Blog 2016

WOOD WORKING BY DESIGN

Help! Our Table Has A Gap In It!

05MARCH

The title should have really been 'People who think that wood should behave like they think it should behave'.

If I sound a bit gruff, you're right. To be clear - I do not suffer fools gladly. This all began with a simple request to help some folks who claimed that their table had developed a gap and could I try to fix it? I said I would take a look at it. Fine!

When I arrived to take a look at the table the first thing the husband said was, "the legs are loose because the table was sagging in the middle which is causing the gap.". There you go. Problem solved.

I took a look beneath the table and noticed that all of the latches were closed but were very loose. Wood movement came immediately to mind. Why else would the latches be so loose? The next thing I noticed was that the adjoining side aprons were butted directly against each other as they should be. Now I was certain it was wood movement.

To back up a bit, the table in question was a extension table with two inserts. I was aware of this before I arrived, but had not noticed how the table was actually constructed.

Extension tables, IMHO, are a pandora's box of predictable problems due to wood movement. Let me explain.

An 8-ft board from the moment it is cut from the trunk of the tree to the time it is ready to be used in the shop (7-8% moisture content) will only shrink in length about 1/16-inch. The width of that same board - the tangential plane, will shrink approximately 8% in this same time period. But more importantly, this same board dimension will continue to contract and expand due to changes in relative humidity throughout its useful lifetime.

If you think of wood as a hard sponge that is continously absorbing and expelling moisture, this will help you mentally visualize a boards dimensional transformations from contraction - periods of low humidity, to expansion - periods of high humidity.

Now, if you add up the shrinkage across the tangential plane of the table-top boards you will soon have a very measurable change in dimension between the two halves of the extension table when closed with or without the table inserts.

Back to our extension table.

Most extension tables have their top boards bonded together perpendicular to the length of the table. This means that the top will vary in width parallel to the table length due to changes in relative humidity. The table aprons that run the length of the table do not vary in length seasonally as explained above. So in periods of low humidity, the top contracts due to moisture loss. The side aprons, on the other hand, remain constant in length. The differences in these changes causes the gap to appear across the width of the table top, which precisely describes the condition the extention table was currently in.

This is not rocket science.

I tried to explain this in several ways, but try as I might, each explanation fell on deafened ears.

So, I decided to flip the table over and tighten those 'loose legs'. I even went so far as to ask for a crescent wrench. The legs were fastened very securely to the corners of the table. So much for that.

They appeared very frustrated with my diagnosis of their table. I felt badly for them, but if a person does not understand wood movement they will be very perplexed at how their expensive wood table suddenly developed a gap where a few months earlier there was none.

I went the extra yard and explained that if I were to trim the protruding length of the aprons on both sides that would eliminate the gap - for now. I futher explained that when the relative humidity increased the table top would still be fine save for the new gaps between the adjoining side aprons.

That earned me the official 'deer in the headlights' look from both of them. I apologized for not being able to help them and left.

Years ago my dear Grandfather used to say, "You can lead a horse to water, but you can't make him drink." Grandad would be happy to know that his truism is still true today.

I tried!

Can you make a knock box for us?

09APRIL

Why sure, I can make you a nice knock box. Maybe. What is it?

This nice couple just wanted a small wooden 'box' to replace their particle-board box that holds their stainless-steel coffee ground container.

And, these are not just ordinary run-of-the-mill coffee grounds, mind you, these coffee grounds are ground in a very special Italian coffee maker - Pavoni. Frank Sinatra had an identical model if you must know.

This 'box' is not a box in the conventional sense because it has no top or bottom - just four sides, thank you! So, I guess you could call it a case and not a box. Its real purpose is to simply hold the stainless-steel tray that holds the coffee-grounds.

It's complicated, I know.

So the wooden case and its stainless-steel pan together make what is known as a knock box. And now we know what a knock box is.

dovetail joints
Ah-hhh ... can you smell the coffee? I can. Oh, yeah - the knock box is the walnut box in the center.

One other important aspect of our good friends' knock box is that it has a hard rubber rod that extends across the stainless-steel tray. As you may already suspect, this is used to knock the coffee grounds out of the portafilter into the stainless-steel tray.

dovetail joints
This image shows the portafilters resting on the knock box rod. The portafilters are knocked against the rod to dislodge the spent coffee debris into the stainless-steel tray.

As you may have been able to see in the images, I made the knock box out of walnut. The joinery is hand-cut dovetails.

Dominoes vs #20 Biscuits

04MAY

I've used biscuits for over 20 years or so. The Domino is the new kid on the block. For those of you who don't get out much you can come up to speed on Festool's Domino here. (Once on the page just click on the Festool Domino DF 770 link and it will zoom you down to the Domino info.)

I have always been in the habit of stacking biscuits when I wanted a tighter fitting joint. While that does work, using domino's puts biscuits to shame in every respect. This is not to say that Domino's can replace biscuits for every application because there are many instances where biscuits are the only 'joint' that will work. Thin book-matched panels come immmediately to mind.

First of all, Domino's do not let the boards slide laterally like biscuits do. That may not be a huge issue, but it is one thing you must be aware of if alignment is a concern.

Will you sign our piece for us?

16MAY

Sure, I can sign your piece. I would be happy to do so.