C Channel for dining table build

[Ray Gannon]

Hi,
I'm building a dining table with live edge cherry from 3 slabs. The total dimensions are 8'x3.5' (and 1.6" thick). I've read in several places that it's a good diea to put c channels to stop the table from bowing with changes in temperature and humidity. I was thinking of putting three c channels. I had two questions:
1. I've seen people use steel c channels. Will reasonably thick aluminum work as well? I have it available for free versus buying steel.
2. If my table thickness is 1.6", is it ok for the c channel to be 1 inch (the legs going up into the slab in the slots that i cut) or is that too much/risky and would affect structural integrity and it's better to keep it shorter (0.5inch)?

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[Mike Henderson]

I can't give you an absolute answer but I have used aluminum angle in a similar situation and it's held up fine.

Mike

[Andrew Hughes]

I don't think its necessary. If the wood is dry and finished why would it bow.
If it not dry it shouldn't be used.
That c channel thing show lack of confidence in woodworker.
Good luck

[Edward Weber]

I use dovetailed battens

[John Kananis]

I would use steel instead of aluminum on a piece that big and I definitely wouldn't epoxy it in. You'll want the center mounting hole to fit the appropriate fastener and the others slotted so the wood can move with the seasons.

[Michael Burnside]

100% would use c-channels on this, no way I'd risk it. If the length of the "C" is 3/4" or longer then aluminum is fine since it shouldn't flex much, otherwise I'd use steel. Your labor is worth the insurance. I think 2 is sufficient for 8' though, spaced 1.5' in from both ends. And 1" deep is fine, the c-channel will be stronger than the wood. For threads to attached the channels I would use steel inserts too, not brass. The stainless threads are wicked sharp and are worth their extra cost. Also, I would not expoxy the channel into the inlay.

[John TenEyck]

I have to agree with Andrew. Why would one expect properly acclimated and finished wood to cup? I think a lot of people working with slabs are using material that is far from really dry; and that's the reason they use these reinforcement ideas. I wonder how they look when the wood does dry?

John

[Michael Burnside]

I have to agree with Andrew. Why would one expect properly acclimated and finished wood to cup? I think a lot of people working with slabs are using material that is far from really dry; and that's the reason they use these reinforcement ideas. I wonder how they look when the wood does dry?

John

Acclimated to what? Your shop? Your house? Your customers house? Do they have a humidifier? What season? Where are you located and how much variation do you see in relative humidity? Is the meter you're using a quality meter and are you testing multiple locations top and bottom? Are you just assuming it's acclimated becuase you properly stickered it and it sat long enough? Way too many variables NOT to use c-hannels but that's just my opinion and says absolutely nothing of my confidence as a woodworker and more to experience with wood movement.

[Jim Becker]

I think the aluminum will work fine. Watch a few Blacktail Studios videos for the technique to route for the c-channel so it's fully recessed and how to install the threaded inserts cleanly. Never use epoxy or other adhesive...you need slots for the bolts so the wood material can expand and contract across the grain. The sole purpose for the c-channel is to keep the construction flat.

[ChrisA Edwards]

Shortly after the 9 minute mark


https://www.youtube.com/watch?v=lQ41TIGhovM

[John TenEyck]

Acclimated to what? Your shop? Your house? Your customers house? Do they have a humidifier? What season? Where are you located and how much variation do you see in relative humidity? Is the meter you're using a quality meter and are you testing multiple locations top and bottom? Are you just assuming it's acclimated becuase you properly stickered it and it sat long enough? Way too many variables NOT to use c-hannels but that's just my opinion and says absolutely nothing of my confidence as a woodworker and more to experience with wood movement.

I imagine you know the answers to your questions so why the challenge?

Ever see a C channel in a Nakashima table?

John

[Andrew Hughes]

Thank god we have the internet to document the evidence and sound reasoning for epoxy tables with steel channel embedments.
In the future they wouldn’t have to make up theory’s about some unseen force that spurred woodworkers to coat tables with incredibly hard plasic resins and structural steels.
Think of all the research we saved. :)

[John Kananis]

Not fair. George Nakashima is an artist whose knowledge and skill far exceed a collective of knowledge and skill on this forum. He's also sourced a lot of those slabs himself, right from the tree, dried them, aged them, etc and could tell you exactly where on/in that tree the particular piece came from.

Edit: I'm not implying that every slab turned into furniture needs a steel c channel but when large enough and enough variables are at play, it doesn't hurt to be safe. That said, it's nice to be able to use the actual base to keep things flat (when appropriate and aesthetically correct).

