Beam scale is off

[grubbylabs]

So what all is involved with "tuning up" a scale?


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[Reeferman]

Is the scale repeatable? And what is the amount of grains that you load at most of the time? Going over those numbers your wife did don't look bad to me. I understand what you are saying as it annoys me when a scale doesn't weigh like I think it should.
I got some information from 1066 on what to do to the knife edges and a few other tips but with these curled up sausage mechanic fingers I have and not being able to see what I need to I gave up on the one LNL beam scale I still have. But maybe you can do it with success as it ain't rocket science but it is like working on a watch.

 

[LiveLife]

Ohaus 10-10

RCBS 5-0-5

I have two Ohaus 10-10 beam scales that are accurate to Ohaus ASTM class 6 stainless steel check weights down to .15 gr. Both are sensitive to one piece of 1/4"x1/4" 20 lb copy paper that weigh around .05 gr and weigh two pieces at .1+ gr.

I use the following to clean and "tune" beam scales. The key to repeatable zero and consistent readings is the knife edges need to pivot on agate stones that "free float" on posts (see pictures above). Remove the covers and not only clean the stones at "V" notches but make sure the posts are clean and area is free from debris. To check for sensitivity, block ambient air movements by closing air vents/windows/door and may need to use glass bowl. And as many posted, make sure the bench top is level - http://www.thehighroad.org/showthread.php?p=9893632#post9893632

- Remove the bearing covers with a Phillips screwdriver (see pictures below)
- Make sure the posts the agate bearings free float on are clean
- Clean the agate bearings, especially the "V" notches
- Re-install the covers
- Clean the knife edges
- Level the bench surface using a bubble level at 90 degrees
- Turn HVAC/vent off and close the window/door to the room as any ambient air movement will affect scale reading/zero
- Place the powder pan on the pan support
- Set both large and micrometer poises to zero
- Lock the micrometer poise with the nylon bolt (for Ohaus/RCBS 10-10)
- Adjust the leveling foot so the pointer is at the zero line"

 

[Reeferman]

That works for the Ohaus style bearing and straight knife. But the Hornady/Pacific M and the new Hornady LNL scales use curved knifes and round steel bearings.

 

[1066]

So what all is involved with "tuning up" a scale?


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Here's a Redding No 2 with round bearing that recently received an extensive makeover:

https://www.youtube.com/watch?v=np2XyJlN3Js

 

[grubbylabs]

So I have been testing a couple different scales.

My wife pulled a NO,NO and brought home her labs check weights.

As it turns out, my Hornady scale is off.
I picked up a RCBS 5-0-5 scale and it is spot on all though the weight ranges.
I also picked up a Redding scale. It did pretty good, but some where between 230gn and 250gn it starts to go off by about .2. Which is out of the range I am likely going to use it.

Since I think the Redding is easier to use than the RCBS, I am going to take the RCBS back and sell the Hornady since it apparently can be "tuned up". I am going to sell it to some one who knows what it is and knows it's story.

Even though the RCBS was more accurate, it's still more difficult to use. The Redding was still spot on in the range I will be using it and it's easier to use. So it gets a spot on the bench.

But the best news, my most expensive scale was spot on all the way around. Every weight we put on my Charge Master was spot on. So I feel good about that.

Here are some pics of the scales.



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