Casting Process Advice

[SteveO]

Certain types of pattern masters can be made quite easily through etched components, and this is the method I'm going to use for some of the castings for the upgraded 04 I'm working on. The only comparable component on your steam prototypes and my diesel is your chimney and my exhaust stack. The easiest way to achieve this is by turning the main component part and then fabricating the curved fixing plate with an appropriate material, depending on what you're casting with.

However, below is one example of where I can use the etched layer method:

This is the brake actuator bearing, highlighted in red. It's conveniently 3 frame thicknesses so can be made from 3 layers. This is it separated from the drawing so it's easier to see (plan and section):

The first layer will contain the rear plate, the bolts and the first layer of ribs. The height of the bolts will be full thickness, but the plate will be half-etched. Below, you can see a simplified section of this first layer:

The next two layers containing only rib and bearing detail, but when all three are soldered together will produce this:

I can then file away the bevels of the ribs and this will be a solid pattern to produce a casting from. This will almost certainly be cast in pewter in a vulcanised mould so the solder I will use will be 188C. Vulcanising can get pretty hot and the pressure is quite intense so I have to make absolutely sure that the layer joins are perfectly sound.

The air tanks you can see in the first picture will be constructed with thick-walled tube and soldered end caps, which will then be filed and sanded to shape and also cast in pewter.

This is intended more as a practical way of building patterns quite quickly from etched components, rather than constructing them in a machine workshop – which I don't have. There are other ways of achieving this with a full workshop, but all my masters should cost around £45 to build this way, instead of spending several £hundred or a couple £thousand on a lathe, mill, etc.

 

[Ian@StEnochs]

Hi
Using etches to make casting patterns is perfectly feasible but I have a kit where this has been done and the castings look like laminated etchings!
Making patterns from scratch is not rocket science and for our type of stuff does not require access to expensive machine tools. Simple hand tools, average metalworking skills and a bit of knowledge of the process is all that is required.
Ian.

 

[oldravendale]

After a day of NCT classes I haven't got the brain power to fully read all the above at the moment, but something I'll definitely come back to..

Just one thing I would like to say though regarding the quality of castings in kits.. Take a look at Ken De Groome's castings on the Met BoBo.. One word, stunning! And he does them all himself with a centrifuge mould..

JB.

....and soon he'll have the E and F tanks too. I agree about the quality of his castings 100% and I have a Met Bo-Bo to build. I believe Ken will take on casting work, but whether he can do lost wax I'm uncertain and I don't have the kit to hand in order to check.

As far as poor lost wax castings are concerned there is no doubt they are about - see my thread about building the Sentinel. On the whole I'd rather have a poor white metal casting for a non-working part as I find them easier to modify although anything in the slightest vulnerable needs to be in something stronger, and I have the experience with an Oakville Black 5 to advise, as has been done above, not to cast the motion parts in white metal.

Although not appropriate to motion parts I've also used Araldite cast in to a Plasticine mould along the lines of Railwaymaniac's suggestions. As has already been rightly said, though, you have to be comfortable with mixed media construction for them to be satisfactory, and they are not appropriate for anything approaching production quantities.

Brian

 

[mickoo]

Steve, interesting way of achieving a casting master, using layers as such

I'm old school and would approach it differently with no etching required, first I'd make the base plate from appropriate thickness sheet brass, then drill holes to take scale hardware bolts or bolt heads (insert bolt heads of choice), next, I would solder an appropriate sized tube to the base plate followed by the three flanges.

Like you, the flanges would be rectangular for ease of handling whilst soldering to the boss/base plate, then I'd use a slitting disc in a Dremel to rough out the flanges to the right shape and finish off with a file etc, finally I'd add the bolts and solder them in place.

Cost wise it might be cheaper as no etching is involved but it might be a little more complex with the hand tools and skills but importantly as Ian points out, you won't get ridges between your etch layers, especially in the flanges and boss where I think they will show up quite easily.

 

[SteveO]

Absolutely true, Ian and Mick. The quality of the finished piece will depend entirely on the finishing. Removing etching cusps and ensuring a good sweated bond between layers will eliminate any signs that it is made with sheets.

The problem is I own very few tools which are not designed for DIY, nor do I have any material stock to fabricate the component parts. I don't even own a Dremel!

It's just a simple way to construct certain types of patterns if you don't own any sort of workshop. But it's not suitable for everything of course.

Mick, that is precisely the way I was going to build it until I started to evaluate the costs involved to do it. Just the bolts being shipped over took quite a chunk out of the budget (hex rod could be used) and buying various thicknesses of sheet material and a saw, etc and becoming proficient with them was too much.

 

[mickoo]

Steve, I know you have a fret saw and you must surely have plenty of scrap etch material from other kits to source raw material Ok so the Dremel is a luxury one could do without LOL

Fully understand costs and materials and yes, hex bar is a definite alternative source, maybe even preferable to scale hard wear bolts, but, the expenditure is only once, that's the whole reason to cast.

To my mind a little extra on the master will be rewarded in the future castings, but as to how you achieve that is down to individual taste and preference.

I went the other way and spent a small fortune on moderately good tools, that way when it all messed up I couldn't blame bad tools and had to accept that what I did wasn't good enough, so I ended up doing it again, and again and again as many times as I needed to get it right....at least six attempts at the Std 5 firebox!

 

[SteveO]

Haha! How did you know I have a fret saw - I was trying to hide that piece of evidence!

Point taken though, ultimately you are correct, and these are skills you'll never forget.

 

[Ian@StEnochs]

Steve,

If you are retailing an etched kit you must have built one as a test build surely? Therefore you must have the basic tools required for making simple patterns. A few bits of scrap etch and some wire plus perhaps a length of brass tube will make the bracket you illustrate.

