5 0 5 scale trouble

[shoot57]

just trying to zero my rcbs 505 scale and noticed that i set the zero and every time i tap the beam the pointer never comes to rest in the same place, any suggestions on why this is happening?

[Cambsman]

Because you are tapping the beam?...... I'll get my coat............

[shoot57]

ok, just tried blowing on the beam, same result

[Blunderbuss]

Is the blade at the end of the beam running centrally in the magnetic damper slot?

[shoot57]

no not dead centre, its closer to the pointer end of the slot, i would say a 1 ml gap and a 3 ml gap the pan side approx

[Floating Chamber]

Are the agate bearings clean?

[Redgum]

Hate to state the obvious, is it on a level surface,give the bearings a little dust with a small paint brush.

[1066]

If you're sure the damper isn't actually touching the bodywork then it shouldn't be a problem, just check that there are no hairs of wirewool in the slot that the magnets have picked up. The bearings need to be clean and should be free to wobble about, if your not happy with them, take them out and give them a clean is some sort of spirit and a toothbrush, also clean the bearing housings.

 

Have a look at the knife edges through a glass, they should be sharp with no dull areas or burrs, also the ends should come to a sharp point, inline with the knife edge. If they are dull then a very careful dressing with some 1200 grade wet &dry will do the trick. I use it stuck to a flat strip of metal with double sided tape to make a small "file".

 

Have a look at the little wire loop where the pan hangs, it should be free to swing, right in the middle of the tiny knife edges there.

 

Here's a video I made about tuning up the RCBS scales:

 

[sackot]

Nice video-- can you tell us what the deal with your improved pan-hanger is?

 

I'm interested in the OP's problem because I have one quite similar with my 505 when used with your trickler. I will set it to throw a charge, and 9 times out of 10 it will be spot on, and the other time significantly over. I've watched it do this, and the symptom is that when the quantity is approached, the beam hesitates to lift from the bottom, then moves up sharply and overshoots. It's behaving as though there is some friction there, but in my case, not always. I looked at all the obvious things but was never able to see anything wrong.

[Vince Green]

I have had some funny problems in the past that has been down to a tiny bit of grit in the V on which it pivots. Other than that there are no moving parts that touch so there's not a lot else.

[1066]

Nice video-- can you tell us what the deal with your improved pan-hanger is?

 

I'm interested in the OP's problem because I have one quite similar with my 505 when used with your trickler. I will set it to throw a charge, and 9 times out of 10 it will be spot on, and the other time significantly over. I've watched it do this, and the symptom is that when the quantity is approached, the beam hesitates to lift from the bottom, then moves up sharply and overshoots. It's behaving as though there is some friction there, but in my case, not always. I looked at all the obvious things but was never able to see anything wrong.

 

Ahh!. Stuck at the bottom syndrome. This happens on a few scales where the beam is a little "top heavy". The way to fix this is to stop the damper blade bottoming right out in the damper slot. I place a small strip of felt or even polystyrene in the bottom of the slot, only about 1-2mm thick to act as a buffer. This also stops the damper blade crashing down every time you remove the pan - It sounds better, feels better and works better.

 

Here's my idea about the pan hanger.

 

http://img.photobuck...tirup070510.jpg

 

Dull knife edge. Easily fixed.

http://img.photobuck.../Knifeedge2.jpg

Chipped knife edge. Not easily fixed.

http://img.photobuck.../Knifeedge1.jpg

Edited November 23, 2012 by 1066

[shoot57]

thanks for the feedback and tips, on checking with a spirit level i found that the surface my scale was on was not quite level, so moving to a level surface seems to have cured the problem. it seems strange that such a small change in angle causes this problem as you adjust the level for a start. so thanks redgum for stating the obvious, and thanks 1066 for your pics

[sackot]

Ahh!. Stuck at the bottom syndrome. This happens on a few scales where the beam is a little "top heavy". The way to fix this is to stop the damper blade bottoming right out in the damper slot. I place a small strip of felt or even polystyrene in the bottom of the slot, only about 1-2mm thick to act as a buffer. This also stops the damper blade crashing down every time you remove the pan - It sounds better, feels better and works better.

 

Here's my idea about the pan hanger.

 

http://img.photobuck...tirup070510.jpg

 

Dull knife edge. Easily fixed.

http://img.photobuck.../Knifeedge2.jpg

Chipped knife edge. Not easily fixed.

http://img.photobuck.../Knifeedge1.jpg

 

"stuck at the bottom syndrome"! I know what to call it now.

 

Thanks for that 1066, that sounds exactly right and the fix easy to try-- I'll give it a go next session. Making a replacement loop looks slightly more tricky, but I'll see what I can do.