Beam Scale 101, a look at the tried and true

This is going to be a mult-part thread. Hope you find Part 1 an enjoyable read.

Part 1: The Basics

After going thru quite a few beam scales, and finding the strengths and weaknesses in each, I thought I'd share a bit, and also suggest the correct way of absolutely calibrating the scale. I'm putting all this down because there's a lot of misinformation on the web. I went looking for answers, and had to go a bit deeper into things than average Joe Reloader would probably want to go before throwing his hands up and calling it quits. So here goes!

First thing to realize, is the accuracy of a modern beam scale is its beam. The beam has machined, or punched stops for the various poises. The rest of the scale is just the icing on the cake, and while they don't contribute to the accuracy, they are important for repeatability and ease of use.

Lets start with the concepts.

Consider a beam scale with no stops on its beam. Just a weight. You've got the item you want to weigh on one side of a pivot, and a counterweight on the other. If the beam were equal length on both sides of the pivot, and level, you'd need a counter weight or poise, that was the same weight as what you wanted to weigh in order to keep the beam level. That really is the concept behind the apothecary scale, or perhaps better known to all as the “scale of blind justice”. Hows it work? You want a pound of beans. You put a known pound weight on one side, the scale tips. You pour the beans on the other side until the scale is level again. One pound o' beans comin' right up!

What if the counterweight were able slide along the beam? At that point, you could use a beam that was longer on one side than the other, but you'd need a fixed “balancing weight” on the short side, to keep the beam level when the main sliding counterweight was at some position close to the pivot. Simple math would illustrate how by moving the sliding counterweight along the beam, a certain amount of leverage could be utilized to exactly level the beam when the item to be weighed was placed on the short side of the beam. If one could very accurately measure how far the sliding counterweight had moved, and could account for the actual weight of the counterweight you could determine the weight of the item you wanted to weigh. Back to the beans, you take an unknown scoop of beans, put it on the short side of the beam, then slide the counterweight until things are level again. Measuring from the pivot to the counterweight, you could figure out that you've got 1-1/4 pounds of beans (more or less). Very hard to do accurately, and rather than math, it would probably be on a chart that was figured out before hand. That's complex, so it was made simpler.

Now imagine the modern beam scale. It has fixed stops for the counterweight, which I'll call a poise from now on. By using fixed stops, that have been accurately cut into the beam, the distance is all figured out. The scales designer has calculated the weight needed for the poise, and markings have been made along the beam to let you know at which stop the poise is located. That is the basis for the modern scale.

The problem with what has been described so far, is that however finely the stops on the main beam are cut, they're not fine enough for the precise measurement of very small weights, or small fractions of larger weights. What to do....

There are a few ways to tackle the need for higher precision, but what works best is to make the “balance weight” on the short side of the scale also variable with its own set of markings. The scale designer could have made a second portion for fine tuning on the longer side of the beam, but that would add additional length and also need a greater fixed balance weight. In practical terms, making the balance weight variable is the most efficient means of accomplishing fine tuning. In terms of actual practice, the balance weight isn't completely variable, only a portion of it is. That is to say, the pan, any weight in the pan, the pan's support are all part of the balance weight, but only one (or sometimes two) very light poise comprise the adjustable part of that weight.

As a reference to when I talk about calibration, notice that the large main poise is at “zero” closest to the pivot, and the fine tune poises are at “zero” farthest in their movement from the pivot. This gets a little weird to follow but, if both the main and balance weights were at zero closest to the pivot, the scale would still work if it were level. However, you'd have to “subtract” the markings on the fine tune scales from that of the main scale. That would be confusing, so... its set up to make it all addition, and the fine tune poises are simply added to the weight already shown on the main poise.

Whew. That's a lot to handle for the first installment of this multi part essay.

More to come.....

(There will be more on pivots, pointers, frames, beam construction, maintenance and calibration very soon)

Part 2: The pivot, the frame and pointers

The scales of justice hang from a chain. However good that is, we need something better, and less tiring to use than holding out that chain and scale at arms length, blindfolded or not. A beam scale is situated on a pivot. The idea is to have a very low friction, low wear, and fairly precise placement of the pivot point. Lets take those one at a time.

