It's easy to come across a box of old files or rasps at yard sales or markets. These are normally a bit rusty and maybe a little dull. It's actually possible to clean these up and sharpen them.

Supplies

Required

White Vinegar
Dish scrubbing brush
Dishwashing liquid or soap
Something pointy

Optional

Pressure Washer
Dish Washing machine

Step 1: Take the Handle Off

You should be able to carefully knock the handle off the rasp without damaging it. You can reuse this later if you want or replace it, I'll be replacing mine since it's already damaged.

Step 2: Cleaning

As an experiment, I used a pressure washer to clean off the rasp as there was a fair amount of old material clogged in the teeth. It worked pretty well and removed nearly all the debris. I then carefully picked out the remaining material.

Please don't use a wire wheel to clean up the rasp as it will damage the rasp!

If you don't have a pressure washer you can give it a good scrub down with soapy water or you can stick it in the dishwasher. I didn't try the dishwasher as my Wife wouldn't like that, if you try it let me know how it worked out.

Step 3: Acid Sharpening

Now soak the rasp in vinegar overnight or for a day. These will also clean off any remaining rust as well as sharpen the rasp. If it's still rusty you can soak it a bit longer if needed.

Step 4: Wash, Rinse and Oil

Now rinse off the rasp in water, I've heard some people say to neutralise the acid with water and baking soda but I've never done that. In my experience washing the rasp in soapy water and rinsing it off gets rid of all the acid/vinegar.

Now thoroughly dry the rasp and give it a light oil to stop it rusting.

Step 5: Fix the Handle

When I originally started this project I was going to make a new handle, but I figured this was a great opportunity to show how to fix a handle.

The first step is to flatten the broken part of the handle, I recommend you carefully use a plane to cut the handle back until it's smooth and flat.

Now select a piece of wood to make the repair with, I'm using a small piece of dried walnut. Use an axe to split the wood in half and plane the wood flat. Use a pencil to trace around the handle and then quickly saw the wood to the approximate size.

You can now glue and clamp the wood onto the handle. Once the glue has dried you can use a knife or rasp to bring the patch to a rough finish. Now finish smoothing the patch with a file and sandpaper.

Lastly, apply some oil to protect the handle, I used Linseed oil.

Step 6: Put the Handle Back On

Now put the handle back on and try it on and you have completed the repair. If the handle is lose may need to use a small amount of glue to tighten it up, I recommend 5-minute epoxy.