Bowl RPM's

[Dan Cannon]

Hello Everyone,
Been lurking for a while and am finally getting a lathe...so now the questions really start. Money is not abundant, so I am "indefinitely borrowing" a lathe from a family friend. The lathe is in great shape, and I think it will be great to learn on before I decide if/when to invest in a new one.
My only concern is the low RPM's. Right now, it is set up with an RPM of 820 for the lowest setting. I know this is considered very high, especially for bowl work. However, if I use the "RPM x Dia = 6000 to 9000" formula, I should theoretically be able to turn around a 10" diameter piece at this range. So, why is it that most people would tell me turning a 10" bowl at 820 RPM is crazy? Is there a different formula for bowls? I know it would take some more bandsaw work, but if I can get it decently balanced, will I be able to at least get a chance to learn and practice bowls on this lathe, maybe up to 8" Dia? Or am I limited to very small pieces?
ps - I'm looking into putting a larger pulley at the spindle (reeves drive below) to reduce RPM's, but not sure it will work.

Thanks for any input.

Dan

[John Keeton]

Dan, you will get some input from much more experienced turners, but I think you will find that rough cutting a bowl at that speed could be challenging, unless the blank is cut VERY round off the saw. Even then, you could still have a piece that was out of balance, and at 820 rpm, I am afraid you could have a dangerous situation.

Most of my finish work on bowls is done in the range you are talking about.

[alex carey]

like John said, unless you can get it perfectly round you will definitely get that lathe to dance. Even then wood is not the same density throughout and a perfectly round 8" bowl will shake a medium sized lathe at 800, especially if its not a weighed down.

Wear a face mask, chuck up the piece of wood, and try turning on the lathe, im guessing it'll dance pretty bad and you'll be too scared to use it.

[Tony De Masi]

As the others have said, 820 is pretty high for the low end of bowl turning. Even if you were able to get the blank perfectly round on the band saw you still have to deal with wood density, wetness of the wood, and are the opposing faces flat and parallel to each other.

I personally wouldn't do it but that's just me.

Tony

[Hilel Salomon]

I think that if that is the lowest possible speed, you might want to do something other than bowls. It may be ok for spindle work, but I would never start off a bowl at that speed. Even 4-500 rpm can be rough on you when the blank is not round.
Hilel

[Jeff Willard]

Hmmm. An off-balance 10" blank of any significant depth, 800 RPM at startup...I hope you can outrun it:eek:.

Just curious, how much does the machine weigh?

[Dan Cannon]

sounds like I'm out of luck for bowls as it's set up now then huh? I know I can get it down to 500 RPM with a 5" pulley at the spindle, not sure a 6" will fit, that would get me right around 400. Maybe that would be possible?
Not exactly sure, but the lathe weighs in around 350 lbs, give or a take a few. I'm planning to anchor it down to concrete and adding weight. Not sure what else will be necessary/possible.

[Charlie Reals]

Dan,
PLEASE pay attention to the folks above as I personally out ran and ducked one yesterday morning. Thank God i always stand to the side. It did force me to clean my work bench as is sailed 6 feet, hit the wall and bounced onto the bench knocking everything in its path onto the floor. I almost had to clean my shorts also :o:o Charlie

[Steve Schlumpf]

Dan,

My first lathe was a 1954 Craftsman mono-tube with a slow speed of 875 rpm. I used that lathe for 2 years and turned a number of bowls on it but have to admit - it was a challenge! I honestly believe I launched 1 out of 3 that I roughed out - sometimes, multiple times! But, that was before I found SMC and discovered that turning was not a contact sport!

Can you turn a bowl at 820 rpm? Yes. Is it the safest thing you could do? Probably not.

Best advice I can offer is to get with your local turning club and have some of those folks show you how to turn a bowl safely. Then you can decide if it is something you can tackle with your borrowed lathe.

Meanwhile - read, watch DVDs and get with some local turners and learn as much as you can.

Turning is fun and can be very addicting! Just had to throw that in there so I can say you were warned!

Have fun! Looking forward to seeing photos of your lathe and turnings!

[David Walser]

...My only concern is the low RPM's. Right now, it is set up with an RPM of 820 for the lowest setting. I know this is considered very high, especially for bowl work. However, if I use the "RPM x Dia = 6000 to 9000" formula, I should theoretically be able to turn around a 10" diameter piece at this range. So, why is it that most people would tell me turning a 10" bowl at 820 RPM is crazy? Is there a different formula for bowls? ...

