Tegger: Craftsman Torque Wrench writeup

Nice writeup on opening your old torque wrench.

Is it right that the upper nut in the handle was held in place by the
plastic molding of the handle? So there is less chance of it rotating
out of place than the lower nut?

Also, didn't exactly see where the detent feels come from. I guess
from the plastic lock ring area?

The Lowe's Kobalt torque wrenches are also made by Danaher, but do
carry a lifetime warranty.

 

wrote in :

The upper and lower nuts together clamp together the handle and the
threaded shaft. This is how the wrench maintains its calibration. The
handle and the shaft MUST NOT ever come out of phase.

The upper nut does indeed sit in a matching hexagonal recess in the handle.
Unless the handle should pull down sufficiently to allow the hex recess to
come fully away from the upper nut, the nut and handle will stay in phase.
However...if the lower nut comes loose, the upper nut will be loose as
well, and will rotate relative to the threaded shaft (coming out of phase),
throwing calibration off, which is exactly what happened to me.

If you look closely at the bottom of the wrench's body, you will see a
series of long, shallow slots milled into the body. These are oriented
axially, and spaced radially, around the body. (If they were cut all the
way through, they would make the bottom of the body resemble a military
rifle's flash suppressor.) There is a small nib, or protrusion, on the
inside top of the plastic handle that indexes into the slots. When you turn
the handle, its top flexes sufficient to allow the protrusion to ride out
of one slot and fall into the next, giving the handle that "click" feeling
as you wind the setting up or down.

There are ten slots, of course, one for each pound as you rotate from 1
through 0 up each ten pounds of scale marking.

I'm not sure how the locking ring functions; it never occurred to me to
examine that assembly.

That's interesting. Sears' "lifetime" warranty essentially only covers
tools without moving parts, so the torque wrench is not covered.

 

I've updated the relevant page on the site to clarify handle "click"
operation. You may have to hit Refresh/Reload in your browser to see the
changes.

 

Thanks for the detailed explanation. I see the slots now. Looks like
I'll be putting some threadlockers in mine to help keep the lower nut
in place, as it's not worth it for me to send it in for calibration.
$25 plus shipping both ways will cost the same as a new wrench with
the annual sale, and I don't need a laboratory-grade certification.

I wonder if the detents have something to do with the high rate of
complaints about the plastic lock ring breaking (the Kobalt uses a
metal ring without detents). I suppose if the lock ring isn't loosed
up fully before adjusting, the force of turning will be transferred to
the plastic ring. At least that's what I supposed will hold the
setting when "locked".

I was at Lowe's earlier, their Danaher-made torque wrenches say no
hassle lifetime in big letters under the brand name "Kobalt", but the
same 90day/1year in fine print as Sears. Oh well, until I get a $400
Snap On I guess. Thanks again!

Among the excellent articles, torque wrench calibration on motor.com:
http://www.motor.com/article_pdf_download.asp?article_ID=516

 

The only other breakdown diagram of a torque wrench I find is the
Harbor Freight 1/2" clicker. Hand drawn and not properly named parts.
The operations aren't as smooth as the Danaher, but the last time I
checked it was very close. Really not bad for a $14 on sale torque
wrench. Guess it's time to borrow a beam type.

http://www.harborfreight.com/manuals/0-999/239.pdf

 

Interesting info on torque wrenches. I have an old Sear beam type --seldom
used any longer -- and have often wondered how accurate it is. Unless
abused or damaged in some way, I should imagine a beam type would hold its
accuracy over a long period of time or perhaps the life of the instrument?

 

bending beam offer the best accuracy/price ratio. their main drawback is
not being able to see the dial in all orientations, but other than that,
they're great. they can have advantages on things like cylinder heads too
because you can torque and hold - essential when dealing with a blind bolt
hole where lube is slowly squeezing out and would otherwise give a false
torque reading.

tilt-block type torque wrenches are notoriously difficult to keep in
calibration. split beam wrenches are accurate and robust and don't have
any of the tilt-block drawbacks because nothing is loaded when not being
used - they tend to be much more expensive though.

 

A tilt-block wrench also has no loaded parts when not in use, provided you
dial it back down after use.

 

wrote in

Thanks for the link. I've added it to the page.

 

wrote in @q26g2000prq.googlegroups.com:

That diagram is pathetic. My 11 year-old daughter could make a better one.

 

not as simple as that. one of the reasons there is a problem with
calibration issue with tilt-blocks is because virtually all manufacturers
use polymers in construction.

http://www.tegger.com/hondafaq/torque_wrench/exploded_view.jpg

the polymers in the actual tilt block unit are subject to "relaxation".
if you set the spring and measure torque at 10 seconds, 30 seconds, 60
seconds, 2 minutes, 5 minutes and 10 minutes, [etc] you'd get a
progressively lower torque trigger reading every time.

a load path that only loads momentarily and when in use, like you have
with split beam, doesn't have that problem.

