Estimating RPM's

[Jim Kountz]

Well this has been bugging me for some time now so I thought I would throw it out here and see what happens. When speaking of rpm's and lathes I often hear the complaint that a certain lathe wont go slow enough to turn larger items like bowls and such. More recently there was some talk about the Grizzly lathes that only go down to 600 rpms. So exactly how much too fast is this and for what size of blank are we talking about? In other words could I do a 12 bowl but maybe not a 16"?? Assuming of course the lathe can even do that size but you know what I mean I hope. Whats some given rpms for some given sized projects??


Thanks!

Jim

[Brian Weick]

These are guidelines for you but you can increase/decrease the speeds as you see comfortable.
Here are the guidelines for Turning between the center speeds ~ to ~ stock size ratios :

STOCK SIZE UP TO 24" OVER 24"
up to 2-1/2" 2000rpm 1500rpm
2-1/2" - 4" 1500rpm 1000rpm
between 4" and 6" 1000rpm 750rpm
6" - 10" 750rpm 400rpm
10" -24" 300rpm slowest speed possible- use your judgment

Faceplate turning:
STOCK SIZE UP TO 2" thick OVER 2" thick
up to 8" diameter 1000rpm 750rpm
8-12" 750rpm 750rpm
12" and over Slowest speed available-then adjust speed up accordingly: use your judgment


Happy Turning,
Brian

[Bob Hallowell]

Jim,
I did some bigger bowls 13-14" inch on my old lathe that down to 350rpms but I don't think I would try anything slightly out of balanced over 10" at 600 rpms.

Bob

[Ken Fitzgerald]

Jim....it's the "out of balance" blanks that present the problem. They can make you lathe try to take you for a walk. In my case, it turned the "diving board" into a "spring board".

[Brian Weick]

Ken,
What happened-?
Brian

[Jude Kingery]

Jim, I think you've been given excellent advice on RPM's and diameter coorelations - only thing I'd add to that is I pay close attention to sound. I usually round my blanks on the band saw and the big lathe won't have any vibration so can amp it up fairly quickly after truing up the blank. But sound - to me - is key. If something's got deficits or may fly apart, you can tell by sound. So often I don't even look at my gauge, but judge by feel and sight and sound. Best wishes! Jude

[Ken Fitzgerald]

Brian.....I did a double back flip off the spring board and hit the OFF switch at the same time....



Jude.......I only have about 30-40% normal hearing. I'm stone deaf in my right ear and have tonitus in it too! I hear a high pitched frequency in the right ear. That tone subtracts from my less than perfect hearing in my left ear. Believe it or not.....when I had that Jet VS Mini mounted on the 2x12 between the two halves of the Little Giant Ladder....I could tell when something I was turning was starting to split or crack by the increased vibration in the "diving board". My PM3520B delivers on Wednesday and guess what I'm worried about? By the time that 700 lb. monster starts vibrating...it'll be too late and I might not hear the change in sound before that.....

[Brian Weick]

Ken,
Glad nothing serious happened to you - don't some turners put weights on the base somehow to keep the lathe stable. One of my fellow woodworker Friends that I correspond with uses sand bags and that seams to work pretty well. I bet you are anticipating the arrival of that condiment- I am afraid we won't hear from you when it arrives- the yellow vortex!!!!!!
Brian

[Jude Kingery]

Ah Ken, yep, that's a drawback for sure. Guess we just rely on what we have and go from there, my hearing's ok, but my sight is for doo-doo so hence I ALWAYS wear my safety glasses (prescription tri-focal safety glasses). And not so much for safety, well there is that - but for the simple fact that without them, I can't see.

PS - Glad you were ok!!!! Jude

[Marvin Hasenak]

Jude will vouch for my estimate of the correct RPM, if the lathe is not shaking the speed is too slow, I crank it up and turn as fast I can with out the lathe walking out the garage door. I slow it down for the sanding.

I do mostly game calls and they are mounted on steel mandrels through a drilled hole in the center of the blank. The mandrel is a 5/8" steel rod and is mounted in between a collet chuck on one end and the tailstock on the other. I have never lost one off the lathe yet.

When I do other things like a bowl, I still try to redline the tach when working between centers, but when the blank is only being held by a chuck I tend to slow it down. I usually have my blanks pretty well centered and balanced so that I do not have a major off balanced piece to work on.

So I guess the best way to describe my RPM estimate is "As fast I feel safe with"

Marvin

[Jude Kingery]

Yep, I'll vouch for you, Marvin. He and I both tend to turn pretty fast. Long as it's as safe as you can make it. Key would be starting with something fairly true already when you mount it. Have only lost one piece of a Mesquite bowl (threw a knot) and that's what taught me to pay attention to sound. It had an odd sound to it and right about the time I shut it down, it threw the knot. Nah, everything was fine, but it is important to pay attention. Let us know how it goes for you, Jim. You'll find what's comfortable. Jude

[Harvey M. Taylor]

Hi Ken,
I am suffering from hearing loss too, but not as bad as you. I believe you can place one hand on the lathe and increase the rpm's to where you want. I dont go for weighting the lathe down to stop vibration, just slow it down.In the low range, it will go down to about 50 rpm's.

[joe greiner]

Tables of rpm's versus diameter usually boil down to a narrow range of surface speeds. Surface speed is really what cutting is all about anyway. Add some ballast to the lathe support to reduce vibration; I use two 5-gallon buckets of railroad spikes. If the lowest speed produces excessive vibration, the piece is severely out of balance. Stop and cut the heavier part off with a chain saw, power planer, hammer-and-chisel, or whatever. Cutting the blanks round with a bandsaw can get you pretty close, unless there's a significant lack of symmetry - cut that off in advance; it'd be turned down anyway.

Joe

[Jim Becker]

Glad nothing serious happened to you - don't some turners put weights on the base somehow to keep the lathe stable.

Brian, an out-of-balance blank of modest size can walk a 900 pound OneWay 1236 across the floor with no problem. The laws of physics are quite amazing...

Sometimes just a few RPM in either direction can make a difference in this, too...resonance can cause vibration and even "walking" if things are out of kilter enough.

My comment on some of the RPM figures given in previous responses to this thread is that they are a bit aggressive in my mind relative to getting a larger piece started. When I'm playing with a large and likely out-of-round and out-of-balance blank for a turning, I start very slow...200-250 rpm or so max, an gradually increase the speed as things develop through refinement. I only use the low range on my Stubby which gives me 0-1200 rpm or so and rarely have it up to 1200 unless it's a small to mid-size object for final finishing cuts.

[Brian Weick]

No - I know, that was a guide I took out of my wood turning book- just a guide,- Your absolutely write- start off very slow-
Brian