[Ray Gannon]

Thank you so much everyone. I'll go with aluminum in that case for now. And to confirm, the edges being 1" (in a 1.6" slab) is ok? or should i get something shallower?

[chuck van dyck]

1” is fine. Whatever do, do not epoxy it in. I usually use lags screws in elongated slots for movement.

I recently visited a 8x4 c shaped banquette seat I built with 8/4 white oak. Being winter and near baseboard heat, its a 1/2” narrower than it was when I delivered it. Wood will move, and the bigger it is, the more it moves.

Whoever is bringing Nakashima into this, have you ever put a straight edge on one of his slab tables? Neither have I but I can tell you I have visited his Alter for Peace many times at St John the Divine here in NYC. Its one of my favorite pilgrimages. The table is not flat. He was also a fan of massive battens and screws. Steel lets you keep the design low profile. If thats not the goal than by all means go GN style and screw 12/4 braces to it.

You could take it a step further and put stopped kerfs into the underside. Then aluminum or a number or other materials would not struggle to keep it flat. You see this technique on contemporary danish modern designs. Replicating the past is all well and good, but its even better to learn from it.

Edit: and definitely undersize the c channel leaving at least a 1/2” on either side.

[George Yetka]

If your worried about getting too close to the top you dont have to fully sink the channel. as long as the the flanges and part of the web are sunk. I would stick to steel it has a lot less flex. I have been purchasing these from Fractal designs canada https://fractaldesigns.ca/collections/inserts-bolts-and-table-reinforcement The fit and finish have been very good. Make sure the holes are oblong so the wood can move in them slightly. And the Ez-lok SS inserts are very nice but get very expensive if you have quantity. The Rampa ones are also pretty nice and quite a bit cheaper

[Jim Becker]

Not fair. George Nakashima is an artist whose knowledge and skill far exceed a collective of knowledge and skill on this forum. He's also sourced a lot of those slabs himself, right from the tree, dried them, aged them, etc and could tell you exactly where on/in that tree the particular piece came from..

I've been in the slab storage at the Nakashima compound...what a treat. At the time, they indicated there was still material in there that George had selected but just had not spoken as to what it wanted to be. :) The place I buy most of my domestic lumber is one of the suppliers for them.

---

I think that the individual slab or construction is what determines the value of using c-channels or not. It's just a method to use when warranted by the specific project and nothing that folks should scoff at. My reference to Blacktail had nothing to do with the resin work which is certainly a subjective thing, however. It was all about the use of and installation method for c-channels because Cam does it very well and very consistently.

[Michael Burnside]

I imagine you know the answers to your questions so why the challenge?

Ever see a C channel in a Nakashima table?

John

My point was that there are so many variables to woodworking that using them is sound judgment, but you do you.

And to compare to Nakashima is absurd. They probably have moisture content measurement down to a science when your charging THAT much for a piece of fine furniture.

[Edward Weber]

Not fair. George Nakashima is an artist whose knowledge and skill far exceed a collective of knowledge and skill on this forum. He's also sourced a lot of those slabs himself, right from the tree, dried them, aged them, etc and could tell you exactly where on/in that tree the particular piece came from.

Edit: I'm not implying that every slab turned into furniture needs a steel c channel but when large enough and enough variables are at play, it doesn't hurt to be safe. That said, it's nice to be able to use the actual base to keep things flat (when appropriate and aesthetically correct).


Wow, how to unpack all that.
It doesn't take a genius or a woodworker of Nakashima's caliber to understand that a plank, or 3 planks glued together like the OP's project, can bow or cup. All you're trying to accomplish is to restrain the wood from moving. This can be done in many ways, a metal channel is just one of them. Not my personal choice but it does the job.

[John TenEyck]

Not fair. George Nakashima is an artist whose knowledge and skill far exceed a collective of knowledge and skill on this forum. He's also sourced a lot of those slabs himself, right from the tree, dried them, aged them, etc and could tell you exactly where on/in that tree the particular piece came from.

Edit: I'm not implying that every slab turned into furniture needs a steel c channel but when large enough and enough variables are at play, it doesn't hurt to be safe. That said, it's nice to be able to use the actual base to keep things flat (when appropriate and aesthetically correct).


What's not fair? There are many folks here that understand how wood moves, what causes it, and how to deal with it. And they know the best way to deal with it is to make sure the wood is at equilibrium with their shop before using it, to work it in stages, and to finish all surfaces equally. Nakishima was no smarter than anyone else in this regard. He was just willing to adhere to a process that gave him wood that would remain stable. The guy was a great woodworker, not a wood whisperer.