Low friction is addressed with a knife edge on the bearing surface of the pivot. If the pivot were a shaft, even the nicest miniature Class 4 (ABEC VII) bearings would not be suitable due to the the very small fractions of weight that reloaders require when measuring powder. Too much friction. If a shaft was used on a hard flat surface, the friction would be very low, but the scale's pivot point would move, much like a marble on a table top, it would roll forward and back as the scale achieved balance, and the placement of the pivot would really never be at a fixed point. I'll explain more about the fixed point a little further down. The knife edge solves the dilemma by providing a very low contact area, and thus low friction.

By using a V notch in the support for that knife edge, the placement of the pivot can be maintained at a fixed point. In practice, the V notch isn't really very sharp a the bottom. In practical terms, the V is really a very small U shape. That is fine, because it still limits the placement of the knife edge and provides a point for the knife edge to ride that doesn't let the beam move around too much. Similarly, the knife edge isn't all that sharp. The edges are usually anywhere from 45 to 60 degrees angle and may actually have a very small radius at the actual point of the “knife”. That situation is ok too. The friction is very low, and the placement remains fixed within a very small tolerance.

The problem with small contact area, like a knife edge, is wear. A few ways have been used to counter the wear of the components. Since the beam is the most expensive item, the knife edges are usually hardened to a degree that will reduce wear to a very small amount. I once had an RCBS scale that got constant (daily) use for fifteen years, and after all that time there was some slight wear, but it was very minimal (and correctable... more later). The pivot points vary greatly on almost all models of modern scales. RCBS used agate (a form of quartz) bearing. The newer RCBS scales use ceramic. Almost no wear occurs, but both are fragile, subject to cracking with impact. The design allows for their easy and precise replacement (when parts were available). Hornady/Pacific used a hard U shaped button on the M scale series. Redding uses V shapes ground into horizontal bars. They all work to accomplish the job.

As an aside, sometimes in the quest for less expensive ways to accomplish things, design improvements can provide some benefit that wasn't easily accomplished with the more expensive “old way” of doing things. I've examined the ceramic inserts on RCBS scales and I like the way they were designed. They have the “V” notch on top, but also have a convex bottom. They rock a little side to side, perpendicular to the beam. The benefit for RCBS was lower cost to manufacture. The benefit for the scale's owner is that the rocking allows the bearings to self level under the weight of the knife edges. I thought that was a slick trick.

The old Hornady/Pacific M scale has an interesting setup on its bearing. One side is a straight knife edge, the other side of the bearing is a curved semi-circle knife edge. The bearings are not “V” blocks but wider “U” shaped buttons. The curved side of the knife edge keeps the beams lateral position steady. It works, but repair of the knife edge is more difficult because of the curvature.

Years ago, the frames of scales were made of heavy aluminum castings. These days, the frames are magnesium, aluminum, ZAMaC or even plastic. It makes no difference as far as accuracy is concerned. The perception that a weighty, rigid frame is necessary for scale accuracy a absolutely false. On the other hand, a nice heavy frame does keep the scale from moving about on the bench. Moving on the bench, besides being a bother, may alter the level adjustment of the scale if your bench isn't perfectly smooth and flat.

Shooters have strong preferences. Back in the day, mercuric/potassium chlorate primers were the norm, and called “corrosive”. They were not corrosive, but instead left potassium salt in the barrel, which in humid conditions would attract the moisture from the air and cause rusting. The salt would get into the pores of the steel and rust would form pits. The fix? Wash the barrel with fresh water. And that, was a totally foreign, hated, dread concept to shooters. The idea that water would actually prevent rusting I suppose. At any rate, shooters have strong preferences to how a scale “feels”. Heavier must be more accurate but the real accuracy isn't the frame. All accuracy is in the beam.

Personally, I do like heavy framed scales since they stay put and don't move on the bench. I've actually taken badly cast bullets, fishing sinkers, shot from disassembled 12 gauge shells, and used electrical potting resin to add weight to scales. That method works great, but, before and after use and testing of the scale showed no difference in accuracy. I haven't handled one, but I think the Lee scale is plastic framed. And by the way, if you're going to weight down a scale like I did, make sure to get a non-expanding resin. The product I used had an expansion of less than half a percent. You may deform, or worse, crack the frame if you use any old resin. I'll post some pictures of a weighted scale down below.

So what's the frame do beside hold the bearing for the beam?

