strange scale behaviour

[bow shot]

Anyone run across this using an RCBS 10 - 10?

1) you are loading in a breeze/air curent free room
2) you check zero/level before loading and do not move the scale.
3) the scale pivots points "seem" very clean

4) you I throw a charge, trickle it, and get a perfect weight (in this case 26.5gn). Then you dial the adjustment barrel up 0.1gn (say, up to 26.6gn) for the next charge but go back, re-weigh the original (26.5gn) charge, and re-weigh it and the beam indicates a perfect (?!) reading again as if the powder in the pan added to itself .

Comments? Ideas?

Makes me wonder how much of my unusual test group readings are owed to this behaviour? I know that in ladder tests, I'll can sometimes see as much as see 1" change in POI with as little as 0.2gn powder change...

[RAMOS]

I have the old Ohaus version of your scale and have not come across this. Even though they "seem " clean, try cleaning the knives and bearings with rubbing alcohol. Also, as you most likely are, make sure you hold your head in the same position every time. The only difference that I'm aware of between our scales is that mine has agate bearings and yours are probably metal, doubt it makes a whit of difference. If all else fails, send it in and I'm sure they will take care of you.

[bow shot]

Thanks RAMOS, I'll give the bearing surfaces some close attention and clean 'em up as you recommed. If I see a difference before and after, I'll see if I can post pics (of the bearings).

I do keep a level viewing angle, I actually sit on a little stool that my kids used to use for #1 in the bathroom when they were little tykes (both US Army now...) so that I can seel the pointer without parallax.

[RAMOS]

I'm not worth a darn at posting links, pictures and whatnot. However there is a website (omegepowdertrickler.com) that has a prism that you set up in front of your beam pointer that allows you to look down at the top of it (the prism) and see the indicator. I've often wondered how well it works.

[bow shot]

hmmm... that sounds good. It gets kind old squinching down like that after 100 throws or so...

[Neil S.]

I have had problems keeping my eye at the right level to get consistent readings from my balance scale. I would always have to duck slightly and it made for a very sore neck after an hour of loading . I have recently started using a webcam positioned level with the scale and it is great! I just take the readings right off of my laptop screen and the camera stays in the same place the whole time. Granted there is one more thing to set up, but I love it! It works great!

[Fred_C_Dobbs]

I was having a similar "lean over and squint" problem with my portable loading bench, so I fashioned a shelf constructed like a simple box from some wooden trim, fastened to the bench with a small Irwin Quick-Grip, that elevated the scale to eye level.



I'm not much of a woodworker but this is couldn't be much simpler. A little measuring, a little cutting, some Elmer's glue and some wood screws and you're on bidness. There's a beam of the same material as the stay in the back and the reinforcements at the corners under the top piece, running its entire width, to prevent it bowing under load and making the surface under the scale un-level.

The magnifying lens is a 2x "Helping Hands", $16 at Radio Shack.



The two Quick-Grips you can see hold down the plywood deck my press is bolted to. There's a third that's not quite visible behind the spray nitro solvent that clamps the bottom of my box/shelf to the far edge of portable the bench.

Coincidentally, that electric powder trickler next to my scale is the same one sold at the site RAMOS linked to above.

[bow shot]

Yankee inginuity in action, great ideas right there...

[RAMOS]

Bow Shot, how is that scale treating you these days?

[bow shot]

Howdy RAMOS

Well, I cleaned the bearing surfaces with a lint free wipe and alcohol, and have been paying (even) more attention to how the powder sits in the pan. Discerning between 0.1 gn of powder is still pretty difficult, but it is possible. I think it has to do with being at the very low end of the weight range. But at my budget level, I'll just have to be content with what I have.

I still obsess over getting the pointer EXACTLY on the mark, and ever 'couple rounds or so, I'll rotate the barrel and do a sanity check on what 0.1gn over/under will appear. As time and $ permit, I'll likely do the web cam trick, mainly for magnification.

[RAMOS]

I stil believe you got a pretty decent scale there. One thing I did a couple nights ago thinking about this was to take a 8X lupe and examine bearings and knife edges. The only other thing that I don't recall having been mentioned is to take a look in the slot where the copper tab on the beam sits in the main housing. That is where the damper magnets are. Just take a Q-Tip and swab it out, some times they will pick up tiny metal shavings. I don't know but, maybe enough of them would have an effect on the magnetic field?

[Fred_C_Dobbs]

bow shot, there are load development methods that lessen the impact make such minor differences in loads. Optimum Charge Weight, for instance, is specifically geared to selecting a load that is tolerant of the inevitable small variations.

My second point is that I'm thinking your problem is caused by the fact that, so long as it is in motion, the pan on a beam scale has inertia. And the pivot has some level of friction, even if extremely slight. The two combined can affect at just what point the pan comes to rest, depending on whether the pan is moving up or down when it finally comes to a complete stop. You might not be able to prevent what error this might cause but you can at least make the error consistent.

When you put your powder in the pan, push the pan down gently all the way to the bottom, then release it smoothly. That will tend to make the pan always be moving in the same direction as it finally reaches its point of equilibrium and comes to a stop. That does mean you can't just dribble the powder in the pan until the marks line up, so it might not be your ideal solution, but it does neutralize whatever error the pan's inertia might otherwise cause

[bow shot]

Ahhh! great input!

ok RAMOS, I'll look at the magnets with my Loupe tonight...great idea!

Good advice there, Fred, thanks kindly! I've done both the OCW and round-robin styles working up my golden round, so I'm confident on the charge target. I think you are on to something there with your beam inertia advice. I'll likely experiment with that too.

Lately, my method has been to place the pan in the holder, gently bottom out the beam, and introduce a slight pendulum-swing to the pan as it raises and I trickle... perhaps that's a step in the wrong direction. More experiments to follow.