Novice help with volume properties

I am new to the site but have been a long time novice at Acad. I look forward to learning from the wealth of knowledge on this forum.

I have a 3d solid I am working with and I would like to know if my calculations of the volume are correct so I used the mass properties and what it says and what I have calculated manualy do not jive.

Here is the text list of the mass properties function

---------------- SOLIDS ----------------

Mass: 2.0384

Volume: 2.0384

Bounding box: X: -1.5900 -- 1.5900

Y: -1.5900 -- 1.5900

Z: -64.6009 -- -64.1800

Centroid: X: 0.0000

Y: 0.0000

Z: -64.3876

Moments of inertia: X: 8452.1422

Y: 8452.1422

Z: 2.9746

Products of inertia: XY: 0.0000

YZ: 0.0000

ZX: 0.0000

Radii of gyration: X: 64.3934

Y: 64.3934

Z: 1.2080

Principal moments and X-Y-Z directions about centroid:

I: 1.5042 along [1.0000 0.0000 0.0000]

J: 1.5042 along [0.0000 1.0000 0.0000]

K: 2.9746 along [0.0000 0.0000 1.0000]

The 2.0384 if in Cu/in (which is the drawing properties I am using) would equate to 33.4cc's. My calculations show I should have a volume of around 29cc's, or maybe a tad less, when taking into account the complex, yet mathematicaly simple, shaping.

Any input would be greatly appreciated!

Well I agree with your conversion of cu. in. to cc's, so it appears you and AutoCAD disagree on the volume. So the question is, did you err in drawing the solid, or in your manual calculations.

Well I agree with your conversion of cu. in. to cc's, so it appears you and AutoCAD disagree on the volume. So the question is, did you err in drawing the solid, or in your manual calculations.

That is what I don't get...

My reasoning for my volume calculations should be correct. I have ran the numbers so many times and the mathematic logic holds true when expressed in long form. Like I said it is a complex shape but due to its symetrical properties it should be easy to derive a proper calculation.

Lets me go through it and see if you think MY math is wrong...

It is actualy a volume between two solids that was created from subtracting the two oposing entities from a solid of larger volume than the end volume.

In the calculation I have two oposing volumes of a radiused nature that have a height of .160" and a diameter of 3.18". These will be labled volumes A and B. Now when these volumes are oposing each other at a given distance from the top outer edge of the top volume to the lower outer edge of the bottom volume I end up with a dimension of X. The radius, being symetrical between the two is expressed as Z. The total volume of the distance and radius of X & Z is volume D. The Volume in between Volumes A & B is labled volume C. Volume C is what I am trying to calculate for.

What I have so far is this;

A+B+C=D and A= B

If I move either volume A or B I get A+C=D-B.

That means I should be able to take the height from the radiused extremity of either A or B (.160") and subtract it from the total height between the A + B, which is X. X= .4209 So I have then .4209 - .160= .2609". This would be the same as calculating the total height (x) and using the radius of Z to equal volume D -(A)-(B)= C

Therefore at a radius of 1.509" and a height of .2609" I get a volume of 1.8684cu/in, rounded up. That equals 30.617cc's. Now the actual shape has a outside taper inward of .0833"/ side. That means the close to ACTUAL, calculated radius would be 1.509-(.833/2)= 1.46735" At determined height of .2609" that equates to 1.7655cu/in or 28.931cc's. The number is actualy less by virtue of the outer extremity of the calculated volume area having a .125" fillet at the vertical and horizontal junction at the outer extremities.

Also I ran the numbers this way.. using the properties function itself...

I take the volume given by mass properties before the final shape was derived I have 2.6743cu/in. I then subtracted the bottom radiused shape which led to the 2.0384 in the final properties check. 2.674- 2.0384 = .6356cu/in. That is the volume of A & B each.

So if I go back to C= D-(A)-(B) I would then calculate the total volume of D with R= 1.509 x H of .4209 = 3.0122cu/in. If I then take 3.0122 - (.6356(2)) = 1.74cu/in = C or 28.53cc's.

Like I said, I should have 29cc's or a tad less...

But if I go backwards from the mass properties the volumes don't jive.. Even using it's volume for the radiused entities vs my simple calculations of the cylinder.

what I have calculated manualy do not jive.

Any input would be greatly appreciated!

Zip and attach the file here.