The Welded Nut Mechanism

I have mentioned several times that I like this simple technique.  It isn’t elegant craftsmanship like drilling and tapping and wouldn’t be acceptable in finished products but it is quick and effective for making jigs and other shop tools.  I use it today mostly when making dies.  

It is important that the hole through which the bold will pass is oversize so that there is no chance of obstruction and no chance the welding current will pass through the treads and create a contact point gall.  I use both the drill press and the torch to make the holes and don’t see much advantage with either one.

I like to screw the bolt in all the way and lock it in place on the opposite side of the hole with another temporary nut.  This assures the perpendicular orientation and can lock the bolt in the centered position protecting the threads.

The outside nut is secured with MIG beads.  I may just tack the nut and remove the bolt before adding more weld.  Finally, I apply anti-seize and insert the bolt again.

As, I said before, these are usually 7/16” bolts.  I’ve twisted off some smaller thread stock but not 7/16” that I recall.

Forging press die saddle with locking bolt.

Drill over-size hole.

Lock in position to weld with temporary nut.

Remove positioning nut, apply anti-seize and chase threads

Nut and Bolts

I don’t recall anyone ever talking to me about how to position bolts and nuts in the things I build.  With experience I have made some rules of thumb for myself.

Rule one:  Give it some thought.  The idea of thread joinery is to hold some assembly together which can be disassembled when necessary.  Design to satisfy both sides of that equation.

Rule two: Avoid obstructions to bolting and unbolting.

Rule three: Pay attention to strength needed.  Most of the time Grade two hardware will work but in some cases plan for Grade 8.  I use mostly 7/16” size stock as the other part of the strength consideration.  

Rule four:  Pay attention to the security required.  Usually I use a split ring lock washer but sometimes Nyloc nuts, thread locker, paired “jam nuts” or fabricated wired nuts to avoid unintentional loosening.  Sometimes, in special cases,  I place a weld between either the bolt and the assembly or the nut and the assembly and, rarely, both.

Rule five: Think about fail-safe.  How many fixation points are really needed for safety?  The more the better for holding together but excessive parts make disassembling awkward.

Rule six: How should the bolt be placed?  If the bolt is oriented in the vertical plane and only the top side is visible during operation of the assembly, the nut can fall off and possibly not be noticed.  However, the bolt can’t fall out.  If the nut side is up and visible, loosening might be noticed before the nut comes off, but the bolt will fall out when that happens.  Which is better in the particular case at hand?

Rule seven: Lubrication?  I like to put anti seize on the threads of most everything I use.