A few weeks ago I went to a local estate sale and picked up 2 pair of Starrett dividers and a pair of Lufkin outside calipers. They were pretty rusty but the price was right, $15 for all three, and they were good brand name tools so I picked them up. You can never have enough dividers as far as I'm concerned. I'm starting to really see their usefulness in transferring measurements and laying out dovetails, among other uses. They're pretty cool tools and you can usually pick up vintage ones at a reasonable price. I could see myself developing a divider "problem" in the future.
Anyway, I was reading a post on WoodNet the other day where they were discussing de-rusting tools with citric acid. Vinegar was also mentioned as a good way to remove rust from tools. Hey, I have some rusty tools. AND Ihave some vinegar. Sounds like it's time for a little chemistry experiment. Well, I think I'd give myself a B- or a C in THIS Chem class. I'll let the pictures do the talking.
As you can see, the 10" dividers didn't fare so well. Cleaned up nicely, but I guess I left them in a little too long. From what I understand, vinegar removes the rust, but also eats away the good metal if the tool is left to soak to long. Hopefully I can find a spring to replace the broken one on the 10" dividers.
Other than that little snafu though, I'd say I was impressed with the de-rusting ability of plain old white vinegar. Just a very little bit of wire brushing after a soak and things cleaned up almost like new. If you try this, just remember to immediately blow the tools off to remove the water that you rinse the tool with. I used an air compressor but you could use a hair dryer also. After I blew them off I sprayed them down with WD-40 for good measure. All and all, even with the little mishap, not bad for $15.