[wiggy25]

Hi all,

Reading through lots of posts on different forums, I noted how expensive the large scale models actually cost, and even when buying a kit it's still very expensive.

I'm a service engineer for a company that makes thermoforming machines, all different sizes to do a wide variety of products, from sandwich packs to salad bowls, blisters etc etc.

I was at a customer the other week servicing one of his many machines and thought about the idea of thermoformed body shells, just like RC cars have the clear replacement body shell why can't it be done with loco bodies.

The machine I was working on, can form 15mm thick sheet. We have customers using these making bath tubs and the complete inside of a fridge freezer, the white plastic part that the shelves sit on.
Yes this is one mould and the sheet material is heated then vacuum draws the almost molten material over the cold forming tool.

It would be possible to have a female tool made so that the heated material, once vacuum is applied can be drawn into the inside of the mould.

The tooling would be much much cheaper than an injection moulding tool, ok the finished article may not have as much sharp detail, but this would be shown in the price of a body shell.

This body shell would just need to be fitted to some sort of base plate that fits onto the chassis, after being painted.

I just want others thoughts and opinions really, I can always speak to the tool makers that our customers use and our customers, to see if it would be possible to produce something:-



A typical Lexan body shell for RC car, these are just cut out and then sprayed, masking off individual areas.
Strengtheners could easily be glued into the bodyshell, along with appropriate parts for fixing to a chassis.
All required parts could be included in a kit.
Ok the body will not be as rigid as an injection moulded body, due to the thickness of material that would be required...too thick and the material wouldn't pull into the tool so you would loose detail.
If you goto some supermarkets you get the salad bar with the bowls made from clear APET or PVC that you fill up with salad, these are produced on our machines, it gives an idea of rigidity.(also depends on material thickness)
Surely though this has to be a cheap way to get into the large scale sizes, lets be right the body shell above costs £25 with all required decals; it's about £10 with no decals!

Compare that to a brass or resin kit.
For those who would like lots of different bodies could this be a cheap alternative, all the fine detail items could be bought and glued to the body shell

What do you think?

Is there any thing like this already being made, I googled but couldn't find anything.

Just some ramblings that was going through my head whilst driving back from Livingston today, so apologies for the long post that maybe a complete waste of time!

Ian

 

[mikeg]

Ian, this has been done before, I can't remember the company that did it, but they made some coaches and wagons in both OO & O gauges. The problem was that the definition of the models was not good as the plastic tends to have rounded edges. I tried to make a QM brakevan from one but found it easier to make from scratch.

Its a good idea and worth trying again for the gauge 1 and above I think as it may be easier to form in the larger scales, although I think the mould cost could be quite a lot to get a good model and the number that could be sold limited so the unit cost would be high.

A number of years back I tried to get O gauge coach bodies formed in the same way but it required a run of 10,000 to make it viable for each type of body so I dropped the idea!

look forward to any updates

regards

mike g

 

[wiggy25]

Mike,

I know what you mean, the detail would be hard to get, as you will need quite thick material for stiffness, unless reinforcement strips are glued in later.

The mould tool would have to be made from resin, speed wouldn't be an issue, not talking about making millions a week..or year for that matter!
So resin would be much cheaper.

The 10'000 units would be about right to justify the cost of an aluminium tool, plus cost of machine time.

We have a small machine in our office showroom at the minute so I will need to speak to one of the tool makers and ask how much for a resin mould, obviously need type of material and thickness so they can work out shrinkage rates and the like
Don't know how much it would cost, obviously more for lots of detail..I think a diesel or electric loco would be best that could be formed using this method, also need a suitable chassis that it can be fitted to.

Any ideas or suggestions with pics if possible would be great.

Ian

 

[John Webb]

Would be OK for wagons, coaches and diesels, but I think there would be problems for steam locos unless the mould could be dismantled to release the moulding around the boiler etc. This would put the price up, I suspect.

Regards,
John

 

[wiggy25]

John,

Yes it is possible to have moving parts in the mould, normally used for large undercuts, the material is formed then the segments are retracted into the tool so the formed part can be released.

Only seen it done with an aluminium tool on a fully automatic machine, and yes does add quite alot to the tool cost.

I need scaled drawings of a loco or coach in O or OO so the tool maker has something to work with, I've had a tour around the factory which is quite impressive.
Hopefully they can take the scaled drawings and put it into a CAD program then convert it to a CNC program and send it down to one of the machines for the positive mould to be made.
From which the resin negative mould can be made, need to speak to the MD of the tool makers.

Oh and before you ask, yes our company does make tooling but it takes a while to get and cost about 3-4 times the price of tooling made over here!!

Ian

 

[John Webb]

Peco used to publish drawings by an Ian Beattie, who died fairly recently. A number of his drawings have been published in a book 'Drawn and Described' also published by Peco. There are various books of drawings I've seen in the reserve stock my County Library has available at its central resource centre. It might be worth checking with your nearest library or looking at their on-line catalogue.

Regards,
John

 

[7113]

Having been thinking about this the only loco I could think of that might work is the unloved class 14 (unloved when introduced I mean). Another item that could be useful is the possibility of producing long rows of low relief buildings liike terraces or shops etc.

Just a thought.

Regards

 

[Bilbo]

There used to be /maybe still is a company that produced brickarches and viaducts out of vacuum formed plastic.

My thought on this is that from my experience of RC cars the body detail would not be anywhere near injection moulded plastic or some of the silver fox resin kits .

 

[pedromorgan]

"I need scaled drawings of a loco or coach in O or OO so the tool maker has something to work with,"

How long is a piece of string??

EXACTLY what loco/coach is it that you want to do? in what scale? What chassis are you going to use? there are drawings and then there are drawings, its the latter you will need in order to make a model! the ian beattie drawings are ok if you want a general outline but they are very difficult to produce an accurate model from. outlines are no good, you need to know from measurements the radius of the window and the width of the door and the radius of the tumbleholme ect.... you cant rely on someone else to have gotten it right.

Someone taking a measurement 1 possible error
someone communicating it to the chap with the notepad 2
that person writing it down 3
someone reading his handwriting 4
someone putting that measurement into the computer 5 the computer accepting the input correctly 6
the list goes on.

As has already been mentioned above its very difficult to get sharp corners on a vacuum formed object. so you need to choose your prototype very carefully.

making a model locomotive shell is a very different kettle of fish to producing a bath tub.

Peter