The Smell of Molten Projects in the Morning
Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Making the world a better place, one piece at a time
The OEM padding on the ends of my spring clamps wore off long ago; it was some sort of entirely-too-soft dipped plastic.
Some large-diameter heatshrink tubing seems like it ought to be a good replacement… the tips are a bit floppy, but maybe that’s not entirely a Bad Thing.
We shall see…
Having mounted & wired the switches, the next step involves defining the homing sequence & configuration for each axis. All this goes in Sherline.ini and is adapted from the doc there.
The travel limits are somewhat empirical and I think the Y axis will require some adjustment due to the tooling plate switch extender gadget.
The HOME_SEARCH_VEL values may be a bit too high, given the rather lethargic 5.0 in/sec^2 acceleration I’m using for X & Y, with just 3.0 for Z. I’ve heard the occasional thwack as the switch trips, so maybe 20 mils of overtravel isn’t quite enough.
For the X-Axis:
[AXIS_0] ... snippage ... MIN_LIMIT = -1.0 MAX_LIMIT = 9.5 HOME_IS_SHARED = 1 HOME_SEQUENCE = 2 HOME_SEARCH_VEL = 4.75 HOME_LATCH_VEL = 0.016 HOME_FINAL_VEL = 0.25 HOME_OFFSET = 9.1 HOME = 4.5
For the Y-axis:
[AXIS_1] ... snippage ... MIN_LIMIT = -0.5 MAX_LIMIT = 4.95 HOME_IS_SHARED = 1 HOME_SEQUENCE = 1 HOME_SEARCH_VEL = -4.75 HOME_LATCH_VEL = -0.016 HOME_FINAL_VEL = 0.25 HOME_OFFSET = 0.0 HOME = 4.5
For the Z-axis:
[AXIS_2] MIN_LIMIT = -0.1 MAX_LIMIT = 6.9 HOME_IS_SHARED = 1 HOME_SEQUENCE = 0 HOME_SEARCH_VEL = 0.333 HOME_LATCH_VEL = 0.016 HOME_FINAL_VEL = 0.25 HOME_OFFSET = 6.9 HOME = 6.5
The A axis doesn’t get a home switch because I can’t imagine needing one for a rotary table:
[AXIS_3] ... snippage ... MIN_LIMIT = -9999.0 MAX_LIMIT = 9999.0 HOME_SEARCH_VEL = 0 HOME_LATCH_VEL = 0 HOME = 0.0
Real men have real CNC milling machines and real CNC milling machines have home switches. I have an itsy Sherline CNC mill, but now my mill has home switches just like a Real Man’s mill.
Sorta, kinda.
Truth is, I really don’t need home switches for the Sherline. I haven’t done any “production” milling with fancy fixtures, so zeroing the coordinate system to the lower-left vertex of the part-to-be-milled works reasonably well. But I figured it’d be fun to see what I was missing…
The first step was to hack another jack on the Sherline controller box and connect it to parallel port bit 10. The process is pretty much the same as I used for the probe switch jack documented there. I actually put the jack in the hole used for the power LED and drilled a new hole for the LED smack in the middle above the connector.
The simplest way to do home switches is to wire them all in parallel using a single port pin. You can even wire the probe switch in parallel with home switches, too, but I figured it’d be nice to have separate jacks… and, besides, the controller still has a few port pins left.
Adding the home switches requires a few lines (adapted from there) in custom.hal that connect the sense inputs in parallel:
net homeswitches <= parport.0.pin-10-in-not net homeswitches => axis.0.home-sw-in net homeswitches => axis.1.home-sw-in net homeswitches => axis.2.home-sw-in
Using the -not suffix flips the sense of the input so the signal is True when the buttons get pushed. I don’t know of any algorithmic way to determine the actual logic states for a given button configuration, so just try it, use Halmeter to see what happens, then flip as needed.
The catch with adding home (or limit) switches is that Sherline mills have an attentuated mechanical structure with no good places to affix switches. I figured a trio of microswitches and a few dollops of JB Quik epoxy would suffice; if I must remove the switches, a quick shot with a chisel should pop the epoxy right off the metal.
The microswitches have about 20 mils of overtravel. I located the switches so the actuator buttons are bottomed out against the cases with the axes at the far limits of their travels. The steppers are puny enough to stall when the mechanical bits hit their hard limits, so there’s no risk of wrecking the machinery or knocking the switches off.
