Wacky PVC Bending idea. Will this work?

[Doug Shepard]

I'm pretty close to deciding to go with 6" S&D PVC for DC ducting but one particularly gnarly area is going to give me some trouble. It would have been trouble with metal ducting as well. But I need to come out the side of my DC closet and get up into the rafters in a fairly short area. Using fittings to make the bends is going to eat up a lot of that area. I think I can still get gradual enough bends for DC and clear my space problem if I can bend the PVC. I asked a few days ago about the PVC heat blanket benders that Bill Pentz site mentions. A few folks replied that they were going to be expensive and some Google searching shows that option even costlier than their estimates. I dont really relish the idea of torch or heat gun heating with all the dangerous fumes. So I'm sitting here today and had either a totally great idea or a totally foolish one. Can I use a steam pot and plug up both ends (one would have a opening for the steam) and bend the PVC with steam?? My next thought was - Naw that'll never work because I've heard of folks making steam benders for wood out of PVC so it must not get hot enough for PVC. So I searched past posts here about steam bending, and voila - found a bunch of warnings about using PVC as a steam chamber as it gets soft. Geez, maybe this isn't such a wacky idea??
Anybody ever tried this?

[Jim Dunn]

Uh Doug, if it's hot enough to bend how are you going to handle it and keep from crushing it at the same time? Seems to me that generally if you are using a blanket or a heat gun you start with a fitting that generally fits your needs then adjust from there. Now that's how it's done with electrical pvc. As they are much longer sweeps and such. A pvc sewer 90degree is just that a right angle with minimum amount of material.

If it works have your wife film it while your doing it. I can see a funniest home video about to happen. Good luck!

[Doug Shepard]

Jim
That crushing question actually brought up another benefit I hadn't thought of. I could gain a bit of space by converting 6" round into an oval until I got past the rafters. Obviously I'd have to wear some heavy gloves but that would have been true with the other heating methods too.

I should also mention that the upward slope coming out of the DC blower is something like 15° so my bend would have to be about 75° rather than 90°. I'll also need to gradually start the upward transition before exiting the closet wall so the hole through the closet wall wont be round but some sort of ellipse.

Oh - and no wife either,

[Ben Grunow]

2 thoughts Doug.

I think that 6" electrical conduit will fit with s&d and comes in long sweep elbows with about a 18" radius so maybe that will work and save you the trouble of making a sweep.

I have a steam bending setup made from 4" Schedule 80 PVC like Norms and the pipe does get slightly soft but not enough to bend by hand reliably. Even after 3 hours or so.

I would find a construction site and ask the electrician to heat a piece for you. Make a mold with some plywood and a couple scraps so the job is easy and there is no guess work.

Good lUck

[Carroll Courtney]

Doug,when I use to do electric we would use a hot box to bend pipe.Some times we would heat it using the tail pipe of the truck.But that was 2".A hot box is nothing more than electric heat and box open on both ends.If you have a elec.heater build a box just big enought to conceal the area you need to bend.Set up a V shape on both ends to hold the pipe and to be able to rotate it.Take a couple of wet rags and plug both ends and that will help keep the pipe from collapsing.

[David Wambolt]

I've used a heat gun to bend up to 3" PVC. To do 6", you would probably need two guys working both sides of the pipe. PVC retains it's heat pretty well and you can always reheat it to finish your bend.. However I use adjustable temperature heat guns, staying around 500 degrees F. That allows you to get in closer to the pipe without burning it.

[Bruce Wrenn]

If you have a way to heat a lot of sand, you could use it to bend pipe. Cap one end, fill pipe with hot sand, slide cap on other end, and bend to desired shape. Sand would prevent pipe from colasping. Heating the required amount of sand could present a problem though. I don't recommend using the household oven.

[Gary Bordeaux]

I have only bent PVC up to 2 1/2". I have slipped a 20' stick on the exhaust pipe of a vehicle to allow the stick to make compound bends and it works well if you don't get it too hot. I have also used a propane torch and an electric heat gun for smaller sections. The best thing I have used is an electric element hot box. For large dia. a properly designed steam box will work well. If you don't get it too hot it won't collapse. It starts to soften at about 170 deg. F.

[David Epperson]

Doug
Soft PVC gets real difficult to manage, if you could come up with some sort of form, wood perhaps, to define the shape you want, AND if you can get the PVC hot enough in a uniform manner, then you could put the pipe into the form and force the PVC into the forms shape with air pressure. Probably 3 to 15psi depending on how soft the PVC was. The form will beed to be able to support all of the PVC surface to prevent the soft PVC from bulging out too much. It's called blow molding and ALL plastic (and some glass) soda bottles are made this way.

Another route might be to use standard 90° fittings, but to cut them at an angle, and then glue them back together in the configuration you need. Methylene Chloride should work for this if you can find it. If not then you could heat weld it together with one of those Harbor Freight units (Around $35 on sale) Plus with 6" pipe you will be able to sand the interior smooth again if needed.

[Al Killian]

I second Bruce's idea about sand. The eye glass place uses a hot plate with sand in a container. This how the bend the arms. But, how much of a bend are you trying to get? PVC will only bend so far before it will crimp.Maybe a picture or scketch of the area with diemension would really help figure out what would work best.

[Doug Shepard]

Thanks for the feedback everybody. It appears I've misplaced a couple of pages I did a few months ago with a bunch of measurements. If I cant locate it I'll get things re-measured next weekend along with a sketch or two and pics of the area. Once I can get that first 3-4 ft section up into the rafters things should be pretty easy.

