vane171

This video made me think that you could use standard socket wrench together with this luggage scale. If you choose wrench with some given arm length, you could figure out a point on it and a chart to read off torque values and bingo, you got super precise torque wrench without needing to buy one, for the low torque range anyway (but with longer wrench handle, you can get higher torques). I have this scale and it goes up to 40Kg which is some 80+ lbs (I use it for airline luggage weight checking as probably most folks do).
Most simple it is for the 12" long wrenches, could make a fixed eye for hooking up the scale, maybe even incorporate with the eye a six inch long wire at ninety degree so you could watch for the scale pull to be in the right direction, and voila. Also maybe that excel table is available somewhere on the net.


As to OP query, am I correct in thinking that you might get by with just one size torque wrench, I would guess the smaller size is more important to have, the bigger torque parts you can go by the seat of your pants, so to speak? Not overdoing it and then watching if the BB or whatever doesn't show signs of low tightening? I presume some mechanical acumen on the mechanics part.

70sSanO

A don’t think arm length, or an extension on the wrench, will change the torque applied. It will only change the scale reading; and give you more leverage.

The other thing is there are tolerances where you could be off by 5% from one actual torque to the next without any changes in the settings.

I did a quick run with a luggage scale and it is interesting in that you have to catch the high reading, especially for wrench that releases at torque.

It is good to make sure the wrench isn’t off by 50%, especially if it is torquing higher than the setting. For a bike that is really all you need. Get within 10% and call it a day.

John

vane171

Re the 'arm length', the point is that when it is 12" long, the read out on the scale shows directly the torque value in ft/lbs. Dead simple, easy to understand even by me, who has shivers when it comes to these composite units, even metric ones I grew up with, never mind imperial.

Longer or shorter handle require that you make the conversion as per the formula shown in the video and so is not as convenient. And it is no good trying to get around it, say by pulling on half way point of the 2' long handle, or extending some 6" handle to make it 12". There is a reason why handles come at given length. I am sure you all know that, I am just making it clear for myself by writing it out.

Second, if what you do is calibrating, than it is kind of hit or miss reading off the exact value on the scale, which is why you repeat it. However with normal ratchet wrench, it becomes a simple thing of pulling on the scale until you reach the desired value reading on it, there is no sudden jump in value. That is, you don't need to catch the point at which the torque releases which can't be quite exact since the reading jumps suddenly, as when you are calibrating.

I suppose the torque calibrating is more important at low torque values, like bike handlebars/stem screws, whereas BB torque can be off by several ft/lbs and it is OK, whereas it would not be good on the stem screws at all being off by several pounds. For those low torque screws, it is best to use those dedicated, single setting wrenches.

I have this brand new low torque wrench I bought last year, the click kind, and find it hard to trust it at the low end torques from my testing on nuts I have around the place, didn't use it on my new bike yet. I will test it as per this great video tip and report how it fared.

70sSanO

Yes it is hit or miss; maybe more of a trend usually lower or higher over multiple tests. And I think accuracy is more important at lower torques.

I understand now you are referring to using a scale on a standard socket wrench and you tighten till you hit that value of the scale. That is probably not much different than a beam or dial torque wrench. The biggest problem though would be to get a consistent 90* pull at an exact point to get a certain accuracy.

Once you calibrate, or are confident about how close, the wrench is to the “perceived real” torque, you don’t care about juggling a scale 12” out, you just tighten stuff.

In some ways a recommendation is a bit like a bike. New and expensive is best, and probably overkill, new and cheap will work fine initially but longevity may be hindered, good old may not be as close tolerance wise but will be good enough and not have to be replaced.

John

billridesbikes

A couple small issues with this video.
Torque is a vector, it's the angular acceleration around a body. It's defined as t = r*F*sin(theta). Where r is the distance, F is the applied force, and theta is the angle between r and F.
You can see in the video he's wiggling the strap connecting the handle and the scale and doesn't seem to be exactly at a right angle as the wrench twists, could be the camera angle maybe, this in itself will cause a few % error. It would be more accurate to use a thin rigid connection.
It also doesn't matter where you apply the force on wrench, it doesn't know where you apply it. You can use this scale method to know this is true. For example if you apply the force at the middle of the wrench it would take you twice the amount of force for any given torque then at the handle. Same if you added a bar to the end of the wrench and find you need less force for the same torque. For his long wrench he could have just measured out 12 inches and done his test at the point of the handle. The wrench is still reads 'accurate' torque under these conditions.

70sSanO

The scale I have has a metal hook that fits around the handle so it is easier to keep it at a certain point. Yes the angle and also pulling on the same plane as the handle influences the reading. And using a socket is not the best choice. Using a 1/4 to 3/8, 3/8 to 1/2 adapters are much better.

The process is one of multiple pulls and trying to keep it square and catching the number. The tough part is catching the right number since it doesn’t lock in on the highest in a split second. But it gives a good idea if the torque is close.

My old JoLine was made with a soldered end cap so customers couldn’t easily open it up and would have to send it back for repairs/adjustments. I read that it uses a stacked washer system to calibrate it. No way I’m opening that can of worms.

But it is nice to know that if I have a 260-400 in lb range setting it around the mid-point will be fine.

