Measuring Deer Antler Volume

[erobz]

TL;DR

Trying to figure out simple low-tech solution

My idea is that I want to use immerse Whitetail Antlers in a fishtank to measure their volumetric displacement (the Boone and Crockett system is the current record measurement standard to place in a juxtaposition with) I would use some sight glass plumbed into the side of the tank to get the change in height so that I can multiply by the tank cross-section. Simple Idea. But...

Is there a simple mechanical way to amplify the height in the sight glass to increase measurement precision? Nothing is jumping out at me.

 

[sandy stone]

Fill the tank up to an overflow point, then immerse the antler with the overflow from the tank being directed to a narrow graduated cylinder. Would that work?

 

[erobz]

Fill the tank up to an overflow point, then immerse the antler with the overflow from the tank being directed to a narrow graduated cylinder. Would that work?

Thank you, that technique would make precision adjustable. Also, this measures the volume directly; skipping a computation step and minimizes propagated error.

Way to think outside the box! (fishtank)

 

[Baluncore]

Add a drop of detergent to the water so it wets the surface of the antler and does not trap air bubbles.

What is the thermal expansion coefficient of antler volume?
Must you regulate the temperature of the antler or water?

It should not be necessary to equilibrate the temperature of the antler to the water, as the thermal mass of the water will be much greater than the sparse antler.

Identify the density variation of antler, by weighing the dry antler before measuring its volume.

 

[erobz]

Add a drop of detergent to the water so it wets the surface of the antler and does not trap air bubbles.

What is the thermal expansion coefficient of antler volume?
Must you regulate the temperature of the antler or water?

It should not be necessary to equilibrate the temperature of the antler to the water, as the thermal mass of the water will be much greater than the sparse antler.

Identify the density variation of antler, by weighing the dry antler before measuring its volume.

This will be a quick duration dip (done slowly as not to make waves), it won't be soaking. Just enough time for the water level to settle. But thanks for the tip about the air bubbles.

Before we get to scientific/precise, take a look at the Boone and Crockett system of scoring (https://prod10-boone-crockett.s3.am...df?VersionId=wR4JXJzq5NmoxMFcf54j.03HIMVSuah3) ; it is just a linear measurement proxy for a volume measurement.

 

[JT Smith]

If you weigh them submerged as well as in air with a good electronic scale you could get a precise volume. You'd have to make a jig to do that but it isn't particularly difficult.

Do antlers sink? You might need to add a weight. Will they absorb a significant amount of water? That could throw things off as well. Another possible option is a DIY gas pyncnometer.

 

[erobz]

They are bone, so pretty sure they sink and are relatively impermeable over the short timescales needed to make the measurement.

 

[sophiecentaur]

What accuracy is needed for the measurement?
Hopefully the deer is dead by this stage.

 

[DaveC426913]

The detergent also breaks the surface tension (meniscus layer) around the lip of the tank, which would otherwise interfere with run-off and results.

 

[sophiecentaur]

If Eureka can, anybody can.

 

[JT Smith]

They are bone, so pretty sure they sink and are relatively impermeable over the short timescales needed to make the measurement.

I made a quick search and it seems that the density may hover around 1.0g/cm3 (see here). That would make underwater weighing problematic without adding weight. Likewise with measuring water displacement. Here's what the authors of that paper had to say about their methods:

Volumes for reference were determined by water
displacement, following a modification of the method of
Miller et al. (1985). Previously, the bases and all porous
surfaces of the antlers were varnished to exclude water from
entering internal spaces. Then the casts were submerged in an
overflowing bath with a control tube and the water displaced by
each antler was collected. The most common problems found
with this method were the difficulty of measuring large
specimens, the damage to cast appearance because of the
varnish and the floatability of casts of lower density. We
resolved the floatability problem by using an additional weight
previously submerged, with the possibility of holding the cast if
necessary.

 

[DaveC426913]

I made a quick search and it seems that the density may hover around 1.0g/cm3 (see here). That would make underwater weighing problematic without adding weight.

No need to attach weight. You finger (attached to your body, presumably) is weight enough. As long as you can submerge the test subject you should be good to go. It doesn't have to be for more than a moment.

So, essentially, you can hold it down with your finger.

Submerge it slowly, so you don't overshoot. Hold it so that every part of it is under water, without actually sticking your finger in (error here will be miniscule compared to other sources of error using this setup).


Frankly, I think your bigger problem will be collecting every drop of the overflow.

 

[JT Smith]

No need to attach weight. You finger (attached to your body, presumably) is weight enough.

That may be true for measuring the displaced water but it obviously wouldn't work for underwater weighing, which is the part of my post you quoted.

They also mentioned varnishing the antlers to prevent water ingress. I guess that's not a big issue either? Maybe it comes down to how precise a measurement you're interested in.

