rpm limitations

[darryl]

I sometimes wonder about the rpm limitations when running a spindle with a large bore, which of course means larger bearings, and then chucks of any kind. The larger the slower, but what's an example of a chuck, for instance, that has a large diameter AND a high rpm rating?

How fast can you turn a spindle with a large bore- if you don't consider using a large diameter chuck at the same time? Can it be as simple as a bearing limitation, or is it the ability of the chuck jaws to stay in place under tension and at high speed- and the ability of the chuck body to stay in one piece at speed?

I know you pay a price to operate a large bearing at high rpm- the heat produced. You pay for this energy to begin with when you run at high rpm, and you are forced to take measures to keep a constant temperature for proper operation of the spindle- which means a design for a high cooling ability would be needed.

Do they even make a machine that is optimized for large bore/high rpm? Or would that just be stupid?

[redlee]

It depends I guess, what is the max RPM of the machine ?
Whats the rating of the chuck ?
4 Jaws typically do not have a RPM rating.

Large bore machines have a max RPM I dont really understand the question.
I guess if you are building your own then a lot of considerations come into play.

[lakeside53]

My Howa is D1-6. It's "rated" for 2000 rpm. I have chucks ranging for 6 to 16 inch, rated for 3000 , 2500, 2000 and 1000. The 16 inch 4 jaw is 1000, but that assumes it is "balanced workpiece". In other words, for the 16 inch it's up to the end user to figure out how bad it is for the machine.

[darryl]

If a 16 inch chuck can turn 1000 rpm, that's faster than needed for almost anything you would mount in it to machine. In all practicality, you wouldn't use a chuck of that size if you're turning 1 inch bar for example- but if the chuck is on the machine and you want to turn a smaller diameter on something, you can use up to 1000 rpm without having to change out to a smaller chuck. I guess that's part of my question- looking for a good holding ability out to say about 2 and something inches (2-3/8 spindle bore) and yet allow several thousand rpm for turning small diameters. Perhaps the design of the chuck is the limiting factor- or perhaps the 2-3/8 spindle bore isn't reasonable for the home (hobby) shop. I'm just wondering how far you can push the envelope.

[lakeside53]

There's a lot of other stuff in a gearhead head lathe that rotates other than the chuck. Mine's pressure oil fed, has massive bearings and I'd feel ok at up to 2500 rpm with a smaller chuck. It's a tad shy of 2-3/8 as I can't get a schedule 40 water pipe though it, but with 60 inches between centers, there other solutions.

You could design a simple well balanced large pass though lathe for say a D1-8 spindle, but is there a market to buy it in sufficient quantities to justify the expense? Surely not for the home shop crowd.

1000rpm for 16 inch 4 jaw - perfect for wood burl turning But seriously.... the problem is that you need a high enough speed with large part to machine the part nearer the center. It really sucks having a beautiful finish for 1/3 at the outside then increasingly crappier as you go into the center. Cranking up the speed isn't an option with large parts (example - pipe flange covers at 12 to 14 inch). I have some pictures... dark black chips at the outside, bright razor blade streams near the middle.

[lakeside53]

Anyhow... 2-3/8 isn't big enough. Ae soon as you have that, someone will bring you a 3 inch problem that would have been so easy if it could have been passed though. Had to mount two bearings into each end of a auger (spiral welded on after) pipe for a harvester. Pipe wasn't round enough for the steady so had to machine two running collars for that too. That's a 10 inch chuck. Oh, farmer need a 4 foot pipe finished, so he bought me 48 inches PLUS 1/8th. Damn farmers.

[lakeside53]

The other end of the problem - 16 inch drill press table that a buddy just had welded up (restoration of really old DP). Putting the lines every inch looks cool, but it also allows you to change the speeds. Grabbed by the spindle so 10 inch chuck. With the 16 inch I could have grabbed the outside after cleaning it it up, but too much work. low res pic. sorry

[LKeithR]

...With the 16 inch I could have grabbed the outside after cleaning it it up...

Would the jaws have cleared the bed? That looks pretty close in the picture...