[Jim O'Dell]

I take it that there is no way to orient the inlet from the cyclone to be the right direction to go with the rafters? Mine went perpendicular to the rafters which meant I had to cut 2 rafters and re-support them with two cantilevered arms off the top of my DC closet to get the pipe up above the rafters on it's natural rise coming off the Clear Vue. And with all my roof work this week, walking all over the roof in this area, it didn't even offer to creak, much less move. Maybe a picture of the area you are trying to negotiate would help us "thinkers" Jim.

[John Terefenko]

Why not use metal and get a metal worker to bend what you want. You do not say what size dust collector you are talking about and I suppose you figured 6" is needed but there are times when just because the inlet is 6" doesn't mean you need to run 6" throughout the shop.

[Bill Pentz]

Doug,

Boiling water, hot oil, hot antifreeze, a vehicle tail pipe, a heat gun, a small heater, and PVC heating blanket will all work amply to bend your pipe. Many choose to bend smaller pipe simply because that provides an exact rather than close fit without having to buy or deal with fittings. The larger pipe is tougher to work because you need to work a far bigger area so need a good heat source.

With it typically costing $40 for a 6" diameter long sweep bend, I have just made my own.

I start by making a female end on one end of the pipe to bend. I do that by using boiling water and a wooden mandrel I turned on my lathe. If you are only doing a few then rounding over a piece of pipe works, but you have a little more trouble getting that started. After the pipe is heated the greased mandrel slips in with considerable work and expands the pipe just right.

Making the bend is more difficult. PVC will retain its shape when it first becomes flexible, but if you try to bend too far it kinks. You can avoid the kinks by first wrapping the outside of your pipe in something to keep it round. Some say duct tape works well. I don't know about duct tape but have had good success using a spring, cord, and strapping. The strapping seemed to work best for me. You can actually buy bending springs but they are pricey. To heat the pipe, I made a couple of donuts with insulation on the outsides that fit snugly into the pipe. My heat gun fits into the hole on one side and I slip the donut in as far as my heat gun tip will reach, about 4”. That leaves the ends unheated so they hold their shape. The other end has a smaller hole to let some of the air out blown in by my heat gun. You can tell when the pipe is ready to bend because a gloved finger will push on it and the pipe will give then spring back. This can take as little as five minutes for my big heat gun to as much as twenty minutes for my small one. When the pipe is ready, I remove the heat gun, slip the pipe into a bending jig which is a simple plywood form. My plywood form was made by using my router to cut an inner and outer groove into which I glued thin plywood 4” tall strips. When making a bunch of these I ran out of patience and began using the garden hose to avoid the near twenty minute wait it took for that plastic to cool. Remove the strapping and its done.

bill

[Doug Shepard]

I take it that there is no way to orient the inlet from the cyclone to be the right direction to go with the rafters? ...

Jim
It's at a bit of an angle but more parallel than not
.
Bill - the cost of the fittings isn't what I'm concerned about. My concern is that the space of the slip joint fittings where the pieces meet I'm guessing is about 1-1/2". I think the number of fitting I'll have to use to get this up and over my first hurdle is going to mean I have a whole bunch of length taken up by the joints themselves in an area that's already tight. I realize there's a limit to how small I can make any of these bends without compromising the DC operation. But I'm stuck with the physical limits of where I can locate the ducting. I think if I can somehow bend one or two continuous pieces I can save a lot of space getting this up overhead. I fully intend to use fittings everywhere I can once I get the ducting above the rafters.

My problem stems from the shared use of my shop as a garage. There are some hanging storage items that really dont have any other place to go. But the main reason I'm trying to get it overhead in the shortest possible space is that any ducting that projects out too far from the closet wall is going to block a window.

I'm supposed to be doing my taxes today but I went out and took some pics this afternoon and re-measured some things. The bike hangers (there's usually 2 hanging there) can be moved about 10-12" to the left - just enough I think.
- The upward slope of the inlet on the DC is 15° so I've got to bend 75° more to get vertical
- The forward angle of inlet is about 55° if measured from the back wall of the garage
- If the current upward slope of the inlet is followed straight through the wall, the center of the duct would be roughly even with the hub on the bike tire.
_ If the current forward angle of the inlet is followed straight through the wall, I come out between the 2nd and 3rd rafters. I need to put a gradual forward bend in as well to bring it up between the 3rd and 4th rafters (on the side with the bow) otherwise I dont have enough overhead room for a gradual elbow above.
DuctIssue6.jpgDuctIssue2.jpg

Here's a pic on the inside of the closet. The LH wall has a light penciled circle (actually a bit of an ellipse) where the intersection of a 6" pipe was traced if the upward and forward angles of the intake are followed. The distance on the backside of the intake to the wall is 6" and on the front side about 13".
DuctIssue4.jpg

From the top of the rafters to the bottom of the trusses (not sure if that's the correct term here or not) I've got 7-1/2" on the back side and 11" on the front, but 13" and 18" to the roofboards. I'm planning on angling the 90 elbow above the rafter at about 45 from the DC closet corner to get it into the most open area with the most height the soonest.
DuctIssue5.jpg

I realize this is going to complicate cutting the hole through the closet wall but I'd like to start the upward bend before I even exit the closet wall. It's already going 15°. Maybe I can get to 30° or 45° before coming through the wall? Then continue with the rest of the 90° after coming through the wall.
The forward bend to get it between the right rafter set I dont think I can do before exiting the wall. I'm pretty close to coming out by the closet post (the LH door jamb section) as it is.