Trouble getting inside bottom of a bowl flat.

[Jerry Lear]

I have been having trouble getting the inside of my bowl flat. I have used the bottom of the bowl gauge, regular bowl gauge and scrappers.
It seems no matter what I try, I end up with slight lumps and sometimes raised center. I know I am doing something wrong but I can't seem to get it right! Any help would be appreciated.

Jerry

 

[odie]

I have been having trouble getting the inside of my bowl flat. I have used the bottom of the bowl gauge, regular bowl gauge and scrappers.
It seems no matter what I try, I end up with slight lumps and sometimes raised center. I know I am doing something wrong but I can't seem to get it right! Any help would be appreciated.

Jerry

Funny that you'd ask this question just now, because I'm running a related thread about the differences in a NR scraper and standard scraper right now.......and, this is exactly where the NR scraper excels for my bowls. Use the NR scraper after the gouge work, and your sanding experience will be greatly improved, because you won't have to rely on sanding to even the surface.

If you haven't been using NR scrapers for smoothing/evening out the surface of bowl interiors, you should give them a try.

-o-

 

[Bill Boehme]

Getting a perfectly flat surface in the bottom of a bowl is often an exercise in futility especially if you want to apply a glossy finish. My suggestion is consider having a smooth continuous curved shape from the rim to the bottom. It’s easier and I think that it looks nicer.

Also, using a NR scraper as odie suggested is a good idea whether you want a flat or curved surface. A NR scraper should be used with a feather light touch. And use your body, not your hands to glide the NR scraper smoothly across the surface.

 

[Aaron Harris]

Odie-I do this when I need to clean up any humps or tear-out left behind from my gouges. My jumbo round-nose D-Way NRS can work miracles for smoothness if I glide it right as Bill suggests above. For me, I will cant mine down into a cutting angle and gradually come up to center as I swing it through. Then maybe a couple of feather-light scraping passes going for those fine angel-hair shavings to finish.

Maybe someday I will be able to get those perfect "wings-up" finishing cuts across the bottom like I sort of learned to do with Ellsworth last summer, and sometimes I can if hold my mouth just right on an easy turn. But it's nice to have that plan B when it's not. The more I use them, the more I love scrapers! And unless I'm mistaken, doesn't the legendary platter turner Tom Wirsig finish every surface with a scraper?

 

[hockenbery]

I try to get the smoothest surface I can with the gouges.
I do an inside curve so I cut from rim to bottom center riding the bevel.

Flat bottom you can try cutting from center out as well as toward the center. This can remove your center bump.

I can’t see your tool use. Ridges are common if you come off the bevel which lets the nose cut deeper. Your brain takes over and levels the cut leaving a groove. Then the process repeats leaving a washboard surface of grooves and bumps.

Taking the heel off the tool shortens the bevel, reduces bevel drag, eliminates the heel contacting the wood.
I have about an 1/8” bevel making the tool easier to control.


It is difficult to turn away bumps. The tool wants to follow the bumps. If I feel a bump I try riding the bevel over the smooth suface taking no cut or a very light one until I get to the bump then follow the curved or flat surface through the bump while riding the bevel lightly over the cut surface.

 

[Brian Gustin]

I have been known to use a skew as a negative rake scraper to get a flat bottom where needed, but I think I have learned (not yet mastered) getting a nice shallow radius bowl bottom instead - Works better with smaller bowls - Larger bowls diameter still give me a struggle sometimes - so what I wanted to get a slight concave surface end up being fairly flat with a "rolling hillock" somewhere near to the middle and then a bit of a little valley as I come into center. I believe it is just my technique (and likely would improve if I had a better lathe than an H.F. 12x36 due to its inherent tiny vibration from a slight half-a-thou runout in spindle) I have been able to almost fix those with the skew-as-a-NR-scraper trick but I can still feel a slight hump and in a raking light can see the undulation of it (the "hump" being around 3/4" wide "hill" about an inch from center) .. IMHO< Practice makes perfect, and I feel I am improving on it with every larger bowl I turn... and probably by the time I get that new Jet I'm saving my pennies for, I'll probably not notice a big improvement from developing my techniques on a crappy lathe

 

[john lucas]

I was taught to never make a bowl or platter bottom completely flat. Put a marble inside and it should find dead center. It should however be close to flat.and not have any ripples. I do that on smaller pieces with the Hunter Badger used as a bevel running tool. I can usually do 4 or 5" bottoms really clean. Bigger pieces I almost always have a few ripples. I use a round nose negative rake scraper and position my tool rest to match my bottom. Then I use my fingers like a clamp and gently slide the tool and my fingers along the rest.

