Interesting Lathe Speed Numbers

Vaughn McMillan

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How fast would you spin a 14" diameter bowl?

In a discussion on the World of Woodturners site, Richard Raffan posted a picture of a 14" red gum bowl that detonated while he was turning it. It happened while he had stepped away from the lathe, so he was well out of the line of fire when it blew. This was wood that was riddled with voids (gum pockets) and is known for being tricky to keep in one piece.

Later in the thread Richard mentioned he "wasn't spinning the wood that fast", somewhere around 1000 rpm for the 14" piece. Another poster mentioned that there are about 200 Gs trying to rip the rim off a 14" bowl spinning at 1000 rpm. Yet another poster said that reducing the speed to 700 rpm would cut the G forces in half. Reducing to 500 rpm would be one fourth of the G forces as 1000 rpm. (Smaller diameter pieces would have lower numbers and larger pieces would be higher.)

I just thought those were interesting (and eye-opening) numbers. Something to think about the next time you're cranking up the speed on the lathe to get a better cut. Richard has been a professional woodturner longer than I've been driving cars, so I'm sure he felt comfortable turning a piece that size at that speed. I don't think I would be.

When I started turning, I kept the speeds pretty low, because catches were all too common, and low-speed catches were less dangerous and destructive. As I've gained turning experience, I'm bumping the speeds higher and higher, since I get a better cut when the lathe is spinning faster. I've gotten very comfortable with a bowl gouge, and catches are very rare (and typically very minor) these days, so the risk of catastrophe feels lower to me than it used to. Still, 1000 rpm on a 14" piece would feel awful fast to me. (My current limit for finishing cuts on a piece that size would probably be around the low to mid 800s.) I'd probably love the cut I could get at 1000 rpm, but in the back of my mind would be this little movie running, showing how quickly an edge could break off and stick into anything in its path.
thud.gif


So...how fast would you spin a 14" bowl?
 
Very early in my bowl turning career, which was a short career at that, I received two redgum bowl blanks 8" square and 2" thick. I do not recall the speed I was turning when the first one blew apart but I was wearing my faceshield at the time. I immediately thought that the problem was speed as I did not know that this wood was prone to flying apart.

To answer your question I may have turned a 14" bowl as fast as 1000 rpm but I doubt it. I am a bit of a chicken when it comes to turning larger pieces.
I turn boxes at 2200 or more RPM but they seldom exceed 3 or 4 inches in diameter.
 
It's that thing you're buying the SawStop bowl drying table for. :D

Funny guy :rolleyes: :D :rofl:

The forces involved are eye opening, to be sure. I always knew that rim speed of a 14" bowl was a LOT faster than say a 6" bowl, but the Gs produced is really something:eek:

Myself, I turn as fast as I "feel" safe, and that has a lot of variables, like the wood the thickness of the wood and such, I will admit to being somewhat fearless, but, I hope, not too stupid, for example, I always wear my Triton powered respirator when roughing, for a number of reasons, all dealing with safety; one, the face shield/helmet combo is quite robust, and would help a lot if one really exploded, two, the respirator part of it keeps the dust on the floor, instead of my lungs, and the third reason is I get a lot fewer chips down my shirt with the Triton on :D

I've also learned how to stay out of the line of fire, but that is a bit of a false sense of security, sure, if one goes "BANG" and you are not directly in the line of fire, that is good, but I'm sure most of us have our lathes against a wall, so ricochets are always a problem :eek:

Good info just the same!:thumb:
 
Vaughn, Like you say Richard Raffan has been turning since before I could drive. But I have not found all that much need even on a 8" or 9" bowl to go over 750 to 800RPM to get a good finish cut or shear scrape with a bowl gouge. Like you say, as I have gotten more comfortable with my tool control the speed has come up but I understand about the rotational forces at work and quite frankly it is pretty scary if a bowl or other large chunk of wood comes apart.

While I always wear a Uvex Bionic faceshield when I am roughing a bowl. I still just like to wear my safety glasses when I am really getting into the final shaping of a bowl. Hearing stuff like this always makes me think twice about that.

Vaughn by the way how can I get invited to participate on the World of Woodturners site? I would love to get an invite.

Thanks,

Alan
 
1000RPM seems quite fast to me too...Having a bowl come apart while nothing is touching it would make me turn the speed down quite fast, er I mean slower.:D

Most of my finish turning is down at about 700rpm. Then again if a blank is pretty balanced so is the roughing. Belt changing although not hard ranks right up there with cleaning up the curlies for me...that doesn't happen very often either. :eek:
 
Interesting facts!

Very interesting information!

As far as what I turn big bowls at, it depends. If it's a solid chunk, then I turn the speed up. With one that has punky areas, or a large number of voids, I think I would keep it around 800 rpms or less. But I suppose the mass of lathe matters as well. I maybe have too much confidence with the speed, just cuz the ole' Rollstone, is around 1500 lbs. Also, when I do choose to bump it up, I make sure my body isn't in the "throw" path. That way if something does happen, I will be well to the inboard side of the piece as the projectiles fly out. I know this isn't foolproof, but it's kept me bruiseless so far. :thumb:

Hutch

P.S. BTW I have turned a 20" bowl at around 600 RPMS. It was very well secured, and the speed was very critical to producing the finishing cuts at the 1/2" rim. There was so much flex that the chatter was causing serious issues. In situations where the rules of the road are streched (or broken) I am always aware of the dangers. I make sure that I "test the waters", away from the lathe at the circuit breaker, before I approach such a workpiece. I don't want you to think that I am careless or reckless.
 
