Thread: Trying to drill Very hard metal

I think the OP is drilling the plug for lockwire which would be .032" maximum requiring a 1/16" hole so a masonary drill will not work. If this is a genuine aircraft part it would most likely be made from chrome moly which work hardens very easily if drilled at too high speed, try around 400 rpm for hss drills.

Lex.

Originally Posted by BobL

Get yourself a brand new tungsten carbide (masonry) bit.
Use slow (<200 rpm) speed and lots of lube.
Ideally you need a high pressure such as you would get via a drill press and use very steady pressure.

Thanks Bob went through no trouble certainly was quite good quality steel the plug was for a corvair engine like a Volkswagen engine with two more pot'sonce again thanks for your help.David

Originally Posted by woodfast

Thanks Bob went through no trouble certainly was quite good quality steel the plug was for a corvair engine like a Volkswagen engine with two more pot'sonce again thanks for your help.David

Sorry, I cannot see how a standard masonry bit could drill through hardened steel or even mild steel?

A masonry bit has no cutting edges?

woodfast, what size hole did you drill and can you show us a picture of the drill bit you used please?

Originally Posted by shedhappens

Sorry, I cannot see how a standard masonry bit could drill through hardened steel or even mild steel?
A masonry bit has no cutting edges?
woodfast, what size hole did you drill and can you show us a picture of the drill bit you used please?

I have cut several dozen holes from 5 mm to 8 mm through the very hard stuff used in the nose bearings of chainsaw bars with masonry bits. The bit effectively scrapes its way through the metal using the method I described above. I say scraped, because the chips generated look much more like scrapings than twist drill swarf. The bit does the same through mild steel so is of course much slower than a twist drill. Notice I also said "new" bit in my first post which normally has enough of an edge to perform the scraping. Old bits can be used but the carbide needs to have enough of the edge restored to do the job.

A problem can arise at breakthrough where the edges of the hole can grab and snap the carbide. To reduce the possibility of this I usually drill to breakthrough and then drill from the other side. disintegrating the carbide. I have probably wrecked 3-4 bits either because of this problem or by pushing too hard. Most people that try this do not push hard enough but it is also possible to push too hard thereby totally disintegrating the carbide