Anyway to save this old beam?

[John Sheppard]

Hi all,
  Looking for some advice.  I have a old beam that I salvaged that was used in a local dock from the turn of the last century.  I've used 4 other beams from the same dock successfully and they are still structurally sound.  This one, however, is giving me fits.  I want to use this beam ( 12" x 13" ) for a principal rafter.  I am joining the rafters using tongue and fork joinery.  This particular rafter was to have the fork cut into it.  I tried every way I could to lay it out so that the crack didn't run through the tines of the fork, but due to so many other considerations in the layout ( metal rods where struts were to join, 3" holes where post tongue and seat goes, etc) , I was unsuccessful. So now I am left either trying to salvage this timber or having a new one cut.  I've attached to pictures to show the problem.  Does anyone know of any epoxy that would hold up in the tine of the fork?  I feel that if I could make that one solid piece using some sort of solid epoxy that doesn't break down under load it should hold.  The seat for the strut, that carries the bending moment of the rafter to the post, is 48" from this joint so this tongue and fork isn't carrying all the load for the rafter.  The other consideration for this particular tine is that it will be carrying the load of one end of the ridge purlin using a 1/4" thick saddle bracket. 

I'm thinking I need to cut another beam but man I'd like to use this one.  So much history and it matches the other rafters. 

Thanks,

John

[Jim_Rogers]

I guess you can't rotate the fork 90° to cut it where the split is?

I don't have any experience with epoxies.

Jim Rogers

[John Sheppard]

No unfortunately I can't rotate it because of all the other foreign objects ( 1" metal pins ) and prior alterations ( multiple 2" through holes for pipes to carry power) that would then fall where other joints need to be.  Figured I'd try to see if anyone has any experience with any kind of filler that would hold up structurally, maybe like the System 3 resins https://systemthree.com/products/sculpwood-epoxy-putty or https://systemthree.com/products/silvertip-gelmagic-non-sagging-epoxy-adhesive.

Thanks,

John

[Brian_Weekley]

I'm not sure that split in the fork is necessarily too big a deal.  Seems like the forces from the roof and the other rafter would want to push the crack together?  Posts and beams get checks in them all the time--doesn't necessarily weaken things too much if the forces are in the right direction.  Might not be ideal, but might be OK?

[VictorH]

You might also be able to run a couple timber lok screws from the top of the forks to add some more strength to them.  I would think two one each side would do the trick.

Victor

[John Sheppard]

Brian,
    Typically I don't think that cracks are that big a deal.  From my understanding, and I could be off base here, that if you look at a profile of beam in bending stress you can visualize the areas of highest stress in the beams as two sets of triangles with points touching in the middle of the beam, overlaid onto the cross section of the beam.  With the long side of each stress triangle at the top and the bottom of the beam.

     These triangles represent the highest areas of stress.  I had seen this diagram somewhere on this forum in a discussion about tusk tenon/rafter joinery and the loading of the rafter.  So if the checking occurs in the area of lower stress on the sides of the beams I don't think it is a big deal.  I would imagine that the check may weaken the beam if they penetrate the stress triangles, but I don't know to what extent.

The crack going through the tine of a fork, I imagine to be different because the loading on the tine is different.  I'm worried about the small 3" x 4" piece of the tine carrying all the weight and breaking perpendicular to the crack which could lead to rafter failure.  Not cool. 

My theory with the epoxy is if I can get a hard epoxy that flows into the contours of the crack and hardens, it should allow the tine to act as one solid tine again.  While possibly slightly weaker than the original tine, it would should still be acceptable because I have oversized the beam.  I think I like Victor's recommendation of adding a couple of timber locks to the mix as well to carry some of the weight to the upper portion of the tine in addition to the solid epoxy to bridge the crack.

I'm definitely an amateur at this and I often over think things.  :laugh:  I just want to ensure this won't come down on me and my families head. My wife would never allow me to build anything again, which is a fate worse than death I'd imagine...  ;D

Thanks,
John

[canopy]

What about shouldering the receiving fork so the entire rafter width at the peak can help support the weight rather than loading just the center tenon.

[John Sheppard]

Canopy,
   Great idea.  I had already put a 2" shoulder on the beam with the fork to add more support to the one with the tongue.  You can see it in the cross section view of the beam as the vertical line on the left.

   Did forget to mention, this is an 8/12 pitch roof which affects how much load will be on the rafter joinery.

Thanks,

John

[Justin Bailey]

Perhaps rout out the crack walls to be parallel and straight and glue or epoxy a walnut or oak shim/wedge in to the void, a contrasting wood may add visual appeal.   You wouldn't have to go the whole way, just partial depth and also only where the gap is widest, removing a minimal amount to limit weakening what is there.  I had made a walnut slab bench where I used a wedge shaped piece, but made the wedge a "I" shape that can't slip out but the total thickness was only 2" or so.  Maybe there is a super/long deep t-slot bit that could undercut such a shape.   Also thought of bowtie splines, that prevent opening and also compression, that could be epoxied in as well. Or wedge a parallel piece in and cross pin it permanently with wood dowels. IDK  Too hard to match a piece to the age and color, unless you have similar scrap material to use, otherwise contrasting woods look cool. 

  

 

[sprucebunny]

Epoxy is usually stronger than the wood.
Put some tape over the end and pour it into the crack(s).

[John Sheppard]

Justin,
   I really like the wedge idea.  The crack at it's widest is 1 1/4".  A little wider than I feel comfortable with filling entirely with epoxy.  I've got a 6" x 1/2" end mill bit for my router that would clean that up nicely.  Epoxy a black locust wedge for about 11" up the crack and fill the rest with colored epoxy.  That should work.  I've even thought about putting a larger 1/8" powder coated steel plate on it but that is probably overkill.
  Thanks for the ideas!

John