Speed question

[HarleySteve]

Being new to this I have a question about lathe speed. I am working with bowls and turn my lathe speed down to the lowest for getting the round and balanced piece. I am uping the speed to 1200, I do not get a clean, no sanding needed, cut at all. I some parts the look great and some that I can not get anything but a ragged surface. I am using a ellsworth gouge and scrapers. I read that the faster the lathe the cleaner the cut. Is this true and when do you know to turn up the speed. All information is very welcome.

 

[john lucas]

Harley usually it's the cutting technique more than speed. On some cases higher speed helps the cut but usually you are getting a bad cut due to either dull tool, forcing the cut through the wood, going against the grain or a really steep cutting angle on the tool edge.
Scraping usually causes more tearout although shear scraping will sometimes produce really good results.

 

[Steve Worcester]

dull tool, forcing the cut through the wood, going against the grain or a really steep cutting angle on the tool edge.
Scraping usually causes more tearout although shear scraping will sometimes produce really good results.

I would also add not riding the bevel and too much tool overhanging the tool rest are contributing factors to a ragged surface. An unsupported too will not present a clean edge to the wood and will bounce around.

In addition, any doubts, go sharpen the tool.

 

[Bill Grumbine]

The gouge and grind you are using is capable of everything from heavy rough shavings to wispy thin angel hair stuff. It will leave a surface that looks like the Rabid Beaver tool chewed it out, or something that is as smooth as the proverbial hind end of a baby. It all depends on the presentation of the tool. Different species of wood will cut differently of course, and wet or dry will affect the cut as well. There are a tremendous number of variables here. Even the lathe you are using can affect the cut. A 50 lb piece of wood on a $500 lathe is going to vibrate more than a 50 lb piece of wood on a $5000 lathe. That is not to say you need a bigger lathe (unless you want it to say that) but you do need to tailor your expectations a bit. A lot of good work is being done on inexpensive lathes, and a lot of rich beginners have expensive machines. But as has already been mentioned, tool technique is usually the biggest culprit.

We all start at the beginning. If you can find a club or someone to give you some instruction, that is always a big help. Books and videos are a help as well, but there is nothing like hands on instruction.

Bill

 

[davidwalser]

In addition to the quality of cut, you should be concerned with safety. As the diameter of you turning increases, the speed of your lathe should decrease. When just learning to turn, I was taught a formula for the appropriate safe speed for a balanced object: RPM x diameter in inches should equal a number between 6,000 and 9,000. (That's from memory. I hope someone will supply the correct numbers if I'm wrong.) So, if your bowl blank is 7.5" in diameter, 1,200 rpm would be the maximum rpm you should be using. If the blank is "only" 6" in diameter, you could turn the rpms up -- but not much. 1,500 would be the maximum rpm for a 6" blank. At a safe turning speed, a sharp tool and good technique will give you a good cut.

Hope this helps.

 

[hockenbery]

When I teach and demo I often make cuts turning a bowl with one hand.
This is in an rpm range of 0-3. The cuts are clean. The hard part is not advancing the cut into a spiral as the work come around for the second and third times.

Sharp tool and bevel riding.

That said. a faster speed is usually a cleaner cut for the same reason I have to watch turninng the spiral - tool feed rate. With a faster lathe speed and the same cutting motion you take smaller lighter cuts which are cleaner cuts.

Happy turning,

Al

 

[Bill Boehme]

.........Even the lathe you are using can affect the cut. A 50 lb piece of wood on a $500 lathe is going to vibrate more than a 50 lb piece of wood on a $5000 lathe. That is not to say you need a bigger lathe (unless you want it to say that) but you do need to tailor your expectations a bit.........

You are a silver tongued devil, aren't you.
Bill

 

[john lucas]

Ah so price is the deciding factor in how good a lathe works. All this time I thought it was quality workmanship, good bearings, and mass. Man I looked for the best price I could get on my powermatic. If I had simply looked for the highest price I would have gotten a better lathe. Thanks for straightening me out.

 

[Marc Himes]

I have been turning for a relatively short time and can relate to the problem of obtaining a smooth surface especially on the inside of bowls. Several things have helped me improve. Learning how to sharpen the gouge or scraper may be the most important. Learning how to present the tool is the other key. Having someone show you how it is done is by far the best way to learn. A local chapter of AAW, a class, even tapes or CD's can be very helpful. It is hard to use words to describe the best techniques in a way that is understandable (unless you already know the technique) so to save yourself weeks of frustration, get some help. Besides, getting together with another woodturner is usually a lot of fun.

 

[MichaelMouse]

Sharp tool and bevel riding.

That said. a faster speed is usually a cleaner cut for the same reason I have to watch turninng the spiral - tool feed rate. With a faster lathe speed and the same cutting motion you take smaller lighter cuts which are cleaner cuts.

Yep, tool control in many forms is the key to good outcome. Giving the piece the advantage in inertia or leverage over you isn't really necessary in 99% of the cases, so keep the speed where you can feed and keep the rest close.

Disagree on the lighter cut business as relates to speed, however. That's what the bevel is for, to limit the depth of cut. Otherwise we might as well scrape, and we all know what happens when we push a scraper too hard.

 

[CTutor]

Harley, It might be how you are using the gouge. Try this. Lower your toolrest below the center of the bowl. Put the Ellsworth gouge at 90 degrees to the rest up and down with the flutes facing you. Tilt the top of the gouge 50 degrees to the left (if you are using a true Ellsworth grind 62-65 degrees but wheos being picky here) then rotate the gouge counter clockwise so the flute that was on the left is now on the right and facing the wood. Now lower what is now the left wing of the gouge so it just touches the spinning bowl. Keep the right flute about 1/8 inch above the wood so only the right (old left) flute is shear scrapping the wood. You will be able to get a shaving about the thickness of a human hair that way. Most nobbys will be simply sheared away.

 

[HarleySteve]

Thanks All

I am going to the local meeting on the 29th and I have already talked to the person running the meeting. He told me to bring my tools in, they would check to see if I have sharp enought and will watch me work so, they can make corrections, dang nice of them. Can not wait to go. After reading what all everyone had to say I think its my use of the tool and how sharp it is. Speed is not the problem. Once again many thanks

 

[DeanGThomas]

In addition to the quality of cut, you should be concerned with safety... appropriate safe speed for a balanced object: RPM x diameter in inches should equal a number between 6,000 and 9,000. (That's from memory. I hope someone will supply the correct numbers if I'm wrong.)

Pretty good memory. If you care to, you can visit THIS LINK for a PDF of an Excel spreadsheet of this little formula, set up for pieces from 2" to 32".

I heard this theory promoted by Dale Nish and give him credit when I share it with others. It's a good rule of thumb from what I deem to be a pretty reliable and safety minded source.

If you want more, including the explanation that Dale offers when he teaches it, drop me a note OFF FORUM and I'll provide the whole enchilada.