OT: Drilling armor plate ?

[SScnc]

A buddy has a bullet backstop that has AR500 steel plate as the back, it's also got a 3" layer of rubber glued to the plate. we need to drill a couple of holes in it.

I used a brand new 5/8" Cobalt bit and it started off cutting fine, very low RPM and cutting oil, as soon as it reached the depth of the angle of the tip, (about 1/8" deep) it stopped cutting at the point completely. I know a smaller starter hole would help but this 5/8" bit was 38 bucks and didn't want to buy any additional at the time.

What type of drill bit can be used to drill this AR500 plate ?

Thanks,

Steve

[Dano523]

EDM or blow your holes in it with a plasma or water jet cutter.

Short of such, you would need to anneal the metal to drill it (get the metal softer than the drill bits your using), and you just defeated the purpose of using it in the first place.

[knudsen]

50 cal. armor piercing bullet

Try a cheap carbide tipped mortar bit. You definitely want a pilot hole. Mild steel is hard to drill without a pilot hole. The cobalt may have worked if you had drilled 1/8, 1/4 then the 5/8. Smaller cobalt's are not near as expensive. But carbide is you best bet short of what Dano said.

[jbcman]

Dano523 has it right annealling is your best bet. I do alot of drilling n tapping ar400 was changing drill almost every hole till tried annealing work fine after that.