Answer: When it’s actually a metric tool that has been intentionally mislabeled in inch units.
I’ve run into this quite a bit actually, Chinese-made tooling (especially collets), is often mis-labeled as the nearest inch size. Sometimes it’s not much of an issue, but often it is. In this case I bought a 1/4” (.250) Square 5C collet which I suspect is actually a mis-labeled 6mm (.236). Collets are normally split after the hole is made which tends to make them spring-open a bit, so a collet with a 1/4” hole is normally a few thousandths over until clamped which makes it easy to install/remove stock. In this case it measures .244 before being clamped, so it’s definitely undersize. The stock that I’m holding is .249 (ground) and needs to be forced through the collet from the back side since the collet closes more when the stock is inserted from the front. Notice the scrapes that the collet made in the material. What a hassle, buyer beware.
The original control panel on my Denford Easimill had a bunch of mechanical switches, black & white CRT etc. Once all this legacy stuff was removed, the original panel looked like Swiss cheese. There were so many holes in the panel that it wouldn’t make sense to to patch it like I did on my Denford Orac lathe. Instead, I cut a new panel out of .080” thick aluminum on my bandsaw using the outline of the original panel as a template. Bandsaws leave pretty jagged edges on sheetmetal, so I hit the cut edges with a mill bastard file to remove the really rough spots and then ran it across the Scotchbrite wheel on my 6” bench grinder. I used transfer punches to copy the locations of the mounting screws from the original panel. This normally works great, but since Denford had buggered the original hole locations and ovaled out most of them to make it fit, some of my transferred holes missed the mark and had to be ovaled out too. While I was at it, I decided to relocate the (3) original lights/switches to the top of panel so that the clear the tool changer. These are the E-stop, power-on pilot light, and the green enable button that enables the drives for the axes. I powder-coated the panel black with my Harbor Freight powder coat gun. This worked out well for two reasons, first Denford machines of this vintage used black as their base-color, second, black is the only color that I ever use in my powder coat gun since I haven’t figured out how you’re supposed to clean it and change colors. The panel was too big for the normal spray booth, which is just a cardboard box. Instead, I sacrificed one of those big “wardrobe” moving boxes. I cut a picture window in one side, being careful not to cut all the way to the edge so that the box would retain the stiffness of the corners and not collapse. Once it was sprayed, I used one of my favorite tricks and cured the powder with an infrared propane camping stove. The powder goes on looking dry and dusty, and needs to cure at about 400F for 5 minutes or so. When I cure in the toaster, I just leave the parts in for 15 minutes and call it good. When doing large parts outside, I literally sit there to watch the paint dry. First, it loses the dusty appearance and starts to shimmer, it will look very “wet” and shiny, after a few minutes it will start to take on more of a matte appearance, this means that section is cured, and you can shift the heater slightly to start curing the next section. Altogether, the process took about 30 minutes and that included making a new spray booth. Better results than spray paint and the parts are ready for use hours faster than the alternative. I contacted Denford to see if I could buy some logo stickers, but they didn’t bother to respond to my email, so I traced the original logos in my CAD package and had replicas made by a vendor that I found on eBay. Total cost was about $5 delivered. Here is the completed panel without bezel installed.
I’ve been working like crazy to meet my self-imposed Friday deadline for completion of the auto-leveling lightbar. Actually, I told that engineer that I mentioned previously that I’d have something to show him on Friday (today). So now my fake-deadline is a real deadline, 4 hours to go.
I’ve made a tremendous amount of progress. Will it be finished in time? Keep checking-in to find out. I’ve taken a lot of pictures and video along the way, and there’s good information to share, but it’s going to take me a couple of days to get everything posted. My video here is a blatant rip-off of the one that I mentioned previously, but I’ve tried to route the wires cleanly and show everything in a way that will hopefully make it a little more clear. Different Arduino’s often have their pins in different places, so be careful about counting pins and assuming that it will match yours. The servo is pulsing because it is drawing its power from the Arduino and it’s drawing too much. Powering it from a separate power supply makes that issue go away, but I wanted to show the wiring in its simplest possible form. In my previous post, I listed the wiring connections and program.
