I’ve almost used up all my CT-90 drilling and cutting oil, I have still some drilling and thread cutting to complete. Will engine oil do the same thing without blunting my drills and taps?

I think any oil/grease more or less works, from my machining class.

I use WD40 or similar with no probs at all when tapingout with my cordless drill but I spray it onto the tap not the material. Watch out for that emulsified oil (the milky stuff) I remember seeing a poster of someone with cancer of the scrotum coz he did’nt wash his hands before a wazz, it looked pretty bloody nasty.

It depends what you are drilling really. Brass need nothing, light oil for alloy, machine oil for steel.

Engine oil etc is not the same thing although might be better than nothing, you will notice the difference soon enough when you start drilling.
Try Cromwell Tools or ebay for proper cutting oil / grease.

Engine oil might not blunt the cutting edge, but the finish of the cut on eg mild steel will be extremely poor.

just mix Oil with Water thats all it is

I use ‘Rocol’ RTD – it’s very good