The X-axis home switch goes on the right side of the table, where it contacts the Y-axis slide at the end of travel. Putting it there also means I can remove the table by simply running the leadscrew out of the nut and pulling the whole affair off to the right. I lashed the switch cable to the motor cable with (wait for it) cable ties, which is probably a Bad Idea for larger machines, but seems to be OK in this situation.
The Y-axis home switch goes at the rear of the machine base, aligned with the plastic bushing I put there to capture the end of the leadscrew. That’s the travel limit for the bare table, but the Sherline tooling plate sticks out another half-inch: the plate hits the column before the table hits the bushing. Alas, I use the plate a lot.
Rather than futz with an adjustable switch position, I made a removable extender. The 3 mm (1/8″ nominal) thick plastic strip has 1 mm milled off the bottom, leaving a tab on the left side that snaps over the dovetail. The screw extends down past the dovetail on the right, so the whole affair slides back & forth just enough to connect the Y-axis slide with the button. The brass tubing exactly fits the tit on the switch actuator and is urethane-glued to the strip.
It’s removable by lifting the left end and sliding the whole affair out under the leadscrew.
The alternative, putting the Y-axis home switch on the very front of the base, would expose the switch & cable to all the slings & arrows of outrageous fortune to be found around the area of the countertop I use most. That may still prove to be a better location: if the back doesn’t work out, it’s easy to move.
The Z-axis switch had to go at the top-of-column mechanical limit, as homing to the downward limit of travel seemed fraught with peril. I epoxied the switch in place by clamping it to a shim atop the Z-axis slide to align the switch body, then applying gentle sideways pressure with a small screwdriver.
This is what it looks like after the epoxy cured. The square key bar sticking out of the extender block clears the switch with plenty of room to spare, no matter what it looks like.
The cables from all three switches go to a common junction where they’re connected in parallel to the cable leading to the green plug in the top picture.
Tomorrow, the configuration file that makes all this work…
Herewith, the discharge test results for all the generic Sony NP-FS11 battery packs I have (click for a bigger image).
The five mostly overlapping upper traces consist of:
The rebuilt packs now have cells from batteryspace.com that are working fine: nominal capacity 600 mAh, actual around 1200 to 1400 for a parallel pair. It’s surprising to see a cell producing its rated capacity…
The two lowest traces (G & I), plus the purple trace (J) are from the eBay source. The first two are obvious junk, but pack J is actually pretty good. The fact that it’s the best of six packs from that vendor tells you all you need to know about their QC.
For those of you joining us via search engines, the rest of the story:
So I dismantled the three junk packs I got from halfway around the world and rebuilt them with better-quality cells. Search for NP-FS11 and you’ll find the rest of the story.
Some observations…
These cases are the thinnest plastic that doesn’t actually break when you pick it up: to crack the case seam, you must push firmly. Two of the three packs were already cracked and the third yielded to a slight squeeze.
What’s inside? Welly, welly, welly, what do we have here?
The cells are labeled Sony Energytec, which ought to be a reputable brand name. Some possibilities:
I don’t know why you’d bother putting counterfeit cells inside a generic case; it’d be more profitable to sell a completely counterfeit battery with a fancy Sony label. So I’m guessing these came from a batch of cells that failed inspection and were miraculously saved from destruction.
They have the usual protection circuit board on the top. What’s a bit tricky is that you must unsolder the three leads connecting to the case terminals before you can extract the cells. I unsoldered the strap from the negative terminal while I was at it; the positive lead is inaccessible beyond the black IC on the left.
After that, it’s a straightforward rebuild.
Magnet wire wants to unspool itself, so it comes with a wrap of tape that eventually turns into a gummy layer. Rather than put new tape on the spool, gash a notch in the rim with a utility knife and capture the wire therein.
If you’re really clever, you’ll angle the notch so the wire folds backwards and holds itself snug. If you’re not, well, there’s nobody going to notice having two opposing notches in the spool, right?
They used to do this with thread and string, back in the old days when such stuff came on wooden spools, but it seems a lost art…
I finally rebuilt the snowblower gas cap, this time before the splash cone worried its way through the plastic stem and dumped all the parts into the tank.
The black rubbery domed thing conceals a chunk of open-cell foam that evidently separates the gasoline from the vent channels under the rim. The plastic stem was quite eroded, but probably had another season or two left in it; now I need not worry about it.
Unlike with the shredder cap, this time I put the screw head on the outside and the jam nuts on the inside; there’s also a jam nut under the cap to keep the screw from walking outward. Just in case, I wrecked the threads to keep the nuts from walking off the end, too; you can see the gouge just above the nut.
The Smell of Molten Projects in the Morning 