The View Up Here

Random scribblings about kites, photography, machining, and anything else

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Posts Tagged ‘Machining’

Finishing the DIY Microphones (v.1.1)

Posted by Tom Benedict on 14/07/2015

The more I thought about the hot glue closure on the back of the microphones, the less I liked it. Don’t get me wrong. It works well. But it’s… permanent. I know the BT-EM172 capsules are only $10, and I know the rest of the microphone is largely scrap-boxed, but I hate to make a thing that can’t be serviced when it needs it.

So I re-designed the enclosure to include an end-cap. It’s drilled out 1/4″ to take a cable grommet, and has three #2-56 screws placed every 120 degrees around the periphery to hold it in place.

BT-EM172 Microphone Enclosure - Exploded View

The end caps took about fifteen minutes apiece to make, and were a comfortable fit in the back of the microphone bodies I made previously. Unfortunately, drilling and counter-sinking the screw holes for the end cap meant I needed to re-coat the microphone bodies along with the end caps. Since I had to re-coat them, I added grooves to each mic body to accommodate a Shure RK183T1 lavalier clip. I’m pretty sure a generic clip for a 9/16″ diameter mic would’ve worked fine, but these turn out to be tough to find. There are several listed on Ebay, but if you look at the metric equivalents, the specs say they fit something around 7-9mm in diameter. 9/16″ is closer to 14mm, so I think something was lost in translation. The clips from Shure will fit. (For shure! Har!)

Countersinking Screw Holes

I wasn’t happy with my previous coating job, so I came up with another way to apply the coating. I shoved each part onto a wooden dowel of the appropriate diameter (3/8″ for the end caps, 1/2″ for the mic body), and chucked it in a drill. I applied the Cerakote with the drill spinning. This gave each part a very uniform coating, and let me hit every outside surface without running into my fixture. I loaded the parts in the oven, dowels and all. On a whim I coated the screw heads, too, so I wouldn’t have shiny stainless screws in a black microphone body. Unfortunately the spray gun malfunctioned, so two of the mic bodies didn’t turn out as nice as I’d like. I slated those for the pseudo-SASS array, where they won’t be seen, and saved the two “good” ones for lavalier mics. Note to self: test the spray gun before loading product into it!

Parts Ready to Cerakote

Once the Cerakote cured it should’ve been a simple matter of assembling each of the mics. But I love to fiddle. I assembled the two for the pseudo-SASS array since I already had that cable made. But I needed more cable for the lavalier mics. Even though I’m already using Mogami W3031 cable for the other mics, I ordered 100′ of Mogami W2697 from Redco Audio to use for the generic lavs (only 20′ of which I plan to use). W2697 is almost identical to W3031, except for the way the shield is constructed. W3031 uses a braided shield. W2697’s shield is served (wrapped). Electrically they’re identical. But a served shield is easier to work with when making cables. I’ll have to wait for the cable and clips to come in before finishing the generic lavs.

Completed Mic Bodies

Rather than waiting like I did with the mono mic I built out, I grabbed my pseudo-SASS array and my recorder, and hiked out to the rocks south of Hapuna Beach. The last time I was there the waves were big, and made big, dramatic crash-bam-booms on the rocks. Of course that was in the winter. The summer wave pattern is a lot more bathtub-like, so the sound was a lot more subtle. Still, I ran several side-by-side comparisons of the pseudo-SASS against the built-in mics on the Tascam DR-05. I put together a set of 30-second clips comparing the two. The recording has eight tracks, alternating between the DR-05 built-in mics and the BT-EM172 array, done at four locations. When listening, keep in mind that the gains are different on the two mics, as are the frequency responses. I did no processing on the tracks aside from cutting and fading, so some tracks are louder than others. That’s a function of my technique in the field (or lack thereof), not the microphones themselves. This test was only so I could tell how well the pseudo-SASS array was separating the two channels.

