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post #1 of 13 (permalink) Old 05-22-2013, 12:21 PM Thread Starter
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Default Jerry's Latest Challenge...

I'm presently envolved in a challenging project that those of you who have plenty of experience with would be able to accomplish with great ease, or at least I suspect that such is the case.

What I am attempting, and am pretty sure will accomplish with some care, is to make a table top that is about 16 X 30 inches. The main part of the table is made from a piece of walnut that to start with was about 1.5" thick, 32" long and 8.5" wide. I started by re-sawing the workpiece into two parts. After milling the two parts, which required that they be ripped into four parts due to my jointer only being a six inch machine, the parts were glued up and the resulting single workpiece squared up, I started making a frame to go around the perimeter of the that first part. The challengs of course is to make the frame just exactly right for first workpiece to fit inside of and having the whole table top with zero gaps both in the mitered corners of the frame and all the way around the inside the frame. The inside part must be exactly square and exactly the same length and width of the inside of the frame, only then will the table top be free of any gaps and look decent before adding the finish. Right now I have two sides of the frame cut out and will start on the other two sides next time I'm in the shop. If I pull it off to my satisfaction, I'll post a photo, and if I fail, well, I may just hide in the weeds. The point being, I really do like challenges like this and should teeach me some new skills, fortunately I do have good tools to do the job with.

Jerry
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post #2 of 13 (permalink) Old 05-22-2013, 02:40 PM
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Here's some things to consider Jerry. Wood tends to move across the grain with humidity changes, i.e. swell or shrink across the width. For some reason I am not familiar with, wood moves very little along its length. When you make wood panels that go inside a frame, as in raised panel cupboard doors, you aren't supposed to glue the panel into the frame or it can push the frame apart or split the panel. I have had success with putting a wooden frame around mdf and particle board which don't move but my early woodworking attempts where I glued the panels in because I didn't know any better came apart. One in several places.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.

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post #3 of 13 (permalink) Old 05-22-2013, 03:07 PM Thread Starter
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Charles, sure do thank you for the tip. I made a desk for my wife's granddaughter recently. I gave it to her at Christmas last year. The desk was constructed as I described that that I am trying to contruct the table top. It has been about five months since I've seen the desk, I will phone her ask if she can see in cracks in it yet. How long does it take for the problem that you have just descirbed to occur? I'll get back to you and other members of the forum on the project.

Maybe it would be a good idea to to just do a very slight round over on the inside of the frame and all around the inside part that fits in the frame, then give the inside some room to move, just a little, as is normal when when framing a picture. Then without glueing the part could move, of this would require constructing the top so that the inside part won't fall through. That would be fairly easy. You sure do have me thinking.

Thanks again,

Jerry
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post #4 of 13 (permalink) Old 05-22-2013, 05:11 PM
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Jerry,

have a look at the TV table I built a couple of months back and see if that is the sort of frame you are looking for. The main section is 32mm laminated chipboard which gets around the expansion/contraction issues that Charles mentioned. That by the way is a seasonal thing so you will see it expand across the grain in summer and contract in winter. As the wood dries over time, it contracts more than it expands. I have a 100 year old house where the doors are made like this, and some of the panels no longer meet the frame regardless of the season.

Anyway, if the TV table has the same type of frame you are after, then it is more a matter of being careful and accurate than anything else. I have a digital protractor and use that to set the angle on my saw bench. If that is not handy, I also have a 45 degree builders square that I use. 1/10 of a degree variation will show up in the mitre. I make sure that I am measuring the saw blade only and avoiding touching the teeth as they protrude out from the blade.

The other trick I use is to clamp a scrap of wood on the cross-cut fence and run it through the saw to make a temporary fence with zero clearance. That way I know exactly where the blade is cutting and can line up the marks on the real piece exactly. This is a bit difficult to explain without a picture, but I'll try anyway. I put the real piece upagainst the fence but clear of the blade. Rest the scrap on top of the piece and against the fence, making sure it is extended far enough to be cut by the blade. Clamp it there for a tight sliding fit with the real piece and then cut through. I don't cut it off completely - juse raise the blade enough enough to make a channel cut through. Sometimes you use the inside edge and sometimes the outside edge of the blade. Now that I know where the blade is cutting, I line up my pencil marks with the appropriate edge in the temporary fence and cut straight through. I will typically err on the side of caution and make it a fraction longer so that I can gradually take it down to the required size, but I have found this to be fairly accurate.

I guess this is similar to making up a sled which is configured for 45 degree mitres, but I haven't got around to doing that sort of thing, and by using a temporary fence I know that I have a cut which is exactly the way the saw is cutting on that day. The kerf exactly matches the blade now, not as it was last year, or for another blade, etc. etc.

Something else I have done is to round over the sharp edge of the mitre slightly with a file. This not only makes it a bit more user friendly without the sharp edge, it can also hide minor misalignments with the mitre.

