Rong Fu RF-25 Mill Digital Read-Out (DRO)
Last updated onLast updated on Wednesday, March 10, 2021 05:55:14 AM Mountain US Time Zone

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Instrumented Mill, Enclosure, Zeroing, Offset Milling,
Mount, Red Filter,
DPU-550 Daughterboard Upgrade

Instrumented Mill

Rong Fu RF-25 Mill/Drill with 3-axes DRO.  
The mill is at the upper limits of weight &

size that I could safely move down
a hill & into my lower-level walkout.

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EnclosureEnclosure


Setup shown for milling the lathe DRO case.
1-2-3
"Johnny" blocks fixed at right angles to the table.
Plastic box sides slightly squeezed by the blocks.
Toe clamps with protective tape gently secure the box.
The X & Y axes DRO scales were zeroed at the front
left corner (0, 0) using a
Starrett wiggler center finder.
Then use the supplied layout drawing of the (x, y)
coordinates to drill & cutout out all the holes. I like to use
a
Unibit
step drill to make holes in thin materials.

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2 styles available, 1-pk or 2-pk:
3-5/8" x 3/4" & 5-1/2" x 1-1/8"

 

 

 

 

 

 

 
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Zeroing

The US made Starrett wiggler set is
far superior to imports except Mitutoyo.

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Imperial or metric

 

 

 

 

 

 
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Offset Milling
To make the rectangular holes for the LED displays,
I used the DRO's tool offset functions.

The offset function takes into account
the end mill's diameter when cutting.

Use
Function 5 (tool offset define) to
first specify all the tool sizes where the

Tool # is always the numerator & 16 is
always the denominator of a fractional size.

Tool #/16 of an inch. I find this a very easy table
layout to remember, though it is of course, arbitrary.

I used 0 for the Z offsets. The DRO-350 will only allow
three significant numbers input after the decimal point.

TOOL #3 TOOL SIZE
DIAMETER (inch)
EQUIVALENT
FRACTION
(inch)
EQUIVALENT
DECIMAL (inch)
CORNER
RADIUS (inch)
1 1/16 1/16 0.0625 0.03125
2 2/16 1/8 0.125 0.0625
3 3/16 3/16 0.1875 0.09375
4 4/16 1/4 0.25 0.125
5 5/16 5/16 0.3125 0.15625
6 6/16 3/8 0.375 0.1875
7 7/16 7/16 0.4375 0.21875
8 8/16 1/2 0.5 0.25
9 9/16 9/16 0.5625 0.28125

Function 6(tool offset use), followed by a Tool # (1 to 9),
turns ON diameter compensation & selects the previously defined tool.

 First, select the tool size diameter being used. To cut a
rectangular/square pocket or hole, move the cutter to the (x, y)

coordinates of the front left corner but don't plunge, yet.
If you are starting in a corner, you must compensate for two milling

edges; e.g., both left & front. When you press a compensation key,
you will see the scale offset by the appropriate tool radius.

If 4, 6, 2 or 8 are pressed, the far left decimal of the
corresponding scale lights indicating an offset was selected.


High RPM cuts using a two-flute,
1/8" end mill.

Mount

The DRO bracket is placed closer to the keys where
pressure is applied. I protected all exposed cables

with spiral wrap. The
80/20
aluminummarmarm (see below) is mounted
off a triangular, 1/4" thick aluminum plate that is held under two

of the motor-mounting bolts.
All cable plugs are held
in place with a spot of hot glue. Black plastic 80/20

inserts are snapped into the channels to hold the
cables in place & to give the arm a nice, finished look.

The DRO is plugged into a surge protector.
The 80/20
website has software tools to help construct a kit for assembly.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   

    
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I have now removed all of the quill levers so they do
not contact the piece when working close to the vise.

This configuration allows much better access to
the
two column locks, belt tension lock & DRO.
I made & installed 1/2-12 threaded aluminum
plugs to give it a finished look & keep the chips out.

 I like the extra control afforded by the fine down
feed & typically have no need for the levers.

Red FilterRed Filter

Adding a deep red filter enhances the LED
display contrast. The five LED indicators have

circular (punched) red filters, too. Note: the
blurred LED display is a photographic artifact.

DPU-550 Daughterboard Upgrade

The DRO-350 has been upgraded with the DPU-550
daughterboard & overlay to add ehanced capabilities & performance.


OpenDRO User's Guide Rev 5OpenDRO User's Guide Rev 5
OpenDRO Supplemental Guide
OpenDRO Software Upload Manual 

OpenDRO


Scales' directions & polarities must be
correctly defined in the DRO setup for

several of the functions to work properly.
Refer the Open DRO Supplemental Guide.


DRO-350 baseline. Removal of the 28-pin PIC16F876A
(far right) is required before soldering in the headers.

The PCB is not of the highest quality so take care
to not damage any traces when desoldering.

DPU-550 UPGRADED
Processor Attribute DRO-350 PIC DPU-550 ARM7
Register Width 8-bit 32-bit
Speed 20 MHz 50 MHz
Program Memory 8 K 256 K
Working Memory 368 64 K
Non-volatile Memory 256 8 K
Processor Registers 1 16
USB Device Interface No Yes
Free & Unlimited C Compiler No Yes


Unassembled DPU-550 lite daughterboard kit.