[lakeside53]

yes "just", camera angle make it look close. I think I can do 17.5 to bed interference.

[Rich Carlstedt]

There are several limitations:

First is the Chucks material !
"Cast Iron" Chucks are considered Lower RPM chucks
"Semi-Steel" Chucks are considered medium range RPM
"Steel" Chucks are High Speed chucks
Always check with the chuck manufacturer for max speed !

Second is Lubrication !
Higher speeds are not desirable for greased main bearings
You want oil flow for constant lubrication AND Cooling and for even thermo expansion

Third is the Life rating of the main bearing depends on the RPMs and number of turns ( 100 Million Revs ie)

Remember that as speed increases , the jaws have less force to hold the part and that means lighter cuts and higher danger !
Rich

[lakeside53]

Btw, I often run a 5C collet system on this 5000lb lathe - machining 3/16 inch parts. Urgh... need a Feeler and 5000 rpm. one day...

[JoeLee]

There are several limitations:

First is the Chucks material !
"Cast Iron" Chucks are considered Lower RPM chucks
"Semi-Steel" Chucks are considered medium range RPM
"Steel" Chucks are High Speed chucks
Always check with the chuck manufacturer for max speed !

Second is Lubrication !
Higher speeds are not desirable for greased main bearings
You want oil flow for constant lubrication AND Cooling and for even thermo expansion

Third is the Life rating of the main bearing depends on the RPMs and number of turns ( 100 Million Revs ie)

Remember that as speed increases , the jaws have less force to hold the part and that means lighter cuts and higher danger !
Rich

I find that hard to believe. If the jaws are cranked down tight on a part I can't see how centrifugal force could sling them away or move them from the part their holding.
The jaws would actually have to move away from the part.

Who needs to run their lathe at 2000 r's??

JL.............

[J Tiers]

There are several limitations:

First is the Chucks material !
"Cast Iron" Chucks are considered Lower RPM chucks
"Semi-Steel" Chucks are considered medium range RPM
"Steel" Chucks are High Speed chucks
Always check with the chuck manufacturer for max speed !

Second is Lubrication !
Higher speeds are not desirable for greased main bearings
You want oil flow for constant lubrication AND Cooling and for even thermo expansion

Third is the Life rating of the main bearing depends on the RPMs and number of turns ( 100 Million Revs ie)

Remember that as speed increases , the jaws have less force to hold the part and that means lighter cuts and higher danger !
Rich

And, then the larger bearings get to some really high "rpm" on the rolling elements at high overall bearing rpm.

If you have a copy of the New Departure bearing manual set, they have some limits given in that, and they have (IIRC) areas of the chart for grease vs oil lube. RPM does not come into it alone, but in combination with the OD/ID, to give a sort of "figure of merit" for the bearing, which you use to enter the chart.

[Doozer]

I find that hard to believe. If the jaws are cranked down tight on a part I can't see how centrifugal force could sling them away or move them from the part their holding.
The jaws would actually have to move away from the part.

Who needs to run their lathe at 2000 r's??

JL.............

Dude, that is how physics works.
Whether you believe it or not.

-Doozer

[Rich Carlstedt]

I find that hard to believe. If the jaws are cranked down tight on a part I can't see how centrifugal force could sling them away or move them from the part their holding.
The jaws would actually have to move away from the part.nWho needs to run their lathe at 2000 r's??JL.............

This was about 28 years ago
We had a Large Dainichi CNC Lathe I think it was a 26 x 144 in Size.
We had a 200 pound part in the Lathe and it required that the 1/8 drill would need 4-5000 RPM or such and that was in the program
We had a Hydraulic Chuck with a 5,000 PSI oil pump supply
When the drill cycle came up , the Lathe increased its speed substantially and then exploded when the part came out of the chuck and destroyed a large
part of the Lathe . The Dainichi repair man advised us that there was a speed limit on Hydraulic Chucks because the jaws want to move out as speed increases
The operator was behind the tailstock at that moment..probably saved his life..
The Pump was checked and was perfect . the chuck was destroyed
Programed speed settings were revised to say the least

Rich