The flashlights were dismantled to get to their LED arrays. The trick is to only snip once, then peel the rim away with a series of movements can-opener style. The entire rim should come off in one jagged piece. One of the flashlights actually had a glass lens in it, the other *identical* flashlight had a plastic Lens. Here’s a picture of the contents of the flashlight. The part that I’m calling the “Retainer” also ensures contact between the circuit board on the back of the LED array and the body of the flashlight.tThe task that I was most concerned about was programming the Arduino to track the gyro. When I found a YouTube video that showed it being done, I thought I had it made. Even the sketch (Arduino-speak for program) was posted. It will be running in minutes! or maybe not…
My first clue that it wasn’t going to be quite that easy were all of the comments under the video saying things like “I can’t get it to work”, or “Yeah, I tried that and it still won’t work. The author had patched his code several times, but it didn’t seem to help. I imported the libraries that he said were needed, but I was still getting these weird “Function not defined” errors. Every time I made one error go away, another cropped up. It was whack-a-mole with Arduino libraries. Around 1am I decided to sleep on it. The next morning, 5 minutes after waking up, I thought “I wonder why the ‘Servo’ library isn’t loaded, seems like it might be handy for controlling servos…” Sure enough, it instantly worked. That video has been up for over 3 months and “fixed” by the author several times and it’s still not quite right. In the world of open-source time savings or losses scale tremendously. This video has over a thousand hits, even if only 200 people tried to reproduce it and wasted an hour figuring it out (took me two), that’s 200 hours of labor down the drain. Even worse, how many people just gave up? The wiring connections were also not listed, and are not clearly visible in the video. I found conflicting information from various sources. Here are the correct connections:
Pins XDA, XCL, ADO and INT on the MPU6050 are not used. The servo’s signal wire is connected to Pin9, and the +5v and GND are connected to the same on the UNO.
Here’s the sketch that is referenced in that other video.
Here is the working sketch with the missing library added:
int16_t ax, ay, az;
int16_t gx, gy, gz;
Serial.println(mpu.testConnection() ? “Connected” : “Connection failed”);
mpu.getMotion6(&ax, &ay, &az, &gx, &gy, &gz);
val = map(ay, -17000, 17000, 0, 179);
if (val != prevVal)
prevVal = val;
I removed the paper decals from the truck using one of my favorite tricks. First, you slowly and gently peel the sticker off, starting from a corner. If it starts to tear away from the paper backing, move to a different corner and continue. Once you’ve removed as much as you can, apply some WD40 to the remainder. I drip it on using a small bottle with a syringe tip (intended for refilling inkjet cartridges). It doesn’t take much, let it sit for 5 minutes and wick through the label. Then using a combination of your fingernail and paper-towels, scrape and wipe away the glue and paper. Once the labels are gone, you still have WD40 to contend with. No problem, Windex takes it right off. The process is very similar to how Australia used Cane Toads to eliminate the Cane Beetle and then got rid of the Cane Toads with…. Actually, I forget how they got rid of the Cane Toads, but I’m sure that it worked out ok.
Harbor Freight has been giving away these cheap little LED flashlights for a couple of years now. They are incredibly bright and I’ve got at least a dozen of them. I’ve decided that they would make excellent functional lights for our self-leveling light-bar. I used snips to remove the old fake lights from the truck. Normally I would use a razor saw to get a smoother cut, but the plastic on this truck is flimsy and would likely crack if subjected to sawing. Snips work great in these situations, and I will be able to smooth the rollbar using those drum-sanding wheels on my Dremel. Here’s a picture.
Last week I had an interesting discussion with an engineer that I know. He posed the question “How would you design an automatically-leveling lightbar for an offroad vehicle?” For those who aren’t familiar with them, light bars are frequently mounted on Jeeps and other burly vehicles, usually on the front grill or over the cab. I answered that I’d probably use an Arduino to control a servo system that keeps the lights pointed correctly despite the vehicle’s changing pitch angle. A low-cost solid-state gyro mounted to the vehicle would provide the necessary position feedback. Last night, while looking at my long-neglected Arduino collecting dust on my desk, I decided to see if I could make it work. To make it interesting, I’ve decided to see if I could have it finished by this Friday (Today is Tuesday). I installed the Arduino software on my laptop and with my Arduino gleefully blinking at me (running various blinking LED tutorials), I started digging around online to see what was available to interface a gyro. I was pleased to see that Arduino has a module to do exactly what I want, it’s the GY-521 MPU-6050 3-axis gyroscope accelerometer. Even better, it’s only $10 and I can get it overnight using Amazon Prime for $4. I also ordered a cheap sub-micro servo since all of my servos are full-size.
This morning I headed to my local Walmart to check out the RC car selection.
I figured that a pickup truck would be best since the payload could sit in the bed allowing easy access. I picked the biggest one that they had to give myself a little more room for mounting everything. Here’s the truck, now I just have to wait for my gyro & servo delivery to get here.
ATC Done!!* Actually, it’s been done for 3wks, don’t tell anyone.
It’s been 110F in my shop which has sapped my will to blog. After spending just 15 or 20 minutes in that heat, I want to collapse in a sweaty heap rather than document my efforts. I have been working on many things and taking pictures as I go, so I’ll try to get caught up in the next few weeks. The final steps on the ATC were wiring & adjusting the feedback sensors, building & installing the mount for the spindle orient assembly, and writing a macro to control the changer. The macro was the part that I dreaded the most, but it wasn’t bad. It probably took me a day and a half to look over a bunch of Mach3 macros to learn the syntax and put something together. Some Mach3 functions can be called with more than one command and some have become obsolete over the years, so there was a little more trial and error than I expected, but the final script is short and simple. Everything works based on feedback rather than timing. Each step in the process waits for the sensor from the previous step to signal that it has moved to the expected position before starting its step. Here’s the video of the whole thing working under computer control. In the next few days I’ll fill in the blanks on a lot of what has gone into this.
