The New Hotness

Cabin Fever Tchotchke: Engraved Dog Tag

Once again I’m planning to attend the Cabin Fever Expo in York; my shop assistant says this year she won’t barf in the kitchen sink Thursday evening just before bedtime…

If I’m going to haul a Sherline CNC setup that far and spend all day talking machining, I must have some tchotchkes / swag to talk about. We figured a small plastic dog tag with relevant URLs would be appropriate.

I modeled the tag after my father’s WWII tag, including the mysterious notch. The rounded ends actually have three curves: two small fairing arcs blend the sides into the end cap.

The G-Code routine figures out all the coordinates and suchlike from some basic physical measurements & guesstimates, so tweaking the geometery is pretty straightforward. There was a blizzard going on while I wrote it: a fine day to spend indoors hacking code.

My assistant fired up Inkscape, laid out the text, figured out how to coerce G-Code out of Inkscape using the cnc-club.ru extension, then aligned it properly with the center of the chain hole as the origin on the right side. My routine calls the text G-Code file as a subroutine.

The extension’s header and footer files wrap EMC2’s SUB / ENDSUB syntactic sugar around the main file. The default files include an M2 that kills off the program; took a while to track that one down.

The header file:

O<dogtagtext> SUB

And the matching footer file:

O<dogtagtext> ENDSUB

The Inkscape-to-gcode instructions come out with absolute coordinates relative to the origin you define when you create the layout. The nested loops in my wrapper slap a G55 coordinate offset atop each label in turn, then call the subroutine.

The result is pretty slick:

I carved out that proof-of-concept label atop double-sided adhesive tape, but peeling off the goo is a real pain; a 2×3 array will be much worse. I’d rather do that than figure out how to clamp the fool things to the sacrificial plate, though.

The engraving is 0.2 mm deep with a Dremel 30 degree tool. My shop assistant describes it as “disturbing” the acrylic, not actually engraving a channel. This isn’t entirely a Bad Thing, as the font isn’t quite a stick font and the outline of each character mushes together. We must fiddle with the font a bit more; she favors a boldified OCR-A look.

Some lessons:

The Kate G-Code syntax highlighter isn’t down with EMC2’s dialect
Be very sure you touch off the workpiece origin in G54, not G55
Xylene doesn’t bother acrylic and works fine on tape adhesive
Symlinks aimed across an NFS link work fine in ~/emc2/nc_files/
That 2×3 array may be too big for the Sherline’s tooling plate
Tool length probing FTW!

The G-Code:

(Cabin Fever 2011 Dogtag)
(Ed Nisley - KE4ZNU - December 2010)
(Origin at center of chain hole near right side)
(Stock held down with double-stick tape)

(--------------------)
(Flow Control)

#<_DoText>      = 1
#<_DoDrill>     = 1
#<_DoMill>      = 1

( Sizes and Shapes)

(-- Tag array layout)

#<_NumTagsX>    = 3                         (number of tags along X axis)
#<_NumTagsY>    = 2                         ( ... Y axis)

#<_TagSpaceX>   = 60                        (center-to-center along X axis)
#<_TagSpaceY>   = 35                        ( ... Y axis)

(-- Tag Dimensions)

#<_TagSizeX>    = 50.8                      (2.0 inches in WWII!)
#<_TagSizeY>    = 28.6                      (1-1/8 inches)
#<_TagSizeZ>    = 2.0

#<_HoleOffsetX> = 4.0                       (hole center to right-side tag edge)

#<_NotchSizeX>      = 3.5                   (locating notch depth from far left edge)
#<_NotchCtrY>       = 5.0                   (locating notch from Y=0)

#<_NotchAngleBot>   = 30                    (lower angle in notch)
#<_NotchAngleTop>   = 45                    (upper angle in notch)

(-- Fairing Curve Dimensions as offsets from end arc center)

#<_EndFairR>    = [0.68 * #<_TagSizeY>]
#<_CornerFairR> = [0.25 * #<_TagSizeY>]

#<_PCRadius>    = [#<_EndFairR> - #<_CornerFairR>]
#<_PCY>         = [[#<_TagSizeY> / 2] - #<_CornerFairR>]
#<_PCTheta>     = ASIN [#<_PCY> / #<_PCRadius>]
#<_PCX>         = [#<_PCRadius> * COS [#<_PCTheta>]]

#<_P1Y>         = [#<_TagSizeY> / 2]                    (top / bottom endpoint)
#<_P1X>         = #<_PCX>

#<_P2X>         = [#<_EndFairR> * COS [#<_PCTheta>]]
#<_P2Y>         = [#<_EndFairR> * SIN [#<_PCTheta>]]

