I made this holder for my GCSE engineering coursework, I have copied and pasted directly from that so sorry if there are parts that don't make sense.
Controlled assessment Task 4: Tablet and Smartphones are becoming increasingly popular and a range of apps means that they are being used around the home and car. You have been approached by a company who manufacture tablet and phone accessories to design a stand to support the device while the user is viewing the screen. Two examples of the product could be used are in the kitchen and the car. Essential parameters: -It must support either a tablet or phone- it should be adjustable to fit a range of tablets or phones - It should hold the device securely and prevent it falling over. It is not necessary that the device is being charged while supported.
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Step 1: Sandcasting the Base
Firstly, I looked at the production plan to see what I had to do first. I looked at steps 1 and 2 told me what to do so I made the mould of the base. I made it out of MDF, the technician cut out the pieces, I PVA glued them together and after it dried (about 10 mins) I had to smoothen the mould with sandpaper then with wet dry paper. I varnished the top. That took about half an hour to dry. After that finished to dry, I varnished the bottom then waited for it to dry again. The mould had to be perfectly smooth so it didn’t stick to the sand and ruin the metal base. This whole process of making the mould took nearly 2 hours including the marking out of the piece (so I knew where to glue) and making the mould smooth.
After that, I used a sieve to sprinkle sand a layer of sand on top of the mould and around the box. I compressed the top of the mould and around the edge with my fingers. After that, I had to carry on adding heaps of sand compressing it after every layer with a mallet by pounding it until the sand wouldn’t move anymore. I carried on doing that until the sand was heaped over the top. Using an engineer's rule, I levelled off the sand in the sand holder then slowly lifted it up (making sure no sand falls out (it shouldn’t if the sand is compressed enough)) and flipped it over.
Then I put the second half of the sand holder, stick the mould for the runner and riser near the base mould on opposite sides in the sand and sprinkle more parting powder on top. Again after that I sprinkled and compressed the sand onto the work. I carried on adding sand as well as cramming the sand together. After I had filled the sand holder I took out the riser and runner, lifted the top and put it on its side on the side. After that, I screwed a screw into the base, tapped it a bit then took the base out (I had to tap it so the base would come out cleanly and so it did not ruin the cast shape).
I used a trowel to create a path from the base to the 2 holes, used a paintbrush to take out loose sand and put the top half back on.
The DT technician then poured molten aluminium into through the runner and into the mould until you could see the aluminium come out on the other side. To finish off, we waited for it to cool, took it out, cut off the excess material and then I used wire wool to clean, polish and smoothen the base.
Sand casting- To make the aluminium base, I brought out the sandbox and the 2 halves of the sand holder. Firstly, I put the bottom half of the sand holder upside down then I put my base in the middle and sprinkled parting powder all over the bottom plank of wood and my base. Then I used a brush to make sure the parting powder was laid evenly.
Step 2: Main Holder
The lines I drew in black was cut and the lines in green were vector engraved. I made too many mistakes when I was drawing so when they were cut, the parts did not work so I had to redraw parts of it again on techsoft then get it printed.This method created too many mistakes.
Strip heating- To make the clamp pieces curved; I turned on the strip heater and waited for it to warm up. After it warmed up, I put the acrylic piece on there making sure that engraved line was directly above the heating strip. I left it on one side for 30 seconds then I flipped it and heated that side for another 30 seconds. I tested to see if the plastic would bend with a bit of pressure put on it- if it did not I had to heat it up again for 15 seconds on both sides.
Countersinking- Some of the holes I cut out where for screws. The panel screws interfered with parts of the mechanism and the phone would not fit. So to fix this problem I countersink these holes. To countersink: Firstly I used the chuck to open up the vice on the pillar drill, then I put the countersink bit into the vice and used the chuck to wind up the vice. I took out the chuck and put my goggles on. I turned on the pillar drill and made sure the drill bit was fixed in. I turned off the drill and put my work underneath the drill. I used the lever to make the drill come down and lined my work into the right place. I clamped my work down with a G-Clamp then countersink the hole. I did this with all the screw holes.
