Softening and bending PVC pipe has become a regular activity for my engineer. He has done everything from forcing straight pipes to fit into anchor slots to form a hoop house cold frame, to using a blowtorch to make the stand for my underwater swimming timer. The problems with forced bending are limits of degree of bend, it takes brute strength, and there is high potential of snap back leading to pain. Applying a torch allows for softening of exact points, but easily gets so hot as to scorch or irreparably damage the PVC pipe.
There are contraptions for sale to help soften PVC pipe. The ones my engineer has seen cost from $300 – $700, so he kept looking for less expensive options. A couple of months ago, our electrician came to do some work on some outdoor wiring that is encased in PVC pipe. He pulled out a PVC softening oven to create the necessary bends and my engineer was able to examine it and ask questions. Then, my engineer made his own.
- heating element from electric oven, from oven saved from kitchen remodel or buy at junk yard for approximately $15
- piece of Romex wire – ours was about 18 inches long, but it just needs to be long enough to work with and have the plug a few inches away; your local electrician would probably sell you a piece for a few cents
- 3 prong plug – this can be purchased some place like Home Depot or Grover’s Electric for about $2
- section of old stove pipe – ours is about 2 feet long, but any longish, heat resistant metal cylinder, that the PVC pipe can fit into and possibly through, will do
- scrap piece(s) of basic fiberglass insulation, large enough to cover stove pipe
- heat resistant base – we used my engineer’s table saw
Additional helpful items:
- tiles, bricks, or other square heat resistant items to keep stove pipe from rolling
- various pieces of scrap metal to prop PVC pipe in place as needed
- insulated gloves for handling heated PVC pipe
- thin sheet of metal to tent over fiberglass insulation, both to hold it in place and to retain heat if necessary
The oven element was hand bent into a long rectangle that could fit into the section of stove pipe. The long, confined space keeps the heat where it is wanted. The terminals on the oven element were left in place. A piece of Romex wire was stripped of enough of its plastic insulation at both ends to attach it to the terminals on one end and the plug on the other. The plug comes with instructions to unscrew it and expose where it can be attached to wires, then all be screwed back together.
The section of stove pipe was positioned horizontally on the table saw base. The reshaped and wired oven element was now ready to slide inside the stove pipe. (It can just lay there however it fits, hopefully being bent in a flat enough plane that it only takes up space in the bottom of the curve of stove pipe.) A couple of short stacks of tile remnants were pushed up against side of the pipe to steady it. A piece of fiberglass insulation was put on top of the stove pipe. The amount needed may depend on outside air temperatures and how open the ends of the stove pipe are. At this point the thin sheet of metal, bent to form a tent, could be placed over everything.
Softening PVC pipe should be done outside or in a space open to plenty of airflow, as PVC can let off toxic fumes. Do NOT soften PVC in your kitchen oven.
My engineer plugged his PVC pipe oven into a basic 110 volt outlet. With this power source and one incomplete layer of fiberglass insulation (and the day’s temperature in the mid 40’s°F), the oven quickly heated to around 200°F. This was measured at both ends of the stove pipe with a laser thermometer. When more insulation was added, to more thoroughly cover the top of the pipe and the ends a bit, the temperature inside the oven easily rose to 400°. The temperature continued to be manipulated throughout the project by small changes in this blanket of insulation.
The PVC pipe was measured and marked with pencil before softening. A bending guide was also drawn on a scrap piece of wood because once the PVC pipe is removed from the oven, it has to be worked with immediately, before it cools. This is why insulated gloves are highly recommended. When it has been manipulated to the desired shape, its cooling can be encouraged even more by wiping it down with a wet rag.
If the bends are very close together on the pipe, it is best to try to form them basically at the same time. Otherwise, if that part of the PVC pipe is heated again, the bends may be lost. The PVC pipe tends to return to it original shape when heated again. There is also the risk of melting or scorching the pipe with too much heat.
We made a PVC pipe towel rack for my swimming pool area to get most of the photos to explain this. This involved trying a new technique of cutting the ends of the PVC pipe with heavy duty scissors (Cutco brand). I was pleased to see that the scissors were not damaged, and there wasn’t melted PVC left adhering to them. These cuts were designed to allow the pipe to be shaped to fit around and be bolted to some metal bars near the swimming pool. This worked fine on one end of the towel rack, but the other end snapped off. The point is that once the PVC pipe cools, it is stiff again. We probably could have avoided the break by using more gentle, controlled motion. However, I still got my towel rack, and I am brainstorming about other PVC pipe bending projects.
Here is a video by Laura that might help as well.