How to drill through a hardened tang?

[Laurentius]

I have phoned the engineering department of the local college and the guy there has said he will take a look if I bring it in tomorrow.

 

[petrochemicals]

Whatever you do, do not drill pilot holes and then chase down them with larger drills trying to enlarge the hole. This is often repeated advice, and sort of works, but it makes for inaccurate holes and tends to trash the drill. Twist drills require the centre of the hole they are creating to keep them centred. Drill in a pilot hole and get shake and vibration and out of round hole. If the difference between pilot and final hole is too small, the bigger drill won't cut and just rubs its way down, then breaks. If you drill into a pilot hole the bigger drill encounters a sharp corner at the pilot hole edge and chances are it will chip. I have broken and damaged too many solid carbide twist drills, while in a press, attempting to enlarge holes in harden tangs to think its even remotely a good idea.


Use a chunk of steel underneath the tang, clamp it so that you can lean on your drill, drill through into the support block. The block will help cool the work. The only thing that drills hot is Stellite, everything else is better cool. That's why industry spends so much on spray cooling and cutting fluids. The support block also helps control break out and gives a cleaner hole. Does not need to be hard steel, some mild will do. Aluminium will too, but steel would be better in this case.


Good luck!

Thats a good point, the method is important, especially with people firing ideas at you.

Without the backer block of hard material, wood will not do(i know from experiaence), the burr as the hole is finished will likely snag the carbide bit and break the dril if your lucky. If your unlucky it will snag the work and either twist the work or twist the drill, and a very sharp knife rotating at 600 rpm is quite frightening. Or the drill is painful. Make sure the work is clamped immoveably !

 

[Shelley]

I have phoned the engineering department of the local college and the guy there has said he will take a look if I bring it in tomorrow.

Take beer with you, I know engineers.

 

[Stew]

How did you get on?

 

[Laurentius]

How did you get on?

He failed, he has still got it as he is going to get a more capable drill bit.

 

[Leshy]

+1 Bosch multi purpose bits.
They're the muts nuts ...


(No affiliation etc.)