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Inserting a round block in the center of a segmented bottom (Read 816 times)
 
David Muehlbauer
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Inserting a round block in the center of a segmented bottom
May 17th, 2016 at 7:00pm
 
It's pretty difficult to have all the segments in the bottom of the bowl form a perfect point, which for me can result in a small hole in the very center. I have seen some bowls with a small round block inserted in the center and that looks like a good solution. I searched and didn't find any discussions of this. Can anyone point me in the right direction?

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Len Layman
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Re: Inserting a round block in the center of a segmented bottom
Reply #1 - May 17th, 2016 at 7:31pm
 
Dave ,

What I do is after deciding what size I want the "plug"  I put a forstner of that size in a chuck on my tail stock and drill the hole.  Then I turn what ever the accent plug will be to the exact size needed for a good fit.  I do not always get it right the first time.  When I do have it right I simply glue it in.  I tried to over think it but finally just did it and this system works well for me.
I am sure others will have similar or different solutions. I look forward to learning how others approach it.
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« Last Edit: May 17th, 2016 at 7:31pm by Len Layman »  

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Ed Weber
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Re: Inserting a round block in the center of a segmented bottom
Reply #2 - May 17th, 2016 at 7:37pm
 
David Muehlbauer wrote on May 17th, 2016 at 7:00pm:
It's pretty difficult to have all the segments in the bottom of the bowl form a perfect point,


This is why some of use prefer to glue up in sub assemblies.
Let's say you have a 12 segment base. You can glue up 4 sub assemblies of 3 pieces each. Each sub assembly or quarter can easily be sanded to a 90 degree angle. This makes lining up the center much easier.

Sometimes you need to plug the center, my advice is simple, taper the plug and hole. If you try to drill a straight hole the fill it, chances are the fit won't be tight enough. Putting a very slight taper on the mating parts allows you to press, tap or hammer, (your choice) into place, resulting in a tight fit. Try to keep the center as small as possible (while aesthetically pleasing) so that there isn't too much potential for movement. The larger the center , the more it can move causing joint failures.
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« Last Edit: May 17th, 2016 at 7:38pm by Ed Weber »  
 
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Walt
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Re: Inserting a round block in the center of a segmented bottom
Reply #3 - May 18th, 2016 at 10:12am
 
I will over size these segments slightly just so I can creep up on a perfect fit (using a disc sander), gluing pairs then quads and the halves together. 

A slight taper works best when fitting a plug, it doesn't take much maybe 5-10°.
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Julian Roslanowski
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Re: Inserting a round block in the center of a segmented bottom
Reply #4 - May 18th, 2016 at 10:15am
 
David, I often make the bottoms segmented with a very tight center using the wedgie sled.  I found the smaller the bottom ring, the easier it is to get a good center. I use a hose clamp to glue it up because it applies even pressure to all the pieces. The photo actually has a large bottom and there is a very small gap in the center but that can be easily filled with saw dust and glue.  I have seen Youtube videos where a center piece is inserted into the bottom.  Search Gordon Rock woodworker on YouTube.  I believe he shows how to do the center piece.
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Ron Sardo
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Re: Inserting a round block in the center of a segmented bottom
Reply #5 - May 18th, 2016 at 12:34pm
 
When gluing in a plug on the bottom of a segmented piece you may have problems if the wood decides to expand or contract. I've seen more than a few bottom plugs that cracked when the plug shrank or the side of a form crack when the plug expanded.

There are two common ways to prevent this problem
1) Only glue the plug to 1 or 2 segments where the face grain meets face grain leaving the rest of the plug with no glue.
2) Create a floating plug by making a tongue and grove.

The second method is a little more complicated but doable and is my preferred method. Consider frame and panel doors, the proper way to build one would be to have a floating panel encased by a frame which prevents a failure of a glue joint or wood splitting

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« Last Edit: May 18th, 2016 at 12:37pm by Ron Sardo »  

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Re: Inserting a round block in the center of a segmented bottom
Reply #6 - May 18th, 2016 at 12:55pm
 
Julian Roslanowski wrote on May 18th, 2016 at 10:15am:
The photo actually has a large bottom and there is a very small gap in the center but that can be easily filled with saw dust and glue.


Please, take no offense, this is my own view on segmenting, I only offer my views, not try to force them on anyone.

While everyone has their own methods and standards IMO a gap is a joint failure.
If it can't be glued up all at once without a gap, then it probably shouldn't be.
If I know I have a gap, I repair or replace it before gluing. If I find a gap after glue up, depending on the piece, I'll try to repair it.  If I can't repair it to my standards, it's a failure and either gets trashed or may sit on the shelf as a reminder.
I posted about 3 years ago Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register showing a failed piece. I kept the base and threw some finish on to make it easier to see the failure., which is not in the center as you might expect. I believe I was so focused on trying to get a good tight center I failed to see the gap near the outer edge.
I keep this around to remind me that I can do better and that there is no excuse. i know it can be done, it's up to me to execute it properly.
JMO,
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Julian Roslanowski
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Re: Inserting a round block in the center of a segmented bottom
Reply #7 - May 18th, 2016 at 8:51pm
 
Just to clarify; when I was referring to the gap (or hole), this is at the convergence of the segmented pieces. I was not referring to a gap between segments.
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Ed Weber
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Re: Inserting a round block in the center of a segmented bottom
Reply #8 - May 19th, 2016 at 9:12am
 
I understood what you were saying.
I was trying to point out to all the members that,
1. Gaps can occur in less than the obvious places
2. Gluing an entire base at one time is not always the best method.
3  Sawdust and glue is not a "generally accepted" method of segmented construction or repair.

Walt, Ron, myself and others try to give suggestions, alternative methods and even examples of failure to help other improve their craft.

As a safety note. A gap in construction is quite obviously a weak spot and an area where a tool could catch. Depending on it's location it could be potentially dangerous when turned, causing catastrophic failure.
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Walt
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Re: Inserting a round block in the center of a segmented bottom
Reply #9 - May 19th, 2016 at 9:35am
 
I stated this in another thread but its worth stating again.  We must strive for perfect joint which requires precision.  As Ron stated a dark joint means excessive glue or the wood was burned during cutting.  Sanding removes the burn and if done on an old disc can cause even more burning.  These are things we've learned the hard way.  Sometimes, even when everything goes right you can have joint failures.  Wood moisture, grain orientation, open and closed grain woods and the coefficient of thermal expansion of different species of wood can all contribute to joint failure.
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Ed Weber
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Re: Inserting a round block in the center of a segmented bottom
Reply #10 - May 19th, 2016 at 11:05am
 
Walt wrote on May 19th, 2016 at 9:35am:
We must strive for perfect joint which requires precision.


Exactly to point I'm trying to emphasize.

This is also why no matter how you cut your segments, (wedgie sled or otherwise) your construction must be accurate for a proper glue-up which "usually" does not need to be done all at once. Dry fit, glue in sub-assemblies or whatever method works for you to refine the wood to achieve a proper fitting joint. As a result, the strength, the safety and the look will be better.

You can't cut corners in segmenting,    or can you?  Undecided
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