Balance scale problems


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NotSoFast
December 7, 2008, 07:37 PM
I recently purchased a RCBS 5-0-5 scale. Yesterday I was working up a new .30-06 load for my Garand and was measuring out the powder then weighing it before loading it in the brass. For a while I wasn't getting repeatable readings on the balance scale but was on my RCBS Range Master 750 electronic scale. Eventually, though it settled out and began giving me readings that were less than a grain different from the 750 and didn't vary more than half a grain between readings.

Have you ever had a balance beam scale vary by 3 to 4 grains? If you did, how did you resolve the problem? I don't want to have to return the scale if I don't have to as it seems to be working now. I did check and can't find any binding points or any damage to the knife edge it pivots on.

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Galil5.56
December 7, 2008, 08:38 PM
Was it leveled to zero before reloading, moved after, accidentally miss a poise? If the Agate bearings and knife edges are sound and clean, not much else to go wrong. My Ohaus made 505 has been reliable and accurate for many decades, and I you figure this out.

ranger335v
December 7, 2008, 08:42 PM
The most common cause of such errors is end friction on the pivot rod the beam balances on.

Check to see if one end of that rod isn't rubbing against the clips that retain the agate bearings. If so, center it. And keep the bearing Vs and knives free of dust, etc.

NotSoFast
December 7, 2008, 08:56 PM
While it was a little out of level, accounting for a couple tenth's of a grain difference, that doesn't explain the variance in measurements. It must have been something on the knife edge(s) or the beam rubbing somewhere. Oh well, if it works I may never know the problem.

Thanks for the help guys. :)

Hairballusmaximus
December 7, 2008, 09:08 PM
Any small air currents can cause the same thing. I always shut off A/C, fans, heaters etc. before using either my 505 or rcbs electronic scale. I have had variances of.2 to 4 or 5 grns just from having the shop door open with just enough breeze outside to feel it.

Steve C
December 8, 2008, 12:42 AM
...was measuring out the powder then weighing it before loading it in the brass.

Why are you making the assumption that the scale is wrong?

Unless as mentioned you have a breeze blowing on the scale, are bumping it and upsetting the level or moving the poise there's no reason for a balance to give improper measurements, after all they're relatively uncomplicated pieces of equipment. Its more likely that your powder dispenser is throwing initially erratic charge weights than a balance is not measuring correctly.

You can always check the scale by emptying the pan, moving the poises back to zero and see if the beam zero's. It you have any breeze on the scale you'll see it move.

fireman 9731
December 8, 2008, 01:46 AM
I have heard that fluorescent lights can affect scales.... creates a slight magnetic field or something...

NotSoFast
December 8, 2008, 01:51 AM
Steve - There was no breeze and I used the same powder throw over and over, switching between the electronic scale and the balance beam scale so there should have been absolutely no deviation at all. And there wasn't any deviation in the electronic scale, only the balance beam. I was rezeroing it each time I took a measurement, then readjusted until I balanced it.

And no, I wasn't bumping it either, only stopping the swing of the measure scoop after placing it on the hook.

I wish it was me, or a breeze. Then I wouldn't have to doubt my scale. There was a little misadjustment of the level on the scale but, as I said before, that only accounted for a couple tenths of a grain, not 3-4 grains.

Fireman - Thanks, I'll try playing with that since I have one close to the scales that might account for that.

Hairballusmaximus - I wish it was a breeze. I didn't have the heater or air going either one. Maybe Fireman is right.

243winxb
December 8, 2008, 08:05 AM
Avoid locating mechanical scale within three (3) feet (one meter) of fluorescent lights. The electromagnetic fields generated by such lights can cause weighing errors.
http://74.125.95.132/search?q=cache:_9X-vZX2ykgJ:www.speer-bullets.com/default.asp%3Fs1%3D5%26s2%3D19+effects+of+floresent+lighting+on+reloading+scales&hl=en&ct=clnk&cd=1&gl=us

243winxb
December 8, 2008, 08:20 AM
Static electricity near a scale can affect measurement accuracy just as much as a stray air current. Always use a powder pan made from metal or from static dissipative plastic (e.g. the Lyman Powder Pal). PACT recommends washing their powder pan occasionally with soapy water and allowing the soap film to dry on the pan. The soap film helps dissipate static electricity. Keep any plastic materials away from the scale, including plastic loading blocks, die storage boxes, ammunition storage boxes, AkroBins, Styrofoam and vinyl. Keeping a clear space around the scale is generally a good practice anyway http://www.northeastshooters.com/vbulletin/archive/index.php?t-2023.html

Ol` Joe
December 8, 2008, 12:55 PM
A cheap scale check wgt kit will show any problems. I use one everytime I set my scales up, either digital or balance to insure they are reading a proper charge.
(I know the digital comes with a calibration wgt. Mine`s 25 and 50 grams, I load 4.8gr of powder in my 45acp.)

rcmodel
December 8, 2008, 01:24 PM
Balance beam knife-edge rubbing on one of the side-plates is the most reasonable explanation for that much variation.

The scales need to be level both end-to-end, and sideways, then zeroed, every time you use them.

Then the balance beam centered in the bearings, and kept that way during use.

rcmodel

Oddbod
December 8, 2008, 04:57 PM
Use canned air to blow any dust or fibres off the scale's bearings.

Make SURE the scale is levelled before you start - errors become greater once you add weight to the pan.

NotSoFast
December 8, 2008, 07:06 PM
I have a 20 and a 30 gram weight that came with the electronic scale. That's 308.8 grains and 463.2 grains respectively. When I measure them on the beam scale, they come out within .1 grain so I'm happy with that.


I guess I'll just have to write this off as unknown and make sure I am doing everything right from here on out. While it could have been the knife edge rubbing on the side, it may also have been that I had one of the counterweights slightly off the mark, likely the grains counterweight.

Thanks for the help. I've learned some from y'all and from this experience.

(added)
By the way, I leveled the scale before I started using it. :)

rfwobbly
December 8, 2008, 09:53 PM
I guess I'll just have to write this off as unknown....



I think your scale is possessed by a left-wing liberal spirit, and that you should rush it to me for an immediate exorcism. Of course I'll need to keep it for several years to protect you and your family.

No extra charge for that !

:D

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