Repairing an Albrecht chuck

Long time ago I was waiting for my turn to use the weighting scale on a scrapyard when I stepped over something curious.

Inside a sturdy chunk of mud there were the remains of an electric drill but what got my attention was the keyless chuck. I asked at the counter and got it for free.

It slept for some time on a shelf until I found it again cleaning. It resisted a civilized dismantling intent so I bathed it overnight in a mix of gasoline and paint thinner.

The front came out easily and looked good enough given it’s history except for a couple of spots with tool wounds and corrosion with significant missing iron. Seems it had been passivated on the inside.

There’s a two hole pig nut on the back and that one gave more trouble. I first tried with a round nose pliers and then a punch but it only made things worse.

I used a heat gun to clear any remnant of gasoline, hoping that it would loose the threads but no cigar. So I welded a piece of scrap and with that I managed to pry it.

Compared to the rest this part looked much better. I expected a ball bearing but there was only a hardened steel ring instead.

I padded a couple of beads on the body and after a bit of careful grinding it’s like it never spent time buried.

Now I only have to fix the horrible amount of run-out and play of the drill press.

Park bench

A while ago we were given a bunch of weathered wood from a deck. Some of us have been thinking of installing seats on the sidewalk and this looked like a good opportunity.

I looked around Core77 and there’s an entry just about seating that produced this helpful guide:

I built a simple frame with square tubing and used one of the wood packs to try it out. I need to select the best planks but it’s comfy and with a bit of paint will look good.

Backyard archaeology

While preparing the existing floor for the new pouring I discovered remnants of the old building.

In its latest years (circa 1970-1980) it was used in a wine bottling operation as a storage room and later my grandad started to build a small studio for my uncle (but that project was cancelled due to things better not to speak of).

Before that, around the 30’s and 40’s, the whole house was a ceramic tile factory. Giant ovens to fire the clay, castings and all that.

As I started to dig the trench for the new waste plumbing I found what looked like the walls of a chamber or well of sorts. The top was made of reinforced concrete and had all the appearance of being a lid.

I tried to break and lift it with very little success. On the other extreme of the room there’s a hole that seemed to be a small opening made on purpose. I dug with my hand but only got sand, gravel and fragments of old tiles.

I gave up as whatever I removed from the floor had to get back and then some more to make a proper base layer for the next one. But I plan on digging further later on.

The early bird gets the worm.

And a giant grinder.

Today I woke up early and instead of staying in bed reading until it’s a more convenient hour to start the normal daily activities I grabbed some fruit, a thermos and started to walk.

Just a block from home I spot a very old industrial grinder with a flexible coupling on the sidewalk. It’s quite heavy.
I continued to stroll around the city and saw the sunrise amid a gentle mist.

By the time I returned my brother was already awake and he lend me a hand to pick it up.

Surprisingly, it only took a couple of beats with a hammer and a wooden block to remove the coupling from the motor housing. The motor, a big and old three phase one, has all its wires crumpled and turns freely, albeit with a loud noise of broken bearing. On the other hand the shaft at the stone rides smooth, just like new.

Dumpster heaven

If there’s a heaven I think I visited it today.

After running a couple of errands early in the morning I headed to Lisandro Olmos on the outside of the City to buy some scrap metal for my welding classes.

A couple of members of the group said good things about Grúas Mársico so I went there, it was also a good opportunity to travel a bit on this part, as I don’t know almost anything about it.

As I entered the warehouse I became speechless. There are shelves that extend up to the roof with parts from all kind of machines neatly organized on one side. On the other pieces of metal plate and tubing. Some big planers, milling machines and spot welders among them. And on the background, the tallest pile of industrial waste I ever seen in person. All of this on sale by weight save for a couple of weird stuff.

The shop was run by a very nice lady and her brother. This morning I only bought some iron but the next time I come around I’ll bring a small truck to pick some very , very interesting stuff.

Reduce, Reuse Recycle summary December 2017 – January 2018

(Sounds nicer than saying dumpster diving eh?)

We can learn a lot about a society just from looking what we throw away (see Garbology).

When I lived in Berisso it was really odd to see on the curb something that worked or was fixable.

Here in La Plata and without even trying I stumble upon stuff that is just a little bit broken if not working (albeit a tad old).

