MY Trestle Table Design Feedback Sought

[thumbsucker]

I have some large size Quarter sawn English Oak. As it is drying I am starting the design process, by the time I finish the design and build all the jigs the timber will be ready.

Here is my take on a Trestle table. I had originally planed it to be 1200 x 2400mm long but opted to limit it to 980 x 2000mm as the larger size may one day be to big if I were to move into a smaller home. It should still seat 6 to 8 people. I plan to make Windsor chairs to go with the table.

OR SHOULD I JUST GO BIG with a 1200 x 2400 table?

I have included the basic dimensions.

My idea at this point is that the under table top lattice structure is part of the base and that the top is secured to the base using figure 8 washers.

My concern is the connection of the top of the legs with horizontal member that is part of the lattice structure and if will be strong enough to hold the table top?

Since this will not be a glue joint. I am planing to add two 10 mm dowel pins to reinforce the structure.

So with 4 legs this would give me 8 dowel pins.
Each leg has two pins with a width of 72mm.
Making the total area on which the top is resting/pivoting 328mm if you include the 20mm gap between each pair of legs.

The top I feel needs a gentle but almost imperceptible curve to complement the 4 legs.

The legs feature a heavy 25mm chamfer as a decorative element but also to increase edge durability.

It maybe not obvious but the end legs are actually a pair with a 20mm negative space between them.

The top is 40mm thick. I have 100mm x 250 x 2400 oak. If I resaw two 100mm oak in half and bookmatch them then I will end up with 4 boards that will span the width of the table top.

Here are some initial sketches.

What have I missed?

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[KahoyKutter]

Correct me if I'm wrong, but the laminated top is only secured to the base with 6 figure 8 washers. My concern with this design is I don't think they would be sufficient from preventing the top from cupping. Unless you're planning to use breadboard ends or a more stable material (e.g. ply), then you really want something to prevent cupping whilst allowing for seasonal movement. My suggestion would be to use stopped sliding dovetails to attach the 3 shorter "lattice" rails that run perpendicular to the grain direction of the top. If you make the dovetail groove about 10mm longer and only glue one end of each rail, it should keep the top flat whilst allowing for expansion. The only negative about this method is you have to use a "filler" dovetail piece to cover the entry groove on one edge of the table and trying to make this invisible by matching colour and grain direction is almost impossible. This is one of my favourite woody YouTuber's (Ishitani) preferred method.

Just my 2cents. Feel free to ignore me as I'm just a noob when it comes to woodworking.

EDIT: here's a link to a video of Ishitani using this method (https://www.youtube.com/watch?v=x51zMg7roIs) to better explain what I'm referring to. Check out the 6:40 mark.

Cheers,
Mike

[thumbsucker]

Great to hear from you Mike well from anyone. I was getting lonely.

The top will be quarter sawn Eglish oak so cupping is not a possible problem.

I have thought of using sliding dovetails. However I thought of a different way of doing it.

Instead of gluing the top as one piece then routing into the top from one edge and then needing to plug it.

Which I think looks ugly and can never be hidden.

Instead I would glue up the top into two parts.

Then route the dovetail groove from the centre of the table towards the outside on both sides.

Then insert the dovetailed stretcher.

Then glue the two sides of the table together as a single top with the dovetailed rails being able to move freely side to side while helping to increase table top stability.

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See picture should make it clearer that way I will have no ugly plug.

This solution however makes the interface joinery between sliding dovetail and the top of the legs a little more tricky.

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[KahoyKutter]

That's a great solution. Or you could go one step further by gluing the top as one piece, drilling a shallow hole large enough for your dovetail router bit on the underside where you want the groove to begin allowing you to rout the sliding dovetail. Then you can rip the top straight down the middle to allow your dovetail stretcher to slide into the grooves before re-joining the 2 halves. This will ensure perfect alignment of the grooves. I think I'll employ this method next time myself. Cheers.

[thumbsucker]

That's a great solution. Or you could go one step further by gluing the top as one piece, drilling a shallow hole large enough for your dovetail router bit on the underside where you want the groove to begin allowing you to rout the sliding dovetail. Then you can rip the top straight down the middle to allow your dovetail stretcher to slide into the grooves before re-joining the 2 halves. This will ensure perfect alignment of the grooves. I think I'll employ this method next time myself. Cheers.

