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Double Drilled Hole

Double Drilled Hole

Double Drilled Hole

I have a joint location that is not on primary structure, but in an equipment bay.
The joint has been double drilled and once it’s reworked to clean/round, will have a diameter of .3125.
This stackup is multi-layered (0.040~.063 thk); angle, web, channel and another angle. All totaled, the thickness is just under 0.25 inches. Given that its four layers, I’m not going to install individual pieces of freeze plugs (bushings). Instead, I’d like to fabricate a flanged spacer, to be pressed fit into this joint.
My thought is that it would act like a large bolt (while calling out similar drawing’s hole tolerance), with the center drilled to install the drawing’s required fastener (3/16th hi-lok). I don’t have the actual loads, but trying to justify this as a suitable method. What rationale could I use while staying within an equivalent strength's guidelines.
Thanks in advance for your suggestions/ideas.

RE: Double Drilled Hole

Its not equivalent.
You need to check edge distance for tearout, bearing etc, and check net tension, in each of the 4 joint members.

RE: Double Drilled Hole

The drawing's fastener has a allowable tension & shear loads of 2,940 lbs & 2,703 lbs respectively. The tear out, bearing and net tension are less than half of the fastener's capabilities. I guess I'll need to design a repair fitting of some kind to reinforce this joint's stackup material...

RE: Double Drilled Hole

I don't get ... "with the center drilled to install the drawing’s required fastener". Why not use a 5/16" bolt and leave it ? or an LZ10 rivet, maybe with a touch CSK for the tail, then drill for #10 ? Also two washers to ensure the "rivet" is retained.
but of course eD. One issue will be an almost certainly lower tear-out.

One thing to help would be if the BP fastener was shear critical (it had higher tear-out and bearing allowable). Then so long as your tear-out and bearing are higher than BP fastener shear, you've got a "story". I assume you don't have any OEM data (loads) ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: Double Drilled Hole

I would highly doubt an equipment rack joint was designed to be fastener critical. Actually that would be poor design practice for any joint. Joints should be designed to be bearing critical to provide for load redistribution between fasteners.

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