Dan,

Welcome to the vortex! I hope you'll find turning as enjoyable as the rest of us do.

Since you've already received good advice regarding safe turning speeds, allow me to address your specific question. No, there's not another formula for bowls. The RPM x Diameter = 6,000 to 9,000 formula applies equally to bowls and to spindle turning. However, the originator of the formula, Dale Nish, suggests staying at the low end of the suggested rpm range until the blank has been turned round. With 820 rpm, that would suggest a maximum diameter of about 7" -- NOT 10" -- if you're starting with a square (or out of balance) blank. If you've rounded the blank on a bandsaw, then you should be able to handle a 10" bowl. Does this make sense?

Here's a link to Dale Nish's write up of his formula and how to use it: http://www.woodturnerscatalog.com/woodturners/Images/safe_lathe_speeds.pdf

Hope this helps.

[Frank Van Atta]

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

[Dale Sautter]

Don't know how long you'll have it on loan... or if it would be worth your time...

Check your local Craigslist for a used treadmill, the motors are pretty strong and you can dial it down for very slow rpms. I picked up a treadmill last winter for about $20, stripped the motor and controller board out and replaced the stock speed pot for a new one from RadioShack for a couple bucks. I use it to power my home made 2x72 belt grinder and it's worked beautifully from anything from plane irons to chisels to lawnmower blade to kitchen knives. Never a burned tool so far since I can dial the speed down to roughly "scary-sharp by hand" speed.

Recently picked up an old lathe myself (newbie alert), again at Craigslist, again for about $20. Replaced the bearings after de-rusting. It will be powered by the next treadmill motor that I find, hopefully soon. I've seen them for free many times the owner just wants them gone... it's a timing thing. Good luck with your quest!

[Bernie Weishapl]

820 rpm is way to fast for bowl turning unless you have it cut round and pretty well balanced. I start turning all bowls that are out of balance or square at 200 rpm most times and as it get more balanced/round I will up the speed. I rarely turn a bowl over 1100 rpm when finishing.

[Dan Cannon]

Thanks for all the replies everyone. Safety is surely my main concern here, I don't plan to push any boundaries, especially as a new turner. I plan on ordering the pulley needed to get the RPM's down to 500 so I can eventually feel better about possibly turning small bowls, but will just have to make sure things are balanced.
This lathe should be sufficient in getting me hooked so I can "justify" spending money on my next!

Dan

[Charles Bouchelle]

just a thought......If you join a local club perhaps you can at least turn the blanks to roundat the club or a mentor/members home ,than take them home to do the work on your lathe that way you can work safely.

[Curt Fuller]

Dan,

My first lathe was a 1954 Craftsman mono-tube with a slow speed of 875 rpm. I used that lathe for 2 years and turned a number of bowls on it but have to admit - it was a challenge! I honestly believe I launched 1 out of 3 that I roughed out - sometimes, multiple times! But, that was before I found SMC and discovered that turning was not a contact sport!

Can you turn a bowl at 820 rpm? Yes. Is it the safest thing you could do? Probably not.

Best advice I can offer is to get with your local turning club and have some of those folks show you how to turn a bowl safely. Then you can decide if it is something you can tackle with your borrowed lathe.

Meanwhile - read, watch DVDs and get with some local turners and learn as much as you can.

Turning is fun and can be very addicting! Just had to throw that in there so I can say you were warned!

Have fun! Looking forward to seeing photos of your lathe and turnings!

Like Steve, I learned on a tube lathe with about the same minimum speed. You can do it with a few precautions. Besides getting the blanks as round as possible, get the thickness as uniform as possible. That will resolve most of the vibration issues. Then just be careful presenting the tool to the spinning wood, taking very light cuts until it gets round and the tool isn't in the hit and miss mode.

[Reed Gray]

For me, as a production turner, on my big heavy lathe, I start up bowls that size at that speed and higher all the time. It has taken me 12 years and thousands of bowls so that I feel mostly comfortable doing that. I do make it a point to stand out of the line of fire. You can slacken the belt so it will slip easily if you are cutting too much at once or have a catch. On smaller bowls, it isn't as much of a problem, but not an ideal situation for learning to turn bowls.

robo hippy