PVC pipe gadget techniques — no glue no screw

In building PVC pipe furniture and gadgets, glue or screws are often used.  I doubt it is necessary, and arguably weaken the structures.

If you insert a standard PVC pipe into a standard PVC tee, all the way in with a rubber hammer, it's almost impossible to pull it out, even for the thinnest 1/2" CPVC pipes.  To pull the pipe out, you have to have a clamp securely holding on to the pipe, and then twist the tee with hand or tools.  You have to twist clockwise and anticlockwise until the joint come loose, and then the pipe can be taken out.

So, in your end structure, if you can't twist the pipe against the coupling by hand, and there's no direct force to pull the pipe straight from the coupling, you don't need any glue.  This is easy to design and usually very natural thing to do.  For example, if you have one pipe jointing with two tees at each end, and they are of different orientation, you can't twist the pipe against anything else since the tees are fixed in space in the end structure.

The only way you can twist the pipe is to use a clamp directly on the pipe.  Even so, the force needed is great and don't do much damage since the pipe is still in the same position.

The disadvantage of glue is that it is usually toxic or at least contains some undesirable volatile compounds.  It takes time to apply and dry.  And the coupling cannot be reused.  If you don't use any glue, when you change your mind about the design, you just need to cut the pipe and twist it out with pliers.  All parts are reusable.

Some people drill through the coupling part and use bolt and nuts to prevent the joint from coming apart.  Any drilling will weaken the coupling and the pipe.  The nut and bolt will only be effective when the joint already come loose.  They don't come loose if designed properly.  In my roof top rack, a Christmas tree carrier, I don't even use glue or bolts.

Tips for plans.  To be glueless, the plan has to be precise.  I always use spread sheets to calculate the dimensions.  You need the dimension of your structure modified by the dimensions of the couplings.  For example, the top bar of the T character is about 2.5", the height of the vertical bar is about 11/16".  The extra pipe length to insert into the tee socket is 3/4".

I always use standard tee's and occasionally 90 deg turns.  They are much cheaper than the couplings designed for PVC furniture with more variety.  Arguably the standard ones are better too.  You can use two standard tee's to replace a 4 way coupling on the same plane, or a 3 way coupling in the x,y and z axis.  Even though a standard tee joints everything on one plane only, if your dimensions are reasonably accurate, you can put together a cube quite nicely and squarely.  You just hammer the pieces together with a rubber hammer and the pieces will fall in shape.

Tips for the ugly markings on the pipes.  I don't know why but the cpvc markings can be easily removed with sand paper or steel wool.  But it's almost impossible to remove the markings on white PVC pipes.  Solvents will remove the markings but stain the white pipe with whatever colour the ink is.  Most of my gadgets are by the wall and stationary.  So I just need to turn the markings furthermost from the usual line of sight.  It's almost totally hidden unless you go squarely at the back, which is impossible if the gadget is by the wall.

Tips for reusability and flexible joints.  If the joint depth is 0.75", and you want to joint two tee's back to back together, the best pipe length is twice that at 1.5".  If that part does not need to be structural and you want it to be taken apart with reasonable force, make the pipe length 1 1/4".  If the joint is for the purpose of a "lock", that you may take it apart occasionally, make the pipe length 1", and insert the pipe all the way into the stationary coupling first.  In this case, you can also make a hinge.