Tail centre - how tight?

[Stigmorgan]

So as some may know I've managed to break two revolving centres in a few months, the first time I contacted the manufacturer and they sent out a free replacement, then last week I managed to break that one, it seems there is a weak point at the break site as both broke at the exact same point, I cant help but wonder though if I was also a contributing factor and as the amazing @Phill05 has very kindly made new morse tapers I want to ensure I don't break them, the main thing I can think of that I do is tighten the tail stock up as tight as I possibly can, is this overkill? Also the majority of my turnings are out of balance for a lot of the turning duration, should I wait until I've completely rounded/balance the wood before moving to mid speed or is OK to jump up as soon as the lathe stops shaking/bouncing?

 

[Terry - Somerset]

By doing the tail stock up tight you are transferring all of the out of balance vibration and stress into the centre - no great surprise it may fail after a short period.

For out of balance blanks I normally bring the tailstock up to fairly lightly contact the blank - as much as a safety measure as to centre it. If a few kilos of wood comes adrift from the chuck at several hundred RPM it will make a serious dent in what ever it hits.

I tend to run at low speeds until the blank starts come into balance - this minimises the stresses on the centre. If the lathe is bouncing, it is going too fast - particularly if the blank is close to the limit of lathe capacity.

 

[Orraloon]

As terry says lowest speed until the things come into balance. Tailstock pressure needs to be firm but you dont need to sweat it up. As well as wrecking the live centre it will not be kind to the headstock bearings either. Vibration is a guide as to if you are on too high a speed and sometimes more stock prep is the only answer if the whole thing wants to walk across the floor.
With out of whack bowl blanks I some times mount them with the lathe switched off just to check the balance. The heavy part will rotate to the bottom. Mark that then take a bit off with an electric plane. Repeat the process until you get closer to balance before spinning up the lathe.
Just as an observation I have never had the wood fly off because the tailstock was not tight enough. Its always a failure of the wood itself like the tennon breaking off.
Regards
John

 

[clogs]

thank u Orraloon.....
I can never understand for normal'ish turning why everyone has so out of balanced wood....
and then CRANKS UP the speed....madness....
it's so easy to take the big lumps off....elec chain saws etc......
wiered lumps of wood for turning need a big, heavy old fashioned lathe....
not this modern stuff.....

 

[Paul Hannaby]

I have tightened many live centres up extremely tight at times and over 20+ years and have turned many out of balance pieces of wood and have never had one snap. To have two go in succession would point to either a design flaw such as a stress point on the centre, causing it to break or incorrect heat treatment making it brittle. Either way, I doubt it is what you are doing to it.

 

[Stigmorgan]

@Paul Hannaby here's a pic Phill sent me showing a relief cut at the break point, poor design but can't help but think maybe I've done something wrong too.