Scale Wagon Wheels - A Saga

[Overseer]

With the ready availability of a couple of ranges of reasonably accurate wagon wheels in Scale7 (and in P4) it is not necessary to think too hard when selecting wheels for wagons. However, if you model in a different scale things are not so straight forward. As well as modelling UK prototype in S7, I model Victorian Railways circa 1900 in 1:48 or quarter inch scale. The scale was chosen as it has been the standard O scale in Victoria for many decades. The prototype gauge in Victoria is 5'3" so the few 7mm models made over the years look quite odd on 32mm gauge track. The wheel profile used by members of the Victorian Model Railway Society since its formation in the mid 1930s was and is finer than current O finescale. Three rail never seems to have been popular in Melbourne, stud contact being preferred. Wanting accurate wheels and with no trade support there was no choice but to either make my own or have some made to commission.

So this is will be a record of the saga to have accurate scale wheels for my (and a few friends) models. We are using exact scale reductions of the prototype so the back to back dimension is 5' or 31.75mm in 1:48 and the gauge is 33.3375 (although 33.34 is more practical to build to). There is enough tolerance in the prototype to allow Scale7, Proto:48 and even RP25 Code 110 wheels to operate successfully. Code 110 is only just possible, due to the oversize flanges in proportion to the wheel width - all the RP25 standard widths have flanges approximately twice the width and depth they would be to scale.

As a starting point some prototype information. The main wheel needed is a 3' 1 1/2" with eight open (or split) spokes, the same or very similar to the common British wagon wheel of the 19th Century and later. The next is a 3' 2" nine spoke wheel introduced in about 1910. Not sure why 9 spokes were selected for the cast steel wheel instead of 8 spokes, possibly there was some European influence. No drawings survive for the open spoke wheels, but they do for the 9 spoke wheels. Fortunately a fair number of open spoke wheels survive on preserved vehicles so these were measured to produce CAD drawings.


This is part of an 1870s photograph with quite good detail of the standard open spoke wheels.


The inner face of one of the wheels measured.

One interesting thing with these wheels is that there is raised lettering and patterns on the inside faces of the open spokes. It can just be made out in the photo. It seems that the wheels are actually cast in segments and then assembled. I had always believed the mantra that split spoke wheels were fabricated from wrought iron which resulted in the characteristic shape. Early ones certainly were but even the 1870s photo shows wheels that look cast. The recently posted photos of the underside of an NER hopper on another thread also seems to show cast open spoke wheels, although they look like they may have been cast in a single piece with the mould separation line halfway through the thickness of the wheel.

Enough background, next time we will get started with modelling.

 

[Overseer]

Well maybe just a bit more prototype to round out the background.

First, a photo of a preserved set of open spoke wheels in the railway museum at Newport which more clearly show the raised lettering and diagonal patterns on the inner face of the open spokes. I have no desire to model it but am interested to know if any UK examples have similar markings.



Also a couple showing the standard 9 spoke wheel so you know what we are aiming at. Note the tapers in the spokes, radiused connections between the spokes and hub and rim, and the visible mould parting line on the centre line of the wheel centre casting. All are typical of cast steel spoked railway wheels of the first half of the 20th Century. British 8 and 10 spoke wheels have similar features. I don't know of any 9 spoke wheels used in Britain but there may have been some. They were very common in Europe. Anybody able to explain why 8 or 9 spokes would be preferable?




A drawing for the 9 spoke wheel exists so this was used to prepare a CAD drawing, with some measurement of prototype wheels to confirm that the full size ones matched the drawing.



Early in this drawn out saga a friend offered to try making wheels using his laser cutting machine. We didn't think the open spoke wheel would work so the trials were with the 9 spoke wheel and a 10 spoke wheel. 10 spoke wheels were introduced here in the mid 1920s to carry higher capacity wagons. There were a few different versions over the years but all were known as 'heavy duty 10 spoke wheels' and were 3' diameter. We haven't proceeded with model versions of these at this stage due to one of the 'team' back dating his modelling interests so the need was less pressing.

The trials were cut from polymethyl methacrylate (Perspex) sheet. It was interesting to see what a laser could do and also the variations between samples made using the same CAD drawing. There was some variation in spoke thickness which I hadn't expected. After turning the wheel to the produce the correct taper in the face and rear a substantial amount of work with files could have resulted in a usable master with all the draft angles modelled. However, we decided there must be a better way. And still the issue of a master to use for casting open spoke wheels.

