Curving 1/16” plastic sheet to 2” radius for coved water-sky transition

[leighant]

I am planning an 8 foot long liftout with an N scale scene representing long parallel rail and highway causeways across an arm of a bay to an island seaport.

Galveston prototype: http://www.railimages.com/albums/kennethanthony/aca.jpg
Old computer rendering of layout concept: http://www.railimages.com/albums/kennethanthony/aby.jpg

Eight foot (or just under) I consider as the maximum length to fit my space, store on end in a bedroom with 8-foot ceiling, and to pour water in one continuous surface. I am trying to fit scene in only 14 inches of depth. One problem was hiding a transition between modeled water of bay and painted horizon. I think I have solution…. Flat horizontal surface of bay will make continuous curve up to vertical background of bay and sky, with horizon near track level, 2 inches above surface of bay. I built a cardboard and foamcore test mockup-- about a foot and a half of the 8 foot liftout dummied up at full scale.
I think the bridges will obscure enough of the transition to make it work.

cross section/ end view of mockup: http://www.railimages.com/albums/kennethanthony/aez.jpg
typical operator’s view about one foot above track level http://www.railimages.com/albums/kennethanthony/aey.jpg
N scale boater’s view looking up at bridge from water level:
http://www.railimages.com/albums/kennethanthony/aex.jpg

I have not figured exactly how to go from poured water surface to painted bay background but I think I am over halfway there on the transition.
Now I am trying to do detailed design of the actual structure, framing etc. for the liftout. My “old thinking” was frame with 1x4 wood, Masonite ® for water surface and background. But that would be kinda heavy. Tony Koester’s G-gauge layout article in the current Model Railroader about styrene foam base framed with aluminum angles got me thinking. I would NEVER get Masonite® to bend to the 2” radius curve I will need to fit two causeways and a pier nightclub on a 14” deep liftout. The thin styrene I use for small scratchbuilding projects would do fine--if I could get a big enough sheet. Being thin though, it would need some kind of support.

I figure I will need a piece of plastic 8 feet long and 2-3 feet wide to make a 14” water surface that transitions into a background approximately 12 to 18 inches tall. I went to the building supply store today and found 4 x 8 foot sheets of plain white plastic, 1/16 inch thick, $18.99 a sheet. It didn’t feel like it would bend to anything sharper than about a foot radius, without special “help” but it would be plenty strong enough to provide structural strength to a liftout.

So here is my proposed structural design. To prevent sag of 8 foot long liftout, I think of using wood as wide as 1x4 but cutting slightly thinner in thickness, and also cutting in to support 1” “blue foam” sheet. The foam sheet will support the plastic sheet flat across the water surface. I will need some kind of uprights behind the sky background to support and probably a light stick across the top of the plastic to stabilize and keep it flat.



My question will be bending the 1/16” plastic sheet (I assume it is styrene…) to make a 2” radius curve. Perhaps I could set up some kind of a rig with a curve-forming support (like a piece of PVC pipe) under where I want the curve, clamp weight at several points along what would be the top of the sky background, and using a hair dryer, heat gun or blowtorch to heat the plastic sheet until it bends to the desired curve. The curve forming operation would be done “upside down” to allow gravity to pull it into shape as heat softens the plastic. Has anyone done this? Any cautions (other than not setting the plastic on fire or melting it completely!) or helpful hints?

[TomDiehl]

If you're talking styrene, don't go any hotter than a hair dryer, especially if it's only 1/16 inch thick.

[ukguy]

I dont think a hairdryer would cover sufficient surface area, but maye it would. A couple of other options off the top of my head.

1: use a steel pipe instead of pvc and run very hot water through it to heat it up, maybe a blow torch to get it started on the heat increase but dont get it too hot, (maybe the blow torch was not a good idea) anyway, run HOT water throught the tube to heat it and then lay the sheeting across it (prob need an extra pair of hands) this should give an even heat distribution along the full 8' for a straighter bend. (when done you could take the steel tube back for a refund as it should be un damaged and as new, unless you know someone with some scaffolding poles & you could borrow one)

2: rent one of those big space heater jet engine things from HD or lowes, although this would be close to my final option when all else fails.

Just 2 initial ideas to get the ball rolling, keep us 'posted'

Have fun & be safe,
Karl.

[ndbprr]

Years ago there was a custom builder by the name of Bill Clouser who lived in St. Louis and did unbeliveable modeling using a high quality paperboard called Strathmere or Strathmore. It was available at art stores and would be a little more durable. Before settling on styrene a visit to an art supply stor might yield a more suitable material. If I was going to do that cove I would do it with joint compound and a curved tool to make the surface. Then I could use two straight edges on the base and backdrop material. It would take several coats but would be doable cheaply.

[ukguy]

I thought about that too ndbprr, but it's going to be a lift out section I believe and I think the joint compound would crack too easily, maybe a flexible substitue would work.

Karl.

PS. VERY nice illustration of what you are aiming for Leighant.

[Medina1128]

How about a piece of 2" PVC cut in 1/4s lengthwise? Then just clamp along the top and bottom edges and with liquid styrene cement and the capillary action allow it to flow along the joints. Since the support will be under and outside the styrene backdrop, it will be invisible AND have your 2" radius that you want. I think 1/16 inch styrene will bend to that radius without heating. Shoot me an email... I'll have a drawing for you...

[ericboone]

What you probably want is to heat the plastic with a hot air gun, which is basically a super hair dryer. You can probably find them at Lowe's, Home Depot, or Menards. Since they are typically used for heating heat shrink tube, you could find them at a good electric supply store too.

[leighant]

Thanks for the helpful suggestions.

