Vibration issue?

[mark ahlenius]

Hi

I have an older Delta Rockwell circa 1953 wood lathe which IÂ’ve been using for several years now. IÂ’ve learned to turn bowls on it and it was working fine. I rebuilt the unit with new bearings and a new motor system. I mainly have been doing twice turned bowls, from logs which I have cut, turned the 1st pass then dried the bowls and did the 2nd pass at least 6 - 8 months later. IÂ’ve experienced no issues during this process until lately.

Now over the past week, IÂ’ve tried to do the 2nd pass turning of the bowls (cherry, walnut and birch) and each time I start to get vibrations on the outside of the bowl near the rim. When I first put the dried bowl on the lathe I use a wooden plate mounted on a flange on the lathe. It has carpet foam glued on the board and I use the tail stock to press the bowl against the flange so I can true up the bowlÂ’s tenon and also the outside of the bowl. While doing this I have no chatter issues when truing up the outside of the bowl, even near the rim.

When I take the bowl and mount it in my 4-jaw chuck (Super Nova 2) and then try to trim the outside of the bowl, I keep getting chatter marks within 1 inch or so of the rim. I find no play in the spindle shaft in the headstock, nor wobble in the chuck. The sound it makes when I am truing the outside, is ear piercing. IÂ’ve been trying push cuts (bevel riding) and pull scraping cuts with a spindle detail gouge, but still the problem occurs. These are the exact same cuts IÂ’ve used successfully many times before.

Any suggestions as to what might be the problem(s)? I do think its something to do with the lathe and not my technique.

Please see the pix below.

Thanks in advance.

Â’mark

[Brice Rogers]

Does the vibration only occur when the bowl inside and outside has been turned and the wall is getting thin? If so, you are getting classic wood vibration. Often, as you are cutting, you can rub one of your fingers on the other side of the bowl to dampen the vibration.

[mark ahlenius]

Does the vibration only occur when the bowl inside and outside has been turned and the wall is getting thin? If so, you are getting classic wood vibration. Often, as you are cutting, you can rub one of your fingers on the other side of the bowl to dampen the vibration.

I had not started turning the bowl inside yet when these vibration patterns occur. I was just reshaping the outside of the bowl first when I remounted it in the scroll chuck. For the bowl shown, it was at least 3/8” thick when this is occurring. I added a picture below.

What is so strange is that I’ve not had this issue before and have made at least a dozen bowls using the green-turned process.

I’ll try your suggestion to try to dampen the vibrations using my hand but normally I have both hands on the gouge.

thank you Brice.

[Prashun Patel]

The size/thickness of that bowl does not look like it should cause vibration.

Are you SURE you are sharp? Do you get the same problem at slower speeds? Are your jaw screws tight?

[mark ahlenius]

The size/thickness of that bowl does not look like it should cause vibration.

Are you SURE you are sharp? Do you get the same problem at slower speeds? Are your jaw screws tight?

Yep, I’ve resharpened them and honed as well. I can try slower speeds, was running between approx 1000 and 1100 rpm.

thanks for your response

[Reed Gray]

This may be a case of too much bevel pressure, which can cause vibration issues. It is really astounding how little pressure you need. One good exercise to practice is the one hand push cut. If you are gripping at all with your hand you have on the shaft of the tool, that is too much pressure. It is a bit nerve wracking when first learning it, but once you get the hang of it, it opens up a whole new world of tool control.

One other possibility is that the chuck jaw screws have worked loose. That does happen some times.

robo hippy

[mark ahlenius]

This may be a case of too much bevel pressure, which can cause vibration issues. It is really astounding how little pressure you need. One good exercise to practice is the one hand push cut. If you are gripping at all with your hand you have on the shaft of the tool, that is too much pressure. It is a bit nerve wracking when first learning it, but once you get the hang of it, it opens up a whole new world of tool control.

