Drilling, Boring, and Reaming Notes
are my notes on drilling, boring, and reaming holes. Many of them are
relevant to mills too.
They are to date a rather
disorganized collection of anecdotes found elsewhere. Over time I will
organize these and test each one, discarding those that don't work so
well and emphasizing those that do. For now, I am using a font convention
to differentiate the tips:
If I have written a tip
in this font, I have personally verified it.
If it is written like this, I found it on the Internet and am awaiting
verification. These are the ones to take with a grain of salt.
Locating and Drilling Holes
If you are just wanting to layout within +/-.030"then a good
scale and a sharp pencil are fine. But if you desire closer tolerences
then more precison is needed.
Typically if all I need is +/-.005" I will cover the area where
I will be marking with marks-a-lot and then use my calipers as a scribe
and work off the edges of the part.
If greater precison is needed,then stock preperation is needed first,all
edges need to be square in relation to each other and the edges need to
be smooth and straight.
The tools to use then would be a surface plate,a hieght gauge,machists
squares,angle plates and etc.Learning to use these +/-.0005" is possible
in the homeshop.
The real challenge then is drilling the hole where you want it. A
sharp prick punch helps mark the hole but can be off by as much as 10
thousandths. An optical punch can reduce this to under 5 thou. Then you
need a tight setup to hold the work and move it around til the punch mark
is centered under the spindle.
This is where milling machines have it over drill presses. Use of a spinner
tool helps to center the spindle. Then the pilot hole should be drilled
with #3 or 4 centerdrill, depending on the ultimate hole size. For 1/2"
holes in al you could probably just go to the 1/2" drill size, but
a better method, almost mandatory in steel is to drill a pilot hole at
least the thickness of the drill web first and then go to the final size.
The center drill deflects very little compared with standard drills. Try
putting a 1/4" drill in the DP or mill and punching a good solid
drill punch marker in al or steel and see how much the end of the drill
can deflect when you are off center 10-15 thou. The end of the drill bit
just slides down the conical side of the punch hole and bends the drill
slightly. Center drills will do this too but not nearly to the same extent.
Measure off "one" side or a known square side if possible.. We never
get perfect cuts off the cheap arse saw I have. The lil notch in the end
of the square is there for a reason.. You can lay a pencil in it, stroke
the square down the square side of stock and you have a parallel line
to the edge. If you have another side on the stock that is squared off,
you can do the same there. The lil scribe in the craftsman square is there
the for laying out perfect lines, but when you pull it half a dozen times
it falls out and is lost. A tri-square, sometimes they are not square.
A box square always is, till you lay it on tubing with a radius'ed edge,
then it can follow the edge and not be. To measure something, you have
to have a known point to measure from. (one flat edge.)
Personally, I locate holes using the X-Y travel of my milling machine.
I do layout first, but only as a guide to provide a check on where I'm
drilling. But if you are locating/drilling ONLY from layout, the first
thing to do is probably to establish a reference edge, from which you'll
take all measurements. Then put some layout blue on the surface of the
workpiece and with a sharp scribe and steel scale, carefully scribe locating
lines. Magnification helps. Then with a sharp prick punch, make a tiny
mark at the intersections. Check locations with a magnifying glass. If
slightly off, you can move the location of the prick mark over by tapping
the punch at an angle. When looks as good as you're going to get it, make
the mark deeper.
When you go to drill, locate each prick mark under the spindle in turn
with a "wiggler," then switch to a center drill and drill a
One book that describes the process is the Starrett Book for Student
Machinists, which I imagine is still in print.
In regards to marking and drilling accurate holes. I am suprised that
nobody mentioned "toolmakers buttons". With these you can drill and tap
a small hole where you have prick punched then attach the buttons. You
then mike over the buttons in all directions and adjust them to the correct
location. Once this is done you can indicate the the button true to your
spindle,center drill then drill to the correct size. Move to the next
button and do the same thing. Oh I forgot to mention that after indicating
you remove the button before drilling. This will work well for the guy
who has minimal machining capacity such as a drillpress with no way to
adjust the work.
If you scribe your lines with a very sharp point you will leave a
very fine "X". This "X" serves as a guide if you have a sharpened center
punch. It's actually possible to get them perfect in the dark simply going
by feel of the scribed marks. When you're dead on, the punch tip is very
stable and won't slide around on the work when you try to wiggle it. Make
sure the punch is as vertical as you can make it and then give it one
good rap with a hammer. Something I discovered late in life is when you
are making stuff up on your own, always use a standardized measurement.
As an example, mark all holes to be drilled on multiple's of 1/8th inch.
That way, if you have to repeat some holes a year from know you will know
that the center of the hole is likely to be 7/8's and not 15/16th's I
use to do it just randomly and then had trouble makeing mating holes.
By the way, you can buy really fat magic markers that work good for "blueing"
the area you're going to be marking on with the scribe. I would suggest
you use a scribe when measering for metal or wood. It makes a finer line
and causes you to work more critical. A line has three components when
you are going to try and cut it. It has a right, left and center to it.
Usually if your making inside measurements you leave the line on the finished
cut. On outside measurements you take the line. If you are measuring with
a tape then it's all up in the air unless you can really mark precisely
and indicate with an "x" on the material which side of the line is waste.
I read through these posts, and didn't see anyone mention how to move
your center punch mark. Let's say you've done the layout, and with a light
tap punch the mark. Then you discover it ain't where you intended, exactly.
