Smaller bowl

[Wood Dog]

Carole I decided to try the bowl in Issue 37 SSWC mag.
I am going to print out the pattern at 50 %, just because I want to make it smaller. My question is, do I keep the 28° angle? Should I still use 3/4 inch thickness wood? Did I post this at the right place?
Thanks

[handibunny]

WD, you can make the bowl smaller, and you can use 3/4" wood, but the ring width and cutting angle are related to each other, and you can't change one without changing the other. Easiest way to handle this is to forget the pattern and draw a circle the diameter you want, then draw concentric rings. If your ring width is 3/8", you use 28˚, if it is 1/4" use 20˚.

If you want to print out the pattern at 50%, measure the width of the rings then PM me, and I'll compute your cutting angle.

[KtownScroller]

Wood Dog

If you cut the bowl size by 50% you can cut the 28° angle by 50%, giving you a 14° angle. Using 3/4" wood the pattern rings should measure 2 3/8", 2 3/4", 3 1/8" & 3 1/2".

Not to step on your toes Carole. This is what my program calculated the angle to be.

[KtownScroller]

Wood Dog

If want to keep the 28° angle or something close to it then you need to use 3/8" thick wood and change the angle to 27°. The diameters posted in my last message will still hold out.

[KtownScroller]

Wood Dog

If you only have 1/2" wood then use a 21° angle. Is that enough numbers for you?

[woodgeek]

Just an observation but on my second bowl I used the ring method rather than cutting to a pattern and the rings did coincide remarkably better which means of course less sanding which I greatly favor and you don't have to peel and clean off a pattern which is a bonus.

[handibunny]

Rick, the thinner the wood, the steeper the angle for the same ring width. For 3/4" thick wood and 1/4" wide ring, the cutting angle is about 20˚. For 1/2" thick wood and 1/4" wide ring, the cutting angle is about 28˚. It's a tangent function: ring width divided by wood thickness gives the tangent of the cutting angle.

More important, however, is the fact that the steeper the angle, the more quickly you'll get to the center of the blank, which may mean an adjustment in the number of rings you want to cut. Also, the thinner the wood, the lower the bowl, which is why wood thinner than 1/2" is not really practical. And, it's suicidal to try using a ring narrower than 1/4" because you need sufficient wood to sand out irregularities and drill marks. So theoretical is one thing and practical and realistic is another.

[Wood Dog]

Thanks everyone, after reading all those numbers, I decided I need to have breakfast, and coffee first. I'll be back to re-read. How do you keep all that stuff in your heads is beyond me......math challenged I am for sure.

[handibunny]

Rod, the ring method is definitely the way to go. However, if the cuts start to go "off" you may need to redraw the next ring slightly.

For round bowls, I just draw the outline and first ring directly on wood with a compass. For other shapes, I use a pattern for the outline and first ring, then remove the pattern. My book was designed to be used both ways, depending on someone's preferences and experience.

[KtownScroller]

Originally Posted by handibunny

Rick, the thinner the wood, the steeper the angle for the same ring width. For 3/4" thick wood and 1/4" wide ring, the cutting angle is about 20˚. For 1/2" thick wood and 1/4" wide ring, the cutting angle is about 28˚. It's a tangent function: ring width divided by wood thickness gives the tangent of the cutting angle.

Carole:

A 20.0° angle with 3/4" thick wood would yield a .270 wide ring.
A 28.0° angle with 1/2" thick wood would yield a .270 wide ring.

Now if you really want a 1/4" wide ring then:
A 18.5° angle with 3/4" thick wood would yield a .250 wide ring.

Originally Posted by handibunny

More important, however, is the fact that the steeper the angle, the more quickly you'll get to the center of the blank, which may mean an adjustment in the number of rings you want to cut. Also, the thinner the wood, the lower the bowl, which is why wood thinner than 1/2" is not really practical. And, it's suicidal to try using a ring narrower than 1/4" because you need sufficient wood to sand out irregularities and drill marks. So theoretical is one thing and practical and realistic is another.

Wood Dog's proposal is to simply reduce the pattern size by 50%. That would require him/her to use 3/8" thick wood to maintain the original shape of the bowl.

To use 3/4" thick wood:
A 28° angle with 3/4" thick wood would yield a .400 wide ring. Per plan.
A 14° angle with 3/4" thick wood would yield a .190 wide ring, BUT the ring sizes would fit the 50% reduced pattern.

To use 3/8" thick wood:
A 27° angle with 3/8" thick wood would yield a .190 wide ring and the ring sizes would fit the reduced pattern.
A 21° angle with 1/2" thick wood would yield a .190 wide ring and the ring sizes would fit the reduced pattern.

The key to my numbers is working with the original problem, changing the cutting angle or wood thickness to fit the 50% reduced pattern.

I am not a bowl expert and I will admit that making the bowl walls thinner than 1/4" may be suicidal! I do think that producing a reduced size reproduction bowl is maybe not practical, but doable. Knowing how Wood Dog loves to shrink things I'd bet my money he/she could pull it off!