Scales

[Louca]

How much influence or better put bias does this have on the actual weight results? If for example I place a precision 20 grain weight on the scale, with and without the magnet you mention, will I see a difference in the measured weight? Magnetic dampening does not involve a weight under the pan is why I ask. While it may reduce oscillations will it bias the measurement?

There is no influence or effect of a damping magnet if there is no movement. Once the oscillation has stopped, the reading should be the same as if no magnet was there.

I just don't understand why placing a magnet below the pan as explained would have any dampening effect

As the pan moves relative to the magnet, there is a force produced by the magnet in the opposite direction. That is caused by something called eddy currents that are generated in the pan as it comes toward and moves away from the magnet. Those eddy currents produce an opposing magnetic field that pushes (or pulls) on each object. If there is no pan movement, there are no eddy currents, and therefore no pulling or pushing effect on the pan. Sorry for all the gory details, but you asked

My RCBS 5-10 scale has a copper plate that moves through two sets of magnets as the beam balances.

 

[rfwobbly]

Until then I will use my FX120i milligram balance that is accurate to .015 of a grain and responds in a second. Every charge gives me a confirmation that the scale is right on. When I take the zeroed pan off to put the powder in the brass it shows me the negative pan weight. Since it is fast enough I can glance down while pouring the powder and see it.

Very interesting products. We all use the products we like and trust. All are welcome to find what works best for them. Some thoughts...

• If a pill maker offers their medicine in 10mg, 20mg, and 30mg capsules, does anyone think they would get well faster with 21.030mg ? Doubtful. While it may be reassuring to have excess accuracy, it is misleading to think accuracy improves when you measure powder down to the individual flake. At that point the effect of variations in the cartridge case, barrel, bullet, etc far outweigh the effect of any variation in powder weight. So while a Palma shooter might enjoy the psychological advantage of knowing his loads are exact, for most of us that generally falls into the "over kill" category.

• Any digital scale with the ability to measure to 0.015gr and settle quickly is most likely not telling the exact truth. The reality is that at that level of sensitivity, breezes are not the only issue. People walking across the floor, trucks driving by on the street, and trains 1/2 block away also become inputs. Because of these external stimulus, software within the scale tells the display to 'stop jumping around'. The number on the screen is really a calculated mathematical result derived from thousands of separate readings. If this "averaging" didn't happen, the the right hand digits would simply be a flutter of unreadable numbers.

Just saying.

 

[doubleh]

Balance beam scales are very sensitive to air movement. Don't believe me? Zero your scale and gently blow on it and see what happens. I have two ceiling fans in the room my reloading bench is in for relief in hot weather. They are off and no windows are open when I'm using my scale.

I usually cheat and do my scale using early in the morning or after sundown when it's cooled down some.

 

[Reloadron]

There is no influence or effect of a damping magnet if there is no movement. Once the oscillation has stopped, the reading should be the same as if no magnet was there.

As the pan moves relative to the magnet, there is a force produced by the magnet in the opposite direction. That is caused by something called eddy currents that are generated in the pan as it comes toward and moves away from the magnet. Those eddy currents produce an opposing magnetic field that pushes (or pulls) on each object. If there is no pan movement, there are no eddy currents, and therefore no pulling or pushing effect on the pan. Sorry for all the gory details, but you asked

My RCBS 5-10 scale has a copper plate that moves through two sets of magnets as the beam balances.

I am good with the eddy currents. OK, lets look at a RCBS 5-0-5 scale. I am sure if you turn your 5-10 inverted you will see the magnets but before the scale lets look at the basic principal with a pendulum in a magnetic field.



Note in (a) the circular motion of the generated field. Without getting all techie I believe this is how magnetic dampening works. Now let's look at a RCBS 5-0-5 Scale.



As I mentioned, invert the scale and you will see the magnets in there which compliment the first image. There is a knife edge in the slot and if we look at the knife edge we can see it was copper plated or copper clad.



So if we take the first image and flip it horizontal I can see where eddy currents would apply in magnetic dampening. We have a copper conductor swinging through (oscillating) through a defined magnetic field from a fixed magnetic. So here is the problem I mentioned earlier. If I take a magnet, just a little disk magnet and slide it under the pan as such:







What will the bias be on the measurement?

With the small magnet shown earlier my error was between about 4.0 to 5.0 grain offset. Now if I re-zero and offset that error will the scale still be linear? I would guess not because the pull of the magnet on the pan is not a linear function so even if I zero again with the magnet I simply do not see an accurate measurement plane.

So looking at eddy currents and looking at what we have I simply do not see how eddy currents apply or how with a scale as designed placing a magnet below the pan will assist in dampening the pointer coming to rest anymore than the scale as designed will accurately come to rest?

<EDIT> I added the image which included the small disk magnet. </EDIT>

Ron

 

[Louca]

What will the bias be on the measurement?

