Mortises split after finishing :(

[eyekode]

For background on the project check out this other thread: http://www.ncwoodworker.net/forums/showthread.php?t=36236

When I made the second set of bunk beds I felt like I knew what I was doing and I didn't take as much care fitting the tenons. Confidence may not be a good thing for me... Without even using a mallet I split some of the mortises when I drove in the tenons . They were hairline cracks and I put some glue in them as best I could using a card/paper to fit into the cracks. After letting the glue dry I trimmed the tenons and fit them a gain. They fit better this time and no split.

But after finishing I got this:

View image in gallery​

Another coat of milk paint and I think they will be invisible. And when I torque the joint the crack doesn't widen. But I am afraid about the longevity of this joint. Any recommendations?

Thanks!
Salem

 

[Bill Clemmons]

As for the first part of your post, fitting the tenons, here's my approach. I always cut the tenon just a little fat, then "sneak up on it" for a good fit. I like it to be an easy slip-in fit. That leaves room for the glue and a little bit of expansion.

If you're concerned about the longevity of the joint, you might try pinning the tenon w/ a 1/4 or 1/8" dowel. The end of the pin will probably be slightly visible even after painting, but at least the joint will be reinforced.

HTH

Bill

 

[eyekode]

I think the big problem is I made the tenon a little too wide. Should have made it more narrow to leave more meat in the mortised piece. This was my first time working with poplar.

Pining the joint is a good idea though. I have used 1/8" bamboo skewers with success in the past:

View image in gallery​

 

[Greavous]

I agree that pinning the joint will keep things together and a good idea. But the split will likely return as the joint is still too full and the dynamics of kids on the bed will probably open the crack back up again. If this happens you might consider counter boring a hole for a screw near the joint on the wall side of the bed and sucking things tight. Then fill the counter bore with a wood plug and finish over it once sanded smooth and flush.

I make the mortise first and then fit the tenon to the mortise. If the tenon is just a tad too snug and or you need to beat the joint together use a chisel and make a few light cheek cuts to bring it to a nice slip fit.

 

[eyekode]

Thanks Chris. This is actually how I did the M/T. Mortise first, tenon slightly oversized, trim to fit. I didn't even use a mallet to force it in! I am actually not very concerned that the tenon will pull out. I am more concerned that the post will split due to torque. I will leave more material in the mortise next time .
Salem

 

[mkepke]

The rule of thumb for M&T is 1/3's: 1/3 the stock for one shoulder, 1/3 for the tenon, 1/3 for the other shoulder.

I too would pin the joint for extra piece of mind.

BTW, what type of wood ? Could it be a moisture control problem ? E.g. the tenoned stock was not dry when you cut the M&T and it shrunk over the course of finishing....

-Mark

 

[Joe Scharle]

Actually, you may not have caused a problem. It could be caused by shake. I've had it happen to me too. And yes, the problem usually remains hidden until too late! I'd drive a few brads or pins beneath the surface and re-paint.

If it is caused by shake, you may see future separation along the grain. That's when it needs some strategically placed screws or even bolts.

 

[eyekode]

And that is where the mistake lies. I did not observe this rule of thumb . Live and learn.
The wood is poplar. It lived in my garage for quite some time. I doubt it was dry.
Thanks!
Salem

 

[toolferone]

I have always used the old dollar bill fit. If you can fit your tenon in with a dollar bill on the 2 sides and you don't force it in then it is a good fit with room for glue.