Search the Community
Showing results for tags 'workshop machines'.
On my workbench thread @Galteemore asked about turning buffer housings and smokebox doors- I had thought about a thread on here about using machines for model building and about the machines themselves for anyone looking for info. So here we go;- First up Galteemore's request, there will be more about machines later as we go. Smokebox Door;- There is a few ways to do this, the two main ones are to spin a sheet of metal to form the door that way, or to turn it from a solid bar. Spinning a sheet of metal requires a former to be made out of hardwood first, which has the inside profile of the door, the former is mounted in the lathe chuck with the sheet of metal pressed up against it with the tailstock, its then 'spun' and a burnished tool is applied to the metal to push it into shape! This discussion will deal with the solid bar option. This option is simpler than spinning but is a more advanced lathe operation than most because of the curves to the door- 2 curves are generally required, a small radius curve at the outside edge with a larger curve across the door, some doors have compound curves. This is done by hand turning which requires additional tools. The round bar stock is mounted in the chuck with the minimum amount protruding for the part and a bit of safety from the chuck jaws, if the bar is the same size as the door a four jaw chuck is used and the bar has to be clocked to centre, if the bar diameter is larger than the door a three jaw chuck can be used as the bar will be turned down to size, then the part will be concentric. A four jaw chuck will hold the bar stock far better than the three jaw, very handy because we don't want the tailstock to be used as it will get in the way. Take light cuts and all should be OK. 1. Rough cut. The rough shape is cut to approx size, the cut to the rear of the door should allow for a flange to fit into the smokebox face plate, a parting tool is used to do this cut, just to the depth of the flange initially, allowing for the flange and the final parting cut. 2. Step Cuts to Curves. The front face is step cut to just over size of the final curves on the door to prepare for hand finishing. A flange is also cut on centre to a width n depth for the door handle detail. The centre hole is drilled to size- always use a centre drill to start a hole. 3. Hand Tool Curves. Hand turning is done with a Garver Tool held over a bar tool rest, the rest should be adjustable so that one can angle the tool to form the desired curve. Hand turning takes a bit of practice but once mastered any shape can be created, as long as its round! The other option is to use files to do the curves, ensure there is a handle on all files one uses on the lathe. The door handle flange could be ignored and a washer could be soldered or stuck on when the part is finished. 4. Parting Off. Use grades of emery paper or Scotchbright pads to finish the surface taking care not to loose the edges on the detail and then part off with a parting tool, ensure all slides and the saddle are locked when parting off, and if its a deep cut don't forget to allow for this in the initial setting up. Also don't forget to leave the flange on the back of the door! This is where the tailstock should be used but the centre hole is quite small, an adapter can be used to fit in the hole of the door and apply pressure on the handle flange with a revolving centre in the tailstock. Using a Garver Tool. Some chaps use a bar mounted in the toolpost as a rest, I have done this it works but I reckon the proper stand is better. Play with some aluminium bar stock to practice forming curves Hole setting out can be done before the part is parted off, a punch mounted in the tool post set on centre height can be employed to do this, the chuck is rotated by hand and the cross slide is used to locate where the centre pops are required. A handy device is a printed paper 360deg scale to fit around the chuck and a pointer mounted to indicate the deg of rotation. Tables are available in booklet form or on line to workout rotation. A long Hilti nail close fit in a block of mild steel makes a grand punch, just need to ensure one can get it on centre height. Garver tools, my paper 360deg strip and indicator. I do have an indexing tool but the paper strip is far quicker to set up and accurate enough for this kind of work. No workshop should be without this little booklet- threads, drill sizes, tolerance fit tables, PCD radial hole charts and log tables! Next well do the buffer housings....... Eoin