CNC Machining the Bar

Source:shengfe Date:2018-07-29 21:24

CNC Machining the Bar
Now we need to mount the bar between centres. This is simply a matter of putting the bar between centres and tightening the tailstock so it is lightly pressing into the centre in the end of the work. To drive the work, a carrier is fixed to the shaft and
engages a pin in a catch plate mounted on the lathe mandrel. A catchplate is sim- ply a blank disc with a pin sticking out to drive the carrier that is fitted to the work. The carrier is fitted to the work using an Allen screw or bolt. To stop any movement
of the bar in relation to the catch plate, the carrier can be wired to the catchplate pin. This will stop the carrier and the work flapping about. It is particularly impor- tant to stop the work from moving in relation to the catchplate when screwcutting
between centres.
Facing off a bar using the half centre.
Now that the bar is safely mounted between centres, we can start turning it to size. Normally the first thing to do is to face the ends of the bar to the finished length. Decide which end of the bar has the shallower centre. We will machine this
end first. You will need a half centre, so-called because almost half of the centre is missing. This means the lathe tool can reach right across the end of the work with- out touching the half centre. When using any fixed centre in the tailstock, put a bit of oil or grease into the centre before use and top up as necessary. Lightly wind the tailstock barrel against the centre and lock the barrel so it can’t move. Switch the lathe on and wind the tool across to clean up the end. Reverse the work and clean the other end up at the
same setting. Both centres should now be the same depth. Measure the overall length of the bar. Take the finished length required from the overall measurement you have just measured. Divide this by two and this is how much we need to take
off each end of the shaft so it finishes at the required length.
CNC Machining