So, no progress yet.

 

[JimG]

The trials were cut from polymethyl methacrylate (Perspex) sheet. It was interesting to see what a laser could do and also the variations between samples made using the same CAD drawing. There was some variation in spoke thickness which I hadn't expected. After turning the wheel to the produce the correct taper in the face and rear a substantial amount of work with files could have resulted in a usable master with all the draft angles modelled. However, we decided there must be a better way. And still the issue of a master to use for casting open spoke wheels.

So, no progress yet.

Have you thought of investigating 3D printing, which should reproduce all the shaping in your 3D CAD drawings? You might have to do a bit of looking around to get a supplier who would give a print quality which would not require a lot of finishing work on your part - otherwise you might just be as well using laser cutting and finishing off by hand. 3D printing might also let you reproduce the lettering on the spokes if you are that keen.

Another option might be to use CNC milling, and you could use wax as a material which is a lot easier to cut with very small diameter cutters and also burns out of moulds. You could machine front and back to get proper shaping of parts like oval cross-section spokes.

I've been messing around with cutting loco wheels on a CNC mill - see here

http://www.westernthunder.co.uk/index.php?threads/wheels-for-a-pug.2488/

and I'm restricted to 2 1/2D in the main. I'm just about to have another go at it using some hand written GCode to do a bit more spoke shaping and tapering. But I will still need some hand finishing to get something like the correct spoke cross-section. At the moment I'm limited with equipment and software, but that situation might improve in the next few months with further developments of one of the software packages I use at the moment.

I'm cutting in brass and I will cut all six wheels required. I think that it's hardly worth going through the whole master/casting process for one set of drivers, and I also need the wheels quite quickly, so don't have the luxury of the time required to find someone to do the casting, and then setting up the process.

Jim.http://www.westernthunder.co.uk/index.php?threads/wheels-for-a-pug.2488/

 

[Overseer]

Jim

I am very impressed with you CNC milled wheel thread and I think your results are already far more than just messing around. Maybe I should have made it clearer that this thread is intended to record the steps taken to obtain scale wagon wheels which dragged out over more years than I expected at the beginning. I can give away the ending - we have achieved a satisfactory outcome. 3D printing featured in the process, as did CNC milling and other processes. I am writing it up in small chunks as I am fitting it in when I can, mostly lunchtime at work.

 

[JimG]

Jim

I am very impressed with you CNC milled wheel thread and I think your results are already far more than just messing around. Maybe I should have made it clearer that this thread is intended to record the steps taken to obtain scale wagon wheels which dragged out over more years than I expected at the beginning. I can give away the ending - we have achieved a satisfactory outcome. 3D printing featured in the process, as did CNC milling and other processes. I am writing it up in small chunks as I am fitting it in when I can, mostly lunchtime at work.

I mis-read your first message - I thought you were just starting the saga. I shall await the rest with interest.

I'm actually just re-starting the work on the pug wheels and right now I'm working on the CAD drawings before generating the GCode. I did get a copy of the official drawings of the loco wheels from the Caledonian Railway Association archive, so I can now get the spokes close to prototype without guessing.

Jim.

 

[Overseer]

While working through the possible methods of making wheel centres we decided that tyres would definitely be required. I have a couple of lathes and suitable form tools, one the Scale7 Group tool and also a Proto48 form tool, so can make tyres. Making a few is OK but not something I really enjoy doing and the thought of manually making dozens or hundreds was enough to make the decision to outsource easy.

The Scale7 and Proto48 form tools are interesting. The Scale7 one is a brilliant design as it can be sharpened when it wears without altering the profile. From memory it was designed by the late Peter Turville with input from Ken Cottle, but I stand to be corrected. Mounting it in the lathe tool post requires a holder. I made a temporary one when I first bought the form tool out of a largish bolt and nut, with most of the thread ground to a square shape to be held in the tool post, but have never got around to replacing it with a more presentable holder. The Proto48 form tool looks more like a standard lathe tool, I am not sure how it is made but the profile is made in the end of a standard blank, possibly by spark erosion or laser. It would be possible to sharpen these by grinding off the top of the tool then shimming up to get the tool back to centre height. The two profiles are very similar and operate interchangeably, possibly the difference in the prototype flange size is cancelled out by the difference in scale.