This last two months among other things I picked up with my bike basket:

  • A vacuum cleaner, complete with hoses. Only needed a carbon brush replacement.
  • Home audio amplifier. The cd tray is stuck but we feed it from the line in. A bit heavy but very nice sound.
  • Mantle top fan. Works fine as a fan but the pivoting mechanism is acting up. Just needed a thorough cleaning.
  • Leather briefcase. Sold in less than a day as a theater prop.
  • Wooden wine rack. Works fine for other beverages too.

This is not exactly dumpster diving but I also helped the widow of a neighbor silent key to clean up his shop.
Out of the deal I got:

  • Two 100Mbps rackable switches. They work but at that speed I only want them for the chassis and supplies
  • An antique lamp. Already restoring it.
  • A Commodore 1541 dirve and some original CompuServe disks. On their way to a museum.
  • A very old (when telegraphs were the norm) glass insulator and threaded pole made of hardwood. Has the right volume to make a shot glass.
  • A modern medium voltage insulator. It’s quite heavy but in nice condition. I’ll probably make a lamp out of it.
  • Lots of heatsinks and coolers.
  • Old cans of candy and medicines. They don’t have a high monetary value but are collectible and can be traded for something else.

Time for cleaning up.

On the back of my current house there’s a shed where my parents dumped most of the stuff that belonged to my grandparents, even a car.

For quite a while I was in need of a personal space to work and store some tools. So earlier in December I started to move things around, give away some stuff and trash the rest.

It’s a pity I didn’t take pictures of the initial state but before this I could only peek from the door.

Looks messy but this is an incredible progress:

Fixing a microwave oven with a broken keypad

This is by far one of the most productive things I did this week outside of work (at least the one I can write about here).

A couple of months ago my ex gave it to me, it started with intermittent display issues and one day it stopped completely. I picked it up and stored it.

The other weekend I was in a bit of cleaning frenzy and I remembered that it was using valuable space on the shack doing nothing so I set to see if it had any hope of working again. Otherwise I’d take the transformer and dish motor, the magnetron would go to a friend and the rest sold as scrap.

This is the second time I fix a microwave oven and I’m amazed at the amount of grease and acid stench that accumulates inside them.

I bridged the safety interlock pads on the control board and powered it with an isolation transformer. It kinda turned on but was not responsive and only some digits were dimly lit. It was also very sticky.

After that I cleaned it using lukewarm water, detergent and a toothbrush, a scoop with a hair drier and then another bath with alcohol.

Now it works!

The keypad is a mess, besides being sticky and stenchy too the conductive traces were broken, like dissolved, on the connector side. For some models there are still replacements on the market but they aren’t cheap and also what’s the fun on that?

I peeled away the layers, traced it and make a replacement using tact switches. The decal will be glued on top of that. It works fine, there’s less waste (but I’m short of a spot welder) and off it goes to Radio Futura.

Detachment

During these last days I went to my parents house to grab the rest of my things and head up to the unknown (well, for the next couple of months I kind of know where I’ll be at).

I was amazed at the amount of stuff that I’ve long forgotten. Books, tools, clothes, even toys… I gave away most of them. If I haven’t used a thing in ten years or more, even to the point of not remembering they were in the house there is little sense in keeping them. And some feel like an anchor tying me to the past, so out to the door it is.

The first day I hauled boxes to the street I felt terrible, sad and empty. Then it became more natural, like a relief.

The other Monday (it was a holiday here) I organized my clothes and kept only what I need and use. Some are so worn out that barely hold together. I’ve found some that I used when I was a teen (that is, about 13 years ago). Some fit me and some don’t, so in a sense at least I grew up.

I’m still childish in a lot of ways and honestly looking at how so many of the adults behave I’m positive that I don’t want to end up like that. Curiously enough, some people told me that trait is charming.

I’m still a long way from Nekkhamma but it’s a tiny step forward.

Next on my list: killing the Buddha.

(clothes)

(clothes)

 

(trying to) Measure temperature

In a while I’ll need to characterize an oven and perhaps build a new one.
Just to start I have to apply a power step and measure how the internal temperature evolves.

In order to save time I searched my local distributors and bought a K type thermocouple with amplifier and cold junction compensation. It is not the most accurate but it is more than enough for now. There are a couple of ics available that give a direct digital output but the work needed to breadboard them and have a meaningful reading is beyond the scope at this stage.

This is what I bought:

Appears on many places as a “Grove High Temperature Sensor”. It sports an OPA333 precision opamp and a CJ432 adjusted to provide a 1.5V reference. The rest of the circuit is nothing special, except that the manufacturer called the thermistor “light”. It can be consulted here.

