Can I use WD40 as a wood finish, or am I an idiot?

I did it once and it seemed to semi-work. I have no idea what the properties of a wood finish are and am limited in my woodworking skills

There are a lot of option to finnish wood - WD40 is not amoung them ;)
If you want oil try boiled linseed oil, gives a really nice finnish when dry.
To finnish off the wood:
Sand with the grain structure - not against it.
Use white vinegar after each sanding session to make the remaining fibres stand up.
Sand with finer paper after each step.
When done the wood will be so smooth that a good oil finnish will look just great.

No. WD40 leaves toxic residues, some of which can pass through the skin barrier. Choose something else. Preferably food safe.

seandogue1 year ago

I often use simple mineral oil. It does evaporate with time, but it's odorless and available at your local grocer (sometimes) and pharmacy. It's also pretty safe for use on food utensils.

I no longer use linseed due to a developed sensitivity to its (imo) over-powering "aroma" after using it on various carvings for about two decades and teh lingering smell of it in my at the time workshop. A good whiff gives me a headache now.

And for the record, Linseed oil is known to be quite hazardous due to it's tendency to generate combustion in "soaked" rags, when they're stored in a warm area.

rickharris1 year ago

WD40 contains materials that will go stick after the solvent has dried out. Not really what you want in a wood finish.

Go with DU35m's suggestions.