Torque Block?

[jeejay]

Just bouncing an idea off the wall here...

So I have a big torque wrench (like this) for heavy truck wheels that I'd like to test the calibration of (indoors), through a digital torque adapter with a 4-point socket, and I've tried using a vise and 1-inch square steel bar to torque on, but the vise doesn't seem to clamp that tightly for up to 500 ft/lbs or so (right now I have it on a stand that isn't bolted down, so I've only gone up to 300 or less torque and the bar was starting to move out of position, then of course bolting the vise down to anything might not do, if I can't clamp it enough without pounding on it or breaking something).

Anyway, I was thinking of embedding the bar in a concrete cube instead (call it a torque block). Seems like it could work for really holding that bar in place, and I don't have anything to bolt it directly to otherwise (there don't seem to be brackets for that and what not, besides actual torque testing equipment that costs a fortune). How large do you think such a block would have to be (poured around a steel bar suspended in the middle, sticking out a few inches), so that it would hold under that kind of stress and not tip when torqued on? Or would you have other thoughts on this...

My guess would be 1x1 foot (about the size of a file cabinet drawer)... let's see I looked up the density of a cubic foot which says concrete would weigh about 133 lbs. Doubt I'd be moving that off the ground with a wrench (but then trucks are weighed in tonnage). Well I might have to try it (and maybe embed some square u-bolts for handles). Hmm, I also checked a torque calculator to get an idea of force on the object, which seems to say 500 ft/lbs from about a 45 inch wrench handle would generate something like 670 newtons or 150 pounds-force pushing down on the bar. So I gather pound-force and pound-mass are the same quantities on earth, and it's questionable if I'd tip it by exerting around 20 pounds more force on one side of a cube than it weighs (not sure, may need to make it heavier). Probably, yeah I did a rough estimation using two large sockets, putting a paint brush handle through the locking pin hole that's below center on the heavier one, then set a slightly lighter socket on top of the handle, and it tipped the heavier one. So I think the block would need to weigh more than the force being applied to a bar protruding from it (perhaps 18 inches/200lbs, considering that the handle in my little simulation was sticking out quite a bit more than the bar would, although the torque adapter adds an extra 10 inches, so maybe it was pretty close).

What else to consider? I also briefly looked up how torquing on steel might play out in concrete, and for example a 1-inch rebar anchor has a recommended torque for nut tension at 550 ft-lb (while its max load is in thousands of foot pounds, or over a hundred kilo newtons). So I suppose that's about the right size bar, although their embedment depth goes up as anchor diameter increases, being 16-inches for this one, while the 1/2 inch anchor has 7-inch embedment. I'm guessing my 12-inch bar may not need to be as deep, if their increased embedment is for load more so than tension (or toward an extremely high level of torque, since they're both measured as such).

A semi-educated guess then... or it'll be a sword in the stone.

 

[bad_idea]

Weld up a piece of the 1" square stock to a piece of 2x2" square tube and bolt into the receiver hitch on your truck? I doubt you will move the truck around.

 

[Nor'Easter]

^This guy has it.

The concrete block would likely tip. You can do a simple moment summation using the weight of the block at it's center of gravity, and the force via your torque wrench. Use the edge of the block that is closest to the end of your torque wrench.

In this case what you are fighting is the fact that your downward force via the wrench will be outside the footprint of the block. If you can reduce this distance or somehow move the force inside the footprint of whatever stand/block you make, you'll be set.

 

[blindley]

Jeejay, your 1'x1'x1' block of concrete will only weigh about 150 lbs. Nor'Easter is right--you'll tip it over long before you see the force you need to calibrate 500 lb/ft. Plus, do you want a big block of concrete in the middle of your shop? Bad_idea's on the right track with a welded frame, at least something you can use and then put in a corner out of the way (of course that depends on how often you have to calibrate this wrench). Good luck.

 

[jeejay]

Thanks, yeah if I were to use the torque adapter outside, I'd just test it on the truck wheel, but it isn't supposed to be exposed to the elements (direct sunlight, moisture, dust, etc). I guess stacking plates of weight on top of a block could make it more stable if needed, without it being too heavy otherwise.

I think before I do that though, I'd better try bolting the vise directly to something stable, then use its pipe clamp around a socket and plug the wrench & adapter/extension into that to see if it resists spinning vs how a square piece was being pushed down in the flat jaws. Perhaps wrapping a piece of large hose around the socket would make the pipe clamp grip it enough (likely more than the flat jaws clamp anything). I was using a square bar because the little flat sided square socket that came with the adapter for testing in a vise didn't hold as well (not as much area to clamp on), but this vise I got says it's multi function, so I'll have to test its torque capacity on something round and see what happens (before I go crazy pouring concrete).

 

[jeejay]

Seems to work, just barely. Got the vise bolted to a bench, and with the pipe jaws biting substantially into a 3/4 drive impact socket I was able to torque at 500 ft/lbs with a 12 inch extension (which feels to be at the limit there, the shorter the better but my torque adapter is long too).

Wrapping rubber around the socket didn't work though (I guess that's only good for smooth surfaces), as the jaws cut through it and also didn't bite enough, which wasn't exactly what I was going for (cutting into a socket), but as long as that works... forget the fabrication, thanks.

Oh, and now that I've plugged the torque adapter in, I'll say it looks like I was going up around 600 foot pounds or so there (no, wailt that was in newton meters)! Gotta check everything on that note (maybe I'll remember next time).

 

[jeejay]

In this case what you are fighting is the fact that your downward force via the wrench will be outside the footprint of the block. If you can reduce this distance or somehow move the force inside the footprint of whatever stand/block you make, you'll be set.

I did mount the vise more toward the middle of a bench too (depth wise that is, and 9" in from one side), used two 9 x 9 blocks of wood underneath to raise it high enough for the vise lever to clear the bench top, setting these nine inches back (so the jaws open fully to the edge of it). Four hardware store variety bolts at 3/8 x 7 inches held up okay. I was going to use 1/2 inch, but drilling through three things was somehow tricky (surprisingly it lined up squarely even though my bolt holes were all over the place)! Today I went back and upgraded some hardware, using eight oversized and extra thick grade 8 washers (1.25 diameter on top of it and 1.5 on the wooden bench bottom) with 3/8 fender and split washers over them to make sure nothing gets sucked into a sinkhole... you never know.

Dumb luck might be on my side, this setup was an afterthought, as the bench was framed in such a way that I couldn't mount the vise on a corner, but now I'm glad it's set back to balance things a bit more (besides, I can't walk into it and hit my funny bone there)... it's pictured in the vises topic.