Safe Turning Speeds

[Richard Kennedy UK]

Hi all

As a newbie to the delights of Variable speed I was wondering what your thoughts were on safe speeds to work with. I know many turners turn very fast and that in some cases its the only way to get the required finish etc but for the most part what kind of speed range do you employ for basic bowls and platters like 8inch diameter 3 inch thick stuff. I set the belt to the higher speed range on the 3520B but (and this is a seperate question) should I work more in the bottom range 50 - 1200? is it better or the motor to have the higher fan speed?

I am totally enjoying the ability speed up and through vibration but I am concerned in light of recent events that I don't, trough ignorance, push the envelope too far.

any help gratefully received

Richard

[Fred Belknap]

Richard I'm probably the best to answer your question but I will give my opinion.
My machine has a two belt with electronic variable speed and I keep it on the low speed range. I do mostly bowls. I changed it to the high speed to check it out but put it back.
The general rule for me is the diameter of the turned piece and the balance. The larger the diameter and the more out of balance the slower I turn. I'm not real comfortable with the higher speeds. I can see that something like a pen would need a considerable faster turning speed.

[Dale Miner]

Richard,

When asked from people about turning speed, I usually reply "Turn at a speed you feel comfortable with". I may or may not turn at a speed that others feel comfortable with. An 8" diameter piece of sound wood? For me, a comfortable roughing speed is about 1000 to 1200 rpm, and a finishing speed of about 1000 to 1600. If roughing at 800 seems uncomfortable to you, then don't do it. If you feel comfortable roughing an 8" blank at 3000 rpm, I would suggest rethinking things. I do examine the wood closely before mounting it, and again every time the lathe is shut off or an unexpected sound is heard. Many times small indicators of problems are not visible at the onset of roughing, but are revealed as the wood is pared away. Some pieces get taken off the lathe part way through the roughing and put in the burn pile. Life is short, wounds take too long to heal.

As to which belt range to use, I prefer to keep the motor running in the middle two thirds of the setting on the knob if possible, and don't like to work the lathe hard with the motor running in the bottom third of it's range. Sometimes with an out of balance piece the lower third of the range has to be used though. These are just my preferences of course. Spindle work is almost always done in the high speed range, larger bowls almost always in the low speed range.

[Steve Schlumpf]

Richard,

I agree with Dale's advice of never turning at a speed you are uncomfortable with - ever! I have the little brother to your lathe, the Jet 1642, and I usually keep the belt in the high range position. The only time I use the low range is when roughing out large blanks and I like it then because of the lower speeds, more torque and most important - faster braking!

When shaping bowls or hollow forms, depending on the size of the blank, I usually rough out at 800 to 1000 rpm - but that is what I have become used to. If the wood is full of voids, bark or other natural 'character', then I slow the lathe way down until I have a better idea of what lies beneath.

There is an old formula for determining lathe speed: Diameter X RPM = 6,000 - 9,000. Using your example of an 8" bowl blank, then 8" X 750 rpm = 6,000 and 8" x 1125 rpm = 9,000. So, with a sound piece of 8" wood, the recommended safe speed range would be 750 to 1125 rpm.

Hope that helps!

[Reed Gray]

From Pat's Fan over at Woodnet Forums, "When sphincter tightening exceeds chuck tightening, you have a problem!"

Pretty simple to understand. If you are uncomfortable with your speeds, slow it down. Easy to do with the variable speed lathes. You will most likely find that the more you turn, and as your tool skills improve, the more comfortable you are with higher speeds. However, you don't need to increase your speeds if you don't want to.

As a bowl turner, (well, mostly) I need speed and torque. My lathe, a Robust American Beauty, has one advantage over some of the other lathes, and that is 3 speed ranges. With my PM 3520A, the low speed range was up to 1500 which was good for most bowl turning, but slow for spindles. The B model has a low speed range of 50 to 1200, which isn't slow enough on the low range for sanding my warped bowls, and not fast enough on the high range for medium and small bowls. I kept it on the slow speed range most of the time, especially for bowl coring. It was sufficient for bigger pieces, but some times I needed more torque, especially on larger pieces. The 3 speed ranges on my Robust are a lot better. I have slow speed for big pieces, medium speed range for most of my turnings (0 to about 2200 after some fine tuning on the phase converter with Brent English's help), and over 3000 on the high range. The formula for lathe speeds given above are good suggestions, but you will adjust them to suit yourself.

Some one really needs to develop an automatic transmission for lathes.

robo hippy

[Ed Morgano]

Richard,
PowerMatic has a chart located here: http://content.powermatic.com/manuals/m_1791254.pdf. This might help.

[Curt Fuller]

Richard,

I agree with Dale's advice of never turning at a speed you are uncomfortable with - ever! I have the little brother to your lathe, the Jet 1642, and I usually keep the belt in the high range position. The only time I use the low range is when roughing out large blanks and I like it then because of the lower speeds, more torque and most important - faster braking!

When shaping bowls or hollow forms, depending on the size of the blank, I usually rough out at 800 to 1000 rpm - but that is what I have become used to. If the wood is full of voids, bark or other natural 'character', then I slow the lathe way down until I have a better idea of what lies beneath.

There is an old formula for determining lathe speed: Diameter X RPM = 6,000 - 9,000. Using your example of an 8" bowl blank, then 8" X 750 rpm = 6,000 and 8" x 1125 rpm = 9,000. So, with a sound piece of 8" wood, the recommended safe speed range would be 750 to 1125 rpm.

Hope that helps!

I've never seen that formula before, but it makes very good sense to me.
Another very important factor is the "sound piece of 8" wood". Sometimes it can be nearly impossible to visually detect a defect or crack in a piece of wood that could result in it flying apart. But I've found that there is usually a telltale sound that comes from a piece of wood, a clicking, weird vibration, or something that gives a little warning that the wood is doing something that warrants your attention. Never ignore that. Stop the lathe, look it over closely, grab it and pry it a little to see if you can feel it flexing or something to indicate why it's making that sound, check to make sure your chuck is tight or you have plenty of pressure on the tailstock to keep it against a drive spur. But always treat those suspicious sounds as an indication that something isn't right and then take care of it before proceeding, using a slow speed until you're confident that everything is going to be OK.

[John Hart]

Yeah...I agree with what's been said already. Speed is something that can be your friend or your enemy. Certain cuts really require a fast speed....But I think it's important to understand that there is no magic formula to apply to all cases. The formula that Steve posted is a really nice calculation that would work in most instances, however, we are not all from the same mold. There are thousands of artistic turners with thousands of different styles and tastes. Heck...Curt Fuller will go dig up a tree and stick in on his lathe....while others will only turn 6 inch bowls....some only pens. With all that variability, there may not be a quick answer. I would suggest that if you are doing something out of the ordinary...ask here. Or...always keep in mind that the rules you followed for your first bonker, aren't necessarily the same rules for the hollow form filled with voids and bark inclusions.
And no....do not trust ANY piece of wood as being sound. Wood hides defects....a spinning lathe hides defects that become uncovered. Curt's right....Listen and feel, then act when something doesn't sound or feel right.
These "explosions" happen so fast that you don't have time to gasp.