First ligths

While I have more capable hardware at hand I grabbed an Arduino Nano and the official library from https://github.com/Seeed-Studio/Grove_HighTemp_Sensor and lo and behold I had it streaming temperature to my terminal.

Let’s get graphical

I cooked a simple gui on python using Qt and Qwt while listening to Olivia Newton.
It is pretty barebones, only has facilities to export into csv, a couple of tracking cursors and gracefully handles device disconnections (say, I yank the cable). I expect to post process the data using QtiPlot or Kst.

Tweaking

One of the first things I noted was that the measured temperature jumped in big steps of about 2°C.
Using the default setup with a 5V “reference” and considering the amplifier gain every adc bit amounts to:

 Vbit = \frac{5000mV}{1023*54.16} = 0.09024 mV

Looking at the polynomial coefficients used by the library (ITS90) and taking a first order approximation one bit corresponds to a 2.26°C step and it grows bigger with the measured temperature as other terms start to influence the result. Even tough the output is low pass filtered at about 1.6KHz and it is averaged over 32 points there’s still noise.

Changing the reference to use the regulated 3.3V makes it about 1.5°C but even if it is more than enough for what I need it can be better.

With a couple of bits more I can achieve better resolution. Instead of using an external adc I took advantage of the inherent noise on the reference and output and chose to apply a 16 times oversample in order to have 12 bits out of the 10 bit adc. Application note AVR121 explains that nicely. Now I am limited (in theory…) to 0.37°C steps and I can average on top of that to further reduce variations.

The last source of error (besides not knowing for sure the “real” value of the references) is that the library assumes a fixed 350mV output, the circuit ideally floats the amplified thermocouple voltage around that. In order to measure it I added a small relay from my stash (TQ2SA-5V) to short the input. It is not meant to be used as a dry relay but does fine so far.
Upon startup it reads 348 mV; while a 2mV difference may not seem that big it turns out to be at least 185m°C. Anyway the main sources of error now are the thermocouple and adc reference.

From busted magnetron to incense holder.

It’s been a while since I made something nice.

A couple of weeks ago I spotted a neighbour taking a microwave to the curb and brought it home with me, as they are always full of useful bits. This one was not very old but of a very simple construction. It has a mechanical timer that makes a lovely ‘ding’ when finished. It also went through a bit of hard love.

Cavity magnetrons are very cool devices. Besides providing a couple of strong magnets and aluminum plates they are made of a very pure copper allow with interesting shapes.

From time to time I like to burn some lignum vitae and upon opening this one I knew what to make of it. I chucked it on the drill press, gave it several passes of wet sandpaper and then a cloth with polishing compound. It took quite a good shine but the handling with greasy hands is giving it a light patina. The holes are filled with glow in the dark paint. I haven’t managed yet to capture the effect but they look quite good at night (and also with uv light).

I left the rest without a final polish, partly as a testament of its origins and also because probably I’ll make a cherry wood stand for it.

Adventures in smps carnage I.

A while ago while cleaning the trash pile I thought that it’d be nice to mod one of the many computer supplies to have a variable output. So I picked up the less crappy, replaced the transformer with a one with better turns ratio to achieve a higher voltage output and put a pot on the feedback loop.

At first it kind of worked but with a lot of unstable points and weird modes. Then I realized that I fed the feedback from about 50K when the nominal was near 10K (and also there is considerable input current there). A simple emitter follower took care of that, now there only remains plain oscillations.

The operating point moves a lot considering that I want the output to be adjustable between 5V and 50V and without a fixed load. The original compensation scheme was a plain integrator plus a zero, I can make things a little better slowing it down a lot but what’s the fun on that.

So instead of blindingly doing things I set out to measure the loop response using Middlebrook’s method. I cobbled up a quick python program with Gtk and GStreamer to generate the test signals with a computer soundcard. Initially I expected to just sweep the frequency and measure some points manually on the scope but there is a lot of 50Hz induced interference that together with switching residuals make that task impossible, I really need to perform a synchronous detection in order to get a meaningful result. That means I’ll have to make room for some more quality time coding to get the scope samples in an automated fashion. The usb protocol is documented here ( http://elinux.org/Das_Oszi_Protocol#0x02_Read_sample_data ).

The setup is a far cry from the ones depicted in the famous AN70 by Jim Williams. I used an H-Field probe to rule out magnetics as an interference source. I expected the output filters and the transformer to be troublesome but their effects on the point of injection are negligible. On the other hand, long wires on the feedback path (even twisted) and the snap recovery diodes aren’t a good match.