As we are modelling a specific prototype we decided to follow the prototype as closely as we could. A CAD drawing was prepared from a prototype drawing, in this case Victorian Railways drawing 5912 dated 1967. I would have preferred an earlier drawing but the differences are minor. This profile is actually the then Australian and New Zealand standard which all the railways worked to standardise during the 1920s, and very similar to British profiles. A copy of the CAD profile drawing follows for interest.



We are fortunate in Melbourne to have at least two companies set up for, and capable of, producing high precision turnings in short runs. I wouldn't say they are cheap but the quality is very high and the cost is reasonable. As usual the larger the run the lower the cost per item. Most of their business is not model railway related, but thanks to a couple of local model railway manufacturers who commission the precision engineering firms to produce their wheels and gears they are familiar with the tolerances and shapes required. Anyone who has used a Steam Era Models 'Black Beetle' or a Hollywood Foundry 'BullAnt' drive will know the quality of the wheels and gears produced by Hargo Engineering and APT Engineering.

Some discussion with APT Engineering resulted in an order being placed for several hundred scale tyres to the profile provided. We decided on mild steel as the material. The result is shown in the following photos.



The tyres look just like the real thing, to borrow a phrase. Only one thing will be different on any further batches, an unexpected chamfer was added as part of the deburring process which would look better if it were not there, although it could represent the scrapping limit line on the tyre. For future batches the plan is to have this on the rear face instead.

Next time - wheel centres.

 

[Overseer]

I should have mentioned in the previous post that when commissioning machined items from general engineering suppliers that the specified dimensions need to be overall dimensions. For example, the size of the tyres was specified to the outer diameter of the flange rather than the running diameter as referred to by railways. It is important to remember that the supplier is just making objects to match the information provided so the information has to be in their language or there can be strange outcomes.

Wheel centres-
We considered the options for making wheel centres for the two prototype wheels. It is possible to hand make wheel centres, either by fabricating strip brass into open spoke wheels or cutting out solid spokes, but it is time consuming. Having reviewed the options for volume production we decided that lost wax brass was probably the best way to proceed for the numbers of wheels needed. White metal was also considered but the local supplier uses vulcanised rubber moulds so would need metal patters to cast from. Hand made masters would have been possible to use for either lost wax brass or white metal casting but we decided to try out rapid prototyping.

I haven't checked the dates but this was over 5 years ago so there were fewer options for rapid prototyping. We found quite a few firms in the jewellery industry offering rapid prototyping. It soon became clear that jewellery production is generally not a high precision industry - a fact which became even more apparent later. The first trial of the open spoke wheel was promising but not a complete success. I drew the 2d drawing for the wheel and a friend converted it to 3d which is quite straight forward for the open spoke wheel as it is just extrusion of the elevation to the required depths. The wheel pattern was produced in wax then cast in sterling silver. The result is below.



First impression was quite good. Closer inspection revealed more differences in the width of the spokes than I was expecting. There was also a dimensional issue, the inside of the rim had ended up a bit smaller diameter than it should have been but that was a design issue that was easy to correct. I had included extra material to enable the flange to be turned on the centre without needing a separate tyre which was unnecessary once the tyres were sorted out. Overall it was a promising start. We had some lost wax brass copies made locally that looked OK but introduced us to some issues which became a feature of this part of the saga.

For the second attempt the 2d drawings were revised and sent to Mark 4 Design in Auckland. Mark 4 Design are model railway friendly, including having done quite a lot of prototyping for Atlas on N scale diesels. Mark 4 produced the 3d files for the wheels and produced the patterns in a red resin. The results were everything we expected, with very little stepping evident in the tapers.



So back to the lost wax casters for some brass ones. (the 9 spoke wheel on the right has had the rim skimmed)



A number of issues became apparent. We ended up trying two different casting firms to try to improve things, but without success. The nine spoke wheel mostly cast well although there was some variability. The open spoke wheel was the real problem, or specifically the insoluble problem was the infilling of the space within the open spokes. This was due to the angle being too acute causing the rubber mould to tear as the pattern was removed. The problem worsened quite rapidly as the mould was used. The other issues with lost wax casting include varying distortion of the castings depending on the care taken releasing the waxes from the mould, varying shrinkage rates (from practically nothing to 5% or so) and varying surface defects. In a small run these would probably not be a major issue. Jewellers expect to hand finish their products and usually don't have any real tolerances to work to, if one ring is a bit different shape to the previous one it is not a problem. Scale wheels are different, they should all be the same.