One thing is it provides a fixed indicator that allows a pointer, or line on the beam to reference as “level”. When the line on the beam, or the pointer at the end of the beam is aligned with the fixed reference, the scale is “level”. That may not be absolute level in terms of the real world, but level with itself, which is all that matters. Most of the time the scale makers will give graduations up and down from the main level indicator, and some state that those graduations show the 1/10 grain increments. Don't trust 'em. I've found them to vary quite a bit. Its better to use those as indication that you're approaching level, not as an absolute indication of the amount of weight.

The other thing all scales have is a damping device. Every scale I've ever heard of has what's called magnetic damping. Magnetic damping is an interesting field of study all by itself. I'm sure more than one reloader has asked themselves “How does that copper tab work magnetically, since copper is not magnetic?”. Good observation, and here's the short answer. The copper, or sometimes aluminum, tab is conductive. When a conductor moves though a magnetic field it creates a what is known as eddy currents. An electrical charge is formed that is inverse to the direction of movement and through that action, its like applying the brakes. One way to think of it is like a generator with fixed magnets and coils of wire. It takes a lot of force to spin those coils though the magnetic field and create electricity. The faster you want them to spin, the more the counter force is created. Not exactly the same, but similar enough for illustration. No iron, or steel or magnetic component is used on beams for that reason. We don't want the beam to be attracted, or repelled by the magnetic field, just damped.

I like the set up of the damper on the newer RCBS scales a whole lot. It used to be the old Ohaus designed scales had the copper tab at 90 degrees to the beam. This limited the size of the tab and made its placement critical. When the tab was “bent” out of 90 degree perfection, the beam would be a little off in its accuracy. The newer scales from RCBS use a larger copper tab as a linear extension to the beam. Larger is better for damping, and placement is less critical. That's another cheaper to produce, but better performing situation.

The indicator lines, and the damper are the reason we can't have the beam move and change position as we attempt to weigh things. A little bit of movement is always going to take place because scales don't use true V bearings or true knife edges, but the amount is very small, and does not effect the indicators or damper.

Frames have one more thing. They have a leveling device. The leveling device is nothing more than a screw, or thumb wheel attached to a screw that extends the screw on one end of the scale. This allows the scale to overcome a small amount of tilt on a bench top in comparison to the scales “self level” position. If you're bench is a little taller on one side, you'll just turn the adjuster a bit to compensate. The leveling screw isn't really a calibration point. A lot of people think it is. Its just a leveling adjustment so the scale can work on a slightly non-level surface.

And that's all for today!

Next installment is the maintenance and real calibration of beam scales.

Some quick pictures.....

The bottom of a newer model Redding scale. These have a really flyweight casting for a frame. After I fine calibrated the beam, and adjusted the bearings, and was sure the scale was good to go, I dropped in some sinkers and bad bullets, then covered them over with low expansion potting resin. The scale is no more accurate, but "feels" better on the bench, doesn't move around.


Next up is a new to me Hornady/Pacific M scale. Great scales, lots of interesting features, but no longer in production. The beam and damper tab are aluminum, which doesn't theoretically damp as well as copper, but it works on this scale really well. Note the stamped markings, not engraved. Engraving would be a pain in the butt for the linearity of the scale as different numbers would remove different amounts of weight from the beam. Nice touch is the angled indicators on the level scale (see top picture). The numbers on the beam were darkened with ink... I see now that all the excess wasn't taken off with alcohol. And finally, but not least - the curved knife edge that rides in the button bearing. The other side is a straight knife on the same sort of bearing. It works really well. This scale need a good cleaning still, and has not yet been finely calibrated.



I'll put some more pictures up after the next (and final!) installment of the text.

Part 3: Maintenance and Calibration

If you've read the past two installments, you're up on the basic concepts of the beam scale, and what all the important parts are, and why they're important.

Now comes the time for maintenance. Don't worry! Maintenance is easy. Its really nothing more than cleaning the scale! Here's the thing: If you're scale is has crud on it, in the stops, on the beam, in the pan, on the bearings.... its just not gonna work right. Simple as that. Remember the accuracy is in the beam. So lets start with the beam itself....

Make sure the stop notches are clean. That smear of Alox you had on your finger, dust, dirt, grime, all that ring-around-the-coller stuff that accumulated over time, needs to be gone from the beam. Don't be afraid to clean the beam, and its notches. Just don't alter the beam!

