Monday, October 1, 2012

Concrete and dowel

This evening I filled my lathe bed with concrete. I said I was going to buy some 10mm dowels and grease them up before putting them into the bolt holes, but that wasn't possible. Because Magnet Mart are so good at stocking usefully sized lumber, I had a choice between 9.5mm and 12.5mm dowel...

Obviously, I chose 9.5mm. The process I used was only marginally more complex than the grease option. I wrapped each dowel (which was cut to just a little longer than the height of the bed) with a small piece of standard printing paper, fastening it with a piece of tape. Then I wrapped each piece with thin plastic packing tape, hopefully preventing the conrete from adhering to it.

The goal of this approach was two-fold: to make up the missing 0.5mm, and to facilitate the removal of the dowels with minimum fuss, ideally without leaving anything but air and concrete behind.

The concrete is curing now, so I'll let you know how it went in a while.

Tuesday, September 18, 2012

Lathe progress - Bed and bedways

The other day I headed back into the workshop to do some work on my lathe, which has been languishing for a while as a result of my working too much, and having uni work to do. Anyway, I bought some bolts from ebay (M8x1.25x80mm), and they turned up not long ago. So I set out laying the holes out on the ways and drilling them, ready for tapping.

I ran into a couple of...snags...during this process. Firstly, and worstly, I snapped not one, but two 3mm drill bits off in the bedways. After much swearing and a lot of dremel work, I managed to remove them. The second issue came as a result of misreading a drill-size chart. I read 7.2mm for M8 taps, when in fact the drill size is 6.8mm... No real drama, I just have shallower threads than I wanted. It seems to work fine though.

My camera was nowhere to be found during this process, but it was all quite straightforward, errors aside. I had 25 bolts, and a metre of bed to join to a metre of bedway. Casting one bolt aside as a spare, I set about spacing the 24 bolts evenly over the length of the bed, about 30mm apart, and centred along the length of the  ways. If you're doing this at  home, make absolutely sure that the bolts are spaced close enough together to go through the bed with no troubles. Had I spaced them 50mm apart, they would have been going through the walls of the bed...bad idea.

Anyway, pilot holes drilled, I clamped the ways to the bed and got them aligned, then proceeded to drill holes through the bed, using four of the pre-drilled holes as guides. I tapped the four holes I had used as guides, and bolted the bed and ways together with four bolts. Next, I drilled the remainder of the holes using a complex multi-step method of my own invention...

I drilled a small dimple into the bed, using the holes in the ways as a guide. Then I removed the ways from the bed and put the bed onto my drill press, which I used to drill 10mm holes through the top surface of the bed. If you have a nice big drill press, drill straight through in one go. Unfortunately for me, I had to drill my holes in two steps. I did all the top holes, then had to fiddle around a LOT to drill through the bottom, while maintaining alignment. I ended up doing this by chucking and unchucking the drill bit for every new hole, which worked fine, but was as tedious as all-get-out.

That done, I tapped the rest of the holes in the bedway and gave it a test fit. Brilliant!

The next step is to put a 10mm dowel through each pair of holes and fill the bed with concrete. This will add mass to the bed, which is always a good thing, but it will also help reduce flexing. Another good thing! The dowels will be greased so that I can just push them out (hopefully!). If not, I can drill them out easily.

Now, in case anyone was curious about why I drilled 10mm holes for M8 bolts, good question. Basically, it gives me about 2mm of wiggle room along the length and width of the bed for getting alignment right, and it absorbs any error I may have made in aligning the holes correctly to start with.

Anyway, onwards and upwards.

Friday, July 13, 2012

Tips for using NeoCat's Arduino Twitter library

This may be obvious to people who are better at programming than me, but I struggled to figure it out for a while. NeoCat's library can only post chars and char arrays to twitter, but readings are not in char format. To get around this I had to do some fiddly type conversions, which I lay out below.

itoa(var, varChar, 10);                               //converts 'var', which is an int, to 'varChar', which is a char
                                                                //If anyone can tell me what the '10' is for, please do

stringone = String(stringone + varChar  );    //make a string called stringone. Append the newly formed  
                                                                  //char 'varChar', which was the int 'var'.

   stringone.toCharArray(msg, 100);             //convert 'stringone' to char array (reads "value of the in
                                                                  //save the char array as 'msg'. 100 is the number of
                                                                  //characters in the char array.;                                       //posts data to twitter

'msg' must be declared as a char at the beginning of the sketch.

var was declared as an int, it could be, for instance, an analog reading.
varChar was declared as a char[].
stringone does not need to be declared until it is made.
More chars and char arrays can be added to stringone by using the + symbol and the char name.


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

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.