Not being able to get the open spoke wheel cast successfully caused a major rethink. Next time a return to a production method we had not seriously considered at the beginning.

 

[Overseer]

A bit of delay in finishing the saga due to work, family and finishing a model so a quick update.

The actual delay between realising that we weren't achieving the results we wanted with the wheel centres and finding a solution was much longer. From the beginning of the project we had thought that injection moulded centres would be nice but didn't seriously investigate them as we thought the cost would be too high. Now, after a number of discussions with David Foulkes of Steam Era Models we decided we had to give it a go. David is a wizard with his pantograph milling machine and produces the injection moulding tools for his range of kits and wheels. After a fair bit of arm twisting, David agreed to help if we provided patterns at 4 times the final size of the wheels.

Two different methods were used to produce the patterns which are 4 times size and the negative of the finished wheels. The first was the open spoke wheel which another friend volunteered to mill on his Roland MDX-20 CNC mill from my 2d cad drawing. As this mill has done a lot of work and has some bearing wear we had some concerns regarding concentricity. The pattern was milled in acrylic (perspex) sheet. The depth was not critical as the shape is just needed to guide the pantograph. It all turned out well and the pattern proved to be round where it was meant to be round. A bit hard to see in the first photo due to the clear acrylic but the second photo explains it better.





The photos are actually of the trial version, the pattern used looked very similar.

For the nine spoke wheel with the tapered spokes we decided to use rapid prototyping again. The first go by a recommended supplier, while far from cheap, was not good. Another supplier was significantly better and even further from being cheap. I don't have a photo of this pattern to hand. I will try to get one but in the meantime you will have to imagine a translucent red 4 times size half depth negative wheel centre. It looked good. Being blinded by the technology I didn't measure the pattern closely, assuming it would be just as it was specified. The size was right but it turned out to not be quite as concentric, or round, as I thought it would be. Something to look out for with even high end rapid prototyping.

 

[Overseer]

With the four times final size patterns sorted it was time for the injection moulding tool to be made. As David had cleverly made the tool he uses to make HO locomotive driving wheel centres with a removable inserts he was able to offer to mill our wheel centres in new inserts to fit into his existing tool. The tool is quite complex as it has removable pins and sleeves at each axle location, as well as for crankpin holes and the ejector pins used to push the mouldings out of the tool. By using two of the existing axle locations a lot of time and effort could be saved.

We were adamant that the wheels had to be correct on both the front and back faces, particularly the nine spoke wheel, otherwise the wheels would look too heavy when seen from an angle. David had some concerns about this as all his previous wheel centres had been cut in one half of the die, with a flat back. The difficulty is getting the registration of the two faces exactly right in the two parts of the die. After some more discussion, David agreed to give it a go.

All went according to plan a not many weeks later the first die trials were done. The open spoke wheel needed to have more than one gate into it to make sure the slender spokes injected properly.



This is one of the first mouldings out of the tool, in glass filled nylon. A trial was also done in acetal (equivalent to delrin) which also worked but is slightly more flexible and the mouldings were slightly smaller. We were very happy with the results. To give you something to compare with the photo below shows a Slaters Scale7 wheel next to our new 1:48 open spoke wheel fitted with the scale tyre and on a axle.



Finally the wheels we needed were definitely going to be achievable. The finished inserts for the injection moulding tool cost somewhere around the equivalent of about 3 Heljan locomotives so not wildly expensive and the cost per moulding produced is not much at all. We were lucky to have friends who were willing to help, which kept the costs down, but even using commercial tooling services it should be possible to achieve something similar for a reasonable amount of money, especially with the availability of spark erosion die cutting and other modern technology.

After a tense time when the tool was slightly damaged during one of the test runs all was ready to go. A batch was produced in glass filled nylon by one of the local injection moulding firms, and the box collected. Almost an anti climax.



Now we have plenty of accurate wheel centres and tyres. At present I am modifying axles purchased a few years ago from Alan Gibson to mount the wheels on. The next task is sourcing axles with tapered centres to match the prototype.

An early flat wagon was built to check that the wheels looked as they should. It is a very simple styrene 'body' with my etched w irons and cast whitemetal axleboxes, springs and buffers.




So after a number of trips down blind alleys we eventually achieved what we set out to do - scale 1:48 open spoke and 9 spoke wagon wheels. We haven't released them commercially yet, and are undecided whether we will or not as it is a very niche market, but if anyone has a need for scale 1:48 wagon wheels you are welcome to get in touch.

