Drilling a round hole

BossDog

BossDog

KnifeDogs.com & USAknifemaker.com Owner
Staff member
This is one of my favorite threads....
you think it would be simple.

How do you drill a round hole?
 
First I start with a half a hole,
undersized say I want a 3/32" I use a #40 bit then chase it with a 3/32" reamer all chucked up in collets in my mill.
 
Are we talking perfectly round here ?

I know the question was "how do you drill a round hole" but ;)
I don't rely on just a drill for precision holes.

I've found that drilling ~ .030 undersize and then moving to a Boring Head will give pretty darn good results, (making 2 passes with the Boring Head)

or

Drill undersize, ream within about .0005 undersize, then use a split lap & Diamond "juice" ;)

or

After drilling an undersize hole, using a Jig Grinder Head on a Mill or a Jig Borer is, I'm pretty sure, about as good as it gets. At least it used to be......... unsure



:)
 
I use a Spotting drill or a Combined Drill and Countersink first, about .015 over dia. of drill size. I get a round hole all the time.......if I need to be .0005/.001 tol. I ream with the correct reamer (over or under size reamer)
 
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most the time i jsut drill holes and make them work but when its a folder we are talking aobut
its predrill undersized and then heat treat. lock in the mill and use a multiflute (4 or more flute)ball endmill made of carbide to chase the hole
i dont have reammers so this is how i do things and so far so good (besides i often fint that the folder pivots are a bit over sized any how
 
Drill bits tend to make three sided holes and reamers four or six. the courners may be so slight that the hole apears round though. I think that the only two possibilities to get a round hole are to bore or lap as stated above. But I reserve the right to change my opinion subject to imperical evaluation.
 
Hard one to answer her Boss. There are a million and 1 factors here. without assuming what you are drilling and assuming it is with a drill press then..... When drilling a hole the drill will tend to wander at the start of the work piece then stabilize as the body enters the hole causing a bell mouth shape at the entrance and possibly beyond. other factors of bellmouthing are unsymmetrical ground drill points, rigidity of machine and part, size and length of drill bit (possible to bend or flex).

The best thing to do is: (also dependent on tolerance)

1) make sure part to drill is rigid and perpendicular to the drill.
2) minimal as possible run out on the drill
3) Center drill the hole first with as short and as large of center drill as possible.
a) step/pilot drilling is also possible (ex. 3/32" , 5/32", 3/16") but not recommended because drills are not exactly designed for this. (unless using core drills.) but it does help.
b) drill leaving .005-.008 per side of finish hole size, then ream to size (probably best for what most have for equipment and tooling.)
4) a square drill

Also as already stated drilling under size and lapping or honing also works and better yet roller burnishing is another way for very accurate holes with great surface finish and work hardened walls depending on the material. but mo money

I could go on and on and on because of all the different scenarios but not enough time..

Travis
 
First use a center punch then drill slowly then fill in the gaps with super glue. Now you know why I don't make knives! :D
 
Bill Burke said:
Drill bits tend to make three sided holes and reamers four or six.
Click to expand...

Oh my Cow you wouldn't believe how many people can't wrap their head around this. Yes! This is very true. This is a real issue with a drilled hole. Drilled holes are not for precision applications.

In school you're taught to:
1 Spot drill (this gets the drill started accurately - the lip angle should be more obtuse than your drill to force it to start at the web)
2 Drill (you're just removing material)
3 Bore (this aligns the hole to the spindle and makes it round, two passes assures the tool didn't flex)
4 Ream (this makes a fairly round fairly smooth hole with diameter control to a few .0001)

In practice you:
1 Drill
2 Circular interpolate
3 Ream if you're feeling randy. You'll get better roundness reaming, but better positional and finish milling - size control can be a wash.

If it is important, you can clamp it to a face plate on a lathe at low speed and install a jig grinding or tool post grinding attachment and grind that sucker to a couple .0001 (if you got good stuff). My folder blades get circular interpolation - which is fine for most folders. Hell, drilled holes work for a lot of folks (though I'll pass).

Tracy, shouldn't this be under shoptalk?
 
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Nathan The Machinist said:
Oh my Cow you wouldn't believe how many people can't wrap their head around this. Yes! This is very true. This is a real issue with a drilled hole. Drilled holes are not for precision applications.

In school you're taught to:
1 Spot drill (this gets the drill started accurately - the lip angle should be more obtuse than your drill to force it to start at the web)
2 Drill (you're just removing material)
3 Bore (this aligns the hole to the spindle and makes it round, two passes assures the tool didn't flex)
4 Ream (this makes a fairly round fairly smooth hole with diameter control to a few .0001)

In practice you:
1 Drill
2 Circular interpolate
3 Ream if you're feeling randy. You'll get better roundness reaming, but better positional and finish milling - size control can be a wash.

If it is important, you can clamp it to a face plate on a lathe at low speed and install a jig grinding or tool post grinding attachment and grind that sucker to a couple .0001 (if you got good stuff). My folder blades get circular interpolation - which is fine for most folders. Hell, drilled holes work for a lot of folks (though I'll pass).

Tracy, shouldn't this be under shoptalk?
Click to expand...

drilled holes for folder pivots might work but im with you on making the hole as clean and round as i can in my shop

i hate all the slop that gets covered up with oversized washers
 
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