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Westline
03-11-2011, 12:03 PM
Is there a max rpm for dead centers?
I guess I have a pretty crummy dead center since I got it with my lathe.
On a job I just did I was machining 10mm leaded steel and I guess I was running it to fast, now it's called a dead center for more than one reason?
Can carbide tip dead centers be run faster?

japcas
03-11-2011, 12:14 PM
Was you running any lubricant on the center? We have some grease at work that is called Center Saver. We use it on dead centers on the grinder and it works great. Some high quality grease should work also though. Here is a link.

http://www.reidsupply.com/Detail.aspx?itm=CMPD-C400

No affiliation with that company, just the first link I found.

Carld
03-11-2011, 12:23 PM
You don't run dead centers fast, without lube and tight. About 300 rpm max. the best lube now is a graphite dead center grease. They used to use white lead but you may not find that now.

As to tension on the work, run the dead center into the center hole in the shaft and back it off until it is just touching the work. As the work expands from machining you will have to stop the lathe and adjust the tension again.

For best results just buy a live center.

BTW, when turning between centers the center in the head stock is the dead center and the center in the tailstock end is the live center even though it will not turn and is stationary in the tailstock. Everybody calls is a dead center now I suppose as to not to confuse what is now a live center, which is a ball bearing center in the tailstock.

macona
03-11-2011, 12:24 PM
You have to watch dead centers. As the work heats it will grow in length and the pressure increases on the center. Then you learn about friction welding. You can use some high pressure grease to lube the tip, white lead works better.

Carbide can be ran faster.

But the best thing is ditch the dead center and buy a good live. Technically they are not as accurate as dead centers but the are still good down to something like 50 millionths on a good one. I have a Skoda that was about $60 new that is real nice.

Forrest Addy
03-11-2011, 01:01 PM
You used to be able to get HSS center that survive better than carbon steel.

I also have a carbide half center when I have work that really fussy.

I used to use white lead for a center lube (I still have two 1 quart cans of white lead carbonate paste in oil) but now I use MolyCoat grease. There's better proprietary center lubes but I have little experience with them.

The key for keeping a dead center healthy is constantly monitoring the tension on the tailstock. You soon learn just how much to back the handwheel off to relieve the expansion and restore the minimum tension needed for positive centering.

Practise this. Put a foot long piece of center drilled round stock between centers - no driving dog. Warm the round stock up with a propane torch so it expands into the centers. Follow the expansion by backing off the tailstock bit by bit while rotating the stock by hand feeling for resistance. (This takes about 4 hands but the dedicated can do it.) Note how little heat is required to stiffen the resistance - just a few degrees. You may not need the torch. The heat of your hand may be enough.

Keep very light resistance when the work is rotated by hand up and down the temperature range. If you relieve the tension so the work spins freely reward yourself with a trip to the ass kicking machine.

Peter N
03-11-2011, 01:29 PM
BTW, when turning between centers the center in the head stock is the dead center and the center in the tailstock end is the live center even though it will not turn and is stationary in the tailstock. Everybody calls is a dead center now I suppose as to not to confuse what is now a live center, which is a ball bearing center in the tailstock.

Just to add a bit of fuel to the debate, the centre that goes in the headstock is the *Live* centre - as it turns with the work - and the centre that goes in the tailstock is the *dead* centre, as it's stationary.

There are also *Revolving* centres (ball bearing centres) which run in the tailstock and turn with the work.

The nomenclature has become a bit confused over the years to the extent that most people now equate a live centre with a revolving centre.

Peter

Westline
03-11-2011, 02:05 PM
Thanks guys.... Not a big fan of the dead center but at least now I know how to use it correctly. Will have to put a live center on my next shopping list.... Sorry revolving center.;) oh yes and a ass kicking machine just for good measure:D

jugs
03-11-2011, 02:07 PM
Some of the bigger revolving centers have spring loaded thrust bearings to take account of thermal expansion (smallest one I've got is MT3) but they are expensive.

john
:)

Forrest Addy
03-11-2011, 03:28 PM
You lot over the pond sure talk funny. Any centRE that revolves is a revolving centER. Over here where we're over sexed and over paid call the item you're mis-naming a "live" center. - the only possible word for it.

I do like "clocking in". It's in my daily vocabulary when I think to use it. "Dialing in" seems so boring now.

jugs
03-11-2011, 05:38 PM
You lot over the pond sure talk funny. Any centRE that revolves is a revolving centER. Over here where we're over sexed and over paid call the item you're mis-naming a "live" center. - the only possible word for it.

I do like "clocking in". It's in my daily vocabulary when I think to use it. "Dialing in" seems so boring now.


That's rich, how can an inanimate object be a "live" center.:p

2 Great nations divided by a common language :D

john
:)

tdmidget
03-11-2011, 06:47 PM
BTW, when turning between centers the center in the head stock is the dead center and the center in the tailstock end is the live center even though it will not turn and is stationary in the tailstock. Everybody calls is a dead center now I suppose as to not to confuse what is now a live center, which is a ball bearing center in the tailstock.

Backwards Carl. A live center rotates with the workpiece. So what would be a dead center in the tailstock is a live center in the spindle because it is now rotating with the workpiece.

The Artful Bodger
03-11-2011, 07:05 PM
Is there a max rpm for dead centers?
I guess I have a pretty crummy dead center since I got it with my lathe.
On a job I just did I was machining 10mm leaded steel and I guess I was running it to fast, now it's called a dead center for more than one reason?
Can carbide tip dead centers be run faster?

Westline, my lathe came with two centres, one hard and one soft.

If I understand correctly the soft one is for use in the head stock where it is skimmed in place to ensure an accurate centre with respect to the spindle axis. This centre will not stand much friction and it does not need to. The other centre is hard and is the one intended to be in the tail stock.