The pseudo-SASS performed well enough I want to build a real one out of some 1/4″ baltic birch plywood I have in the shop. I still haven’t tested my prototype from the air, but it’s easy enough to include 1/4″-20 sockets top and bottom so I can mount it either way. More photos and sound samples to come!

– Tom

P.S. I’m not keen on the way clips from Soundcloud show up on my web site. I’ve seen other people include Soundcloud clips on their sites that are nice, small, and easily worked with. This thing is ungainly! If you know how to fix this, please let me know.

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Posted in Audio, Engineering, Machining | Tagged: , , , , , , , , | Leave a Comment »

Bend a Little and Have Fun

Posted by Tom Benedict on 14/03/2015

Years ago I joined a group called Utata – a group of photographers, writers, and like-minded folks who enjoy lively discussion and creating and promoting art. Utata has several ongoing projects as well as two big annual projects. At the time I joined I was almost exclusively doing aerial photography from a kite, so I found myself unable – or to be truthful, unwilling – to participate in many of the projects. One in particular, the Iron Photographer, routinely kicked my butt.

The Iron Photographer project is modeled along the same lines as Iron Chef: All of the participants are given the same three elements to work with – two compositional and one artistic or calling for a specific technique – and are asked to create new, original works. On the face of it it’s a welcome challenge for any photographer. But if you’re limiting yourself to creating only aerial landscapes it’s less of a challenge and more of an impossibility. Take, for example Iron Photographer 211. The elements were: 1 – a bowl; 2 – something broken; 3 – photographed simply. You can make an aerial photograph that would qualify, but it would be a mighty tall order. I quickly became frustrated and stopped participating.

The lesson I didn’t learn back then was this: bend a little. The whole idea of Iron Photographer is to knock people out of their comfort zone and get them to put their thinking caps on. I staunchly refused and missed out on a lot of opportunities to have fun with a camera.

After a three year dry-ish spell I’m finally starting to get back into photography. This time not all of it is aerial. I figured I’d give Iron Photographer another try. I started with IP 212. The elements are: 1 – the photographer’s hand resting on a flat surface; 2 – an object resting in the palm of the hand; 3 – holga-fied. The only element I needed clarification on was that third one. The idea is to make it look as if the photograph came out of a Holga camera. I don’t own one, so I downloaded Holgarizer – a Photoshop action that would produce a similar result.

The Iron Photographer projects make you think. Yeah, I could’ve done a set of photos of my hand on a table with various objects in it. But where’s the fun in that? Better to ask why my hand is lying on a flat surface. Which flat surface is it lying on? What is sitting in my palm? And who chose to make the photograph? Of course for the requirements of the project it must be the owner of the hand. But from the standpoint of the narrative all of these are open-ended questions.

The first idea that sprang to mind felt cliché even before I made the photograph, but I made it anyway.

As Found

It’s not a happy picture. I wanted it to look like a crime scene: a dingy floor, the weak greenish glow of fluorescent lights, a pallid cast to the skin, and stark shadows outlining someone’s final act. In fact I’d just scrubbed the floor clean so I wouldn’t contaminate my prescription medication. The lighting was all provided by daylight-balanced strobes. And I’m actually pretty tan at the moment. But who’s keeping tabs? The only really stressful moment came when I started to clean up and realized I’d misplaced one of my pills. As tiny as these things are, they’d be lethal to my cats. I spent the time to track down every single one.

Then, of course, I saw that another participant in IP212 had come up with the same idea. Darn!

That’s when I started to wonder: Did the owner of the hand have to be the one who put the object in it? When I figured out the answer was “no” the idea for the next photograph came to mind. I opened the door to my daughter’s room and said, “Wanna be a totalitarian? Grab your boots!”

Of all of the events that mark the passing from childhood to adulthood, one my daughter celebrated with no small amount of gusto was the successful completion of her last high school PE class. She proudly announced that her only reason for wearing tennis shoes to school was null and void, and that she wanted combat boots. She and Rydra picked out a pair that would make any real princess proud.

