Lets talk spindle speed

[Mark Norman]

Optimum speed depends on the work being turned, size, out of balance, and the wood all can dictate the speed at which you want it turnin.

Ultimately you would like a machine that goes from 5 rpm to 5000 and do it all day long at maximum torque. Thats just not practical in building a wood lathe.

Many lathe makers have done a good job with variable speed drives and two step pulleys to get a wide range of adjust-ability from their machine.

If you wanted to primarily turn medium to large bowls out of chunks of trees you would want to have the ability to turn real slow right? variable between 50 to say what 200 or 300 rpm?

To make a machine to do that and still see speeds of 3000 rpm you need some sort of gear reduction or an over powered motor for the task.

My question to you all is; if I use variable speed and gear reduction to get the real low speed, how fast do I need such a machine to go for sanding and smaller pieces? Do I really need to go 2500 ~3000 rpm? ever? whats the fastest speed you want out of your lathe?

And the reason I ask is; I have a 2hp motor with a vfd but from what I am told a TEFC motor should run at least 900 rpm for the fan to keep it cool and not overheat and lessen the life of the motor. To get down in the 50 rpm range for turning the big stuff I would need to reduce the speed with the use of pulleys even with the vfd.

I am thinking of a two or three step jack shaft to be able to obtain 2500 ~ 3000 rpm but how fast do I really need?

Long winded I know but it makes for better conversation:)

[Bob Hallowell]

on the lathe you are making, being a bowl lathe and never going to have a spindle on it I would say 1000rpm would be fine. I rarely spin a bowl faster than that.

Bob

[alex carey]

The powermatic 3520B goes to 3500 rpm I think. I say "I think" because I have never taken mine above 2500 because I never found the need. You are building mainly a big bowl lathe which means you'll mostly be doing big bowls. For big bowl work you don't need extremely high speed. If your lathe could go 1500 rpm that would probably be sufficient, if it went 2000 RMP max that would definitely be enough in my opinion.

Bottom line. 2000 is enough even for the small stuff which you undoubtedly will do.

[Dean Thomas]

An eternal question, I fear, with too many "right" answers.

Speed is a taste thing. Some people, especially those who make their money standing in front of a lathe, don't want to poke along. Gotta move to make money. Cut faster, get done faster and more often, have more to sell!

For us hobbyist types, serious, very serious, or just plain anchored in the vortex, speed is so selective. If I have to turn pens on a lathe with belt only drive, I pick a middle speed around 1500-2000 rpm and turn, sand, and finish right there. If I have variable speed, I use it for the sanding steps to get it slowed down so I don't have to be quite so careful about heat.

Big stuff? Doesn't matter. You're not going to be using that much speed for larger objects. Dangerous.

How much time are you actually going to spend turning under 1000 rpm? I mean really. Slow speed to get an unbalanced, out of round piece to a point of workability. Then you're going to turn it up to a working speed.

According to one accepted formula for figuring safe speeds on a lathe, 900 rpm is the maximum safe speed for a 10" bowl. If you're going to be turning larger than 10", you will need to address the 900 rpm threshold for the cooling of your motor, whether you address it through belt changes or whatever. Maybe a separately driven fan motor? Safe speed for a 32" bowl, by the way, is a whopping 280 rpm. :eek:

[Mark Norman]

thanks Bob, Thats what I was thinking.
As I have it now I have a 9:1, 6:1, 4.5:1 and 3.6:1 reduction with the pulley set up I have. whitch equates to a theoretical 100 rpm at the low end and 500 rpm up top. I could add a 2:1 jack shaft to get 1000 but dont want to have to make it go faster if I dont need to.

[Mark Norman]

Thanks for the promp responses.
Dean,
As for how long I would be under 1000 would be dictated by the piece I guess:p but I would bet I could expect an hour or so to get a big piece balanced enough to go more than that right? at my speed anyways... lol

I guess it is safe to say I won't be needing more than 1200~1500 rpm for what I am planning on doing?

Excuse me... for I am a noob but I seem to be stuck in a vortex of some kind:D

[alex carey]

1500 should be enough. I use a chainsaw to cut the corners a few times before I mount. I would suggest you do the same otherwise roughing will be hell.

[Mark Norman]

I have a chain saw to trim the corners off;)

[Jeff Nicol]

Mark, The motor on the pm3520B is a TEFC motor and I use it at slow speeds and the fan moves plenty of air. If you use good techniques and sharp tools a big bowl can be roughed out it 10-15 minutes. I was turning a 15" white pine calabash yesterday and it had some big knotty areas with a lot of pitch in it. I never could get it completly balanced as that one area was always heavier. This meant that I had to turn a lot slower or the lathe would start to dance. So if the big manufacturers use the motors they must be able to withstand the amount of slow and fast that a lathe will be used at. I put a 1hp 3ph motor on one of my other lathes and it does not have a fan. I run it slow, fast or whatever. It is set so I can run it faster than 60hz and it will really fly! Need a tach to see how fast some day, I never turn that fast but it can do it!

