All posts by Simon

Various

LH0021CK Power Opamp: an analog autopsy

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From an earlier test equipment repair, I had two broken LH0021CK power amplifiers, both died because of a design issue with an YIG driver board (lacking distance of a heat sink from a board trace leading to an occasional short circuit).

The LH0021CK are +-12V output, +-18V input, 1 Amp capable devices, and if treated nicely, they will last 40+ years of service. Still available today, despite being obsolete, at prices ranging from 10 to 300 EUR a piece. These were quite common parts in high-end controllable power supplies, servo drivers for scientific instruments, and similar apparatus.

Finally, I cracked these open – not anticipating the fragile ceramic substrate inside.

I pieces together a picture from multiple images, because this part is a little too large for my microscope, and too small for other cameras to see it clearly.

The datasheet provides an internal circuit diagram, but is there really a 741 opamp inside? What about all these resistors?

Checking the parts, indeed, there are 4 discrete transistors, laser-tuned resistors (you can see the burn lines of the laser to adjust the value of the resistor in processing of the circuit, some have even two tuning lines), and an opamp die.

Eventually, I opened two of the broken parts, an old one, golden case, and a newer one, silver case, both made by National Semiconductors. There are some small differences of these parts, also related to the circuit. The resistance values are rather similar, but the newer part (shown in the picture) has an additional resistor at the COMP input. Both parts have no connection of GND to the negative supply input of the opamp – this is apparently a mistake in the schematic shown in the datasheet, because the circuit wouldn’t work if there is such connection.
The newer part seems to have a small diode chip (marked light blue), but checking it just gave a 0 Ohms value. Maybe just spacer for wire bonding.

The failure mode is clear for both parts – the SC+ bond wire is blown (with molten ends clearly visible), and the Q4 power transistor shot.

Clearly this part could save a lot of space in the old days, replacing it with discrete parts would take about 5 times the space (1 large TO-3 NPN, 1 large TO-3 PNP, 2 transistors, one TO-99 Opamp, and several resistors…. I have been successfully replacing these parts with TDA2030A audio amplifiers, they seem to be be a good substitute, even if they may lack some detail performance characteristics (eventually, the TDA2030A has even higher power and better bandwidth, say, 100 kHz vs. 20 kHz).

Some detail study of the opamp die showed that it is indeed a National Semiconductor part, 741H printed on it, and the shape of the capacitor (the light colored silver area in the middle) is the shape of the typical National 741.

Various

Blaupunkt OSTIA Home Radio: revamping an old beauty

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As a family heritage, we ever had an old radio from my great-uncle (brother of my grandfather) named Modestus, and ever since I can remember is had been standing in the bedroom of my parents. Eventually, it was no longer used there and moved into my mechanical workshop where it still serves to play background music while I am operating machines.

It was build some time in the early 70s, and is based on germanium transistors – to be precise, 11 germanium transistors. The sound is not bad given the relatively simple circuit. However, in the last year it must have suffered some degradation of the FM tuner, because this tends to drift, and the reception is not clear always. Especially in winter, switching it on after a “cold” start, it needs some re-tuning after about 30 minutes of operation. A little inconvenient. Rather than spending a long time trying to fix an old FM tuner, I decided to take another approach – adding a new digital (PLL) tuner.

In my stock of old parts I had a no longer used PCI TV card, which incorporates a Philips FM1216MK tuner, a combination TV and FM tuner use a TSA5523 PLL, and can operate from a single +5 V supply (because of an internal DC-DC converter).

The card is a combined ISDN-TV-FM card. The tuner can be easily desoldered. Control is by i2c bus, two wire interface. Some libraries exist, but I didn’t use those. Rather straightforward to send the bytes needed to set the frequency and to do some more configuration needed. The tuner has a stereo decoder, but I operate in mono mode – there is only one speaker in the OSTIA radio.

A quick setup with a i2c LCD added for debugging. Using a Arduino Nano3 board clone with an ATMega168p microcontroller. But any microcontroller will do.

