Harvey,
? Yes, all good info. My Proxxon just arrived so I will been opening the little box and see what I bought. :)? I figure 8500 rpms will be fine and being it's a hobby I will be ok. I have a large milling machine and learned a lot from using it. Too bad it isn't CNC. :)
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On 3/4/2019 1:31 PM, Harvey White wrote:
On Mon, 4 Mar 2019 12:13:29 -0600, you wrote:
Jim,
? I figured somebody was going to say that. :) I researched the other
Proxxon setup with the high speed tool but didn't want to go that route
for some reason. And I read some good reviews about the TBM 115 where
people use if for PCB's like here:
So I think I will be alright. If not, I could build my own little drill
press and get the high speed motor but I have too many things going on
right now.
You'll find, that just as in machining, the RPM of the press needs to
be matched to the size of the drill.
Slower is used (at least in part) for larger holes. The largest hole
I've drilled with a carbide drill is .125 inches.
The rake on the bit is not as sharp as you might like, and there's
sufficient torque that if you don't have the board held down, it can
grab and it will wobble in your hands. That give you (at the best) an
oblong hole.
For smaller holes, around .060 or smaller, you can hand hold the board
without a clamp if the board is large enough. That's one reason that
the drills are cut the way they are, the intended use is to have a
high stability CNC head moving over a very well clamped in place
board.
The effect of runout is to make a hole oblong for larger drills. For
smaller drills, you get the same (with worse results) until the stress
breaks the bit.
So for a drill press, you want very little runout, a good way to clamp
the board for larger holes (you'll get the idea of how much on a
practice board), a good way of making sure that the drill is centered
on the pad (critical the smaller the pad is), and the highest speed
you can do (makes the hole go faster, because you have *no* idea of
how much force you put on the drill when you use a drill press. The
faster the drill speed, the quicker it can cut and the less likelyhood
you will have to break the bit through excessive pressure. You'll get
the idea after a few trials.
(yes, I did fix the problems, but it involved some significant
machining and some programming, and I ended up using a linear bearing
set to align the drill bit, and it was upside down, too).
I've seen a pneumatic PC board drill, drills from the bottom,
magnified image projected onto a glass screen. Of course, nobody
could afford it, either.
Harvey
Thanks
On 3/4/2019 11:57 AM, Jim Higgins wrote:
Received from Dave at 3/3/2019 02:41 PM UTC:
I bought a new Proxxon TBM115.
The Proxxon TBM115 has a max spindle rpm of 8,500. Conventional wisdom
is to use an rpm at least 3X or 4X as fast as that to reduce the
chance of breaking a lot of bits. At 8,500 rpm your feed rate will
have to be extremely slow to avoid breaking a lot of bits... perhaps
slower than you can achieve consistently with the Proxxon TBM115.
Jim H
