Table Extension Question

[Dave Richards]

Alright, you were helpful with the joint between the legs and rails of the table idea I'm working on so let's see how you do on the next puzzle. I'm trying to work out an elegant, yet not over-engineered solution. (I'm trying to turn over a new leaf on that over engineering thing. ) In this view you can see that the top has been split and the leaf is about to be installed. The leaf is 22" wide so I figure the top halves each need to slide out about a foot to allow clearance. After the leaf is installed the top can be pushed back in.

So, how do I attach the top to the leg assembly to allow the halves to slide? It needs to be strong enough to allow the table to be picked up by its top because someone will do it.

I did a search for table extension mechanisms but everything I found was too bulky. Any ideas? Thanks.

 

[larry merlau]

dave i am not an engineer and may be looking at this to simply but why couldnt you incorparate a large dovetail in your top frame and leg mechanisum that would allow the main sections to be pulled out and back in yet have some strength like the old slides had. the top insert could be connected threw pins and holes like the old tables did.. just a redneck engineering problly wont work but it might trigger your mind to somthing that will i hope .

 

[Doug Shepard]

My first thoughts were along the lines of Larry's suggestion. Then I coughed up an overengineered hairball idea. I'm not even sure if this is doable, but could you take short ball bearing drawer slides and mortise them into the top frame? If this could even work, you'd have to mount the portion on the table so that when the table halves are closed, the slides are "pulled out". Those would only be about 1/2" thick if they could be made to work.

 

[Don Baer]

Dave,
Larry right the dovetails will work.

 

[Dave Richards]

Alright, sliding dovetails. I thought about your suggestion, Doug, and haven't completely dismissed it yet. I might come back to it. In the meantime, I thought I'd see about sliding DTs. I am worried about have the tail made of wood because it could expand and contract with moisture changes and this would change how the top slides and fits. So I came up with the bright idea (well, maybe not so bright. Ok, dim idea) of using Delrin or UHMW for the mating parts of the sliding DTs. The pieces mounted to the top would be in stopped dados that would run a little longer than the plastic parts. The holes nearest the center would be round but all the rest would be short slots so the table top can exapand and contract as it will.

The tails are split into chunks so that the leafe doesn't have to have dados across the full width right at a point where the leaf would be stressed if someone leaned on the edge of the leaf. There would be some mortises cut instead for clearance over the short pieces of DT.

when the table is closed up without the leaf installed, none of the works are visible. Except for the split down the middle, there's be no sign that the table is an extension table.

I'm also thinking that some small stops could be worked out to to prevent the top pieces from sliding out completely but could be released to remove the top if desired.

I found another little detail in a drawing of this table that may make me rethink this arrangment but so far it doesn't seem too bad.

 

[Travis Porter]

Slow to respond on this, but how about the 3 part wood mechanisms like used on a lot of tables. They are 3 pieces and you would attach the center piece to the frame, the rest are free.

 

[Dave Richards]

Travis, I looked at those but they are too bullky.

 

[Marty Walsh]

Hey Dave,

I started thinking about this, and then realised the el-cheapo table I have in the kitchen slides open, yet the legs don't move. Here's how they did it:



It's a simple version of what I think Larry suggested. You could change the openings/rails to dovetails, instead of the ones shown, but these are easier to make.

If the 'holes' in the apron don't bother you, than this idea is probably one of the easiest. It would mean adding a center apron though, for the slides attached to the underside of the top to slide into to.

While you're designing your table, have you given any thought to making the extension a gullwing, with the leaf "hidden" inside the table until it's needed. I decided, the first time I saw a table that did that, that any dining room table I build will incorporate that feature...

See how I am...make the slide easy, but complicate the leaf...

- Marty -

 

[Travis Porter]

You're right, they are too bulky. I like Marty's table the best I think, dovetails on the top not on the frame.

I especially like the "hiding" leaf. That would be way neat!

 

[Frank Chaffee]

Dave,
You don’t pick easy ones, do you?

I don’t have much of a feel for woodworking, but it is difficult for me to imagine that dovetails could sustain the moment at the ends of the stringers were the table picked up with leaves extended.

Any mechanism that would come out through the ends of the stringers seems to affect the clean lines of the table.