Now, integrating the new tuner to the OSTIA – my objective was to not destroy the old beauty, integrate minimally invasive. A first attempt to use the build-in transformer failed, because it could not provide the roughly 200 mA current needed for the Philips tuner.

To feed the audio signal, I cut a bridge on the board (which carries the FM audio from the old tuner), and injected the audio from the new tuner via a 100 nF foil capacitor.
For control of frequency, there is no an incremental encoder on the back of the radio (I rarely change the station if at all), and when you push on that encoder, the last frequency set is stored in EEPROM. The LCD has been disconnected, not needed during operation.

Finally, the OSTIA back at its accustomed place in the workshop. Reception is good and stable now, all frequency locked to a small quartz crystal.

Certainly this radio now has no longer just 11 transistors – maybe 500 transistors now!

Well

A Garden Pump: a surprising level of complexity

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Now, after winter has ended and frosts are no longer severe enough to endanger my outdoor water system, time to restart the pumping system. For garden watering and general outdoor water needs I operate a small well, including an automatic pump, but during winter time, this is shut down and the pipes all emptied to protect the pipework and pump from freezing.

Normally, just a task of a few minutes to start the pump after filling it with water, but this time, no success. No water, no suction. Checked the well – plenty of water there. Also the pipework is all good and sound.

After some searching hear and there, I decided to open to pump and found a very unexpected defect – one of the critical inner parts, the so-called ejector which is needed to prime the pump (by removing air from the system) had a crack. Probably because of fatigue of the plastic material.

This part uses the water circulating inside the pump to essentially pump air out of the suction pipe going to the well. With the crack, it can’t effectively evacuate the suction pipe, thus, no water can be pumped.

The plastic material is good, a special form-stable and durable hard plastic, reinforced with glass fiber. Maybe a low-quality material batch, or some design flaw?

The pump, purchased in late-2020, is of the brand “Stahlwerk”. It was not expensive at the time, just about 100 EUR at the time of purchase, stainless version, including a small buffer tank and pressure control system. Anyway, the price is good, but the quality of the “Stahlwerk” goods, you judge yourself! Shouldn’t a garden pump last more than just three summers?

To check if the crack really is the root cause, I sealed it with some hot glue, and despite the deviating geometry of the ejector nozzle, the pump worked right away.

But such temporary repair is no good solution for my garden water system, which requires automatic, unattended and reliable operation all through summer. So I checked “kleinanzeigen”=classifieds and found an almost new, barely used pump close-by, for a very reasonable price.

It is called “Neptun”, after the Roman god of the rivers and seas, hope he will be able to ensure the water flow to my garden for years to come.

The pump, easily capable of 4.5 bars of pressure, stainless construction, and a solid 1 kW motor delivers very nice quantities of water, good pressure, and was easily installed on the existing buffer tank.

For the “Stahlwerk” pump, at least spare parts are available and the customer service was responsive. The spare part was reasonably prices, so I decided on a permanent repair – and after a few days got a new ejector insert delivered in a package.

Still made of the same polymer, but looks a bit heavier and the color has changed from black to white.

It matched nicely the dimensions of the old part. Cleaned all the old O-rings, and re-used these with no problem at all. Just take care when installing not to twist and of the O-rings, keep all nicely aligned and avoid undue force.

Now, while the Neptun will do the job, there is a spare “Stahlwerk” pump in the basement, just in case!

May the well never run dry!

Ancestry

The Schrödle Ancestry: a little time-consuming effort and investigation into local history

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Recently, much of my time was occupied with serious work at the my chemical professional job, business travel and, during free time in cold winter, research into the old ancestors and forefathers. The objective being, to publish a little booklet about the “Schrödle” family (my father line) for this year’s Christmas, and one about the “Pabst” family (my mother line) for next year, say, 2026.

Already may years back, in about 1993, I did some investigation simply by interviewing and recording the recollection of relatives that were still alive at that time. Archive records were hard to come by at that earlier time. Still I was able to collect quite a bit of information up to the level of great and great-great grandparents including great-uncles and great-aunts.

