Brewduino

I put down my first all-grain batch of beer the other day, and discovered that the arduino-based thermostat I had made for it had stopped working. I put the beer inside to keep warm, and it seems to be ok, but it prompted me to continue work on my brewing computer.

I now have a functioning network, so I've decided to add a reporting feature to my device. I've written the first revision of the code, but haven't yet got all the hardware going.

Here are the functions planned:

Internet enabled
Temperature sensing
Thermostatic control (hopefully with PID/PD)
Specific gravity sensor
Temperature calibration for gravity readings (reads gravity and spits out what the value would be if the liquid were at a set temperature)
Alcohol content calculation
Daily report of gravity, alc% and temperature via Twitter and email
Thermostatic control failure alert via Twitter and email
'Time to bottle' alert via Twitter and email
Datalogging

I'm yet to get the gravity sensor working, but that shouldn't be too much of an issue. I also haven't trialled the datalogging to SD card or PID yet. So far I know I can get it to send me an email with the readings, and I know it can control the temperature. More to come when I'm closer to completion.

Furnacey fun

I made the rest of my casting patterns the other day, and after painting them with glossy paint, set to finishing the furnace.

I lined it with the clay mix from before after grinding it down to a very fine powder. Because I knew I was short on volume I added all the sawdust I could find, most of a bag of perlite, some more sand, and the last of my bag of bentonite. I also filled the bottom of the body with dirt to fill up some of the extra space.

When lining furnaces it's important that your clay not be too wet. That was my problem the first time, and the loss of moisture caused a lot of shrinkage, and thus, cracks. This time I made the clay much drier. I spread the dry clay out as thinly as I could on a plastic ground sheet and sprayed a very fine mist of water over it, then mixed thoroughly with a rake. I repeated this until the clay was uniformly damp. It looked a bit like breadcrumbs and clumped together when squeezed, but did not feel wet. After that, I covered it for a while so it could percolate a bit, and to give me time to get the body ready to be lined.

The inner form was made by wrapping the metal from an old canola oil tin around a pair of wooden discs. Before doing this I rolled it up as tightly as possible and tied it like that for a few days. This meant that the metal was springy and would hold the discs, but also that it would pop in on itself when the discs were removed. I packed about an inch of clay down straight on top of the dirt, making sure there was a former for a drain hole. That done, I set the inner form on the clay bottom and began to ram clay in around it. When I got to the level of the burner I put the pipe in and continued to ram. You should build the lining up in very small layers, working around the furnace as you go.

To line the lid I just placed it on a piece of plastic sheet on the ground, inserted a piece of PVC in the middle as a former, and packed the clay in. I rand wires all through the lid to add stability. After using the concrete here it occurred to me that I should have used concrete in the bottom instead of dirt too...

Unfortunately, I was STILL short of clay, so the lid was only 2 thirds full, and the body lining stopped short about an inch from the top of the steel wall. To compensate for this I ground the steel on the body back to the level of the clay, I also filled the top of the lid in with quick set concrete. This is not a hotface, so concrete was fine. It was just to add stability.

I also began work on a lifting mechanism for the lid, but haven't finished it yet.

I cast my first four lathe parts the other day, and they came out reasonably well. Some had little pockets caused by loose sand, but the pockets are in non-critical places. It took all day, but I got the carriage, cross slide, compound base and compound slide castings done, and turned all my scrap into ingots. I'll upload some photos soon, but at the moment I'm busy machining the castings on a friend's milling machine.

Experiments with aluminium bronze

Today I made some aluminium bronze, and it was a partial success I think.

I learnt a few things about the material, but I'm sure there's more to learn.

The first thing that I learnt is that it takes a surprisingly long time to melt copper; I was still trying after 20 minutes at full blast. Its melting point is 1084.62 degrees celsius, but either I couldn't get that hot, or there's some trick to melting copper. I got it to a very bright red-heat, but it wouldn't go any further.

So here's the lesson in that: according to The Complete Handbook of Sand Casting by C.W. Ammen, you should melt the copper first (p189), then add the other metals. I got fed up with w

aiting for the copper to melt, so I added my aluminium, which began to melt almost instantly, forming a puddle in the bottom of the crucible. Once this puddle had formed, the copper began to melt really quickly. If anyone can explain this, please do. Anyway, in future, I'll put copper in the bottom, aluminium on top, then more copper, then fire it up.

