min rpm required for large bowl turning

[Martin Rock]

Hi

I am in the process of choosing a lathe...

I would like to know if EVS is mandatory for turning larger bowls or someone can manage with a low end speed of 400 rpm

I have a band saw, so rounding the blanks prior to turning is no problems

thanks

[Richard Madison]

What size is "larger"?

[Martin Rock]

12 to 20 inch bowl

[alex carey]

i can't think of a lathe with 20" swing that doesn't have EVS.

It's definitely not mandatory but for bowl turning it is highly recommended. Especially in that size range. Have you turned a 20" bowl?

[Martin Rock]

not turned anything yet

You can turn 20" outboard of the general 260-1, it has a reeves drive (mechanical VS)

[Ken Fitzgerald]

Martin,

Reeves drive will require some regular maintenance just because of it's mechanical nature.

Most modern lathes are EVS...electronic variable speed.

400 would be my absolute maximum RPM with a large bowl. I'd prefer less..initially..a lot less but that's just me. I do use faster speeds as the bowl becomes closer to being finished.

Sometimes the piece of wood you are working with dictates what speed is comfortable.

Obviously a lot of turners have turned with minimum or low speeds of 400 RPM or greater. To me it wouldn't be desireable. In fact, 400 rpm is about the speed I use for sanding as it doesn't burn up or gum up the sandpaper as fast at those lower speeds.

[alex carey]

hmm good point, i guess you can outboard any of the smaller lathes and do 20". But to do so would mean you also don't get the tailstock support. Not a huge deal buts its nice to have at those sizes.

Like Ken said it depends a lot on the wood, I roughed out a 15" x 4" bowl blank today. Started it at about 450 rpm, but I have the pm 3520B with 250# of ballast and was able to attach the tailstock. I definitely wouldn't want to rough a 20" x 4" blank without a properly sized/weighted lathe and no tailstock at 400 RPM. I think you oughta go for the EVS, you won't regret it.

[Jeff Nicol]

You have to remember that at the spindle 400 rpm is pretty slow. But add a 20" blank that may weigh 30-50lbs or more the speed is amplified. If the spindle is 1" in dia there will be about 1300 inches of material passing the tool at 400 rpm. With a 20" bowl there will be over 24,000 inches of material passing by the tool. So the more blanced you can make the blank with a higher lowest speed lathe the better off you will be. But to be able to start out at zero or roughly 50 rpm on most larger lathes is a much safer starting point. So in my opinion a EVS is a must for larger turnings. All three of my lathes have EVS and I would never go back!


Can't go wrong with the PM3520 or the Jet 1642 lathes, if you have more $$ the Oneways are great and the American Beauty by Robust is a winner too. The Serious, Vicmarc, Stubby,VB and Vega are big lathes too. Lots of great tools to choose from.

Good luck,

Jeff

[Bernie Weishapl]

When I turn a 20" bowl I rarely start over 100 to 150 rpm. 14" is about as big as I go because the bigger 16" and up don't sell well around here.

[Thomas Canfield]

Having just finished roughing out my 4th 20" blank in the last week, I thing you need to get down to 200 rpm or so for starting with tree sections that are out of balance. I don't think that I ever got up to 400 rpm even doing the inside outside diameter of 17 to 18". The final rough bowls weigh between 30 and 38# and initial weight was up to 100#. The green turned bowl is going out of round during the turning and was at least 1/8" out of round during the 1 hour or less removing the inside. I need a coring tool if I keep finding the larger wood. My Powermatic 3520B has done a good job of handling the large sections and I have done a couple of extremely out of balance pieces.

[Jeff Willard]

I would like to know if EVS is mandatory for turning larger bowls or someone can manage with a low end speed of 400 rpm


Nothing is mandatory. It all hinges on your ability to balance the blank. I once had a lathe that had a minimum speed of 200 RPM. I added enough ballast to it to bring the weight up to about 500#. An off-balance 12" blank would still make it walk. Trust me, a seriously off-balance blank, in the 16-20" range @400 RPM, will make a 600+# machine walk:eek:.

[John Beaver]

You might want to read this article by Dale Nish

http://www.woodturnerscatalog.com/woodturners/Images/safe_lathe_speeds.pdf

[Reed Gray]

I have never had a lathe with a read out. First lathe had 4 pulleys starting at 500 rpm. That was way to fast for chain sawn blanks, but okay for most band sawn blanks. I turn some very unbalanced pieces because that is just the way wood is. A 20 by 6 inch piece at 400 would probably be too fast. While variable speed isn't a necessity, it sure is a wonderful thing to have.

robo hippy

[Mike McAfee]

Good article John, I added it to my files!

Thanks,

MMc

[Dennis Ford]

I don't think that variable frequency is a must but speeds slower than 400 are a must for 16 - 20 inch work. Variable frequency is a good way to get the low speeds and it is also very user friendly.

While you can turn pieces that big at 400 rpm IF they are balanced and the lathe is heavy enough, this is too limiting. Large natural edge or off-center work would be difficult to do safely at 400 rpm.