I recorded this earlier work in simple diagrams. This time I wanted to set up a proper database in GEDCOM format well familiar in the field of ancestry work. Further intention was to go back to about the time of the “30-years’-war”, a critical time in German history, 1618-1648, where a lot of devastation and movements happened at my homeplace.

The homeplace, it is a fertile area near an ancient meteorite crater, the Nördlinger Ries. At the high rim of this crater, the Schrödle ancestors have ever been working the land as farmers, millers and craftsman. Surely busy folks familiar with the hardship of essentially self-sufficient life. Places like Fünfstetten, Gosheim, Huisheim, Mündling were the villages of the dwellings, these are very old villages, with records dating back 1200 and more years, but certainly the are in and around the crater has settled since the stone age, many famous old bones have been found.

Two reasons facilitated the new wave of ancestry research: firstly, my father’s family has ever been from this famous spot in Northern Swabia area of nowadays Bavaria, Southern Germany, the old Sualafeldgau dating back to the 8th century AD. Secondly, there are now large numbers of records online available, in particular, the old church records about birth, marriage and death. And, fortunately, these have been well-preserved over the centuries in this area.

Surely, it is all a matter of patience to find the right records, assign them to the family tree and record the information in a digital format, say, a GEDCOM file. Some, like the marriage record of a son of one of the oldest Schrödle ancestors, a certain Balthasar Schrödle born in the 17th century Fünfstetten, and which is relatively easily read after some practice, and with my training of ancient latin received at school – final I can put that to some use.

Other records are difficult to read – even relatively recent records from the 19th century, because of bad handwriting of some priests, and there lack of attention to readable handwriting.

But after all, I have been able to reconstruct the family roots back many generations, here, for my grandfather Georg Schrödle, born in 1901. He was a farmer with patience, a kind man duly respected, still in good memory.

Similarly my grandmother, a descendant of the large Reitsam family in Mündling.

Despite all the wars and difficulties of time, some items including books, papers and photographs still remain in possession of the family, but without knowledge of the ancestry, it is hard to assign these to the right people and to understand how these objects relate to family history. Accordingly, one part of the effort is also to identify all the persons on these old pictures and documents, to avoid this information getting lost over time.

One example is a book, which was in possession of the Reitsam family, the family of my great-great grandparents. While the book itself is nothing of particular value, a history of holy people that was similar to a bible probably the only book in the possession of common people, but with hand-written notes about the family members and birthdays. The last entry, written “Simmon”, is my great-grandfather Simon Reitsam, which which I inherited my first name.

Then, with the proper birthdays and other records, I did further research to find sources in archives, also, military archive collections, and many good records could be found.

One sad thing of the more recent history is also to number of people lost to wars, for example, Josef Reitsam, my great-uncle (mother of my grandmother, father side).

After all the years and only unclear recollection by hearsay, at least we now know the exact place and circumstances of his tragic and futile death during World War I.

Many other tragic events also came up during the research, which can serve as a warning to the current day: a Schrödle child, drowned in the river feeding the Schrödle grain mill, a Schrödle ancestor, who got pulled into the gears of the mill and died, a Reitsam ancestor, a carpentor and builder, who got hit by a tree and died, many children of the old families that died of infections diseases, and so on. We can hardly imagine all the hardship of the old days, and maybe get a better appreciation of modern times and the value of peace and a society based on the advancement of science of industry. After doing a fair bit of ancestry research now, there is certainly no desire to go back to the “good old times”.

Another, much more pleasurable aspect is the number of “far” relatives, and newly-found parts of the family. There are many relatives living in the US, emigrated to Chicago and similar places. Some still carry the name Schrödle, and actually pretty close relatives. Even in the local area, there are several families, whose relationship to us has been only vaguely known or even completely unknown. If you contact some of these members to find out more about the relationships and ancestors, so far I have encountered only the most helpful and kind people, so this is really a pleasure and joy. Also there are some local historians doing research into certain places and family groups in certain villages. These, too, are the most helpful and kind people encountered.

Some examples, the Reila family related to the great-grandmother, with roots in the Huisheim Angermühle, a grain mill.