I do plan to spend more time testing my 1/4” 10-200 in lb wrench.

John

vane171

Yes, I meant using the scale with an ordinary ratchet wrench.

Using the scale to tighten something to a given torque would work even with a classic side wrench, since some nuts are in a place where you can't slip a socket on them and your fancy calibrated torque wrench is useless.

I didn't get to test my torque wrench today, have to leave it to the weekend. I will try to test the sensitivity to not pulling the scale at right angle. Perhaps the angle is not too critical. With the wrench se to a given torque, I will pull at various angles till it clicks and note how many pound reading it would be off. Again, the angle might matter more at low torques, where just one ft/lb is a large percentage of the torque you want to achieve, vs 100+ ft/lbs torques, where several ft/lbs off doesn't matter.

My idea was to attach an eye to the wrench handle for sure hooking the scale at the 12" point if this was to be used not just experimentally, perhaps even a rod ~1/8" diameter, say 6" long sticking out at right angle from the handle at the eyelet to make a reference for easier keeping to right angle.

I understand that torque wrenches need 'exercising' before being used if they have not been used for a while, even instructions that come with the wrench mention that, I think. I guess that even new manufacturer calibrated wrench needs to be checked if it spent long time on a shelf in shop before being purchased.

55tele

I have a Park T Handle torque wrench that has a dial to select between 4 and 6 Nm in half steps. It works as a clutch and will not tighten further beyond the preset.

I also purchased a Precision Instruments 30-200 in lbs 1/4” drive click style wrench for about $120.00.....this for torquing beyond 6 Nm...I selected this because the company supplies torque wrenches to the professional mechanic market, actually supplied Snap On earlier in their history, is made in Suburban Chicago, and is able to be calibrated without taking the wrench apart...

I also have their split beam 3/8 and 1/2 wrenches...

vane171

I tested my brand new 1/4" TWrench I bought last year, still in oily wrapping and only ever been used in try out testing. Its range is 20-200 in/lb (equivalent to 1.66-16.66 ft/lbs or 2.26-22.6 Nms). I 'trained' the wrench by setting it to highest and lowest setting several times. Also redid the measuring pull several times.

Not only is the in/lb scale probably not what is normally used in bike torque specs but the wrench handle is 10" long, which both taken together make the conversion rather involving.

Anyway, I found the wrench would tighten too much especially at low torque end and the error gets proportionally smaller at higher torque. Didn't test the midrange or higher since I don't have a wise grip strong enough.

At the lowest setting 20 in/lbs which converts to 1.66 ft/lbs, it overtightens in testing to 2.5 ft/lbs.
At 60 in/lb which is 5 ft/lbs, it overtightens to 5.8 ft/lbs.

Moral is, test your new wrenches. But the 5ft/lb torque is ~ what is used on the small screws on a bike and the error (5 vs 5.8 ft/lb) is probably acceptable? Also, such testing is not possible on those small 'T handle' bike specific wrenches without some mechanical dodad, on the other hand, those are likely OK.

70sSanO

I honestly don't use a torque wrench very often on my bikes. I used to use them a lot more on cars. But I decided to see how close "theoretically" they were. I got a digital scale with a metal handle and hook and tested a weight against a kitchen scale value to make sure the digital scale wasn't way off.

I have a:
1/4" 10-200 in/lb
3/8" 100-750 in/lb
1/2" 10-150 ft/lb.

The main difference I did was to slightly expand the hook to slide over the wrench handles. This way I can find a shoulder toward the end where the handle knurling stops to use as a more solid location to test the wrenches. This means it is not testing at 6" or 12", it is at whatever the distance to that point. If it measures 10-7/8" for 100 in/lb setting I use that. Turn it to 150 in/lb setting and if it is 10-13/16" I use that distance. There is nothing special about whole numbers, it is just simple math.

What this did was give me a rough range of variances over 8/9 torque settings on each torque wrench. The object is not necessarily to calibrate the wrenches: which I found was tough when an end cap would not unscrew, but to get a feel for where the numbers ended up. Since I didn't want to clamp of the micrometer handle with more force than my bike workstand to loosen the end cap, I made index cards of the different in/lb or ft/lb variances at each setting and put one in each case. I used the cards because 6 months from now I won't remember a thing.

I did a comparative testing between wrenches on a metal carriage bolt on a dolly to make sure I didn't do something stupid and that the adjusting for variances gave me about the same click.

At the end of the day, I will still use a basic allen wrench to secure bottle cases, tighten seat posts, clamp cables, etc. And if I had carbon I'd probably spend the money on Nm T-handles.

John

vane171

My 10" mark on the handle from the above post is right behind the lock nut where about half an inch of the 'handle' still protrudes and scale metal eye nicely fits on it, which means it stays at those 10" no matter what torque setting I chose.

Same here, saves you re-figuring it out again at a later date.

Right, that's what I will do for all those smaller critical nuts, like handlebar/stem screws and for the large torques like BB I will use an ordinary socket ratchet wrench pulled by the scale. Here the torque doesn't even need to be that exact.

BTW I was able to read off my 10" out setting from the charts the guy shows in the video to confirm my conversion and calculation.