• We just finished a major forum upgrade. Please check out the "Whats New and Help" Thread at https://aawforum.org/community/index.php?threads/forum-upgrade-whats-new-and-help-march-2021.17436/ If you are having problems using the forums, please clear your browser cache and that should clear up any issues. Otherwise post in the Help Thread or email us at forum_moderator@aawforum.org. Hope you enjoy the refreshed site!
  • 3/30/21 - We finished what was hopefully the last part of the forum upgrade we started earlier this month, the rebuilding of all of the permissions. In our testing everything seems to be working correctly but if you have any problems please post in the "Forum Technical Support" forum and we will take a look at it. You will also see a few changes with the main forum index. We have moved the AAW Member Forums to their own group and the Marketplace Forums to their own group. This simplified the permissions configuration for the forums and hopefully it will make the forums a little easier to naviagate. Thanks!
  • Gallery Images: Title and Description Required

    Please read the new sticky announcement HERE for full details.

  • Welcome new registering member. Your username must be your real First and Last name (for example: John Doe). "Screen names" and "handles" are not allowed and your registration will be deleted if you don't use your real name. Also, do not use all caps nor all lower case.

Bowl Bumps

Joined
Jul 24, 2008
Messages
403
Likes
43
Location
Montfort, Wisconsin
When I make a bowl many times try as I might I'll find a small bump inside the bowl, typically about half way down. When it's on the lathe I'm sure it's fine only to find when I take it off and finish it, there it is. I use a negative rake scraper and sand of course. I've even found a small bump that was only on one side of the bowl and didn't go all the way around. I suppose end grain vs cross grain or possibly rot?
Point of information: I have arthritis so most of my work is done while seated so the swing your hips is a wish for me. My cuts are not smooth but I try to remediate with the NRS and sanding.
 
Joined
Jan 22, 2009
Messages
189
Likes
105
Location
TN
Dave,
I have a confession, I sand too much. Could it be that the bumps you find are from over sanding resulting in an uneven surface between soft/hard grain?
 
Joined
Feb 12, 2018
Messages
211
Likes
100
Location
Millington, TN
Sounds like the bowl is going out of round a slight amount. Green wood moves a lot as you know, but so can dry wood as you relieve the internals stresses. Try leaving as much wood in the center as finish cutting and sanding a small section at a time starting from the lip. Try not to go back to a finished section or you may get cuts that don’t go all the way around as the bowls gets out of round. If this doesn’t help then post some pics of your problem area.
 
Joined
Jun 6, 2018
Messages
913
Likes
365
Location
La Grange, IL
It might be informative to see when in your process the bump develops. I haven't tried this, but an inexpensive contour guage might allow you to see the curvature at several stations along the inside.


Another trick for finding high spots is to position a tool rest (preferably curved) 1 or 2 mm away from the bowl surface. Then slowly hand rotate the bowl. Your eye is very adept at accessing changes in that tiny air gap. You may just need another pass or two from the NRS.
 
Joined
Aug 14, 2007
Messages
3,281
Likes
997
Location
Eugene, OR
Well, your fingers can make an excellent feeler gage, and a shear scrape is great for taking out smaller bumps. I get mixed results with NRSs. They are still scrapers and work best across the bottom of the bowl, and some what okay up the sides. I do have a video dedicated to shear scraping on You Tube.

As for getting a bump on one side and not the other, first cause that comes to mind is too much pressure when 'rubbing' the bevel. "The bevel should rub the wood, but the wood should not know it." Hard to put into practice.... Some times a card scraper can be handy for removing those little ripples down the sides of the bowl.

robo hippy
 
Joined
Feb 28, 2021
Messages
84
Likes
38
Location
Roulette, PA
Not mentioned so far, and depending on the kind of bump, and the wood, but might also want to verify sharpness of tool before making final pass.. I frequently got a "lump" that seemed to follow right over a section of the grain in Ash especially (it didn't follow any cut paths) .. It also caused tool vibration as the tool hit that bump and bounced away .. I went through endless "trial and error" to see if it was tailstock, headstock, balance, etc, etc.. (I was thinking runout in a bearing somewhere) .. It finally occurred to me that if the tool is bouncing over wood instead of cutting it, maybe my tool was not sharp enough.. (Duh!?) even after grinding, I had that happen.. then I decided to touch up the ground edges of my bowl gouge (only grinding wheel I got is very coarse grit, so it leaves very visible striations in the grind) with a 300 grit diamond card (credit card sized hone) .. which solved the problem! I am guessing it is just because Ash is such a hard wood (I'd suspect I'd have the same issue with Oak, if I had any green) ... But - just because it is fresh off the grinder and correctly ground, doesn't mean the edge is truly sharp.. I suppose I could solve that if I went and got a finer grit grinding wheel, but as my grinder is just a re-purposed lawnmower blade sharpening machine, I figured I'll just wait and save up the money to buy a Rikon , which looks to be about the same cost as buying a couple of quality Aluminum Oxide wheels.. and that Rikon comes with the nice wheels already, so... buy 2 wheels and get a free grinder? :)
 
Joined
May 4, 2010
Messages
1,234
Likes
517
Location
Bozeman, MT
One thing I've recently discovered is that watching the shavings as I gently draw the NRS over the inside surface can tell me if/where there is a ridge or depression. I think it makes a difference how you've shaped the end of the NRS, as you need to keep the edge of the scraper in continuous contact with the curve. Immediately after you pass a high spot or ridge, there is a momentary halt in the shaving generation, indicating you are passing over an area with slightly greater diameter. It's taken me a long time to realize this, as for my old eyes it appears fairly subtle. I suspect this is obvious to most other turners. In any case, if you watch the edge as you draw the NRS over the surface, you should see a continuous and uniform production of shavings. Maybe that will help.
 
Joined
Jan 18, 2008
Messages
33
Likes
9
Location
Chicago Heights, Illinois
Ring pours woods and fast growing wood have summer vs winter density in the grain. First sanding should be done with a firm density form and s stiff backed sand paper. They will not sand into the softer Summer grain, but glide over it. 220 and up will be ok with softer pad and paper.
 
Top