Hope this helps,
Darryl
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post #5 of 13 (permalink) Old 05-22-2013, 05:32 PM Thread Starter
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Jerry,

have a look at the TV table I built a couple of months back and see if that is the sort of frame you are looking for. The main section is 32mm laminated chipboard which gets around the expansion/contraction issues that Charles mentioned. That by the way is a seasonal thing so you will see it expand across the grain in summer and contract in winter. As the wood dries over time, it contracts more than it expands. I have a 100 year old house where the doors are made like this, and some of the panels no longer meet the frame regardless of the season.

Anyway, if the TV table has the same type of frame you are after, then it is more a matter of being careful and accurate than anything else. I have a digital protractor and use that to set the angle on my saw bench. If that is not handy, I also have a 45 degree builders square that I use. 1/10 of a degree variation will show up in the mitre. I make sure that I am measuring the saw blade only and avoiding touching the teeth as they protrude out from the blade.

The other trick I use is to clamp a scrap of wood on the cross-cut fence and run it through the saw to make a temporary fence with zero clearance. That way I know exactly where the blade is cutting and can line up the marks on the real piece exactly. This is a bit difficult to explain without a picture, but I'll try anyway. I put the real piece upagainst the fence but clear of the blade. Rest the scrap on top of the piece and against the fence, making sure it is extended far enough to be cut by the blade. Clamp it there for a tight sliding fit with the real piece and then cut through. I don't cut it off completely - juse raise the blade enough enough to make a channel cut through. Sometimes you use the inside edge and sometimes the outside edge of the blade. Now that I know where the blade is cutting, I line up my pencil marks with the appropriate edge in the temporary fence and cut straight through. I will typically err on the side of caution and make it a fraction longer so that I can gradually take it down to the required size, but I have found this to be fairly accurate.

I guess this is similar to making up a sled which is configured for 45 degree mitres, but I haven't got around to doing that sort of thing, and by using a temporary fence I know that I have a cut which is exactly the way the saw is cutting on that day. The kerf exactly matches the blade now, not as it was last year, or for another blade, etc. etc.

Something else I have done is to round over the sharp edge of the mitre slightly with a file. This not only makes it a bit more user friendly without the sharp edge, it can also hide minor misalignments with the mitre.

Hope this helps,
Darryl


Darryl, thanks for the help, that sure is a nice mitered joint. I don't have much trouble cutting 45s as I use an Incra miter gauge and their sled. I might just have to eliminate the frame and let the edges go naked with a slight round over to finish them off. My problem with that is that after milling the pieces the final glued up parts are only about a half an inch thick, a little to anemic to suit me. I'll have to think a about this. I have no idea where to buy chip board, I've never used it and besides that I want to use the walnut top that I have put together at this stage of things. Right now I'm thinking that letting the top float inside the frame might be the best answer, don't like it, but, well, we'll have to see.

Jerry
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post #6 of 13 (permalink) Old 05-22-2013, 06:13 PM
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Jerry,

I wouldn't be too depressed about shrinkage if you have thoroughly glued and clamped the laminate. I have a table (bought) that is laminated in a similar style to yours and the laminates aren't pulling apart. It is a cheap Malaysian table, and old enough for the legs to be pulling away from the rails they are attached to, but the table top itself is still good.

Darryl
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post #7 of 13 (permalink) Old 05-22-2013, 07:05 PM
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Originally Posted by Jerry Bowen View Post
How long does it take for the problem that you have just descirbed to occur?

Thanks again,

Jerry
The worst one that I remember the best was an aquarium stand that I made for my daughter. It may have only been a year before it split up in 2 or 3 places. Of course the aquarium made it worse as there is always high humidity around it because of the aerator.

I have seen end grain covered with what I have heard called a "breadboard" end. It is a tongue and groove joint or, better yet, a sliding dovetail that is maybe only glued to the middle part of the center board and the rest allowed to move.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #8 of 13 (permalink) Old 05-22-2013, 07:07 PM
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Jerry a 1/2 inch thick top will look odd and I don't think you will be happy with it. The frame is a good alternative to resolve your thickness issue. Make sure you finish the top before placing it the frame. That way as it moves there won't be an unfinished line showing.
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post #9 of 13 (permalink) Old 05-22-2013, 07:16 PM Thread Starter
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What does anybody think of putting the frame under the half inch table top instead of around it, all I want to do is to make the final top thicker. I could give the top a round over cut or an ogee edge to dress it up. Just wondering.

Jerry
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post #10 of 13 (permalink) Old 05-23-2013, 11:09 AM
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Charles,
In regards to wood movement, and why it moves the way it does. Think of the grain of the wood as a series of straws bundled together. Now imagine those straws filled with so much fluid they start expand. Each straw girth will start to expand, resulting in the width of the bundle overall expanding. Since the straws are open ended (and so is the grain in wood) there is little to no movement along the length of the bundle.

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