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Spindle turning jitter

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theallan

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Hi all,

I'm trying to turn a baseball bat and running into some issues and I was wondering if anyone might have some advice.

The bat is basically the maximum my lathe bed can work with, and I'm using a drive spur at one end, and a live center at the other - they are slightly off center from each other when push next to each other.

When turning the bat, I get a lot of "jitter" and resting the tool on the top (mainly using a skew for this) I can feel it bouncing around. You can see a spiral on the bat when it is stopped:

1625848723721.png


There is no way I'm moving the tool fast enough along the rest to cause a spiral like that (the speed is 7 out of 12 - not sure what that is in rpm!). The grain is also ripping somewhat, presumably due to whatever is causing the spiral, even with a freshly sharpened skew.

1625848937169.png


Presumably the wood will be under stress between the two centers, but I don't think I've got it overly tight, and loosening it off a bit seems to make no difference.

Does anyone have any ideas why this might be happening?

Thanks,
Allan
 

minilathe22

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Make sure you are using a high enough speed and regularly sharpening your tools. To get rid of final imperfections you could use sandpaper on a flat block of wood.
 

Jacob

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Everybody gets it at some time it's really common. A bit of vibration sets off the spiral and once it's there it gets sort of amplified as you carry on turning. Change speed, change/sharpen tool, use sandpaper etc as minilathe22 says above
 
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MARK.B.

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If your two holding points are slightly off center as you say,i would think you will always have a wobble problem:eek:I could be wrong but it seems to make sense in my head:LOL:
 

Robbo3

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You possibly either have vibration or are pressing too hard with the tool. The second can cause the first.
Seasoned turners steady the wood by cupping it in their fingers whilst holding the tool rest or tool post.
A centre steady isn't too difficult to make.
 

Inspector

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The misaligned centres only become a problem when you try drilling with the tailstock.

There is a harmonic vibration that occurs from the suggestions above synchronizing with the resonance of the lathe. The suggestions above may also fix it as will dampening the vibration. If you have a light weight lathe putting a couple sandbags on the bed might help as would more weight in the stand it is on. You will just have to play with different things starting with the easiest like different speeds, sharper tools, the weight I mentioned, making a steady rest, wearing yellow socks and changing your tongue from the left cheek to the right. Keep experimenting and you will get it sooner or later.

Pete
 

JimB

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The misaligned centres only become a problem when you try drilling with the tailstock.

There is a harmonic vibration that occurs from the suggestions above synchronizing with the resonance of the lathe. The suggestions above may also fix it as will dampening the vibration. If you have a light weight lathe putting a couple sandbags on the bed might help as would more weight in the stand it is on. You will just have to play with different things starting with the easiest like different speeds, sharper tools, the weight I mentioned, making a steady rest, wearing yellow socks and changing your tongue from the left cheek to the right. Keep experimenting and you will get it sooner or later.

Pete
I'd go with all that advice except the yellow socks ;) You could also try moving the drive spur through 90 or 180 degrees and see if there is any difference and even take out the live centre and do the same, checking for crud first before replacing. Then there's exorcism and the last resort, yellow socks;)
 

chemist_dan

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I see this phenomenon occassionally and it was only yesterday I was re-reading through Mike Darlow's Fundamentals of Woodturning and found an explanation. I don't know if its the same issue you observe, but I've attached a picture of the relevant pages.

My first thought was sharpness, but I was getting fine angel-hair type shavings from the skew so considered either vibration issues (too thin a cross section for the length of wood) or tool presentation.

On a side note I highly recommend all of Mike's turning books; the only one I don't have is "Turning Chessmen" but I will acquire when needed.

PXL_20210710_075356060.MP.jpg
PXL_20210710_075546935.MP.jpg
 
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Paul Hannaby

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It's probably down to the way you are using the skew. Try a cut with a roughing gouge or a spindle gouge. If those produce clean cuts, that confirms it.
 

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