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SWISSmachining By Kip Hanson,
Contributing Editor
Microboring: when drilling just won’t cut it
20 | MAY/JUNE 2012 | MICROmanufacturing
If the editor doesn’t change the font size on
me, the period at the end of this sentence
measures about 0.02" (0.5mm) across. It’s
tough to drill something that small or smaller,
but with a modern CNC Swiss-style machine
and the right drill bit, it’s doable.
But what if your customer wants a coupletenths
tolerance on that hole or an ultrafine
surface finish? Could you bore it?
You might if you could find a tool that
small. The boring bar would have to be
smaller than a 12-lb. fishing line, and even
if bars that small were made, they would be
hellishly expensive, right? Not really.
Utilis quick-change boring system.
GenSwiss
Dale Christopher, president of Scientific
Cutting Tools, Simi Valley, Calif., noted that
most of the small boring bars his company
offers cost less than a pair of movie tickets and
a bag of popcorn.
“A bar like a 1-8-5 (0.185" minimum bore) is
in the $23 range,” he said.
OK, but what if I need an ultrasmall
bar, one that could cut the cataracts out of
a bumblebee? Christopher consulted his
catalog. “Our smallest goes down to 0.015",
with a maximum depth of 0.05". That one’s
$28.74. It goes up a little because of how small
it is. They’re a bit harder to set up.”
A bit harder to set up? The failure rate
must be awfully high, grinding something that
small. “It’s not so much a high failure rate as
it is having to scrap out a few before you get
going,” said Christopher. “We make all our
tools in-house on Rollomatic CNC grinders.
When you set up your machine, you measure
your wheels as accurately as you can, but the
first tool never is going to come out exactly
right. So you throw that tool away, adjust your
machine and then you cut another. By the third
one, you should have everything dialed in.”
‘The first tool never is going
to come out exactly right.
By the third one, you should
have everything dialed in.’
So dialing in the grinding machine to make
these tools is no big deal, but what about
dialing in the lathe the tool runs on? You can
forget about achieving proper surface speed—
boring a 0.015" hole at even 200 sfm means
main-spindle speeds of over 50,000 rpm.
Boring at those speeds is just not possible.
And how do you find centerline when you can
barely even see the tool?
Again, Christopher explained, it’s not as
tough as it sounds. “Our tools have a small
locating flat on the top of the boring bar, and
we also offer sleeves with a backstop. So,
after you qualify the boring bar—usually on a
presetter or by using turret-mounted gages—
you can just take them in and out. You’ll be
real close.” And what about proper cutting
speed? “That’s limited by the machine tool. So
you just have to crank up your spindle as fast
as it will go and take light cuts, and that’s the
best you can do.”
Christopher also suggested using tools
coated with TiAlN, which improves tool wear
while retaining edge sharpness. “The nonstick
surface reduces edge buildup when you don’t
have the proper surface footage. Also, we use
a premium, submicron-grain carbide and put