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Max rpm for dead centers

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  • jugs
    replied
    Originally posted by Forrest Addy
    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.

    2 Great nations divided by a common language

    john

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  • Forrest Addy
    replied
    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.

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  • jugs
    replied
    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

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  • Westline
    replied
    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
    Last edited by Westline; 03-11-2011, 02:07 PM.

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  • Peter N
    replied
    Originally posted by Carld
    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

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  • Forrest Addy
    replied
    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.
    Last edited by Forrest Addy; 03-11-2011, 03:33 PM.

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  • macona
    replied
    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.

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  • Carld
    replied
    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.

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  • japcas
    replied
    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.

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  • Westline
    started a topic Max rpm for dead centers

    Max rpm for dead centers

    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?
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