A MODEL ENGINEERING APPRENTICESHIP

Part five by David Carpenter

Let’s make something – something you will use practically every visit to the workshop. Buy some 1.5mm thick aluminium sheet (or 1/16in. or 16 gauge) from which you can cut two pieces that are about 50mm wider than your vice jaws and about 50mm deep. You can easily cut this with the snips in your tool kit.

Place one piece centrally in the vice so that the lowest part of the aluminium completely covers the serrated inside face of the vice jaw and the top of the vice is in the middle of the piece of aluminium. Grip the aluminium in the vice (does not have to be too tight, just enough to hold it securely in place) and tap the protruding piece of aluminium back over the vice jaw using a wooden mallet if you have one, or use a hammer to tap a bock of wood to make the bend.

Now cut the aluminium to make a slit, which runs to the corner of the vice from the outside edge. You can now tap the vertical end protruding from the vice round to the side of the vice jaw. You can also tap down the top to form a corner (you might need to trim the top of the side piece to allow that). Repeat for the other end. Repeat for the second piece of aluminium on the other jaw. Be sure not to bash the side pieces too hard to that as it is difficult to remove these later.

These ‘soft jaws’ will prevent the vice damaging metal you work on in future. As a model engineer you will probably never use the vice without them.

With that first exercise done, you are going to carry out a simple fitter’s exercise to make a dice paperweight. You might like to make this a paper exercise making a drawing of it before cutting any metal. Many new model engineers are drawn to the hobby and the business of cutting pieces of metal and can’t wait to make swarf. However, the design side of the hobby is perhaps the more challenging aspect. This exercise will include both design and production.

First obtain a piece of 25mm square mild steel (or 1in square) .

You will probably have to buy a piece around 300mm long from which you will need to cut a piece 25mm long. But first you will need given the basic instructions for the processes involved.

First - how to use the hacksaw to get the pieces to the size you want. Choose and insert a suitable blade in the saw and tension it enough to keep it stable. Mark with a scriber, rule and square, where you wish to cut. Hold your piece of metal in the vice (using your soft jaws) so that the piece you want can be cut off.

Start the cut by positioning the lower half of your left thumb thumb (if you are right-handed) next to the cutting line, to keep the saw blade in place for the first few strokes of the saw. Once the saw has cut a groove, hold the free end of the hacksaw with your left hand and cut right through the piece of metal. Cutting only takes place on the forward stroke, which must be straight and with moderate downward pressure and with the front of the saw held at a slight downward angle. Don’t rush. You want to ‘feel’ the blade cutting not listen to it screech.

Next, file the ends of the two pieces so that they are flat and square with the sides. The technique for filing is to hold the file handle in you natural hand and hold the tip of the file with the other hand. Slowly push the file across the surface, applying sufficient pressure for the file to ‘bite’, and cut only on the forward stroke. Ensure that the full width of the workpiece is covered by pushing the file at an angle. The only tricky part is keeping the file horizontal. If the file ‘rocks’ the work will not be flat. Check regularly with the edge of a rule for flatness and with your engineers’ square for squareness.

Use a fairly coarse file to get close to your required surface, then finish off with a 6inch smooth file to get a good finish and to ensure it is flat and square. You can cheat a little by using the tip of the file and using it more like a scraper to produce the finished flat. You can get a super finish by draw filing the surface – gently rubbing the file along the surface holding the file at 90 deg to the piece, so that it cuts from side to side rather than from front to back. For a really fine finish complete the draw filing with chalk rubbed on the file teeth, and for a polished finish wrap smooth emery cloth around the file.

Once you have got that first piece square and flat you are on your way to being an engineer. Congratulations!

When you have both ends flat and square and 24mm apart, repeat for the other four sides making sure each side is cleaned up with a good finish. Measure with your micrometer at various points to see how close you can get to 24mm.

Now, on the sides, paint on some marking blue (or use a blue felt pen) and mark the positions of a series of holes using your scriber, rule and square. Mark it out as a dice with one to six on each face. Use you own measurements for the hole locations – might be an idea to do it on paper first (you are now an engineering designer, too) and make sure that the holes will not run into each other. With the hole positions marked, lightly centre punch the hole position. Get this just right – any error will be very visible. If your first centre punch is slightly off line tap it at an angle to get it to the right position.  Give all the locations a final vertical tap with the centre punch to provide the location for drilling.

Now you can finish the dice by drilling holes, around 6mm or 1/4in., say 5mm deep, excluding the drill point. If you have split point drills you can drill the holes direct with the full size drill. If you have conventional jobber drills, start the hole using a BS2 centre drill, and then drill full size. Use a countersink or a larger drill to lightly countersink each hole to remove sharp burrs. Give it a coat of wax polish to prevent rust.

When that is done you can check how well it is made by taking two short lengths of silver steel the same diameter as the hole diameter. Measure across them in various hole positions using the vernier caliper or micrometer to see how well you have done.

We have covered this without mentioning a machine for drilling. If you do not yet want to invest in expensive machinery you can use a domestic power drill in a drill stand. The workpiece must be held in a vice.

Alternatively you can buy an inexpensive ‘hobby’ type drilling machine like the one shown above to get going. Later you will probably go for a better spec drilling machine costing several hundred pounds, or a mill/drill.

Well, how was that?

Want to continue?

Next time we look at the lathe.

Meanwhile, if you are not in the first flush of youth and your hands cramped up, or found another problem sawing and filing, all is not lost. Today there are plenty of band saws or even mitre saws that you can use to take the effort out of cutting metal bars. And a range of band and disc sanders that can replace a lot of filing.

Be sure to follow safety instructions carefully when using all machinery.


Part one here. Part two here Part three Part four part five


 
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