By healing over the end of the punch, and tapping some more, you can move
the mark. When you're satisfied that it is indeed centered, then it can
be deepened. Personally, I'll use a fine punch with a 60* point for layout
and 'placement correction', then switch to a heavier punch with a flatter
angle (118* maybe?) for that final whack. A drill will walk out of that
60* dimple sometimes. All I'm saying is, you don't have to take a crappy
punch mark laying down!
I use a magnifying lens to help position the punch when marking the
holes for drilling. My two usual methods- one is to use a sliding square
and set it for the required distance from an edge, then pencil mark. Mark
all equal distances from an edge without changing the setting. Then reset
it for the crossing lines to mark holes, then mark all at that distance.
Then squint and curse and spin around to try getting the light just so,
then I can see my marks. Using a magnifying lens, position the punch and
mark the location. Second method is to use the caliper to scratch the
marks, then carefully feel for the crossing of the marks with a sharp
punch, using the magnifying lens as well. Same squirming about to get
the light just so- The trick here is the use of the magnifying lens. No-one
mentioned it, so I did. It's actually pretty easy to mark a hole to within
a few thou using scribed lines if you can actually SEE where you're putting
the punch. Combine vision with the feel of the point in the scribe marks,
and you'll get very close. I like to have a good solid backing as well,
so the punch marks are made very crisply. Now for what this has reminded
me of, yet again. A lighted, magnified center punch project. That would
get a lot of use in my shop.
Thoughts from Swede on drilling 1/16" and other small holes that
must have accurate fits for making model engines:
Having holes go oversized is not uncommon, and as you noticed, a misalignment
can in fact cause them. Aluminum especially tends to drill oversized,
especially when the hole is deep. One way to avoid a small hole (in a
small part) from going large is to drill it first perhaps 8 or 10 thousandths
shy of the target, then remove it from the lathe. Switch the job to a
drill press, and drill out the final hole by allowing the part to "float"
a bit and find its own center. Another technique - if you've ever actually
miked a small, wire-gauged drill, you'll perhaps have noticed that they
mike slightly smaller than the hole they are supposed to drill. All drills
actually cut a hole physically larger than the space that they occupy,
otherwise, they'd simply stick in the hole! I hope this makes sense. The
drills are ground to a specific dimension with the knowledge that the
hole they will cut will be ever so slightly larger than the physical size
of the drill. This effect, as a %, is more pronounced in the small wire
gauge drills than a heftier drill bit. What this means - If I have the
mating part or pin, I'll often try sneaking up on the final hole by drilling
it out one or two wire gauge sizes smaller, and physically checking with
the mating part. For example, rather than drill straightaway with a 1/16"
drill you might try a #53 first. If that works, you're done. If not, proceed
to the 1/16" drill, and since you've pre-drilled, the subsequent hole
should be closer to 0.0625" rather than oversized. HTH - I really can't
see the need for a 1/16" reamer. If you ultimately need to make a 1/16"
d-bit or other homemade cutter, you might want to try a nice little piece
of 1/16" music wire, and simply grind a 1/2 flute into the tip with a
dremel cutoff wheel. It won't last, being spring-tempered carbon steel,
but it should ream a hole or two in aluminum or brass. One last option
- take a 1/16" drill bit (they're cheap), chuck it in a drill press, and
lightly apply a fine diamond or oil stone to the drill's flutes while
it's spinning. You'll probably ruin the drill bit, but it's possible that
a light stoning like that might cause it to drill 0.0005" or 0.001" less
than it normally would. Obviously use it in a pre-drilled (undersized)
hole, and check the outcome on scrap first. Good luck!
of Cut With Boring Bars
Use as a minimum 60% of the tool tip
radius. 1/64" radius gets 0.009" DOC.
Geof on how to hand sharpen a drill bit:
Step one; turn the bench grinder on. That is the really easy part.
Look closely at the drill and note the cutting edge is a straight line.
Hold the drill so that the edge you intend to sharpen is facing up and
parallel with the shaft of the grinder and very close to the wheel; NOT
touching yet!!!! Imagine a radial line drawn from the center of the shaft
to the cutting edge of the drill and project this line out for about the
length of the drill. Because the cutting edge of the drill is parallel
to the shaft of the grinder the drill and imaginary line will form an
angle that depends on the point angle of the drill. Now imagine you are
looking from the side; the centerline of the drill itself should be below
the radial line by around 3 to 5 degrees. This is what starts your initial
clearance angle on the cutting edge. 'Looking' from the side is necessary
so you 'see' the projection of the radial line onto the drill centerline.
So far things have been easy; now you go into imagination overload but
first a little explanation. If you simply brought the drill into contact
with the wheel in the position it is currently held the cutting edge would
be ground okay but further around there would be insufficient clearance;
the 'heel' of the drill would rub. You need to be able to grind heel clearance.
Now imagine a line that runs parallel to the cutting edge of the drill
but which is located about 1/4 to 1/2 the drill diameter back from the
edge and about 1/8 to 1/4 the drill diameter below the level of the cutting
edge. You are going to rotate the drill around this line with the cutting
edge moving upwards. Naturally if you just did the simple rotation the
cutting edge would rotate up and away from the grinding wheel so it is
necessary to move the axis of rotation down and closer to the wheel simultaneously
with rotating the drill around the axis. This is the hard part; it is
difficult to describe other than to say the cutting edge of the drill
performs a sort of 'scooping' motion. The radius of the the scoop and
the depth of the scoop determine the heel clearance on the drill but if
you scoop too far you hit the opposite cutting edge against the wheel
and destroy its cutting edge. And once you have perfected this for one
cutting edge you do the other exactly the same.
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