> We obviously have different
> standards of right and wrong - I can back my statements up with
> machine tool design in industrial applications, you cannot.
I'd be a fool to even try since these homebrew projects were never
intended to be industrial applications? Maybe you should add "fool"
somewhere in the subject line.
--- In
Homebrew_PCBs@yahoogroups.com, "lcdpublishing"
<lcdpublishing@y...> wrote:
> Again, as I have stated before, using software backlash
compensation
> is not an excuse for poor machine design and construction. I agree
> completly that a small circuit board drill would not move the
table,
> however, the larger the drill, the greater the problems. I really
> don't care to debate this with you. We obviously have different
> standards of right and wrong - I can back my statements up with
> machine tool design in industrial applications, you cannot.
>
>
>
>
> --- In Homebrew_PCBs@yahoogroups.com, "derekhawkins"
> <derekhawkins@y...> wrote:
> > >A 40 pound table would not move, the drill
> > >bit would break.
> >
> > LOL! Where is the force trying to move the drill bit coming from?
> > Assuming such a force existed, why would this force suddenly
> > disappear with a perfect zero backlash setup and not break the
bit
> > then also? Both a 40 pound table and a zero backlash setup would
> have
> > the same thing in common "THE TABLE WON'T MOVE".
> >
> > Any slop would be manifested as spurious ∗∗movement of the
table∗∗
> in
> > the backlash dead zone since the X and Y screws are "fixed" at
> drill
> > time by the holding torque of the motor. You seem to be confusing
> > drilling and milling in the same random thought.
> >
> > >There will be others here that will be using dremels and will be
> > >using very lightweight tables with loose construction.
> >
> > With the right size hole the bit will be piloted to some extent
in
> a
> > lightweight setup just as in manual drilling. Most of us are
> alrady
> > familiar with that trick. Long story short....You're making a
> > mountain out of a mole hill. However, I would agree with you 100%
> if
> > discussing milling or drilling.
> >
> >
> >
> >
> > --- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing"
> > <lcdpublishing@y...> wrote:
> > > Considering that most of the drill bits used for circuit boards
> are
> > > so small, they probably would bend or break before they cause
> the
> > > table and part to move. A 40 pound table would not move, the
> drill
> > > bit would break.
> > >
> > > There will be others here that will be using dremels and will
be
> > > using very lightweight tables with loose construction. So,
> while
> > > you may not agree, fact is fact, software backlash compensation
> is
> > > not the "Solution" to poor machine design and construction.
> > > However, sometimes you can get away with it.
> > >
> > > Furthermore, you make the statement "If you know what you are
> > > doing", well, considering that most of the people considering
> > making
> > > a CNC machine will be their first CNC (and probably machine),
> it's
> > a
> > > bad assumption. Again, "trickery", is not a good solution to
> poor
> > > machine design and construction.
> > >
> > >
> > >
> > >
> > >
> > > --- In Homebrew_PCBs@yahoogroups.com, "derekhawkins"
> > > <derekhawkins@y...> wrote:
> > > > >When drilling, the position will be off and the
> > > > >holes will not be on size.
> > > >
> > > > I don't agree with this. Perhaps with a light table and a
high
> > > runout
> > > > drill such as the ubiquitous Dremel one may have an issue.
> With a
> > > > heavy table (the X axis and saddle in my setup weighs over 40
> > lbs)
> > > > and a low runout drill this is not an issue. Backlash
> > compensation
> > > in
> > > > software is very effective when it comes to precision
drilling
> > IMO
> > > > provided you know what you're doing. Milling and routing is
> > > another
> > > > story.
> > > >
> > > > --- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing"
> > > > <lcdpublishing@y...> wrote:
> > > > > While I don't fully know the exact details, I can tell you
> > right
> > > > > away, you cannot rely on software to eliminate the backlash
> > > within
> > > > a
> > > > > CNC system. For basic positioning, perhaps a little, but
in
> > > > > practice, no.
> > > > >
> > > > > While software can compensate for the static deviation
> between
> > > > where
> > > > > it told the motor to position and where it really is based
> on
> > > > > encoder feedback, the "Slop" is still there. During
> cutting,
> > > the
> > > > > dynamic cutting forces will cause the axes to move around
> > within
> > > > the
> > > > > mechanical slop. When drilling, the position will be off
> and
> > > the
> > > > > holes will not be on size. When milling, all sorts of
> > > dimensional
> > > > > problems pop up and in the end, you will have wished you
> took
> > > the
> > > > > time the eliminate the mechancial backlash.
> > > > >
> > > > > While there is backlash compensation within all CNC systems
> I
> > > have
> > > > > used in the industrial world, it is primarily only used to
> > > > > compensate for a very samll amount of backlash .001" or
less
> > > > > usually. Beyond that and it is time to correct the
> mechanical
> > > > > problems.
> > > > >
> > > > > So, don't waste your time or effort in thinking of a
> software
> > > > > solution to backlash - backlash is a mechanical problem and
> > must
> > > be
> > > > > designed out of the system for even the most basic of
> machine
> > > > > performance.
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > --- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan"
> > > > > <stefan_trethan@g...> wrote:
> > > > > > On Tue, 28 Jun 2005 08:36:23 +0200, mikegw20
> <mikegw20@h...>
> > > > wrote:
> > > > > >
> > > > > > > Now I have never built a CNC anything and I am not
> overly
> > > > > mechanical.
> > > > > > > Right that is my qualifications out of the way...
> > > > > > > I was thinking about high torque motors to drive a
> linear
> > > > thread
> > > > > and I
> > > > > > > thought about those really cheap cordless drills. That
> is
> > > idea
> > > > > pt1.
> > > > > > > Now of course you need some sort of feedback for the
> > > position,
> > > > > the
> > > > > > > normal way would be to put a shaft encoder on the
> drive.
> > My
> > > > > thinking
> > > > > > > is that if you used a linear encoder then you would get
> > > absoulte
> > > > > > > positioning thereby negating the need for backlash
> > > > > compensation. Now a
> > > > > > > quick look around ebay reveals that linear encoders are
> not
> > > > > cheap. So
> > > > > > > has anyone used optical mice for a linear encoder?
(idea
> pt
> > > b)
> > > > > > > Here endith todays musings.
> > > > > > > Mike
> > > > > >
> > > > > >
> > > > > > cordless drills usually use a motor what the model-
vehicle
> > > > > builders would
> > > > > > call similar to a "speed 600".
> > > > > > Not a bad motor, and you can get replacements really
cheap
> as
> > > > well
> > > > > as
> > > > > > better motors the same size.
> > > > > >
> > > > > > I would try to find drills with metal gears for this
> purpose.
> > > I
> > > > > recently
> > > > > > bought a very cheap one with plastic gears, it is still
> > > working,
> > > > > but i'm
> > > > > > always expecting it to fail any time. It was cheaper than
> a
> > > > > replacement
> > > > > > battery for a better drill.
> > > > > > There are often ebay lots of many drills.
> > > > > >
> > > > > >
> > > > > > As for linear encoder, there are those striped plastic
> strips
> > > in
> > > > > printers,
> > > > > > but a much easier solution would be to use digital
> calipers
> > > and
> > > > > use the
> > > > > > data-out, 'cause you would get absolute position not only
> > > > > relative.
> > > > > > Probably more expensive than shaft encoders and certainly
> > more
> > > > > expensive
> > > > > > than steppers.
> > > > > >
> > > > > >
> > > > > > ST