John

[Christopher Charles]

Maybe I missed it, but what do you plan to use for a base? The slab and base can work as a system to achieve the same effect, depending on the details of the base.

Best,
Chris

[John Kananis]

Wow, how to unpack all that.
It doesn't take a genius or a woodworker of Nakashima's caliber to understand that a plank, or 3 planks glued together like the OP's project, can bow or cup. All you're trying to accomplish is to restrain the wood from moving. This can be done in many ways, a metal channel is just one of them. Not my personal choice but it does the job.

I don't disagree with anything you said. It's basically the last paragraph you quoted.


What's not fair? There are many folks here that understand how wood moves, what causes it, and how to deal with it. And they know the best way to deal with it is to make sure the wood is at equilibrium with their shop before using it, to work it in stages, and to finish all surfaces equally. Nakishima was no smarter than anyone else in this regard. He was just willing to adhere to a process that gave him wood that would remain stable. The guy was a great woodworker, not a wood whisperer.

John

The juxtaposition isn't fair. You're comparing Yo-Yo Ma to a guy practicing violin in his basement. The knowledge, experience and resources did not necessarily make George Nakishima smarter but it did afford him wisdom that exceeds that of most. Imho

[John Kananis]

Jim, I'm envious. To my shame, New Hope, PA isn't that far from me but I haven't been.

[Richard Coers]

I suggest you have an engineer buddy figure out what strength your C channel has. I bet you a box of donuts the wood is stronger when it moves than what the metal can resist. I saw a desk that the wood movement of the slide out writing surface broke the entire side off the desk when it expanded in the spring. Just adding metal isn't a solution if it's weaker than the wood. All this steel under a table is a very recent on-line trend created without real knowledge of what they are attempting. A very large percentage of on-line new woodworkers have no idea about wood movement in the first place. Look at reddit, those folks ignore it constantly and there must be no one with a YouTube entertainment channel that teaches them.

[Jim Becker]

Jim, I'm envious. To my shame, New Hope, PA isn't that far from me but I haven't been.
Check their website, as I believe they historically have public hours on Saturday mornings, but I don't recall the details and if it's year-round. These regular tours are not comprehensive, but give a nice view in general of what goes on there. A number of years ago, the Michener Art Museum in Doylestown had a benefit event at the Nakashima compound which not only included a box lunch and a talk and other interaction with Mira and Kevin, but also a tour of EVERY building on the property. It was mind-boggling. They haven't done it since, to the best of my knowledge, but I'm so thankful that Professor Dr. SWMBO and I got to do that event. It was worth every penny of the fifty bucks donation! The museum has a Nakashima room as a permanent display and gosh darn it, you can sit in several Nakashima chairs and fondle a whole bunch of other things. :)

[Michael Burnside]

Maybe I missed it, but what do you plan to use for a base? The slab and base can work as a system to achieve the same effect, depending on the details of the base.

Best,
Chris

Very good point. Before I felt comfortable building my own full-sized table, I hired a local artisan to build a 36" x 9' table for our dining room. He brilliantly constructed a large X frame metal base, as my wife wanted a modern flare, and then inset the top along the width of the table in two places, making for an effective c-channel.

[Edward Weber]

In all but the most extreme circumstances, there is no need to introduce an external metal brace.
Mortise a hole through the blanks and insert a proper sized square tube. It won't bend, it can float and it won't bee seen. You can also do this with round rod or pipe.
This can all be inserted during glue up and will be unseen to anyone.

Routing out 3/4 channels and securing C-channel to the underside is a rather crude way to approach stiffening the top IMHO.

[John TenEyck]

FWIW, aluminum has 1/3 the stiffness of steel. I'm certainly not advocating any C-channel, but if you must, use steel. Also, FWIW, a square tube will be about 4X stiffer than a C-channel of the same dimensions and cross section.

John

[Christian Hawkshaw]

In all but the most extreme circumstances, there is no need to introduce an external metal brace.
Mortise a hole through the blanks and insert a proper sized square tube. It won't bend, it can float and it won't bee seen. You can also do this with round rod or pipe.
This can all be inserted during glue up and will be unseen to anyone.

Routing out 3/4 channels and securing C-channel to the underside is a rather crude way to approach stiffening the top IMHO.

