Wooden Bowl Problem

[Ghornet54]

Carole or anyone who can answer,

I'm making another checkerboard bowl bowl. I cut it out and glued it together, but apparently I tightened the bolts too tight and one of the rings came loose. Its the second ring from the top. Everything is now glued tight, but the second right has about 1/8" gap where the maple and walnut came loose. None of the other rings did this. Can this bowl be saved? Or is it just firewood?

Any hints on how to save it?

Charles

[handibunny]

Charles,

Can you post a picture of the bowl to make it clearer? I'll be away today, but can look at it tomorrow.

[bluelucky]

Originally Posted by Ghornet54

Carole or anyone who can answer,

I'm making another checkerboard bowl bowl. I cut it out and glued it together, but apparently I tightened the bolts too tight and one of the rings came loose. Its the second ring from the top. Everything is now glued tight, but the second right has about 1/8" gap where the maple and walnut came loose. None of the other rings did this. Can this bowl be saved? Or is it just firewood?

Any hints on how to save it?

Charles

Fill it with glue and you can rub some saw dust left from sanding it with it and let it dry then sand it again..I've done that before just remember to only tighten till the glue starts to come out.

[Ghornet54]

Thanks for the suggestion. The gap was large enough that I cut a strip of the walnut and forced it into the slot and glued it in place. I'm letting it dry tonight and going to shape it tomorrow.

[handibunny]

Charles, probably a bit too much pressure, or pressure unevenly applied, and a joint that may not have been completely solid. You can get away with joints that are not perfectly tight as long as you're gentle.

I agree with the suggestion not to over-tighten the press, especially with glue-ups. I've ruined at least one bowl by being a little too aggressive--squashed it right out of shape. Part of the learning process . . . .

Quick solution is to put the good side to the front and no one will ever see it.

[hotshot]

In an effort to be helpful, and definately not critical, I think your cutting angle is a little off resulting in the slight stair steps. I guessed 30 degrees on my first project and sanded forever, and was then thus motivated enough to hit the Math sites to figure out the calculation. I don't have Carols' book yet, so I probably don't have the best approach, however, I'll tell you how I do the calculation . . .

My approach: In Windows XP, I bring up the calculator, select scientific calculator, then take Ring Width/Board thinkness. With that result, I click "inv" checkbox, then click TAN. (I also have an excel spreadsheet that calculates this, let me know if you want it.) If my result if greater than 45, I decrease the the ring width until I have an angle my saw will cut.

My base formula for cutting angle is arctan(RingWidth/Board Thickness).

My next formula will be to determine ring size given the cutting angle and board thickness. I'm trying some projects where I vary angle and thus the ring widths throughout the bowl. So far so good. If I'm right, you can keep the ring widths the same throughout, but vary where the rings begin to alter the angle without altering the thickness. I have it planned out, but haven't grabbed the scrap wood to try it yet.

[Ghornet54]

Thanks Carole. I've put a "shim" in the hole and hopefully tomorrow night I will get to see the results.

Hotshot. Thanks for the suggestion. I usually have a better cutting on the bowls, but this time my angle was a little off and I didn't really want to throw away the bowl, so I just continued to glue it up. Yes, I would like to see the excel sheet. Thanks for the offer.

I really like Carole's book and have been using it quite a lot for my craft shows coming up this fall. I think the book was worth every penny!!!! If she has another one, I'm buying!!!

Charles

[handibunny]

Hey Hotshot,

I've included in the Appendix of my book the formula for computing the cutting angle for any width ring and board thickness, and yes, it is a tangent function. However, the theoretically correct result does not take into account kerf width and human frailty, so it's prudent to add a degree or two. And yes, you can cut at any angle greater than the computed minimum angle needed to allow for consecutive rings cut from the same blank. However, depending on how you go about it, you may need to re-cut the outer edge of the ring.

My first chapter on varying angles (Ch 4) uses a single cut method, which results in a ring that gets progressively wider at the base (or top, if inverted), useful for certain projects. Chapter 6, the last project chapter, uses the double cut method, which allows for the insertion of rings from other woods for decorative effects, and keeps the ring width constant. I will be posting a video on my blog about these two methods as soon as I get it edited.

Most of the bowls that have been posted on the forum have a constant cutting angle. I fully expect that as more and more people start playing around with rings, we'll also start seeing some curved sided bowls, as well.

All of this makes a lot more sense once you actually start working on the bowls, and seeing how it all comes together. And the tan formula is especially valuable for situations when the wood thickness is not standard, such as as after sanding a glue-up, or when you want a non-standard width ring.

Try making a bowl--it's fun!

[hotshot]

Very good stuff. I look forward to getting the book :-)

----Randy

[handibunny]

Thanks, Randy. I appreciate your curiosity as to how the rings work--it's really cool stuff. Looking forward to seeing your bowls.