Flat bottoms

[Burt Alcantara]

One problem that plagues me is getting a smooth ridgeless bottom on my bowls. At my local club, many of the show and tells that are passed around have slight undulations while some are smooth as glass so I know it's not just me.

Part of my problem is I can't seem to do a smooth even sweep from rim to center. What ever point that the gouge lifts from the surface is where a ridge develops. When I try to pass over it again the gouge seems to "ride the wave."

The other problem, which may be indicative, is too much material removed where the sides join the bottom. Somehow, as I'm dropping down the sides I dig in too much at that transition point. I'm never aware of this no matter how much I concentrate.

Any suggestions are greatly appreciated.
Burt

[Patrick Taylor]

What ever point that the gouge lifts from the surface is where a ridge develops.

I think you mean that the bevel is losing contact with the wood during cut on the inside of the bowl, near the bottom? If so, some people use a second bowl gouge with a steeper bevel on it for that portion of the inside in order to maintain contact.

[Mike Vickery]

I would say what that this is very common. I have a couple bowl gouges ground in different ways that help me get the bottom on some pieces. Thought in general I normally just use a 3/8ths or 1/2 fingernail grind gouge with about a 55 degree angle for everything. It is a lot easier to do on shallower bowls then deeper ones. It may be considered sacrildge by some but I have a heavy round nose scraper that I will use to clean and blend the bottom if it is not to bad.

The one I use most if I am having problems on the inside is a 3/8ths fingernail grind with a shorter bevel. It is ground at about 70 degrees instead on the 55 degrees I normally use. I then shorten the bevel more by grinding away the bottom of it I think it is called a double bevel. This shorter steeper bevel is better able to keep contact throught the transition but is more difficult to control.
The other is a 1/2 inch bowl gouge with a straight gring on it. I use it with the flute in a more vertical position to cut through the transition and roll it to the right as I get towards the center.

Not sure if this helps or is right, but it is what I do.

[Ron Sardo]

I use a 2" sanding pad with a 100 grit disc while the lathe is spinning to get the bottom smooth as glass.

Form there I stop the lathe at each grit and sand with the grain.

[Paul Engle]

Burt ,
Bills reply on earlier thread, check it out , get the dvd or tape.Dont guess at it .
http://www.sawmillcreek.org/showthread.php?t=7413

[Frank Kobilsek]

Burt

Get one of your club members to come to your shop for a 'Play Date' as one of my nieghbors call it when I have a fellow turner visit my garage.

Mike is right about the angle of the tool but presentation of the tool makes a big difference. Sometimes a big arc through the transition area sloping back down to the very center of the bowl will solve your trouble regardless of grind angle. I learned or use two ways straight across tool amost level to the floor, riding the bevel on the left side of the tip or the big swoop method. It depends on shape and how the wood is behaving as to which gets used.

Now I know that didn't make any sense so get a coach for an hour or two or even a whole Saturday you'll be glad. Buy him lunch, bribe him with free wood whatever you gotta do.

My problem is a turn a nice bottom and then ruin it with the sander. Too much pressure on the pad and in life lately.

Frank

[George Tokarev]

One problem that plagues me is getting a smooth ridgeless bottom on my bowls. At my local club, many of the show and tells that are passed around have slight undulations while some are smooth as glass so I know it's not just me.

Part of my problem is I can't seem to do a smooth even sweep from rim to center. What ever point that the gouge lifts from the surface is where a ridge develops. When I try to pass over it again the gouge seems to "ride the wave."

The other problem, which may be indicative, is too much material removed where the sides join the bottom. Somehow, as I'm dropping down the sides I dig in too much at that transition point. I'm never aware of this no matter how much I concentrate.

Any suggestions are greatly appreciated.
Burt


Depending on grain orientation, interval and the difference in hardness between early and late wood, some "undulation" is going to be present even with careful sanding. It's easier to abrade the softer wood when sanding, after all, leaving the latewood proud. If you've got wide annual rings on the bottom, you've got the problem. Only way to minimize is to use a firm backing and little pressure on the paper to get a best average. My problem is the very bottom, where there's a tendency to twist out a bit of wood because the tool's underneath the wood, wedging it out. I leave a bit of a button rather than resort to a scraper, then sand.

