DRO-2
2-axis digital readout box
User Manual
Feb-14-2003
Product Description
Overview
The DRO-2 is a multi-function remote digital readout box displaying both two linear axes and spindle RPM. It also displays cutting speeds on a lathe and electronically signals limit positions to a power feed. DRO-2 is meant to be used in conjunction with digital scales, that feature a 4-pin data port connection. These are usually no-name units imported from China by various vendors and can easily be found on ebay using search words DRO, quill kit or scale. They are available as horizontal or vertical units and DRO-2 works with both kinds. In our experience these units are remarkably accurate for their price and make a great basis for axis readouts on machine tools.
horizontal type scale vertical type scale
DRO-2 interfaces to two scales and has five digit plus sign
7-segment LED displays that offer vastly superior readability over the scale’s
built-in LCDs or external LCD based boxes.
It is available with either high intensity red or green LEDs
in a housing made of either black or light gray ABS.
Features
DRO-2 is packed with features that no competing product has
to offer.
- Fast Readout -
In standard mode the scales output about 3 readings per
second, which is appropriate for calipers and well matched to the low refresh
rate of LCDs. The scales also have a fast readout mode of about 40 to 50
readings per second. Unfortunately this mode is practically useless because the
readings are too noisy and blur the last digit on LCDs. Not so on DRO-2. We
implemented a smart digital signal processing filter that eliminates the
readout noise to give a stable display when the scale sits still while retaining
fast display updates when the scale is moving.
- Dual Display
Functions -
DRO-2 has two separate display settings. The user toggles
between the two by pressing the center (mode) button. The two settings are
freely programmable, to display any of the different modes.
- Zero Buttons -
Of course, each scale has its own zero button located to the
left of each display. Pressing the button will zero the display. It should be
noted, that since the scales’ own LCDs cannot be zeroed in high speed mode
their reading will not change. Not a problem, because you will never have to
look at them again…
- Inch / MM modes
-
The displays can be programmed to convert the scale readings to either inch (imperial) or mm (metric). The range in mm mode is -999.99 to +999.99 with a resolution of 0.01 mm. In inch mode the range is –99.9995 to +99.9995 inches with a resolution of 0.0005 inches. The half mil is displayed by the decimal point to the right of the least significant digit.
- Sign Selection -
The direction of the scale readout can be programmed. This
allows the scale to be mounted in a way that is easiest from a mechanical
viewpoint without having to worry about the direction of the readout. This is
programmed once during setup and retained in non-volatile memory.
- Diameter Mode –
Each display can be programmed to read either 1x (radius) or 2x (diameter). 1x is the normal mode as it should be used on a milling machine for example. The 2x mode is useful for lathe cross slides when the user is more likely to be interested in the diameter of a part being turned. Just make sure to turn it back to 1x when using a milling attachment on your lathe.
- RPM Mode -
DRO-2 has an input for an optional photo-interrupter sensor
on the upper scale connector to detect the rotation of a spindle and display
its RPM. The range is 30 to just under 100,000 RPM.
When the range is exceeded either –SLO- or –HI- will be
displayed. The RPM number is updated once per spindle rotation, but no more
than 4 times a second to facilitate easy readout.
- SFM Mode -
DRO-2, when equipped with an RPM sensor, also calculates cutting speeds in surface feet per minute for lathes. This works by taking the reading from the upper scale, which on a lathe should be connected to the cross slide, and calculating the cutting speed using the following formula:
SFM=RPM * 2 * Pi * cross slide
reading in inches / 12
The cross slide has to be set to zero when the cutting edge
of the lathe tool bit is at the center for SFM mode to work correctly. The SFM
reading will be calculated properly regardless of the readout mode of the cross
slide scale (1x or 2x)
The display range is 0 to 100,000. Just as in RPM mode when
the range is exceeded either –SLO- or –HI- will be displayed. Just don’t try
cutting anything at 100,000 SFM…
- Limit Stops -
When pressing the zero button while holding down the center
button the current position is stored as an electronic limit. Whenever the
scale is moved across this position a pin on the lower scale connector changes
logic states. This can be used by some external circuit to stop a power feed
and thereby limiting a cut to not go beyond the set position. The two scales
have separate limit memories, but act on the same pin. This shouldn’t be a
limitation even if a lathe or mill has two power feeds as they wouldn’t be used
at the same time. Just make sure to set the limit of the unused axis at a
position outside the work envelope of the part you are machining so you don’t
accidentally trigger the limit bit. If there is enough interest, we will design
a control box to hook up to this. If you are interested in building your own
circuit please contact us, so we can help you get started.
- Display Off -
Removing power from the DRO-2 box will erase position
information and the scales will be reset to zero on power-up. When you want to
turn off the display without losing position, just press the center button for
3 seconds. The scales are still being read, so it will keep track of position.
