Last week saw us doing two full days in the workshop. Yes, they actually happened (unfortunately we have now been told that this week's workshops may not happen due to staff shortages)! Our group was split into two, with roughly nine of us in each class. For the first day, my group was to learn how to safely change grinding wheels on both hand held machinery and bench/pedestal grinders. This was actually a day long short course that will give us a certificate showing we can safely change these. Sound a tad overdone? That's what we thought at first, however if a grinding wheel bursts (fractures) on a bench grinder, the flying fragments can actually kill you, so you do have to play it on the safe side. So, we were taught how to check everything is in order before replacing, how to replace them, and how to identify what wheels are appropriate for what material and activity. We learned all the information in the morning, and then had a one on one test each with the examiner so he could sign us off. If you forgot anything a prompt was allowed to hint you may have not covered everything in full. I passed with no prompts, and once I have my discharge book, may go and get the certificate printed. Apparently this is a useful certificate as when you are on ship a few people are listed as being allowed to change these wheels. Once they have been decided, only they must change the wheels and nobody else. Most people can use the equipment, but they must only get one of those people to change the substrates of course.
On Thursday, our second day of workshop we actually had some hands on time making a small tool called a 'drift' (see photo at bottom). Basically, when you have a drill bit that is too big to fit in a chuck on a lathe or drill, then you use what is called a Morse Taper (http://en.wikipedia.org/wiki/Machine_taper). This allows the bit to fit. You can also use a Morse Taper for chucks too as far as I'm aware. Anyway, once you have used your piece within the taper then it will be too firmly lodged into the Morse Taper for you to remove by hand. Thus, to remove the bit, the wedge shaped drift that we are making is tapped into a hole on the side of the Morse Taper and this removes the bit.
We started with a roughly cut piece of metal and set about filing the edges until they were square, roughly smooth, and without burrs. Thanks to my many many hours of filing at Paxman, this task was made easier. Once we had squared the sides we applied red dye to one surface of the piece to allow lines to be drawn on it. Then we used a special table that is engineered to be exactly flat and a bigger tabletop version of a Vernier Caliper, used to draw precise lines on the work piece. We measured out 25mm by 100mm lines then set about cutting the piece down to the required size with a hack saw. After cutting, we then spent a long time filing to get it square again and to make sure that it was level with no high or low spots. This had to be precise to 0.2mm (as measured with a DTI - dial test indicator http://en.wikipedia.org/wiki/Dial_indicator#Probe_indicator ). How close the line you saw makes a difference as to how much pain you will go through getting this correct. We used engineers blue (http://en.wikipedia.org/wiki/Engineer%27s_blue) in combination with the DTI and this is a very thick dark blue ink. It's spread on an engineered level surface and then the work piece is applied work side down to it. It will place ink on the high spots so you know where you need to file to get it level. We kept using the DTI and the blue until we finished with a level surface. Then we measured out the position for the hole to be drilled, drilled it a few mm deep with a centre punch (this makes sure the hole will be central), then drilled it through completely with a 5mm drill bit. We then countersunk the hole to whatever depth we thought suitable. Once this was done, another piece was to be cut off forming a diagonal edge. I cut this off and was filing the edge down to precision level when we ran out of time, so I'll have to finish next time. From the photo you'll be able to see I've not got too far to go. It's weird to think I spent almost a day doing that, as not much has been accomplished. I relished the challenge though.
Friday went down with nothing much of note, except a really great four hour journey home courtesy of England's fine M25 rush hour.
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