You are right alignment would be a challenge having the table in two halves.

When routing with a dovetail bit. You never remove the bulk of the material directly with the dovetail bit. Because the stress on the bit can cause it to break. You need to waste out the bulk of the groove with straight cut bit then only skim the edges of the groove with the dovetail bit.

Unless you have a massive sliding table saw it would be difficult rip a 1000 x 40 x 2000 mm table top it would weight over 100kg.

Also you would end up with your two inner boards being about 6mm narrower then the two outer boards. Due to saw kerf and jointing.

I would suggest gluing a sacrificial pine strip say 10mm wide down the middle length of your table. A racing stripe.
Route out the dovetail grooves in a single piece tabletop.
Then use a circular saw to rip down the middle of the pine strip then joint away the pine and re-glue the table back together.

[auscab]

With an oak top 40mm thick, and its properly dry , I wouldn't be making the frame under the top as complex and I wouldn't be screwing the top to the base but just sitting it on locating pegs . I do all my heavy tops this way and screw only for some reason I cant get it to sit flat. The frame doesn't need to go out past the base ends under the top either. Unless you like the look of it .

Rob

[thumbsucker]

The design has evolved from the figure 8 washer towards sliding dovetails.

I like the look of the lattice frame structure, the two longitudinal under table structure members are almost decorative.

This gives a closer idea of where the design is now. I hope it makes sense.

[thumbsucker]

Sorry if some of my CAD is wonky I am no expert.

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[auscab]

Looks good and it'll work . The only thing I can see ATM that I'd change is the size of the top V rail that is the dovetail.

If your Red top is 40mm thick then the end view of that rail looks to be 50 high x 30 wide . Your top is 1/4 sawn so that's a help but the rail should be a lot stronger . More like 80 wide x 90 deep at least. Even 90 + the dovetail on top sounds better.

I'm not so sure the rail going through and sitting in a V just pegged and glued will hold tight for ever as well .

What happens when you have a party and the girls get on top of it and dance ??

Rob

[KahoyKutter]

I'm not sure why you'd make the whole top stretcher a "V". I think part of how the sliding dovetail keeps the top flat is the strength of the dovetail's shoulders pushing against the top all down it's length. By making the whole stretcher a big dovetail you've pretty much deleted the shoulder.

[thumbsucker]

The idea of the V came from this piece. I think it is very striking feature.

Thinking aloud

The question of the shoulder is valid. Is it the shoulder in conjunction with the dovetail or the dovetail splay alone that holds the top flat. I feel that the shoulder will help but the splay is major force contributor. If the table top wanted to pull away from the dovetail the splay is what stopping it from doing so. If it was manly the shoulder then any mortise and tenon joint would suffice to restrict distortion. This is only conjecture and only a practical test would prove it either way. However since I will have a quarter sawn material for the top distortion is not a big concern.

As for dancing girls I know no girls let alone dancing girls.

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[KahoyKutter]

Mate, you may be right. I thought it maybe the wedging action along with shoulder that keeps the top flat but judging by that pic, it may be enough. Please take whatever I write with a grain of salt. I'm relatively inexperienced when it comes to woodworking and some of my ideas and "theories" may be completely way off the mark. Auscab seems to be fine with your updated design, with the exception of the thickness of the top stretcher, and he's a professional fine furniture maker. I'd put more weight on his opinion over mine if I were you. The aesthetics of your design looks good btw. I like the slight curvature to the top. I'd maybe add a heavy chamfer to the underside to make the top loo less "heavy" but that's my taste.

Cheers and good luck with the build.

[thumbsucker]

I quickly drew some dovetails in assorted sizes. Honestly only the 50 x 60 one looks okay the others are way to big. Otherwise we make the table 35mm thick and add a 4th dovetailed stretcher in to the mix.

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[thumbsucker]

I'd maybe add a heavy chamfer to the underside to make the top loo less "heavy" but that's my taste.

I agree a good solid chamfer is essential. Especially in a piece with such a strong Arts & Craft aesthetic,

I am a high school woodwork teacher, I have a degree and a post graduate degree in furniture making. I have taught woodworking to adults. I however see no harm to get feedback nor am I so arrogant to believe I know it all. I feel everyone has something to contribute.

Sometimes we miss the obvious right in front of us because we are to close to involved in the project.