I use a small “parts brush”. These are available by the 10 or 12 pack, have bristles about ½ inch long. I trim the bristles to half that or so. That keeps them rather stiff. Then a bit of rubbing alcohol, or naphtha on the bristles, and scrub those stop notches to rid all the crud. Take care to control the spills that can take the ink out the the stamping indications on the main beam. If you use even a little bit of care, and a paper towel of two you'll do fine. Clean out all the notches. If the the notches and the poise were designed correctly, the poise won't seat fully down in the notch's bottom, but ride on the edges of the notch. Either way, just keep everything clean.

Clean the bearings! A Q-Tip and some alcohol or naphtha can clean them really well. Do the same for the knife edges on the beam.

Be very careful of numbers on the beam if they're applied with a sticker. You can't replace the sticker. I've never seen one for a “spare part”. Alcohol or naphtha may smear or even obliterate the numbering on a sticker. However, if you have stamped in markings, those can be re-inked.

The way to re-ink the markings is pretty simple. Just fill them in with a Sharpie pen. Then, with some alcohol, rub the flat part of the beam to remove the excess ink. It might take a few tries, but its really a very easy process. Don't use paint or anything else but ink from a Sharpie pen. If you use paint, the weight of the paint will throw the accuracy of the beam all to heck.

The rest of the scale can be cleaned just for appearance sake. A clean scale is a happy scale. Better yet, keep your scale covered with a towel, plastic, or in its built in cover.

Now on for the scary part: Calibration

Back in installment number one, we learned that the accuracy is in the beam. It is. What we have is a series of precisely machined, or punched stops in the beam, on either side of the bearings. Weights (poises) rest in the stops, and at the stops marked “zero” - the beam should be level.

There are two considerations for accuracy. One is absolute accuracy, the other is linearity of the stop graduations on the beam.

The linearity part is important and it may drive you nuts if you care to measure it. How each stop graduation compares to its neighbor, and to the overall length of stops on the beam is really important. There is no adjustment that is easily made for a scale who's stops are not accurately cut. Plain and simple, its up to the reloader to rely on the beam being made correctly. Fortunately, its not a hard thing to accurately machine stops at precisely regular intervals into the edge of a metal bar. My own shop experience tells me they probably use the knife edge opening as a reference in the fixture, and gang cut all the stop notches in one pass. The use of ganged up cutters allows them to be precisely set in their fixture and allows each beam to exactly like the other. In fact, they probably cut many beams at once with that method.

We're gonna have to just trust and assume that the stop notches are exactly where they ought to be. Let me give you a little forewarning: They're not. They're off by a just a little bit. And if we try to calibrate to one notch, the others may not follow in their calibration. You can spend a lot of time chasing your tail with calibration, but fortunately in most cases the amount of error is very very small, and only noticeable at higher weights that are measured.

Knife edges can be touched up. Have a look at the knife edges with a good magnifier, or eye-loupe. If there are burrs they can be very carefully stoned off with a fine, flat stone. Use nothing coarse here. Don't use a file. Don't use sandpaper. Use a stone. I've used that flat, pink ceramic stone from a Lansky sharpening set to touch up burrs. I like the ceramic stones because they don't cut very much, and you have to put more than one pass into getting a burr off. Touching up the knife edge probably won't be needed unless the scale has been in long use, or has been mistreated. But, even on a new scale, you should check the knife edges to make sure they're true and free of burrs. If you're not comfy doing that sort of fine metal work, it might be wise to enlist some help. I'm sorry but I grew up with gunsmiths that knew what they were doing, and machinists who made injection molds for a living. I can't recommend who might be best to bring a beam to if there are knife edge burr issues. You might have to resort to the scale's maker.

In a more perfect situation, with all the notches perfectly made in perfect locations, the only issue one could have is the poise on the beam. And since we can't easily control the notches, but can control the poise, that is the place where calibration can be made.

Calibration is actually fairly simple, but you need to have a precise “check weight” set to accomplish a good calibration. Calibration may involve permanently altering your scale, so a few warnings are in order.

1. You perform any alteration, calibration, modification, adjustment, or the like, at your own risk. I cannot control what you do, how you do it, or the results you'll achieve. Its your scale, your actions, your risk. Capisce?
   
