Bending solvent weld waste pipe?

[Donkmeister]

I'm about to plumb in the sink in my new kitchen project. Due to bit of a rubbish design to the sink waste, I've had to use a straight McAlpine trap (the sort with the diaphragm, intended for kitchen use).

The result of this is that the angle the pipe comes out is not ideal and I can't simply swivel it.

Ideally I want to curve about 10-20 degrees, much less than a 135 degree bend (although I could get away with one, just). So, my options are:
1) Use a 135 degree bend and have it look a bit awkward
2) Use one of those swivelling adjustable bends with compression fittings and have it look a bit chunky (NOT a ribbed flexi... yuck)
3) Heat and bend a bit of pipe to the right angle...

I've never seen 3 done. Can it be done, and still be the right fit into solvent weld?!

Anything else I've missed?

 

[Burnerman]

Solvent weld plastic is notoriously difficult to bend successfully.....depending on its chemical structure it is closer to a thermoset than a thermoplastic plastic - if you get my drift.
Heating it will make it slightly pliable over a short length, over heating will cause the pipe to collapse so I reckon you only have a few degrees to play with.
Good luck with it!
John

 

[Hugh Jaleak]

We did a bit of playing about, bending waste pipe at Tec in the 80's, but had the benefit of a rubber 'spring' that helped prevent the pipe collapsing during the process. Recall it was notoriously difficult to get a happy medium with the heat, not enough and the pipe wouldnt be pliable enough, too much and you either scorched the plastic, melted a hole in it or both.

Never had a waste yet I couldn't connect though without playing around with a few different fittings.

 

[Burnerman]

When all seems to be going well, the solvent weld starts to bubble and then falls apart.....game over!
John

 

[bobasd]

its straightforward enough to bend plastic pipe - best using steel springs if they come near to a diameter fit.
but springs are not necessary.
all plastic pipe bending needs blown hot air, and helpful to grease the inside pipe diameter, and the spring.
bend it very slowly after a few practices.
the biggest problem can be the plastic memory - the pipes determination to return to its original shape. a jig will help shape retention.
that can be hit and miss from my limited experience of doing this kind of bending.

 

[Jackrae]

Or you could try packing it with fine sand or salt, plug off both ends then using a heat gun or hair drier, warm it gently until pliable and bend to the shape you want, then immerse in water to set before removing the packing. Avoid heating the area where you want to make the solvent joints so's pipe roundness is maintained

 

[Donkmeister]

Right, it looks like I might be sniffing some plastic fumes at the weekend then! Thanks all. I'll report back.

 

[Gasguru]

Get a marker pen and mark the pipe along it's length with another perpendicular mark to give you a reference when bending.
Heat the pipe gently at least 150mm along the pipe constantly rotating it to make sure the full radius is kept at a uniform temp.
Using welding gauntlets or similar keep testing the pipe until you feel it becoming pliable.
Then holding the pipe around the bending point set in the desired angle and allow to cool.
Done it many times to get an awkward angle where there's no room to re-route etc.

 

[dilalio]

1shot is good at bending ABS
NO... DON'T TRY IT!

 

[Donkmeister]

Well, I gave it two goes and I don't think I'm destined to have a career as a professional bender... But if anyone else finds this here is what I tried and what I think went wrong (apart from my lack of skill!).

I cut a couple of 2-3 foot lengths of 40mm in black (to hide the scorchmarks!), then took two short lengths of 32mm and wrapped gaffa tape around until they were a snug fit in the 40mm, in order to maintain the shape... I probably needn't have bothered as the ABS remained rigid apart from the area I heated.

Using an electric heat gun that was stood pointing upwards, on a medium setting (and finding the manual had instructions on forming plastic pipe... albeit much smaller pipe!), I rotated the pipe whilst moving it too and fro. The first pipe (bottom) I was surprised how long it took, but when it went it suddenly became quite plastic and I put a bit of a kink in the interior radius of the curve and stretched the outer radius a bit more than I'd like. Second pipe (top), I used a beer keg as a former to try and avoid the kink, and heated a greater length of pipe... still managed to kink it. Pah. That would be a nice place for drain clogs to grow.

I think the "Pack with sand" suggested somewhere above might help, but I think my two key faults were:

1) I think I was trying to heat the pipe too quickly. Obviously some of you have had success with a hot air gun so skill comes into it, but a novice approach might be to pre-heat the whole pipe in the oven to around 90celsius, then using the heat gun just to finish off the area for bending.
2) I think I tried to bend the pipe too quickly so it only bent in one place... Once it became pliable it just went, but if I had it laid down on a sheet, I could have nudged it a bit, moved along, nudged it a bit, moved along etc.

Thanks for the advice, at least I know it's possible!

 

[Madrab]

I would suggest that you want to make up a wooden former on a jig too to keep the inside radius as smooth as possible as that's where it will kink. A piece of thin ply bent to the radius you want and cover it in foil or use a heat mat