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)?

Screenshot 2023-02-28 at 11.34.07 AM.jpgIMG_4160.jpg

[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

[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.