Is there a trick to dry fitting PVC

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Tbbarch

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I must be missing something or maybe just be trying too hard.

Dry fit assemblies are not as tight as glued assemblies. The glue acts as a lubricant and the joints slide together tighter.

When there is some room to work that does not have an impact but in tight areas with a lot of fittings it throws off my dimensions and alignments.

I typically cut my pieces based on the female bell inset depth and taper the ends to get a bit of overlap at the inside bevel. These never go together dry like they do glued.

Am I misreading the point of dry fitting?
Is there a mystery lubricant I have never heard of?
Other?

Thank you
 

Reach4

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You are not missing anything.

Dry fitting is only going to be a rough indicator. If things are critical, measure. Maybe glue part and after that measure and cut that last critical piece. Maybe mark xx inches from the end of your pvc pipe. Note how much space is between your mark and the fitting. Then add on some length when you mark for cutting.

I guess you could drill out a set of fittings that you only use for that fitting purpose, but I have not seen anybody do that.

https://terrylove.com/forums/index.php?threads/why-cant-i-dry-fit-pvc-fittings.2523/
 

CountryBumkin

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I have dry fit PVC and then not been able to get them apart (even with a vise and pipe wrench). So I don't dry fit anymore, I just measure carefully.

If I had to dry fit I would try putting some plumbers silicon grease on the fittings (then carefully clean before priming/gluing).

If any Pros have any tips, I'd love to hear them too.
 

Jadnashua

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IOW, almost always on a properly manufactured PVC fitting, it is near impossible to get the pipe to the full design insertion of a fitting. The fittings are intentionally tapered and only when the cement melts the plastic can the pipe be bottomed out in the fitting. If you CAN get it seated dry, you're literally stretching the fitting, and you're going to end up wedging the pipe in there and may not get it apart. In reality, you are going to end up 1/4" or more short for each fitting in the run if you cut and dry fit the whole thing at once. The diameter of the pipe means it may be a bit worse for larger pipe than for shorter pipe as the fitting depth tends to be longer but has the same taper angle. This also means that until the solvent in the cement evaporates, that taper can literally push the pipe out of the fitting, making for all sorts of hassles if you're not careful. The amount and freshness of the cement can make a difference, too, in how long you need to hold things before they'll actually stay put.

This is where experience comes to play and being able to visualize things in 3D becomes very important when something must be installed exactly in a certain place.
 

FullySprinklered

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All the advice so far is spot on. I wish I could impart some wisdom on you about dry fitting parts, but I ain't got none.

I peaked out some 15 years ago when I pulled off a threebee. I painted myself into a corner and had to make three simultaneous connections inside a joist bay. The wasteline came up in the end wall of a garage. In the first joist bay above that, over in the hallway, I had a pipe coming at me from the second floor and one coming straight at me from the third floor. After much anguish, I did a preassembly on the floor, ran up the ladder with it, did a supersonic glue-slathering job on all six joints, pushed the assembly onto the pipe coming down the joist bay at me, then rotated the whole assembly to connect with the pipe going down and the other pipe going up. Dead solid perfect, but it took three hours to put it all together, including multiple check-fits.

You gotta work with the slack and the flex sometimes. Plastic bends a little, and it doesn't have to absolutely bottom out to work.
 

Dj2

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I almost never "dry fit" PVC.
Measure twice, then cut, prime and glue. If I made a mistake, cut it out and re-do it with new parts.
 
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