Author Topic: Need help: A-Frame for Baby play bar - Lap joint?  (Read 368 times)

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Offline grobkuschelig

  • Posts: 575
Need help: A-Frame for Baby play bar - Lap joint?
« on: March 03, 2020, 04:45 PM »
Dear FOG,

I want to build a play bar for our friends who are expecting.

A play bar, if that is the right translation, is a double-A-frame connected by a rod. The newborn would be laying below this construct, bedazzled by some toys and stuff hanging from the bar to grab, feel and look at. ;)

Now here comes my issue:
The recipients of the gift mentioned they would like a „bright“ wood.
I have some roughly 21mm square sticks of maple as well as some 25mm/1“ dowels.

So not a problem on the supply side.

My problem is of mechanical nature.
I want to avoid the cross member of the A-Frame.

I am thinking of some kind of “keyed/stepped” lap joint on top of the “A”.

Making this a little more challenging is, that I do not want to glue the joint, to allow stowing the whole product in disassembled state.

So I would use a threaded insert in the rod and screw through the lap joint to keep everything together.

I did a test piece (only one side) and am not overly happy with the “strength”.
Possible reasons for less than optimal performance:
- lack of craftsmanship/precision on the joint (certainly!)
- maybe the wrong joint?
- is there a better way of achieving what I want to get at?

Thank you for any guidance! :)

P.S.: The visible crack is proof of my poor craftsmanship. Too much force on a big chisel that might not have been too sharp... ;)

« Last Edit: March 03, 2020, 04:47 PM by grobkuschelig »

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Offline jeffinsgf

  • Retailer
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  • Posts: 229
Re: Need help: A-Frame for Baby play bar - Lap joint?
« Reply #1 on: March 03, 2020, 10:02 PM »
I would widen out the stock to something around 2 inches, bring the angle between the legs in to something like 75 degrees, and simplify that joint to a simple half lap (without the step). Even in your prototype, put the threaded insert into the dowel and use a bolt to test the joint. That screw isn't going to tell you much and may have contributed to your joint failure.

If you're looking to keep it light, you could trim the thickness down to around 5/8", but a wider board will give your half-lap more shoulder to bear on.

Offline FestitaMakool

  • Posts: 232
Re: Need help: A-Frame for Baby play bar - Lap joint?
« Reply #2 on: March 04, 2020, 12:36 PM »
I would widen out the stock to something around 2 inches, bring the angle between the legs in to something like 75 degrees, and simplify that joint to a simple half lap (without the step). Even in your prototype, put the threaded insert into the dowel and use a bolt to test the joint. That screw isn't going to tell you much and may have contributed to your joint failure.

If you're looking to keep it light, you could trim the thickness down to around 5/8", but a wider board will give your half-lap more shoulder to bear on.

Agreed, and I would have used a flat head bolt or screw, countersunk. Tapered screw heads are a disaster waiting to happen in solid wood near edges. Drill the hole so all the fibres in the wood are cut, not forced to the side. Maybe smear wood glue around and inside the hole and let it dry before assembly.