How do I know when my lathe speed is wrong or could be better?

Question

I'm about a year into learning to turn on an inexpensive mini-lathe. I mostly turn small lidded boxes or bowls. With both boxes and bowls, I like them big, so I'm often within an inch or two of the width capacity of the lathe.

I turn mostly walnut or spalted maple, though I'm not sure if that makes a difference.

The machine is a great starter lathe, but because it is a pain to change speeds, I end up using the slowest speed almost all the time.

My question is, am I missing something when I go from roughing all the way to final sanding/polish using only the slowest speed?

The main problems I notice in my finished pieces are tear-out that leaves a rough feel on two sides of the piece, no matter how long or attentively I work my way up the grits (I start at 80 and go all the way up to 800 most of the time).

I guess my pieces take longer than the folks I admire on Youtube, but I can't tell if that is due to the slow speed, my hesitation, my tools, or the videos' editing...or a combination of all three.

It would be really helpful to hear the ways you recognize while you're working that you can or should increase the speed.

Thanks in advance!

Answer 1

Yes, speed can make a huge difference. My first lathe was a PSI midi-lathe (not mini) and it required stopping the lathe, opening a panel, and switching the belt to another set of pulley's. A pain. However, you need to do it.

While it is recommended to have it slower for unbalanced pieces (roughing it to a cylinder), speeding it up will make a lot of things better.

Slower speeds don't always cut as cleanly and need a sharper blade to do a good job.

To improve your finish, you can do several things. speed up the lathe will allow for cleaner cuts. When you get near the end, sharpen the chisel and the will also help make cleaner sharper cuts and not tear the wood, which causes the rough spots, especially on the end grain. Last by going faster it dramatically improves the ability to sand the piece quickly and well. I tend after all the cutting is done, to speed up the lathe anyway just for the sanding. It really does help a lot. The time it takes to change the speed is made up in how much faster you can get your piece finished and it looks so much better.

Answer 2

am I missing something when I go from roughing all the way to final sanding/polish using only the slowest speed?

Try increasing the speed and see for yourself. You could even just pay attention to the difference between working at the perimeter of a large piece compared to working at the center -- the linear speed will be 5x greater at the edge of a 10" diameter piece than it is 1" from the center.

tear-out that leaves a rough feel on two sides

If you're getting actual tear out, more speed (and very sharp tools) will help. That said, end grain feels different than long grain, so you're always going to have some difference. To get a smooth finish all the way around you'll need to fill the pores with a grain filler.

How do I know when my lathe speed is wrong or could be better?

You need to try working at different speeds so that you know which speeds give you the best results in which situations. If your tools are sharp but aren't cutting as well as you think they should, speed is likely part of the problem.

Answer 3

I've found that it is best to start out with a slow speed at first while the piece you are working is still not rounded. For bowls, usually they are pretty wobbily, so turning up the speed is a bad idea since the lathe will start jumping around.

However, once the piece is nicely rounded and the center of mass is more or less in line with the axis of rotation, it is time to turn up the speed. Increasing speed will result in a cleaner cut and smoother finish, in my experience.

Also, are you keeping your tools sharp enough? That could explain the tear out. Additionally, I like to go from using gouges for roughing and finishing using scrapers. After using the scrapers, I've usually got a pretty smooth surface that requires little sanding and burnishing.

Answer 4

I have the same lathe and agree it's a great starter lathe, and that the speed change is a major PITA!

I also don't change the speed often (or at all really), but instead of leaving it on the lowest speed, I leave it in the middle - slow enough to not be too dangerous for starting, but fast enough to get a reasonable cut.

To answer your question directly, I think the general rule is you should go as fast as you (safely) can as it will cut cleaner and faster. You only want the lower speeds for starting large, untrue forms.

Answer 5

The speed of the lathe is important for a couple reasons. Safety of course, but also the smoothness of the bowl gouge cut.

There are charts for recommended speeds but there's an easier way. The speed of the lathe, when turning bowls, should be turned up to the point where vibration begins and then backed down until the vibration is removed.

If you have a fixed speed lathe you may need to experiment with various belt settings. Generally, the lathe needs to be slowest when you first start a bowl blank as it will usually be a bit unbalanced. Once the bowl shape is formed, the speed can be safely increased. I don't turn a bowl over 1,000 rpm. regardless of size.

As for the two rough areas on your bowl, YOU FOUND IT. THE WOOD BOWL TROUBLE ZONE!!! I'm not kidding. This has bothered me for some time and nobody talks about it. Check out this article that covers the whole thing - https://turnawoodbowl.com/wood-bowl-turning-trouble-zone-dirty-little-secret/

Good luck with your bowl turning!