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