Drilling mild steel? Will cobalt do it?

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Squashfan

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Jun 6, 2012
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I need to drill a hole in a T post. If you haven't ever seen one, this is what they look like: http://www.bing.com/images/search?q=Metal+T+post&qs=n&form=QBIR&pq=metal+t+post&sc=8-12&sp=-1&sk=

I don't think it is that hard because a hacksaw will cut it. I tried out a titanium coated bit that I have spares of and went less than half-way through. Had a carbide tipped masonry bit that I got as a spare in a set of bits. It did better but still didn't go through and I was going slowly. I have a black oxide in that same set. Maybe I should try that?

But, I am thinking that I will take a cut off wheel on my angle grinder and put in a slot instead. The stupid thing is that I have carbide cutters that can inlarge a hole but not drill it. I am just annoyed that drilling steel this seems to be such an issue. We can put a man on the moon but we can't even come up with a good way to drill one of our own creations!
 
A good quality high speed steel bit should work just fine. Check your RPM's (might be too high). A little cutting fluid wouldn't hurt. You can get carbide drill bits, but I can't understand why that would be necessary.
 
Any sharp, good steel bit should drill that without a problem, masonry bits aren't going to do it. I've got a set of Dewalt and a set from SnapOn that would drill that in a few seconds, I've also used Bosch titanium bits that worked real good. The secret is knowing when your bit is sharp or not and what to do about if not.
 
I've got a few of those DeWalt carbide bits I've used in my messing around with mild steel. If I go slow and steady the 1/4" bit will cut through a 3/8" piece of 1018 mild steel just fine.
 
I think tiguy7 has the right idea. How big of a hole are you drilling? I googled "drill rpm for mild steel" and found a nice pdf from Irwin tools with speeds for multiple materials along with a bunch of other good info. You also need to feed the drill enough so it doesn't rub, that can dull a drill just as fast as to fast of rpm.

Bruceter
 
Are you using a hand drill or drill press? A hand drill with a relatively large diameter bit will be slow going while a drill press would allow you to exert more force. If you are forced to use a hand drill you should start with a smaller diameter bit then use larger bits to enlarge the hole. If your bit isn't cutting into the metal then it probably isn't sharp.
 
I drill metal regularly at work, and any metal bit should work fine for a T-post.

If your metal drilling project is a one-time-only deal, these ACE bits work just fine and cost less than others. Use some cutting fluid to keep the bit from getting too hot and dulling quickly.
pACE3-977612enh-z6.jpg
 
My guess is you are starting with too large a hole. try a smaller bit and work your way up. however, smaller bits are easier to break, so make sure you are holding on tight and the piece is secure.
 
It was a 19/64th bit with a hand drill. I don't have a way to measure what the RPM is. And I suspect you guys were right about the bit being to large What size should I have started with? And would I have taken the smaller size all the way through or just part way? Cutting oil would have been I good idea but I don't have any. Would regular 3-in-1 oil have worked?
 
3 in 1, WD-40, gun oil, will all work, just something to help lube and (to some extent)cool the bit. For hand drilling I like WD-40, I usually have some around and it's easy to apply.

Bruceter
 
I'm thinking maybe slightly over 1/8th, but its been a while. Just pick something smaller and see if it works.
 
There's no reason that a sharp19/64th drill bit shouldn't be able to drill through a t post, I generally start out with a 1/4" bit in something like that. My guess is either your bit isn't sharp or your turning it way too fast and heating it up which in the end would ruin the cutting ability of that bit anyway.
 
beau5278 said:
There's no reason that a sharp19/64th drill bit shouldn't be able to drill through a t post, I generally start out with a 1/4" bit in something like that. My guess is either your bit isn't sharp or your turning it way too fast and heating it up which in the end would ruin the cutting ability of that bit anyway.
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I suspect that the bit is mostly at fault. My technique isn't perfect by any means but I know this a cheap set of bits, too. I may try again on a spare post sometime.
 
19/64" should be fine without a starter hole. I suggest trying again with a new bit; it's likely the edge of your bit is too dull for the job now.

...this a cheap set of bits, too.
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You don't have to spend a bunch of money for a basic job like yours. Spend $5-10 on the bit you need, and make sure it's labeled for "Metal." Use a generous few drops of oil, cutting oil or whatever, enough to fill the hole as your drill.

Maybe you aren't pushing hard enough. ;)
 
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