CNC machined parts-Centring the Bar

Source:shengfe Date:2018-07-28 00:13

CNC machined parts-Centring the Bar
First, we have to put the centres into each end of the bar. If the bar is short, say up to about 6in long, hold the work in the three-jaw chuck and use a centre drill in the tailstock drill chuck to put a centre into the bar. A centre drill is a short drill with a
small pilot on the end that has a 60-degree taper to the body diameter. A better method of centring the bar, especially long bars, is by using a three-jaw chuck and the fixed steady. The bar is held in the three-jaw chuck with the other end supported in the fixed steady and the centre is formed in the end with a centre drill. A useful tool that can be used to find the centre of the shaft is the centre square, which is a metal blade with a Vee on it that locates on the diameter of the bar. Mark a line across the end of the bar with a scriber, turn the centre square 90 degrees and then scribe another line. Where the two lines cross is the centre of the bar. To make it easier to see the scribed lines, blacken the end of the bar with a permanent felt tip marker before scribing. Centre punch the point where the two lines cross and put a 60-degree centre in each end of the bar using a centre drill in a power drill. Hold the bar in a bench vice while doing this. Put a centre drill into the tail- stock drill chuck and insert the bar in the three-jaw chuck. Make sure the lathe is on a low speed, about 300rpm, wind the tailstock in and just lightly clean up the centre hole with the centre drill to true it up.
Another useful tool to find the centre of a bar is a bell centre punch. This com- prises a cone with a centre punch in the middle. In use, place the bell end on the end of the bar and tap the centre punch with a hammer to mark the centre. The end of the bar, though, needs to be reasonably square if using the bell punch method. There are other similar methods of centring bars but those given here will be all the turner needs to learn.

CNC machined parts