The Sebald aunts, daughters of a postman who left the farm villages to follow job opportunities in Augsburg, the largest city in the closer surroundings.

Very unexpected also the huge number of relatives related to my great-grandmother, Therese Schwendner – a kind and distant relative had a picture of here sister will all her children, dating 100 years back.

Let’s see how things will proceed over summer, with less time and more outdoor work to do.

Various

Sennheiser Momentum 4 Headphones: water and a corroded connector

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Normally, I don’t repair consumer electronics, but in this case, a good friend asked me to have a look at these expensive Sennheiser headphones. Apparently, some water had entered the case, and since then, these were not operational. When charging, it blinks the red led 3 times, pause, 3 times, and so on. No other sign of activity and no success to reset it by pushing the button even for a long time.

To have a look inside, you have to first remove the ear protectors, then remove 4 screws, and gently pull-out the speaker. Exercise great care! There is a flat cable to connect the microphone to the intermediary board (the same board that has the battery connector). The flat cable and connector can be easily damaged, better use small tools and a microscope.

The battery connector had signs of visible corrosion. Probably cause by the combination of water and electric power. The battery has about 4 Volts when charged, so it can easily cause electrolysis of water and generate corrosive products if the water contains traces of salt, etc.

Unplugging and re-connecting it, using some contact cleaner, I was able to establish a stable (electrical) connection again.

The battery is contained in a small case, broke it a little when opening, all these internal parts are pretty fragile. But still functional. Inside, the cell is just attached by some double-sided sticky tape.

Here, a close-up of the microphone connector. It needs to be opened with a needle or tiny screwdriver by lifting the black part carefully. Easy to break!

For the current headphones, there battery was still good, but there are spare cells available. The quality of these may be variable so you may better check them before using as a replacement (e.g., by giving them 10 or 20 cycles by an external lithium ion charger). The price is quite OK, but you wouldn’t want to open up the speakers every few months for a battery replacement. The Sennheiser factory battery may last for about 3 years of use.

CNC Tools

Tool Grinding Machine Saacke UW II: many new copper nerves, and a new silicon brain

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With the basic installation of the servo motors complete, still some work to connect all the motors and encoders solidly to the controllers inside the (massive) control cabinet. First, wiring the cables through the base of tool grinder, a heavy iron casting. This casting is made of a rather hard type of cast iron, difficult to drill larger holes by hand tools. So I tried to to re-use existing plugs and connectors as much as possible. While for the power connections, there are plenty contacts of the big industrial connectors and cabling available, for the encoders I wanted to use twisted pair cable and plugs that are physically separated from the power cable feed-throughs and plugs.

Shopping around, I found these Aliexpress plugs, from China, but with good IP rating, IP68. The cost is very moderate, and the size “SP20” happens to fit the openings and screws of the former fan power connectors.

Fortunately, these connectors arrived quickly and there was no need for any modification of the machine base.

To guide the cables of the encoders (total of 4 cables, 2 twisted pairs each), there was not enough space in the existing duct. So rather than wasting time with pulling heavy cables, I just decided to add another duct from the machine base to the control cabinet, dedicated to the encoder cables.

Installation was not easy – drilling a sizeable hole in the machine base took quite some effort, but eventually, the cast iron could not resist a sharp Cobalt-alloyed core drill.

Next, some important work inside the control cabinet. After removing all the old controls and motor drivers, there is now ample space available, but all we will need is a 160×100 mm board, and even that is mostly needed to connect all the cables.

Key part is a ESP32 board, which does all the heavy work, on the other side, a W5500 ethernet interface, connected through SPI.

The soldering went faster than I thought, and the board is now mounted to the frame of the old control system. All powdered by a single 5 V power adapter (and an on-board 3.3 V regulator).

More time consuming that was all the other cabling, each of the controller has a 50 pin high density D-sub plug, with the fault, step and direction signals. I used some twisted pair (CAT) cable to make the short connections from the servo driver to the ESP controller.

At the driver side, it now all looks neat, and also the connectors of the encoders were cabled with IEEE1394 (SM-6P) standard. Lots of work with tiny wires, heat shrink tubing, etc.