One other possibility is that the chuck jaw screws have worked loose. That does happen some times.

robo hippy

Ok I will try that approach. One thing I noted was that once there are these little “gouges” in the wood from the vibrations (see pix) that then when the bevel rides on them its riding on a bumpy surface, even though the cutting edge is ahead of the bevel. So it makes it a bit more challenging to remove these grooves. So for that I changed to a pulling or scraping cut from the other direction but that did not improve it much either

thanks

[John K Jordan]

Ok I will try that approach. One thing I noted was that once there are these little "gouges" in the wood from the vibrations (see pix) that then when the bevel rides on them its riding on a bumpy surface, even though the cutting edge is ahead of the bevel. So it makes it a bit more challenging to remove these grooves. So for that I changed to a pulling or scraping cut from the other direction but that did not improve it much either

thanks

I agree with the likelihood of bevel pressure, common with skew chisels. Pressure against the bevel can deflect the cutting edge a tiny bit causing a bump which the bevel hits causing another bump and so on. Difficult to get rid of at times. With a skew chisel on a spindle I usually make a pass with the short point of the skew, not possible with the bowl gouge.
One thing I do is round the heel of the bevel on bowl and spindle gouges, decreasing the likelihood of bevel contact. Contrary to some advice, the bevel is not "rubbed" on the wood and actually shouldn't contact for more that a tiny, tiny bit. Look at Mike Darlow's photo of how much of the tool is optimally in contact with the wood (fantastic book by the way: Fundamentals of Woodturning, a must-have and must-read IMO):

Darlow_peeling.jpg

With some practice and a light touch the tool control needed for this method of removing wood becomes second nature. Also, it's widely accepted that developing expertise in spindle turning will improve all types of turning.

Also, you might try a scraper to remove the bumpy surface before making additional cuts with the gouge.

If something related to the chuck, lathe, or holding is loose, you might be able to tell by grasping the mounted bowl and see if various motions cause any movement. If I suspect something has gotten significantly out of round I check the run-out on both the chuck and a smooth part of the turning using a dial indicator, turning the work by hand of course. This can also reveal any wiggle in the system.

BTW, I often hold tools with one hand, spindle and bowl gouges, skew chisels, etc., often for cuts other than rigorous roughing. What works best for me is holding the shaft of the tool fairly close to the cutting end with my right hand then pushing the end of the tool handle into the underside of my forearm. This frees up the other hand for support when turning thin spindles, thin bowl, goblets, boxes, and bells, and more. Here's an example of one-handed grip turning a thin spindle with a 1/2" skew chisel. The end of the (relatively short) tool handle is supported by underarm pressure, although not visible in this photo. (All this is to control vibration, a real problem with thin spindles.)

D02_thinner_IMG_5030.jpg

Richard Raffan has some advice about using too much pressure for this type of support: since the fingers of the left hand have to balance that pressure from the tool, if they get hot there is too much tool pressure.

BTW2, I've seen expert turners showing off, er, making continuous finish cuts down the inside of a bowl by holding the tool between thumb and one finger at the end of the handle, guiding the cutting end with fine movements. This may require some practice!

BTW3, one other possible solution: I've switched from the bowl gouge to using the Hunter tools for most face work, bowls, platters, etc. The tiny round carbide bit is incredibly sharp and works just like a gouge. The bevel is very short and has never been a problem. They can also be used as a scraper if needed. And never needs sharpening. I like the small Hunter Hercules tool for most work. Another advantage is the Hunter throws the shavings to the side while some cuts with the bowl gouge direct hot shavings down the flute toward my hand!

JKJ

[Dave Keele]

You mentioned new bearings. Did problem start after replacement? This happened to me. I took spindle and bearing to machine shop and had old bearing removed and new installed. I think they pressed on the outer race vs the inner race.... came back worse than when I took it in. I ended up buying a new bearing and clam-shell puller and doing it myself. Fixed the vibration problem.