Richard,
sorry.. yes, skate bearings .. I think faster than I type !
The reason skate bearings are so useful is that they are used in such
large quantities, there is an economy of scale.
They are a pretty useful size as the bore is 8mm which is the same as
the thread size of the proxxon collet chuck (8 x 0.75).
It is possible to get superb quality bearings at a fraction of the
price of other sizes.
I bought ABEC 9 steel bearings for something like 8 for $20. I am
informed that they are good for more rpm than I am likely to ever need.
I guess the ultimate is the skate bearings with ceramic balls, but
they may be overkill.
I don't have any pictures of my high speed spindle, I would have taken
some but it's stripped down at the moment as I am using the stub shaft
as illustrated in the photos folder for a more conventional setup to
mill out an injection mold. My shaft is specifically designed to run
inside the standard shaft of the seig micro mill so it may not be
relavant here except for the geometry. It is based on a length of 8mm
drill rod threaded at the bottom end for the proxoon collet chuck. The
thread extends a little further to where there is a nut. The nut is to
preload the bottom two bearings (which have a spacer between) against
a washer and circlip. The bottom bearings are in a machined housing
which fits into the taper on the bottom of the sieg spindle. The
shaft then extnds up through the top of the seig spindle where there
is a third bearing in a small housing which sits inside the top of the
seig shaft. Above that is a pulley driven by a dc motor. The biggest
problem is that after a eriod of time, the bottom housing comes loose
in the taper.. something i will work on when I have finished the
mold I am working on.
Chris
--- In Homebrew_PCBs@yahoogroups.com, Richard <metal@f...> wrote:
>
>
> ahhh....skate bearings....of course! <g>
>
> Sorry 'bout that...I should've figured that one out
> myself. Put it down to late-night fatigue.
>
> Aren't ABEC-9 bearings an ultra-tight machine-tool
> grade? What the heck are they doing in -rollerskates- ??
>
> I'd think they'd be $50 to $100 bearings!
>
> I guess if you're only drilling a few holes, limiting the
> feedrate is OK. I have had to drill boards with 600+
> holes; and have no desire to -slow- the machine! <grin>
>
> I'm currently running my Techno table at 400ipm slew,
> and around 400,000 steps/sec/sec accelerations, so the
> drill-down time has now become the larger portion of
> the overall job-time. And with 60krpm instead of 25-30k,
> I could -double- my trace-cutting speed...which would be
> really sweet!
>
> Don't know about you guys, but whenever I'm waiting
> for a board to finish isolation, I'm alway chomping at
> the bit wanting it to be DONE, so I can build it and
> see how it works! <g>
>
> I can't spend $3000 for a spindle, but I've worn out
> so many crappy Dremels over the past 15 yrs, that I've
> easily burnt up $300-400 so far. I'd gladly spend, say,
> $300, for a nice little 50-60krpm unit with decent runout
> and not-outrageous noise. If one were available.
>
> Buy one decent spindle, and be done with the problem
> forever. But the market is probably too small for anyone
> to make such a thing; especially if nobody is willing to
> spend more than $39.
>
> Air: I've always kept my compressor outside under a
> little 'shelter', for lack of a better word. Also, I chose
> a unit with a 60-gal tank...it hardly runs at all. So the
> worry about compressor-noise hasn't been an issue for
> me.
>
> I would think that a purpose-built PCB spindle would
> consume far less air than those cheap die-grinders.
> I know that the 200krpm dental handpieces use hardly
> any air at all. The airlines feeding them are only about
> .100" ID !
>
> Air-consumption is directly proportional to both precision
> and power-output; and PCB drilling/isolation isn't a high HP
> job. It would seem that 50-100W would be plenty. The
> Dremel is...about 125W -input- power, if I recall right.
> Of course, it's such an inefficient motor that it's -output-
> power is probably only 75-100W, and that's at full load.
>
> What it actually produces during drilling might only be
> a fraction of that...25-50W of mechanical power maybe?
> A well-made 50-100W air-motor spindle might be pretty
> reasonable on consumption.
>
> Die-grinders are noisy because they run open exhaust; right
> there in your face. But if the exhaust is plumbed away,
> and if the tool is made well, an air motor can be pretty quiet.
> I once worked on some air-powered factory-automation
> equipment that used plumbed exhaust; and was pleasantly
> surprised at how easy it was to stand right next to it while
> discussing it in normal tones.
>
> Heck, it's not like these cheap electric tools are very quiet
> themselves... <g>
>
> Appreciate everyone's thoughts and viewpoints on this.
> It's very interesting. The spindle is such a key portion
> of the setup.
> --
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