“Ok,” I told her. “I’m gonna lie down on the ground outside, and you’re going to stand on me.”

Stunned silence. “What?!”

Even I had to admit she had a point. But once I described the photo to her she got into the swing of things.

The Regime

It took a while to work out the balance of the lights. Then it took a while to work out the best angle for my arm. Then it took a while for us to work out how she had to stand so it looked like she was bringing all her weight to bear on me without actually crushing my hand under her heel. In the end she wound up with one boot on and one boot off, standing en pointe on one sock-covered foot while squishing my hand with her booted heel. Early on she was tripping the shutter, but the contortions she was having to go through were more painful than what she was doing to my hand. We switched to a self-timer for the final few frames.

Though the Iron Photographer project lets you tag up to six photos for submission, you’re only really supposed to post one to the discussion forum. I chose this one. This becomes important later.

I had a couple of other ideas I wanted to try, but by this time I realized my first two photos were real downers. Despite the smiles and the laughter and the fun my daughter and I had making The Regime, I knew that no one looking at it would feel anywhere near as upbeat as we did. So I set morbid aside and went after something different.

The challenge called for something to be in the palm of the hand. It didn’t say that it had to be a physical object, just that something had to be there. I thought it would be neat to put something less tangible than a physical object in my hand. “I know!” I thought, “Light!”

I went through a couple of iterations on this one: I could have a beam of light coming out of my hand. (I might still try that one at some point, but not as part of this IP.) I could make the palm of my hand glow. The idea I finally settled on was to have an object in my hand influence light rather than generate it: a prism.

Years ago I worked in a lab that etched diffraction gratings into silicon using MEMS techniques. It was kind of a one man show, so I was responsible for the photolithography, the anisotropic etching setup, maintaining the safety and materials in the lab, characterizing the gratings we were making, etc. I also photographed the bejeebers out of everything we did on color transparency film. To see how much power went into each order of the gratings we were making we aimed lasers at them and measured the power in each of the return beams. It was an important step in characterizing the gratings. But it made for an even better photograph.

Each photograph was done as a single long-exposure frame. I’d turn off all the lights in the room, open the shutter, “paint” out the beams using a business card or some other flat white object (my hand stood in a couple of times), then turn on the lights for the prescribed amount of time and close the shutter. As painstaking as it sounds, once you got into a routine it went pretty quickly.

I used the same technique with the prism.

Can We Get There By Laser Light?

Even having used the technique, it took awhile to work out the details for this photo. Initially I illuminated the prism from the side. But the human palm isn’t all that flat. The prism kept rolling toward my fingers, directing the outgoing beam into the table or some other part of my hand. And painting a beam that’s going toward the camera is tough if you’re using a business card. The camera’s looking at the back side of the card! Eventually I figured out I should place the laser under the camera, and aim it back toward my hand. This gave me a way to see how well aligned the prism was to the beam: put the reflected light back into the laser’s aperture. It also made painting the foreground beam a lot easier since the camera could see the illuminated side of the card.

The difficulty was the outgoing beam. No matter what I did, the prism moved around in time with my heartbeat. You can see it as tiny wiggles in the painted beam. I could’ve Photoshopped that out, but where’s the fun in that?

Since that’s my own hand there on the table, I really didn’t have the option of turning on the room lights at the requisite time. Instead I set up a single strobe and a shoot-through umbrella up and to camera right. I kept the wireless transmitter handy on the table. Once I’d painted the beam I triggered the strobe and closed the shutter. It worked like a charm.

For my last IP212 photo I wanted to make something of a visual pun. The two compositional elements were a hand resting on a flat surface and an object resting in the hand. What if the object in the hand was a flat surface? In keeping with the whole optics theme I considered using a mirror, but honestly that’s kind of a boring photo. Besides, I’d already touched on the optics side of what I do for a living. I wanted to touch on the mechanical side, too. What if the flat object in the hand was being made into a flat object? Milling machine!

