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I have 2x10’s that I will be sandwiching together to make a big stiff beam for an adult swing set.

I’m about to put it together, but then I thought “how do you drill the screws for swings into a sistered beam”? Because the boards are mated together, the screw will want to push those boards apart.

  • +1 for "big stiff beam" and "adult swing set" in the same sentence. – Alaska Man Jul 3 '19 at 17:48
  • You didn't mention what your planned orientation for the 2x10s will be. – Jean-Paul Calderone Jul 3 '19 at 17:59
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You could use a pair of large clamps close to and flanking the screwhole to prevent the screws from pushing the plies apart. Once the screw is in at full depth the clamp is removed. It might take four clamps--from both edges of the beam.

Also you might want to use wax or other appropriate lubricant on the screws and be careful to avoid making the "pilot" holes too small.

EDIT If the pilot holes are properly sized (large enough), then there may be no significant separating force and so clamps may not be necessary. If you don't have clamps, try it without them and see what happens. If separation occurs you can always take the screw out and get some clamps.

  • Thanks. So you’re thinking that it won’t pull apart after the clamps are released? – Jeff George Jul 3 '19 at 16:03
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    No. If the pieces are clamped, then the screw moves into the second ply as if it were one piece of wood. The force from the screw pushing the plies apart is negated by the force of the clamps and the plies cannot separate. The separation of un-clamped plies occurs just as the point of the screw enters the second ply and before sufficient threads engage the hole in the second ply. Once the threads engage the separating force disappears. – Jim Stewart Jul 3 '19 at 17:42
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    Given the forces involved with an adult swing if the boards are not secured together very well ( after the clamps are removed and the swing is in use ) the eye hook could start to work the boards apart over time. Then again that could make for an exciting Danger component of "Lets play on the swing" – Alaska Man Jul 3 '19 at 17:44
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    If the pilot holes are properly sized (large enough), then there may be no significant force and so clamps may not be necessary. If you don't have clamps, try it without them and see what happens. If separation occurs you can always take the screw out and get some clamps. – Jim Stewart Jul 3 '19 at 17:55
  • If separation occurs then two ( or more ? ) lovers come crashing to the ground and then - separation occurs :) – Alaska Man Jul 3 '19 at 18:03
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Another option would be to use carriage bolts on both sides of where the eye hooks are going in. Glue the boards together with construction adhesive. Use 4 bolts, two on each side of the eye hooks, top and bottom. Use 3/8" bolts, ( or 1/2" ) large washers and nuts.

Personally i would just glue the boards together with construction adhesive and screw them together with extra screws around where the eye hooks are going to be.

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Instead of screw into the seam You can use a bolt through the seam and use a washer+metal plate on the other side to spread the load.

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