The second thing I learnt is that either aluminiun bronze is not nearly as golden as the internet would have me believe, or that it's a lot harder to get the ratios right than I thought. I aimed for 10% aluminium by weight, so I put 9 parts copper and 1 part aluminium in (2kg copper, 222g aluminium). One thing that leads me to believe that the ratio is hard to get right is that there was an awful lot of dross (or something that looked like dross) stuck in the bottom of the crucible after the pour. Thus, much of either or both metal oxidized. At what ratio, I can't say, but surely it is likely to skew my intended ratio.

In all honesty, I don't care about the colour, and the colour came out being pretty nice anyway. It looks almost like steel, only shinier. What I care about is the mechanical properties.

Here's an idea of the colour: the watch is stainless steel, the light has made everything a little yellower, though there are some patches about the place on other ingots that actually are that yellow. Also, notice how smooth the side is, and the two big flat bits on the top. The bumpy bits were loose bits of sand. This implies that I can get a pretty good finish with this alloy even with reasonably coarse sand.

The third thing I learnt is that aluminium bronze needs to cool slowly, otherwise it becomes very brittle. I quenched most of the ingots that I cast, with the result that I could break them by hand, or by dropping them from a height of about a metre. This had me worried, until I found an ingot I had forgotten to quench. I couldn't break it at all, I didn't try with a hammer though. In future, NO QUENCHING.

Here is a n ingot that I quenched, it was so brittle that I could snap it in my hand. It leaves a very sharp edge, I discovered the hard way. Notice how shiny the inside is? Also, you can see how it's quite crystalline. This has to be the result of the quenching, as the alloy ratio is almost certainly similar to the range of 'real' aluminium bronze, and I have one ingot, which wasn't quenched, which isn't brittle.

A new project: ambitious, but possible

OK, I have a new major project. I'm going to build myself a Gingery-inspired lathe. If you don't know who Gingery is, google him. In short, he was a man who needed a machine shop, but lacked the funds for one. He had plenty of time though, so he decided to build one. He made many machines out of cast aluminium, which he melted in a furnace in his back yard. I admire his ingenuity, but feel that his lathe design is somewhat lacking in some areas. Those areas are:

size - his lathe is very small

fittings - his lathe has no standard tooling fittings

engineering - there are numerous engineering points that I disagree with, I'll cover these as they appear though

So, the first part that needs doing is the bed and ways. (Engineering flaw #1) Gingery cast his bed out of aluminium, making a 60cm hollow ribbed block for rigidity. Being aluminium, though, it is not particularly rigid. I imagine this lightweight casting introducing many inaccuracies, mostly through flexing and sagging. The other major downside to the bed is that it's a very big casting, especially for novices, at whom the series is mostly targeted.

To counter both of these problems, I have decided to skip casting the bed, and opt instead for a steel I-beam. This should give me the extra weight and rigidity that I yearn for, while also allowing me to scale the whole lathe up a bit (this addresses flaw #1, size). I plan on scaling it up to a 75mm swing, with around 60cm between centres.

Here is my basic idea for the bed: The black I-shaped section is, strangely enough, the I-beam. The thin grey piece is an aluminium match plate that I will cast up, and the red is a piece of bright flat bar.

The purpose of the match plate is simple. I will first scrape one side of it to fit the I-beam perfectly, then I will scrape the other side to match the bright bar perfectly. This will mean that the inaccuracies on the surface of the I-beam won't matter, as they will be averaged out by the aluminium plate. Then, given the very close tolerance of the bright flat bar, the matched aluminium surface will be almost perfectly flat. This will mean that I can bolt the bright bar onto it and not have to worry about it deforming.

Now, the only problem I can see with using I-beam is that it is not designed to withstand torsional force, which is exactly what I will be putting on it. I have two thoughts on this:

1) it may be so grossly over sized that it doesn't matter

2) I could weld straps into it, between the two parallel surfaces, and perpendicular to them. This would change the side view from being a long, wide channel, to a series of boxes. I feel that this should strengthen it sufficiently against the torsional forces.

So, those are my current plans. I'll update you as I build. But for now, google Gingery and see what he's all about.

Experimenting with etch resists

Today I tried two substances as etch resists for electrolytic etching. Etch resist marker, designed for chemical etching of circuit boards, and black acrylic paint. Neither were great, I must say. The etch resist pen worked, but came off very easily when I brushed the surface to remove copper crud. It could work, but I'm not doing any fine art with it. The second, acrylic paint, was a TOTAL FAILURE. Tip: Never use water-based substances as resists. They dissolve in the bath. Photo one is before etching, photo two is after.








I didn't touch the front surface on the second one before taking the photograph. Once I scraped the paint off, I noticed that the whole surface had been etched the same amount. I reiterate: Never use water based substances. Ever.