What I would do is this: (Assuming 6 ½” overlap of extended leaves & stringers.)
• Get some heavy extruded and anodized aluminum T-track.
• Mill a groove in two stringers to accept the track, stopping the groove about ½” short of each end. The groove would be slightly deeper than the height of the track.
• Remove by milling, the top legs of the track three inches each side of its center.
• Drill and countersink for screws along the length of the track.
• At the center of the track(s), drill a ½” dia. hole.
• At the center of the stringers, drill and tap ½-13 x ~ 2” deep.
• Using a fixture that keeps the top of the track flush with the top of the stringers, bed the track in epoxy. Cure.
• Screw the track down.
• Mill Delrin tee sections (4), about 5 5/8” inches long that are sized to fit the track sections in hand. Attach them to the inner ends of the sliding leaves.

Now, the sliding leaves can be dropped into the track, pulled out, and a ½-13 SHCS can be screwed into the center(s) of the track for a stop.

To further strengthen the tabletop, how about this?
• Make a 2 tube/1 rod sliding assembly that incorporates springpins and detents to keep the rod engaged to both tubes when extended.
• Take each of the edge pieces that run under the table parallel to the slide direction, and split in half with a bandsaw.
• Mill hemispherical grooves through them, again stopping short of the visible ends.
• Embed the ½” I.D. steel tubes into the grooves and glue each piece back together.
• After assembling the first leaf to the table, insert the two ½” dia. steel rods into the tubes, and push them all the way in.
• Assemble the second leaf to the table, pull the rods back from the first leaf, and engage the second. Now the rod will float between the two leaves.
• Construct the parts beneath the center leaf as a downwards facing C section, so the rod supports the leaf ends.
• If desired, a detent or lock could be used here as well.

I look forward to seeing both how the original is constructed and how real woodworkers approach this challenge.

 

[Dave Richards]

Marty and Frank, thank you for the suggestions. I had thought about something similar to what you showed Marty but I didn't like the idea of the the notches in the rails. Frank, I had thought about the T-track thing, too. I kind of thought my Delrin dovetails would serve the same purpose and there's be nothing of the sliding mechanisms exposed when the top is collapsed.

On further investigation of the images I was able to find of the Thos. Moser-built version, I discovered there must be some sort of mechanism hidden inside the rails. I noticed that the crossing rails seem to be cut and I'm guessing they did something like the latest version of my drawing.

I found some of these self-centering extenders that are short enough to fit inside the frame from VanDyke's. I don't like the bulk but their height is less than the height of the rails and I think I could trim the wood of these extenders enough to make the rails even less obtrusive.

 

[Don Baer]

Now that makes sense.

 

[Travis Porter]

That looks good to me. Aren't there some metal ones that are even lower profile?

 

[Dave Richards]

Thanks guys. Travis, I did find some metal ones but I figure it I'm going to end up with commercial slides I might as well make it so the top can be opened by one person. These were the only ones I could find that would do that.

By the way, the version of these with the sprocket and racks was found on a website as a DWG file. It needed some clean up to make it into a decent component but I didn't have to draw the whole thing. If anyone wants the component, let me know.

 

[Marty Walsh]

Dave,

Looks like you found a good solution...albeit a pricey one!

Although, being able to open/close the table with only one person is a biggie. Denise is always complaining that we both have to grab an end and pull to get ours open.

So, will there be enough room between those openers for the gull-wing leaf? (My cheap table is in fact a gullwing. I can take pictures if you're interested.. ).

- Marty -

 

[Dave Richards]

Marty, I guess I'm not sure what a gull-wing leaf is. A picture would be appreciated. Thanks.

 

[Marty Walsh]

Dave,

I have no idea if these things have an 'official' name, but I've always referred to them as 'gull-wings':

We start by pulling the two top sections apart:



This exposes the leaf in its 'folded/storage' postion. We then simply lift the top side of the folded leaf:



We lift the leaf until it's completely unfolded, and now level with the top of the table:


We then simply push the two tops in towards the leaf until they touch (engaging the pins):



The actual hinge is pretty simple:



The plus side of this design is

There can be as many leafs as can be fitted under the table.
The leafs are stored safely without any additional room/space required.
There's no leaf to lift up onto the table when the extra size is needed.
No need for 'leaf bags' to protect the leafs while they're being stored somewhere.
​

The only down side I see is the extra 'split' you see on the table from the split leaf. But to me that's not an issue. There are already splits on either side of a normal leaf. This simply adds one in the middle of each leaf.