Pressing any button will turn the display back on. This is a handy feature to
have if your machine shop also happens to be your bedroom (!?!) and you can’t
sleep under the bright light of our high efficiency LEDs…
- Data Output -
For use with future products all readings are also sent out
over a serial data link on two unused pins of the power connector. We currently
have no concrete plans for this, but thought it would be nice to have…
Installation
General
To connect the scales to the DRO-2
remove the small plastic slider that covers the data port of your scale or
caliper. Insert the supplied data cable. Make sure it is
seated firmly and straight. Be careful to avoid jamming and bending the contact
pins. These connectors are rather
poorly designed and don’t hold too well by themselves, especially on the
horizontal scale units. For permanent installations it is therefore highly
recommended that you provide strain relief to assure a reliable connection. The
scales are sensitive to cutting fluid and chips and we suggest you to protect
them as much as possible. Mounting them in a U-channel as shown in this picture
would be a good idea.
horizontal scale mounted in U-channel (hardwired
cabling)
It is important to mount the scales
in a way that the head can move freely along the entire length. This is not all
that easy to achieve, since binding in a completed assembly is difficult to
detect when the table is driven by a lead screw. The best way is usually to
mount the scale first and measure the position of the sliding head relative to
its desired mounting point at both extremes of the motion. Then adjust one or
both mounting points of the scale and repeat the process until the head’s
position perpendicular to the motion remains the same at both ends. Now you can
attach the mounting bracket for the head. A good bracket design will allow some
adjustment for alignment. The bracket in the picture was mounted by sliding it
up on the 45deg slope until it sat flush with the back plate mounted to the
scale’s head. The mounting screws to the base were then tightened followed by
the screws into the back plate. Some slop or oval holes are needed to give room
for this adjustment.
Some thought should be given to the
cable routing. A strain relief at the mounting bracket of the head is mandatory
and the cable should be routed to a place where any loop formed by the movement
of the table or carriage will not interfere with the cutting action or the
removal of chips.
The DRO-2 box itself should also be mounted away from any cutting fluid and chips.
Setup
The DRO-2 display modes are easily programmed using this
simple procedure.
To enter program mode press all three buttons at the same
time until P0 is displayed. When you then release the buttons the current
readout modes for the first setting (P0) will be displayed.
You can select the desired mode for each display by
repeatedly pressing the button next to each of the displays. This will cycle
through the available modes shown in the table below.
|
1.000 |
Inch mode |
|
2.000 |
Inch mode diameter |
|
-1.000 |
Inch mode reverse direction |
|
-2.000 |
Inch mode diameter reverse |
|
1.00 |
mm mode |
|
2.00 |
mm mode diameter |
|
-1.00 |
mm mode reverse direction |
|
-2.00 |
mm mode diameter revers |
|
0 |
RPM mode |
|
F |
SFM mode |
When you have selected the desired modes for each display
press the center button and the display will show P1 followed by the current
modes for the second setting (P1) when you release the button. Now select the
modes just like before and press the center button again when done. This will
store the mode information in non-volatile memory and reset the DRO-2.
Cross Slide Zeroing
Here is the easiest way to zero a cross slide on a lathe:
Take a scrap piece of round stock and turn it down just
enough to get a smooth surface all around. Zero the cross slide reading and
take out the piece. Measure the diameter of the section you just turned with
some calipers. Move the cross slide in until the display reads minus the
diameter you measured (or half that if you like to run your lathe in radius
mode). Hit zero again and you’re done until you change tools or move your
compound.
DRO-2 power supply
DRO-2 scale interface cable
Troubleshooting
Display only reads –OFF-:
Make sure the connectors are plugged into the scales
properly. On rare occasions, a scale can lock up and can only be revived by
removing its battery.
A more intricate reason for a scale misbehaving can be a
ground loop. The scale’s body is electrically connected to the positive supply
of the battery. This puts it at about 1.5V relative to the ground reference of
the DRO-2. If you are using your own 5 Volt power source make sure that is
floating relative to earth ground, else you would be shorting the scale’s power
supply if the machine that the scale is attached to is grounded as it should
be. The power supplies we supply have no connection between ground and earth ground.
Be aware that you can also create an unintended ground connection via the RPM
sensor or limit output. Make sure that the RPM sensor’s ground is not connected
to earth ground and use an opto-isolator to avoid grounding issues on the limit
output.
Display shows –LO-:
This can happen on startup when the reading is out of range
with a large negative number. The condition can be cleared by pressing the zero
button. If this happens during normal operation it indicates that you might
have a problem with your cable connection or grounding issues.
Display shows –HI-:
This code is shown under two conditions. The first is when
similar to when the display shows –LO- except that the reading is out of range
on the positive side. The second scenario occurs in RPM or SFM mode when the
readout would exceed 100,000.
Display shows –SLO-:
This happens in RPM or SFM mode when the spindle speed drops
below 30 RPM. This can also indicate a problem with the spindle sensor, if
–SLO- is displayed at faster spindle speeds.
Technical specification
Power consumption: 5V,
400mA max
DRO-2 provides power to the scales. However for reliable
operation in noisy environments it is still recommended to leave batteries in
the scales.
pinout of connectors
scale connector pinout
Ordering information
DRO-2 is available in two different box colors and two
different display colors.
