Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
While pulling together a talk on OpenSCAD modeling (more on this later), I ran off a batch of calibration and “torture test” objects, with the intent of seeing how my somewhat modified M2 performs. The short answer is that you (well, I) can’t ask for anything better…
That level of as-printed cleanliness is typical: no stringing, no hair, no misplaced globs, no retraction problems. Basically, the plastic shape on the platform matches the mathematical shape on screen.
All of the linear features are with ±0.1 mm of nominal; both the 0.5 and 0.25 mm walls came out at 0.40 mm, because that’s the thread width. Slic3r doggedly puts a thread down the middle of hair-fine walls, which I think is a Good Thing.
The holes came out less than 0.3 mm undersize, which is about what you’d expect because they’re not pre-distorted and have far too many sides. The 1.0 and 0.5 mm diameter holes are present, but just barely visible; those simply aren’t reasonable sizes for this technology.
The bottom view shows a few strings in the bridge test area and more detail of the overhang:
M2 – Calibration Block – bottom
Grouping the overhangs like that produced a flat surface that tended to curl upward, so the final slopes don’t match the design. In round numbers, the M2 can handle something like a 60° overhang reasonably well.
The top view shows the shape in the box looks fine, but with some curls in the main structure. The arch closed over a few random strands, so it’s rougher than I’d like:
M2 – 3DHacker object – top
The spires are lumpy and there’s more striation than I’d like, but this lies well outside the realm of stuff that I build. If I were doing it for real, I’d add some support structures here & there.
A box of surplus Vexta NEMA 23 stepper motors arrived:
Vexta C6925-9212K stepper motors
The data plate sayeth:
Model C6925-9212K
2 phase
1.8°/step
2.3 V
3 A
According to Dan, who happened into the deal, that Vexta model number applies to their custom motors, which accounts for the fact that there’s no further data available anywhere.
Dividing 2.3 V by 3 A = 0.77 Ω windings. Multiplying 2.3 V by 2 A suggests a 7 W maximum dissipation.
Poking around with a meter identifies the windings:
Blue – White – Red
Green – Yellow – Black
Given those colors, the Y G B W R K color sequence on the connector doesn’t make any sense to me. Most likely, there’s a standard I’m unaware of.
The resistance from the center taps outward measures 1.0 Ω, which is close enough to 0.8 Ω for me. Measuring across the whole winding gives 1.8 Ω.
The inductance is 1.0 mH from the center tap and 4.0 mH across the whole winding. Remember that inductance varies as the square of the number of turns.
The time constant for a complete winding = 2.5 ms = 4 mH / 1.6 Ω.
For reasons I won’t go into, I just installed another water heater. This one, nominally a GE that’s made by Rheem, has a perfectly aligned anode rod access port. This view shows the insulation filling the port, after removing the plastic cap:
GE Water Heater Anode Rod – as shipped
A bit of excavation reveals the top of the rod:
GE Water Heater Anode Rod – excavated
And the 1-1/16 six-point socket fits exactly through the port and mates perfectly with the rod:
Evidently, it’s impossible to make a spring both good and noncorrosive:
Garden sprayer – corroded spring
I found a suitable (i.e., good, but rust-prone) spring in the Big Box o’ Medium Springs:
Garden sprayer – spring replaced
Unlike the repair for that sprayer, this spring turned out to be long enough to work perfectly. I have no idea how long I can keep this up, but … at least I’m now keeping pace with the failures.
This is a classic case of investing more time and effort creating the fixture than machining the parts.
Start by squaring up the block, which came from the end of a random chunk of smoke gray polycarbonate, with two 10-32 holes matching the tooling plate hole spacing:
Corner Clip Fixture – squaring
Then drill-and-tap four holes:
Corner Clip Fixture – tapping
The left station will be for drilling the blanks clamped under a sacrificial sheet, so those screw holes aren’t used for anything other than clearance; the top millimeter will get chewed up pretty quickly. The screws in the right station will clamp a stack of drilled blanks under a cover plate. If I went into production, I could see using both stations for both functions, but …
There’s a locating pip in the front left corner that works perfectly with laser alignment:
Corner Clip Fixture – aligning
The blank sheets show where they’d be located for drilling, minus the sacrificial sheet and its clamps that you’ll see below.