Ian

 

[SteveO]

Ian, this only exists on my computer and in my head at the moment. I bought the rights to the Right Price 03 and 04 kits and it was this that spurred me on to produce a MUCH more detailed kit, requiring a total redesign.

I haven't got to the pattern making stage yet as the design is far from finished.

 

[adrian]

I was a little wary about contributing as giving advice is always easy when it's someone else's job. However I remembered I had couple of part finished patterns to show so I hope you don't mind my 2-pennorth. As mentioned by few others I think the etched route for making the patterns is a bit of overkill, if it can be built up from a few etches then why not leave it in the kit to be built up from etchings for the kit builder?

IMHO the bracket could be made up with a few simple hand tools and few bits out of the scrap box. Believe it or not but the following patterns were made on a Black and Decker workmate with a few hand tools, piercing saw, needle files, riveting tool and a small blowtorch. Many moons ago when I started building my Ivatt 2-6-0 there were no suitable castings so I started making the ones below - halfway through making them then Shedmaster finally produced some castings for Ivatt 2MT! So these never got completed!



A cruel enlargement - the small fitting on the right is the mounting flange for the filter boxes under the footplate on the tender - it's 7mm long and 4mm wide.

One thing to point out for these, and the other patterns I used to make for my Dad, is that they are all silver-soldered. It might be a bit of overkill these days with room temperature curing rubber - but many industrial casters did use heat and pressure to create the vulcanised rubber mould and soft soldered patterns would just fall apart. Anyway I prefer the permanence of silver soldering plus the fact that I like the way you get a nice clean fillet along the joints. Neither of these patterns have been cleaned up - they are straight out of the acid bath to remove the flux. I took evening classes in silver-smithing at the local college and it was really useful.

 

[Dan Randall]

Using etches to make casting patterns is perfectly feasible but I have a kit where this has been done and the castings look like laminated etchings!

That made me chuckle!

Regards

Dan

 

[adrian]

Forgot to say - I'd also recommend having a look at the book "The complete car modeller" by Gerald Wingrove, they are bespoke models but he does show plenty of techniques for building up complex shapes from simple pieces etc.

 

[alcazar]

I took evening classes in silver-smithing at the local college and it was really useful.

I REALLY hope some on here are aware how lucky they are.
Years ago I went to our local tech college to learn to use a lathe, milling machine etc.
The course was cancelled after three weeks as insufficient people enrolled......and that's in Scunthorpe, hardly an engineering town, but we do have the country's biggest steelworks.

Nowadays you'd be lucky to find anything in evening classes outside the basic maths, english, computer basics etc courses. Even an MFL is hard to find.

 

[SteveO]

I'm a budding jewellery designer (budding in that I have a lot of books but no practical experience yet) so silver soldering is definitely on my 'to do' list.

Forgot to say - I'd also recommend having a look at the book "The complete car modeller" by Gerald Wingrove, they are bespoke models but he does show plenty of techniques for building up complex shapes from simple pieces etc.

I have this book but only read the first chapter so far. Looks really interesting!

 

[JimG]

I have this book but only read the first chapter so far. Looks really interesting!

It could put you off modelling forever when you see the standard of model he produces.

Jim.

 

[SteveO]

Oh I have – they are outstanding. Jaw dropping. I was at an auction a couple years ago and it was on display. I think it was a Cord, but my memory is a bit sketchy.

I have a very long-winded project on the go at the moment.

 

[Ian@StEnochs]

Hi all,

I have not had much time for modelling recently what with houshold DIY, Beer festivals and holidays but I am now getting geared up for my next project. As the weather has been horrid what could be better than keeping warm over my casting machine turning out a few components ready for when I get to the workbench?



This is my home made centrifugal casting machine, other sweet tins are available, along with the speed controls and melting/pouring ladle. The ladel came from Tiranti and the speed control is ex train set. The turntable is driven by a Canon motor and gearbox, Ron Chaplin I think.



This shows the RTV rubber two part mould in place. Before casting a top plate is screwed down to hold the mould in place and to keep the two parts in close contact. To cast the lid is fitted and the mould spun while molten whitemetal is poured through the hole. the spinning mould forces the metal outwards filling all the cavities. I melt the metal in the ladle over the gas ring, skim the slag from the top with a bit of bent brass and pour at the lowest temperature that lets the metal fill the mould. The first couple of pours will probably not fill completly but once the mould is warm most spins are fine.



This view shows the brass patterns, moulds and some of the castings. I use RTV rubber from Tiranti. The moulds are made in a slice of plastic drainpipe with some plasticine to hold the castings while the first half is poured. After 24 hours the plasticine is removed and the 2nd half poured making sure that the joint faces have been sprayed with mould release first! The white dust on the mould is talcum powder to help the metal flow and to lubricate the moulds.

Hot metal can be hazardous so take appropriate precautions. I have a leather apron, gloves and safety glasses. I also work with the machine inside a wooden tray with high sides and only cast when my wife is out.

Happy modelling,

Ian

 

[Scale7JB]

Brilliant Ian, thanks for that..!

All I can say is, I can't wait until we move into a house where new methods requiring a little space can be tried out and used.. The day can't come too soon..

JB.

 

[Osgood]

….Hot metal can be hazardous so take appropriate precautions. I have a leather apron, gloves and safety glasses. I also work with the machine inside a wooden tray with high sides and only cast when my wife is out…..

Safety being paramount, in this situation I would lock all the doors in case she comes back early.

 

[mickoo]

Blimey, that's seriously impressive casting, I think I might look into this myself, rather than constantly sourcing bits elsewhere. I've no issue with other bits but often the quality is a bit hit and miss I'm afraid.

What sort of RPM are you spinning at and do you happen to have a photo of the turntable motor arrangement under the tin please (good choice of tin BTW)