This is one of the easiest, safest, and least abrasive ways to remove surface rust from old steel tools.

Supplies:

Citric Acid Powder (available at drug stores or grocery stores as a health food supplement or a baking ingredient)
Warm Water
Container
Scouring Pad / Brass Brush
Rusty Parts

Safety:

Rubber gloves are a good idea
Don't splash it in your eyes

Precautions:

Do a test before trying this on something important - I've noticed it caused a swan chisel to turn very slightly yellow.
Do not try this on something like a saw blade with an etching you want to preserve - it might disappear.

Other Ways to Remove Rust:
Wire Wheel on a Grinder - this is probably the quickest way to remove rust, but it's still abrasive, so be careful around logos you want to keep.
Electrolysis - works well, but you have to be careful with batteries and water. not for the novice.
Sandblasting - very quick, but can leave a rough finish depending on the media. requires masking on painted parts.
Sanding - tedious and dirty and removes metal, but it works. sanding in very tight places can be impossible.

Advantages to using Citric Acid:

Does not remove painted finishes.
Less messy.
Requires nothing you don't already have in the kitchen.
Can be poured down the sink (citric acid is the main ingredient of some biodegradable cleaners).
Way cheaper than sandpaper.

Step 1: Clean the Parts

The rust on this wood plane wasn't too bad. The chip breaker was the worst part, but it was mostly just thick surface rust.

The first step is to clean off any dirt with water and a sponge.

Step 2: Prepare the Solution

Find a container that is large enough for the parts to lay down flat. This way you only need to cover them with a shallow pool of water.
Place the parts in the container and cover them with warm water.
Add the citric acid powder and stir it in. Experiment with the proportions here. I used probably a 1/2 ounce of citric acid with 15 ounces of water.

Step 3: Wait, Scrub, Wait, Scrub

After a few minutes small air bubbles will form on the part from the chemical reaction.
After 30 minutes or 1 hour you may see flakes of rust in the solution.
Scrubbing the parts with a scouring pad or brass brush will speed things up.
There will be a black haze on the part, but it will scrub away.
The blade and most of the screws were ready to come out after 1 1/2 hours.
Add more citric acid to the solution if needed.
Wait, scrub, wait, scrub until the rust is gone.

I left the chip breaker in for 7 hours with no damage. A very lightly rusted part should be rust free after 30 minutes and some scrubbing. A moderately rusty part only needs 2-4 hours depending on how often you scrub it.

The solution can be poured down the sink when you're finished.

Step 4: Oil the Parts

After removing the parts from the solution, rinse them off with water and dry them thoroughly.
Oil everything or the rust will reappear when the parts get wet. I used camelia oil, made for rust prevention, but any oil is better than nothing.

What's really nice about this process is that the rust is removed even in hard to reach places, and it helps preserve the original markings without over-restoring the part. The finish is a little bit dull straight out of the acid, but can easily be shined up with fine steel wool or fine sandpaper.

Step 5: Before / After

The before and after results are pretty dramatic considering how little you need to scrub the parts.

I wanted to share it here because it would have saved me countless hours of sanding over the years!