Tools: Socket adaptors to use with Torque Wrench

[Andre Jute]

On the left an 8mm socketed hex key from a BBB torque wrench kit, ruined by the drive stang of the 3/8in adapter on the right breaking off in it. The drive adapter is necessary to use a common engineering torque wrench in a range to which the BBB torque wrench, intended for working on carbon bikes, doesn't go. The BBB goes from 2-16Nm (I think, I don't have it in my hand) but for a crank bolt you want 30-35Nm, which is towards the lower end of a torque wrench I bought for automobile use and which my bike inherited.



This is the assembly of grown-up torque wrench, adapter, BBB socketed hex wrench before it all went wrong, with the result higher up. This is the second adapter, of a different make, which has broken off in a BBB socketed hex key, ruining it. This one was the 8mm hex, the other the 6mm hex.

I have bit and socket sets coming out of my ears, but what I don't have is other socketed 8mm and 6mm hex keys. Nor do I appear to have a source for good adaptors, 3/8in female to 1/4in drive male, and 1/2in female to 1/4in drive male. Suggestions will be gratefully received. (I have a super 3/8in to 1/2in adapter, rock solid, German, weighs about pound all by itself...)

I'm looking at this:

http://www.chainreactioncycles.com/Models.aspx?ModelID=47405 -- damned expensive though €37.80 for a bit and socket set that merely duplicates sockets and bits I already have -- but the main thing is it contains the two adaptors I need so if something twists off, BBB has to replace it, I'm not left sitting on my thumb. Does anyone have experience of this set of bits, or an opinion?

Thanks.

Andre Jute

[Danneaux]

Hello Andre,

My, what rotten luck, and I'm sorry you had such a bad result.

Looking at your photos, I believe the real problem is the abrupt transition in the adapter socket where it meets the square drive portion and possibly the materials/means of manufacture. Though I don't know what torque it was pulling when it failed, it can't have been much overall, and it appears the drive adapter was of poor quality despite the brand -- the metal appears crystallized. Usually, when a forging of this sort fails, there is a true twist to the shank. I have at times needed to overuse such adapters to remove frozen fasteners and have twisted them a good 18-20 degrees off- center and still did not fail as yours and one of mine did. I have gotten the occasional 3/8"->1/4" drive adapter that had been cast and not forged as claimed. It happens surprisingly often in that size, because the manufacturers (wrongly) figure it will never be subjected to much torque. Though it occurs less often in 1/2"->3/8" adapters, I have seen it (and the results) firsthand. I had a similar experience once -- and once was all it took to go to a different brand of adapter. End of problem.

The hex-key socket can be salvaged by drilling and tapping the remaining slug of the old drive adapter, mounting the hex-key socket tightly in a padded vise, and using a slide hammer to extract it.

The ultimate solution to prevent future problems is a new drive adapter. Here in the States, I would suggest Snap-On or S-K. Where you're located, Facom have an excellent reputation: http://www.facom.com/fr-en/h-30-Facom.html If you could salvage your damaged hex-key sockets and simply replace the adapter, you'd be all set with the rest of the tools you already have. If you can't find something where you are, let me know and I will be happy to look for something here. 8mm and 6mm hex-key sockets can be obtained separately as well.

Excellent photos, by the way.

Best,

Dan.

[Danneaux]

Andre,

When it comes to high-torque use, I employ my impact sockets (black-oxide finish). For ordinary hand use, the chromies are fine (see below).

Here are the results of just a short online search; examples below:

8mm hex-key sockets

Snap-On: USD$25
http://buy1.snapon.com/catalog/item.asp?P65=&tool=all&item_ID=632361&group_ID=674910&store=&dir=catalog

Sears Craftsman: USD$4.67-USD$5.49
http://www.craftsman.com/shc/s/p_10155_12602_00942678000P?vName=Hand+Tools&keyword=8mm+hex&prdNo=1&blockNo=1&blockType=L1

Harbor Freight: Set of 6/USD$6.99
http://www.harborfreight.com/6-piece-38-drive-metric-hex-bit-socket-set-67891.html

Don't laugh at the latter, despite the price and reputation. The keys and sockets are made of forged chrome-vanadium steel, and are of excellent quality. I picked up a set as "disposable", figuring on using them for occasions when I wished to save my "good" tools. They have now become my go-to hex-key socket set, and I use them without hesitation on my bikes. Never a single problem. The same cannot be said for many of Harbor's tools, but all their hand tools are covered by a lifetime satisfaction guarantee, and I've rarely had to use it.

As for adapter-reducer sockets, we have this selection:
1/2"-> 3/8":

Snap-On: USD$14.35
http://buy1.snapon.com/catalog/item.asp?P65=&tool=all&item_ID=631531&group_ID=674828&store=snapon-store&dir=catalog

Sears Craftsman: USD$5.09-USD$5.99
http://www.craftsman.com/shc/s/p_10155_12602_00904259000P?keyword=adapter&prdNo=2&blockNo=2&blockType=L2

S-K are another excellent brand, generally lacking in pizazz, but solid as can be. My first "real" mechanic's toolset was an S-K, purchased 37 years ago. It is still in daily use, never failed, and right up there among brands with greater name recognition: http://www.skhandtool.com/products.aspx

Clearly labeled personal prejudice: Though I don't believe it was a factor in your present adapter failure, I would also suggest using a beam-type torque wrench for precision torquing of relatively small fasteners. In my own experience, I have never found a click-type torque wrench to be as consistently accurate as a beam-type, even if one is as careful as I am to always store them untensioned. Even extremely expensive, digital click-type wrenches have proven inconsistent for me at low torque values on small fasteners; the beam-type has always proven accurate against calibrated standards. It is a shame good ones have become so terribly difficult to find; yet another victim of consumer prejudice against analog readouts.

Hope this helps; certainly cheaper than an entire, new set for the bike with duplicates.

Best,

Dan.
(who still likes slide rules and Starrett high-precision vernier and TESA dial calipers and micrometers but also likes Mitutoyo digitals a lot)

[Andre Jute]

Dan, thank you so much for all that information. I'll digest it later but now, having stayed up to assemble my Cospea crank, stainless chainring, and the ring bolts that eventually arrived in stock at my parts pusher, it is hours past my bedtime. Both those wretched adapters failed at under 33Nm, which is nothing, or should be, for forged parts. -- Andre

[Danneaux]

Both those wretched adapters failed at under 33Nm, which is nothing, or should be, for forged parts.

<nods> Off the top of my head, that's about 24 ft-lbs., which the adapter should have been able to handle easily. Something's wrong. It is possible the torque wrench is internally miscalibrated, but my money's on an adulterated forging (i.e. it has been cast, not forged, or there was an error in forging and temper/normalzation. I don't like the design of this example). The photos support that thesis. It wouldn't look "crystalized" at the point of fracture at anywhere near that torque if it were truly a forged part with integrity.  With instantaneous, extremely high torque loadings...possible. With slow, cyclical torque gains (20%, 40%, 60%, 80%, 100%) as one would do in this application and on these fittings...nuh-uh. The allen hex socket would have been torn out or the hex key would have twisted if it were subjected to excessively high torque. The hex key is even smaller than the adapter drive, after all 3/8" ~ 9.5250mm. If it were a 3/8"->1/4" adapter, then 1/4" ~ 6.3500mm; still a wash with the smaller hex key. No, the adapter should not have failed. That it did is a sign of something metallurgical.

Get some well-deserved sleep, Andre. Looking forward to pictures of the completed assembly when done.

All the best,

Dan.