Mike Pekovich from Fine Woodworking has said that every piece he has built is an experiment and he is trying out new ideas and watching then for 5, 10, 20 years and beyond to see if they work.

[thumbsucker]

I'm not so sure the rail going through and sitting in a V just pegged and glued will hold tight for ever as well .

Maybe its not clear from the drawings but their are 4 legs with a total of eight 10mm dowel pins. That much draw bored joinery should in theory be plenty strong.

[KahoyKutter]

Keep in mind that you're not going to see the bit that is inside the table because they're stopped sliding dovetails on both ends. I don't think anyone would notice them at all to be honest. It's different in the pic of that other table because the stretchers go all the way to the edges of the table and that design is able to get away with shallower top stretchers by having more of them and his "trestles" have legs that are wider apart. Your stretcher is more cantilevered from the middle and has less support towards the edge of the table. In your case, I'd err on the side of function over form, especially as I don't think anyone would notice the. I'd go with a 90mm or higher stretcher with a rectangular cross section with normal dovetail. If you're concerned about it being too high, you can put a slight taper from the middle. This would give you a standard bridle joint at the legs which IMO would be a lot stronger. I think Ishitani has done something similar. Also, have you considered adding a bottom stretcher to help counter racking or the legs from splaying out?

[KahoyKutter]

Check out the 11:20 min mark of Ishitani's trestle video (https://www.youtube.com/watch?v=x51zMg7roIs). His table is much smaller than yours but his top stretchers look quite substantial in comparison. They're definitely more than 90mm high at the middle at the leg joint. I'd be going higher if I were you. He's also "housed" (I'm not sure if that's the correct term) the bridle joint which I think makes it even stronger.

[thumbsucker]

Adding a bottom stretcher would maker it less prone to racking. However in all the antiques I have seen the bottom stretcher always gets the kicked out of it. Because people rest their feet on it.

I have opted instead opted to have the two top stretcher each being 125mm high. This will give big shoulders to counter racking forces.

I would be happy to add more dovetails and to spread my legs further apart to reduce the cantilevered affect.

Function should not usurp Form their must be a balance between the two.

Give me time to redo the CAD to look at options.

[KahoyKutter]

Adding more top stretchers dovetailed to the top won't help help with the cantilever unless they're directly attached to legs (i.e. adding a 3rd middle leg, which isn't what I'm advocating because it'd ruin the aesthetics). Take your middle stretcher, it will help stop your top from cupping but it won't help at all when a couple of fat blokes sit on the edge of your table. The things that will help with the cantilever are the height of the top stretchers (particularly at the leg connection), the width of the leg at the bridle joint, and to a lesser degree the thickness of the top stretchers. Basically, the cross-section of your table is a big I-beam. I think the bottom of the I is fine but the top needs strengthening.

[thumbsucker]

Fine woodworking published an article on this sliding dovetail and tabletops I will dig it up tomorrow to get it from the horses mouth.

[auscab]

Maybe its not clear from the drawings but their are 4 legs with a total of eight 10mm dowel pins. That much draw bored joinery should in theory be plenty strong.


Yeah I was seeing it as 2 legs and 4 pegs . 4 and 8 is better . It'll be good !
The picture of the other table looks good to, with the smaller dovetail rails like yours .

Bottom stretchers are a comfy thing for feet to rest on . I sit at one and love it . They have to be real low for that to work . Yeah over time and with shoes on they get marked . Looked after they get buffed up and dusted off all the time .

Trestles are a great table to sit at and use . One thing I like is the possibility of a lower top than other tables allow. How high is yours ? I couldn't see a height.

Rob

[thumbsucker]

Looking at this image and gauging size by his finger nails - it looks like the stretcher ends are max 50 x 50 its only in the middle were it has the bridal joint that it expands to 90 high so to accommodate the connection with the leg.

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Rob the table height is set at 765 mm on the tall side because I am.

[KahoyKutter]

You're probably right.

[thumbsucker]

I awoke this morning with an idea that may reconcile the varied concerns while further increasing the tables rigidity.

By turning the single sided V dovetails into double side sliding butterflies ><.

Since the sliding butterflies would be housed/embedded in all of the table members.

This would lock the lattice structure (red) to the tabletop (blue) to the legs (black) & the two major horizontal stretchers (green) in two directions not only one.

I have also rendered the major horizontal stretchers in an faint green to illustrate their size and capacity to resist racking.



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