CNC Your Own Parts

[BlackBart]

I think it “squishes” the hole so the diameter gets smaller.
No work - did it all in my head.

[BlackBart]

I might be wrong. That might be backwards.

[BlackBart]

All the metal around the perimeter of the hole is expanding, so how can it get smaller? I shoulda multiplied by -1.

[volvolugnut]

I leave these questions for extra credit home work for tomorrow.
volvolugnutr

[MrAl]

Hi,

Yeah the ring must expand when heated or the ball would never fit through.

Here's another question:
CNC an ignition key?

[volvolugnut]

Material expansion is the result of all of the molecules vibrating faster as the temperature increases. Each molecule will increase slightly in size in all directions. A ring of material or a ball will each grow in all three dimensions. The ring will get thicker across the edge, and larger in both internal and external diameter.
If the ring and the ball are both the same material and both are heated the same amount, if the ball could not pass through the ring when cool, it will still not be able to pass through the ring when both are heated.
If the ring and ball are different materials, then the relative coefficient of expansion and amount of temperature change would need to be compared to determine if the ball can pass through the ring. Every material from wood to metals to concrete have their own coefficient of expansion available in material handbooks.
Trivia: The coefficient of expansion of steel and concrete are very similar. This allows the use of steel for concrete reinforcement over wide temperature ranges without failure of the weaker concrete.
volvolugnut

[MrAl]

Material expansion is the result of all of the molecules vibrating faster as the temperature increases. Each molecule will increase slightly in size in all directions. A ring of material or a ball will each grow in all three dimensions. The ring will get thicker across the edge, and larger in both internal and external diameter.
If the ring and the ball are both the same material and both are heated the same amount, if the ball could not pass through the ring when cool, it will still not be able to pass through the ring when both are heated.
If the ring and ball are different materials, then the relative coefficient of expansion and amount of temperature change would need to be compared to determine if the ball can pass through the ring. Every material from wood to metals to concrete have their own coefficient of expansion available in material handbooks.
Trivia: The coefficient of expansion of steel and concrete are very similar. This allows the use of steel for concrete reinforcement over wide temperature ranges without failure of the weaker concrete.
volvolugnut

Hi,

The interesting thing about the ring is that the circumference grows more than the thickness of the ring.
For a ring like a wedding ring lying flat on a flat table surface, the thickness would be the outer radius minus the inner radius, and the height would not influence the fit for the ball inside.

Also, since the thickness grows also, perhaps we can view the inside radius as being out from the center of the ring thickness and the outside radius being out from the center of the ring thickness. So if the center of the thickness had a 1 inch radius, that would increase to 1.01 inches for a 1 percent thermal expansion, and so the inside radius would be 1.005 inches and the outside radius would be 1.015 inches.

Here's another question. Consider a disk of brass or copper maybe 1 inch radius and 0.1 inches thick. Since the radius is 1 inch that mean the center of the disk is exactly 1 inch in from any edge measured across the diameter.
The question is, if we heat it a lot but not enough to melt it, do we see a small hole develop in the perfect center of the disk?
Now let me ask this same question two different ways.
1. If at the very center of the disk there is a hole of diameter equal to approximately the size of one atom, does the hole expand?
2. If at the very center of that same disk we place an atom in that hole before heating, does a hole develop after heating?

I'll ask about the ignition key CNC project in another thread.

[volvolugnut]

My gut says a hole will not form in the center but I have no science to prove it.
volvolugnut

[BlackBart]

Material expansion is the result of all of the molecules vibrating faster as the temperature increases. Each molecule will increase slightly in size in all directions.

The question is, if we heat it a lot but not enough to melt it, do we see a small hole develop in the perfect center of the disk?

No, I don't think so. As lugnut says, all the molecules are vibrating and expanding to fill all the volume. The whole disk will expand outward in all dimensions.

[MrAl]

Material expansion is the result of all of the molecules vibrating faster as the temperature increases. Each molecule will increase slightly in size in all directions.

The question is, if we heat it a lot but not enough to melt it, do we see a small hole develop in the perfect center of the disk?

No, I don't think so. As lugnut says, all the molecules are vibrating and expanding to fill all the volume. The whole disk will expand outward in all dimensions.

Hi,

It is probably easier to think of this in terms of a pure metal, but maybe it does not matter.

For copper, what if in the exact center one single atom was missing. In reality though it would have to be one column of atoms just one atom in diameter, so it would be like drilling a hole in the center of the disk just one atom in diameter, then heating it up.
I guess theory would tell us the hole would get wider.