 

[Osgood]

Inspirational - just goes to show what can be achieved when you set yourself a challenge. And so worthwhile looking at the result of your efforts!

 

[Locomodels]

Super wagon, it looks as if you have tried the tapered axles already. Beautiful job, so much so it seems churlish to mention the links, so I wont.

 

[Overseer]

Super wagon, it looks as if you have tried the tapered axles already. Beautiful job, so much so it seems churlish to mention the links, so I wont.

You can mention the links. They are commercial 7mm ones as supplied in a well known brand of kits, there for functional reasons. The wagon should have a D link on the hook and two links, instead of three links, another thing still to be resolved. One of the axles is tapered as an experiment to see how visible the tapers would be in the gloom under a wagon.

 

[Locomodels]

Well the tapered axles do show, but only at near eye-level of course. However with the open nature of the wagon, with only the one brake, helps considerably. Worth the effort I feel.

 

[john lewsey]

The wheels look great I asked Colin (eastside pilot) if he could turn down some slaters wagon wheels for me to give them a more scale apearence some time ago I think ill send him some the tyre width really is a big improvement
Regards john

 

[Les Golledge]

Hi,

Exactoscale sold shackle links for GWR screw couplings both long & short, I got some of the short ones which seemto be the correct size for wagon couplings. I don't know if the new company still sells these separately. They are cast brass which is slightly soft making them easy to carry out small adjustments to the shape.
Regards,

Les.

You can mention the links. They are commercial 7mm ones as supplied in a well known brand of kits, there for functional reasons. The wagon should have a D link on the hook and two links, instead of three links, another thing still to be resolved.

 

[Overseer]

Thanks Les,

The Exactoscale D links are a good idea. I will have to check that I don't have some of the GWR couplings hidden away to check the dimensions. I will need quite a few and also need to sort out the correct style coupling hooks so have been thinking about making patterns to have cast for both the links and the hooks. Probably should move it up the to do list, along with the screw couplings which are not quite the same as any of the available 7mm ones.

 

[Simon]

The wheels look great, scale wheels do make a lot of difference to the look of stock. Being critical though (sorry) your wheel is a bit less good looking than the Slater's one in that the outer face of the rim on your wheel is visually split between the plastic centre and metal outer, although painting will hopefully visually "lose" this feature.

I wouldn't bother with the waisted axles myself, I think that is a very subtle point and as you say they are up in the shadows most of the time.

I'm pursuing the same aim in 1/32 G1 albeit through one manufacturer, if I can afford the eventual quote then I'm going to go for it. My axles won't be waisted.

I may have missed this, but one question that is exercising my grey cells is what back to back to set the wheels to. Given that the back to back is a range of values and the less slop that there is then the better the running one is inclined to a value at the "outer" end of the range but then potential wheel non concentricity and general pragmatism seem to suggest a "mid range" value.

Did you and your colleagues come to any conclusions on this point or are you still pondering too?

Great work anyway

Simon

PS Re the couplings: I know you're changing them, but what I do with Slaters coupling links is to fill the gap (which is always too big) with soft solder. This is surprisingly successful and once painted you can't spot the join.

 

[Overseer]

Simon

As noted at the end of post 6 the tyre manufacturer added an unexpected chamfer to the inner diameter of the outer face of the tyres which emphasises the joint. The prototype had an eighth inch groove at this location indicating the wear limit of the tyre, which is more visible on the prototype than I would have expected. The decision to locate the joint where it is was a compromise to suit a couple of different centres with differing dimensions and the production methods. Slaters have the advantage of doing everything in house, moulding the centres into the tyres is a skilled and time consuming operation that you couldn't expect a general commercial injection moulder to undertake for a reasonable price. If we didn't have the over size chamfer the division between the centre and tyre wouldn't be visible once the wheels are painted.

We have settled on directly scaling the prototype back to back dimension, largely because it is a nice round number - 5' for 5'3" gauge, or 31.75mm. The back to back should be the most constant dimension in models as it is on the prototype. The other dimensions follow from the back to back. Flanges can be a range of thicknesses to suit the position on the locomotive eg many steam locomotives had thin flanges on the centre axle. We have found that scaled down prototype flangeways have a surprising amount of tolerance for varying flange thicknesses, including allowing RP25 Code 110 wheels to operate (just) even though they have flanges around twice the width they should be in 1:48 scale.

 

[David Taylor]

Fantastic thread, thanks for posting all that info.