Drill bits for Metal

[David S.]

This weekend I had to drill out three studs on a cast iron exhaust manifold. What seemed to be an easy job as the first stud was replaced in about 15 minutes, took several hours longer than it should have. My run of the mill Dewalt bits became dull and then I proceeded to break a few. While the bits say they are made for wood or metal, clearly not metal.

Does anyone else have experience in drilling into metal? What bits do you use? I seldom do a job like this, but when I need to, I want to have the right equipment.

Thanks,
Dave

[Joe L.]

Re: Drill bits for Metal

This weekend I had to drill out three studs on a cast iron exhaust manifold. What seemed to be an easy job as the first stud was replaced in about 15 minutes, took several hours longer than it should have. My run of the mill Dewalt bits became dull and then I proceeded to break a few. While the bits say they are made for wood or metal, clearly not metal.

Does anyone else have experience in drilling into metal? What bits do you use? I seldom do a job like this, but when I need to, I want to have the right equipment.

Thanks,
Dave

Dave------


Here's the problem: the exhaust studs undergo extreme hardening as a result of the extreme heat and cooling cycles. So, they are not just steel, they are rendered extremely hard steel. Standard drill bits, including those specified for drilling "metal", do not work well on such hardened steel. Special drill bits designed for use on hardened steel are needed. Generally, you won't find these in a hardware store. You will need to source them from an industrial supplier like McMaster-Carr or a machinists supply vendor.

[Gary R.]

Re: Drill bits for Metal

I use High Speed Steel bits and they work well. As Joe mentioned when you get into something hardened you are going to roll the edge. The first thing we were taught in trade school machine shop was how to sharpen drill bits by hand on a pedestal grinder. I had a similar problem one time with a rust seized differential bracket bolt. The diff came to me to rebuild but the bracket was still on because the bolt wouldn't move. I figured I would just press it out, but that didn't work and I didn't want to crack the diff housing. Then I cut off the bolt head and other end and removed the bracket, leaving the bolt body flush in the diff hole. So then I figured no problem, I'll center it in the Bridgeport and drill it out. Well that worked about 1/4" and rolled the HSS bit. So I flipped it over and tried to drill it out the other side, that also rolled it, then I tried to plunge mill it, that rolled the endmill! So I turned a piece of steel to make a lon punch, then heated the housing cherry, then installed the punch and gave it a shot and that broke it loose and out.

[Bill W.]

Re: Drill bits for Metal

try cobalt bits .

[Bill M.]

Re: Drill bits for Metal

i have grond the studs flat and welded a new nut to the stud from inside the nut. if you have acess to the threads from behind add candle wax it seaps into the threads and helps lubricate.

[Gary C.]

Re: Drill bits for Metal

Dave, buy good drill bits from MSC, Grainger, McMaster-Carr or SnapOn. I have a set of Thunderbit 118 degree split point bits. Gary....

This is what I was told years ago; use Carbide bits for drilling hard steel, but are brittle and can be broken easily. Cobalt bits will out last steel bits for regular metal drilling. As with any tool, there are different grades of drill bits.

[Patrick N.]

Re: Drill bits for Metal

When I worked at both B&D and Stanley / MAC, developing tools we'd benchmark every type of tool imaginable as a group. One brand that sticks in my mind that you might want to check into is Artu Profi-Line drill bits for impressive results and speed when drilling harden steel. Artu is a German company, bits are reasonably priced and can be used in a standard drill press set at a high speed. The bits are a blend of Cobalt and Tungsten Carbide. The bits look like masonry bits- those are the ones you want.
Cobalt is also preferred as mentioned above.

[Gene M.]

Re: Drill bits for Metal

When I worked at both B&D and Stanley / MAC, developing tools we'd benchmark every type of tool imaginable as a group. One brand that sticks in my mind that you might want to check into is Artu Profi-Line drill bits for impressive results and speed when drilling harden steel. Artu is a German company, bits are reasonably priced and can be used in a standard drill press set at a high speed. The bits are a blend of Cobalt and Tungsten Carbide. The bits look like masonry bits- those are the ones you want.
Cobalt is also preferred as mentioned above.

Most of these type bits mentioned above have a shallower point angle for better cutting in tuff steels. I have a few solid carbide bits. The bad part is they need to be sharpened on a diamond wheel which I don't have.

[Domenic T.]

Re: Drill bits for Metal

Gary,
The heat trick works great. when I have a similar problem I heat the stud or bolt red hot then put a wax candle at the base and it screws out.
I think when the heat expands the stud or bolt it causes it to expand enough to pull the wax in.
And there is a wax fire also if done right. Works great when taking out the threaded oil plugs on a BB at the base of the pan.

DOM

I use High Speed Steel bits and they work well. As Joe mentioned when you get into something hardened you are going to roll the edge. The first thing we were taught in trade school machine shop was how to sharpen drill bits by hand on a pedestal grinder. I had a similar problem one time with a rust seized differential bracket bolt. The diff came to me to rebuild but the bracket was still on because the bolt wouldn't move. I figured I would just press it out, but that didn't work and I didn't want to crack the diff housing. Then I cut off the bolt head and other end and removed the bracket, leaving the bolt body flush in the diff hole. So then I figured no problem, I'll center it in the Bridgeport and drill it out. Well that worked about 1/4" and rolled the HSS bit. So I flipped it over and tried to drill it out the other side, that also rolled it, then I tried to plunge mill it, that rolled the endmill! So I turned a piece of steel to make a lon punch, then heated the housing cherry, then installed the punch and gave it a shot and that broke it loose and out.

[John S.]

Re: Drill bits for Metal

Most of these type bits mentioned above have a shallower point angle for better cutting in tuff steels. I have a few solid carbide bits. The bad part is they need to be sharpened on a diamond wheel which I don't have.

gene has mentioned what is most important in drilling through harder metals. it is the shallower angle of the drill bit. example is that a standard bit will dull after drilling several holes in a stainless sheet, but if the same drill bit is sharpened to use a shallower cutting angle a person can drill 100 or more holes.

[Bill H.]

Re: Drill bits for Metal

I actually just used a masonry bit on hardened steel. I had to put a 3/16th hole in a Hewland gear selector shaft (1/2 in. round hardened shaft). The 3/16th masonry bit took both hands and all my weight on the drill press, the bit wore out and produced a tapered hole. The second masonry bit cleaned up the hole somewhat. Then I used a Bosch carbide bit from HomeD to finish the hole. I was in a hurry and didn't have time to go drill bit shopping. Wasn't pretty but, it worked.