And although it's not directly relevant here, I'm curious why antler volume is something you'd want to know about. What do you do with that number exactly?

 

[DaveC426913]

That may be true for measuring the displaced water but it obviously wouldn't work for underwater weighing, which is the part of my post you quoted.

Underwater weighing? Why would one do that?

(Actually, in theory, one could do that by measuring the weight of the water displaced by the floating antlers, then submerge them and weigh the remainder. But this would only work if they float.)

They also mentioned varnishing the antlers to prevent water ingress. I guess that's not a big issue either? Maybe it comes down to how precise a measurement you're interested in.

Exactly.

And although it's not directly relevant here, I'm curious why antler volume is something you'd want to know about. What do you do with that number exactly?

Presumably because it is the most precise way to measure the substance of an antler. They could vary a lot in density, so weight might not get the desired results.

What I'm not sure about is the same thing you ask: if no one else uses volume then what use is it? The Boone and Crockett method mentioned by the OP is about length, circumference and spread.

 

[Baluncore]

Since the antler is bone, there will be blood vessels in the centre of the structure. The mass of blood in those vessels may be dried or may retain moisture, which will determine mass and density.

If you need an accurate volume, maybe it is time to consider a 3D laser scanner, to get a detailed external surface map of the antler.

 

[JT Smith]

Underwater weighing? Why would one do that?

To determine the volume. The weight of a submerged object is equal its unsubmerged weight minus the weight of the water displaced.

Of course if you have the means to laser scan it that would be way to go.

 

[DaveC426913]

To determine the volume. The weight of a submerged object is equal its unsubmerged weight minus the weight of the water displaced.

Of course if you have the means to laser scan it that would be way to go.

I don't get it. Why not just weigh it directly?

 

[JT Smith]

I don't get it. Why not just weigh it directly?

You mean the water? Because weighing the object can be more precise than weighing the water that manages to slop over the edge or down a tube or whatever. I think more so the smaller the object but I would expect it would be true with deer antlers. But it isn't clear how accurate the OP wants it to be. Which is why I was curious what the point was for knowing the volume/density in the first place.

 

[DaveC426913]

You mean the water?

No. The antlers. Why weigh them in water? Why not just ... weigh them?

Because weighing the object can be more precise than weighing the water that manages to slop over the edge or down a tube or whatever.

We must have our wires crossed. In my perception it was you who offered the idea of weighing the antlers submerged (post 11 and then 13).
I have no idea why one would do that.

 

[JT Smith]

Why not just ... weigh them?

Because just weighing them won't tell you the volume.

In my perception it was you who offered the idea of weighing the antlers submerged (post 11 and then 13).
I have no idea why one would do that.

In order to determine the volume.

 

[DaveC426913]

Because just weighing them won't tell you the volume.

In order to determine the volume.

Right. That's what the tank is for. It's a very good (low-tech) way of determining the volume of a highly-irregular object.

It is not a very good way of determining the object's weight - not compared to simply weighing it on a scale, which has very little room for procedural or measurement errors.

Different properties require different measuring tools.

 

[JT Smith]

Right. That's what the tank is for. It's a very good (low-tech) way of determining the volume of a highly-irregular object.

It is not a very good way of determining the object's weight - not compared to simply weighing it on a scale, which has very little room for procedural or measurement errors.

Different properties require different measuring tools.

I sense that you are still missing what I thought was a very simple point. The weight of the antlers isn't of interest per se. But if you weigh the antlers both submerged and not submerged you can calculate the volume.

 

[DaveC426913]

I sense that you are still missing what I thought was a very simple point. The weight of the antlers isn't of interest per se. But if you weigh the antlers both submerged and not submerged you can calculate the volume.

So, as with "my" method, it only works if the antlers naturally float, yes?

So, you

1. Place the tank and water on a weigh scale large enough to weigh the entire tank.
2. Place the antlers in the tank, let them float free.
3. Record the weight.
4. Submerge the antlers by any convenient manner (say, with a finger).
5. Record the second weight.
6. Subtract step 3 from step 5.
7. Convert that remainder weight to volume, using the density of the water, i.e. 1.0g/cm³.

Do I have that right?

If so:
Pros: it is more accurate than trying to capture any run-off water in "my" method.

Cons: it requires a scale that is large enough - and is capable of measuring the weight of - the entire tank and its water.

I would be concerned about the accuracy (or is it precision?) of a weigh scale meant to
- measure a hundred (or hundreds of) kilograms and must have a tray that is several feet in both extents (the base of the tank)
- as opposed to a weigh scale that only needs to measure tens of kilograms, and only needs to be large enough to support the dry antlers themselves (or needs no tray at all, since it can hang).