Hand Work

Before getting into the hows and whys of this I need to point out that I take shop safety very seriously. At no point did I do anything that put my hand or my tooling at risk. The only way to pull that off was to do this as two separate frames – one with the spindle moving and one with it stopped – and combine them.

I milled five of the six sides of this block using the 1″ cutter shown chucked in the mill. I milled the last side halfway, then stopped. Lighting was pretty straightforward: an umbrella in front and to the right, and a stofen bounced off the white wall behind the mill to provide speculars on the block and vise. I brought the spindle down until it was pressing the block into my hand, and made the first exposure. I wanted some motion blur out of the cutter, so I made a second exposure using ambient light, rotating the spindle by hand from above. Once I’d balanced the light between the two in Lightroom, I brought both frames into Photoshop for layering.

While going through the lighting for this a number of other photographs came to mind that didn’t fit into the IP212 requirements, but that nonetheless would make for pleasing photographs of machine work in progress. And that, to me, is the real benefit of taking on Utata projects like the Iron Photographer: The final result isn’t the photographs made for the project. It’s the ideas that the process of thinking through those photographs leaves you with. That’s what I missed out when I joined Utata years ago. I don’t plan on missing out on it again.

To my utter delight, Greg, the moderator who sets up the Iron Photographer challenges, favorited The Regime and wrote a really thoughtful comment on it. This is the first time one of the Utata moderators commented on one of my photos. Even more delightful, Debra Broughton wrote a short piece about it for the front page of the Utata web site and wrote a comment of her own. I admit I banged my forehead on my desk a little at my obtuseness for taking this long to jump into Utata projects with both feet. But thanks to Greg and Debra I did it with a smile.

– Tom

Posted in Machining, Photography | Tagged: , , , , , , , , , , , , , | 2 Comments »

Catching Up

Posted by Tom Benedict on 15/10/2010

I missed most of Worldwide KAP Week 2010.  A few weeks previous I’d come down sick with a cold, and just never quite shook off the cough.  It didn’t help that my job took me to the cold dry air at 14,000′ elevation over and over (and over!) during and after the cold.  In the end I came down with walking pneumonia.  This left me with no energy and a wracking cough through most of WWKW 2010.  I did get out, I did send pictures in to the book, but it wasn’t the happy time I’d planned.  C’est la vie.  Until next year.

In the end I was sick for well over two months.  I finally got my clean bill of health today, and should return to duty at the summit tomorrow morning.  Meanwhile I’ve been working on a cryostat at headquarters, and finally started flying kites again about a week ago.  Unfortunately all this came together in a not so comfy way today.  It all ended well, but getting to the end of the day was a trial.

At lunch I broke a spar on my Premier Kites Widow.  Plain and simple.  Dumb crash, dumber re-launch, and now I have to cut a new P-200 spar once I get home.  Thank goodness for spares!

The real fun has been this cryovessel.  I was testing the idea that you could boost the performance of a closed-cycle cooler by using thermoelectric coolers, or Peltier junctions, between the closed-cycle cold head and the cold surface.  It worked, after a fashion, and I think it bears re-examining with a properly sized cascaded Peltier junction.  But for our application I just couldn’t get enough cooling power out of the thing to get the delta-temperature I was after.

During this testing I wound up putting something like 30W of power through a two-stage cascaded cooler, but the cold head simply couldn’t remove the heat fast enough.  Within a few minutes I had a cold head at -150C, a cold surface at -100C, and a Peltier junction at a soaring 38C.  I killed power, brought everything back down, and let things hit steady-state before killing the power to the cooler.

What that told me, though, was that the biggest delta-temperature in the system was across the link between the cold head and the cold surface.  I also realized if I minimized the dT, I could switch the gas in my cooler and possibly hit my target temperature that way.  Time to make new parts!

