Sunday, January 20, 2013

A Broken Weld Repair

My wife found this iron patio chair some time ago.

It's quite an attractive piece, but it has a flaw -- a broken weld at the front left.

I don't have welding gear. I might be able to braze it, but I'm not all that practised at brazing; I'm not certain I could obtain a good outcome. That leaves me with the option of a mechanical repair method similar to one that's already been applied to this chair by someone in the past. Here's a view of that repair at the upper left of the back.

This will be a bit of a challenge. The repair pictured above would have been relatively easy to accomplish, since that  added strap was attaching to a flat piece. I need to do a similar repair, but I'll be attaching to a round piece -- that complicates things a little. Anyway, we'll see how it goes.

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First off, what's left of the broken weld on the underside of the large diameter round has to be ground away -- it will interfere with installation of a strap.

That went reasonably well.

Then it turned out that the upper part of the old weld had to go as well; it would interfere with positioning the end of the  lateral round.

Now I can begin to fabricate the attachment strap, and figure out how to go about installing it.

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Here's what I've rigged for a metal forming jig.

That 's a couple of pieces of 12mm diameter steel rod[1] clamped very tightly in the vise, and very tightly clamped across/to the work by Vice-Grips. The masking tape on the work gave a me a way to mark distinct positioning lines. The material is 1/2" wide mild steel flat stock, 1/8" thick. Here's the short end after forming with the aid of Channellocks.

And here it is almost fully formed.

This method doesn't yield a perfect result, but with a little more persuasion from another pair of Vise-Grips while the work is still in place there, I'll get an adequate approximation of the shape I need for my repair strap. Then I can cut off the excess material and carry on with fitting the strap to the chair.

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I've prepared the strap. I've drilled a 5/32" pilot hole through its upper side. Here it is clamped in place ready for the drilling to be completed.

And here it is done.

After drilling completely through 5/32" diameter, I bored the hole out to 11/64" diameter, and installed a stainless steel 8-32 screw. That will make for a more-than-adequately strong repair.

I'm not entirely done with this. I still want to refine that repair job a bit, and I need to plan out a repaint job for the entire chair. But I'm pleased that my methodology here panned out as I thought it would -- that's a sound repair that will never need attention again.

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The Finished Repair -- SATURDAY, JANUARY 26, 2013

Here it is fully completed.

I've rounded off the strap's corners, and cinched the strap as snugly as I could around the large diameter rod. I shortened the screw by 1/8" so it would fit correctly with two stainless steel flat washers added, and an acorn nut installed with blue thread-locker. The repair is now well and truly done.

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[1] My loathsome day job is as a laser and impact printer repair technician. That gives me access to an excellent supply of discarded steel rod material from parts replacements and from scrapped printers. For an amateur machinist, it's a treasure-trove of useful material.

If your workshop interests are similar to mine, you might want to make the acquaintance of a local printer repair shop -- you'll be amazed at the stuff they throw out.

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Sunday, January 6, 2013

CA Adhesive As A Machinist's Aid

Cured CA adhesive ('Krazy' glue or 'Super' glue) is not terribly heat resistant -- boiling water temperature will soften it. While that's a weakness of the material for some applications, it's a characteristic that can be put to good use in the machine shop at times.

I have a small gland nut from the valve stem of a propane torch with ruined threading on it. [Long story.] If I can turn down the mashed threads so that the nut's shank can at least re-enter the valve's stem-hole, I can get the valve back in working order. The difficulty is in mounting the tiny nut for turning on the lathe. That's where CA adhesive comes in. Here's a view of what I've done up so that I can chuck the gland nut.

A length of 1/4" steel rod and 9/32" brass tubing provide a foundation on which I can squarely place the damaged nut. I've applied CA adhesive and let it cure. Now I've got a 'mandrel' that I can chuck in the lathe.

When I'm done turning that, I'll dismount it, heat it up a bit with a propane torch and the nut will come free of the mandrel easily.

- - -

That worked nicely.

Now I'll free the nut from the mandrel and I can reassemble the valve.

- - -

Here's the valve back together less the knob.

After inserting the now threadless gland nut, I applied CA adhesive all around the perimeter of the nut's hex,[1] and set the thing aside for awhile for the adhesive to cure. That adhesive-secured gland nut should work fine. That nut really doesn't do much -- all it's there for is to provide a sleeve bearing for the valve stem. The gland nut has no sealing function, and it really has no load to bear of any consequence, so held-in-place-by-glue is just as good as held-in-place-by-threads.[2]

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Here's the torch fully assembled and operational.

CA adhesive is versatile stuff. I'm never without it on hand.

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[1] CA adhesive can be treacherous to work with in this sort of situation. The stuff is extremely runny, and it will wick in anyplace and everyplace it can. Never take the attitude 'if a little is good, more should be better'. You'll end up regretting it.

[2] This is a good example of the value of setting aside orthodoxy at times, and pondering what it is that a given component really does. As long as I remained fixated on having a proper screw-in gland nut, this torch just sat idle in a box under my workbench. Once I finally studied the problem more thoughtfully, it dawned on me that the repair method outlined above could work, and was worth pursuing.

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