Note that even this is conservative. Antlers vary widely in shape and dimension. A tank will need to be large enough to hold - fully submerged - the largest conceivable of all three dimensions it will be used for. That could be between a metre or even two metres in each dimension, resulting in several cubic metres.

The weigh scale would have to be capable of supporting and weighing several tonnes of water. Worse, the difference you are trying to measure might be only a few kilograms. (Because the antlers are almost neutrally buoyant.)

A water tank, 2m x 1m x 1m, will weigh 2,000kg. (That's not big enough for a moose.) The difference between floating and sinking might be (a guess) 5kg. So, you're measuring the difference between 2000kg and 1995kg.



Other than that though, your idea has a definite advantage of not having to somehow collect every drop of run-off.

 

[256bits]

Of course if you have the means to laser scan it that would be way to go.

Is there a app that lets one calculate immediately?
You might have to write one.

I would think with the laser scan thing, the antler owner, or owners, if in a competition wouldn't want to wait around a day or two while you scan, then paste images and cut off supports to do the calculations. They might not trust your app if the second place looses by 1 square centimeter and money is involved.

I would if I was an antler guy want to see what's going on even if it could be less precise.

 

[DaveC426913]

Until now, I had an image of a moderate fish tank doing the trick. But after putting a few numbers to it, I see I was off by an order-of-magnitude.

Maybe at this scale, it's not that hard to collect the run-off from a tank that big. Let it run off all around. Build a drip channel all around the lip that runs into a graduated cylinder. Use a squeegee to wipe down the bit of tank wall and the drip channel.

Heck, you could even mechanize the act of holding it underwater (so that an operator can't be accused of "putting his finger on the scale", so to speak). A lid (open or gridded) would ensure no points of the antlers stuck above the water.

 

[256bits]

I was thinking of using sand.
Might add to the suspense for the audience.

 

[JT Smith]

Do I have that right?

No.

It has to submerge completely. You can't be pushing it down it with your finger. You don't weigh the whole tank, just the submerged antlers. That weight will be equal to their normal weight minus the buoyant force, the latter being equal to the weight of the water displaced. Since you know the density of the water (by measuring the temperature) you can calculate the volume.

Actually the "normal" weight also includes a buoyant force due to the air. Scales are usually calibrated with metal weights (e.g. steel) that have a density around 8 g/cm3. In some cases this is the largest source of error in a weight measurement. For example, if you weighed a liter of 4°C water in air on a well calibrated scale you'd measure something close to 999g instead of 1000g.

The point is that you can be very precise once you deal with certain issues.

 

[DaveC426913]

No.

OK, I totally don't get it.

It has to submerge completely. You can't be pushing it down it with your finger.

What if the antlers are buoyant? I thought the whole point was to measure the difference between the weight of water it displaces by weight (i.e. floating) and the weight of water displaced by volume (held underwater)

You don't weigh the whole tank, just the submerged antlers.

I have no idea how one would do that.

I guess, unless you are assuming they are negaatively buoyant, and then I guess you would put the weigh scale in the tank?

No idea. and I think I'll stop guessing.

The point is that you can be very precise once you deal with certain issues.

I'll have to take your word for it. I have no idea how your setup looks. I don't know you weigh a submerged object unless your whole scale is stainless steel.

 

[DaveC426913]

OK, a few questions for @erobz:

1. How do you see this utilized? For your own personal use, or is this open to all - say, at a public contest? This helps us understand practical constraints, such as: will need it to be
   - robust,
   - foolproof,
   - operable by a third party,
   - portable,
   as opposed to, say, you in your basement.
2. Is the idea to (someday) replace - or at least offer an alternative to - the existing system?
3. What are the maximum plausible dimensions of the best rack? All three dims, if you please. Moose antlers can span 2m in two dimensions. This will inform questions 1 and 2. I suspect a portable setup will require a pickup truck.
4. Do all antlers float? Do all antlers sink? It sounds like, for this to be a practical alternative, the measurement proceure will have to accommodate both scenarios. Ideally, for fairness, it should use the exact same setup for both floaters and sinkers*.

* I imagine that might not be too hard. You can attach a standard weight to them, until they sink, then simply subtract that away.

 

[jack action]

You don't weigh the whole tank, just the submerged antlers.

I have no idea how one would do that.

I guess, unless you are assuming they are negaatively buoyant, and then I guess you would put the weigh scale in the tank?

No idea. and I think I'll stop guessing.

$$F_b = W_{act} - W_{app}$$
$$F_b = \rho_{fluid}gV_{fluid}$$
And if the object is completely submerged:
$$V_{obj} = V_{fluid}$$
Thus:
$$V_{obj} = \frac{W_{act} - W_{app}}{\rho_{fluid}g}$$