Thursday, 18 March 2010

Hollow Cylinder Instructable

This is a brief instructable on making a two part hollow cylinder from a waste pipe. I tested this method out for the handle part of my project and was recommended that this technique would produce the same results as turning and milling a piece of material would but in less time. I needed the tube to be hollow so that I can fit electronics inside and so it can be fixed to other parts. I also wanted it to be made in a way that will allow me to take it apart easily if any electronics start to malfunction inside.

So the first step is to acquire a piece of tubing that is similar to your required diameter. I used a 36mm diameter waste tube which was the only part available which was close to the 40mm diameter that I required.

^^ Next is to drill two small holes through one side of the tube which will be fixed to a scrap piece of metal through the use of screws. Make sure the holes are in line with each other.

^^ Then find a FLAT piece of scrap wood which is the same length or longer than your tube. Drill two holes in this which are in the same place as the holes in the tube.

^^ Screw two screws through the holes which you have created making sure that they go no more than half way through the tube. This will cause a problem when cutting the piece in half as it will come in the way of the blade.

^^ You should now have a tube attached to the flat piece of wood. This will make it easier to keep the part steady to pass through the band saw for cutting the tube in half.

^^ Next stage after this is to mark out precisely where the middle of the tube is. Make sure this is marked out clearly along both lengths of the tube and is clearly visible. Then mark the guage on the bandsaw which will allow the wood and tube to pass through the blade slightly to the left of the half way line that you have marked out. This makes sure that the other half of the tube is precisely cut down the middle. The screwed part isn't required, other than for scraps and test pieces. Also cut the tube to the correct length ensuring that you make two of these. It is recommeded to make these a couple of mm larger than the required dimensions.

^^ There will be a lot of residue material on the edges of the tube. Take a sharp scalpel and run this across the edges to remove this.

^^ The edge will be easier to work with when the residue is removed and can be sanded further if neccesery but you don't want to remove too much as this will leave an oval shape when the two halfs are fixed together.

^^ Tape both halfs together so that they can be sanded at the smae time which will allow you to make them the both length without too much effort.

^^ Sand both of ends of the tubes on the circular sander, again remembering not to take too much off as you may go further than your required length.

^^ Using the scrap material from the unwanted half of the tube, cut two strips slightly smaller than the required length of the tube. Sand any rough edges. These parts will act as the lip on one half of the tube to make it easier to join the two halfs together when finished.

^^ Using solvent cement, smear a light layer of this over the strip of tubing and then stick this to the inside of one half of the tube leaving an overhang of about a centimetre. Hold this firmly for 20-30 seconds to ensure that it's going to stick and then place the part into a vice to ensure the two parts want to stay together. Don't tighten the vice too much as this will start to bend the tube and begin to alter the shape and properties of it.

^^ While this is drying, you can begin to prepare the styrene. Due to my part needing a groove on one half of the tubing, the styrene will be fixed over the other half of the tube to make it larger which makes the other half smaller when they are fixed together. The styrene which I used was 1mm thick which brought the overall thickness of the cylinder to 37mm.

If you don't need this groove then this can be skiped, otherwise source the correct size of styrene for your part. Measure out the size of styrene that you will require leaving a hangover of a couple mm. Taking a scribing blade, scribe down the marked area on the styrene with a metal ruler. When this had been done, the styrene can be easilt bend over and will snap across this line.

^^ Using the leftover tubing as a mould, heat the styrene piece gently and it will slowly begin to become flexible.
^^ When the styrene begins to soften place it on top of one half of the scrap tubing.

^^ Then place another half of the scrap tubing on top of the styrene.

^^ Press down firmly as the styrene begins to cool and harden again. This process will allow the styrene to fit nicely around the tubing without having to be forced to stick. Repeat this process until you the shape of the styrene as a semi circle without being held in place.

^^ Using the solvent cement, stick this to the outside on the half of the tubing that you require. This time don't attempt to place the part in the vice, it makes the styrene begin to peel of on one side. Instead press firmly on this as best as possible across the surface of the styrene. You may need to hold tightly for 2-3 minutes just to make sure the two parts are firmly secured.

^^ With the overhang material, take a sharp scalperl or craft knife and trim close to the edge of the tube. Then, working through various grades of sandpaper, sand the edge down as close to the tube as possible so that the edge is uniform.

^^ Repeat this step for the top edges.

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