So I replaced that link with a new one.  The old one consisted of ten strips of 6.5″ x 1.0″ x 0.010″ copper in a nice neat stack, or 6.5″ of 0.100″ sq in copper.  I replaced it with 2.8″ of 1.5″ diameter copper.  At 60W of load the first one got me about 52C dT.  With this new one I should be able to keep that under 2C of dT.  If the cold head reaches its ultimate temperature of -158C, this should give me a cold surface temp of -156C.  If that happens, I can change gases and potentially hit the 77K, or -196C temperature I’m after.  Time will tell.

For the record, I hate machining copper.  Oxygen free high conductivity copper is even worse.  It’s like machining stale bubblegum.  Tools dig instead of cutting, the copper oozes out of the way instead of making nice chips, and it takes all manner of tricks to pull off clean cuts.  I got the parts made, but the final steps of tapping the M3 holes in the thing gave me the willies.  After a thorough cleaning, I opened up the cryostat, installed the new parts, and closed it back up.  It’s on the pump now, and I should have a chance to start cooling it over the weekend so I can work with it on Monday.

But what I’m really looking forward to right now is a new spar for the Widow, a weekend of good weather, and a chance to get out and make up for what I missed during Worldwide KAP Week 2010.

– Tom

Posted in Engineering, Kite, Kite Aerial Photography, Machining | Tagged: , , | Leave a Comment »

Don’t Trust Nuthin’

Posted by Tom Benedict on 03/09/2010

I’m getting seat time on some new tools at work, so I’ve had a chance to try to catch up on some long-standing projects.  One that I’m eager to get back on involves mounting a cryocooler on one of our smaller test cryostats.  It started life as an infrared camera, but several years ago it was recycled into a test cryostat for a new infrared detector.  This involved gutting it of all mechanics and optics, and basically turning it into a cold optics bench, complete with a 1/4″-20 screw hole pattern on 1″ centers.  We added a cold shield, installed baffles for the two rotary feedthroughs, the whole nine yards.  We really just wanted to characterize a new detector, but by the time we were done we had a general purpose cold optics bench and enough bits and pieces to build a complete infrared camera.  We could’ve bolted it to the telescope, but that was never its purpose in life.

Thank goodness we made it a general purpose tool.  Once again we need a cold bench, and once again we’re pulling it off the shelf.  Only this time we’re trying to move away from liquid nitrogen cooling and use closed-cycle cooling instead.  Some months ago I did a poster presentation at SPIE covering our conversion of one of our science cameras to closed-cycle cooling using a Polycold Compact Cooler (PCC).  When we did that conversion we picked up a full set of spares, and a second full set for lab work that we got off of Ebay.  (Yep, even science nerds buy hardware off of Ebay.)  The idea is to use our Ebay set to convert the cold optics bench to closed-cycle cooling.

Luckily this cryostat has all sorts of nice service hatches you can pull off and work with.  I popped off one that had enough surface area to mount the PCC cold head, and used that to get some seat time on the new tool.  It needed a clean face for mounting the cold head (0.020″ deep circular pocket clear with final outside clean), a clear bore (0.550″ deep circular pocket clear with final outside clean), and a bolt hole circle (drill cycle with a spot drill followed by a peck drill cycle with the tap drill).  I can’t say the machining was relaxing, but it went pretty quickly.  The seat time is paying off.

When it came time to tapping the holes, I went back to the cold head we had sitting on the shelf.  It had a #10-24 screw through it, so that’s what I used: #10-24.  The body tube bolted straight on, but when I tried to put the cold head in, the #10-24 screw jammed.  !!!!!  Turns out it’s threaded #10-32, but someone had driven a #10-24 screw through it.  This did a number on the thread, but nothing some cleanup work with the #10-32 tap wouldn’t fix.  The cold head and body tube cleaned up nicely, but the mating holes on that access panel were tapped to the wrong size.  Grrrrr!

Can’t trust nuthin’…

In the end we opted to keep things the way they are and just mark the two sets of bolt holes.  One is marked #10-24, the other is marked #10-32.  Same tool, totally different screws.  It’s aggravating, but that’s life.  Next time, I’ll check.