Your picture above is the first I knew of there being a "steel screw" in the pan assembly. I made the mistake of assuming an all-non-ferrous pan and assembly. Sorry I didn't ask about that before giving my answer.

So the answer to your question above is, "gee, I don't know." It sounds like a good physics problem, and one I probably cannot answer, even if I had all the necessary data like the strength of the magnet, the distance from the magnet to the screw, and probably a bunch of other things. In such a situation, I would agree it probably does not involve eddy currents at all, but would likely be addressed using < fill in physicist's name here >'s Law.

In your situation, we do know that there will be some force as the magnet pulls on the steel screw. And that force is greater the closer the magnet is to the screw, likely following a non-linear, inversely proportional relationship. That means, the more powder you are weighing, the more the pan will drop because of the higher weight of the powder, and the more force the magnet will have on the screw. How much? Who knows? Again, it will probably not be a linear relationship.

Great pics BTW, Ron.

 

[Reloadron]

See, this stuff can make anyone's head actually hurt. This is also an example of what retired people with a surplus of time on their hands do during March / April in NE Ohio do. My range is under snow or maybe mud so I do at home science experiments. Heck, if someone gets good results doing something, then do it.

Ron

 

[armarsh]

Very interesting products. We all use the products we like and trust. All are welcome to find what works best for them. Some thoughts...

• If a pill maker offers their medicine in 10mg, 20mg, and 30mg capsules, does anyone think they would get well faster with 21.030mg ? Doubtful. While it may be reassuring to have excess accuracy, it is misleading to think accuracy improves when you measure powder down to the individual flake. At that point the effect of variations in the cartridge case, barrel, bullet, etc far outweigh the effect of any variation in powder weight. So while a Palma shooter might enjoy the psychological advantage of knowing his loads are exact, for most of us that generally falls into the "over kill" category.

• Any digital scale with the ability to measure to 0.015gr and settle quickly is most likely not telling the exact truth. The reality is that at that level of sensitivity, breezes are not the only issue. People walking across the floor, trucks driving by on the street, and trains 1/2 block away also become inputs. Because of these external stimulus, software within the scale tells the display to 'stop jumping around'. The number on the screen is really a calculated mathematical result derived from thousands of separate readings. If this "averaging" didn't happen, the the right hand digits would simply be a flutter of unreadable numbers.

Just saying.

You could use the internet (if you have it ) and see for yourself. The reservations you mention do not play out in use. Here is a very short video - there are dozens of them on youtube with different milligram balances.



What costs money is that good balances are both accurate and fast. I shoot 600 yard benchrest so I do load to the kernel for matches. I'm not alone in doing this. I don't need this level of accuracy all the time, but its there when I do.

I have been doing things the hard way for 35+ years. Now that I have seen the light I want others to know there is a better way.

 

[Reloadron]

What costs money is that good balances are both accurate and fast. I shoot 600 yard benchrest so I do load to the kernel for matches. I'm not alone in doing this. I don't need this level of accuracy all the time, but its there when I do.

That alone gets pretty interesting. My regular range is a place called Kebly's Range which in the benchrest community of 100 and 200 yards is home of the annual Super Shoot. This event runs over several days and looks like most matches.





The attendance is global, shooters from all over the world compete in this event. When you register for the Super Shoot your entry includes table space where the shooters load and tweak and peak their rifles. Each shooter has a table in any of the large buildings on the land as well as various vendors. As a range member I have attended many super shoots over the past 25 years. The one thing I have never seen on a table and used for reloading is a scale. Now again, these guys are 100 and 200 yard shooters and shooting cartridges like the 6 PPC and 30 BR, they are not shooting longer range rifles in larger cartridges. When you wander back in the buildings most are loading Berger Bullets with VihtaVuori powders and no scales but Micrometer adjusted precision Harrell's Powder Throws. Truth be known most can't tell you their loads in weight of powder but know exactly in clicks of the micrometer exactly what their powder volume is. Again, these matches run over several days and I have never seen a scale used, powder is always volume metered.

So what I have always quietly wondered about is when or where between 200 yards and beyond weighing down to a kernel matters much? When does the precision shooter stop using a well machined powder volumetric measure and start worrying about weight?

Ron

 

[armarsh]

....So what I have always quietly wondered about is when or where between 200 yards and beyond weighing down to a kernel matters much? When does the precision shooter stop using a well machined powder volumetric measure and start worrying about weight?

Ron

I can't answer your question from direct experience because I have never shot short range benchrest. I know you are right as far as 100-200 yard benchrest - almost all is thrown. There are lots of threads on this topic if you are interested. Not so much here but on accurateshooter.com and benchrest.com.

Now, on the topic of this thread: A reloader can't make do without a scale. Since a reloader needs a scale he might as well get a good one that is a delight to use. For me that means a milligram magnetic force restoration type.

 

[Nature Boy]

A Gempro 250 is a decent scale, and an upgrade from what I was using, but it’s not up to 1 kernel accuracy