Variable speed lathes

[Burbank Bill]

Hello;
I have a question about speed control on the Nova 3000 lathe, How do the numbers on the speed dial relate to RPMs or are they just arbitrary? How do you know what speed you are turning at? This never bothered me before because I turned realatively small spindle turnings which a fast speed is good but I want to start bowl turning and am concerned about the speed of the wood. Any help would be welcome.

Bill

 

[Jim Carroll]

The speeds indicated are spindle speed.
With faceplate turning you have to remember the larger the diameter the faster the peripheral speed.
With variable speed start slow then build up till you are at a comfortable speed for you and the timber. This can vary from peice to peice depending on the makeup of the timber.

 

[MichaelMouse]

Sort of confused by your question.

The Nova 3000 is a step-pulley lathe, where the ratio of the motor to spindle pulley is multiplied by the nominal speed of the motor. For example, a motor to spindle ratio of 1:8 with a 1725 motor would yield a theoretical speed of 215. The 3000 does not have a "dial" in its standard incarnation, which means you may have a variable-speed motor in addition to the pulleys. To further complicate the issue, you may have an AC or DC motor. If you have the DVR head, of course, it's all electronically variable.

However you are equipped, make the piece as balanced as you are able prior to turning on the motor. Remove where you can with the saw or bore holes where you'll have space anyway to lighten, and then start low. There is no merit whatsoever in roughing an out-of-balance piece, no matter how often people may brag about it. There is additional danger and wear and tear. If you have a straight 1725 motor, start at second from largest spindle pulley, which gives about 360 in 60Hz motors. This is slow enough for most reasonably balanced pieces, without being so slow that you have to get a haircut after fifty revolutions.

If your motor is of the variable speed variety, you'll probably want to start at the same pulley setting, so you can get enough RPM to cool the motor. Some worry a lot about the torque curve, but if you're pressing so hard that you slow the motor, you're not making a good cut anyway. If DVR, select something around 350 and begin there. You may add speed if you care to, or lower it if it seems appropriate.

If it seems too fast for you - it is! Rules to live by. Remember, energy available to bust your chops varies with the square of velocity. Larger the diameter, greater the leverage of a heavy spot, as well. Smooth and slow is the way to go.

 

[hockenbery]

Bill,
For the first couple of bowls make your blanks a disc 2-3" thick and 8" diameter.

Actual RPM will vary a lot from lathe to lathe and blank to blank
for roughing an out of balance piece you want a speed that is fast enough for efficient cutting and slow enough not to vibrate too much.

To find the best speed:
1. Set your belt on the slowest pulleys. (small one on the motor Big one on the spindle) This gives you the most torque and finest ajustment of speeds.
2. With the lathe off turn the speed all the way down.
3. Mount the blank and set the tool rest in place rotate the piece for clearance.

4. Turn the lathe on and bring the speed up until you have a bit of vibration then back off the speed and start cutting. Sometimes there is a slightly faster speed that has less vibration but don't try this on the first few.

5. As you get the blank into round you can increase the speed.

All of this works a lot better if you get to see someone else do it or guide you through it.

happy turning,
Al

 

[Burbank Bill]

I have the Leeson dc motor and variable speed drive. The dial is calibrated 10,20,30 to 100 with 4 increments in between so I guess I take it that 10 would be 100RPM and 100 would be 1000RPM. If I was using the pulley system instead of the variable there wouldnt be any problem because it is clearly marked as to what speed each set of pulleys are.

Thanks for all the help

Bill

 

[Bill Grumbine]

Bill, there are only a few lathes out there that show the actual spindle speed, and it is not really important anyway. I tell my students to start the lathe out as slow as possible and turn it up to the point where either they are comfortable with the speed or the lathe starts to vibrate. In the latter case, I tell them to back it off until it stops vibrating, and from that point begin the roughout. While the advice has been offered that it makes no sense to turn out of balance pieces, if you stick with that, you will not be turning much in the way of natural edged, winged, or other artsy type pieces.


Bill

 

[MichaelMouse]

I have the Leeson dc motor and variable speed drive. The dial is calibrated 10,20,30 to 100 with 4 increments in between so I guess I take it that 10 would be 100RPM and 100 would be 1000RPM. If I was using the pulley system instead of the variable there wouldnt be any problem because it is clearly marked as to what speed each set of pulleys are.

There are pulleys, are there not? I suspect that the numbers represent percentages of full power, with the motor's maximum speed available on the web at places like http://www.electricmotorwarehouse.com/dc_motors.htm. If you have 108023, it's a 1725 motor at 100%, and all the printed values are good. Use the pulleys as your base, fiddle if you feel you must in-between.

I suppose if you were curious, you could work out the pulley ratios and chart up the speeds. Not that it makes much difference, really. Because you can figure approximate values does not mean you must. If precise values are that important to you, install a tachometer on the spindle.

 

[Burbank Bill]

I understand now. I always kept the belt on the fastest speed and did not realize that all I had to do was divide the speed (3600) by ten and that would give the speed at any of the 10 posistions. So at the 3600 RPM setting each setting indicates 360 RPM. I also realize that I can change belt positions and get different speed options. I know there are handheld Tachs for checking RPM but how would you mount one on the lathe.

Thanks
Bill

 

[john lucas]

Bill You have gotten some good information. I'll add one more. If you have a DC motor you will have much more torque when you slow the speed down if you change to the smallest pulley on the motor. As bill Grumbine said just turn at the speeds you feel comfortable turning. Don't worry so much about what speed it is. As turnings get larger the outer surface is traveling faster so in affect you are turning at a different speed even if the lathe rpm stays the same.

 

[hockenbery]

I know there are handheld Tachs for checking RPM but how would you mount one on the lathe.

Bill,
The point most of the responders were making is that you never need to know the speed.

The only use I have seen for a tach was in one of those magazine Lathe test articles where they checked the max speed against the manufacturer specs.

One of the most speed sensitive operations that I have done is thread chasing.
I have had success using Alan Batty's specific speed setting - Slow the lathe down until you can see the threads on the spindle.

happy turning,
Al

 

[Burbank Bill]

Thanks for all the help you all have provided. I am going to order Bills video today,I should be able to learn alot from it. Sorry for the slow reply been swamped at work.

Bill

 

[Bill Boehme]

Burbank Bill,

The following link will take you to one of the recent issues of our club newsletter where I wrote an article on making a simple lathe speed strobe:
Simple Lathe Speed Strobe
There is a link in the article to a "PDF" file that includes a strobe disc that can be pasted to a six-inch faceplate (you can't click on the link -- just copy and paste into your browser). You will also need a fluorescent light with a magnetic ballast. Electronic ballasts will not work. Turn out all of other lights when checking the speed. The strobe will give you only certain distinct speeds so it does not work well with a lathe that is not variable speed.

Bill