(-- Tooling)

#<_TraverseZ>   = 1.0                       (safe clearance above workpiece)

#<_DrillDia>    = 3.2                       (drill for hole and notch)
#<_DrillNum>    = 1                         ( ... tool number)
#<_DrillRadius> = [#<_DrillDia> / 2]
#<_DrillFeed>   = 200                       (drill feed for holes)
#<_DrillRPM>    = 3000

#<_MillDia>     = 3.2                       (mill for outline)
#<_MillNum>     = 1                         ( ... tool number)
#<_MillRadius> = [#<_MillDia> / 2]
#<_MillFeed>    = 150                       (tool feed for outlines)
#<_MillRPM>     = 5000

#<_TextDia>     = 0.1                       (engraving tool)
#<_TextNum>     = 1
#<_TextFeed>    = 600                       (tool feed for engraving)
#<_TextRPM>     = 10000

(-- Useful calculated values)

#<_TagRightX>   = #<_HoleOffsetX>           (extreme limits of tag in X)
#<_TagLeftX>    = [#<_TagRightX> - #<_TagSizeX>]

#<_EndFairRtX>  = [#<_TagRightX> - #<_EndFairR>]
#<_EndFairLfX>  = [#<_TagLeftX> + #<_EndFairR>]

#<_NotchCtrX>   = [#<_TagLeftX> + #<_NotchSizeX> - #<_DrillRadius>]

(--------------------)
(--------------------)
( Initialize first tool length at probe switch)
(    Assumes G59.3 is still in machine units, returns in G54)
( ** Must set these constants to match G20 / G21 condition!)

#<_Probe_Speed>     = 400            (set for something sensible in mm or inch)
#<_Probe_Retract>   =   1            (ditto)

O<Probe_Tool> SUB

G49                     (clear tool length compensation)
G30                     (move above probe switch)
G59.3                   (coord system 9)

G38.2 Z0 F#<_Probe_Speed>           (trip switch on the way down)

G0 Z[#5063 + #<_Probe_Retract>]     (back off the switch)

G38.2 Z0 F[#<_Probe_Speed> / 10]    (trip switch slowly)

#<_ToolZ> = #5063                    (save new tool length)

G43.1 Z[#<_ToolZ> - #<_ToolRefZ>]    (set new length)

G54                     (coord system 0)
G30                     (return to safe level)

O<Probe_Tool> ENDSUB

(-------------------)
(-- Initialize first tool length at probe switch)

O<Probe_Init> SUB

#<_ToolRefZ> = 0.0      (set up for first call)

O<Probe_Tool> CALL

#<_ToolRefZ> = #5063    (save trip point)

G43.1 Z0                (tool entered at Z=0, so set it there)

O<Probe_Init> ENDSUB

(--------------------)
(Start machining)

G40 G49 G54 G80 G90 G94 G97 G98     (reset many things)

G21                                 (metric!)

(msg,Verify G30.1 position in G54 above tool change switch)
M0
(msg,Verify XYZ=0 touched off at left front tag hole center on surface)
M0

O<Probe_Init> CALL
T0 M6                           (clear the probe tool)

(-- Engrave Text)

O<DoText> IF [#<_DoText>]

(msg,Insert engraving tool)
T#<_TextNum> M6         (load engraving tool)
O<Probe_Tool> CALL

F#<_TextFeed>
S#<_TextRPM>

(debug,Set spindle to #<_TextRPM>)
M0

G0 X0 Y0                (get safely to first tag)
G0 Z#<_TraverseZ>       (to working level)

G10 L20 P2 X0 Y0 Z#<_TraverseZ>         (set G55 origin to 0,0 at this point)
G55                                     (activate G55 coordinates)

O3000 REPEAT [#<_NumTagsX>]

O3100 REPEAT [#<_NumTagsY>]

O<dogtagtext> CALL

G0 X0 Y0
G10 L20 P2 Y[0 - #<_TagSpaceY>]         (set Y orgin relative to next tag in +Y direction)

O3100 ENDREPEAT

G10 L20 P2 X[0 - #<_TagSpaceX>] Y[[#<_NumTagsY> - 1] * #<_TagSpaceY>] (next to +X, Y to front)

O3000 ENDREPEAT

G54                                     (bail out of G55 coordinates)

(-- Drill holes)

O<DoDrill> IF [#<_DoDrill>]

T0 M6
(msg,Insert drill)
T#<_DrillNum> M6
O<Probe_Tool> CALL

F#<_DrillFeed>
S#<_DrillRPM>

#<_DrillZ> = [0 - #<_TagSizeZ> - #<_DrillRadius>]

