Thread: PVC Reducer Cone

DVW 150 mm pipe has a nominal OD of 160.25.
This means it outer perimeter is 503 mm

The internal perimeter of that rectangular port of the blower unit is 540 mm.

This means if the pipe is formed into a rectangular shape it will easily fit inside the rectangular port.

You could do that and pack out the difference with some MDF but here's what I would do.

Shape a piece of wood into a 2D wedge that can be jammed into the pipe. Then heat the pipe with a heat gun or hot oil and force the 2d Wedge into the pipe so as to expand its internal dimensions until it is slightly greater than the internal size of the rectangular port. One you have reached the size, cut, heat and fold the end of the now rectangular pipe to form 4 flaps that match with the rectangular port flange.

Good project

Great idea, Bob.

I would definitely use hot cooking oil when following Bob's advice ... much faster and you are sure the temperature is even for the entire section of pipe. If you use a heat gun you might not get even temperature, and making the shape could be problematic. I learned this the hard way, and use cooking oil wherever it is possible.

Cheerio!

Originally Posted by John Samuel

I would definitely use hot cooking oil when following Bob's advice ... much faster and you are sure the temperature is even for the entire section of pipe. If you use a heat gun you might not get even temperature, and making the shape could be problematic. I learned this the hard way, and use cooking oil wherever it is possible.

Yeah on ends of pipes I would go the cooking oil - leave the hot air gun for PVC or mid-pipe work where it is harder to use oil.

Thanks Bob and John.

Before attending to the rectangle to round transition I tried something a little easier, the flare from the separator to the blower. This will hopefully assist the transition of airflow from separator into the straight pipe. I used the heat gun and molded it over an upside down dog bowl I found at M10. Overall I'm pleased with the outcome although there is a very slight lip/bump where the bend starts. I suspect this may be caused by the very slightly larger than 150mm diameter of the bowl base. I struggled to get the start of the flare (open end) to flatten out into the lip of the bowl which I was hoping would help attach the flare to the separator. I could make do as it is though. The max flare diameter is 200mm, pretty much the length of the longest open corner to corner measurement of the metal flange on my separator and blower (first post).

Appreciate both your suggestions. I'll need to put some thought into forming a wooden transition block and will need to buy some oil if I choose the oil route. Given the diameter is much the same as the longest corner to corner measurement I was considering just flattening four sides of the flare to align with the sides of the metal flange. I'll not have as much control as with a preformed block but I reckon it'd do the job. It does however mean I'd be missing the four corner bolts but I do have rubber gaskets to help with sealing.

Feedback and thoughts?

Flare.jpgBowl.jpg

Firstly good job on the flare. I reckon if you had use oil it would have been less likely to create the bump.

Originally Posted by GarethR

. . . It does however mean I'd be missing the four corner bolts but I do have rubber gaskets to help with sealing.

To deal with this, because I can weld plastic I would cut 4 squares out of PVC sheet and weld these into the missing corners.

It would also be possible to PVC glue in the missing corners especially if a supporting rectangular PVC flange was glued on underneath at the same time

Thanks Bob.

I was wondering how far I could push thermoforming the pipe? If I over-flare the end so that the flare diameter extends to the longest corner to corner measurement of the rectangular flange I could then flatten and form to a preformed block. This way I'd not have to worry about an auxiliary PVC flange or missing corners. I'd end up with overhangs but those could be cut and squared up with the metal flange.

Just not sure how far I can push the thermoforming.

How about if you tack a couple of plates (about the width of the shortest sides) to your bench-vice jaws, sit the pipe over 'em and heat the sides as you open the jaws? That should give you some mechanical advantage and 'preset' one side of the rectangle so you only need to measure the stretch in the one, long dimension.

Just a thought. Dunno how it'd work in practice...

Originally Posted by Skew ChiDAMN!!

How about if you tack a couple of plates (about the width of the shortest sides) to your bench-vice jaws, sit the pipe over 'em and heat the sides as you open the jaws?

Good idea but not sure how it'd work as the longest width of the rectangular opening is approximately 150mm, close to the pipe ID. It'll be pushing out the corners to start off with, so it may just work. It should give a reasonable amount of control so I might give it a go in the morning.

Originally Posted by GarethR

Thanks Bob.

I was wondering how far I could push thermoforming the pipe? If I over-flare the end so that the flare diameter extends to the longest corner to corner measurement of the rectangular flange I could then flatten and form to a preformed block. This way I'd not have to worry about an auxiliary PVC flange or missing corners. I'd end up with overhangs but those could be cut and squared up with the metal flange.

Just not sure how far I can push the thermoforming.

I assume you mean starting off by flaring as in A but then I'm not sure if you mean going to B or C



I doubt you could push the thermoforming enough to form the corners for B, and C requires shrinkage at the corners which is impossible once the PVC has been deformed. C is also a very turbulent junction.

Just a thought get a sheet of acrilic cut the square to suit and cut a round hole in the center to suit the pvc pipe, glue a sleeve on the pve pipe( from the next size up pvc pipe ) maybe 1cm long onto the pvc pipe, push it through the hole in the acrilic, then glue the edge of the sleeve onto the acrilic, to make it even stronger do the same sleeve and glue on the other side of the pvc pipe to the acrilic

Originally Posted by BobL

I assume you mean starting off by flaring as in A but then I'm not sure if you mean going to B or C

Was thinking of going from A to B.

Originally Posted by GarethR

Was thinking of going from A to B.

That would be nice but I doubt the corners can be formed out of the expanded dust. You could always give it a try as a short length of 150 mm ducting doesn't cost all that much.

Originally Posted by Ashore

Just a thought get a sheet of acrilic cut the square to suit and cut a round hole in the center to suit the pvc pipe, glue a sleeve on the pve pipe( from the next size up pvc pipe ) maybe 1cm long onto the pvc pipe, push it through the hole in the acrilic, then glue the edge of the sleeve onto the acrilic, to make it even stronger do the same sleeve and glue on the other side of the pvc pipe to the acrilic

If maximizing flow was not a problem this would be a solution and one I would advocate. However, the cross sections of the pipe and rectangular duct are very poorly matched, so as well a constricting the cross section of the connection it would also create two "shelves" on either side of the pipe which will generate a significant amount of turbulence and further constrict flow.

Completed the preformed block and thermoformed the first transition piece.

The preformed block was made from some spare fence paling offcuts, cut to size and planed smooth and to shape. I didn't put too much effort into the finish but was happy with the outcome. I also beveled off the inside of the tube slightly to help with the transition over the block, thought a sharper edge might get caught. Top of the block was slightly under-sized so the ID of the pipe fitted over snugly.

I used the heatgun which seemed to work just fine. Was aware of keeping everything as evenly heated as possible and broke down the heating and forming into stages.

Overall I'm really happy with the outcome. I now need to cut and bend the ends to allow attachment to the metal flange. Below are some pics of my progress.

Thanks heaps for all your inputs, certainly made the task less daunting than I had in mind.

Block B4 Forming:

Block_B4_Forming.jpg

Block Preformed:

Preformed_Block.jpg

Pipe on Block B4 Thermoforming:

PreformedBlock_PipeStart.jpg

Thermoformed Transition:

PipeOverBlock.jpg

Preformed Block in Thermoformed Pipe:

BlockInPipe.jpg

Great job.

About the only improvement I would suggest is to double the length of the transition!

I have thought of another way to make the flange but it requires PVC angle (or sheet bent into angle).
The angle could be cut and glued to the transitions so the corners are filled. and then fill any small gaps with a bit of sealant.