Drilling holes in metal

B

Bill S

Senior Member
I read an article that said do not center punch before drilling in metal as it work hardens the metal. Also if drilling a hole like 1/2" do not drill a smaller hole 1st than go to 1/2". Start with the 1/2" bit. There are machinist on Ford Barn. So is this correct information?
Bill S
 
Bill S said:
I read an article that said do not center punch before drilling in metal as it work hardens the metal. Also if drilling a hole like 1/2" do not drill a smaller hole 1st than go to 1/2". Start with the 1/2" bit. There are machinist on Ford Barn. So is this correct information?
Bill S
Click to expand...

NO

Bob
 
Always use a pilot drill for larger bits. The size should be at least as large as the web of the large drill. Center punching is a plus if you want to be accurate. A little cutting oil helps preserve the sharpness of the bits used.
 
It's my understanding (and I could be wrong-) that if you have a very small center punch and you want to drill a large hole, use a smaller drill that will center in the punch and just drill a "spot" that will be large enough to accept the web of the point of the final size drill. You may have to do this in steps.
Ditto on using a cutting oil to lubricate the drill.
I also bought (and am happy with) a Drill Doctor to resharpen bits.
 
Waldo is 100% correct and I would add this; pilot holes reduce the force necessary to let the drill cut. Also use high speed steel drill bits. Sheetmetal is another story; different drill point angle and a lot of techinique, or Blair hole saws.
 
If your using a drill press, I do not start with a smaller bit, using the 1 size bit you need actually creates a pool of the cutting lube and uses less lubricant. I try to use a center punch always.
 
If you are drilling a large hole in very thin metal, such as sheet metal, you must start with a small hole and work up gradually. Going straight for the large bit will end up tearing the hole out at the end of the cut.
 
A lot also depends on steel - stainless - aluminum - thickness etc. Original post NOT accurate. Center punch work hardening?

R
 
I supose in some procedures with certain materials this information might have some merit. But to apply it to all operations & materiels is ludicrous. I have become proficient at drilling out rivets without much use of a center punch but it is amusing to watch a novice try this. They will slip off every time and damage the base metal. Plus the rivet is usually already work hardened.
 
Bill S said:
I read an article that said do not center punch before drilling in metal as it work hardens the metal. Also if drilling a hole like 1/2" do not drill a smaller hole 1st than go to 1/2". Start with the 1/2" bit. There are machinist on Ford Barn. So is this correct information?
Bill S
Click to expand...

you got it *** backwards
 
I find that the cleanest holes with no metal warpage is accomplished by using a pilot hole in the centerpunched dimple, and then a step drill to the size you want. As the drill is enlarging to the next size it is also cleaning the hole of any flashing. Makes for the perfect hole in sheetmetal.
 
I think you got it mixed up with wood.The center punch is the put it in right place and not have it walk off location.
Start with maybe 1/8 ,1/4,then 1/2 or go right to 1/2 inch skip 1/4 drill.
 
Bill S said:
I read an article that said do not center punch before drilling in metal as it work hardens the metal. Also if drilling a hole like 1/2" do not drill a smaller hole 1st than go to 1/2". Start with the 1/2" bit. There are machinist on Ford Barn. So is this correct information?
Bill S
Click to expand...

Totally 100% incorrect. Take a piece of 1/2 thick mild steel and try it both ways for yourself. Also, the work hardening theory is pure bunk.
 
Some good answers here! Guess it depends on the application in my experience I have probably done them all, and still do some! In my employment I work on machinery that has 1000.00 dollar bolts :eek:. I use a center punch and pre drill or have them cut using computer control, Some days I don't like to miss.
 
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