I hope to have the test cryostat bolted together some time next week.  So there should be some pictures to share.  I probably won’t be able to show the machining job since it’ll be buried, but a picture of the cryostat itself is worth a thousand hand-waving descriptions.

The part that really makes this project fun is that the PCC can only get down to about -150C the way we have it set up.  We need 77K, or -196C.  That’s 46C more than the PCC can give us.  We’ve got a test plan in place, and should know some time in the next two weeks whether it’s going to work, or if we’re just plain stuck.

– Tom

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Making Big Parts on a Small Mill

Posted by Tom Benedict on 25/06/2010

Or how to get a mill table extension without having to add the extension…

I have a Taig 4-axis desktop mill at home.  It’s a great machine for its size, and I’ve used it on countless projects.  If you’re in the market for a small mill, I highly recommend the one from Taig.

But “small” is the operative term.  On small parts, it’s a blast to use.  I stuck a G540 driver on it, and swapped out the stock 1/10HP motor for a 1HP variable speed DC motor, but otherwise mine is stock.  And for small parts it’ll hog material out and still have the finesse to hold +/- 0.001 tolerance, or better if you’re careful.  On big parts?  Well…  Until recently I’d have shrugged and said, “Get a bigger mill.”

A friend of mine is working on a project and needed some parts made.  He sent me the 1:1 drawings, and without looking too closely at them I said, “Sure, I can do it.”  Then I started dimensioning things and realized I was way the heck out of my depth.  16″ wide?  My mill only has 7″ of travel in that direction!

This is actually a pretty common problem to run into in machining.  And there’s a really simple answer:  Reposition the part, re-indicate, and keep cutting.  Tackling a part piecewise like this, you can theoretically make arbitrarily large parts on even a very small mill.  Of course there are still practical limitations, like the throat depth of the machine and the physical constraints of the room the mill is installed in.  But the idea works.  I’ve used it on manual machines a number of times, and each time it saved my butt.

The real kicker with this approach is that you have to re-indicate the part each time you reposition it.  The parts I had to make didn’t have a lot in the way of features that I could indicate off of, so I knew I had to come up with another plan.

I have a tooling plate on my mill that I use almost all the time.  It has a grid of threaded holes that let me bolt down vises, jigs, stop blocks, or anything else I need to use to make parts.  Step one was to take off the tooling plate and add a grid of precision dowel pin holes.  A couple of hours on a manual mill at work over the weekend took care of that.

The mating part is a second tooling plate with two pressed-in dowel pins on the bottom.  These slip into the dowel pin holes on my main tooling plate, and let me reposition the second plate to any number of positions.  Through holes for bolts that line up with the threaded hole pattern on the main tooling plate allow me to bolt it down once I’ve got it positioned.  The dowel pins are regularly spaced, so plate offsets of 2.000″, 4.000″, or 5.000″ are a matter of picking the right set of holes.

With tooling plates in hand, I gave the big parts a try.

Big Parts

It worked perfectly.  The only issues I ran into were because I was cutting the part out of a sheet rather than working with pre-squared stock.  There are tricks for doing this, such as leaving small tabs in strategic locations to make sure the part doesn’t shift as the contour is finished and the part comes loose.  The tolerances for the outside contour on these parts were pretty loose, so I skipped the tabbing and just cut them out.  I’m very pleased with the results.

I’ve got another project lined up where I might want to make parts larger than the work envelope for my mill.  I still like to design inside the capabilities of the tools I have, but now at least I know I can.

– Tom

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Re-CNC

Posted by Tom Benedict on 04/12/2009

I’ve owned a benchtop CNC mill since the middle of 2000.  The first real machine tool in my shop was my Taig lathe, so when it came time to find a CNC mill to go with it, the Taig mill was a natural choice.  The two tools have identical spindles and take much of the same tooling, so this was a money-saving measure at the time.  But in terms of transferring work from one tool to the other it has added benefits as well since the same chucks will fit the lathe spindle, the mill spindle, and the rotary table on the mill.  All in all, it’s a nice combination to have in the home, even if it is a little small by industry standards.

