Inexpensive DRO for the Mill
a thing worth doing is not worth doing well. In this case, I present a
very inexpensive no frills DRO for my Industrial Hobbies Mill. Since I
intend to convert it to CNC sometime in the next year, it made no sense
to purchase an expensive DRO. Yet, it had become clear to me that a DRO
would be particularly valuable on a mill, and I do intend to use this
mill manually for a while in order to gain maximum familiarity before
converting to CNC. After a quick perusal of DRO scales on eBay, it dawned
on me just how cheaply this could be done. I rounded up three scales for
less than $200 and set to work. I figure when I take the scales off to
convert the mill to CNC, I can always put them to use on some other machine.
They may even prove useful in calibrating the CNC software initially.
The only thing that gave
me the slightest bit of pause on this project was drilling and tapping
into the mill castings. Having seen the various detailed photo essays
on installing the CNC kit on the Industrial Hobbies web site, I knew it
would be straightforward so long as I took it slowly and carefully.
seemed the easiest place to start, so I set about making custom bracketry
to mount a DRO scale on the Z-axis:
Z-Axis (Quill) DRO
The brackets are all very
simple, and made from scraps I had lying around. They're basically aluminum
Mic-6 plate cut into appropriate shapes with holes drilled and threaded
as needed. I made use of the mounting bracket from the old quill depth
gage to mount the lower bracket. The upper bracket attaches to the rear
of the scale with 2 screws. A brass rod held in the brackets with set
screws ties them together.
The primary challenge on
the z-axis is making sure to clear the gear shift levers. In this case,
I have a little interference with the Low/High lever at the extreme up
level. I sacrificed a little z-travel off the bottom by starting the DRO
below the interference. All I need to pick up the lost travel is to replace
the socket head set screw with a true headless set screw that sits flush
with the bracket. I've never yet fully extended the quill, however, so
I probably won't bother. Also note a little bit of scale protruding from
the topmost mounting bracket. In fact, I needed a little shorter mounting,
so rather than cut down the scale, I just milled the end of the bracket
and slid it on through. I have to loosen the bracket to access the socket
head cap screw when I remove the scale, but that's no biggie.
The Z-Axis was a piece of
cake, X-Axis will be next!
To mount the X-Axis DRO
I made use of the travel stop system that already existed on the lathe.
This system consists of a center bracket that is fixed to the saddle and
does not move when the X-Axis travels as well as two moveable stops affixed
to a T-slot in the table's front edge. Step one was to fabricate two mounting
brackets to go in the T-Slot. The DRO end brackets would be attached to
these two brackets using 10-24 socket head bolts. I just reused to T-Slot
Nuts and socket head bolts that were used to mount the original round
DRO mounting bracket in table's edge T-Slot...
these two brackets using some 1/2" thick Mic-6 (precision ground
surfaces) aluminum plate I had sitting around. Step two is to use the
center bracket to attach to the moving DRO head. In reality, we will hold
the head stationary on this center bracket while the scale moves under
it as the X-Axis moves. The finished head mount looks like this when assembled
on the mill:
DRO head attached to the travel stop center bracket...
challenge here is making everything line up without any binding, and doing
so in a way that all the fasteners are acceptible. I used the following
arrangement to get the job done:
Modified travel stop bracket and the sandwich plate
that attaches it to the DRO head...
Making it all
work involved countersinking the holes in the sandwich plate (the plate
that fits between the DRO head and travel stop bracket), relieving the
travel stop bracket to allow access to the 2 DRO mounting screws, milling
a groove in the sandwich plate as well as grinding a bit off the socket
head to make sure there was no interference with the mill and that the
whole works sat in the same plane as the mountings for the ends of the
DRO scale. In other words, it took a little bit of fiddling to get right!
DRO Head, Sandwich Plate, and Travel Stop Bracket
To make the
sandwich plate I started with a piece of squared steel I had laying around
from another project. The milling
and drilling required were straightforward. I needed to get the countersink
depth right on the 2 screws that mount the DRO head to the sandwich plate
(you'll notice how small the screws are!), and I found the already completed
Z-Axis (Quill) DRO to make that operation a snap.
Here is a view
of the completed X-Axis DRO:
X-Axis DRO Complete! I like the way the DRO head
is protected under the shelf provided by my Kurt 4" Vise...
One axis left to go...
The nasty thing
about the Y-Axis is that unless something innovative is done about where
the scales are mounted, it will be impossible to read without crawling
under the table with a flashlight. For this axis I will mount the scale
rigidly and move the head, as I have done with the Z-Axis. If you look
at the picture immediately above that shows the front of the mill, the
idea would be to make a bracket that attaches to the front of the saddle
on the left that will grab the DRO head and keep it positioned just in
front of the saddle as I traverse the Y-Axis. That should be a pretty
convenient spot for it. This may leave the scale protruding slightly beyond
the front edge of the mill base if I want to measure full travel, so I
need to plan things carefully.
More news when
I figure it out...
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