Replacement Magnets for Chinese RCBS 505?

[flyingbrass]

The TLDR for this: What magnets should I use to replace the crappy ones in my Chinese 505 scale?

I have a Chinese RCBS 505 that I bought a few years ago. I recently "tuned" it by cleaning the bearings, lightly polishing the insides of the bearing caps, lightly polishing the nubs the agate bearings ride on in the scale body, stoning the knife edges, polishing the insides of the pan hanger wire loops, adding a brass pointer slightly set out from the beam face to clear the zero plate, and adjusting the weight in the pan holder to level the beam. I bought a cheap webcam like thetargetmaster uses in his Youtube videos (works great for the purpose). I use VLC to view the video stream from the webcam on my computer monitor fullscreen from about 10 feet away from my loading bench.

Since the webcam arrived this past week I've done some testing. I take screen captures in VLC, open several of the resulting images in GIMP, view at 800%, adjust opacity so I can see the pointer tip positions in the images, then use the measuring tool to measure the number of pixels between pointer tips.

I calculated pixels per tenth of a grain by capturing images while moving the tenth slider weight up and down. I measured the distance of the pointer tip between each tenth and also took the average of wider spans. The way I had things set up, .1 grain was an average of 27 pixels.

I put 3 .177 caliber pellets in the pan with the beam weights set to 21.4 grains, which put the pointer close to zero. I removed the pan, held the beam down while replacing the pan, then lightly bumped the beam down before releasing the beam. This is how I normally use the scale. When the pointer settled I took a snapshot.

Often, watching the big fullscreen image, the pointer never did completely settle. In those cases I captured an image in the middle of its range of sway. This balance is almost annoyingly sensitive. Walking up to or away from it, even slowly, makes it move -- and it keeps going. Other air currents that I can't even feel send it moving out of the blue. This is with the A/C turned off and the door to the room closed. Forget trying to use it when the A/C comes on.

I repeated this pan removal and replacement test 10 times while being extra careful. I set the pan in the holder gently, trying not to disturb the pan hanger wire. The extreme spread of the pointer position was 5 pixels, which in this case was about .185 of a tenth of a grain. That is extreme spread. Most of the 10 were closer.

I tested again the same way with 20 weighings, and not being so careful. I jostled the pan hanger a few times, moved the beam sideways, etc. The extreme spread of the pointer tip was 6 pixels, or about .22 of a tenth.

I've done other tests of smaller sample sizes that came out even better. I've also had similar results after trickling powder up, then removing and resetting the pan. Precision seems to be extremely good.

My main issue with this scale is that the damping magnets are weak. Compared to my old Hornady (Pacific) balance, this pointer sways forever. A friend has an older American made 505 that has more reasonable damping.

I'd like to replace the magnets in mine. I've done some searching and reading, including here about magnets in scales. I haven't found anything specific about magnets for 505s. The factory magnets in mine measure .844" x .242" x .216". The slots in the scale body for them are wide enough to accommodate 1/4" x 1/4" width magnets by probably up to an inch long.

I tried to test the pull force of the Chinese factory magnets. I measured about 7.2 to 7.4 ounces before one slid/pulled off a steel plate.

Neodymium magnets come in different grades. I'm leaning toward magnets polarized through their thickness that are 3/4" or 1" long x 1/4" x ? with a pull force of less than 10 lbs. each. But, I don't know how much strength is needed for adequate damping that isn't overkill. Maybe any neodymium magnet would be more than I want.

I understand how damping works, and that its effect is zero when the beam isn't moving. However, I'd like the beam to rise and fall a time or two before settling. I suspect that a few beam movement cycles before settling help center the knife edges on the bearings and also perhaps level the bearings themselves, which may contribute to consistency. Or maybe not. Has anyone tested the strength of damping on repeatability? Has anyone replaced the magnets in 505 scales? What were your resutls? Funds are tight, and I don't want to pay $15 for magnets that turn out to be the wrong kind, then maybe need to pay that much again for the right ones, so any advice is welcome.

 

[Rsadams]

Boyd Allen is who you want to talk to..... If you use the search feature you will find a few post he has on these scales , mainly the 10/10 etc.... He helped me alot with the newer 10/10 scale....

 

[BoydAllen]

Someone gave me a new Chinese 10-10 to play with some time back, and after tuning it, I tried to use some different magnets to increase damping, without success, and put it back on the shelf. The only thing wrong with it is that it takes a bit longer to settle than my Ohaus built scales. I have three, which is why I have had little incentive to go back to this scale. A little while back someone posted that he had figured out how to get the magnets (of a Chinese RCBS scale) closer to the copper blade. I need to look at mine and see if I can figure out how to do that.

 

[flyingbrass]

I tried flipping the existing magnets around so the flat sides were closest to the copper blade. I didn't notice any difference.

 

[flyingbrass]

I figured out what the problem is with the magnets in the Chinese scale. One is defective/weak. Earlier I had only tested the strength of one of my magnets. I (wrongly) assumed they were both about the same.

A friend has an older American made 505. A few years ago, about the time RCBS came out with the M500 scales, 505's were cheap on closeout. We each bought one of the Chinese 505 models. Today I borrowed both of his scales to compare with mine.

To compare magnet strength I put a steel plate on a kitchen food scale. I attached a magnet (flat side of the magnet down), tared the scale, then lifted using my fingers while watching the readings until the magnet pulled loose. I did this multiple times, trying for the best pull. I think fingers work better for this than a string because you can try to prevent the magnet from tipping and giving a low reading. Still, this doesn't give super consistent results, but it's close enough for comparison.