(debug,Set spindle to #<_DrillRPM>)
M0

G0 X0 Y0                (get safely to first tag)
G0 Z#<_TraverseZ>       (to working level)

#<IndexX> = 0
O1000 DO

#<IndexY> = 0
O1100 DO

#<TagOriginX> = [#<IndexX> * #<_TagSpaceX>]
#<TagOriginY> = [#<IndexY> * #<_TagSpaceY>]

G81 X#<TagOriginX> Y#<TagOriginY> Z#<_DrillZ> R#<_TraverseZ>
G81 X[#<TagOriginX> + #<_NotchCtrX>] Y[#<TagOriginY> + #<_NotchCtrY>] Z#<_DrillZ> R#<_TraverseZ>

#<IndexY> = [#<IndexY> + 1]
O1100 WHILE [#<IndexY> LT #<_NumTagsY>]

#<IndexX> = [#<IndexX> + 1]
O1000 WHILE [#<IndexX> LT #<_NumTagsX>]

G30     (go home)

O<DoDrill> ENDIF

(-- Machine outlines)

O<DoMill> IF [#<_DoMill>]

T0 M6                   (eject drill)
(msg,Insert end mill)
T#<_MillNum> M6         (load mill)
O<Probe_Tool> CALL

F#<_MillFeed>
S#<_MillRPM>

(debug,Set spindle to #<_MillRPM>)
M0

G0 X0 Y0                (get safely to first tag)
G0 Z#<_TraverseZ>       (to working level)

G10 L20 P2 X0 Y0 Z#<_TraverseZ>         (set G55 origin to 0,0 at this point)
G55                                     (activate G55 coordinates)

O2000 REPEAT [#<_NumTagsX>]

O2100 REPEAT [#<_NumTagsY>]

G0 X[#<_NotchCtrX>] Y[#<_NotchCtrY>]     (get to center of notch hole)
G0 Z[0 - #<_TagSizeZ>]                      (down to cutting level)

G91                                         (relative coordinate for notch cutting)
G1 X[0 - #<_NotchSizeX>] Y[0 -  #<_NotchSizeX> * TAN [#<_NotchAngleBot>]]
G1 X[0 + #<_NotchSizeX>] Y[0 +  #<_NotchSizeX> * TAN [#<_NotchAngleBot>]]
G1 X[0 - #<_NotchSizeX>] Y[0 +  #<_NotchSizeX> * TAN [#<_NotchAngleTop>]]
G90                                         (back to abs coords)

G42.1 D#<_MillDia>                          (cutter comp to right)
G1 X[#<_TagLeftX>] Y0                       (comp entry move to tip of left endcap)

G3 X[#<_EndFairLfX> - #<_P2X>] Y[0 - #<_P2Y>] I[#<_EndFairR>] J0    (left endcap front half)

G3 X[#<_EndFairLfX> - #<_P1X>] Y[0 - #<_P1Y>] I[#<_P2X> - #<_PCX>] J[#<_P2Y> - #<_PCY>]

G1 X[#<_EndFairRtX> + #<_P1X>]                                      (front edge)

G3 X[#<_EndFairRtX> + #<_P2X>] Y[0 - #<_P2Y>] I0 J[#<_CornerFairR>]

G3 X[#<_EndFairRtX> + #<_P2X>] Y[#<_P2Y>] I[0 - #<_P2X>] J[#<_P2Y>]    (right endcap)

G3 X[#<_EndFairRtX> + #<_P1X>] Y[#<_P1Y>] I[#<_PCX> - #<_P2X>] J[#<_PCY> - #<_P2Y>]

G1 X[#<_EndFairLfX> - #<_P1X>]                                      (rear edge)

G3 X[#<_EndFairLfX> - #<_P2X>] Y[#<_P2Y>] I0 J[0 - #<_CornerFairR>]

G3 X[#<_EndFairLfX> - #<_P2X>] Y[0 - #<_P2Y>] I[#<_P2X>] J[0 - #<_P2Y>]    (left endcap complete)

G0 Z#<_TraverseZ>

G40

G0 X0 Y0
G10 L20 P2 Y[0 - #<_TagSpaceY>]         (set Y orgin relative to next tag in +Y direction)

O2100 ENDREPEAT

G10 L20 P2 X[0 - #<_TagSpaceX>] Y[[#<_NumTagsY> - 1] * #<_TagSpaceY>] (next to +X, Y to front)

O2000 ENDREPEAT

G54                                     (bail out of G55 coordinates)

G30         (go home)

O<DoMill> ENDIF

M2

The doodles leading to the equations:

We’ll see you there!

2011-01-02