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1-800miner
06-13-2015, 11:37 AM
I milled some pieces of my mystery metal to .5" cubes to make some dice.
I am going to drill the spots into them.

I got thinking about center of gravity and how to balance them.
My first idea was to drill the number one hole six times deeper than the holes on the number six side, and use the same formula for the other numbered sides. But a deep hole on one side and shallow holes on the other will offset center of gravity. ( I think?)

Second thought is that the "one" side should have the same depth hole as the "six"side, but six times the diameter.
Some how that doesn't feel right either.

So how do I keep center of gravity centered?

PixMan
06-13-2015, 11:47 AM
There is no such thing as gravity.

It's just that the earth that sucks.

:D

I'd never noticed commercially made dice having any sort of balance compensation that was visible. It seems a very complex scenario as you have varied numbers on all sides and problems with adjacent to opposite sides and number of marks. Is this too much thought? Is it a matter of just make all the spots the same and see how they roll?

Mike Burdick
06-13-2015, 11:59 AM
The concept:

For equilibrium, the sum of the moments of the material removed must equal the sum of the moments removed on the opposite side of the die.

1-800miner
06-13-2015, 12:11 PM
For equilibrium, the sum of the moments of the material removed must equal the sum of the moments removed on the opposite side of the die.

I agree. But won't the depth of the holes change center of gravity? Six shallow holes versus one deep hole will shift things.
The total material removed should be the same distance from center of gravity.

Trying to balance a flywheel that spins on three different axis's

lugnut
06-13-2015, 12:29 PM
How to make "loaded" dice is a well kept secret.:cool:

Mike Burdick
06-13-2015, 01:02 PM
1-880miner,

Let me make my statement more clear...

For equilibrium, the sum of the moments of the material removed must equal the sum of the moments removed for each axis of the die.

Peter.
06-13-2015, 01:19 PM
Why is it even required? A perfectly balanced dice will randomly fall on any side, but so will a non-perfectly-balanced one to the extent of mis-balance provided by different numbers of dimples. It's not like you could rely on it even in the smallest way for any kind of manipulated result.

A.K. Boomer
06-13-2015, 02:22 PM
I guess I don't own any dice so don't know what they do but if I were to build some I think id put one and two at odds and three and four and then five and six,,, that way they are all balanced to within one small divots worth - would call that good enough for who it's for...

1-800miner
06-13-2015, 02:57 PM
I guess I don't own any dice so don't know what they do but if I were to build some I think id put one and two at odds and three and four and then five and six,,, that way they are all balanced to within one small divots worth - would call that good enough for who it's for...

The one opposes the six, the two opposes the five, and the four opposes the three. Two opposite sides always add up to seven.
Which I had never thought about until now, I wonder if there is a reason for that configuration?

Davidhcnc
06-13-2015, 03:14 PM
Stamp the numbers

RussZHC
06-13-2015, 03:17 PM
the internet is a wealth of info:

Casino dice have their pips drilled, then filled flush with a paint of the same density as the material used for the dice, such that the center of gravity of the dice is as close to the geometric center as possible

among other things, there are also right and left handed dice

neatest thing I read so far was one way to "load" dice is to inject a substance that changes form at roughly human body temperature so that holding the dice in the hand for a longer period of time can cause this state change and affect the balance (face more likely to be showing up)

dp
06-13-2015, 03:21 PM
Use engine-turned or jeweled dots rather than drilling. No material is removed.

Toolguy
06-13-2015, 03:21 PM
Well there's your answer! Stamp the numbers. They've been making them wrong for all these years! Mr. Davidh you are a genius, sir!

Mark Rand
06-13-2015, 05:19 PM
Given the density of material you're starting with, drill holes about 2D deep and Loctite in 22 carat gold pins. that should come pretty close to balanced and will look pretty as well.

Peter.
06-13-2015, 05:22 PM
Stamp the numbers

Can't do that. Snake eyes would become snake legs and we all know that snakes don't have legs :)

1-800miner
06-13-2015, 06:53 PM
Given the density of material you're starting with, drill holes about 2D deep and Loctite in 22 carat gold pins. that should come pretty close to balanced and will look pretty as well.

Any one have a bit of gold they want to part with? I will trade for equal weight in mystery metal.

I will also pay shipping.

oldtiffie
06-13-2015, 10:23 PM

https://en.wikipedia.org/wiki/Dice

Don Young
06-13-2015, 10:56 PM
It seems to me that "unbalanced" is the same as "offset center of gravity" so correcting one should not cause the other.

CalM
06-13-2015, 11:50 PM
Is the degree of "imbalance" determined by floating the die in a suitable liquid? Brine, anti freeze , woods metal, mercury ? "loaded" side would roll down every time!

