Flared ends from sheet
A flat sheet of PVC can be heated and pushed onto a mold
This method looked promising, but when a large flare is attempted, the PVC sheet tears.
It should be possible however, to get up to a 25mm radius flare.
The method could be useful if you absolutely must have a mounting flange on your flares.
Where do you get the flat sheet? - Cut a length of PVC pipe and then slit it lengthwise. With a heat gun, open it out into a flat sheet. The width will be pi * diameter, or roughly 3 * diameter. make your length the same and you'll have a square to start with.
The picture above shows a sheet cut from some 86mm pipe, 2mm thick.
It was pushed over a 35mm radius mold that was left over from playing around with the Molded Port technique.
A 20mm hole was cut in the centre of the sheet. This expanded as the sheet was pushed onto the mold. A smaller hole was tried, but it tore, and a larger one allowed the sheet to slide down the mold too easily. This was for 2mm thick sheet, so other thicknesses may have a different optimum.
It was not possible to get the sheet to stay down on the mold across the full profile, so different approach was tried
Instead of forcing the sheet over the style of mold that was used for the "pipe" method,
it can be pushed into a mold constructed along the lines of the Custom built flares.
A rounded plunger which is slightly smaller in diameter than the port diameter can be used to push the sheet into the mold.
Once the flare is formed, a 20mm hole can be cut in the centre and the plunger pushed through,
forming the section that will later fit into your PVC joiner
The sheet will need to be trimmed to a circular finish
As the sheet goes into the mold, the surrounding plastic needs to shrink inwards. There is only so far that you can do this successfully. Apart from the tearing problem, this would also limit flares to 25mm or smaller. For example, the next photo shows what happens if you try to make a flare that is too big!
This is as far as I've gone with this method. It still holds promise if you need a mounting flange, otherwise the "heated pipe" method is much better!