My shop has seen several moves over the years, the most recent being a move from Texas to Hawaii.  It wasn’t the kindest thing to do to my tools, but a set of good stout shipping crates kept things from going too horribly wrong.  Even so, the performance of the mill began to degrade once it arrived, and a little over a year ago it finally gave up the ghost for good.

Luckily none of this had anything to do with mechanical damage of any sort.  I’ve tested the tramming on my mill over the years, and unless I do something really stupid, like dig in a tool and keep driving one of the axes, it’s never had any problems of that sort.  I replaced the spindle motor on both the lathe and the mill with 1HP variable speed DC motors at one point, which was a good change for the lathe and a vast improvement over the mill’s stock 1/10HP AC motor.  Other upgrades came along as well, such as a relay box for the mill’s spindle and coolant, a quick change tool post system for the lathe, and a number of other things.

But once the mill was dead, none of that really mattered.  So it sat.  And I fumed.  And eventually I more or less walked away from it.

If it had died a violent death with smoke and loud noises and all the trimmings, I probably would’ve had an easier time of things.  Instead it died a slow death of having random position loss in various axes.  Parts started to come out wrong, and toward the end I couldn’t make a “there and back again” pair of moves in any of the axes and have it come back to the same place.  The thing still moved, but in essence it became useless as a machine tool.

Digging into the electronics indicated that there was a problem in the high voltage power supply.  But as with most problems, that was just the symptom rather than the cause.  Digging deeper, it became apparent that the mill’s electronics weren’t designed well in terms of heat extraction.  Over the years they had run a little too hot a little too often, and things were starting to fall apart.

Despite what people may believe about computers, heat doesn’t instantly kill electronics.  But it does reduce its expected lifetime.  Every electronic assembly carries with it an expected mean time between failures, or MTBF.  It’s been a while since I’ve done an MTBF search, but once upon a time most hard drives had an MTBF in the several tens of thousands of hours.  Running a hard drive hot wouldn’t instantly kill it, but it would reduce the expected time before failure for that individual device.  A well-treated drive might have an MTBF of 20,000 hours.  One that was in a computer with a busted cooling fan might have its TBF reduced by a factor of ten or more.

Which is essentially what happened with my mill controller.  The big electrolytic capacitors in the high voltage power supply had cooked.  And chances are the FETs in the motor drivers were cooked as well.  Everything was suspect.  So I either faced a whole string of test-and-replace operations, with the certainty that it would fail again unless I re-designed the case and cooling fan layout, or I could skip all that and replace the whole mess.

I chose the latter option.  But not having the money readily available, I couldn’t actually make good on the plan.  So the mill sat.  And sat.  And sat.

Then the miraculous happened and I got a bonus at work.  Ever since I first bought my lathe and mill, my wife and I have had an agreement:  Bonuses are bonuses.  Half goes to the family accounts, but the other half goes to the individual who earned the bonus so they can enjoy the fact that they were rewarded for good hard work.  This is how my mill was purchased in the first place, and this was exactly what I needed to get it back up and running again.

I knew the controller I wanted: a Gecko G540.  It’s a beautifully engineered piece of electronics capable of driving four stepper motors at up to 48V at 3.5A.  My motors weren’t a great match for it, but I knew I could replace those later.  The G540 is just the driver electronics, though, so in addition I knew I’d need a power supply.  And a case.  And a cooling fan.  And an E-stop switch.  And a power switch.  And a whole host of other doodads that seem simple but add up fast.  In the end I skipped all that and picked up a G540-based controller from Keling.