Vaughn, I believe that is too general a question to give specific advise on.
The 1000 rpm does sound too fast, IMHO. But, a lot depends on the shape and balance of the rough blank. There have been times when hitting those high spots at low speed got tiresome. Sometimes spinning that puppy faster makes cutting easier. (keep yer eye on the 'shadow')
Without having been there and watching him, I think conclusions are going to be highly debatable.
I currently have a John Jordan video I checked out from my club. At one point, Jordan has a large bowl blank on that is vibrating badly. To smooth out, he turned the rpm UP. :eek: He explained there are speed 'points' that run smoothly and one must experiment.
All of which boils down to, I dunno. :dunno:
That was a singular incident that we are unable to diagnose after the fact from here.
I use whatever speed 'feels' right to me.
 
800 seems like a good number, but I'm out of the running because my Jet doesn't have 14" over-board :doh:. Using my BIL's POC Central Machinery Lathe and his tools last weekend I was barely happy at 800 on 10" maple. But at home, I'll turn boxes and stoppers at 12-1500, pens at 3k. But the wood should dictate the speed :bonkers: That manzanita with the big inclusion...no freakin' way thats going over 800. The hollow form/bowl that Vaughn :)bow:) put out the other day was done at slow speed. Common sense over time constraints and comfort level should determine speed. A chunk of Cocobolo flying at your skull at 800 fps regardless of a face shield can shorten your day :(, and isn't the goal to Live To Turn Another Day ;)
 
I haven't turned a 14 inch bowl yet, and on my lathe that would be an outboard turn since my lathe is only a 1442 and a true 14" wouldn't turn over the ways, 13 7/8" might..:dunno:

But right now I still tend to run the lower speeds until I begin to feel the piece is smoothing out to spin (or like Frank I get impatient with the constant thump of the high spots at 450).. my lathe is a Reeves speed control at 450, 650, 800, 1100, 1450 (I think) and one or two more speeds over that. On larger pieces I stay at 800 or below... smaller pieces I'll kick up to 1450 or next speed... haven't gone to top end yet, even on a pen... mostly on little pieces I use the mini jet anyway, 'cause it is smoother at the high speeds. And I haven't taken it to the top speed yet either.

I've seen a few of the 'pros' videos and watch them crank up, but I'm still a little cautious... so far I've had two blows that could have resulted in body damage... one was a 2x2 chunk that hit my face shield and knocked it askew, the other was half a bowl that came apart and hit me in the chest .. it was about 8" and split in half, running at about 800 at the time... I got a bruise out of that one.

I've also had a skew catch and shoot back through my hand.. since then I wear a leather glove on my left hand... I didn't get cut since it kicked straight back, but my knees hurt from having to get down and crawl under the toolbox where that skew wound up.
 
...Vaughn by the way how can I get invited to participate on the World of Woodturners site? I would love to get an invite...

Ding! You've got mail (to your Yahoo address). If not, let me know.

If anyone else wants an invitation to the WoW site, drop me a PM. :wave:
 
Vaughn, I believe that is too general a question to give specific advise on...

I agree wholeheartedly, but I figured it might spark some interesting discussion. :) Every piece truly is different, so the only hard and fast rule is that there are no hard and fast rules.

I posted this question on a few other other forums, and it's been very interesting seeing the responses. :rolleyes:
 
My rule of thumb, once the piece is balanced is one I read somewhere.

Diameter X Speed > 6000 but < 9000. Therefore, a 14" bowl, if smooth would be no more than 642rmps. With the holes, I believe that I would back off some.

The best bet is always creep up on your speed. No wiggles allowed.

Bruce
 
Agreed, better safe than sorry.

There is one feature on my Grizzly G0632 EVS lathe that I simply love. The 'soft start'.
If I should put a big, clunky, out of balance hunka wood on and forgetfully have the speed control set to warp 10, it still begins slowly and builds gradually. While this is happening, if I see it getting ready to launch, there is a big red emergency shut-off button I can hit and all is well again. Great-great safety feature.
I know PMs, and probably others have it also, and for good reason.
 
My rule of thumb, once the piece is balanced is one I read somewhere.

Diameter X Speed > 6000 but < 9000. Therefore, a 14" bowl, if smooth would be no more than 642rmps. With the holes, I believe that I would back off some.

The best bet is always creep up on your speed. No wiggles allowed.

Bruce
Good rule of thumb and very sound advice, but I've turned quite a few pieces at speeds a bit faster than those guidelines would suggest. For example, the ash root ball I finished recently was beating me up pretty badly in the 500 rpm range, but once I bumped it up to the lower 800s, I was actually able to take finer cuts with better control since the voids weren't kicking my gouge all over the place. (It's the washboard road theory...at a certain speed, a washboard road feels smooth to drive on. Go much faster than that, though, and you can lose control.) I still made it a point to stay out of the line of fire to the extent possible.

That said, I think people should turn at the speeds they are comfortable with, and still be fully prepared for ugly surprises. ;)
 
Vaughn normally on a good piece of wood like cherry, maple, etc. being turned for say 10" to 14" utility bowls I will turn up around 950 to 1000 rpm on my DVR for finishing cuts. Roughing is slower for sure till it gets balanced. Smaller bowls up to 10" I will run 1000 to 1250 rpm for finishing cuts. I like you over the past years have kicked up the speed. I can remember trying to finish cut a bowl at 300 to 500 rpm. Boxes like Mike I will run 2000 to 2500 rpm. I do wear my Trend and don't stand in the line of fire. I agree with the comfort zone but just don't get careless.
 
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