Drilling hardened steel

Will a carbide drill drill through a piece of air hardening steel that was hardened to a Rockwell hardness of that of a drill bushing? Or will it have to be edm'd?

For the hardened drill bushings I've seen this side of the pond, EDM.

A carbide die drill will make holes in steel up to Rc 65 no problem, even deep holes. A carbide die drill is not the same thing as a carbide twist drill, a carbide tipped twist drill or the infamous masonary drill some have mentioned in other threads.

This link has a photo and a bit of information to familiarize you with the tool, it's not meant as a recommendation of the vendor.

http://www.newmantools.com/drills/drctdie.htm

A solid setup and machine are required.

drilling out broken taps

we use carbide spade drills to drill out broken taps. they work best on shallow holes but they do work. it helps to have extra drills. they tend to break or chip more easy so you have to be gentle with them.

Flood coolant worked better for me than dry when drillng. I used a die drill to drill punch dies to install pilots.

Get two drills. Not enough pressure and it won't cut, a little too much pressure and the drill shatters! I was using a .125" drill though.

A straight flute carbide drill as shown above would be best for drilling out bushings.

I have used resharpened masonry drills with a negative rake for non serious holes,such as drilling holes through large HSS hacksaw blades to make rivet holes for knife handles. Or,for drilling through a file to attach a wooden handle on 1 side for filing guitar frets. Masonry drills work for these type jobs. However,their brazed tips can get too hot,and let go. Also,for drilling through HSS power hacksaw blades,I have found it necessary to resharpen the tip for each hole,or the drill pops the hacksaw blade in two.

Those were the non critical jobs I have done with masonry drills,Dave,and they work fine for that. So,if your little face was for me,take it elsewhere.

Also depends on how much you have to open it up. Up to .015 or so, lap it out. If it is more, send a carbide reamer thru it. If you have a grinder, making a 2 or 4 sided reamer is not too tough. Or resharpen a masonry drill into more of a reamer, even it you have to step thru 2 or 3, it is easier on the tool.

gwilson said:

A straight flute carbide drill as shown above would be best for drilling out bushings.

I have used resharpened masonry drills with a negative rake for non serious holes,such as drilling holes through large HSS hacksaw blades to make rivet holes for knife handles. Or,for drilling through a file to attach a wooden handle on 1 side for filing guitar frets. Masonry drills work for these type jobs. However,their brazed tips can get too hot,and let go. Also,for drilling through HSS power hacksaw blades,I have found it necessary to resharpen the tip for each hole,or the drill pops the hacksaw blade in two.

Those were the non critical jobs I have done with masonry drills,Dave,and they work fine for that. So,if your little face was for me,take it elsewhere.

Click to expand...

Ditto, All I buy are straight flute carbide drills. I have even used them to drill out the center web of broken taps. I would recommend alternating between coolant and air blast to get the chips out

I have used the straight flute carbides for reconfiguringing hardened dies. I find a peck-drilling technique works well. Be careful and don't use too much pressure especially when you break thru on the other side or you will shatter the drill.

RHC - Rockwell Hardness C

HSS Drill Bits - Work well up to the 50ish RHC
Drill - Mild steel, Some tool steel, Some Spring Steel
No Drill - Hard Plate, Anti Drill Plate, 404c Stainless Steel
Pro - Good in Hand Drills and most drilling applications
Con - Has limitations in hardened steels

Cobalt - Works up to 58ish RHC
Drill - Mild Steel, Some Spring Steel, Some Tool Steel
No Drill - Hard Plate, Anti Drill Plate, 440C Stainless Steel
Pro - Good for hand drills and most drilling applications
Con - Has limits with hardened steel

Carbide Tipped - Will drill almost any steel, Hard, Stainless or Mild.
Pro - Drills all steel
Con- Blunt tip requires extreme pressure to produce cuttings. Drill bit is hard to start on all steels.

Diamond Coated Drill Bit - Cuts on most steels(Not Hard Plate) just not for long.
Pro - Will Drill most steels (Not Hard Plate)
Con - Cutting stops quickly after diamond grit has warn off, Then behaves like HSS bit

Solid Carbide Drill Bit - Cuts all steels.
Pro - Sharpened points wont "walk" like carbide tipped bit. Cuts all steel
Con - Sharp tip and fine edges can chip easily and ruin drill bit. Not for hand drills. Expensive!

For more information enter “The Ultimate Guide To Drill Bits” ____ Tube video into your favorite search engine and watch the video.