Vacuforming a steel ribbed culvert?

Hi there,

Like your idea about the lathe. How about drilling it out when you are finished with the lathe? Seems to be a simple solution. Just an idea. They sell long drill bits at the local hardware store. Hope you solve your problem.

Jim

fox wrote:

Hi there, Like your idea about the lathe. How about drilling it out when you are finished with the lathe? Seems to be a simple solution. Just an idea. They sell long drill bits at the local hardware store. Hope you solve your problem. Jim

Okay, I see what you mean about drilling out the inside with a bit, but the thing is is that when you see the inside of the culvert, it would have a smooth surface, and not a ribbed surface like the exterior. You will be able to see both the outside and inside surfaces of this culvert.  A good idea though. 

You say it will be as wide as the treaat at 1/50.  What street?  For the street I live on that would not be all that big.  But now if we're talking all 12 lanes of the New Jersesy Turnpike... that's big

How about making the basic shape of the culvert out of wood or PVC pipe and wrapping it tight with some wire and vacuform that in short section.  That should give a nice corrugated look.  They can be glued together to whatever length you need. Or if oyu have access to lathe, machine the grooves right into a length PVC pipe.  Only problem with the pipe on a lathe or drilling out wood is that the insdie would be smooth, not corrugated.

Determine the peak and valley diameters you want for a vacuum form buck. This is determined by the scaled part peak and valley diameters, AND the thickness of the plastic sheet you intend to use. Then find a dowel or tube or other rod the size of the valley diameter. This will be your core diameter. Then find a coil spring whose inside diameter is about the same as the core diameter, and whose outside diameter is about the sam as the peak diameter. Hopefully the spring will be a loose enough fit over the core. If the spring coil pacing is too tight, it can be stretched by pulling either end of the spring. But do this carefully so as not to overshoot the desired spacing. This typically doesn't work as well in reverse if the original coil spacing is too loose too begin with. Anyway, make sure the spring is degreased, and the core is likewise clean, and glue or cement the spring to the core. Perhaps superglue is best.

I presume you realize you can only vacuum form over one half of the buck, otherwise you can't separate them later. What this means is, you have a couple of choices. You can either half immerse the horizontally oriented buck in a tub of some liquidy substance that will become hard, or sever the buck lengthwise. If severing is the route you take, you must realize that spring wire is hard, and a motor tool with a cutoff wheel would be best to cut that component. Remember to cut up to the half way mark, don't just split it down the middle. The reason is,the cutting tools will remove a swath of material, and if the cut is centered, you will end up with less than half a buck, or under 50 cents (O.K., bad joke).

You might be fortunate, because there are plastic spirally-spring-like doodads out there. For example, the coiled cords that attach to pens at some checkout counters to keep the pens from walking off. I don't know if that size would work for you, but it would be much easier to work with. There may be other sizes of plastic coils for other uses, but it is very late for me and my mind is shutting down.

Anyway, I think you get the idea.

Try these steps on for size:

(1)  After computing the scale size for the inside/outside diameters, go to a good building supply store. ( one of the big box stores, ex: Home Depot )                             

(2)  Buy a length of molding called "half-round" of such size that when 2 pieces are held together, flat-face to flat-face, it'll give you the diameter you need for the INSIDE of you pipe.  Get it long enough  to give the length you need.

(3)  Get a can of spray adhesive and some thin paper.  Cut the molding into 2 working pieces and spray the flat faces with adhesive, then lay single layers of paper on one face and then bring the flat face of the second piece of molding  together, face-to-face.  You're making a "paper sandwich" .  The result you're looking for is to have a round dowel with  a layer of paper running through the round dowel's center.

(4)  Step #3 has given you a dowel  you can put into a lathe and turn scale corrigations into its surface; resulting in a mold for vacu-forming all of the "pipe" you'll need for your project.

(5)  Once you've gotten the corrigations just right ( you'll want to make them extra pronounced so they'll translate good to the plastic sheeting ), separate the piece back into 2 half-round pieces.  The paper you glued between the pieces created a weak line that will tear open when you are ready.  That's a technique used in woodturning for turning mirror pieces  for custom furniture decorations--among other things.

(6)  Now that you have your mold pieces, don't forget to coat them with some good "release"  substance, such as spray-on wax before bringing the hot plastic sheeting material into contact with them.  Re-apply the release before each molding use.  NOTE:  You'll need to use thin sheets of plastic; such as .010 or thinner, to get the good inside and outside detail transfer from the mold.

(7)  Glue the new plastic pipe halfs together and there's your scale corrigated pipe ready for finishing and detailing.  Note:  want an aged, bent end showing out from under the road bank?  Heat that end with a good heat source ( heat gun, hot soldering iron, etc ) and press the pipe into shape with a wooden tool you've made from a piece of scrap.

(8)  This method can be used for making barrels, trash cans, etc.