Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Having recently converted to EMC 2.4 and switched the tool table to the new format, I took the opportunity to add a few useful drills.
Low numbers are random end mills & suchlike. Number drills run from 100 to 180, and I’ll add more as I need ’em. Fraction drills run from 201 through 264, although it’s highly unlikely I’ll ever fit a 64/64-inch drill in a chuck that also fits in the Sherline spindle.
All the Z lengths are exactly 1, because I now have a tool length probe that is absolutely wonderful.
In practice, I use the tool table mostly to tell Axis how to draw the tool cylinder in the backplot, because I feed in most diameters directly in the G-Code. The Axis “manual toolchanger” routine prompt will now serve as a mnemonic for the actual size, but I write the G-Code to emit a (debug, #Drill_Size) message for clarity.
The Sherline.ini file references the tool table with the line:
It turns out that the tool table has an undocumented limit of 50-some-odd entries, at least in EMC2 2.4.1. That puts the kibosh on my plans to add a bunch of entries to cover all the drill sizes Eagle might require for a PCB. More on that in a while …
The shop spec says the lug nut torque shall be 104 newton·meter or an equally odd 77 lb·ft. Let’s not get into quibbles about the differences between lb·ft and ft·lb here, OK?
Anyhow, based on the wildly differing and grossly excessive tire pressures left by the guys who installed the new tires, I figured the lug nuts would be over-torqued… as, indeed, they were. My bending-beam torque wrench goes up to 140 n·m and didn’t even come close to breaking those puppies loose.
So I deployed a manly breaker bar and applied most of my weight to the far end. A back of the envelope guesstimate says they were well over 200 n·m, with a few grunt outliers.
Yes, the breakaway torque can be higher than the tightening torque, but they were far beyond even that level.
Lubed the threads, tightened to spec, and it’s all good. I’ll check them next week just to be sure, but sheesh if we had to fix a flat on the road, it would have gotten ugly.
Quite a while ago, I built this slab mount to hold an amateur radio antenna on our daughter’s Tour Easy. It worked fine until the bike blew over and whacked the antenna whip against something solid, at which point the mast cracked.
The antenna screws into an ordinary panel-mount UHF connector secured to the bottom of the slab, with a hole through the slab just large enough to accept the antenna mast. That put all the mechanical stress on the slab, not the connector.
Modified antenna mounting plate
Alas, the new antenna had a slightly different mast outside diameter, so I machined a new adapter to clamp the connector atop the slab. The antenna screws down into the adapter against a brass washer, again keeping the strain on the fitting.
I recently found the commercial mobile antenna cable that I’d been meaning to use on her bike, which required Yet Another Modification to that slab. It turns out that the UHF connector on the cable expects to be secured to sheet metal found in a car body, rather than a half-inch aluminum plate: the threads aren’t long enough!
So I machined circular recesses on the top and bottom to hold the mounting nut and washer, respectively, with 2 mm of aluminum remaining in the middle of the slab.
Milling top recess
The recesses are just fractionally larger than the nut & washer, so most of the stress gets transmitted directly to the slab. Even in the high-vibration bicycle environment, I think there’s enough meat in there to prevent fatigue fractures.
Milling bottom recess
I recycled a G-Code routine I’d written to chew out circular recesses. It does a bit of gratuitous (for this application, anyway) spiraling in toward the center, but got the job done without my having to think too much.
The bottom view shows the washer in action. The recess is deep enough that the cable just barely clears the slab.
Modified mounting plate – bottom
The top view shows the recessed mounting nut. The nut has an O-ring around the connector threads, but the water will probably drain out through the four through-holes left over from the old panel-mount connector.
Modified mounting plate
I turned the top nut down as far as I could with a wrench & (ugh) needle-nose pliers, then tightened the bottom nut about 1/3 turns with a wrench.
You’re not supposed to notice the crispy edges on the PVC bushing holding the reflector to the antenna mast. The high setting on that heat gun is a real toaster…
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.
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.
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.
Sherline Controller with Probe and Home Jacks
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.
X Axis Home Switch
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.
Y Axis Home Switch with Extender
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.
Epoxying the Z Axis Switch
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.
Z Axis Home Switch
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…
The Smell of Molten Projects in the Morning 