- Location
- Vancouver Island
Got a bit bored today, so decided on check out something I had been wondering about for a while: whether placing my weighing pan in different locations on my balance beam's weighing platform would affect the reading of the scale when dispensing powder.
I've noticed this seeming to be the case previously, but had mostly ignored the effect and concentrated on getting the pan consistently in the centre of the platform to (hopefully...) cancel out any impact of this.
Methodology: to be able to see exactly where the weight is located, instead of using my actual weighing pan, I used a scale weight that I could position relatively consistently in one of 9 locations: dead center, plus 3, 6, 9, and 12 o'clock a short way out from center, and 3, 6, 9, and 12 o'clock a bit further out. The outer set was probably about half an inch from center, the inner set was about half that.
I then zeroed the scale (an older RCBS 5-10 that looks a lot like the older Redding one, rather than the modern, angular 5-10) against a 20gram weight sitting in the center of the weighing platform.
Once zeroed, I started weighing and recording the results for each position to see if there was a pattern of where it would read high or low. I measured each location 10 times.
I discovered two things: a) there was a pretty clear pattern that location does matter, and b) there was more variability within each location than I was expecting OR comfortable with. Some of the readings had an extreme spread of more than a tenth of a grain (using the 20 gram weight).
At this point, I removed the weighing pan from the equation by taking the 20g weight and attaching it to a twist tie, and hanging that directly on the wire loop on the beam. My thinking was that this should take all possible variation due to weight location out of the measurements, as it's hanging pretty much straight down. I then re-zeroed the scale for this, and proceeded to record 20 measurements of this arrangement.
This resulted in an extreme spread of 0.15 grains amongst the measured values. NOT what I was wanting to see.
Prior to all the above measurements, I had cleaned the pivot points and lightly dressed the knife edges to remove a slight rounding where they contacted the v-grooves, being careful to maintain the same angle. As well, I ensured that the ends of the knives were not hitting the retaining plate - there's not much clearance on either side, but there was some on both.
The movement of the needle during each weighing makes me think that the problem is not with the knives/grooves - each time before the needle settled down, it moved in the same sort of pattern around the location it finally settled in - it didn't give an impression of stopping somewhere suddenly due to sticking. The problem was that both the pattern AND final location would both vary from one weighing to the next.
It really did behave like the weight was different each time, but that was not the case - it was the same test weight, hanging from the same point.
Any thoughts out there as regards what could be the issue here? You can't get much more simple of a device than a balance beam, but I'm completely at a loss to explain where the variability might be coming into play.
Thanks for any/all suggestions.
I'm really hoping this can be fixed without sending it to either RCBS or to Scott Parker, who has made a name for himself accurizing reloading scales.
(There's no crap in the magnets area, by the way - I made sure it was clear of filings/debris before starting.)
I've noticed this seeming to be the case previously, but had mostly ignored the effect and concentrated on getting the pan consistently in the centre of the platform to (hopefully...) cancel out any impact of this.
Methodology: to be able to see exactly where the weight is located, instead of using my actual weighing pan, I used a scale weight that I could position relatively consistently in one of 9 locations: dead center, plus 3, 6, 9, and 12 o'clock a short way out from center, and 3, 6, 9, and 12 o'clock a bit further out. The outer set was probably about half an inch from center, the inner set was about half that.
I then zeroed the scale (an older RCBS 5-10 that looks a lot like the older Redding one, rather than the modern, angular 5-10) against a 20gram weight sitting in the center of the weighing platform.
Once zeroed, I started weighing and recording the results for each position to see if there was a pattern of where it would read high or low. I measured each location 10 times.
I discovered two things: a) there was a pretty clear pattern that location does matter, and b) there was more variability within each location than I was expecting OR comfortable with. Some of the readings had an extreme spread of more than a tenth of a grain (using the 20 gram weight).
At this point, I removed the weighing pan from the equation by taking the 20g weight and attaching it to a twist tie, and hanging that directly on the wire loop on the beam. My thinking was that this should take all possible variation due to weight location out of the measurements, as it's hanging pretty much straight down. I then re-zeroed the scale for this, and proceeded to record 20 measurements of this arrangement.
This resulted in an extreme spread of 0.15 grains amongst the measured values. NOT what I was wanting to see.
Prior to all the above measurements, I had cleaned the pivot points and lightly dressed the knife edges to remove a slight rounding where they contacted the v-grooves, being careful to maintain the same angle. As well, I ensured that the ends of the knives were not hitting the retaining plate - there's not much clearance on either side, but there was some on both.
The movement of the needle during each weighing makes me think that the problem is not with the knives/grooves - each time before the needle settled down, it moved in the same sort of pattern around the location it finally settled in - it didn't give an impression of stopping somewhere suddenly due to sticking. The problem was that both the pattern AND final location would both vary from one weighing to the next.
It really did behave like the weight was different each time, but that was not the case - it was the same test weight, hanging from the same point.
Any thoughts out there as regards what could be the issue here? You can't get much more simple of a device than a balance beam, but I'm completely at a loss to explain where the variability might be coming into play.
Thanks for any/all suggestions.
I'm really hoping this can be fixed without sending it to either RCBS or to Scott Parker, who has made a name for himself accurizing reloading scales.
(There's no crap in the magnets area, by the way - I made sure it was clear of filings/debris before starting.)
