I agree with your conclusion that the Dremel in a drill press does not
make a good milling machine; however, I would argue that most of the
tasks it is designed for involve side thrust. You could argue whether
its design is adequate for its primary purpose, but the Dremel tool is
not a drill, it is a rotary tool that can function as a drill. I would
be interested to know how the design of a drill press or a milling
machine compares to the Dremel. I'm also not so sure I believe this
stuff about side thrust- I know it is standard lore in machine tool
world, but wonder whether in the real world the bearing surface
alignments of the two types of tools are that different.
I bought a Dremel drill press thinking it would be kinda neat to get
more precise drilling. There's so much slop in it I can do just as
well by hand.
I'm want to avoid the use of the term 'Dremel. These are properly hand
'motor tools'. The Dremel is a fine and popular version, but far from
the only one. This also include most of the 'flexible shaft' machines.
On the much larger end, you also move up to the so called 'die grinders'
(air and electric) ... the same fundamental type of tool. On the smaller
end, you have the various 'dental' type hand tools (mostly air powered).
I'm NOT criticizing the motor tool, but pointing out it's limitations.
ALL things have limitations, and you can always push your luck.
The bearings in such a motor tool may not be much different in design
than those in a milling machine, but the SIZE of them are sure
different. As are the bearing mountings (quill, etc.), arrangement, and
the machine spindle. The main spindle of a motor tool would flex under
the cutting load of even a small mill. Flex means 'wind up', deflection,
and 'chatter'. Even a tiny benchtop 'micro mill' machine will have a
spindle and bearings MANY times the size of those in any motor tool
(perhaps an inch or more in diameter). My little benchtop milling
machine has a spindle about two inches in diameter at it's smallest
point, and bearings considerably larger than auto wheel bearings. It's
still a SMALL mill.
In the common motor tool all this is mounted in a plastic case ... there
goes any hope of rigidity. Of course, these are HAND tools, so no
rigidity is even possible for their intended purpose. It's NOT a design
fault ... the motor tool is FINE for what it's for.
Motor tools also have inadequate provision for mounting the cutters for
milling. Chucks are near useless, as they will not grip the hardened
shanks of milling cutters. The tiny motor tool collets may grip to SOME
extent, but are too feeble, and NOT dependable. Even far larger and
stronger collets (like R8) can have trouble gripping a mill adequately.
There's not much joy in having a cutter pull out of a collet under load,
and dig into the work. If you're still fully functional after, and
haven't wrecked the machine, you're doing pretty well. End mill holders
are the proper low cost solution, but they won't fit in any motor tool,
and in few drill presses.
As for side thrust, it will cause a taper-shanked toolholder or chuck to
work loose in it's socket in the spindle (hence the need for a drawbar).
This is one of the biggest problems with trying to use a drillpress as a
milling machine, even for light work. You also have to observe a big
cutter, or the structure of a big milling machine flex under the load of
the cutter to appreciate the forces involved. Or worse, have the machine
throw a big piece of metal across the room when something digs in,
slips, breaks, or is not properly fastened down. Cutting metal,
especially rapidly, takes a lot of force and power. Things flex and
'wind up'. Learning to control such forces by machine design and proper
technique is what the game is all about. You can't get rid of these
forces, you have to control them.
And, yes, all is relative to machine size. Nobody expects a 'micro mill'
to remove vast sums of metal per hour like a big production mill can.
But it can out 'chew' a motor tool by a factor of hundreds, and maintain
something like precision while doing so.
You can minimize many of these problems by taking VERY light cuts. But
then you've also minimized much of the advantage you'd have with a
proper milling machine.
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