The G54 coordinate system origin sits at the locating pip. The G-Code then slaps a G55 origin at each of the two stations in turn to simplify their coordinates, with offsets from M54:
Drilling = (+5,+5)
Milling = (+40,+5)
With all that in hand: stack, clamp, and drill some blanks:
Corner Clip Fixture – drilling
I tried milling a single drilled blank with a sacrificial plastic top plate:
Corner Clip Fixture – first milling setup
But that didn’t work well. I don’t know if this was due to an inept combination of climb milling, using the wrong speed / feed / material / cutter, and just poor style, but the edges of the blank mashed against the clamp plate and curled, instead of cutting cleanly:
Corner Clip Fixture – rounded-over milled edges
So I made a pair of aluminum plates to clamp both sides of the blanks, then milled another stack:
That worked quite well, although the top and bottom clips needed some slight attention from a riffler file and I did break the edges on all the clips. This shows four new clips along with a hand-cut prototype:
Corner Clip Fixture – end result
So I made a dozen more clips, picked the best eight for two sets, sent one set to Dan, installed the other, and … now I have a bunch of spares.
I suppose I should sell clip sets on Etsy / eBay to all the other M2 owners, but I have no idea how to price ’em. If you want some fancy corner clips, send whatever you think they’re worth … [grin]
The CNC version of the corner clips looks much better than the prototypes:
M2 glass retaining clip
Tightening the screws until the clip just flattens puts enough force on the glass + heat spreader stack to hold it firmly against the balls in the bottom pad. The solid rubber L-shaped bumpers and screws hold the glass in position against XY forces… and the whole affair looks much better than the original (and perfectly serviceable) bulldog clips. These clips free up the entire surface of the glass plate, minus four 12 mm triangles that you could, if you were desperate, print right over.
Although it’d be easier to just hack out an angular clip, I wrote a bit of G-Code to put a nice radius on each corner. The clip sits atop the rubber bumper with a 0.5 mm margin to keep the metal edges away from fingers; they’re smooth, but it’s still a strip of 6 mil (= 0.15 mm) phosphor bronze and feels a lot like a knife edge if you press hard enough.
The radius on the three outside corners is a special-case solution of the general circle-through-three-points problem, taking advantage of the symmetry and right-triangle-ness of the corners. This sketch shows the details:
M2 Platform Clip Doodles 4 – corner fairing with margin
The two corners on the bevel over the glass plate have a fixed radius. I reworked my original fairing arc solution for outside cutting and doodled it up for this situation:
M2 Platform Clip Doodles 5 – bevel full solution
The outside corner radius worked out to 5 mm and I set the bevel radius at 3 mm. I think the latter made those corners a bit too sharp, but it’s Good Enough for my simple needs.
Drilling and machining the clips required a fixture:
I used cutter diameter compensation to mill the edges, starting oversize by 1.5 mm and working downward by 0.5 mm on each pass to the actual diameter. That gradually trimmed off the edges without any excitement, so I could start with rough-trimmed stock and not worry about precision hand trimming.
I thought climb milling (CW around the part) would produce better results, but it tended to smear the phosphor bronze against the fixture:
M2 Corner Clips – Climb milling tool paths
Conventional milling (CCW around the part) actually worked, but it required fancier entry and exit moves:
M2 Corner Clips – Conventional milling tool paths
This part is the kind and size of machining perfectly suited to a Sherline CNC mill…
The LinuxCNC G-Code source:
( M2 Build Platform Corner Clips )
( Ed Nisley - KE4ZNU - July 2013 )
( Fixture origin at right-front corner pip )
( Flow Control )
#<_Do_Drill> = 0 ( Drill two holes in clip )
#<_Do_Mill> = 1 ( Mill clip outline )
#<_Climb_Mill> = 0 ( 0 = conventional 1 = climb)
( Fixture info )
#<_Drill_X_Fixture> = 5.0 ( Drill station origin )
#<_Drill_Y_Fixture> = 5.0
#<_Drill_Num> = 30 ( Drill number in tool table)
#<_Drill_Retract> = 15
#<_Drill_Depth> = -1.0
#<_Drill_Feed> = 300
#<_Drill_Speed> = 3000
#<_Mill_X_Fixture> = 40.0 ( Mill station origin )
#<_Mill_Y_Fixture> = 5.0
#<_Mill_Num> = 3 ( Mill number in tool table)
#<_Mill_Dia> = 4.60 ( actual tool diameter)
#<_Mill_Dia_Incr> = 0.50
#<_Mill_Dia_Steps> = 3
#<_Mill_Retract> = 15
#<_Mill_Depth> = -0.5
#<_Mill_Feed> = 300
#<_Mill_Speed> = 8000
(----------------)
( 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
(-------------------)
(-- Mill one pass around outline with tool diameter passed in #1 )
O<MillOutline> SUB
#<X_Size> = 22.0 ( size of support spider pad = nominal clip size )
#<Y_Size> = 22.0
#<Base_Bevel> = 3.2 ( X or Y length of corners clipped from spider pad )
#<Bevel_Size> = 9.0 ( remaining part of trimmed edges on clip )
#<Bevel_Radius> = 3.0 ( fairing radius at bevel corners on clip)
#<R_Div_Root2> = [#<Bevel_Radius> / SQRT[2]]
#<R_1M_Recip_R2> = [#<Bevel_Radius> * [1 - 1/SQRT[2]]]
#<R_Root2_M1> = [#<Bevel_Radius> * [SQRT[2] - 1]]
#<Margin> = 0.5 ( recess inside of nominal )
#<X_Min> = [#<Margin>]
#<X_Max> = [#<X_Size> - #<Margin>]
#<Y_Min> = [#<Margin>]
#<Y_Max> = [#<Y_Size> - #<Margin>]
#<Corner_Rad> = [[#<Margin> * [1 - SQRT[2]] + [#<Base_Bevel> / SQRT[2]]] / [SQRT[2] - 1]]
O<Climb> IF [#<_Climb_Mill>]
G0 X#<X_Min> Y[#<Y_Max> + 3*#<_Mill_Dia>]
G1 Z#<_Mill_Depth> F#<_Mill_Feed>
G41.1 D#1
G3 X[#<X_Min>] Y#<Y_Max> I0 J[0-1.5*#<_Mill_Dia>] ( cutter comp on: entry move)
G1 X[#<Bevel_Size> - #<R_Root2_M1>]
G2 X[#<Bevel_Size> + #<R_1M_Recip_R2>] Y[#<Y_Max> - #<R_1M_Recip_R2>] J[0-#<Bevel_Radius>]
G1 X[#<X_Max> - #<R_1M_Recip_R2>] Y[#<Bevel_Size> + #<R_1M_Recip_R2>]
G2 X#<X_Max> Y[#<Bevel_Size> - #<R_Root2_M1>] I[0-#<R_Div_Root2>] J[0-#<R_Div_Root2>]
G1 Y[#<Y_Min> + #<Corner_Rad>]
G2 X[#<X_Max> - #<Corner_Rad>] Y#<Y_Min> I[0-#<Corner_Rad>] J0
G1 X[#<X_Min> + #<Corner_Rad>]
G2 X#<X_Min> Y[#<Y_Min> + #<Corner_Rad>] I0 J#<Corner_Rad>
G1 Y[#<Y_Max> - #<Corner_Rad>]
G2 X[#<X_Min> + #<Corner_Rad>] Y#<Y_Max> I#<Corner_Rad> J0
G40
G0 X#<X_Min> Y[#<Y_Max> + 3*#<_Mill_Dia>]
(G3 X#<Bevel_Size> Y[#<Y_Max> + 3*#<_Mill_Dia>] I0 J[1.5*#<_Mill_Dia>]) ( cutter comp off: safe exit)
G0 X#<X_Min> ( return to start)
O<Climb> ELSE
G0 X#<X_Size> Y[#<Y_Size> + #1/2]
G1 Z#<_Mill_Depth> F#<_Mill_Feed>
G42.1 D#1
G1 X#<Bevel_Size> Y[#<Y_Max>] ( cutter comp on: entry move)
G1 X[#<X_Min> + #<Corner_Rad>]
G3 X#<X_Min> Y[#<Y_Max> - #<Corner_Rad>] I0 J[0-#<Corner_Rad>]
G1 Y[#<Y_Min> + #<Corner_Rad>]
G3 X[#<X_Min> + #<Corner_Rad>] Y[#<Y_Min>] I#<Corner_Rad> J0
G1 X[#<X_Max> - #<Corner_Rad>]
G3 X[#<X_Max>] Y[#<Y_Min> + #<Corner_Rad>] I0 J#<Corner_Rad>
G1 Y[#<Bevel_Size> - #<R_Root2_M1>]
G3 X[#<X_Max> - #<R_1M_Recip_R2>] Y[#<Bevel_Size> + #<R_1M_Recip_R2>] I[-#<Bevel_Radius>]
G1 X[#<Bevel_Size> + #<R_1M_Recip_R2>] Y[#<Y_Max> - #<R_1M_Recip_R2>]
G3 X[#<Bevel_Size> - #<R_Root2_M1>] Y#<Y_Max> I[-#<R_Div_Root2>] J[-#<R_Div_Root2>]
G2 Y[#<Y_Max> + 3*#<_Mill_Dia>] J[#<_Mill_Dia>*1.5] ( get away from corner)
G40
G0 X#<X_Size> ( cutter comp off: safe exit)
G0 Y[#<Y_Size> + #1/2] ( return to start)
O<Climb> ENDIF
O<MillOutline> ENDSUB
(----------------)
( Start machining... )