Paul Alciatore
06-14-2015, 01:59 AM
If you are going to drill the holes and not fill them, then you will need to remove more material from the side with fewer holes because some of it will be removed from a greater depth which will be closer to the center. For instance, if you have a 5/8" die and you drill six holes on one side 1/32" deep, then the single hole on the one hole side, which is opposite to the six hole side, will need to be deeper than 6/32" in order for it to balance.

A calculation, although possible, would be difficult because the center two holes on the six hole side will be closer to the center and the four corner holes will be a bit more distant from it. The single hole on the one hole side will be even closer to the center than any of the six holes on the six hole side. You may reach a point of diminishing returns on that one hole and even have to increase it's diameter.

Calculus would be needed for a precise solution. And for a further complication, assuming you use a standard drill, you would have to treat each hole as a cylinder with a cone at it's root. But you could always just drill and measure (cut and try) until it balances.

The three and four hole sides would be an interesting calculation too as one of the three holes would be at a different distance than the other two.

All in all, the idea of using a filler with the same density as the dice is a nice idea.

Paul Alciatore
06-14-2015, 02:06 AM
Footnote:

When I was a lad, my dad obtained a large number of dice from a gambling establishment (legal/illegal ??? I don't know) and he made a nice looking jewelry box by gluing them together. It was interesting to see how he made the patterns on the sides, top, tray, and handles with the dots. Apparently they discarded them for even the slightest defect; anything that could be seen, measured, or even suspected. They must have bought them by the thousands.

My brothers and I had as many dice as we could want to play with.

Deus Machina
06-14-2015, 02:39 AM
They buy them by the case, and a case is a shoebox at the least. Hobby suppliers often refuse to offer new ones for sale to the public, but give credit for used ones and, while I assume they melt down a large number, they sell ones they've marked so it would be impossible to reuse them.
My supplier sells them by the pair but with others, it's possible to buy them by the pound.

Me, I'd do what those same manufacturers do for their 'precision' RPG gaming dice: use the number, not pips. Stamp in three sides good and deep, then skim off just enough to bring it back flat and square. Repeat for the other three sides. Some will still be slightly heavier, but to a statistically negligible degree as far as anything at home is concerned.

Or do some math. Six small pips on one side, one big one on the other... as long as you remove the same total volume, and thus weight, from each side, you're okay. Heck, you could do this by using a small end mill and machining the lower numbers into whatever shapes you like, as long as the removed material remains consistent.

Boostinjdm
06-14-2015, 03:07 AM
You could prolly get a pretty good balance by keeping the higher number sides shallow. Drill the lower numbers deeper and fill back up with paint. Paint being lighter than metal would fill the holes to look right, but not replace all the weight removed. If you filled them up flush and sanded flat, nobody would ever know how deep the holes were.

To make loaded dice. Do the deep drill and fill on the side you want to come up. Drill and press in some tungsten, then paint over on the side you want down. I think that would do it anyway.

thaiguzzi
06-14-2015, 05:50 AM
I made a 1" aluminium dice for my son a couple of years ago to play with board games. Drilled the spots to the same depth. Looks better too. I have not noticed it going to "favoured" sides or numbers when i play a game of Ludo with him.
Mike.

Tony Ennis
06-14-2015, 09:01 AM
I would emulate what the casinos do. They don't need to cheat to make money - they let math do the talking. They just have to make sure the expected probabilities assert themselves.

As an aside, I have played games with metal dice. They are very unpleasant to listen to and can damage table tops.

RB211
06-14-2015, 09:17 AM
I would make the dice in Solidworks, select the correct material, then do a mass analysis to tell me the CG of the dice

Glug
06-14-2015, 10:44 AM
I recently read about a simple automated dice testing machine someone made. It would shake and drop the dice, and then read the outcome using a video camera.

It was verrry interesting. It was very easy to skew the outcome. With plastic dice, something as minor as changing the surface tension of one side can alter the way they bounce. Plasic can behave a lot like metal when heated and cooled. You can heat one side slowly, then cool it quickly, etc, to change the overall tension of the structure. With some science, or trial and error, someone could probably alter the probability distribution in a specific way (cheat). I would guess that extreme cold might result in similar physical changes. Spray one side with liquid nitrogen?

Davidhcnc
06-14-2015, 04:54 PM
Well there's your answer! Stamp the numbers. They've been making them wrong for all these years! Mr. Davidh you are a genius, sir!

I should have said stamp the dots, Yes?

Lee Cordochorea
06-14-2015, 05:10 PM
Turn a bar of the same material to the appropriate size and braze it into the holes with a contrasting fill material. (Of course, you would have to find out what fill material is correct...)

JoeCB
06-14-2015, 05:47 PM
I like the idea of floating a die to check for balance around it's centroid.. but how would a perfect die float? surly not with a face level... perhaps a corner point up or maybe an edge up ???

Joe B