Finally, I mounted a CAT6 panelmount connector, so the whole grinding machine is now controlled by one ethernet cable, running UDP protocol.

Key part of this is the software, and while I have other machines running with (expensive and – in Europe – difficult to get) MESA cards, this time I resorted to a public domain development found on Githup. A really great project there. I managed to get some bugs removed and to make it work for my needs with 4 axis and one ESP32. The pin layout is quite critical, because the signals and the ethernet SPI will basically require almost all outputs of the ESP32.

Some issue existed with the configuration, so I decided to hard-code the pins. Anyway, for now it is the only machine I have to control by this ESP32 motion control software, and there is no problem to customize it directly in the code.

For those interested in detail, here is the port layout.

As before, the motion control will happen through LinuxCNC, with a HAL driver that is talking to the ESP32 through UPD updating the motion commands every few milliseconds. All the step generation and time-critical motion control tasks are done directly in the ESP32, so the communication between the LinuxCNC and the ESP32 is not that time critical. I won’t describe all the driver tuning and LinuxCNC configuration here in detail. Drop me a line if you are interested. Probably I can get you started on some own projects.

From Aliexpress, also another part arrived – a handwheel – rather low cost but good look and feel. This will be connected to a parallel port, because there is no time-critical events there, just reading the signals and linking them to a software quadrature encoder in the LinuxCNC HAL.

Various

Agilent 4352B VCO/PLL Signal Analyzer: see you again, after 5 years

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After some years, again on the bench, a trusty 4352B VCO/PLL Signal Analyzer. A rather specialized instrument, but hard to replace with any more recent instrument, unless you are shopping in the 50 kEUR+ category.

he earlier repair: Agilent 4352B VCO/PLL Signal Analyzer: working! – I left a mark inside the cover, as I typically do after performing significant repairs.

Over time, the display has aged and unfortunately became unreadable. Not a big issue, because there is a connector for an external monitor, but still not very practical to use.

The polarizer can be pulled off, but the glue stinks and is very sticky, would be a big effort to do a polarizer repair.

The LCD, a Sharp LQ9D340H is still available, but the cost is high, even when sourcing from China, about 200 EUR a piece. Note: don’t mix up the LQ9D340 with the LQ9D340H – these are not necessarily compatible according to the datasheets.

After some study, I found a good offer for a used LQ084V1DG21 8.4″ 640×480 Sharp LCD panel. These are compatible with the 340H.

Offer of a German IT used parts seller:

The used panel had a special adapter – not compatible with the Agilent flat ribbon adapter of the 4352B – removed the screw and the adapter with no problem at all.

The installation went without any trouble.

The new LQ084 is a little thicker than the 340H, but it all fits into the LCD compartment.

The backlight driver and even the backlight cable position are compatible – just needed to plug the new LCD in.

Finally, not too much to do further – close the case, insert the screws, a quick test run.

Flawlessly working – starting up like before – and, I didn’t even have to remove the inner cover or any boards – just the front panel and LCD compartment.

CNC Tools

Tool Grinding Machine Saacke UW II: fitting new servos to the the old machine (A, X drivers)

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For the X (ball screw driven left and right) and A (rotary) axes, now as the servo motors have arrived, we need to find a way to mount the servos to the existing drive mechanism. My intention is not to modify any of the shafts and precision parts of the Saacke machine, but to determine a way to mount the servos with high precision of axis alignment, and a coupling that can transmit the torque without slop or delay.

The mechanical parts and brackets, I decided to use aluminum alloy rather than steel, even Saacke manufactured the stepper motor mounting plate for the A axis from aluminum plate, and the strength will be good enough, with no need to paint or oil the necessary adapter plates.

The couplings, I used KTR Rotex, size 19, with 92 Shore TPU elastomeric couplers. These were available already machines to the right size, including matching keyways. Found them used, or old stock, a good deal.

To house the coupling, made a cylinder from aluminum alloy, and 4 holes drilled for draw-bolts. The draw-bolts screw into the A-axis head, and nuts will be used in the servo mounting plate to hold things together.