If your centre is a bit munted just mount it in the spindle and give it a little trim.

Nomenclature, the one in the spindle is the live centre and the stationary one in the tail stock is a dead centre, or so I thought, but now people call the revolving tailstock centre a live centre too. Which side of the Atlantic introduced this particular gem of confusion>:rolleyes:

John

jugs
03-11-2011, 07:19 PM
oh yes and a ass kicking machine just for good measure

Adjustable stroke + adjustable speed -

- it's also called a shaper, I'm sure you could also turn up some other useful attachments :eek: :D

john
:)

Carld
03-11-2011, 10:48 PM
:o Aw Geez, your right tdmidget, I don't know why I reversed them. I was taught long ago the headstock center is called live and the tailstock center is called dead.

lane
03-11-2011, 11:18 PM
Ifen it aint got ball bearings it is dead. If it does it`s live , simple as that.

Forrest Addy
03-11-2011, 11:27 PM
Ifen it aint got ball bearings it is dead. If it does it`s live , simple as that.

I got a tomcat with the same attitde. The equipment he bears is his badge of authority and all the other cats better take notice.

Wait, weren't we talking lathes?.

tdmidget
03-12-2011, 06:09 AM
Read my post again lane. If it turns with the work, it is live. Are you saying that a center with roller bearings would be dead?

angelo49
03-12-2011, 08:19 AM
Taken from the Hercus book.
If it turns with the work it's live, with or without bearings.
http://i130.photobucket.com/albums/p266/angelo67/centers.jpg
Angelo

fciron
03-12-2011, 08:43 AM
I think this is an evolving terminology, it depends how old your books are. ;)

'Live' used to mean under power, similar to the way 'live' is used in electricity. So the thing in the headstock is the 'live center' the thing in the tailstock the dead center. As the use of a rotating ball bearing center in the tailstock has become the norm, it has seemed weird to call the moving thing 'dead' and the solid thing 'live' so the names have gotten reversed.

If you go here http://www1.mscdirect.com/eCommerce/NavigationServlet/Lathe-Fixturing-Holding-Positioning/_/N-77dej?cm_re=Category-_-BodyLink-_-Lathe+Fixturing+Holding+%26+Positioning&Ntk=All_MSC&Ntt=lathe+center&Ntx=mode+matchallpartial&Nty=1&rawInput=lathe+center%C2%A2lathe+center You will see a major catalog listing all solid centers as 'dead centers' and all rotating centers as 'live'.

Alas, this crass modern world has not care for the correct use of words. If catalogs in the UK list these tools under their correct appellations I may consider emigration. :D

Peter N
03-12-2011, 08:52 AM
Taken from the Hercus book.
If it turns with the work it's live, with or without bearings.
Angelo

Nice try, but I can trump that :D
According to Messrs A. Greer (C. Eng, MRAes), W.H. Howell (C. Eng., MI Prod E, MIQA, MISM) and F.R. Willmore (DLC Hons, M.Coll. H) who were senior lectures in Mechanical Engineering and Metalworking at some of the UKs formeost colleges, and who wrote the bibles for Mechanical Enginnering and Toolmaking Apprentices, then the following nomenclature applies:

http://www.btinternet.com/~p.neill/Compressor/LiveCentre.jpg


http://www.btinternet.com/~p.neill/Compressor/RevolvingCentre.jpg

It's just that you lot over the water seem to have trouble with proper English, just like the way way you can't spell Aluminium correctly :D

Peter

Peter N
03-12-2011, 08:58 AM
I think this is an evolving terminology, it depends how old your books are. ;)

'Live' used to mean under power, similar to the way 'live' is used in electricity. So the thing in the headstock is the 'live center' the thing in the tailstock the dead center. As the use of a rotating ball bearing center in the tailstock has become the norm, it has seemed weird to call the moving thing 'dead' and the solid thing 'live' so the names have gotten reversed.

If you go here http://www1.mscdirect.com/eCommerce/NavigationServlet/Lathe-Fixturing-Holding-Positioning/_/N-77dej?cm_re=Category-_-BodyLink-_-Lathe+Fixturing+Holding+%26+Positioning&Ntk=All_MSC&Ntt=lathe+center&Ntx=mode+matchallpartial&Nty=1&rawInput=lathe+center%C2%A2lathe+center You will see a major catalog listing all solid centers as 'dead centers' and all rotating centers as 'live'.

Alas, this crass modern world has not care for the correct use of words. If catalogs in the UK list these tools under their correct appellations I may consider emigration. :D

I think you're dead right if I'm truthful, but then if we admitted that all the time we wouldn't have as much fun with baiting each other as we do.

Peter

fciron
03-12-2011, 01:34 PM
I think you're dead right if I'm truthful, but then if we admitted that all the time we wouldn't have as much fun with baiting each other as we do.

Peter

:( OH, NO!

I don't want to ruin our fun. I bet if I look hard enough I can find the word 'dead' attached to one of those rotating thing-um-ma-bobs. ;-)

Carld
03-12-2011, 08:40 PM
This is a live discussion about the dead.:D :rolleyes:

Don Young
03-12-2011, 09:33 PM
It seems that the headstock center is always live, at least when the spindle is rotating. The tailstock center can be either live or dead. So if you have a dead one in the tailstock and you want to bring it back to life all you have to do is put it in the headstock. The ones with bearings are apparently immortal!!

Or something like that.

fciron
03-13-2011, 09:54 AM
It seems that the headstock center is always live, at least when the spindle is rotating. The tailstock center can be either live or dead. So if you have a dead one in the tailstock and you want to bring it back to life all you have to do is put it in the headstock. The ones with bearings are apparently immortal!!

Or something like that.

I've seen some that are better described as "undead". :eek: ;)