If your top is comprised of wide boards, what method do you use to make the mortise? I am assuming one length of tube going across the width of the table, but not exposed on the sides. So you could have some through mortises that could be quite deep if you have wide boards.

[Jim Becker]

That's the same question that came to my mind, Christian. Same for slabs. Internal bracing would be a tough row to hoe, although I certainly like the idea in principle.

[Mike Monroe]

To answer your questions;

1. I'd use steel. FWIW - I purchased steel C channel from a local welding shop at a very reasonable price, they even cut it to the lengths I needed. A machinist friend milled slots into the C channel for me and I spray painted them black. A very economical option vs. purchasing powder coated C channel online. It's not like one sees the C channel or even know it's there in the bottom on the table top.
2. 1/2" legs on the C channel should be sufficient, that's what I went with. I made a hair pin leg table out of some locally sourced red oak slabs. My table dimensions are 63" x 32" x 1.5". I installed two lengths of C channel in the bottom of the table for safe measure against future warping/cupping. My table looks something like the table at this website: https://www.modernlegs.com/make-desk-height-using-hairpin-table-legs/

Also, I finished the table with Rubio Monocoat. I'm very pleased with Rubio Monocoat, from ease of application to look and feel of the finished product. The table is my home office desk and replaced one of those foldup plastic BORG tables.

[Edward Weber]

If your top is comprised of wide boards, what method do you use to make the mortise? I am assuming one length of tube going across the width of the table, but not exposed on the sides. So you could have some through mortises that could be quite deep if you have wide boards.

As I said, you could also drill round, through holes, for pipe, rod or dowels if the board it too wide to mortise. Easily done with a brace and bit.
With mortising, going from each side is usually the best method.
You actually don't have to connect all the way through. If you manage about 80% of the board, it will stay pretty flat.

Here is an outside table I made in 2013, basically a proof of concept for this type of construction. Would it hold up outside?
This is simple construction grade 2x4 cutoffs made into a top. I ran 1/2" wooden dowels through the strips for support. After 10 years outside, I just measured, and the center is 3/32" lower that the outside accross the grain. Flat enough for a 36" wide outside table.
Had this been inside in a climate controlled environment, I have no doubt that it would be as flat as the day I built it. (which is what the photo is)
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[Bill Dufour]

Aluminum can be stronger then steel, it just has to be a little thicker.
Bill D

[Edward Weber]

Here is a retail version of a dovetail solution, much stronger than the widely used steel channel that's being used by many YouTubers.
https://www.hafele.si/en/product/dovetail-batten-for-solid-table-tops-straightening-fittings/P-00872033/?PageSize=48
This approach can also be done with a three section wooden dovetail for slab tops.

[John Kananis]

On one hand, I really like that, on the other, how could you install that AND hide the entry point (on a slab)?

Also, can you expand a little on the three section dovetail? Ty.


Here is a retail version of a dovetail solution, much stronger than the widely used steel channel that's being used by many YouTubers.
https://www.hafele.si/en/product/dovetail-batten-for-solid-table-tops-straightening-fittings/P-00872033/?PageSize=48
This approach can also be done with a three section wooden dovetail for slab tops.

[Edward Weber]

Left side install, right side install, center strip or screw to fill the gap.
There is no "sliding", this fits into a stopped slot.

[Richard Coers]

FWIW, aluminum has 1/3 the stiffness of steel. I'm certainly not advocating any C-channel, but if you must, use steel. Also, FWIW, a square tube will be about 4X stiffer than a C-channel of the same dimensions and cross section.

John
Finally, someone that is talking about real strength and not imagined fixes.

[Richard Coers]

Aluminum can be stronger then steel, it just has to be a little thicker.
Bill D
More like a lot thicker.

[Ole Anderson]

Shortly after the 9 minute mark


https://www.youtube.com/watch?v=lQ41TIGhovM

Yep. If Blacktail Studios use them on $17k pieces that is good enough for me. Go to 3:20 https://www.youtube.com/watch?v=8wYDq9F8J7M&ab_channel=BlacktailStudio

[John Kananis]

The guy definitely has the epoxy pour down to a science (which I don't care for but that's subjective and aside) but I've seen nothing else in his videos to convince me of any other skill/knowledge in his arsenal. Imho, the guy established himself on yt early in the epoxy trend, uses large surfaces (which also brings a crowd) and gets to charge that much because of his popularity on yt and not necessarily because he can trim a miter like a pro with nothing but a rusty nail lol.

