April 04, 2011
By Allan Jones
The ballistics lab I worked in loaded huge numbers of cartridges where every charge was weighed, not metered.
By Allan Jones
It's vitally important for a digital scale to stand on a level surface. Don't guess--check it.
The ballistics lab I worked in loaded huge numbers of cartridges where every charge was weighed, not metered. You can't do that for 20 years without embracing some strong opinions--and some useful habits--about the technology of weighing.
Analog Versus Digital
With reloading scales, this is easy. "Analog, old; digital, new." To better understand the weighing process, it helps to understand the technology. Analog is characterized by an infinite number of possible values between two points. Digital has a discreet number of evenly spaced values. A couple musical instruments illustrate this:
A trombone has a slide that continually changes the sound's pitch through the range of lowest to highest note the instrument can produce. In between lie an infinite number of pitches. That's an example of an analog output. A piano can produce only certain notes programmed by the tuning, and nothing in between. "Middle C" is 261.63 Hz, and the next key up, "C Sharp," is 277.18 Hz. You cannot produce any note between these frequencies using the keyboard. That's like digital output.
With reloading scales, this difference shows up in the way we see values displayed. With the old beam balance, you watched a pointer that swayed past a reference line, and when it was steady, you had your charge. Digital is different, and that difference has caused some consternation for new adopters of this technology. With that in mind, I offer some "Digital Dos and Don'ts."
Calibration is key to success with digital scales. Keep the weights in a safe place.
The first thing a reloader with a new digital scale notices is what we called "toggling," the readings not sticking on one value. All decent reloading scales have an accuracy tolerance of ±0.1 grain, but a mechanical scale's pointer can stop a minute fraction of this tolerance over or under the target value because it's analog. With digital, the scale can show 45.7 or 45.8 grains, but nothing in between. If the charge is close to 45.75, the scale may flash between two readings. Unless this is due to outside influences (discussed below), learn to ignore it.
Warm It Up
Any electronic device should be given time to acclimate to the environment. If Mr. UPS delivers your new scale on a cold February morning, don't expect peak performance until it comes to room temperature. It's also a good idea to turn on the scale and let it idle a few minutes before any use. I have one scale that's not been turned off in years.
Level & Steady
Many of us are accustomed to a mechanical scale's comfort with uneven surfaces because its zeroing methods usually compensate for it. With digital, you must be more precise. Use a carpenter's level to check potential sites for level in two axes--north-south and east-west. Unless level, some scales will not let you past the next set-up operation--calibration. Don't assume a surface is level.
If your scale has a removable platen like this model, keep hands and tools away from the case opening.
I find most "digi-scales" prefer a more stable base than their ancestors. These sensitive devices can act like seismographs on some surfaces, picking up and reflecting household vibrations. We set up one lab scale temporarily on the top of a file cabinet that we determined was level. Still, the thin, sheet-metal top acted like a drum head, magnifying vibrations in the building. Place the scale on a surface with a thick top; I prefer wood surfaces to be a minimum of 3/4 inch thick.
Most digital scales need to be "taught" how to make readings. Although done at the factory, effects of shipping and handling mean any scale should be recalibrated before being put into service. Most scales allowing calibration will ship with one or more special weights that do the job. Read the instructions--all scales have different procedures, even those within one brand. With a new scale, calibration will tell you very fast if something is wrong with the unit.
Place the scale on the surface where it will be used and warm it up before the calibration run. Then simply do what the instructions call out. Most calibration runs take only minutes. This is how we discovered one of our lab reloading benches was not level--a new digital scale failed to complete its calibration until we leveled the bench.
If you are prudent, you will calibrate once a week during continuous use, or whenever you haven't used the scale in a while, or if you move the scale to a different location or manage to give it an accidental bump.
Should you miss a calibration (other than the initial one), charge variance is generally less than 0.3 grain--not a safety problem if you're loading a big case, but could be of concern in a small high-pressure cartridge when loads approach maximum. Oh, and put those weights someplace safe; if you lose one and the scale has become obsolete, it will be tough to get a proper replacement.
Wind drafts are the prime cause of toggling and can be frustrating because you may not notice a draft. Once discovered, if you can't stop the draft, place a cardboard box, open on one side, around the scale. It's an inelegant yet nearly foolproof fix. Make sure the box admits your hands and that no part of the scale touches the sides.
Electromagnetic shielding is a more difficult task, better handled by adding distance than adding hardware. A fluorescent light fixture can affect even mechanical scales. Keep all scales at least 3 feet from any fluorescent lights--more is better. Electric motors can emit magnetic fields, too; don't set up your new scale next to an electric case tumbler.
Care & Cleaning
After calibration and reasonable care in handling, there is really not a lot of special care required other than occasional dusting and cleaning up any powder sp
ill. A well-engineered scale has a case design that diverts propellant spills from the area of the sensor. If the platen--the flat surface upon which the pan rests--can be removed for cleaning, remember to do a calibration run after you reinstall it. And don't stick your fingers or tools in that hole when the platen is off!
Take a little time for familiarization and setup, keep those calibration weights handy, and you will find that you'll never want to use a mechanical scale again.