   
2. You need to be in a draft free area, totally away from ceiling fans, A/C duct, open windows, heating registers, or any sort of place that may cause even the slightest draft. Small drafts will cause the level of the beam to waver. A wavering beam cannot be accurately calibrated.
   
   
3. The scale, its bearing surfaces, its knife edges, its beam, must be absolutely clean. Go back and clean it again, before trying any sort of calibration.
   
   
4. The scale must be in good working order, with bearings and knife edges that are in workable condition. The scale must absolutely return to dead nuts zero every time you deflect the beam. If it doesn't you need to correct the trouble before calibration.
   
   
5. The scale must be in a level spot on your bench, and must be constantly rechecked for level at every step of calibration.
   
   Main Poise Calibration

1. For the purpose of main (large) poise calibration, it doesn't matter if you have a two poise, or three poise scale.
   
   
2. Absolutely level the beam according to its pointer using the scales leveling device. For the rest of the steps, make sure the scale does not move at all on the bench top. If it does, start again with an absolutely level scale.
   
   
3. Assuming you have a 500grain or 505 grain scale, place a clean 50 grain check weight in the pan, and very carefully measure its weight with the scale. It may indicate a few 1/10 grains off. That's ok. Record the measurement.
   
   
4. Remove the 50 grain check weight, and make sure the scale returns to absolute level according to its pointer. If it does, proceed to the next step, if not, go back to step 2.
   
   
5. Using the same method as described above, measure and record increasingly large weights according to your check weight set. Make sure the weights are clean, free of grime dirt that may throw the readings off.

The RCBS Deluxe set of check weights has (1) 200grain, (2) 100 grain, (1) 50 grain, (2) 20 grain, (1) 10 grain, and (1) 5 grain weights, as well as smaller weights. You needn't bother with 5 grain through 20 grain weights for the main poise. Just increment up in 50 grain jumps. Be sure to record each measurement. Don't assume a 50 grain weight will actually be recorded as 50 grains. It may be 49.9 grains, it may be 50.1 grains. Just record what the scale gives you. Do that for the entire check weight set. With the RCBS Deluxe set, you can get 450 grains, in 50 grain increments, using only 4 weights. Again, make sure the weights are clean, and there are no drafts to throw the measurement off.

Have a look at your results. Lets say the scale is imperfect, and readings are as follows:

50 grains
100 grains
150.1 grains
200.1 grains
250.2 grains
300.2 grains
350.3 grains
400.3 grains
450.3 grains

As you can see, as the certified weight was increased, the scale indicated increasingly larger errors. This is a more or less linear error. This tells us two things. First is that the stop notches on the main beam are pretty good, and second, that the weight on the main poise is just a wee bit off on the heavy side. If the results were opposite, then the main poise is a little light.

But, what if we get something like the following?

50 grains
100.1 grains
150 grains
199.9 grains
250 grains
300.2 grains
349.8 grains
399.7 grains
449.8 grains

That sort of recorded weight is actually a bit more likely to occur, mainly because of errors in the stop notches combined with slight error in the main poise. If we look at the table of recorded weight above, we can see smaller error at lower weight and larger, but still more non-linear error at greater weight. Since we cannot correct the beam itself (and have not tested every single notch), the best we can hope for is to get the poise and beam calibrated as closely as possible. Its best to accomplish the calibration at about 350 grains to 400 grains on a 500/505 grain scale when the results are non-linear. If you do that, you'll (hopefully) be off by about half the error you first recorded. Or put another way, if you get the 350 grain position to record perfectly, you probably will only be off by less than .1 grain at 400 grains, and maybe .1 grain at 450 grains, and certainly less than .1 grain at lower than 350 grains. The word there is “hopefully” because we have not, and can not really check every single stop notch on the main poise.

So how to adjust the main poise? Depends on the scale. My RCBS M-1000 scale has an adjustment on its main poise. The part that drops into the stop notch can be moved slightly to the left or right, or rather, the weight of the poise can be moved to the left or right in relation to the part that drops into the notch. The manual doesn't mention the adjustment, but you can loosen the screws on the back of the poise and turn the adjuster on the side just a little, and repeat the whole process over again. I can't say for certain how much to turn the screw, because my M-1000 was dead on the nuts accurate against its own check weight (the only way I tested it).

