Western red cedar tenon size

[Garrett Ellis]

I'm trying to join 1.5x3.5 cedar lumber using mortise and tenon joinery, but I'm wondering how thick the tenon should be. I think the rule of thumb would make it 1/2", but I was reading suggestions in another thread to make them as much as 1" thick. Would 1/4" be enough on each side of a 1" mortise on a 1.5" wide board? Should I just split the difference and go 3/4"?

Thanks!

[Sean Tracey]

I don't know of a rule of thumb that would produce a 1" thick tenon.

The two rules of thumb I generally here of are divide total thickness in half for tenon thickness or divide total thickness by three for tenon thickness.

Generally, I think the divide total thickness in half rule makes a stronger joint in most situations. Fine woodworking did a test proving the joints produced using the divide by two rule were stronger, at least in the species they tested and in the manner they tested.

I think you are correct, the 1" tenon would be too thick, the 3/4" tenon would be better.

[Conrad Fiore]

Garrett,
If you are hand chopping the mortises, then the 1/3 rule will give you better support while chopping. If you are machining the mortises you can use the 1/2 rule because you will be putting little pressure on the mortise sidewalls.

[Mac McQuinn]

I would tend to lean towards overkill on sizing as WRC is not know for it's strength.

Mac