BR Standard class 6 No. 72010 'Hengist' and Clan Discussion Thread

The item is the steam brake cylinder, drawing No. D22-9658.

 

The problem that we had with our inside cylinder that made us cast a second one still saved us money (we only paid £800 fpr the second cylinder and that included pattern, castings and machining!!!)

But for us we have these factors. Inside cylinder traditional pattern costs 35k. And would take 6months none stop.work to complete. But the pattern maker said he wouldnt be able to do none stop as he has other customers to do work for so more realistic time is 12-18months.

Poly pattern cost £2, 800 for pattern and only took two weeks to produce. Plus it required less metal to be poured. So it would take 12 errors in pattern to be cost neutral. Obviously different patterns cost different amounts but complex ones for the pattern maker could see a cost saving.

 

Agreed, agreed, agreed agreed.
I'd struggle to put it better myself.

Always happy to live and learn. How long did it take you comparing the drawings to discover that? Presumably the cylinder cover too?

Wow! You certainly got a good deal there. I suspect that barely covered the cost of (re)melting the iron and labour costs for moulding it!

 

As far as I can see, (correct me if I'm wrong), poly patterns require a drawing in CAD format, from which the poly can be cut to shape. So while there may be cost advantages, it pre-supposes having someone on the team who can produce the necessary drawings in CAD format.

AFAIK, the Bluebell Atlantic has used all traditional wooden patterns, and - again, AFAIK - has done all the drawings "traditionally" rather than using CAD. I'm not saying one way is better or worse, but simply it's a matter of what skill set you have in the group. The Atlantic project is fortunate to be able to draw on the skills of a "traditional" pattern maker, but I've never seen a CAD drawing from the project, so I assume those skills aren't held by any of the core team, at least not to the required level. The one exception to that traditional pattern making emphasis is for the cylinders, which were fabricated: I'm pretty certain that the reason for adopting that strategy was the likely cost of a conventional wooden pattern plus casting. At the time, poly patterns were much less well established: maybe if the project was being attempted now, the chosen solution may have been different. There has been a certain amount of reuse of patterns: for example, the driving wheel patterns were used to cast one pair of wheels and then, when they were seen to be satisfactory, modified for the other pair. I believe also that the superheater header is very similar to that used in Bulleid WC/BB pacifics, and the intention is that, once a header is cast for the Atlantic, the pattern will be available if either of the Bulleids on the railway need a new header.

Tom

 

We are extremely fortunate to have Brians skills creating the traditional patterns for us. We are also lucky to have Geoff (our Engineering director) and Graham who is a member of the engineering committee (although this title sells him far short of the work he puts into Hengist) who not only know their way around AutoCAD but Geoff is a dab hand at SolidWorks for 3D modelling.

Gav, that was an incredible saving! Where did you get the pattern and casting done (if you don't mind me asking)?

Thanks
Dave

 

Forgive the long answer to a short question.

I think we need to define "CAD format" with a little care. At its simplest a CAD drawing may be little more than a traditional 2D drawing created on computer using one of the many freebie drafting packages like Draftsight, which even I can use fluently. (I'll exclude those drawing packages that do not store the information in vector format). Although that is a useful start the file doesn't contain sufficient information to produce a poly pattern using a multi-axis CNC machine. That collection of 2D images (plan, elevation etc.) needs further work to create a full 3D virtual model from which an .stl (or similar) file can be generated. From that CAD information a CAM file will be produced which generates the G code (or similar) to instruct the CNC machine what to do.
Nowadays much of the foregoing is cleverly bundled to make, what is often, proprietary CAD/CAM S/W packages.
You either need the 3D drafting skills in-house or they have to be bought in. Nothing wrong with that.

I must stress there has been an awful lot of huffing and puffing about poly patterns on this forum as if the technology has only just become sufficiently mature to use reliably. As a close relation to the even earlier lost wax process, poly pattern methods have been around for many many years. For various technical reasons a number of foundries are unable/unwilling to used the technique. Again, in your particular case you have chosen to follow the low-tech approach of a wooden re-usable/durable pattern. Again, nothing wrong with that.

Am I seeing a trend here where perhaps the single locomotive groups are focused solely on their pet project whereas those domiciled at an operational heritage railway can see a bigger picture?

Thinking aloud. Having said all that, I don't suppose there is any reason why a poly pattern couldn't be made manually. Something I've not tried myself.

Thinking aloud again. I sometimes muse that my role as Pattern Registrar for BRSLOG may one day also require me to be the keeper of .stl files.

 

Brian
Well .stl files would take up less space than combined stretcher patterns ;-)
We were discussing poly patterns last night whilst preparing the Clan News mail out. With steel castings the pattern is retrieved to avoid adding more carbon content to the steel (metallurgy isn't my strong point!). I do hope that groups don't become self focussed as groups such as BR SLOG are a lifeline for so many projects and helps to save costs to groups when patterns are already extent (be it in wooden, poly or .stl file).

