Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
This is a better view of the alignment process that I endure once a year when I haul my Sherline mill back from Cabin Fever. The whole thing depends on a laser level that I’ve gutted and clamped to the floor joists over the mill, as described there.
The first step uses a plumb bob to position the hacked laser level lens directly over the Sherline’s spindle bore. I’ve shimmed the countertop under the mill to be pretty much level, so a vertical line from the bore determines where the lens must be.
Then I fiddle around to get the beam directly in the middle of the spindle bore, using a slip of paper to figure out where it’s going. The top picture shows the result.
Having done this a few times, the laser level starts out pretty much aligned, but the first setup required quite a bit of back-and-forth twiddling of the screws.
Then I put a mirror flat on the Sherline’s table / tooling plate to reflect the beam back up the spindle. More fiddling around gets the reflected spot pretty close to the outgoing beam; this picture shows the spot just off-center near the top (actually, toward the base of the laser level’s frame) of the aperture.
Reflected spot near laser aperture
When the outgoing and reflected beams converge, then I put the bushing (without the polarizing filter) in the top of the spindle bore to reduce the beam size and fine-tune the positions & angles.
Surprisingly, it stays in position quite solidly. I do twiddle it every now & again, but as long as the beam gets through the bore it’s close enough.
A display across the aisle from the CNC Ghetto at Cabin Fever featured a nice Laser Center Edge Finder with their new polarizing attachment. I played with it for a while and decided that, although my crude lashup gave similar results, I just had to have a polarizing filter, too.
I’d already made a bushing to fit the top of the spindle bore with a small aperture that aids in lining up the laser, so I just added a small recess for a disk of polarizing film. I have, for reasons that should not require any explanation by now, a lifetime supply of polarizing film…
Anyhow, the new polarizing filter sits neatly atop the spindle. The main laser beam lights up the middle of the filter, with junk light spilling on the bushing to the front and rear.
Polarizing film in upper bushing
Getting a good photograph of the spot size poses some problems, but here goes. This is the original, un-attenuated spot on a scale with 0.5 mm divisions: in round numbers, it’s half a millimeter across.
Normal laser spot size
Cross-polarizing the beam produces this attenuated spot on the same scale: it’s 0.25 mm in diameter, maybe a bit less. Call it 10 mils.
Attenuated laser spot size
Obviously, what you’re seeing are overexposed more-or-less Gaussian spots, so their diameters aren’t fixed numbers. But at this level, the inaccuracies of my Orc Engineering lens mount are comparable to the spot size, so reducing the spot any further isn’t going to improve the overall positioning accuracy.
It’s worth noting that the spot size isn’t the same as the positioning accuracy: you can visually align a workpiece mark to less than 1/4 the spot diameter. Claiming 1/10 the diameter would be more brag than fact, at least for me, but somewhere around 2 mils is close. That’s good enough for most of what I do.
Re-running that probe length switch test a few weeks later produced these results for three trials over the course of two days.
Probe Repeatability – Dec 2010
The Z-axis differences are all relative to the first reading on the first day, so this includes whatever Z-axis changes take place without doing anything else on the mill in between the tests. I turned the power off after making the first set of measurements, so the steppers restarted with up to a plus-or-minus one full step offset; that works out to:
(0.050 inch) * (1 rev / 200 steps) = 0.00025 in = 0.0064 mm
Because EMC2 doesn’t actually know where the stepper is, any uncommanded motion will show up as an offset when the probe switch trips, which is exactly what we see here.
Two things of interest:
The -0.05 mm offset between the two days could well be part of a single step offset
Successive probe positions during a single test don’t change by hardly anything at all
(I’m giving a talk and show-n-telling my Sherline CNC milling machine at Cabin Fever Expo right about now, so having this data readily available seemed prudent. The talk & handouts are there.)
The man with one thermometer knoweth the temperature
The man with many thermometers knoweth not the temperature
Drilling the isothermal block
Given the five thermocouples and their meters shown there, plus the Thing-O-Matic’s thermocouple, I had six different temperatures. They’re close, but we can do better than that.
The general idea is to put all the thermocouple beads in close proximity so they share the same temperature, record their opinions to various temperatures, then figure out an equation that adjusts their disparate opinions to reflect consensus reality.
I cranked out an isothermal block on the Sherline mill, using EMC2’s exceedingly handy polar coordinate notation to get a nice hexagon. Touch off XYZ=0 at the middle of the block, then center-drill and drill:
For lack of anything better, 3000 rpm with a drill matching the ID of the brass tubes, plus dripping cutting fluid as needed.
Thermocouples in block
I used a 6 Ω 50 W resistor (the adult version of the resistors on the Thing-O-Matic / MK5 head) as a heat source, clamping the block to the resistors with plastic clamps to provide mechanical force and thermal isolation. Good idea, bad implementation: as you’ll see, those little red tips melt at a rather low temperature.
The TOM thermocouple bead will fit into the empty hole.
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.
Cabin Fever Dog Tag
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:
Screenshot: AXIS Dog Tags
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
I actually did get around to plugging the holes directly under the power resistors on those heatsinks, even though we all know it makes absolutely no difference whatsoever.
Heatsink hole plugs
Start with some 5/16-inch aluminum rod, face and center-drill one end, turn down about two inches to a scant 0.200 inch diameter, saw off a stub on the end.
Grab the stub in the 3-jaw Sherline chuck clamped to the mill table and slice off 0.240 inch slugs using a teeny slitting saw and manual CNC.
No pix of the setup, for reasons that made sense at the time, but that project gives you the general idea.
Repeat three times to get 3 x 6 = 18 slugs, plus a few spares.
Clean out the heatsink holes, clamp a bar (covered with tape) on the flat side, butter up the holes & slugs with JB Weld epoxy, squish ’em in place, scrape off the excess epoxy after a few hours.
Actually, this was a thinly veiled excuse to get my shop assistant some Quality Shop Time on the lathe and CNC mill. Wouldn’t you do the same?
The PC won’t need a CD after it’s up and running, but it’s easiest to boot/install from a CD. Get a random SATA CD drive from eBay or, more usefully, a USB-to-SATA/IDE converter, harvest an IDE CD drive from a old donor box, plug it into the Foxconn box, and tweak the BIOS to boot from that USB device.
Install Ubuntu 10.04 (not the current 10.10) from CD. I use the mini-iso CD (link to Overview), which has the advantage of fetching the current version of everything from the Ubuntu site. You can putz around making a bootable USB image, which is cute, but the USB-to-IDE drive adapter will come in handy for other things.
Toward the end of the installation you get a list of configurations and packages to install. Pick Ubuntu desktop, down near the bottom of the list. Include SSH server if you want to do remote maintenance.
Install / tweak / twiddle to set up some comfort items:
NFS shares to the file server holding my CNC files
Desktop sharing so I can dry-run from a warmer chair
Screen backdrop on file server to show network is running
Lest all this seem like a lot of hocus pocus, remember that you’re
becoming a system integrator with your fingers on all the knobs and
buttons normally hidden behind the “Do Not Open: No User Serviceable Parts Inside” covers.
You could, of course, pay somebody to do this for you… [grin]