[Edward Weber]

Finally, someone that is talking about real strength and not imagined fixes.
Let me add by saying that the channels everyone is calling "C-channels" are technically U channels, yes there is a difference.
Also about strength. The channel is only as strong as it's orientation (which is flanges pointing down in most all applications) and the holding power of the (4) screws used to attach it.

A dovetail system (wood or metal) is attached along it's entire length and can not loosen or strip in the same way as the above. The same applies to an internal stiffening system as well.

The ONLY reason this method has become so popular is because it's easy for most anyone to do.

JMO, YMMV

[Robert Banh]

In all but the most extreme circumstances, there is no need to introduce an external metal brace.
Mortise a hole through the blanks and insert a proper sized square tube. It won't bend, it can float and it won't bee seen. You can also do this with round rod or pipe.
This can all be inserted during glue up and will be unseen to anyone.

Routing out 3/4 channels and securing C-channel to the underside is a rather crude way to approach stiffening the top IMHO.

Can you elaborate on how to do this? I'm new to woodworking and am planning to make a 72" x 40" dining tabletop out of 6/4 white oak. In my research, I came across a table called the "Max Table" by designer, Max Lamb. It looks like he used metal rods as you described inserted into the tabletop prior to glue up. Here's a link to a overview of the table, showing the design. https://www.dezeen.com/2020/07/15/hem-max-lamb-max-table-design/#
511867
This seems like it would be a nice idea since the metal rods would be hidden and they would not only allow for easier alignment during glue up, but strength to resist warping. It would be pretty easy to drill the holes using a dowel jig to the appropriate size & depth. I'm thinking 3/8" on a 6/4 board.
The problem is I can't find any other info regarding this method and with my limited knowledge in wood working, I'm sure I'm missing something. Any help would be appreciated! Thanks!

[Edward Weber]

I saw this the other day and thought of this thread. This is basically the same way I've been using internal rods/dowels to strengthen tops, just like the small patio table I posted.
https://www.youtube.com/watch?v=OH86OiE15GI

[Prashun Patel]

I've used aluminum. I wouldn't do it again. It doesn't resist the force enough IMHO.

[Mark Gibney]

I just read the first page of this older thread. Did the OP ever tell us what he did? - I scanned the other pages but didn't see it if he did.

I'm made slab tables and I've never felt the need for embedded steel cross-stiffeners. So I'm with Andrew on this.
Will the tabletop be secured to an apron frame? Won't this provide enough bracing?
And cannot steel stiffeners be hidden behind the apron and surface mounted? - this would provide a lot more thread of the screws to hold the stiffeners in place, and for sure that's really crucial.

[Ole Anderson]

Check out Blacktail Studio on YouTube, he frequently routers in a recess for a steel C channel, but usually for leg attachment.

[Robert Banh]

I saw this the other day and thought of this thread. This is basically the same way I've been using internal rods/dowels to strengthen tops, just like the small patio table I posted.
https://www.youtube.com/watch?v=OH86OiE15GI

That was a great video, thanks for sharing.
So you would recommend the rods go all the way through each panel or do you think it's enough if the rods go through the majority of the board (for example, say each board is 8" wide and a 6" rod goes in 3" in on each side of the board and 3" into the adjacent board). Also I think the metal rods would be "floating" and not have any glue placed on them like wooden dowels would. If the rod just has to go into the majority of the board, then in the 6" rod example, would you recommend drilling the hole to 3.5" to allow for some space so the rod isn't a super tight fit? I'm thinking about using a 3/8" rod for 1.5" thick board. Thanks!

[Edward Weber]

That was a great video, thanks for sharing.
So you would recommend the rods go all the way through each panel or do you think it's enough if the rods go through the majority of the board (for example, say each board is 8" wide and a 6" rod goes in 3" in on each side of the board and 3" into the adjacent board). Also I think the metal rods would be "floating" and not have any glue placed on them like wooden dowels would. If the rod just has to go into the majority of the board, then in the 6" rod example, would you recommend drilling the hole to 3.5" to allow for some space so the rod isn't a super tight fit? I'm thinking about using a 3/8" rod for 1.5" thick board. Thanks!

Personally, I would go all the way through. Boards can warp, cup, and twist at any point across their width. How tight you make the tolerances is up to you and what wood you're working with. You're trying to restrain the wood from moving across it's width, too loose and it defeats the purpose. There is also no need to put glue on the dowels but it's not a big deal if some gets on them. If you're concerned, you can always wax them beforehand so glue won't adhere during assembly.

[Warren Lake]

they try to allow side to side movement then the focus is trying to keep it flat.