Adding Low Cost DROs to my Lathe
a newer entry into the DRO mix. These are
capacitive pickups similar to the technology used on digital
calipers. They are very inexpensive and have a reasonable
accuracy of about .001 to .002 per foot of scale length. Due
very low cost and acceptable accuracy, these are finding a wide
acceptance in the hobby and home machine shop markets. I
this series of scales on my lathe, as I blew my budget on the mill
I bought several of these DRO scales at a cost ranging from about $21
for the 6 inch ones to about $35 for the 36 inch unit.
These units have a small digital readout at the end of a several foot
wire. I plan to mount the displays on a post behind the
of the lathe.
This is a small DRO from iGaging Co. which has a printed
circuit pattern under the black
stripe. The sensor is able to capacitively read the locations
within this pattern and convert
them to a length measurement. As you can see it has a
relatively small readout panel
readout resolution is .0005 inches with an absolute accuracy
of about .002 per
foot. It is
about 1/10 the cost of a standard DRO.
I plan to mount
a scale with 36 inch
travel on the rear of my lathe to measure the carriage movement, and a
second short one on the cross feed to measure my depth of
cut. I doubt
I will be able to fit a third unit on my compound rest, as it is just
It took very
little time to mount my 36 inch scale on the rear of my
lathe. There is plenty of room and to test it out, I used two
very powerful Neodymium magnets, removed from obsolete computer hard
drives. Mounting consisted of placing a magnet on each
bracket and placing it on the lathe. It holds very
then made a formed sheet aluminum bracket which attaches to an existing
bolt on the carriage and I had a working DRO for the Z axis.
know! Z axis sounds wrong, but technically the Z axis is
as the axis parallel to the spindle on a machine tool, therefore the
carriage moves in the Z axis.
operation it works great. It displays the position to the
1/2 thousandth. You can use a relative mode and zero the
anywhere you like without disturbing the primary readings. It
displays inches, millimeters, or inches and fractions. The
seems totally useless to me, as it reads in 64's of an inch which is
about 30 times its minimum resolution (and who can look at fractions in
64's and instantly comprehend the magnitude?). The biggest
I see with these
scales is that they use small enclosed batteries which risk early
discharge if you forget to turn them off when you are
plan to look into an AC powered supply for them after getting further
into the project.
The first scale I mounted was the lathe Z axis. This is a 36
inch scale. I have
initially mounted it to the lathe with 2 strong magnets. The
read head is attached to the carriage
with a small aluminum bracket. Now that I have proven it out,
I will replace the magnets with
tapped holes and screws. In this picture the readout is still
plastic wrapped and is laying in
I also temporarily mounted a much shorter scale on the cross
there are problems there. As presently configured there is
only one place to mount the scale. That is on the spindle
the cross feed, with the slider between the ways. In this
is quite possible to run the read head into the chuck if you are
close to that end (fortunately, I never did!). There is not
adequate material at the
rear of the cross slide to mount the scale, and in this position, it
accumulates a major portion of the machining swarf. This is
particularly obvious when I machine steel, as each end, where the
magnets hold the scale, builds up a large ball of chips.
This mounting method was just not satisfactory, so I made
some changes to the cross slide and mounted the DRO on the right side
of the carriage.
The temporary cross slide scale is also mounted using
magnets. This mounting is not
satisfactory as the read head will hit the chuck if the carriage is
moved too far. Also it is
mounted in the area where the most chips fall, many of them
hot enough to melt plastic.
DRO Mounting March 26, 2014
mount the scale on the right side of the cross slide, I had to machine
a true mounting surface.
I then mounted a strip of aluminum as a backing plate for the
I used a length of drill rod clamped in the dovetail to align the cross
slide. I then
took a surface cut of about .050 where the aluminum is to mount, to
uniform mounting surface.
I have mounted the backing plate. As the plate covers one of
the gib adjusting
screws, I provided a clearance hole. Also after taking this
picture, I beveled
the end of the plate to allow allen wrench access to the compound
The left picture shows
the aluminum backing plate mounted to the cross
The right picture shows the scale mounted to the plate. I
verified that it is parallel to the travel within .002. The
read head is attached to the carriage
using a thin aluminum bracket, machined to allow flexibility in the two
minor axes, and good stiffness along the axis.
I then went back
and removed the magnets
from the Z axis scale, drilled and tapped the mounting holes and
mounted and aligned the scale.
The longitudinal axis DRO scale is now mounted with screws instead of
I never had a bit of trouble with the magnetic mounting, but this is
secure. You can
also see the narrow flexible bracket driving the X axis DRO in the
upper left of
the picture. The finger will readily flex sideways and
vertically, but is very stiff
in and out, driving the read head.
I mounted the DRO heads and my tachometer on a temporary mounting bar.
As part of the
"Replacing my lathe
motor" section, I mounted the DRO heads in a multifunction control box
instead of the bar of metal I was temporarily using. This is
much more satisfactory!