As I said, I have no idea if there's a 'proper' name for this type of leaf, but I really like it...ever since I first saw it about 15 years ago at a custom furniture show.

Just something else to think about Dave...
- Marty -

 

[Marty Walsh]

FWIW,

I just did some googling on this and find that some folks refer to this table leaf setup as "Butterfly Tables".

I like gullwing better...
- Marty -

 

[Frank Chaffee]

Dave,
This morning when I saw your solution to the sliding leaf problem I was very excited! It certainly distributes loads better than the idea I had come up with. When you edited the drawing to show the rack and gear mechanism that allows one person to extend both leaves with one action, I was further wowed!!!

As the day wore on however, I became increasingly disturbed by the breaking of the rail joint you had so ingeniously constructed. Images of the phony house style proliferating in the southwest, with “vigas” (actually false log ends tacked onto the upper ends of stick framed and plastered dwellings), protruding at right angles to one another and obviously serving neither purpose nor stylistic imitation at all well, came to mind.

So I looked at Moser’s site again to see what his design philosophy is, and found this (insertion and bolding mine):

“I learned a good deal about ornamentation during a year I spent teaching English in Saudi Arabia in 1965. That vast expanse of blowing sand and dry river beds was a universe in beige—ubiquitous beige—without end. As if in protest to this monochromatic world the Bedouins colored and decorated nearly all man-made objects. Like Persian carpets, their buses were an explosion of color and appliqué on Mercedes' [no Marty, not 300 SL’s] frames.

Whether in the desert or on an uninteresting piece of furniture, ornament offers escape from boredom and engages the eye where form fails to satisfy. In a sense, ornament is often used to conceal mediocrity—a kind of visual sophistry that makes the commonplace appear inviting.

In designing our furniture, we strive to create forms that are pleasing in themselves, forms that achieve grace because they serve human needs, with aesthetics predicated on function. The ornamentation in our work derives from the exposed architecture of the furniture and the translucent richness of the wood itself.

The handiwork of the craftsman as revealed in a dovetail joint or the wedged tenon of a chair spindle is ornament derived from function rather than embellishment. The sharpness of a miter joint, the pinning of a tenon, even a plugged screw are decorations of sorts, but with purpose. Hidden inside a drawer or in the back of a case, a finely crafted dovetail affirms our sense that beauty need not be boldly on display to enhance our lives.

Every effort is made to release the natural warmth of the wood through polishing, oiling and waxing, rather than by painting stain or lacquer from a can. Heated linseed oil adds greater visible depth to the wood, like shining light into water. By allowing the work of nature's paintbrush to emerge in the unique grain pattern of each piece, we hope to add grace without artificial adornment.

Years ago a professor taught me that true art conceals itself in apparent simplicity. She was talking about acting, but this can be said of good design as well. Unadorned shape can speak with an authority not found in decoration. A well-designed piece of furniture should be a form to which nothing can be added and from which nothing can be taken. Good design is an exercise in restraint.”

So based on this statement by the artist, I do not think that the rails move from the fixed tails.

Yours,
Frank

 

[Dave Richards]

Marty, thanks for the pictures. That looks like a neat option although as I've drawn the table, there isn't room for that unless the center leaf is folded into 10ths.

Frank, I would love to think that the rails are not cut as my latest drawing shows however I think they are. The attached images are from the tearsheet for the table. You can see in the second where I've drawn in the red circles that the rails do indded appear to be cut just inside the legs. There are some slides of some sort outboard of the base of the table but I expect those are more for guidance than anything else.

If the rails were solid there would have to be some other mechanism to allow attachment of the top to the legs and also provide for sliding. Then I think we're back to something like I drew before with the sliding dovetails or perhaps your T-track suggestion.

I do like the idea of hiding the mechanism between the rails and the top. I think it makes for a much cleaner look from below and it would keep the weight down. Hmmm.....

Maybe I need to take a trip to Maine. I am planning to go there this coming summer anyway for something else. A stop at the Moser shop should be added.