Assembly- I used liquid solvent cement to glue a few pieces together making sure none got onto my hand and let it dry. After that, I put the pieces together and tighten the front part (the claws, front, spacers and guide panel) with wing nuts. Then I put tiny rubber bands (loom bands) then I took the nuts out and put the rest of the parts together and locked them in with lock nuts.
Design- I looked at my production plan again and followed the steps 3 and 4 to do my techsoft design. To make my the holder mechanism. I looked at my prototype model and my final design for the sizes so I could draw out each part on 2D techsoft. The main tools I used were the circle tools, the line tool and the joiner tool. The advantage of using techsoft was that it was really easy to use and it could be sent straight to the laser cutter and be cut out. Different parts had to be cut out from different thicknesses of acrylic. Using CAD is really useful as it is extremely accurate and can be edited if there are any errors before needing to cut.
Laser cutting- I saved the techsoft files onto a USB each file contained unique pieces that needed to be cut in different colours and thicknesses. The USB connected to the laptop that was connected to the cutter.
Step 3: Arm Mech and Assembly
Again, I looked at my production plan and looked at steps 5 and 6 to see what I had to do to make the arm mechanism. I started off by cutting a shaft out of 13mm (½”) thick bar of aluminium into two 100mm length pieces and one 30mm piece with a hacksaw. To clean up the edges I turned the ends on a lathe and the drilled a 3.3mm hole in the middle of one of the sides on one of the 100mm pieces and another hole on one of the sides of the 30mm piece. I only drilled 100mm down so I could tap it, I drilled it using the lathe to get the perfect centre. I also cut out four 40mm pieces out of a 3mm silver steel rod for the base mechanism.
Milling- I looked at step 5 to make the joints perfectly straight and smooth I used a milling machine. I put my pieces that I needed to cut in a machine vice with small parallel plates in (so the bar did not move); I turned on the machine with my piece directly perpendicular to the drill piece. I turned the X-axis handle wheel to mill off the top, then I brought the table back to it first place, then I used the Z-axis handle wheel to make the bench go up and turned the X-axis handle again. I did this until I thought I milled up to the right part. I used a micrometre to see the thickness to make sure it was exactly half way (6.5mm). The milling machine was good because the Z handle wheel was labelled every 0.1mm so I could mill up to accurate points.
Finishing the shaft- To make the edges of the shaft round I first marked out the round edge but using another piece and then I used a file to round it.
Finishing the base- I used steps 7 and 8 for this section. I marked out 20mm lines on the edges directly in the centre of each side with an engineers square, engineers rule and a scribe. I put it in the vice (with soft jaws so it would not deform) and cut to the right point with a 3 blade hack saw. Then I marked out the middle of the base with a combination square (it did 45 degrees lines) and marked it with a centre punch. I secured the piece with a G-clamp on the pillar drill table and I used a 4mm drill bit to get a hole through; I then counter-sunk it. I then marked out 5mm from each side of my plus and drilled 3mm holes through each of the sides.
Final assembly- My production plan indicated me to look at step 9 for this part. I put everything together using a flat head screwdriver to put the screws in and I used normal nuts to keep everything together and I used wingnuts for the arm mechanism.
Tapping and threading- I used an M4 tap with a tap wrench to tap the screw holes in two of the bars. What I did was turn the tapping bit in the piece directly downwards (while it was in a vice with soft jaws so it wouldn’t deform). I made sure I went directly down and I did not wobble the bit by keeping my thumbs in the middle and turning the wrench. I turned 360 clockwise then 180 back anti-clockwise so the trace was perfect. I the used a file to smooth the edges of the 3mm rods and did the same with a thread (a thread die and thread wrench) by turning the wrench and making a thread so a nut would be able to go on the end.
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