Best Way to Drill Large Hole

Fergienewbee

Well-known Member
I'm planning on making a couple of tool bars. I need to drill a 3/4" hole for the Cat 1 pin. Is it better to drill a small hole, say 1/4" first and then enlarge to 1/2" then 3/4"? Or do I just use a 3/4" drill to start? I plan to use a drill press and 5/16" angle.

Larry
 
We drill 3/4" plus all of the time in our shop. You got the first thing right with a drill press. Clamp securely, ease up going through. Power down feed just eases right through it.
 
again dont laugh BUT.. I have used the Harber Freight drill bits that are V shaped and start at like 1/8 and then V out to larger holes.. wish I knew what they were called. Use oil with what ever you use..
 
I needed 3/4" holes for a damper puller. Our local metal shop punched the holes. The flat stock was 3/4 thick. Hal
 
I agree with the hole saw, but get a good one. They're like files and hacksaw blades - pick out the highest priced one in a good hardware store and you'll be proud of it.
 
I normally drill pilot holes first, then go bigger. Also, you might need to consider if it should be a 3/4 "clearance" hole- a sixteenth inch larger to slip the pin in easier. When I made my shop press out of 6 inch channel, I drilled 1 inch clearance holes for the 1 inch pins that set the table height. Much easier to use.
 
Pilot hole helps a lot when you have light equipment or hand held. Where most screw up is making the pilot hole too large. All you have to do to make a sharp 3/4 bit feed easily is to drill a pilot the same size as the width of the point, likely around 3/16" to 1/4" Certainly no larger than 5/16" If your 3/4 bit doesnt feed easily with a 1/4" pilot you need to sharpen the bit, not make the pilot hole larger.
 
The biggest hole I can drill is 6in. and most any size below that. Speed and feed are the critical factors. Step drill,turn it the right speed and keep it cool and lubricated,no problem.
 
I always start small then work my way up. Never yet had a hole saw work worth the cost of one but the bits I have that go up to 1 inch have done me good for decades and many sharpening
 
I was always told a drill bit is suppose to make its own hole. I may drill a small 1/8" hole to help center up the bit. Hole saws work good too just use lots of oil and a bimetal saw.
 
Dosent take long to learn that step drilling breaks drills.Friend broke my 5/8 drill.He tried to enlarge a hole in a trailer hitch.If I knew what he planned to do he wouldnt have gotten the drill.He did replace it.I had used the drill for many years and kept it sharp.Step drilling puts a tremendous load on the corners of the cutting edge.I sharpen drills for others and when I see corners broken off I know they have been step drilling.
 
Using pilot holes can save a lot of wear on larger bits but a pilot hole should be no larger than 1/2 the diameter of the size of the final hole.
 
A 3/4 inch drill has a thick web that makes it hard to start cutting.A smaller drill can be used as a starter but then only to make a shallow starter hole.Anyone who does step drilling better own a lot of drills.I have some old drill motors that will hurt you if the drill catches.
 
Because you are drilling for a cat1 pin, you should have a very snug hole when finished or the pin will be forever loosening. This being said, drill in a good heavy duty drill press at very low speed with plenty of lubricant on the cutting edge. Heat is the enemy of cutting tools. If you have a high quality drill you can drill in one pass. A pilot hole of 1/4" or so will make the job easier.
 
I was taught that the pilot hole diameter should be the size of the web of the final drill bit. One pilot hole one final bit the size of the hole you want. Works for me.
 
I've drilled a lot of hole too and I agree. To large of pilot hole and you can damage the bit. I always use 1/4" for holes up to 1".
 
Just drilled 4 holes 1.375" in diameter by 2.500" deep. No big deal, just center drill, drilled .375, .625, 1.0 and then 1.375. Worked like a charm, and was very easy drilling. Best advice I have is to start into the hole and and it starts to cut, stop drilling(but don't lift out), and notice if both sides of the bit are cutting. If so you will notice equal "spirals" coming of the tips. If not, sharpen accordingly.

Or, you can always use and endmill and interpolate.
 

I use a 3/4 inch HF bit stepped down to 1/2 shank and my $50 HF drill press. works great go slow and use cutting oil.
The small press wants to catch and stall on breakthru so I go easy then.

Drilled over 1 foot worth of total thikness with the HF 3/4 bit so far using this method.
 
You definitely need a pilot hole, like Dave said, it should be the diameter of the width of the web of the larger drill. Although, if the large drill has been resharpened incorrectly it may drill oversize! in this case drill the second hole 1/32 smaller than the finished size and then finish with the final size.
 
Well, be careful.

On a loader I had a 1/4" thick angle iron tack welded across the top edge across the bucket with hooks on each end for lifting. I tore it off. I don't weld and decided to bolt it on using five 5/8" bolts across its width. But to protect the thinner bucket steel, I used two 1/4" flatbars sandwiching the bucket, under the angle iron. All and all, that was the better part of 1" thick. I drilled a couple ok, put the bolts through, snugged the nuts to hold it in place. On the other three bolts, a couple of times my Milwaukee 1/2" drill bound up, stopping the bit in place, torquing me around when I didn't expect it. That was last fall and from time to time, my wrist still smarts if I have to crank down on something hard. I honestly think I cracked a bone, and not being in a cast, it took longer to heal, or never healed right. At least its not as sore as it was a couple of months ago. Roll over on it in my sleep, wake up and "YOUCH!!!".

Good luck with it, be careful.

Mark
 
I have never considered a 3/4" hole a large hole. I would drill a pilot hole in the 1/4" range not worrying if it was a little over or under then drill the 3/4". Without using a locked down mill when ever you drill the next hole after the pilot hole it will pull slightly off your centered pilot hole. The more times you step up the diameter of the pilot hole the greater chance you can get farther off your wanted center which may or may not be a problem for your project.
 
Thanks, Yes I have turned a few tons of steel into turnings over the years. I know what works for me but sometimes it doesn"t work out my way when others are doing the work so I make suggestions based upon my guessing the skills and equipment of those who ask. Actually I don"t pilot drill anything below 1". I thin the webs of my large bits so they start and feed easily but you cant tell somebody who doesn"t know how to thin the webs that they should do that can you? A pilot bit is the next best choice (which is not a step drill in my nomenclature) In the shop we now run spades that pilot in a 1" Hole for anything 1-3" and anything over 3" pilots on a 2" hole. Really nice system but beyond the average guys pocketbook or needs and certainly not for hand held equipment.
 

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