 

[Aaron Harris]

I have been known to use a skew as a negative rake scraper to get a flat bottom where needed, but I think I have learned (not yet mastered) getting a nice shallow radius bowl bottom instead - Works better with smaller bowls - Larger bowls diameter still give me a struggle sometimes - so what I wanted to get a slight concave surface end up being fairly flat with a "rolling hillock" somewhere near to the middle and then a bit of a little valley as I come into center. I believe it is just my technique (and likely would improve if I had a better lathe than an H.F. 12x36 due to its inherent tiny vibration from a slight half-a-thou runout in spindle) I have been able to almost fix those with the skew-as-a-NR-scraper trick but I can still feel a slight hump and in a raking light can see the undulation of it (the "hump" being around 3/4" wide "hill" about an inch from center) .. IMHO< Practice makes perfect, and I feel I am improving on it with every larger bowl I turn... and probably by the time I get that new Jet I'm saving my pennies for, I'll probably not notice a big improvement from developing my techniques on a crappy lathe

Brian-I sometimes do this with the big Alan Lacer UberSkew. In fact, I have ground the radius to sort of match some of my inside curves. I have had other turners look at me funny at our Turning Learning Center for putting such a huge tool into a spinning bowl, but it works. You just have to be super-careful, as with any lathe tool.

 

[Don Stephan]

Richard Raffan has posted several Youtube videos with explanations how he removes center bump with a scraper to flatten the bottom. Handy for checking flatness can be straight edges increasing by 1/2" to hold against the bottom.

 

[John Snow]

Richard Raffan has posted several Youtube videos with explanations how he removes center bump with a scraper to flatten the bottom. Handy for checking flatness can be straight edges increasing by 1/2" to hold against the bottom.

I've watched Raffan several times finessing that little bump. It's not dead simple, but I've been able to make the scraper make the same movements and hey presto! it goes away with very. light. cuts. When I say I make the same movements, I mean I move the scraper so minimally and carefully that I avoid catches, and the scraper magically moves the way Raffan's does.

 

[Dave Landers]

This is something that just takes practice. Remember that a gouge cuts in the direction the bevel is pointing. That's one reason "riding the bevel" (or whatever term) is a big deal - if the bevel is on the wood, it'll keep cutting straight.

When we get to the end of a cut, in the middle of the bowl, we tend to want to exit the cut - so our natural tendency is to move the gouge handle to the left (just a bit) which points the bevel away from the wood, and the gouge cuts a little bump. Sometimes we overcompensate and end up with a divot.

Same thing happens not just at the center, but along the bottom of the bowl where little wiggles of the handle change the cut direction, making speed bumps along the way. Once you have bumps, it becomes harder to remove them with a gouge - the gouge naturally wants to follow the surface, which often just makes things worse. So it all starts with the roughing cuts.

One thing that sometimes helps is to position your tool rest along the same line you want to cut (rather than angling it into the bowl). Gives you a sort of target to look at, and you can ride your finger along the rest to help keep the gouge straight.

But there's really no magic - it's mostly practice.

 

[Kent Jaffrey]

Flat bottom platters are hard to get totally flat, even with all the tips given above, especially if you put on a finish that has any gloss. The gloss of the finish makes any slight ripples more apparent when in glancing light.

What I’ve found helps with that last bit of smoothing is hand sanding the bottom. After the first grit of power sanding I stop the lathe and use the sanding pad to take straight strokes across the bottom. Then slightly rotate it and sand across the bottom again. I repeat until I’ve gone 360 degrees (ending with the grain). This help get that last bit of flattening done and takes care of the waves you can see but not really feel. It does require a pretty flat bottom from scraping already…

 

[hockenbery]

I tend to sneak up on the bottom. Light bevel riding cuts with a sharp tool.

These are sequences of hollowing a seed jaw bottom
This is a near flat bottom but is still curved.

I leave mass in the bottom to turn the thin wall

Cut to the bottom in several passes

Cut the bottom

Feel for a little bump and cut it off

 

[Dean Center]

Since he talked about ridges and the center hump, I believe the OP meant "level" or "smooth" when he used the term 'flat', rather than truly flat/perpendicular to the lathe axis.

 

[Dave Landers]

Since he talked about ridges and the center hump, I believe the OP meant "level" or "smooth" when he used the term 'flat', rather than truly flat/perpendicular to the lathe axis.

I was backing with friends a couple years ago. I'd told them that the trail was flat. When they started to complain about the incline, I replied "I said flat, I didn't say level"

 

[Doug Freeman]

Lots of good suggestions. NRS’s and at least some slight curve to center vs flat help a lot. Then, keep trying with a BG to sneak up on that final cut. Practice, practice, practice. Every piece you make provides opportunity to practice by making several “final surface” attempts as you reduce thickness to where you want it.

 

[Rick Urban]

Here are some things I've found helpful when removing ridges and humps instead of following them up and down...

1. Choose your favorite weapon (I prefer a Negative Rake Scraper.) with the largest radius practical so it spans from ridge to ridge instead of following the countours of the surface. A nearly straight edge may be appropriate in some circumstances.

2. Start with a comfortable relaxed stance to make sure you're not fighting ergonomic stresses when trying to exercise fine tool control.

3. Use a little extra downward pressure on the tool rest to counter any tendency to push the edge into the cut.

4. Be gentle and take your time.