What's the fastest my spindle can go?

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Bill Shields
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Re: What's the fastest my spindle can go?

Post by Bill Shields »

It is an issue with hydraulic drawbar closed chucks...most of which have a listed maximum RPM.

Less of a concern with scroll plate chucks.
Too many things going on to bother listing them.
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Harold_V
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Re: What's the fastest my spindle can go?

Post by Harold_V »

bulgie wrote: Wed Feb 09, 2022 6:42 am Does anyone here think I'm seriously in danger with a "made in Poland" cast iron 3-jaw at 1500? It's been used for 40 years at 1100 so I'd be surprised if I've really crossed some threshold.
Impossible to answer without knowing the chuck diameter. You'd certainly be in dangerous territory if your chuck measured 36". :wink:
I've heard it said that the centrifugal force on the jaws makes them grip with less force, so a workpiece can come loose. Never experienced that myself, but I'll keep it in mind. Sounds "highly theoretical" (unlikely) at my kinda speeds, agreed?
Again, without knowing the diameter, a reasonable answer can't be forthcoming.

As far as centrifugal force causing a chuck to release, yeah, that's fact. I've experienced that very thing.

I run an 8" three jaw chuck and use soft jaws routinely. With steel jaws, I've had the experience of a part coming loose when running the chuck @ 2,000 rpm. This is far more likely to happen when a thin item is being chucked without excessive pressure. It's not nearly as likely to happen if your soft jaws are made of aluminum.

H
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bulgie
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Re: What's the fastest my spindle can go?

Post by bulgie »

Harold_V wrote: Wed Feb 09, 2022 4:02 pm
bulgie wrote: Wed Feb 09, 2022 6:42 am Does anyone here think I'm seriously in danger with a "made in Poland" cast iron 3-jaw at 1500? It's been used for 40 years at 1100 so I'd be surprised if I've really crossed some threshold.
Impossible to answer without knowing the chuck diameter. You'd certainly be in dangerous territory if your chuck measured 36". :wink:
Oh right, sorry, 3-jaw is 6", and 4-jaw is 8". I did mention it was a 10" swing lathe, so running a 36" chuck might cause some scraping noises. :wink:
Harold_V wrote: Wed Feb 09, 2022 4:02 pm
I've heard it said that the centrifugal force on the jaws makes them grip with less force, so a workpiece can come loose. Never experienced that myself, but I'll keep it in mind. Sounds "highly theoretical" (unlikely) at my kinda speeds, agreed?
Again, without knowing the diameter, a reasonable answer can't be forthcoming.

As far as centrifugal force causing a chuck to release, yeah, that's fact. I've experienced that very thing.

I run an 8" three jaw chuck and use soft jaws routinely. With steel jaws, I've had the experience of a part coming loose when running the chuck @ 2,000 rpm. This is far more likely to happen when a thin item is being chucked without excessive pressure. It's not nearly as likely to happen if your soft jaws are made of aluminum.

H
Great info, thanks Harold. I do chuck some thin items sometimes, so I'll be mindful. I hope to get into aluminum soft jaws eventually but so far I use the factory-supplied hard steel jaws.

Making soft jaws with no milling machine is going to be a pita. I got a solid-looking vintage milling attachment for my lathe, but it's immobile at the moment due to rust and/or oil (coolant?) turned to varnish, so I see some quality time with degreaser and evaporust in my future before I can even start to learn how to use it. Never had to mill on the lathe before, since my places of employment always had a milling machine or three. Ah, the tribulations of an impecuniated hobbyist retiree. (I know, things are tough all over.)

-Mark
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NP317
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Re: What's the fastest my spindle can go?

Post by NP317 »

I believe you can purchase soft jaws machined to fit the main jaws of your chuck, and you machine the required radius after bolting the jaws in place.
I do not remember where I saw those, but others here will know.
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Bill Shields
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Re: What's the fastest my spindle can go?

Post by Bill Shields »

Regarding the chucks at 1500 rpm...

The answer is no...not a problem.

As I mentioned...the problem is primarily found in chucks with hydraulic closers and almost never in that size or speed range with scrolls.

The centripetal load is easy to calculate knowing the size of the jaws and closed position diameter.

Having replacible jaws which hang out from the body of the chuck can contribute to the problem as there is some flex in the body face which can lead to the gripping face of the jaws becoming essentially a cone rather than a cylinder.
Aluminum jaws help because if their reduced mass.

It is a balancing act..
Too many things going on to bother listing them.
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