31 replies to this topic

[spartan062]

Which would be lighter: a 1' length of 1" 200 psi PVC or a 1' length of thin aluminum rod?

The reason I am asking is because I plan on making a very large home-made and wish to keep it as light as possible.

Edited by spartan.062, 20 May 2009 - 08:29 PM.

[adama]

Why don't you find out for yourself?

Find the volume (using geometry) of each part in each material. Then multiply the volume times the density of the material to give you the mass and compare.

Also consider the stresses this particular part will be under. You may have to go with the heavier option if you are to maintain the required durability for this particular piece.


What exactly is the piece in question going to be doing for your home made? Knowing this will help many experienced people help you.

[spartan062]

adama, on May 20 2009, 07:39 PM, said:

1. Why don't you find out for yourself?

Find the volume (using geometry) of each part in each material. Then multiply the volume times the density of the material to give you the mass and compare.


2. What exactly is the piece in question going to be doing for your home made? Knowing this will help many experienced people help you.

1. I don't know the density of aluminum rod. Or 1" 200 psi PVC.

2. It will be used as the plunger rod.

Edited by spartan.062, 20 May 2009 - 08:46 PM.

[adama]

Densities and other material properties can be found in a few minutes by using Google.

http://wiki.answers....ity_of_aluminum

As far as the plunger rods are concerned just make sure the aluminum is strong enough so that it won't deform on impact when you fire it.

[analogkid]

Given that you're using Aluminum 6061, the density of aluminum is 2.70g/cm³. The density of PVC is between 1.38 and 1.41 g/cm³, 1.40 is what I would use for calculating purposes. Figure out what dimensions each of these parts would be were you to make a plunger rod from them, and find the volume of the parts based on the dimensions you determine, and finally multiply volume by density. It is impossible to determine which is heavier based on the information you have given so far, because which is heavier depends on the inner and outer diameters of the aluminum tube.

Example: For the SDR21 "thinwall" , typical dimensions of 3.34 cm OD and 2.96 cm ID, the total cross sectional area would be A=pi*radius^2, A=(3.141)*(3.34/2)^2, A=8.76 cm^2. Then you have to subtract the area of the inside, found by A=(3.141)*(2.96/2)^2, A=6.88 cm^2. Then 8.76 - 6.88 = 1.88 cm^2. So now you know the cross sectional area of the pipe/tube, 1.88 cm^2. All you have to do is multiply it by 30.48 cm, which is equivalent to 1'. Final answer: 57.3 cm^3. Then just multiply by the density given above, I'm using 1.40 g/cm^3. Total weight of the tube(if I did everything right): 57.3*1.40= 80.22 g.

Do the same for aluminum, and whichever is lower is lighter. Oh, and sorry for doing this all in metric...

EDIT: A tad late.
EDIT again: How are you making a plunger rod out of 1" thinwall PVC? I thought for sure you meant a plunger tube.

Edited by analogkid, 20 May 2009 - 08:57 PM.

[SchizophrenicMC]

Basically, in English, get the PVC. It's lighter and cheaper. Also, it's probably easier to work with.

[analogkid]

Actually, for a plunger rod Nylon is a much better material. It has more tensile strength and is less brittle than PVC.

[spartan062]

analogkid, on May 20 2009, 08:07 PM, said:

Actually, for a plunger rod Nylon is a much better material. It has more tensile strength and is less brittle than PVC.

Where can you get nylon?

[analogkid]

mcmaster.com

http://www.mcmaster....lon-6/6/=1yp8sf

Every size rod you could ever want.

EDIT: Had a feeling that one was gonna get added that hilarious quote to my signature, while playing with my butthole.

Edited by analogkid, 21 May 2009 - 11:32 PM.

[SchizophrenicMC]

analogkid, on May 20 2009, 10:04 PM, said:

Every size rod you could ever want.

added that hilarious quote to my signature, while playing with my butthole.

And, why didn't I think of McMaster? I guess this stupid thing about PVC and Aluminum had me too dead-set on Home Depot.

[Draconis]

Jeez guys, an easier method of determining mass... is just to weigh the pieces.

[spartan062]

Draconis, on May 21 2009, 10:53 PM, said:

Jeez guys, an easier method of determining mass... is just to weigh the pieces.

I was just thinking about that. Mass is essentially a fancy word for weight. . .

[BustaNinja]

If you find a way to use 1 inch PVC as a plunger rod, then go with that, but its way to think in my opinion. Use half inch CPVC or aluminum.

[Draconis]

spartan.062, on May 21 2009, 10:47 PM, said:

Draconis, on May 21 2009, 10:53 PM, said:

Jeez guys, an easier method of determining mass... is just to weigh the pieces.

I was just thinking about that. Mass is essentially a fancy word for weight. . .

Well.... Technically, Mass is a constant measurement of an object. The object will ALWAYS have the same mass. Weight, however, is a measurement of gravity's pull on an object's mass. Thus, under different gravitational conditions, such as on another planet, the weight will fluctuate.

[analogkid]

Draconis, on May 22 2009, 12:53 AM, said:

Jeez guys, an easier method of determining mass... is just to weigh the pieces.

I was under the assumption that he didn't have a scale, because if he did, I'm sure that he is smart enough to figure out how to weight them instead of asking here.

[spartan062]

analogkid, on May 22 2009, 07:19 PM, said:

I was under the assumption that he didn't have a scale, because if he did, I'm sure that he is smart enough to figure out how to weight them instead of asking here.

Yes, that is an accurate assumption. And it is correct.

[Lt Stefan]

Just use aluminum. It is solid, so it is easier to drill holes into lengthwise and it's stronger and its shiny. But seriously I'd go with that.

[analogkid]

Yeah but if I remember correctly, aluminum is harder to tap for threads.

[Lt Stefan]

Of course, but you can't very well tap into the middle of a pvc pipe when it's hollow.

[Darth Tom]

The obvious solution here is to use an aluminum tube. If you can get solid aluminum for a plunger rod, you can get one that is hollow. At that point, you just need to find a standoff and a screw size that works with it, and put the standoff in the middle of the rod. Apply some JB Weld to keep it in place.

[Lt Stefan]

What you are proposing would not be very secure, especially with the spring he's planning on using.

[analogkid]

Lt. Stefan, on May 26 2009, 02:09 PM, said:

Of course, but you can't very well tap into the middle of a pvc pipe when it's hollow.

Yeah I don't know what he's talking about with the PVC.

[Draconis]

analogkid, on May 26 2009, 03:43 PM, said:

Lt. Stefan, on May 26 2009, 02:09 PM, said:

Of course, but you can't very well tap into the middle of a pvc pipe when it's hollow.

Yeah I don't know what he's talking about with the PVC.

He would probably use an end cap, the tap that.

[Lt Stefan]

That would be a pretty awkward-looking plunger, I must say. Seems to prone to bending.

[Draconis]

Lt. Stefan, on May 27 2009, 08:45 AM, said:

That would be a pretty awkward-looking plunger, I must say. Seems to prone to bending.

Have you seen the PAS plungers? They flex a LOT.