The servo mounting plate required quite some planning to match both the machine side, the servo flange, and the fan cover (which I plan to re-install to protect the servo – the cooling fan doesn’t seem to be required).

For the connection of the coupling and the head drive, made a rod with a long key slot (formerly, the long shaft of the stepper motor was directly fitting into the A axis drive head.

Fortunately, all the parts fit right away, torqued the draw-bolts carefully, and adjusted the couplings for proper clearance. There was a little slop in the coupling, so I bent some thin shim stock to pre-tension the polymer coupler a little more.

The distances and plate thickness was designed such that there is enough strength, without adding to much weight or unnecessary stick-out.

The fan cover, steel, had some other fans originally that you damaged during transport, and the adjustments for new fans were done by hand before, now a good chance to clean these (grit and dust filled) covers (there purpose was to direct the fan air around the stepper motors), and to mill out a little more space for the cables.

Handy to have the manual mill, and various workpiece holding.

With the cover mounted, all looks nice and neat, and overall a few kgs lighter compared to the former stepper motor. The cover is held in place by 4 screws, radially arranged, that have steel (stainless) spheres pushing onto the servo.

For the X axis, similar case, programming the CNC code, milling the aluminum plates. These mill jobs took a little while with some many features, but no purpose to optimize the program for a single piece.

There was no need to drill new holes, the plate was made such that the existing stepper motor threaded holes can be used.

The spindles shaft and the servo shaft have different diameter and key size, but also here I was able to find suitable KTR Rotex couplings.

With the cover, it looks like not much has changed vs. the stepper motor, and there is still enough space for the cables (drive cable 3 poles plus ground and encoder cable – 2 twisted pair plus shield).

With all the work on the X axis, I used the chance to clean the screw bearing thoroughly, and adjusted the ball screw precisely (with a micrometer resolution dial on the table, and checking the pre-tension), but also found that the bellow cover is was badly worn, full of grease and dirt.

Finding a replacement bellow cover, from the original manufacturer, a German company, I was not even able to get a quotation, which would likely be cost-prohibitive anyway. Looking through Aliexpress, found a very cooperative supplier in China – this company provided a custom made cover for just about 30 EUR, shipping to Germany included (no customs to be paid). They were not able to provide small “tabs” at the side to hold the bellow cover in place, therefore I cut some from PVC plate, white color was the only thing I had available – but it will not be visible once installed anyway. Using special PVC glue, which really softens the plastic and welds it firmly, these plates were attached with very good strength. Also made a test piece, and could not actually break the glue joint without destroying the whole piece.

Installation of the bellow cover was easy – some small brackets and 3 screws each side, and the dimensions fit well. The material of the Chinese supplier seems pretty durable, oil and solvent resistant material, and many PVC frames (in each fold) to make it stiff and keeping shape. Let’s see how it will perform over the years.

CNC Tools

Tool Grinding Machine Saacke UW II: steppers to servo motors

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Some more work on the Saacke, the original design had 3 motor drivers for 4 stepper motors – the Y and Z axis being operated by one drive. My original plan was to get another stepper motor driver, but for these 6-phase high current steppers, not an easy thing. While there may be some old controls available, they are pricey, like 1000 EUR and more. Also, I was not too thrilled by every year repairing at least once the driver – 30+ year old electronics doesn’t normally provide a particularly high level of reliability.

Another choice would be to replace the RDM-51117 steppers with some other (2-phase) stepper motors, but rather than 1000 steps per revolution that would result in only 400 steps (half-steps) per revolution, or not very precise micro-stepping. Not good, because the Y and Z pitch is 1 and 3 mm/rev, respectively, and a grinder normally should be controllable in 1 mikron, or smaller, increments.

Analyzing the torque requirements, I had the idea to use a servo motor instead, because the holding toque requirement is actually pretty small (the feed screws turn easily, and once at position basically no force needed). AC servos (with an encoder feedback loop) have become affordable in recent years, why not use one of these?

