Tuesday, September 17, 2013

A Furnace Chain Chuck Key Leash

I have an old Craftsman portable drill whose plastic chuck key leash took retirement long ago. The leash had been retaining the style of chuck key shown below.

Ever since, I've been carefully keeping track of the loose chuck key. I got tired of doing that, and decided it was high time that the drill and the chuck key were reattached to one another; hence, this post.

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While casting about for a way to fabricate a chuck key leash, it dawned on me that furnace chain might be a good thing to make a 'leash' from. Here's the method of making a chuck key leash I came up with:

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First off, the key's T-bar is an interference fit in the key's shank; hammer it out.

Next up is to fashion a short sleeve that will fit over the key's shank, and provide an anchoring point for one end of a short length of furnace chain.

I happened to have on hand some 3/8" O.D. steel tubing with a 5/16" I.D. A 13/16" length of that is what I needed.

The tubing was a little too snug-fitting on the key's shank, so I bored out the tube to 21/64" diameter for a depth of 7/16" at one end. Six millimetres from the bored end of the tube, I drilled the tube through 11/64" diameter. That hole is for the T-bar to go through to retain the tube.

Five millimetres from the other end of the tube, I drilled through No. 43, then drilled through one side only 7/64".[1] I tapped the remaining No. 43 hole 4-40. Here's what I have so far, along with what's needed for completion.

The ty-wrap is 3 3/4" long. The furnace chain is longer than it needs to be; I'll shorten it to about 4 1/4". The 4-40 screw is just over 3/8" long.

And here it all is fully assembled and installed.

I installed the 4-40 screw using CA adhesive as a threadlocker. This should be a durable chuck key leash.

Anyway, I have a leashed chuck key again. Chuck keys, I discovered, like to wander and play hide 'n' seek. It gets annoying. That's why chuck keys are kept leashed.

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A Fly In The Ointment -- WEDNESDAY, SEPTEMBER 18, 2013

I noticed something that I didn't care for about the behaviour of the chain. (I should have seen it coming.)

One twists the chuck key in order to tighten a chuck. That, in turn, twists the chain. Furnace chain has very little twist in it before it does this.

It;s no big deal. It really doesn't detract from the chain's fitness for its job, but it irritates me. (Note that the same effect is operative for a plastic or rubber leash, but a plastic or rubber leash will untwist itself -- a chain won't.)

So, here's a little refinement to eliminate the problem.

I've added a snap swivel right at the cord. That lets me use a more substantial ty-wrap, and it should do away with the twisty/kinky nonsense

I'll see how this works out as I continue to.use the drill.

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Addendum -- WEDNESDAY, SEPTEMBER 25, 2013

The snap swivel works nicely; it renders the leash completely nuisance-free, so I ended up liking that leash for the Craftsman drill so much that I made one for my Bosch hammer drill.

Fastening the chain to the chuck key was much easier here. I filed a flat on the end of the T-bar, and drilled and tapped it M3 .

With CA adhesive applied as a threadlocker, I ran in an m3x8mm screw until it would just allow the chain link to pivot freely.[2]

The snap swivel makes the key easily detachable, and that could be a good thing at times

Years ago, while building some furniture, I noticed that a dangling, swinging chuck key can strike a work's surface and leave a tiny dent. Were one to be working on something that oughtn't be struck, one could detach the key until the delicate work was over with.

Anyway, I'm back to having conveniently leashed chuck keys, on leashes that will never stiffen and crack with age.


[1] 7/64" is not quite clearance diameter for a No. 4 screw -- it's sort of an Interference/clearance diameter. 1/8" is clearance diameter. I went with 7/64'" to obtain the strongest possible screw/clearance-hole interface.

[2] M3 is a little too large to fit freely through the eye of a furnace chain link. Use a taper punch to widen the eye's opening, and an M3 screw then fits fine.

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