Question about drilling holes

I

iron1951

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When I drill large holes on my drill press or lathe I work my way up to the finish size using smaller drill bits until I reach the desired size. My buddy says that this is wrong and I should use the correct size right from the start. He works in a machine shop where power is not a problem. I putter in my garage where I only have 1/3 hp motors and I often stall the motors.

Is there a correct way to drill holes and why?

Thanks
 
I also drill in stages but for another reason------it saves wear and tear on the larger drill bits. My thought is less heat less wear.
 
You have to do what you have to do with what you have. I wish I had a bigger drill press,too. If I have to drill any large holes,my 16" lathe takes #4 MT in the tailstock,and #6 in the headstock. Holding odd shaped work to be drilled in the lathe is another matter!!

I could resort to using a boring head in my Bridgeport type mill,but even it isn't good for drilling real large holes,and only 3/8" holes with the power down feed.
 
I have always been taught that you step the hole up. First if you are off center with the pilot then it is possible to get back on center with the next larger bits. Second, it is easier on the bits and drill. Third, you get a more accurite hole when you drill atleast a size or two smaller and then finish with the correct size. For the most accurite you would drill to a size or two smaller and then ream to the correct size.

Is there a right and wrong way? No.

As long as the hole gets drilled and you arent breaking bits but getting the results you are looking for, I would say you are doing it correct.

Thats my 2 cents worth. You can keep the change.

Turbo
 
You are doing it correctly for what you have. Even in my lathe I work up in increments of 1/8". Trying to drill a large finish size hole with a drillpress with a 1/3 hp motor will only bring you grief.

As George just stated, we do what we have to do and make it work.

"Billy G" :))
 
The textbooks all say that you should drill through in one shot, maybe only drilling a small pilot hole for very large drills. I have drilled 2 inch and bigger in the lathe without centre drilling or piloting the hole first. But unless you've got a lot of horsepower and rigidity the safest way to drill a hole is in stages.

Sandro Di Filippo
 
For me if the finished hole size is less than 3/4" then its center drill and final drill size, 3/4"-1 1/4" its center drill, pilot drill and final size. I use a pilot drill that's a little larger than the web thickness at the tip on the large drill. Holes larger than 1 1/4" I step up with increments. Your increments shouldn't be too small or you'll put too much heat at the outer edges of the drill. You want the chips to be big enough to take the heat with them.

But like others have said if you have limited HP then you go with what works.
 
For holes in material up to 3/8", I often use a step bit. I find that it stays centred quite well.

If you found that your hole has drifted off the desired location and you haven't yet reached the final size, chasing it with a 4-flute end mill might allow you to get closer to the right location. If your machine isn't rigid enough, it could pull off to one side, though.
 
If you have started your hole JUST ENOUGH to get the drill in up to the edges of the lips,but not the whole body of the drill in,you can move the hole: Take a cold chisel and make several whacks radially around the side of the hole in the direction you want the drill to drift towards to get it back on location. The drill will drill more rapidly towards the chisel marks. Repeat till you are on course again. The chisel marks are arranged like an asterisk (*),except the marks are,as said,on the side of the hole you want to drift towards.

It is best if you check the hole for position before the cutting edges get too far in,or your hole will have a beveled side from making the drill drift away to 1 side. Drilling a hole the diameter of the web is a big help both for power needed and accuracy as stated above.

When you center punch for small drills,make sure the diameter of the punch mark is as wide as the web of the drill,or the drill can easily walk off center.

You can use a lathe center drill in your drill press to accurately start a hole. I do that all the time. It's like using a spotting drill,but most small shops don't have spotting drills on hand.
 
OldMachinist said:
For me if the finished hole size is less than 3/4" then its center drill and final drill size, 3/4"-1 1/4" its center drill, pilot drill and final size. I use a pilot drill that's a little larger than the web thickness at the tip on the large drill. Holes larger than 1 1/4" I step up with increments. Your increments shouldn't be too small or you'll put too much heat at the outer edges of the drill. You want the chips to be big enough to take the heat with them.

But like others have said if you have limited HP then you go with what works.
Click to expand...

Unless you have lots of hp this is the most appropriate way to drill holes with a smaller drill press or Bridgeport type machine.
 
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