half dish (an interesting challenge)

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Project by peteg posted 06-16-2011 10:03 AM 2818 views 16 times favorited 32 comments Add to Favorites Watch

This is an interesting little challenge,
The trick is to get a perfect 1/2 sphere both inside & outside with a 2mm wall thickness top to bottom.

I have another couple of variations I am playing with as well which I hope to post in a couple of days which take this idea a bit further. I have done this one with a piece of Kauri.
I know, it looks so simple you could do it standing on your head. The size is realy irrelevant, this one the Brick portion is 2.5” sq, this has only been oil sanded at this stage, I will maybe polish or lacquer it later.
Aplolgies for my lousy camera shots, tried dozens of shots & this is as good as it get, might need a new Kodac
All comments are welcome please.

-- Pete G: If you always do what you always did you'll always get what you always got

32 comments so far

View Bob Collins's profile

Bob Collins

2152 posts in 3014 days

#1 posted 06-16-2011 10:54 AM

G’day Pete, you said it looks simple, well simple Simon on the big Island can’t work it out, specially how you get the flat surface under the bowl. A good challenge though and interested to see your others. Nice turning and the finish looks Ok to me.

-- Bob C, Australia. I love sharing as long as it is not my tools

View Bob Collins's profile

Bob Collins

2152 posts in 3014 days

#2 posted 06-16-2011 11:01 AM

Simple Simon might just have figured it out, I’m thinking turning on two axises (angles or whatever). Maybe tomorrow I’ll waste some wood.

-- Bob C, Australia. I love sharing as long as it is not my tools

View Sodabowski's profile


2301 posts in 2163 days

#3 posted 06-16-2011 12:37 PM

I’m still trying to figure out how you turned the outer part. Looks good anyway!
How about adding a drawer in the base?

-- Thomas - Pondering the inclusion of woodworking into physics and chemistry classes...

View mafe's profile


10935 posts in 2419 days

#4 posted 06-16-2011 12:49 PM

Hi Pete,
It’s beautiful.
I guess you cut the square pieces in shape after finishing the turnings yes? Then it can be done quite simple.
Best thoughts,

-- MAD F, the fanatical rhykenologist and vintage architect. Democraticwoodworking.

View toyguy's profile


1533 posts in 3167 days

#5 posted 06-16-2011 01:36 PM

OK Pete….... You have stumped me. “again” . You guys down under sure come up with some way out there ideas. Must be fun sitting; having a beer and talking with you all…..

This is a cool little piece. I am enjoying it. I want to pick it up and look close. “A tip of the Hat ” to you Pete. Nice job.

-- Brian, Ontario Canada,

View Roger's profile (online now)


19369 posts in 2134 days

#6 posted 06-16-2011 01:57 PM

very unique

-- Roger from KY. Work/Play/Travel Safe. Keep your dust collector fed.

View murch's profile


1311 posts in 1954 days

#7 posted 06-16-2011 02:00 PM

Nicely done Pete. 2 axis I presume.Your second grip would need to be very accurate in order
to achieve a uniform wall thickness but it looks like you hit the bulls-eye.

-- A family man has photos in his wallet where his money used to be.

View SPalm's profile


5241 posts in 3212 days

#8 posted 06-16-2011 02:14 PM

You had me for several minutes. But now I get it.
Turn the outside knob, remount with 90 degree turn and offset center, turn inside.
Very well done.

That is so cool. A very wonderful shape/design.

I love it,

Edit: I guess simpler would be the same offset center holder for both axis. Then they would self align.

-- -- I'm no rocket surgeon

View sedcokid's profile


2710 posts in 2928 days

#9 posted 06-16-2011 02:58 PM

I think that you, murch, Bob and Steve are all smarter then I am…. I can’t figure it out. Once you have played with us all for a period how about giving us a tutorial…. Please, Please, Please

Thanks for sharing

-- Chuck Emery, Michigan,

View Greg In Maryland's profile

Greg In Maryland

549 posts in 2328 days

#10 posted 06-16-2011 02:59 PM

My guess is that you mounted a block of wood a bit over twice as large as the finished piece, turned it as if you were turning a ball or knob. Once the outside shape was finished, you hollowed out the inside using the smallest hole/tool you could get by with.

After you finished shaping/hollowing on the lathe, you took it to the band saw and cut it slightly below the hole. The result is what you see, except you get two vessels.

Now this is all theory on my part—I have never touched a lathe.

So, how far of the mark am I?

View BarbS's profile


2434 posts in 3415 days

#11 posted 06-16-2011 03:50 PM

What an original idea! That is hard to achieve in wood turning. I’m guessing the piece had to be mounted in a separate jig which was held in the jaws of your chuck, the square trapped off-center to spin free of where you were centering the turning, then re-mounted in reverse to turn the other side?


View hairy's profile


2367 posts in 2862 days

#12 posted 06-16-2011 03:58 PM

Well done, Pete! Very clever.

-- stay thirsty my friends...

View Druid's profile


1151 posts in 2125 days

#13 posted 06-16-2011 04:34 PM

Hi Pete.
I’m interested in seeing how many various “techniques” are suggested in the comments. Frankly, the technique that I find most interesting with your project is your conception of the design. It’s totally unique to any other “turning” that I’ve seen. Top marks on that.

-- John, British Columbia, Canada

View drewnahant's profile


222 posts in 2419 days

#14 posted 06-16-2011 04:45 PM

I get the two axis turning, it’s not an overly complicated process, but to get an even wall thickness, perfect hemispheres, and not destroy it when turning off center, that is extremely impressive!
well done Pete

View shipwright's profile


6901 posts in 2128 days

#15 posted 06-16-2011 04:58 PM

Good one Pete
I’ve been following and it seems to me that if the inside hollow were turned first in a longer and wider piece, then rotated to the other axis to cut the outside, things would be easier. no?

-- Paul M ..............If God wanted us to have fiberglas boats he would have given us fibrerglas trees.

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