Magnets in my Chinese 505:
#1 10.2+ oz. (it lifted the plate I was using)
#2 1.8 oz.

Magnets in friend's Chinese 505:
#1 10 oz.
#2 2.7 oz.

Magnets in friend's American 505:
Both about 9.7 oz.

I wonder if the Chinese outfit making these scales had a bad batch of magnets and decided to put a good one and a weak one in each scale. Whatever the case, two 10 oz. magnets dampen adequately. The copper on the Chinese beams is about the same size as the older American beam, though ever so slightly thinner (.059" Chinese, .065" American). The Chinese beams dampen well when placed on the body with the American magnets.

For what it's worth, I did a short test of my friend's Chinese scale. He had touched up the knife edges, but hadn't done anything else. I cleaned the bearing grooves and knife edges with alcohol on a Q-tip , then tested. I put three .177 caliber pellets in the pan and set the poises to 21.5 grains. I removed and replaced the pan 10 times. taking a screenshot each time. Pointer tip distance between highest and lowest was about 7 pixels, and tenths are running about 28.5 pixels. So, that's quarter of a tenth repeatability before doing anything else to the scale. Not bad.

 

[flyingbrass]

Updating for others who may find this:

I put the two good Chinese magnets (both ~10 oz. each of "pull" the way I measured) in my scale. With these, I think the damping is about right. The beam went from about 9 major swings before settling (counting each change of direction), to about 6. This was releasing the beam from bottom with 21.5 grains of weight in the pan. Determining exactly when the pointer has mostly settled is somewhat arbitrary, but I'm ok with the amount of swing I'm getting with two proper magnets of factory strength.

I tested repeatability of my scale with both magnet setups. I trickled up, then removed and reset the pan twice taking screenshots each time. I measured the number of pixels that the tip of the pointer varied from where it had been after trickling. Though the sample size was small, I didn't notice any significant differences. I had good repeatability between trickling and resetting the pan. The average difference was a little under .1 of a tenth, with an ES of .23 of a tenth over 10 trickles (2 pan resets each trickle).

My friend's Chinese beam settles slightly quicker than this in his older American scale body with its roughly equivalent (~ 9.7 oz.) magnets, but his beam is also less sensitive and less repeatable than mine. I suspect the difference is that he hasn't cleaned and polished things yet as I have.

 

[mac86951]

Hmm, I'm tempted to call K&J magnetics and try some neo magnets. That would probably overdamp though and that could be bad.

-Mac

 

[flyingbrass]

FWIW, here is how I added a pointer to my beam. I wanted to use something non-magnetic. All I found on hand were some small brass safety pins. Their diameter was right, but the straight part was a little shorter than I wanted. I've read that some dressmaker needles are plated brass. I would have gone that route if I didn't already have these safety pins.

To stand the pointer away from the beam I used plastic pin headers, as used on circuit boards. I cut them off from the strips they came in and pulled out the exisitng pins. Fortunately, the safety pin diameter was a snug fit through the original pin holes. I wanted two pin headers to straddle the crimped portion of the copper damper. Due to the shortness of my straight piece of safety pin, I had to file one of the plastic headers so it would fit over the damper. This wasn't easy or fun, but I got it done. After some trials using tape to make sure positioning was correct, I attached using Superglue. It's not pretty, but should hold well.

 

[1066]

Well Flyingbrass, it certainly looks like you're getting good results from your 505. I'm pleased you found some of the videos concerning scales on my youtube channel (thetargetmaster) useful.

Concerning the damping magnets, I've found it's more a matter of "suck it and see" rather than trying to predict what you will need. Very often I have found that replacing the original magnets with new "rare earth" magnets is just too much damping, ending up with a scale that responds like a dead fish, I much prefer to see two or three oscillations before coming to rest.

I have found just replacing one original magnet with a neodymium magnet sometimes give the "right" degree of damping - I have also found that I can grind the magnets down to give the required damping effect with a green grinding wheel used for TCT lathe tools.

One thing to think about if you are planning to use stronger neodymium magnets in a 10/10 scale. Although the beam and damper blade are non-magnetic the little stud where the auxiliary weight hangs is just plain steel, although with original magnets it doesn't seem to have any effect on the operation of the scale, with stronger magnets it can have influence.

I was recently working on a nice old 5-10 (exactly the same beam as the 10/10) that was giving very erratic results, after a bit of head scratching I found that the screw that holds the damper blade in place had been replaced by a steel screw rather than the non-magnetic one that should be there.

 

[Macropod]

Hmm, I'm tempted to call K&J magnetics and try some neo magnets. That would probably overdamp though and that could be bad.

-Mac

There is no influence when the beam is stationary so you should be ok.

 

[flyingbrass]

1066, thanks for your videos. I also thank you and others, mostly members of this forum, for posting information about tuning scales. If a guy doesn't have the money for a fancy MFR, a little work can make a beam scale not too far behind in repeatability, which is my primary concern. Accuracy is another matter.

Precise powder charges aren't always needed, but I'm presently working up .223 loads for an AR-15 intended for 500+ yards.

There is no influence when the beam is stationary so you should be ok.

I think too much damping could be a problem. The beam gets jostled to some extent when removing or resetting the pan. When the beam is allowed some oscillations its knife edges can resettle into the bearings. And with scales that have floating bearings, a reasonable amount of beam movement will allow the bearings to level.