But Keling is in China, so while the unit was shipping I had some time to think through everything else I wanted to do.  Since this constituted something of a “do over” from the standpoint of my mill, I made a list of annoyances, both major and minor, and started work.  The list is by no means finished, but here’s where it stands now:

  • Cleaner – At one point I switched to a coolant/lube that did something I’d never run into before.  Even better, I found there is a name for it: “varnishing”.  It had a tendency to cover everything in a nice layer of oil (a good thing for a machine tool!) and then dry out to a hard, tacky film.  This is other-worldly bad for tools.  I took the whole mill apart, cleaned everything to bare metal, and re-assembled it with good quality way oil on every moving part.  The goobery coolant/lube is now gone.
  • Storage – My mill work area has been horrid for storage.  So I ran an eight foot shelf across the top of the mill and lathe bench, and moved a number of tools that had previously lived underneath the mill bench to the shelf.  This keeps them clear of swarf, coolant, and other crud that seems to happen to everything below benchtop level.
  • Lighting – The lighting around the mill, and to a lesser extent around the lathe, has been gawdawful.  I mostly work in the evenings, but I can’t turn on the full lights in the shop once my kids are in bed because they can shine in their bedroom window.  I picked up some under-shelf kitchen LED lighting, and got a nice spotlight set up that points at the mill spindle.  These are switched from the same switch unit that powers on and off the mill controller.
  • Cables – The cables on the original mill motors were very short, and of uniform length.  Which makes sense from one standpoint, but was painful when trying to locate the mill electronics.  The one place that really made sense to mount the electronics was on the mill’s work surface.  Which is a terrible idea when it comes to keeping flying metal out of the cooling fan.  (Hm!  Now I know why there was such poor ventilation on the original controller!)  I installed longer cables that let me put the electronics on the shelf over the mill.
  • Computer – I’m still not where I want to be with this, which would be to run my mill using Mach3 controller software.  But I got a new installation of EMC2 on a faster computer, so my pulse stream to the mill’s motors should be cleaner.
  • Way covers – The mill moves things around using big stepper motors attached to lead screws.  If metal chips or coolant gets on the screws, it can seriously mess them up.  The way covers I had were basically plastic sheeting.  I replaced them with rubber accordion way covers from Little Machine Shop.  It’s a vast improvement that’s hard to appreciate unless you’d spent almost ten years using plastic sheeting.
  • New controller – The Keling G540 controller finally came.  I plugged everything in, set up EMC2 to use it, and away it sang!

One of the big drawbacks with the previous controller was that it did nothing to address something that happens with all stepper motors: midband resonance.  Every stepper motor on the planet acts like a wheel with a detent spring holding it in place.  To move the motor, you move where it wants to detent to by changing the configuration of the magnetic fields in the motor’s coils.  But it’s still acting like a shaft on a spring.  If you make the motor move to the next step by changing the configuration of the magnetic fields being generated by its coils, the motor will very quickly accelerate toward the new position, and decelerate once it hits it.  And it’ll bobble back and forth (very quickly and with very very small moves) kind of like a car with bad shock absorbers will bounce around if you jump on its bumper.  The real catch with this is that at a particular speed, you wind up hitting a harmonic of that bobble frequency, and the motor will resonate.  Typically this results in lost steps and lost position.  And the really unfortunate thing is that this happens at a low speed that you really do want to get past so it can run at high speed.

The G540, in addition to being a 10 microstep driver, also compensates for midband resonance.  So when I said I plugged everything in, set up EMC2 to use it, and away it sang, it really did sing.  The mill is quieter now, doesn’t hit that “growly” sound as it accelerates up to speed, and has no speeds at which it can’t really operate at all.  This is a massive contrast to the way things were.

My mill still isn’t 100% ready for prime time.  There is still some work to be done like adding home switches, installing relays and outlets in the Keling box for spindle control, getting the VFD output from the G540 to drive the Digispeed I’ve got on my mill’s spindle motor so I have closed-loop spindle speed control, and a whole host of others.  But much of that is in the category of “want” rather than “need”.  It can wait.  For now, I have a mill that’s almost ready to go.  I expect the first of the new parts will be coming off the mill this weekend.  Quite frankly, it’s overdue.

– Tom

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