Harold Hall


Cylindrical Square, making and purpose,     Harold Hall

Before you attempt to make the item illustrated in this project it is essential that the lathe is set up to turn parallel. For this, I would suggest at least to within 0.002mm over a distance of 100mm, certainly no more than 0.005mm. More than that and the subject of this project will not be as accurate as its uses demand, this being a cylindrical square. If your lathe is outside this value then do view my pages on setting a lathe to turn parallel before proceeding. In any case, the pages may be worth reading as the information may enable you to improve the situation even beyond the values I quote above.


Cylindrical Square

With the lathe now turning parallel it is time to make the Cylindrical Square, to be precise you need to make two, the reasons becoming known later.  However, you think it is a bit of a gimmick, then it is worth noting that one 150mm high and 100mm diameter is likely to set you back a very large sum of money, it is of course hardened and ground to a very high standard of accuracy and is used in industry as a reference for inspection work. In the home workshop cruder versions can be used for a number of reasons but more about that later.


Mount in the three jaw chuck a length of steel, I would suggest a minimum of 2 times the width of the tee slots in your milling machine and 100mm projecting from the chuck, centre drilling the end ready for supporting with the tailstock centre. With this done face the end, and recess it with the tool set at an angle doing this as close to the tailstock centre as is possible. Sk. 1. I use a home made half centre in the drill chuck, as shown in Photograph. 1,  enabling facing to be achieved completely to the drilled centre.


Next drill to a depth of say 90mm, no more, using a drill large enough to accept the studs you use on your milling machine table. If your drill is not long enough then drill to the deepest possible


Now turn the outside diameter using a finely honed knife tool, ensure this has a small flat on the end, so as to obtain a fine finish,  Sk. 2 illustrates. Turning the outside diameter will have to be done without the tailstock centre engaged, so take only light cuts, 0.2mm initially, finally 0.05mm. Measure the part along its length using a micrometer and if parallel, at least better than 0.005mm over 100mm,  continue reducing the diameter until a convenient value results, say 24mm if made from 25mm bar. Whilst diameter is not vitally important an accurate value may be of help if using it where it becomes part of the measurement being taken.


Workshop Projects



Lathe Half Centre, shop made.


All pictures can be clicked on to provide a larger view