How to drill a hole

[Garage Dog]

I know that sounds like a lame question. The reason I ask is this.

When drilling a hole and your final dimension is say 1/2" or larger, do you drill just a pilot hole and then the final size or do you drill 1 or 2 more times to work up the the final dimension? This would go for flat stock as well as round. What is considered the proper method?

I will add that all my bits are 118 degrees and extremely sharp.

Thanks!

 

[benmychree]

That would depend on a number of factors, including what machine I was using, the material, and desired accuracy, but for drilling flat bar, I'd likely drill anything under a 1/2" diameter hole without any pilot hole, except possibly using a spotting drill or center drill to accurately locate the hole. Using puny machines would perhaps make it necessary to drill the hole in steps.

 

[RJSakowski]

A pilot hole with a diameter exceeding the width of web of the drill being used next will greatly reduce the amount of force required to drill. Whether I use multiple drill depends upon how I am drilling. If using a hand drill, it can be difficult to provide enough force to effectively drill so I would step up the hole size. If I am using the drill press, this is usually not necessary so I will often just center punch and drill to final size. I find that drilling a slightly undersized hole followed by the final drill size will usually produce a cleaner and truer hole. For holes larger than 1/2", I tend to frill ta pilot hole first. Up to 3/4" hole in mild steel can be followed by the final size. Over that and I would most likely step up.

 

[Parlo]

If you want a close size hole & better finish. Stone a small radius on the corners of the cutting lips on the final size drill.

 

[Garage Dog]

Thanks for the replies!
I guess I have been doing it pretty much like everyone mentioned. I didn't know about the pilot hole diameter exceeding the width of the web, I'll give that a try next time. I'll try the stone on the radius too!

 

[RaisedByWolves]

Thanks for the replies!
I guess I have been doing it pretty much like everyone mentioned. I didn't know about the pilot hole diameter exceeding the width of the web, I'll give that a try next time. I'll try the stone on the radius too!

Stoning the lip, or "Lipping" the drill bit is a good idea when drilling grabby materials like brass and can also lessen the amount of grab when breaking through the back surface.

Ive been seen drilling a clearance hole in 3" thick die parallels with a 2" drill bit using nothing more that a 1/4" pilot hole.

Sometimes time outweighs good shop practices and as long an no one and no tooling are hurt.....