New holes for the program switch
(1/8") & USB access (1/2"). Super easy to
program the ARM-7 CPU via the USB.


DPU-550 lite daughterboard mounted onto the DRO-350.
It is easily programmed through its USB port.


For the DPU-550 a 74LS14 Schmitt Trigger was needed
to make this particular
tachometer setup work reliably.
The IC (unused pins removed for compactness) was
spliced into the AUX IN to header wires & then shrink-wrapped.

Pin 7 is ground, pin 14 is +5VDC, pin 1 is the signal
in from the sensor & pin 2 is the signal out to the DRO.

This circuit converts the sensor's somewhat noisy
waveform to a clean, well-defined, square-wave output.

The unused inputs do not have to be tied to ground
because the purported power loss is
insignificant.


Since any value can be displayed anywhere;
the X-axis position (2.3778-inches) was assigned to the top
line, the spindle speed (1642 RPM) was assigned to
the middle line & the X-axis feed (7.0-inches/minute)

 was placed on the bottom line. The Y-axis & Z-axis
feed rates can also be displayed on any line.


 
Updated overlay installed.
Menu driven & shortcut labels speed use, reduce errors.

Note the displays are in high precision mode
showing four digits after the decimal point.

Now there is an
adaptive moving average
filter for the Chinese scales that replaces the

simple moving average filter. It does a much
better job at keeping the scale
reading
 from flickering when the scale is idle yet
rapidly responds when the
scale is moved.



Reverse Polish Notation (RPN) calculator turned on.
Stack of four registers bottom to top: X, Y, Z, & T.

The value in the T (Top) register copies itself as the
stack drops down, just like a
circa 1970s HP calculator.
Many advanced functions are also built-in:
SINE, COS, TAN
,
memory in/out, power of, Pi, square root, axis

preset, hypotenuse, fraction & axis reading.
Results of calculations can be stored into any axis preset.

The last function used is also recalled (retained)
when the OP PRV or OP NXT button is pressed again.


Sine function selected.

Use the Length function to calculate the hypotenuse
  a right-angled triangle with the Pythagorean theorem

given the two other sides. The two sides are taken
from the
two values on the bottom of the stack.
{c = sqrt (a^2 + b^2)}

Entering 4 & 3 (e.g., a 4:3 TV display ratio) for
the sides with the
hypotenuse (TV diagonal) being 5.

The power of function (POW) takes
the penultimate (next to the last) value

on the stack & raises it to the power
of the value on the bottom of the stack.

The example uses 2 to the 8th power  = 256.


Use decimal points to key in the fractional
portion of a number. This example is
2-1/32" for an X-axis preset.



Pressing ENTER then converts the 1/32"
to its decimal equivalent for the X-axis.


For entering just a fraction, e.g., 1/32",
start the key sequence with a decimal point.


The DPU-550 calculator can convert a decimal value
(e.g., 0.1409) to a fraction plus any residual error.


OP PRV or OP NXT is pressed until the
Frac function is displayed, then enter is pressed.


The fraction is 9/64" (0.140625")
with about a 0.0002" error.

TOOL # TOOL SIZE
DIAMETER (inch)
EQUIVALENT
FRACTION
(inch)
EQUIVALENT
DECIMAL (inch)
CORNER
RADIUS (inch)
1 1/16 1/16 0.0625 0.03125
2 2/16 1/8 0.125 0.0625
3 3/16 3/16 0.1875 0.09375
4 4/16 1/4 0.25 0.125
5 5/16 5/16 0.3125 0.15625
6 6/16 3/8 0.375 0.1875
7 7/16 7/16 0.4375 0.21875
8 8/16 1/2 0.5 0.25
9 9/16 9/16 0.5625 0.28125
10 10/16 5/8 0.625 0.3125
11 11/16 11/16 0.6875 0.34375
12 12/16 3/4 0.75 0.375
13 13/16 13/16 0.8125 0.40625
14 14/16 7/8 0.875 0.4375
15 15/16 15/16 0.9375 0.46875
16 16/16 1 1 0.5

The DPU-550 can hold 16 tool sizes vs. the DRO-350's, nine.
I use
Func 5 (tool offset define) to first specify
all the tool sizes where the Tool # is always the
numerator & 16 is always the denominator of a fractional

size.
Tool #/16 of an inch. I find this a very easy
nomenclature to remember, though it is of course, arbitrary.

I used 0 for the Z offsets. The DRO will allow up to
5 significant numbers input after the decimal point.
Func 6
(tool offset use), followed by a Tool #, turns ON
diameter compensation & selects the previously defined tool.


By selecting a predefined tool (Function 6 & tool #6
from the table) this graphic is temporarily displayed.

Front, back, left, right cutting edges & tool #6 are
displayed. The displays then return to positional values.


By pressing 4, the left tool edge is selected
as temporarily indicated by this displayed graphic.

The displays then return to their positional
values. This is the original display mode.


The far left decimal of the X-axis lights to
indicate that edge compensation for a 3/8" end mill is ON.


The latest software upgrade
has changed the edge compensation
display from symbolic to words.

Instrumented Mill, Enclosure, Zeroing, Offset Milling,
Mount, Red Filter,
DPU-550 Daughterboard Upgrade

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