DRO-2BG black box, green display
DRO-2BR black box, red display
DRO-2WG light gray box, green display
DRO-2WR light gray box, red display
Please check our web site for
availability.
Contact
If you have further questions regarding this product or
suggestions on how we can improve it or this manual, please feel free to
contact us by sending email to
Please visit us on the web at http://www.zietlowdesign.com/products/products.htm
Mini-Lathe Installation
The DRO-2 is a particularly good match for
Mini-Lathes.
Here is how we fitted a Grizzly 7*12
with DRO and RPM readout.
RPM sensor
The
RPM sensor is a photo interrupter module that senses the passing of a slot in a
disc mounted to the spindle of the lathe. The sensor is mounted on a right
angle sheet metal strip and is attached to the back gear carrier plate with the
existing M6 screw in the top left corner. The cable is routed to exit through
the back cover opening for the forward-reverse lever. It is held in place by a
cable tie. The mounting hole for the cable tie needed to be drilled and tapped.
To do this remove the cover plate which is only held in place by two M6 screws.
Any drilling should be done on a drill press whenever possible. The sensor
could also be mounted in the area where our cable tie sits, as long as it
doesn’t interfere with the lever mechanism. The disc was also made 
out
of sheet aluminum. We cut a 2.4” square
piece and centered it in the 4-jaw and then bored out a 1.060” hole. Then
changed to the 3-jaw chuck and held it from the inside to turn the outside to
2.300”. We then cut out a notch with a nibbler to complete the disc, which was
then mounted between the two retaining 
nuts
for the spindle.
Scale
Mounting
We used a 6” horizontal scale for the cross slide and a 12”
vertical model for the carriage (A 4” scale should be sufficient for the cross
slide). The modifications to the lathe
itself were kept to a minimum. The center piece of the mounts is an aluminum
L-bracket that attaches to the rear of the carriage. The bodies of both scales
are mounted to this bracket. It is attached to the carriage by two M4 screws.
The mounting height was determined by the required clearance of the cross slide
scale. The 
carriage
was disassembled (remove the two M8 screws attaching it to the apron in the
front and slide it off) and then scribed on a surface plate, drilled on the
drill press and finally tapped 
(M4).
While the carriage is off, we also added a hole toward the front of the cross 
slide to
attach the cross slide mounting bracket. Again, don’t try drilling by hand, but
use a scribe, center punch and drill press. We then mounted the cross slide 
scale’s
mounting block. The block 
is
designed with a lip to catch the edge of the cross slide. This way one screw is
enough to securely fasten it. The geometry of the top of the block has a wedge
that allows the cover plate to grab the slide with a line of contact rather
than flat, giving a better grip.
The next step is adding two tapped holes to the tail stock
end of the lathe bed casting. These holes are needed for the carriage slide end
support. Both slides are only supported on one side, making them easier to
align. The picture shows 
why we
recommend doing all the drilling in the drill press. Hand drilling will
invariably result in offset holes like these making 
alignment
more difficult. The block again is designed with a lip to catch the edge of the
casting, so one screw would probably be sufficient. Next we mounted the 
scales to
the L-bracket and fixed the cables with two strain relief cable ties. The cables
exit near the front of the bracket, but facing back. This is the optimal
position for using the existing mounting holes (for the splash guard) on the
lathe’s bed casting for cable guides. Now we were ready to fix the carriage
scale. When attaching the carriage scale to the L-bracket, make sure that it
remains parallel to the 
edges.
Only minor angular error should be taken up by the L-bracket to carriage mount,
since this will introduce a twist in the cross slide scale. To test level on
the carriage scale we used 1-2-3 blocks as seen in this picture. The upper edge
of the scale was just a little more than 1” below the lathe bed surface. When
it was level we tightened the two M4 screws attaching the L-bracket to the
carriage. Next the carriage slide is fixed to the support block at the tail
stock end. Some shims might be needed to 
avoid
flexing the scale near the end of travel. After the carriage slide is attached,
we did the same with the cross slide scale. This one is easier because the
scale’s body never comes very close to the mounting end (we used a 6” scale for
2.9” of travel). Also angular adjustments are easier since the mounting screws
are reachable without removing the L-bracket. We had to file down one of the
set screws for the cross slide gib 
adjustments,
as it was sticking out too far and would have interfered with the L-bracket. We
took it out and filed its tip down about 0.1” and reshaping the tip to its
original form. When put back in place it ended up being flush with the
retaining nut. The only things remaining were attaching the DRO-2 to the top of
the headstock using double sided foam tape and tidying up the extra cable with
tie wraps to the motor housing. The cross slide cable goes into the upper
display 
connector
and the carriage into the lower. The upper display was programmed to –2.000
(inch diameter reading increasing toward the user), the lower to 1.000 (inch
mode, increasing toward tail stock). The alternate modes were F and 0,
displaying SFM in the top display and RPM 
in the bottom.
Drawings for the mounting brackets we used can be found at http://www.zietlowdesign.com/products/dro2/bracket/acwebpublish.htm
By no means can we guarantee that these will work for you.
They are only meant to give an idea of how it can be done. So please measure
twice, so you only have to cut once…