Something Strange Here....

[Kenja824]

I attached a file of a Shotpin. We are currently in NX1969 but I believe this was created in an earlier version. Please add it as a component and change the reference set to PART.

If you measure (Object Set) solid body, and select the shaft protruding from it, you will find it has a mass of 1.872 kg.

However, if you select any other bodies with it, it will only give you the weight of the other bodies and not include the shaft. Making the entire thing 1.872 kg less than it should be.

Technically, it is gives the correct weight of this component. If it was acting right, it would weigh 1.872 kg too much. I just never realized it wasnt weighing the shaft when selecting it all. Only now I have revved it up and swapped out one of the other bodies (the main mounting body) and suddenly it is including the shaft in the mass and making everything too heavy. Thats why I found this problem.

This is an easy fix. All I need to do is give the shaft a .000000001 density and the entire component is back to the correct weight. So this is not a real big deal. I just want to make sense of it.

Why would a body not be included in the total mass if you select other bodies with it? The shaft is the only body this happens with. If you select all the bodies and look at the total mass, then deselect the shaft, you will notice it doesnt change the mass.

This worries me a little because it makes me wonder what the odds are that we could build a large tool that has to be within a specific weight limit and believe it is, but find out later that it is over the limit because when we measured it, it wasnt measuring some bodies.


Ken

http://www.OneGodLogic.com

My brain is like a sponge. A sopping wet sponge. When I use it, I seem to lose more than I soak in.

 

[Kenja824]

Update: Its not the shaft. It is the bottom cylinder body.

When you select the cylinder alone you get a mass. If you add any other body to it, it wont add the new bodies to the total. If you add the other bodies all together it seems right. Once you add the cylinder it only gives the cylinder body mass.


The way I found the problem just misled me to think it was the shaft.

Ken

http://www.OneGodLogic.com

My brain is like a sponge. A sopping wet sponge. When I use it, I seem to lose more than I soak in.

 

[cowski]

If you measure (Object Set) solid body, and select the shaft protruding from it, you will find it has a mass of 1.872 kg.

Incorrect; the mass reports 1.872E-08 kg. For all practical purposes, this is 0kg.

I went back to the part file and did information -> object (change filter to solid body and window select around everything); NX reported 7 solid bodies, 6 of which have 0 set as the density. I don't have NX 1969 installed, but I checked with NX 1919 and 1992 - same results in both versions. It appears that some of your solid bodies do not have a material assigned to them.

Edit: if the overall mass is correct, I assume that someone jiggered the density of the cylinder to account for the overall weight of the assembled parts.

www.nxjournaling.com

 

[Kenja824]

How does one check the density?

Is it the E-08 that means it is zero mass? I was assuming that was just the typical calculator type of code to say the digits continue on.

Ken

http://www.OneGodLogic.com

My brain is like a sponge. A sopping wet sponge. When I use it, I seem to lose more than I soak in.

 

[cowski]

I used information -> object and selected the bodies. It will output a bunch of information on the body, density being one of the entries.

The "E-08" means "*10^-8". So 1.87E-8 is a shorthand way of writing 0.0000000187.

www.nxjournaling.com

 

[Kenja824]

Ahhh, thankyou

You know what is the sad part? I am the one who created this originally and manipulated it. The family part that creates these had to create them with 3 different weights depending on the stroke. Looking at it with this knowledge I now understand what I did.

They dont like to use sketch here, so when I originally made this family part, I used different solid bodies for each different stroke. I must have chosen to make it simple and put the mass into the three cylinder bodies so that which ever child it created, it would get the correct overall mass.

When it said the shaft was 1.872E-08 KG, I thought that was 1.872 KG and the digits just continued to repeat themselves or something. So it completely threw me off on what had weight and what did not.

Thanks cowski.

Ken

http://www.OneGodLogic.com

My brain is like a sponge. A sopping wet sponge. When I use it, I seem to lose more than I soak in.

 

[looslib]

One of the things we did was make the template start part with a material with a density of 99 pounds/cubic inch. That way it forces the designer to change the material to get a realistic density and weight.

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli