1/4"-20 stainless bolts threaded into 1/8" thick 6063 aluminum. 1

[David Wallace]

I need to determine a safe working load for the tensile strength of this connection and its giving me trouble. Any tips out there? Dave Wallace and then there is the question of torque so as to not damage the aluminum.

 

[racookpe1978]

Threaded into a cast or solid aluminum plate?

What direction is the force to the surface of the plate?

 

[Tmoose]

What an Unfortunate situation if the fastener has to do anything much at all.

Torque a bunch of samples to death.
Repeat with 1/4-28s.

20 tpi = .05" thread pitch. .125/.05 = 2.5 threads engaged at most.
Good design would have a chamfer at the ends of the tapped hole, so you are down to even less.

 

[racookpe1978]

You MUST "damage" the aluminum - if by "damage" you mean compress the aluminium or deform it somehow. The steel fastener is stronger than the Al base metal, and the fasnterner MUST be torques to some preload = It will compress into the Al base metal somewhere.

Now, again, WHAT DOES THE CONNECTION LOOK LIKE?

 

[Screwman1]

For a jopint that has .5D of engagement into aluminum the safe working load is going to be pretty much trivial. This is pretty much a sheet metal joint and any consideration of it as structural will be a gross overstatement. A significant portion of the failure mode will be sheet bending under load, which will reduce the thread engagement even further.
Run away!

 

[drawoh]

David Wallace,

It looks like you can expect the aluminium to fail in shear. The Machinery's Handbook has notes on shear failure of internal threads.

--
JHG

 

[Ron]

David...you have not provided adequate information for us to help very much. What is the application? What loads must the connection carry? What is the configuration of the connection? Which alloy of 6063 aluminum are you using? 6063 is commonly used for extrusions; however, it comes in at least 6 different tempers which will greatly affect the fastener pull-out resistance.

A 1/4-20 bolt in 1/8" thick aluminum will have only 2-1/2 threads for shear area at the threads. Failure will occur in the aluminum, not the bolt. For most 1/4-20 applications, the pullout resistance will likely be in the 150-200 lbf range. For working load, that would be about 50 to 60 lbf, assuming 6063-T6 aluminum.

 

[dvd]

There is always galvanic corrosion potential. Choose fasteners which are compatible.

https://www.fastenal.com/content/feds/pdf/Article - Corrosion.pdf

http://www.eaa1000.av.org/technicl/corrosion/galvanic.htm

 

[David Wallace]

Thank you all for the feedback. As a result of the sluthing we are looking at welding a 1/8 thick backer plate so as to double the pullout resistance. If we need more the bolt spacing will be tightened up. My understanding is that the finer threads may not work well in the aluminum due to difficulty in cutting them cleanly. We could also go to a 5/16 bolt. I noted the there seemed to be an opinion that the working load (due to shear failure in the aluminum) would be 50-60 lbs. How is that derived?
Dave Wallace

 

[dvd]

Threading through two plies is not advisable.

 

[MikeHalloran]

If we need more the bolt spacing will be tightened up.

I was about to recommend piercing and extruding a hole in the sheet before running an 'express' tap through it, but that becomes more interesting for a pattern.

How many bolts are in the pattern?
What is the bolt spacing now?





Mike Halloran
Pembroke Pines, FL, USA

 

[berkshire]

If you start piercing and extruding 6063 you had better be at condition "O" .
For the most part this alloy is used for extrusions which usually come in the T6 condition.
B.E.

You are judged not by what you know, but by what you can do.

 

[David Wallace]

The bolts are to go through a 4x6x 3/8 wall 6061 tube (17/64 hole) and hang a 1x1x1/8 tube The small tubes have only dead and snow load and are welded to an angle also probably 1/8 The loads are not great. Im trying to get a condition where a bolt pair (3" spacing) will support about 150 lbs. I was invisioniing the pairs at 12 o.c. but could go to 6" if necessary. Could also bump the diameter if that would help.DW

 

[berkshire]

David,
Is this for some kind of sun shade on a building ? Can you put a through hole through the 1x1x1/8 tube and weld a 1/4" thick 6061 threaded plate to the tube , or is this appearance critical ?
B.E.

You are judged not by what you know, but by what you can do.

 

[David Wallace]

yes it is a shade and appearances from below are all important The goal is to blind screw from the top and be able to field assemble. no field welding the support frames will be shop fabricated, then 'roof' panels bolted into place My idea is to tap the panels and then hang them from the support arms.

 

[David Wallace]

And I cannot find the notes on shear failure in the Machinerys Handbook (mine is 13th addition 1946). DW

 

[BUGGAR]

Aluminum Association has design value$.

 

[MikeHalloran]

You couldn't drill and tap the 4x6x 3/8 wall 6061 tube, run bolts into those threaded holes, and hang whatever from the bolts?


Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

There are many commercial, low cost, riv-nut type insets that would provide solid cres threads in a thin wall aluminum tube. Probably for less cost as welding a backing plate in place and tapping the threads.

http://fasteners.sherex.com/viewite...s-ca-series/ca-series-stainless-steel-inches-

 

[Ron]

Agree with tbuelna on the riv-nuts or NutSerts. Have used those many times for connecting extruded canopy sections. The will usually give you an increase in pull-out strength for this sections as compared to a tapped hole, partly because they extend the thread engagement length and partly because the stress distribution from the pullout load is handled differently and over a larger area.

Be careful with welding. Keep in mind that for aluminum, the allowable stresses are greatly reduced within 1 inch of a weld.

You also mentioned in your later posts that 6061 aluminum is being used. Make sure you know which you are analyzing. They have considerable differences in their yield, shear and ultimate strengths.