The Clan Project is fortunate to be part of BR SLOG and also being based at Loughborough rubbing shoulders with the Loughborough BR Standards group. Shared knowledge and expertise is essential for so many projects whether they are new build, rebuild or overhauls. Fingers crossed the open community spirit of loco groups keeps going for many many years.

 

Thanks for that detailed reply. I guess I was being sloppy by saying "CAD"; what I was really trying to imply was a format that allows direct machining of the pattern from the computer file, as you outlined, rather than simply producing a drawing using computer rather than pen and paper.

You open up different problems. For example thinking about a pattern for a component that may only be needed rarely (such as cylinders, where, with heritage line use, you might expect not to have to replace them for fifty years or more). With a wooden pattern, if you store it well, you could reasonably expect to use it fifty years later - assuming you haven't been effected by fire or flood, at which point all the hard work to produce it is lost.

With digital, you'll be into digital archiving. With online storage (rather than physical media, such as a CD) you could reasonably expect the file to still exist years into the future, and you have much better security from fire, flood etc. Whether the format is still readable fifty years hence is a different matter! It's definitely an area any of the groups who are producing a lot of their technical material in electronic format will need to consider.

Tom

 

Tom
You raise several good points. The need to ensure the file is readable in years to come, which can be achieved by holding onto copies of the software that generates and reads them (assuming the machines used to generate the patterns are still compatible). You don't have that problem with wood, chisel and woodworking skills such as Brians (assuming that there are still people with those skills in 10, 20, 50 years time).

The need to maintain a reliable and safe archive of the files is another strong point that I have already taken on board with our document database, it's on our own server hardware, held on software that even if they stopped updating it tomorrow we could still use, and is backed up to a cloud server and one of my servers at home! Drawings have also been scanned and are in the process of being drawn into AutoCAD / Solidworks (as required) which will still leave us with the paper originals. This may sound a little extreme but the 00's of documents held now will increase to 000's in 10 years time, the majority of which will be essential to get the loco certified and to keep her that way. As always, for a small donation to Hengist, if any group needs any pointers on document storage or how to get great deals on (legal) software and IT tools please PM me.

Who says loco engineering was all about large lumps of metal!

 

[quote="
You open up different problems. For example thinking about a pattern for a component that may only be needed rarely (such as cylinders, where, with heritage line use, you might expect not to have to replace them for fifty years or more). With a wooden pattern, if you store it well, you could reasonably expect to use it fifty years later - assuming you haven't been effected by fire or flood, at which point all the hard work to produce it is lost.
Tom[/quote]
Talking about wooden patterns, I have just taken delivery of some ex-Swindon Historic Castings patterns . The vast majority of the bodies have been battered a bit and need some TLC, but most of the core boxes are in excellent condition. These patterns will have been made in the 1940s/1950s.

 

Having spent several years, of a former life, in the Business Continuity industry I can understand the lengths Dave goes to to protect his valuable data. Remarkably I've seen, so called, IT professionals store their sole back-up media right next to the server from which it was produced.

And whilst we're off topic the image flashed through my mind of trying to repair a corrupt .stl file with some polyester filler.

Forgive my twisted thought process. It must be the styrene fumes from the filler.

 

Good man, and pop another slice of toast in the disc drive and light a fag with your USB plug whilst about it ....

 

Question for Gav106.
Just out of interest, have any steel components cast using poly patterns been tested by a metallurgist to see if the carbon content of the steel has changed?

 

I'm pretty sure if Gav106 speaks to his technical colleagues he'll find the steel castings have been done using the Replicast (or similar) process rather than the Full Mould process. Reference my drawing of parallels betwixt poly patterns and lost wax up-thread; Replicast is is even more similar to lost wax insofar as the polystyrene model is burnt off after it has been coated in a refractory material. Read up on it here http://www.castingstechnology.com/public/services/specialprocesses/scpreplicastmain.asp
In summary cheaper patterns but more expensive foundry process. Yet further muddying the break-even point once the licence fee is taken into consideration.

 

According to Wonkypedia almost 5000 years http://en.wikipedia.org/wiki/Lost-wax_casting

 

I haven't enjoyed reading a discussion on Nat Pres so much for ages, thanks folk.
All to the point, informative, light hearted and knowledgeable and even covers more than 1 topic in the process, great stuff.

 

I'm sure the Mods wouldn't want me to write a very lengthy MIC on foundry technology as a number of readers here would probably find it far less important than in what colour the P2 or Flying Scotsman is going to appear.

Or; should we really annoy them with a series of discussions on the merits of the Whitworth thread form compared with those of the ASME and ISO, welding compared to riveting and copper compared to steel fireboxes etc.

 

Yes please - go for it

 

You see Brian we can indulge our opinions and fancies ad infinitum, but facts is facts. That doesnt make them less interesting, just more difficult to opinionate over

 

Go for it Brian! Would make very interested reading.