Most other scales don't have an adjustment. If you're heavy, you need to take a bit of material off the poise. If you're light you need to add some material.

Taking off material can be done very lightly with a file, or very very carefully with a Dremel. I'd use a rubber wheel on the Dremel, and in either case, file or Dremel, take some material off an inconspicuous spot. Just a very very little material. Like one very light file pass. Remember, you're only taking a fraction of .1 grain off the poise itself.

If you need to add material, what I've found works well is a tiny dab of Super-Glue. Super-Glue is funny stuff. It dries by absorbing moisture from the air. Here's what's gonna happen when you use super glue to add material to the poise. You can use a fine toothpick to add the tiniest drop of glue, and think you've got it nailed perfectly. As the glue dries... it absorbs water, so if you recheck the measurement in a half hour or so, it will be heavy, and you'll think you made a mistake. Just leave things be! As the glue further cures, it will release some moisture and actually be lighter than when you first applied it. I guess that's why its called “crazy glue”. At any rate, repeat as you need to in order to get the right amount of material on the scale. Chances are you'll “go over” what you need, and that's ok. Just sand off a bit of excess glue, a very little at a time, until you get it perfect. If you want, you can use a Sharpie pen to blacken the glue to better match your poise (assuming its black).

At that point, you can go back and double check your results by running the complete calibration over again. Chances are, with a bit of care, you'll have it nailed to within .1 grains or maybe .1 but not quite .2 grains across the length of the beam. If you're pretty good at the far end, for heavier weights, you'll be better at the close end, for lighter weights.

You can run the same set of incremental tests for the smaller poise (or poises). I've had one poise (on a Redding) read heavy. It was not in alignment with itself. Put another way, setting the main poise a 5 grains and adding weight to the pan to level the scale perfectly, should have given the same reading as the main poise at 0 grains, but the small poise at 5 grains. It didn't. The small poise was a little heavy and was adjusted accordingly.

One final adjustment that seems to be needed on new design Redding scales. The Redding has two bars of steel that appear to be stainless, and are not very hard metal. I'm sure they're adequately hard though. The way they make the scale is to set the bars into holes the frame casting, then grind a V notch across the bars. Finally they put edge pieces on the casting (with rivets!) and call it done. I've examined three Reddings this year, and all had misaligned bearings. Fortunately, you can adjust them, though its a bit of a pain. The rods can be punched out with a small punch from the middle of the scale to the outside of the scale (from left to right as you face the scale). That will also loosen the bars in their holes a bit, which isn't a bad thing. You can then clean out the holes a bit, scrape off excess paint, and reinsert the bars into their proper positions. What's the proper position? When the beam's damping tab is in the middle of the slot in the frame. Both bars must also have their V notches level with each other, or put another way straight in line with each other, as seen across the bottoms of the notches. You can use a small brass punch to rotate the bearing rods in their holes to adjust that. Once its all set, just apply some paint to seal the rods in place. A much better design would have been circumferential notches in the rods, but that would have required factory adjustment. As they're made, grinding a set of notches across the top of the rods must be a cheaper way to go.

RCBS's current scales have self leveling bearings. The Hornady has larger button bearings. I can't see either of those giving fits, but the Hornady can be adjusted with shims if needed.

And that is how calibration goes, and how adjustment is performed!

Just a few really goofy misnomers I've come across on the net while researching beam scales.

If the scale is doesn't read correctly when you get it out of the box, then its way out of “calibration” and is a bad scale. The dumb so and so, who has a whole set of videos about this, is just plain wrong. The scale can be leveled, and the calibration is in the beam, not the level.

On a similar thought, its been said to “never touch the adjusting nuts” on a Hornady scale. That is also a bunch of malarky. The nuts position on the right side of the scale take the place of the shot in the RCBS and Redding pan supports.

RCBS and Redding scales I have, all have shot in the pan supports to help get the level correct, and you can add or subtract shot if needed if you need to replace the pan, or the support. Older Redding scales had a wire support, and they came extra long as a replacement part. The instructions said to trim the wire to get the scale leveled when the adjuster was at its mid range. Not too hard, and it doesn't have to be perfect. The Hornady scale can have its adjustment nuts moved slightly in order to get the scale to level with itself, on your particular bench, when the adjuster is at about half its travel. Again, not hard to do, and it doesn't have to be perfect because the adjuster can fine tune.