 

looks like a [not so] thinly disguised advertising article to me.

 

Hm. I wonder by what amount?

 

I just had a close look at the picture you referenced, plus my original
photos.

I'm pretty certain the item I call the "anti-windup assembly" only had a
skin of polymer around the outside as a cage, serving only to hold the ball
bearings in place. The assembly itself was steel all the way through to the
bottom where the spring bore against it.

This wrench has no polymer load-bearing parts.

 

if that's the case, it's ok to leave it "loaded" when not being used. if
there's any polymer, you have to unload it.

 

Here is another picture of the tilt (or pivot) block in a cut-away
view:

http://www.motor.com/article_pdf_download.asp?article_ID=599

The torque wrench should be kept in the lower 25% of the range when
not in use (according to Danaher), but the Motor.com article suggests
no less than the minimum on the torque wrench in case the tilt block
dislodges!

I'm sure with all trade publications (or TV/movies these days) there
will be plenty of unashamed advertisements. Just read past them I
guess. However, Tegger could have recalibrated his old torque wrench
for $25 + shipping with Angle Repair, if he missed last Friday's 50%
off Craftsman torque wrenches!

 

Is it correct that both ends of the "anti-windup" mechanism actually
rotate with respect to each other? Because it looks like the ball
bearings help reduce friction so all tension from the spring transfer
to the tilt block/ratchet head.

If so that would be the "interface" mentioned in US Patent 5,503,042.
"freely rotatable cylindrical roller" it says. Not too flashy.

Or, similarly, as the following web site calls it "interface mechanism
(toggle, cam or low-friction roller)"
http://www.buyerzone.com/construction/rbic-torque-wrench.html

 

Another one:

US patent 7451674, http://www.patentgenius.com/patent/7451674.html

calls it "spring and pawl". So the "bar" of the ratchet head rests on
the "pawl". Which I guess is the tilt block + roller interface. Then
comes the spring. (Ratchet bar -> Pawl -> Spring.)

Now Harbor Freight ads say: heavy duty cam and pawl mechanism. I guess
the ratchet bar is considered the cam then that rests on the pawl
mentioned in patent 7,451,674??


Excerpt from US Patent 7,451,674:
"The most popular type of this wrench is called a micrometer torque
wrench and has a hollow arm which includes a spring and pawl mechanism
for setting the torque. Within the hollow arm, the pawl is forced
against one end of a bar that is connected to a drive head, the bar
and a drive head are pinned to the hollow arm and rotate as torque is
applied. The pawl is released when the force applied by the bar
increases beyond a set value established by the operator. When
released, the bar hits the inside of the arm, producing a sound and a
distinct feel by a user. The torque value or release point is changed
by rotating the handle, which moves on threads for setting.
Additionally, values are permanently stamped or imprinted on a scale
that is located on an outer surface of the hollow arm. Micrometer
wrenches can overtorque when the operator continues to apply pressure
after release, due to the momentum created by the releasing mechanism.
This overtorque may occur without the user even realizing it. "

 

I didn't think of it earlier, nor did I expect Sears Parts Direct to
sell every single part in their Danaher-made torque wrench. Here it is
Tegger, the description of every part in that torque wrench:

Turns out the "pawl" is the tilt block, the "anti-windup" assembly
Tegger mentioned is the cam assembly.

The Sears version of the Danaher torque wrench seems to have a weak
handle lock ring that breaks often. The SK and Lowe's version use a
metal lock ring. If the plastic ring breaks and people still want a
Craftsman, it's cheaper to buy a new wrench during 50% year-end-sale
than to buy a new handle and send it in for calibration ($25 + round
trip shipping). Who knows, people may even be able to substitute a SK
or Lowe's handle.


Sears Danaher-made torque wrench parts drawing:
http://c.searspartsdirect.com/lis_png/PLDM/P0111046-00001.png


The torque wrench has:
----------------------------------
Ratchet assembly
Dust Seal
Arm pin/retaining ring

Barrel
Pawl (tilt block)
Cam assembly (cam, cam spring, cage, balls)
R. nut pin (??)
Torque spring
Spring cup
Positive engagement spring
Thrust washer

Adjusting screw assembly (ball, adj screw, round nut, handle nut)
Grip assembly
Handle nut
End cap

 

yep, one more victim of the busted plastic sears lock ring here.
otherwise, seems to be a decent wrench. i busted the ratchet out of a
cheaper wrench previously,

still works OK despite the busted lock ring, you just have to be
careful not to twist the handle. any day now i've been planinng to
wrap the lock ring with a screw type hose clamp, that oughta hold it.