G17 G40 G49 G54 G80 G90 G94 G99 ( reset many things )
G21 ( metric! )
G91.1 ( incremental arc centers)
(msg,Verify: G30.1 position in G54 above tool change switch? )
M0
(msg,Verify: fixture origin XY touched off? )
M0
(msg,Verify: Current tool Z=0 touched off? )
M0
( Set up probing)
O<Probe_Init> CALL
T0 M6
(---- Drill holes)
O<DoDrill> IF [#<_Do_Drill>]
(debug,Insert drill tool = #<_Drill_Num>)
T#<_Drill_Num> M6
O<Probe_Tool> CALL
(debug,Set spindle to #<_Drill_Speed> rpm )
M0
G0 X#<_Drill_X_Fixture> Y#<_Drill_Y_Fixture>
G0 Z#<_Drill_Retract>
G10 L20 P2 X0 Y0 Z#<_Drill_Retract> ( P2 = G55)
G55 ( drill station coordinates )
G81 X5.0 Y15.0 Z#<_Drill_Depth> R#<_Drill_Retract> F#<_Drill_Feed>
G81 X15.0 Y5.0
G54
O<DoDrill> ENDIF
(---- Mill outline )
( Start with large diameter and end with actual diameter to trim in stages)
O<DoMill> IF [#<_Do_Mill>]
(debug,Insert mill tool = #<_Mill_Num>)
T#<_Mill_Num> M6
O<Probe_Tool> CALL
(debug,Set spindle to #<_Mill_Speed> rpm )
M0
G0 X#<_Mill_X_Fixture> Y#<_Mill_Y_Fixture>
G0 Z#<_Mill_Retract>
G10 L20 P2 X0 Y0 Z#<_Mill_Retract> ( P2 = G55)
G55 ( mill station coordinates )
#<PassCount> = 0
O<MillLoop> DO
#<Diameter> = [#<_Mill_Dia> + [#<_Mill_Dia_Steps> - #<PassCount>]*#<_Mill_Dia_Incr>]
O<MillOutline> CALL [#<Diameter>]
#<PassCount> = [#<PassCount> + 1]
O<MillLoop> WHILE [#<PassCount> LE #<_Mill_Dia_Steps>]
( Finishing pass with zero cut )
O<MillOutline> CALL [#<Diameter>]
G0 Z#<_Mill_Retract>
G54
O<DoMill> ENDIF
G30
(msg,Done!)
M2
The rest of the doodles, which don’t match up with the final G-Code because they represent the earliest versions of the layout:
In the course of normal events around here, the M2 gets tipped to one side or the other. Every time that happens, I rediscover the blindingly obvious fact that there’s nothing holding the glass build plate and the heater to the support spider:
M2 build platform corner
A few minutes with a metric ruler produced some useful dimensions for the ends of the spider’s arms:
M2 Platform Support Spider Pad Dimensions
The Big Box o’ Foamy Things emitted a mouse pad (remember mouse pads?) of exactly the right thickness to bring the corner pads just barely above the level of the glass plate, thus allowing for slight compression:
M2 corner bumpers
That’s a 1/8 inch hole punch, which is close enough to the M3 screw diameter in foam rubber. It worked fine for the balls in the corner support pads, too.
The long-suffering shop scissors produced results about as pretty as one might expect:
img_3157 – M2 platform retaining clips – raw cut
Which is to say, not very.
The material is 6 mil (about 0.15 mm) phosphor bronze, nice and springy. Combined with ripply edges and sharp corners, you get perfectly serviceable serrated knife blades suitable for use in traditional shop ceremonies of ritual scarification of the fingertips.
I stacked the slips, clamped them to the Sherline’s table between sacrificial plastic sheets, used manual CNC to poke a pair of #31 holes (0.120 inch, about the right clearance for M3 screws) at the right spots, and then stacked everything up on the M2:
M2 platform retaining clip oops – in place
The alert reader will notice a third #31 hole at the wrong spot, which was the first one I drilled and partially explains the lack of pictures of the operation.
Sighting across the platform shows that the clip doesn’t lie quite flat on the glass, due to the scissors-cut bending:
M2 platform retaining clip – edge view
However, four of these clips hold the glass firmly to the heat spreader and eliminate the need for the stock bulldog clips, which is what I wanted to find out.
But they’re ugly and I don’t want to explain that extra hole…
The Smell of Molten Projects in the Morning 