Another great misnomer, or outright falsehood.... I've seen the recommendation that when a scale is off by a small amount at some high weight, say 400 grains, then “trim/take some material” off the pan. No! That only changes the point at which the level will occur with no weight in the pan, and the poises set at zero. If you trim the pan to adjust the scale at a high weight (or any weight really), then when its back at rest, zero's on the poises, it will not be level. If you adjust for level, then its off when weight is applied and you chase your tail until the name Bubba appears on your carry permit!

And that's about it for beam scales. They're simple. If decently made, they can be made to be accurate, and once adjusted they never really need re-calibration, just cleaning.

I certainly hope some folks can benefit from the compiled research I've done over the last year or so. Feel free to correct me! Feel free to ask away, and add your own horror stories.

Thanks!

Some Redding scale issues:

You can see they inserted the bearing rods, then cut V notches in after the scale was painted! The V notch on he three I examined within the last year were all either too far right, or too far left. The problem is when the scale is set that way, the damping tab rubs on the frame, or (or in addition) the knife edges on the beam rub on the frame of the scale. This is just terrible QC. The frames on Redding scales are extremely light, and I'd guess they're magnesium casting, as magnesium casts in thin parts much easier than aluminum does.



Here you can see the bearings have been adjusted, freed of paint, and set into place with a dab of yellow paint at each end of the hole they ride in. That is enough to keep them in place.



Even with adjustment, the tab on the scale rubbed at the top and bottom of its travel. The casting itself was convex on one side, and concave on the other. A bit of careful filing fixed the issue, but also needed the tab to be set at 90 degrees to the beam. The tab on the Redding is copper, and bends fairly easily. On a Hornady, the tab is aluminum and may break off if you try to bend it into position. Fortunately the Hornady has ample room in its slot. When the tab is not at 90 degrees, expect the calibration of the beam and main poise to be off by just a bit.

Here on a Hornady M scale, you can see the beam markings have been impressed into the metal, a better way of marking a scale than engraving. Newer scales have sticky decals to show the markings. You can also see the opposite side of the curved knife edge, and a better look at the button type bearing. Those bearings are adjustable with shims.

South Prairie Jim said:

old scales rule

Click to expand...

That they do!

I forgot to upload this image of a Redding scale.
This scale had a pretty linear deviation along its beam, being off by about .5 grain at the 450 stop, and gradually less at lower number stops. The scale showed "under" the correct weight, which meant that the poise was just a bit too light. I used the super glue trick, then sanded the top of the super glue hill to reduce it a bit since I overshot the amount to add. If you read up above someplace, you'll see why when working with super glue.

It looks like a lot of glue, but its not. Neither did it spread out. The "splotch" you see if from off-gassing of the glue, which shows up as a thin white residue. The gasses of the glue absorb moisture from the air and form that residue. Similarly super glue turns whitish due to high humidity during drying. It needs humidity but a "hot" fast set super glue will trap what has embedded into its mound or run out (if you're gluing parts together). I used what I had - some cheapo stuff I got for a quarter a tube! After it was all done, Mr. Sharpie pen touched it up.

The old knife edge "maybe" could have been salvaged by just eliminating the "knife" at the tip (leaving the rest of the tip to prevent lateral movement. But... I like the replacement!

On the Redding, I can't remember, but I think I reversed the bearings left to right so the rod didn't protrude too badly from the casting. Looks like you can do the same with that one ya got.

And hey.... thanks for the canted knife edge picture/example. One more thing to worry about when getting a scale....

Oh maybe I didn't say it clear enough. Leave the width, so the end play is ok, just take off the offending bit of knife. It will look like a notch on the end, but full width should have it covered... maybe. Depends on the how the scale is designed I 'spose.

Pat Riot said:

@Project355

Does humidity and temperature affect scale balance?

Click to expand...

If the scale is dirty, sure humidity is a factor. Temperature "may" alter things, but not the beam. In other words, your bench's wooden leg may twist a little, or gain a few .01's of length in humid hot conditions, throwing your bench off Dirt in the scale bearings and beam will be a problem no matter what, so clean is best.

Jim what you said about knife edges... I like to make sure they're up to snuff before any beam calibration. Not really a sharpen, as most are adequate, but just to check for little rough edges that have kicked out sideways from the knife edge itself. Your thoughts?