My linear slides for the CNC router are on the way! Soon the build will begin!

Jeff

[Mark Norman]

Thanks for the input Jeff,
I guess I'm just over-thinking it because the guy selling me the motor got me all worried about spinning it too slow he said it would cause premature failure.

Cant wait to see your cnc router project, sounds like fun.

[charlie knighton]

Safe speed for a 32" bowl, by the way, is a whopping 280 rpm. :eek:

good discusion, we are sometimes tempted to use speed to rough out fast or to put the best shear cut on a piece

sometimes the machine will save us, i got carried away one day shear cutting a flat topped 6 inch wide by 7 inch vase, i kept increasing the speed (jet 1642 evs) by 100 rpms til i was at 1800 rpm too fast the machine cut itself off with just a slight line in the top took me 5 minutes to restart the machine still not to sure what actually cut the machine off, looked up some tables for finishing rpms, 1500 for 4" to 6" but i normally finish at about 1000 rpm on that size, a continous curve is better at speed that flat, i believe that was part of it

[Harvey Schneider]

The motor may get hot if you are running it at low speed with continuous maximum load. What we do at a wood lathe is hardly ever continuous (>15min) and it is rarely at maximum load (torque).
I like to work at the upper end of my Jet 1642 diameter limit (16") which means that I am usually at low speeds (<600 RPM). Jet does use a two step pully for low/high speed range selection, so the motor speed may be higher than the spindle speed (I never checked). Anyway, I have never had the motor run hot in the two years that I have been using it.

[Kim Ford]

Mark;

First question is what type of vfd are you suggesting. Is it continous torque or what? Not all vfd's are created equal.

I use one with continous torque and have a full range, but if I want to rough out a big knarlly blank, I will use my step down pulleys to keep the motor running at about 30hz.

Also, you do not put continous strain on your motor when you turn. The strain is only there when you are cutting with your chisel.

As to speed. For me safety, sharpness of tool, tool type, tool presentation, type of wood, moisture content as well as where on the vessel you are cutting is what determines speed, not some general rule of thumb.

I have 16 mechanical speeds on my Oliver that go from 90 - 2900 rpm in my pulley system with a vfd on the motor so my range is very large. But bottom line is I like to cut the wood and not tear it so I rough out usually at 250 - 650 rpm and usually final shape at 750 - 1500 rpm.

Everyone has a different style so this is my two cents.

[Mark Norman]

Great input Kim, thanks, I posted the link for the vfd in my lathe build thread last night.
I'm still collecting parts for it but I hope to have it in operation in a few short weeks.

I'm glad I found such a resourse as the creek, thank you all once again.
Mark

[Wally Dickerman]

Speed within safety standards is a matter of choice even among very experienced turners. I recently watched Cindy Drozda turn a 4 in dia. HF at 3000 RPM. On the other hand, John Jordan claims that he usually turns at about 800 RPM.

A VS bowl lathe should have 3 pulley sizes at least, to give you a good range of speeds with good torque. Torque is best when the motor is running at top speed. If you plan to turn large pieces you'll need good torque.

Don't settle for pulley sizes that'll only give relatively slow speeds. You may find that you prefer to turn at higher speeds. In my own turning I turn faster than most turners, I think. If I'm turning a 12 inch bowl I'll turn at around 1400 RPM. if it's a 6 inch piece I'll go to 1800 to 2000. If I'm turning a finial I'll turn at 2500 to 3000. These are safe speeds for an experienced turner. I find that most woods cut smoother, easier and with less effort at the higher speeds.

I used to teach at a Woodcraft store. We used Jet mini lathes without VS. For beginners I set the belts to run at 1200 RPM. Everybody felt comfortable at that speed because as beginners they hadn't experienced anything else. It was completely safe. (unless they badly misused the tool, and then no speed was safe)

Wally

[Dick Strauss]

Mark,
Don't forget you might be able go to 5400 rpms on a well designed 1800 rpm motor for short periods of time using your VFD. The fan may start to cavitate (not moving enough air) at the higher rpms on motors not designed for faster speeds, thus reducing the cooling capabilities. The higher speed will also cause much faster bearing wear. However, I suspect you'll use the extra speed so very seldom, it should not be an issue! This way you won't have to have pulleys to achieve the speeds between 1500-3000 rpms.

[Mark Norman]

I'm not too worried about the high speeds, having the machine go slow enough without compromising the motor is my concern. I'm thinking of using a secondary fan to cool the motor or maybee a duct off the DC.