Kenneth Leigh Anthony,
alias leighant

[chateauricher]

QUOTE: Originally posted by Medina1128
How about a piece of 2" PVC cut in 1/4s lengthwise? [...] it will be invisible AND have your 2" radius that you want.

You'll have to use a 4" diameter PVC pipe if you want a 2" radius.

---

Leighant,

I don't understand why you need to have a curve anyways. Curve or no curve, you're still going to have a line where the "horizontal" water meets the "vertical" water. So why bother with trying to do such a complicated design ? It seems to me you're over-complicating things when the results will be no better than if you went the simpler route. Also, you said it yourself — "I think the bridges will obscure enough of the transition to make it work." If you're not going to see it, why put such effort into it ?

If I were you, I'd forego the curve and just attach the backdrop to the backside of your benchwork.

[nfmisso]

I am with Timothy on this one. For strength and stiffness use 2" thick EXTRUDED foam for both the base and the backdrop. You will only need to protect the outside edges, and it will be light and striong.

[GMTRacing]

You can end the plastic easily enough, but I agree that a cut 90 is far easier. If you must bend, use a piece of 4"d tube. support the piece you want to be the base with a section of ply to keep it from warping. on the end that will end up bent down, clamp a piece of 2x4 along the entire length so when it's all ready the piece to be bent hangs off the ply and pipe into thin air. If you do this outside on a sunny day, the sun will help and preheat the plastic to soften it. Using a heat gun (or hair dryer if you realllly have a lot of patience) work the heater back and forth along the start of the bend line and continue working as the plastic starts to fold. bend slighty more than you need as the plastic will "spring back" when it cools. If you can practice on a small piece first to get the technique down. On no account should you use an open flame as it's too hard to control. We bend plexi all the time this way, but it is a PIA. Good luck. J.R.

[leighant]

Quote from chateauricher: "I don't understand why you need to have a curve anyways. Curve or no curve, you're still going to have a line where the "horizontal" water meets the "vertical" water. "

No, won't be a line where "horizontal" water meets "vertical" water because it will be a curved "zone" rather than a line. I guess I am particular in wanting the horizon line to be close to the track level, rather than 2 inches below it where the modeled water is. Otherwise, the horizon would be out of sight, behind the bridges.

Mockup to study typical operator’s view about one foot above track level


This is a compromise, between best horizon height for viewer at track level and for typical operator view slightly above.

It is a bit similar to the compromise I made on my Navy blimp base layout. I constructed the view of the blimp hanger (which was about 20 stories tall) as if seen from about 150 scale feet up from the ground. At that height, one would see a slight bit looking UP at the underside of roof, and also looking down at the floor. Typical operators are probably viewing from one foot to two feet above layout, and I liked this compromise, slightly cheating the perspective.

[chateauricher]

QUOTE: Originally posted by leighant

QUOTE: Originally posted by chateauricher
I don't understand why you need to have a curve anyways. Curve or no curve, you're still going to have a line where the "horizontal" water meets the "vertical" water.

No, won't be a line where "horizontal" water meets "vertical" water because it will be a curved "zone" rather than a line. I guess I am particular in wanting the horizon line to be close to the track level, rather than 2 inches below it where the modeled water is. Otherwise, the horizon would be out of sight, behind the bridges.

I beg to differ.

You yourself stated: "I have not figured exactly how to go from poured water surface to painted bay background [...]"

No matter whether the transition is curved (as you're trying to do), or a 90-degree angle, there will be a line where the poured water meets the vertical surface of your backdrop. There is no way to get around that.
Therefore, why go through all the trouble trying to engineer a curved transition ? I'm only trying to save you a lot of unnecessary hard work and several hours' worth of migrain.

[leighant]

Okay, okay. I'm starting to understand your point. Yes, at some point (or yes, "line"), I will need to transition from poured water surface to painted water surface. You have given me something to think about.

Since this is so much of a pet project for me, it will probably lead to several small scale tests and mockups. I will need more experience in "pouring" water surface if I ever expect to make some kind of transition. And I will need to develop ways of painting water surface texture on flat background to match modeled surface appearance, but in perspective. Will need some experience in both those areas, whether I have the curve transition I proposed or a perpendicular meeting of flat horizontal and vertical planes.

So thank you, M. chateauricher, for helping make the situation clearer.

Happy railroading.

[Anonymous]

Your cross section rendering is outstanding!

Two materials come to mind, both available in 8' lengths, neither of which would require heat forming. Check out thin plastic laminate, usually used for vertical surfaces, though the 2" radius may well be challenging. Use the back side which has a texture which will accept latex paint. A better choice might be 4 or 5 mil matte surface mylar, available at any drafting or reprographic supply house...it may be available in even thicker.

Good luck,

[ukguy]

why not........

build the base and back drop as per convention, ie 90degree. insert 1/4 of a 4" diam pvc tube along the 'join', you could use a router (or other tool) to countersink this in to the backdrop and base. This would be very easy to do preassembly and the result would be invisible if you used slightly too much glue so that it oozed out of the joints a little, you can use the excess glue as a filler for the minute line between tube and backdrop/base and sand it smooth.



Now to eliminate the 'line' between poured and painted water.

Eliminate poured water alltogether.

Either :-

a) paint the water/sky directly onto the backdrop/base or onto a LARGE piece of paper/card and then glue this to the backdrop/base. To get a ripple effect on the water use a paint-roller and apply supper high gloss polyeurethane over the dried painted water, you will be surprised how good this looks, you may need to re-roll while the poly dries to maintain the ripples as it hardens/cures.

b) take a suitable water/sky picture to Kinko's or other print shop, get them to print it the size you need, again, over the water roll on poly for ripples. glue this large photo to your curved backdrop/base.

Thanks for the challenge, keep us posted.

Have fun & be safe,
Karl.