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Bench Leg Repair

A long long time ago, I conjured a short bench for our Larval Engineer from a pair of junked folding-table legs and a truly hideous mid-50s Genuine Formica countertop salvaged from the kitchen refurbishment:

Bench Leg - overview

Bench Leg – overview

Most recently, it held a pile of test equipment and random stuff next to the MPCNC, whereupon the welds holding the tube with the feet to one of the vertical tubes on the far end failed. It wasn’t in the critical path, so I broke the welds on the other tube, propped the vertical tubes on wood blocks, and continued the mission. Having finally finished those measurements, I could clear off the bench and repair the legs.

I no longer have my welding gear and, in any event, it’s still winter outside, so a low-excitement repair seemed in order: drill suitable holes into the leg crosspiece, make threaded inserts for the tubes, and join them with 3/8-16 bolts.

So, we begin.

File the broken welds off the foot tube, align it in the drill press vice (where it barely fits!), center drill to make a pilot hole, then poke a 3/8 inch drill completely through to line up both holes:

Bench Leg - through drilling

Bench Leg – through drilling

By the Universal Law of the Conservation of Perversity, a 3/8 inch bolt didn’t quite fit the 3/8 inch hole, so I embiggened the holes with a step drill:

Bench Leg - step-drilling to size

Bench Leg – step-drilling to size

The step drill obviously has hard metric diameters labeled as weird inch sizes:

Quasi-inch step drill

Quasi-inch step drill

I can’t read the second step, either, but it’s apparently 25/64 inch = 9.8 mm, which is just enough over 3/8 inch = 9.5 mm to be useful. The next step is 14 mm = 35/64 inch, so the drill is a bit of a lump.

The leg tubes were a hair over 0.9 inch ID and not particularly round. Tolerances being slack, slice a bit more than two inches off a 1 inch OD aluminum rod:

Bench Leg - sawing rod stock

Bench Leg – sawing rod stock

I wanted more than one diameter in the tubes, but the bolts in my stash topped out at 2 inches and, really, an inch of aluminum won’t go anywhere.

Clean up one end of the rod to 0.9 inch OD, flip, and center drill:

Bench Leg - center drilling insert

Bench Leg – center drilling insert

Obviously, surface finish and concentricity aren’t critical, but the cleaned-up OD of the left end lined up at  barely perceptible mismatch with the (yet to be done) right end.

Sunder in twain:

Bench Leg - sawing leg inserts

Bench Leg – sawing leg inserts

Betcha you can’t spot the junction between the two ODs, either.

Drill 3/8 inch through, then discover you (well, I) have neither a drill big enough nor a boring bar small enough to embiggen one end of the hole for a nasty interference fit against the tips of a 3/8 inch hex nut.

Once again, a step drill to the rescue:

Bench Leg - step-drilling insert

Bench Leg – step-drilling insert

Because it’s a step drill, the counterbore isn’t quite deep enough for the whole nut, so turn the nut to fit the recess left by the drill:

Bench Leg - nut shaping

Bench Leg – nut shaping

Put a bolt through the insert as a guide, spin the nut on, backstop the insert with a machinist’s parallel jaw clamp (loose, just to give the head somewhere to go), line ’em up, and mash the nut into place with the bench vise:

Bench Leg - nut pressed in place

Bench Leg – nut pressed in place

Clean up the broken welds with a rat tail file, hammer the inserts into the tubes:

Bench Leg - insert installed

Bench Leg – insert installed

Which, as I expected, rounded them nicely while producing an absolutely solid, ain’t gonna work loose, dry joint.

Add threadlocker to the bolts and it’s all good:

Bench Leg - repaired

Bench Leg – repaired

Stipulated: butt-ugly.

Tell me you’d have fish-mouthed those inserts just for pretty, after noting the factory didn’t bother fishmouthing the vertical tubes before welding them in place.

But it was good for generous dose of Quality Shop Time!

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