beam scale mystery

[oley55]

A few years ago I bought an O'Haus 505 scale. It was an older scale but unused in the box. In other words new - old stock. Worked wonderfully for a long time. Set it aside to dabble with electronic scales. An electronic scale can have drift and are very delicate I decided to get the 505 beam scale out and it now has a problem. The beam "sticks" in the lower half of its travel/swing. I have tried cleaning the agate V blocks, stoning the knife edges, graphiting the knife edges(rubbing with pencil lead). Now I am at a loss. I would like to have it working reliably to allow double checking the electronic scale periodically. Is there anything else I could do? Thanks in advance.

if you haven't fingered it out yet, I am guessing (as mentioned) the copper vane is just barely rubbing against the back wall inside the slot. DO NOT start removing material. Rather turn it upside down and you will find a 1/4" bolt which holds the pivot in place. Loosen just a bit and you will be able to twist the pivot counter clockwise ever so slightly so the vane stops rubbing. Snug the bolt back up and your are back in business.

edit added. my fix is for the top pic as provided by "1066".

 

[oley55]

View attachment 1146247
Must be one of the differences in 10-10 & the
10-05.
I'm wondering what that lil brass bolt is under your ohaus?
BTW I love my scale, thanks Jim!!

chiming in here. The lil brass bolt holds the point register (or what ever it's called). Just like the lil silver bolt holds the pivot in place. These 505s are different from the 10-10s in that the pivot and register are bolt attached to the scale body, while the 10-10s are a single cast into/with the scale body. That said, the 505 should have been much cheaper/easier to manufacture.

 

[strut64]

I finally figured it out. My attempt to stone the knife edges was not working. The stone was not hard enough. I got out a Fine India Stone and worked them over. Those knife edges are very HARD.

 

[fyrewall]

Don't mess with the hardened pivot edges other than to clean them up. My RCBS 5-0-5 scale should be a copy of the OHAUS 505 scale. It appears to be identical to the OHAUS 5-0-5 scale shown in 1066's post. If it is, the copper vane thingy intended to dampen beam movement by interrupting the magnetic field is simply press fitted into a slot in just in back of the pointer line - no bolt. Flipping the scale over and peering into the body of the scale, near the beam pointer end - two tiny magnets may be seen wedged in and held at the bottom with a stainless? U shaped clip, the top which is secured by a 1/4 inch Philipps screw. The magnets provide a magnetic field which provides resistance to movement of the copper vane thingy.

 

[Rsadams]

I finally figured it out. My attempt to stone the knife edges was not working. The stone was not hard enough. I got out a Fine India Stone and worked them over. Those knife edges are very HARD.

Next time you need ceramic to sharpen them....