Shopping around at Aliexpress, I found these 80SS75 (750 W) AC servos, offered including drive and 3 meters of encoder and power cables. Available from a Chinese vendor (Hanpose), ready to ship from a Belgium warehouse.

Chatting with the sales manager a little, the lady offered my a very good deal, almost too good to be true – so rather than buying just one motor, I ended up ordering 4 sets, and decided to replace all the stepper motors by servos.

These servos come with ASD275 drivers, these are quite similar to other AC servo drivers I have used before, they all follow similar programming and characteristics. One important characteristic is that these drive need tuning of the control loop once installed.

Only a little wait, then 4 boxes arrived – all stuck together and wrapped in plastic, not bad!

These sets include not just the cables but also the connectors, great! Full sets! Even an English manual is available.

Some mechanical differences exist, so we have to make adapter plates, and modify the couplings. The Saacke design has just hard-coupled drives, there are no fancy parts, just a steel sleeve. This works well when all is centered up correctly.

Also the key had to be modified, because the sleeve has a 5 mm keyway, but the AC servos have 6 mm keys. So I milled away half a mm each side, to make it fit.

On the lathe, I used great care to center the sleeves precisely, to avoid excentricity.

Turning it to a larger hole diameter was easy, and a great surface finish.

Before fitting the motors to the machine, I did a quick desk test, and all working fine, out of the box!

For the cabling from the machine to the control system, I selected LiYCY-TP (twisted pair) cables, 2x2x0.5 mm2, for the encoders, and Lapp Ölflex Classic 110 CY (shielded) 4Gx1.5 mm2 control cable for the power drive. These are a recommended and cost-effective solution for all kinds of servo and stepper cabling.

The motors were easy to mount, and the cables installed in the machine – a little oily and dirty task, but also a good opportunity to give the Z axis guides a good clean. Luckily, I had in stock 2-cable feedthrough plugs from a project about 30 years (!) past, from my childhood days! Now finally I can use these for the grinder….

The adapter plates were quickly milled on my CNC machine, all with great care for perfect centering. For efficiency, I used AlMgMn alloy 5183, which is easy to machine to high precision and practically free of warping or internal stress.

Installation went smoothly – a little tight fit of the motor flange, but hopefully, this will be a one-time installation.

The motors are rated to 5 Amps and more, but as expected, the typical currents are just around 1-2 Amps when moving, and 0.3~1 Amp when stationary.

Next will be modification of the X and A drives.

Various

Heraeus K1150/3 Oven: some cosmetics, some bricks, some electronics

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There is always some need for heat treatment in my workshop, for example, hardening, softening, tempering of steel, hardening of aluminum alloys, etc., often just done with a torch and by visual judgement and feeling more than measurement. While this works for small parts and general tool steel quite well, it doesn’t work for hardening of aluminum (precipitation hardening), and larger pieces of steel may crack. Even smaller pieces may suffer from uneven heating, resulting in distortion.

A small electric oven is handy for that so far, a German brand, “Naber”, already pretty dated but it seems to have been very rarely used. Not long ago, added a controller, to allow curves and automatic controlled heating and cooling operation.

But recently, screening to classifieds, I found a much better oven, 4-side heated, Heraeus K1150/3 that can handle much larger pieces for heat treatment.

It came pretty quickly, for just a little over 400 EUR, including delivery and including a cart. First thing I did, painted the cart a little with red paint – RAL3000 “feuerrot” as it is called officially. For years I carried around a can of such red paint, never thought I would ever actually need it.

The oven, it can operate of 3 phase power, 380 V 14.5 Amperes, originally. Now with a mains voltage of 400 V, the power will be about 10% more. In any case, I can connect it to my 16 A outlets.

The oven has quite significant heating power for its size, good for heating up metals quickly, for hardening. Also, it is built such that it can be opened pretty safety in hot conditions, to take out the glowing parts – not all ovens (especially not common pottery ovens) can be opened when hot – the refractory bricks may brake, or the coils may bend, or similar.

The next difficult task was to get the oven back onto the cart, not easy, because of its bulky size and well over 100 kgs of weight. Even with 3 people, impossibly to carry, and not easy to grab. But with various pieces of wood, some small furniture rollers, eventually managed to get it onto the cart with the help of a friend, and no damage or injury!

