Vibration issue when turning a long cylinder

[Mark Ahlenius]

Hi
I am trying to make a few French rolling pins on my PM 3520 lathe. The maple blanks are 20” long, and once I get them round, I keep having issues where vibration patterns keep appearing in the work piece. I can feel them as they are being made and this is while I am trying to get the piece down to diameter. The piece is approximately 2” in diameter (but shrinking!). The picture below show the issue.

All my tools are quite sharp and I have tried regrinding them multiple times. I get this issue whether using my spindle roughing gouge, either of my skews, or a spindle gouge. I have tried to tighten the blank between centers as I have a drive spur on the headstock and a bearing type spindle on the tailstock. I have made sure that the headstock is solidly tightened, and the tailstock as well. I’ve tried tightening the piece between centers and also loosening it a bit, thinking it was too tight. I’ve tried making lighter cuts, going slower, etc, but not found a working solution just yet.

I would really appreciate suggestions on what I may be doing wrong and what I could try.

Thanks you all

‘Mark

 

[Brian Gustin]

I suspect applying too much pressure on the bevel trying to control the skew.. (assuming it is a skew in use) but that pattern is typically just too much pressure or too much feed rate or getting off the bevel... JMHO Perhaps some additional practice on shorter practice pieces focusing on holding the tool so lightly that someone could swat it out of your hands - can't have a death grip or that's also the results you often get... then practice just letting it float on the bevel and let the wood come to the tool - barely even have to push the tool it sort of naturally "creeps" itself along so that you pretty much have to deliberately hold it back to get it to stop cutting... and after that is mastered, it pretty much comes down to the wood and the tailstock tension... learning the "free hand steady" can also be useful (That is, using your tool rest hand to lightly press on the spinning wood and a thumb to draw the edge lightly in to where you want to cut.... is best way I can describe it)

 

[Mark Ahlenius]

I suspect applying too much pressure on the bevel trying to control the skew.. (assuming it is a skew in use) but that pattern is typically just too much pressure or too much feed rate or getting off the bevel... JMHO Perhaps some additional practice on shorter practice pieces focusing on holding the tool so lightly that someone could swat it out of your hands - can't have a death grip or that's also the results you often get... then practice just letting it float on the bevel and let the wood come to the tool - barely even have to push the tool it sort of naturally "creeps" itself along so that you pretty much have to deliberately hold it back to get it to stop cutting... and after that is mastered, it pretty much comes down to the wood and the tailstock tension... learning the "free hand steady" can also be useful (That is, using your tool rest hand to lightly press on the spinning wood and a thumb to draw the edge lightly in to where you want to cut.... is best way I can describe it)

Ok Thanks Brian, I’ll give that a try. Appreciate the feedback.
‘Mark

 

[Steve Tiedman]

@Brian Gustin, well said.

It takes so little force against a spindle, esp. when held between 2 center points, for the spindle to flex away from the axis it is spinning on, and that is the classic pattern I see when it happens to me. Very, very light cuts when it gets to that point. The tool should almost be teasing the wood to come make the contact with the edge rather than the tool going after the wood, metaphorically speaking.

A spindle steady rest would help as well, store-bought or homemade.

I had a 1" diameter x ~38" stick of hickory (walking stick/cane) that was exceeding my patience level with this. I threw in the towel and went to abrasives instead. Hickory, meet 80 grit...!

 

[Mark Ahlenius]

@Brian Gustin, well said.

It takes so little force against a spindle, esp. when held between 2 center points, for the spindle to flex away from the axis it is spinning on, and that is the classic pattern I see when it happens to me. Very, very light cuts when it gets to that point. The tool should almost be teasing the wood to come make the contact with the edge rather than the tool going after the wood, metaphorically speaking.

A spindle steady rest would help as well, store-bought or homemade.

I had a 1" diameter x ~38" stick of hickory (walking stick/cane) that was exceeding my patience level with this. I threw in the towel and went to abrasives instead. Hickory, meet 80 grit...!

Thanks Steve, appreciate the suggestions.
‘Mark

 

[Wyatt Holm]

Sharp tools and light pressure. You can use your hand to counter the pressure of the tool. Richard Raffan does it quite regularly. And if nothing else works you could use a steady rest, they are annoyingly slow to work with.