Rong Fu RF-25 Mill Digital Read-Out (DRO)
Last updated on Sunday, June 15, 2014 03:21:28 PM Eastern 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.

Enclosure


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 layout drawing of the (x, y) coordinates
supplied to drill & cutout out all the holes.
 I like to use a
Unibit step drill to make holes in thin materials.

Zeroing

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

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 # 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 0.125 0.0625
3 3/16 3/16 0.1875 0.09375
4 4/16 0.25 0.125
5 5/16 5/16 0.3125 0.15625
6 6/16 0.375 0.1875
7 7/16 7/16 0.4375 0.21875
8 8/16 0.5 0.25
9 9/16 9/16 0.5625 0.28125

Function 6 (tool offset use), followed by a Tool # (1~9), 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,
" 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.net arm is mounted off a triangular, " 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.


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 -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 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 enhanced capabilities & performance.

OpenDRO 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 to page 38 of 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 UPGRADE
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 (⅛") & USB access ("). 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: sin, 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 of 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 0.125 0.0625
3 3/16 3/16 0.1875 0.09375
4 4/16 0.25 0.125
5 5/16 5/16 0.3125 0.15625
6 6/16 0.375 0.1875
7 7/16 7/16 0.4375 0.21875
8 8/16 0.5 0.25
9 9/16 9/16 0.5625 0.28125
10 10/16 0.625 0.3125
11 11/16 11/16 0.6875 0.34375
12 12/16 0.75 0.375
13 13/16 13/16 0.8125 0.40625
14 14/16 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 ⅜" 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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