong.

In reality, it matters not a jot. Their function is one of location, not retention, and it beats messing about with adhesives hands-down.

Steve

[donashton]

Hello Steve,
I appreciate that your function is location but this is not the case in full size. When a 120 ton forced fit is specified for a 6' diameter wheel the key cannot locate - ie. guide the wheel radially. I presume that keyways on the side of most metal (on the boss side) are less likely to suffer cracks.
The only reason this came to mind is that I am currently involved with a new axle and wheels and the specifications are stringent, but please don't take my remarks as criticism - either of your or Ed's knowledgeable methods.
Cheers,
Don.

[stan]

Hi Steve
I think your build is terrific, and I love looking at your method of doing things gives me some good ideas, just one question not a criticism as I am building a 5" 9F am I right in thinking that the Brits and 9Fs wheels were not fitted with keys.
Stan

[vulcanbomber]

There just a serious press fit Stan.