Damping Scales?

Brad

Administrator
Staff member
#21
Interesting.
What is the arm of your beam made from? If already Al then you may just get by with a magnet in the right place.
 

RicinYakima

Well-Known Member
#23
would it be equal or enough to off-set.
it seems that if he added weight out on the beam and the tipping point wasn't in the middle he would need more on the short side.
It all depends upon where the center of mass is for the beam on each side of the fulcrum. Old models had a little cup under the pan and they added lead shot to make them balance. There are many ways to skin this cat.
 

KeithB

Well-Known Member
#25
Used to have an old beam scale - don't remember the brand - where I worked that used viscous damping. A little paddle/tab stuck down from the beam at the hinge point and into a small cavity that was supposed to be filled with a special light oil. It damped out pretty quickly but everyone hated the mess when they moved it and spilled the oil, even if it was only a thimble full.
 

Pistolero

Well-Known Member
#27
You need some width to get the best effect. A few pieces of copper wire soldered together
to make a 1/2" wide section would work well. The magnet generates circulating electrical
currents in the copper when moving, takes energy from the moving arm. Once stopped, magnets
do not attract copper, so no forces at all.

Bill
 
#28
Going for a strip of aluminium same width as he beam which is around the 1/2" with two dog leg bends in it, some double sided tape and I'm good to go.
 

Pistolero

Well-Known Member
#29
Good point. Copper is slightly better, but aluminum sheet should work, too, if you cannot
get a piece of 1/16" thick or so copper sheet.

Bill
 

Pistolero

Well-Known Member
#31
eBay frequently has neodymium magnets, which are super powerful, on sale
for pretty decent prices, often odd shapes salvaged from disk drives or electric
motors, or actuators. Some are simple cylinders. Any shape will work.

Stronger magnetic field gives stronger damping.

Just watched the video, wasn't anywhere were I had bandwidth to spare until now.
good demo. Make the aluminum (sorry that would be ALUMINIUM, for you) blade
run as close as you can to the magnet without dragging to get highest damping.

Here you go, you can dampen 20 of them for under $1, shipped.

https://www.ebay.com/itm/20-x-Super...135455?hash=item3cf9bfd11f:g:NCoAAOSwrklVUshc

Bill
 
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Brad

Administrator
Staff member
#32
If the arm of the beam is metal why not just place the magent such that it acts on the beam and not add further metal? Adding metal to one end of the beam means adding more to the other end also. I am not an engineer but I would think the weight added would be proportional to the distance from the fulcrum. Bill?

Take a minimalist approach.
 
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#35
I apologize for going off topic but I need to know if I mount a magnetic tool holder/bar on the edge of the shelf below my RCBS 10/10 scale, will it mess with the scale??
 

Ian

Well-Known Member
#36
It might. The static electricity from a plastic bottle of powder placed too close to the beam affects mine. Try it and see.
 

Pistolero

Well-Known Member
#37
If you put a paddle hanging down from the beam, with an effort to be symmetrically
shaped on either side of the pivot, and then adjust zero as needed, either by filing your
paddle, or adding weights to the beam, you should be good. If the beam is aluminum,
then just adding a support for the magnet near the beam at level would be good.

You can put it on one end, no problem, but will need to add more weight to the pan
to zero. My RCBS has a copper tab on the outboard end, so it has significant correction
in the under-pan shot carrier, built that way.

An engineering prof had a demo device, looked just like a full sized axe at first glance,
but upon closer examination, the edge was not sharp at all. It hung from a hole at the
extreme end of the handle on a pin, very free pivot. At the bottom was a very large radar
magnet, an C" shape, opening in the C, up. Probably 4" diameter bar, tapered ends at top
to 1.5" diameter, tips had about a 1" wide gap that the head of the "axe" would swing
through. When it was just hanging there, the axe hung straight down, moved with no
noticable resistance. Lift the axe to horizontal (rotate it ninety degrees about pivot) and
release. Astoundingly, it did a dead stop before the whole head had passed through the
gap in the magnet after that fall, where it picked up a lot of velocity. Turns out the head
was copper, painted black, and the whole rig made to do exactly what it did - make enough
of an impression that this engineering student remembers the demo perfectly, and why it
worked over 45 years later. The eddy currents are proportional to velocity, so when the "axe head"
copper entered the very high magnetic field flux in the gap of the big radar magnet (probably
weighed 50 lbs or more) it damped it so heavily that it stopped before it moved the six inches
that the head was long. If swung from 10 of 15 degrees from straight down, it would swing through
a bit, stop on return, much lower velocity, so much lower damping. Heck of a cool physics demo,
IMO.


Bill
 
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KeithB

Well-Known Member
#39
You could be right, I don't remember the brand, it was stuck away in a cabinet, soon to be joined by all the Ohaus triple beams when digital scales came out.