which plastic tube is the best to build a non wooden dummy?

i mean that disimilar material exspand and contract at very different rates so if it tight and the pvc expands greater than the wood it will become loose , pvc exspands and contracts quite a lot with heat, wood doesnt, wood exspands and contracts greatly with moisture content pvc doesnt.

so youl end up with either the hole getting bigger or the wood getting smaller or the hole getting bigger and the wood getting bigger by a greater amount which will wear the hole and make it bigger when the wood contracts again or or some other vatiation

the net result will be that quite soon it will be come loose
PVC expansion is 4 to 5 times more than metal or steel pipe.
ABS, PVC and CPVC pipe, like other piping materials, undergo length changes as a result of temperature variations above and below the installation temperature. They expand and contract 4.5 to 5 times more than steel or iron pipe. The extent of the expansion or contraction is dependent upon the piping materials coefficient of linear expansion, the length of pipe between directional changes, and the temperature differential.
The coefficients of linear expansion (Y) for ABS, PVC, and CPVC (expressed in inches of expansion per 10簞F temperature change per 100 feet of pipe) are as follows:
Material Y (in./10簞F/100 ft) ABS 0.66 ABS Plus 0.500 PVC 0.36 CPVC 0.408 The amount of expansion or contraction can be calculated using the following formula: e = Y (T1-T2) x Lp h 10 100 e = Dimensional change due to thermal expansion or contraction (in.) Y = Expansion coefficient (See table above.) (in./10簞F/100 ft) (T1-T2) = Temperature differential between the installation temperature and the maximum or minimum system temperature, whichever provides the greatest differential (簞F). Lp = Length of pipe run between changes in direction (ft)

Example: How much expansion (e) can be expected in a 60 foot straight run of 2 diameter PVC pipe installed at 70簞F and operating at 120簞F? Solution: e = .360 (120 - 70) x 60 =.360 x 5 x .6 = 1.08 inches

So for the application expansion should not be an issue. I think the variability of wood will be the bigger factor.
So for the application expansion should not be an issue. I think the variability of wood will be the bigger factor.

As the wooden arms are quite loosely fitted into the trunk using the mortice and tenon method, expansion and contraction are not really a problem regardless of whether you use wood, metal or PVC for the trunk. There is normally a significant amount of "slop" in the joints so that the arms can move. Wear and tear would probably be a greater concern than coefficients of expansion. Good thing too ....since my math skills suck!:p

BTW if the tenons wear and allow too much movement, the joint can easily be tightened with shims, etc. ...or, as I planned to do, slip a piece of bike inner-tube over the tenons for both a snugger fit and less noise. ...and maybe fewer complaints from my wife and neighbors (I had the dummy out on the back porch). Got a cool neighbor now, and my wife tolerates me, so I never got around to it. Been meaning to test the idea though ....maybe with some heavy duty rubber-bands?

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