- Joined
- Nov 19, 2011
- Messages
- 966
was wondering what are the pros and con of a live center vs a dead center thanks much mac:thinking:
Revolving Dead Centre - a Live centre's driven under power by the machine (compare to "Live Tooling" on a CNC machine - traversed cutters driven by either the main spindle motor or auxillary motors in their own spindles on the carriage, similar to milling spindles on manual lathes).
This may be the right term, but that doesn't mean that people will use it...
Dave H.
A live centre is used in the headstock and is the driving centre. They are usually an unhardened centre so they can be turned in-situ for the highest level of precision and used in conjunction with driving dogs.
A Dead Centre is used in the tailstock and used to create heat, friction and gall the end of a shaft, even when copious amounts of lube are used.
The old favourite was White Lead. Dead Centres are available in a variety of types, Hardened, soft, half. Hardened dead centres are generally used in the tailstock to help overcome the friction and they have to be operated at slow speeds due to the immense amount of friction involved. Half centres allow you to face right up to the centre drilled hole so you can face the entire end of the stock. If your lathe is only being used at really low RPM, then the Dead Centre may be helpful, personally, mine only get used if I am checking a shaft between centres for straightness etc. Never or rarely used if the lathe is "ON". Dead centres are the prefered centre for cylindrical grinding operations where the work is being rotated at slow RPMs
A (Ball Bearing) or Bearing Dead Centre is used in the tailstock to support a shaft. This centre has been mistakenly called a Live Centre and the term has stuck. These centres are also available in a variety of configuration; economy, precision, short, long, cup, bull nose, spring-loaded, spider, chucking etc. These centres can be run at much higher RPM's than a non bearing type centre. They can have one or more bearing, with better ones having at least three.
I tried an economy centre when I frist started using a lathe and it was returned to the store I bought it from the next day, the bearing felt like it had gravel in it. I replaced it with a good quality Skoda Bearing Centre and never looked back. A couple years ago, when I upgraded to a larger lathe, 14x40 I found that the Skoda Centre was just a bit too short to reach across the saddle, so I ended up getting a Riten Long Nose Bearing Centre. This centre has a long slender nose and gives that extra room for bridging the saddle and also for getting the tool bit in closer to the centre. It is the number one gotot centre used in my shop.
Cup Centres are handy when you have a shaft that has no centre hole. There are sets available, Skoda and others that consist of a MT shank with Bearing and replacable types. These can be very handy.
Spring-Loaded Bearing Centres are used when high heats are present as the allow for expansion of the shaft being turned. They do not tend to be very common.
Bull nose and Spider Centres are used for larger diameter pipe and tubing.
One of my favourite centres is the 3-Jaw Chuck, Bearing Centre. Mine is a Bison Brand, and is used to support shafts that do not, or can not be centre drilled. They are fairly large, 3" diameter and larger, so they can be a bit cumbersome to work around, but their usefullness make them a fantastic accessory for any lathe. These centres have replaced the old Jacobs armature chucks for non centre drilled armatures.
Walter