Moulded point sleeperwork by Vacuum forming.

[bertiedog]

I have just got out my old vacuum moulding machine after it stood idle for many years after being used mainly for model marine parts, which I no longer make. 

 

It's an A2/A4 frame machine, with a vacuum cleaner as power unit, with a Variac controlled heating array, and the size of the unit is well within vacuum moulding sheets of complete sleeper patterns for points, up to quite long no8 plus or larger radius 00 types. On the diagonal it could handle an O gauge point similar to Peco's in size.

 

The idea is to vac form the whole point sleeper set in say 20 thou into a negative mould, complete with marks for mounting C& L or other plastic chairs, with a backing sheet of 30 added with solvent to keep the lot flat. Once ballasted it would look exactly like an other point sleepering.

 

It will take a few days to build the master unit and take a moulding in reinforced dental plaster of the wood sleepers, to make the master mould.

 

It would be possible to do simple chairs, but the hold and detail would be crude compared to the C&L chairs. I will add a gauged mark on the sleeper to guide fitting the chairs, best finally done in a jig in pairs.

 

I suspect the moulding will have to cool much more in the mould to stabilise it before removal, to attain the accuracy, although the real accuracy comes when the chairs are added. Black sheet would give the basic colour for painting the sleepers to the brown shades.

 

Fixing down such a point would be easy, and it could even be pre-ballasted before fitting down.

 

Anyway worth experimenting with as the plastic sheet is cheaper than moulded sleepers, and faster than cutting out wood, and it gives a consistent appearance to pointwork.

I will publish shots as the work proceeds..

 

Stephen.

 

[Joseph_Pestell]

Be interested to see how this goes. Always been surprising to me that we don't make more use of vacforming in the model railway world, but it had never occurred to me to use it for trackwork. Why not have moulded ballast Roco-Line/Profi-Gleis style?

[Spitfire2865]

The problem I see for small scale things is Vacuum forming tends to radius all edges. It creates much softer angles than we are used to in modelling. So while I would be interested in seeing your results, I dont think they will match your expectations.

[Stubby47]

Have you thought about vac-forming brick sheets, similar to the SEF ones, but with a wider variety of bonding ?

 

For example, Peter Lloyd (peter220950) is making a cameo layout and the platform he is planning is a herringbone pattern. 

 

Also, windows with various pattern frames could be done, with the resulting 'panes' needing to be cut out.

 

Just a thought.

 

Stu

[bertiedog]

I may get around to bricks, it takes time to do the masters,.

 

The radius problem should not occur as the plastic is being sucked into the mould, and as long as the mould is pre-heated, and time is taken for the forming of the plastic into the mould, then right angles are fine. I fact the edges are not at right angles, they have "draw" to allow withdrawal of the moulding from the mould.

 

The only time you get "drape" is where the plastic is sucked down onto a mould, with the intention to make a copy with the top face having the details. Here in the points despite the projection upwards of the sleeper, the detail is on the under side of the plastic if you follow.

 

To get the crispness as good as injection mouldings it needs the mould cooled slowly, no quick pulling of the sheet out whilst still soft. if still hot it tends to "relax" and you get the rounded corner effect.

 

If the vacuum cleaner does not prove powerful enough, I have a vacuum pump that can do it, but it takes more time despite the lower pressure.

 

You certainly could do the lot ballasted, but it might look a bit odd covering up the joins between identical units! It does not take that long to do ballast and it should be granite etc anyway.

 

The tests will reveal how strong the 20 thou is for the job. I suspect strong enough to take pressure that a Peco point would bend at anyway.

 

If there is a problem, the interior of the sandwich, could have a skim of plaster added to the detailed side, to fill in the holes and prevent any potential damage occurring.

 

Should have sample or two over the next few days.

 

Stephen

Edited May 12, 2017 by bertiedog

[Joseph_Pestell]

The problem I see for small scale things is Vacuum forming tends to radius all edges. It creates much softer angles than we are used to in modelling. So while I would be interested in seeing your results, I dont think they will match your expectations.

I think that could certainly be a problem with 20thou sheet. And anything thinner might not be strong enough. Hence my comment about incorporating the ballast.

 

Old railway sleepers do have quite rounded edges though.

[Joseph_Pestell]

When I was considering doing this (20+ years ago), I was going to make the brickwork masters in etched brass or nickel.  That way one can make a master quite quickly (although not so cheaply) by simple step-and-repeat on a 2D CAD.

[bertiedog]

Most of the old moulding plates I made where done on a TTH pantograph milling machine and engraver, but I do not have access to one now.

 I have tried a test with a four sleeper section and it works, but might give troubles over an entire point. It could need application of local extra heat as the plastic moulding forms, and that risks tear holes appearing if you are not careful. As I thought you have to leave the plastic to cool right down to set hard before any attempt to pull it out of the mould. I will now prepare the master for a whole point and cast a mould from it to work with.

 

Stephen

[bertiedog]

Well....the problems have come but may not be serious, the sheets will not stay flat on their own. Even when mounted on a thicker backing, the moulding has to be cut into four sections to remain flat. This does not affect the use of the sleeper unit.

 

The edges are quite sharp, good detail, but it needs a bit more vacuum pressure to pull down the lot evenly, and a longer waiting time to cool off.

 

The thickness that worked best is 20thou black, it absorbs the heat better than white.

 

It may be a struggle to find a vacuum unit that has the capacity, I have one that can meet the pressure but not the flow required. I will try a more modern cleaner unit. Also improving the seal as the platen closes with the hot sheet in place, it may need a silicone plastic seal made, which can take the heat used to soften the Styrene Plastic sheets.

 

Stephen

[Spitfire2865]

Pictures?

[bertiedog]

As soon as it works!

[bertiedog]

Things not going well, the mouldings are still curved due to stresses built up when the plastic is sucked into the moulds. ore heat and holes appear. less heat and it gives poor detail. I am using an industrial vacuum now from the workshop. A bit of a re-think is required, perhaps the sleepering in thirds, assembled on the the back plate. The cuts would be in between the sleepers, so invisible.

I will go ahead with a brick sheet as soon as I can get the etchings done

[bertiedog]

The problems will not go way, I have discussed this with a friend that makes parts for model marine boats, and he thinks it is moulding in stresses in the sheet that will always warp it. It is the close parallel sleepers that are giving the problem. We are looking into other grades of poly sheet to see if there is a cure.

For a single base it has got to be flat before the backing goes on, or risks the top warping the backing. The warping almost goes when finally screwed down to the base, but it needs a lot of screws to get it level enough to fit the chairs.

So getting in other plastics to try, and an etched sheet of bricks is being done in the next couple of weeks. This should cause no issues, as it was what the machine was designed to do!

Stephen

[bertiedog]

The mould has been tried on another vacforming machine used for marine model parts, and it still warps due to stress as it cools, so it looks like an abandonment unless he can come up with an answer. Brick sheets moulds are being prepared though, but it will be several weeks to get them made by etching .

Stephen