FILENAMES:

DRO_Display.jpg
DRO1_Display.jpg 
DROX1encoder.jpg
DROXencoder.jpg
DROYencoder.jpg 
DROZencoder.jpg

DESCRIPTION:

These are pictures of a digital read out system built by 
Dan Mauch (dmauch@seanet.com) and a friend.  Dan provided 
the following description:

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Digital Read Out (DRO)

I have often wanted a DRO for my mill, lathe and mill/drill. The
problem is that they are to expensive. So I decided to build my
own. I have worked on various methods. Finally I came up with a
great linear encoder as you can see by the photographs. The
linear encoder are housed in a nice aluminum extruded case. The
End caps serve as the mounting brackets and support the
lightweight units. The wires come thru a niffty piece of tubing
so that  they don't get  tangled up inside the unit. The encoder
module mounts on a piece of  Ultra High Molecular Weight
Polyethelene(UHMWP) that slides back and forth as driven by the
rod. With this arrangement there are no gears to wear out or to
loose position because chips got caught between a mechanical
link between the rack and pinion. Thus this unit should be
maintenance free and should keep all those nasty bits of chips
and coolant out of the encoder. The encoder itself has a
resolution of 1440 counts per inch in quadrature. There is no
cumulative error. Thus each change of state of the encoder will
register .0006944 inches.  

Having just completed the unit I am still in the testing stage.
I was surprised to find that the leadscrew on my mill/drill was
off .001 per inch or .012 in a foot. I also had .019 backlash in
the X axis and .015 unches bachlash in the Y axis. The Z axis
has .02 slop in the rack and pinion. I verified that  it was the
lead pitch error because with the stepper motors connected and a
dial indicator, I checked each axis. I added 8 steps to the X
and Y axis CNC configuration file to correct for the pitch
problem. Now with a 2-12 inside micrometer and some block I
measured the accuracy of the DRO over a 12 inch travel . It
seems to be within .001 generally and a maximum of  .002 out tho
I can not totally convinced that it is the DRO.

I think my bracket for the Y axis is flexing.  In any case the
DRO will allow me to manually machine far, far, far closer  than
trying to use the manual dials for posistioning. It seems to
take the junkiness out of those imported machines and by
connecting it directly to the moveing axis eliminates the errors
of backlash, leadscrew pitch error and other maladies that are
observed with low cost machines.

	The display was desgined by a friend of mine - Kenneth Maxon. 
The display is quite complex and uses high efficiency LEDs that
can be read easily from 30+ feet. It uses a microcontroller,
flash memory and can read relative or absolute locations. What
is neat is that you can shift back and forth from absolute to
relative without losing your place . You can also re-zero the
display at any time.

	I was so happy  with the performance of the DRO that I have
decided to add them to my lathe and full size mill. Several of
my friend that have seen the unit tell me that I should market
the encoders.. I have decided that they are right and will soon
come out with various length encoders similar to the ones in the
photos. . I intend to try the encoders with a freeware DRO
program and perhaps that  will provide a really low cost DRO for
the average shop. Check my web page at 
http://www.seanet.com/~dmauch for availbility. Right now I am
three weeks away from offering the encoders. Price? I haven't
decided that but will probably sell a three axis set of encoders
for under $300.