Chatter Marks and Spiraling help

[Timm De]

I know this has been discussed(to death you say?) before and searched the forums for answers. If I understand correctly my issue seems to be to much pressure and trying to go back to the walls after I have removed to much material already. The picture is from the second turning of black walnut that was dry.

The two issues shown are:
1: spiraling at the rim which was easy to fix with another light pass with a freshly sharpened bowl gouge at 60 degrees and applying a light pressure to the outside of the bowl with my finger
2: The dotting which I think is referenced by the name chatter marks? If there is a better term please let me know. From reading it seems the marks are from applying to much pressure with a neg rake scrapper (grind is 20/70 per dways recommendation). Not sure if they are burnished or tiny dimpled cuts. These i had to sand out with my drill with 80 grit which was a pain and left scratch marks.

I turned another black walnut bowl this morning and had a lot of the "chatter marks" on the walls of the bowl. I swear I had decent material left when flushing up the wall and this time I tried to apply as little pressure as possible to get a cut (and just sharpened the neg rake). My mantra while working was having the work meet the tool as opposed to pushing the tool into the wood. I made sure to have the tool rest centered and angled the neg rake slightly down. Again I sanded and got them removed but I really would like to not have to do that. The reason I am using a neg rake scrapper to remove the lines you can kind of see at the transition point in the bowls base in the photo.

My thinking is for the next bowl my goal is to remove as little material as possible and keep the wall of the bowl as line free as possible trying and practicing good gouge technique where you cut with left side of the wing(still learning this and its going okay) and us the neg rake sparingly as I go inch by inch down the wall. Is this the correct way to go about it and progress in my cutting skill? Maybe I miss informed and should not be using the neg rake on the walls at all?

I am mainly doing a sanity check on my diagnosis and looking for advice/feed back/good video discussing these issues. Not sure watching glenn lucas's "A trio of bowls" video for the 10th time is going to help here.

side note: Not sure if walnut is prone to this or not but the spalted maple I also turned that day did not seem to have the chatter marks or at least I could not see/feel them

 

[John Torchick]

Following this thread.

 

[John K Jordan]

@Timm De One solution might be to get someone to look at your tools and watch your technique. Might sound like a cop-out but there are multiple possible issues. Hard to guess but might be easy to spot.

 

[Timm De]

@Timm De One solution might be to get someone to look at your tools and watch your technique. Might sound like a cop-out but there are multiple possible issues. Hard to guess but might be easy to spot.

Fair point. I will ask one of the members at the club to watch me turn and look at the tool as well.

 

[robo hippy]

Well, that for sure, is chattering. Most of the time it is from too heavy on the bevel rub. "The bevel should rub the wood, but the wood should not know it." No clue who said it, but I use that a lot. Not sure how big that bowl is, but on larger bowls, you need to finish turn in stages as in finish cut down an inch or maybe 2, then rough out the next inch or two, then finish cut that inch or two, and continue to the bottom. Wall thickness can play a role in this as well as a dull tool. When using your fingers on your left hand to stabilize the wood bowl, finger pressure should equal bevel pressure. If your fingers are getting hot, then you are pushing too hard. Makes me think of the old song by the Seeds from the 60s....

robo hippy

 

[John K Jordan]

...chattering. Most of the time it is from too heavy on the bevel rub.

And I always round the back of the bevel so it doesn't contribute to problems, both bowl and spindle gouges.

I don't round as much as Chris Ramsey - this his is grind for turning a cowboy hat. Ground by hand with no jig. I highlighted the actual cutting bevel with red in the photo.



JKJ