How fast is too fast?

Reddinr

Reddinr

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I am working on a VFD for my lathe, a Grizzly G0509G, 16" gear head lathe. The lathe nameplate rates the RPM at 1800. I'm trying to get an idea of how much faster I can safely run this lathe with a small chuck or collet chuck for 2" and smaller diameter, short parts. The spindle bearings are rated for at least 4000 RPM, maybe 5000 RPM (NHK HR32016 is the PN of one of them). But, there are other bearings and gears in there to worry about too. I'm thinking 20% faster would easily be safe enough. I wonder if 50% or even faster would be out of the question for short periods, maybe 30 minutes at a time and not very often. I realize there is no "right" answer to this but does anyone have experience with this or have recommendations? (Warranty is long gone so that is not an issue.)
 
If you disengaged the gears, )moved the banjo away from the spindle,) you could run the spindle at your 4 or 5000. it's the gears that would (might) fly apart at that kind of speed.
 
Great points regarding gearing and chucks. For some reason my Atlas PB23 hand-wheel collet chuck isn't specified for RPM in the documents that I can find. My 3-Jaw seems to be 3000 RPM rated. I'll need to get in touch with the manufacturer for the collet chuck I guess.
 
Remember that when you go outside what is in the manual, at that point YOU become the test pilot, regardless of whether somebody else says they got away with it. Understand that concept carefully, and maybe study how professional test pilots go about testing new parts, tools, aircraft, and anything else -- and do not want to hurt themselves while doing so. They make sure they understand the risks as well as possible and approach the often dangerous testing as carefully and intelligently as possible, trying to mitigate all potential risks. Most test pilots pass away from old age. Please consider doing the same...
 
There’s a post on Practical Machinist by Forrest Addy about someone who overspeeded a lathe with fatal consequences. You should find and read it.


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Thanks for the safety advice. I'm fairly conservative so I would likely sneak up on any speed increases slowly and methodically. I'll read the Forrest Addy art. for sure. I found the data on my collet chuck too. Surprisingly 2500 RPM only!

Chris, any suggestions on keywords to search? Mr. Addy has thousands of posts and searching on "lathe" with his name does not bring up his post about a lathe disaster.
 
Last edited:
It was a reply to a post under “speeding up a lathe” or something like that. It’s been years since I read it.


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I did find "lathe horror stories" thread there. One was a large CNC lathe with a big chuck and large part accidentally set to 5000 RPM instead of 50 RPM. Chaos occurred. Lots of other cautionary tales in the thread too.
 
Just as an example my Nardini 16" has a decal stating: 4 jaw 400rpm max. That must be with their OEM 4 jaw that is lightly built. My 4 jaw is a Horton steel body chuck. I think I can disregard the decal on the machine.
 
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