Ride the rest rather than the piece, and you'll minimize the tendency to follow into softer portions. That's what people who use scrapers are doing, not "riding" a bevel over differences, but swinging through based on the rest. You can hear and see the difference in this clip between the 1/2 inch deep flute and the 3/16 thick shallow flute, where the bevel is just skating rather than cutting away much wood, as with the initial rounding cut. http://s35.photobucket.com/albums/d160/GoodOnesGone/?action=view&current=Inside.flv

As to steep transitions, especially for pieces which are distinctly composed of walls and bottoms rather than continuous curves, you've got little choice but to turn the corner with a fingernail pattern, rolling from nose to right wing. Problem comes when you have to point the edge in rather than allowing it to trail, which gives the best peeling cut. You can catch real easily. Get that rest in real tight, almost work off the end to give yourelf room to make the roll, and hold firm to the rest, like you do when starting a plunge with a fingernail. The difference in diameter will try to kick the gouge back toward the outside, so anticipate. Some people prefer to scrape the junction, but you get cross-grain tears that can take a while to sand that way. Of course, more you have to sand, more likely you are to get those undulations again.

Or don't make side/bottom patterns. Go to continuous curve. Keeps stuff from getting neglected in the corner if you use the bowl, too.

[Ralph Lindberg]

Question
I haven't tried this yet, but would a shear-scrape work? As I recall, Steve Russell does this by holding a round-nose scraper at an angle. While Jim Christiansen has a most oddly ground SRG (Jim has turned the SRG upside down, then ground the SRG into a round nose scraper. This allows him to rest both sides of the SRG on the tool rest, but still get an angle scrape)

[Bernie Weishapl]

For the final pass or two I use a traditional grind bowl gouge from P & N. Mike Mahoney's tape has directions on it's use. It works really well. Takes care of tear out and smooths the bottom.

[Mike Vickery]

Question
I haven't tried this yet, but would a shear-scrape work? As I recall, Steve Russell does this by holding a round-nose scraper at an angle. While Jim Christiansen has a most oddly ground SRG (Jim has turned the SRG upside down, then ground the SRG into a round nose scraper. This allows him to rest both sides of the SRG on the tool rest, but still get an angle scrape)
yes a shear scrape will work but depending on you angle make take longer. The closer you tool is to horizontal the heavier cut it will make. As it approaches vertical it will produce a finer cut.

If you have a good amount of material to remove I would recommend doing a normal scrape then go to shear scraping to finish the surface once the material is removed. Many different ways to do it though that is just what I do.

[Burt Alcantara]

Lots of good information here. Lots of things to think about and practice. One thing I didn't specify which George pointed out was making the continuous surface rather then a distinct side and bottom.

I'd like to avoid using a scraper for now so I can learn the skill to get a good bottom.

I was able to shear scrape the bottom but it did not reduce or eliminate the undulations, just make the smoother.

Well, I scored a large quantity of Willow so I have some better wood to practice with then that junky pine.

Thanks to all,
Burt

[George Tokarev]

[quote=
Well, I scored a large quantity of Willow so I have some better wood to practice with then that junky pine.
[/quote]

If it's wet, you may end up modifying that comparative. Willow stinks when it's green. It's also really fuzzy and fine-filamented like its cousins, the true poplars or cottonwood, so you'll dispair of ever getting a smooth finish when it's wet. Not to worry. It's bullet-proof in drying, and firms up well enough to respond well to sharp tools. You will want to maintain a higher standard of sharpness earlier in the process than your normal hog and pare method, because you can pull wood to a pretty great depth with a dull edge or improper angle.

Do Not microwave the stuff unless you're all the way outside and upwind to boot. Even then the interior of the micro may smell for a long time. DAMHIKT

With thick, corky bark, it makes a stunning bark-on piece.

[Burt Alcantara]

George,
Are you saying it's OK to turn it green? Or should I let it dry out for a while?

Thanks,
Burt

[George Tokarev]

Sure, turn it green, just make sure you have good ventilation. Bark-on stuff should always be turned green, of course. Make it a tad thick, like >1/4 inch or so, because the bark contracts a bit more than the wood, and you'll want to blend after drying. Don't gum up vast quantities of paper trying to sand it green. It's soft, and sands readily after drying.

Regular bowl patterns dry with little problem beyond standard warp.

Sucks in finish pretty well, so consider something with high solvent evaporation or high solids content rather than finishes that soak in.

[Jim Ketron]

I have one Question.
Are you using a curved tool rest?
They can improve tool control in that area of the bowl transition greatly!

[Burt Alcantara]

I've been thinking more and more about getting one. Because I turn bowls in the 6" range, more or less, my rest stops me from getting up close and personal. Doesn't help that the rest is thick, in the up and down directions.

Burt

[George Tokarev]

It's not fatal to have to reach over the rest, but it sure doesn't help. Are you using convention and trying to point a "bowl" gouge up, or are you cutting at near 90 degrees to the rest? Much easier to control the gouge if you do, and it's control that keeps you from digging.

Time to cook dinner. Would some video help?