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I’ve been obsessively refreshing the UPS package tracker to see if it was actually going to take 6 days to get a small box from New York to Arizona.
Apparently Shapeways has negotiated a level of UPS service that takes longer for domestic shipping than some of my mail shipments from Shengzhou, China. Impressive.
The parts finally got here yesterday afternoon and they look great. These are the mounts for the reed switches that are going to monitor the positions of my air cylinders. I had designed the slot for the sensors to be .015” oversize, but the sensors were a fairly firm press-fit to get into place. They displaced a bit of partially fused powder in the process. If removed and re-installed, the fit was a lot easier, but still not the loose fit that would be expected considering that loose tolerance. They were a not-unpleasant parchment color, pretty similar to “natural” (not white) nylon, but a shade or two darker, almost “toasted”. Since the rendering that I posted earlier showed them in red and it looked nice, I decided to try dying them red. I picked up some “scarlet” Rit dye at my local Hobby Lobby.
I mixed about one cup of water and 1/2 cup of vinegar in an old pickle jar. I added dye powder until the mixture was very dark, almost black, then I dropped in my parts. I put in all six of the “Elasto Plastic” reed switch mounts as well as a “White Strong Flexible” Arduino Lego mount that I sell in my Shapeways store:
The water was room-temperature and after a few minutes, none of the parts had picked up more than a slight pink tint. I moved the pickle jar to the microwave and nuked it for 99 seconds which was probably a little too long since it started to boil slightly. When I removed the jar, the parts had already darkened considerably, I removed them from the dye a minute or two later. The Arduino mount picked up the “right” amount of color, although the shade wasn’t what I was hoping for. It’s darker than it appears in the photo, the flash is washing it out. The reed switch mounts came out much too dark, like burgundy. I rinsed them all in cold water, then set them outside in a 110deg cool breeze to dry.
Here’s a picture of the Reed Switches installed in the mounts.
And here’s the final product installed on the machine. You can see from the LED indicator on the sensor that the switch is active. This means that the piston (hidden inside the cylinder) is at its farthest right position (under the sensor).
The air cylinders each have magnets embedded in the pistons so that their positions can be sensed externally and the toolchanger can behave accordingly. This prevents an air cylinder from activating before the previous one has done its thing. The air cylinders are made by Bimba and are very nice, but I’ve got to say that I’m not very impressed with their cylinder-mounted sensors. They are large and clunky, expensive and massively overbuilt. Here’s a picture of two of the sensors on my VMC8 mill, they’re almost as big as the air cylinder that they’re attached to. Also notice the steel strap that attaches them to the cylinder. It could probably hold 50 pounds, the sensors, clunky as they are, weigh ounces. These sensors cost $80/ea plus shipping from McMaster, my machine is going to need (6), so we’d be looking at $480 plus shipping just for the sensors. Not going to happen.
As much as I dislike those sensors, Bimba makes another style that is intended exclusively for their extruded-body cylinders and it’s very elegant. They’re available on eBay direct from Bimba for only $7 delivered, they have built-in LED’s so you can see if they are active or not and they’re very small and light. Here’s a picture of one installed on a very small air cylinder that I’m using for my spindle orientation. It’s the black thing in the picture that says “Bimba” and it’s about an inch long.Yesterday I got an email from Shapeways announcing a new flexible rubber-like material called “Elasto Plastic”. I quickly designed a mount that can attach this style of sensor to a round-bodied air cylinder using two aircraft ties to hold it in place. According to Shapeways, this new material is “grippy” so it should stay in-place just fine especially since there’s no load on it. I rendered it in red so that it shows up, but the real ones will be an off-white. There are a few features that I’ll point out, the center section is cut-away so that the LED on the sensor itself will be visible. The sides are sharply truncated so that the aircraft ties can be easily snipped without scratching the cylinder if they ever need to be removed or re-positioned. There is a hole at the front so that the setscrew that is part of the sensor can be used to “lock” it into the mount longitudinally. This style of mount could be produced commercially for pennies, even having them rapid-prototyped is going to cost me less than $30 delivered for the 6 that I need. Add that to the $42 for the sensors and I’m in business for $72 total. Besides saving $408 compared to Bimba’s recommended sensor, these look better, are much smaller, and have LED feedback. Assuming that they work as expected I’ll be in good shape. Incidentally, when ordering multiples of something from Shapeways you should always combine multiple items into one assembly. There is typically a per-part setup fee, in this material it’s $1.95. If I ordered one part 6 times I’d be paying $12 just in setup fees. Combine them into an assembly and you only pay the fee once. I got an email from Shapeways this morning confirming that my parts are already in production. Less than 24 hours between Shapeways announcing a new material, me designing a part to take advantage of its unique properties and the part going into production. I love living in the future.I didn’t draw the aircraft ties, you’ll just have to use your imagination until the real parts arrive in about two weeks.
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