The bricks of the oven are all in good state, except for some loose parts at the front door. There, the inner (hot) layer is held to the door by 4 metal parts.

With refractory glue, stable to well up to 1100°C, and easy to use.

To do a proper job, I cleaned up all the old cement, and thoroughly roughened the mating surfaces.

By the manufacturer, the oven has a very sturdy Pallaplat (Au-Pd-Pt vs. Pt-Rh) thermocouple, very thick wire, certainly worth almost the 400 EUR I paid for the whole oven, connected to an analog temperature regulator and a nice 96×96 mm instrument.

These Pallaplat thermocouples have a larger coefficient (several times larger) compared to common Type S (Pt-PtRh) thermocouples.

My intention was to keep the old regulator and instrument as a maximum temperature regulator basically, and add a (secondary) controller with ramp/segment control. The oven, fortunately, has already provisions for a second thermocouple, so I pulled two new isolation tubes and a new S-type compensation wire from the oven to the control cabinet.

Be careful when connecting compensation wires for thermocouples, because the color codes are misleading: BLACK is positive, RED is negative!

To make things even more complicated, there are colors codes that differ from country to country…

To install the new temperature controller, we need to modify the control cabinet a little. There is a timer so far, which will not be needed anymore, but the opening is not quite large enough.

Cutting a a little larger with a grinding disc, filling, quite laborious to do it precisely!

It is a nice part, with many functions and a complicated manual, but it works pretty well.

Rather than an expensive Western part, I resorted to a part imported from China, model PMA-900. It is available in various option, alarms, control output choices and so on.

Heraeus used a Siemens contactor to switch the heater on and off, but for finer control, I selected a 40 Amp solid state relais, which can modulate the power much more precisely, and without wear.

Installed – the heat sink came with the relais, and there is a small fan to keep it cool even in the control cabinet. Later, I added a plastic cover for touch protection, and some warning signs. 400 Volts is no joke!

The S-type thermocouple, about 300 mm long, I also got from China, at a very reasonable price. It is already protected by a ceramic tube, but the diameter didn’t fit the existing hole, and it looked all too fragile to be easily damaged with rough handling and over time.

Fortunately, I found a surplus protection tube, exactly the right diameter (inner and outer), made of 99+% sintered aluminum oxide. Just, a little long.

With a diamond wheel I cut it slowly, because it is a single piece not easy to get again (new protection tubes of this kind nearly cost 250 EUR in Germany, therefore, surplus discounted parts are the only reasonably choice).

Inside the oven, you can easily see the custom Heraeus brickwork (also used for smaller models of that oven), 4-side heating, and the bottom is normally covered with silicon carbide tiles.

Finally, a little brush-up of the outside, to protect it from rush, by using a high-temperature paint. I prefer the MIPA brand, silver paint. A small 375 ml can will go a long way. It is resistant up to 800°C, and from my experience, stops most rush and can be re-applied from time to time if needed without building thick layers.

It is a real paint, with a good small, any many solvents, not the water-based junk for wood. Real paint!

Now, will all repairs done, the oven is looking good again. Everything cleaned up and with a new controller. Great addition to the workshop (only trouble is, it is very heavy, and does consume a lot of space).

One final note – the power cables of machines, especially, industrial machines purchased used from unknown sources, never trust these cables! They may have no ground connected, may have damage, may have been repaired by people without proper education in electrics, and without the proper tools – or these cable may just have suffered from abuse in an industrial environment. In a household, with low power, must not a problem. But here we are talking about larger currents, and these should not flow over cables with compromised integrity.

The same this time – in the plug, the ends of the cable were badly work, short protection sleeves used and overtightened. Mostly, just half of the wire intact.

At the oven end, the inlet to the control cabinet is a little tight – the earlier guy working on that cable didn’t even bother to fit the cable, just removed the isolation and put some tape… asking for trouble.

Luckily, I had a few meters of good cable around, and managed to fit it through, and now all is nice and safe!