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Question for engineers/PEs etc in re: torque multiplying "ratchet" looking tools

proFeign

Cast Iron
Joined
Oct 2, 2007
Location
Santa Barbara, CA
Question for engineers/PEs etc in re: torque multiplying "ratchet" looking tools

McMaster and some other supplier offer (for no small $$ by the way) a thing that looks like a big/long 1/2" driveish ratchet with a slightly larger head on it and apparently a gear mechanism inside that multiplies torque. I have a BS in ME and while that sounds good on paper I wonder if it's possible in real life.

In other words torque in is reaction torque and it seems like the fastener torque will be applied to the handle, gear reduction or not, and the user will have to apply the same amount of torque to achieve equilibrium. If there's a tie down/bolt down point in the ratchet area that's a different thing but for statics if you take your control surface to be around the ratchet head with the fastener torque as your perimeter on one side and your input torque via the handle on the other side torque in = torque out regardless of gearing (?). I think this might be oversimplified as I know you'd be doing more work on the handle than the fastener if it's geared way down, but reaction torque still the same? Equations would be welcome, since it's probably going to take them to convince me that someone a lone person standing on the ground could generate more torque on a fastener than he is applying on the handle of a wrench, in spite of the lesser degree of rotation, respective to each part.

This is something that has bothered me since I first saw parts of this nature... If it works and I've overlooked something obvious that would be great but I figure without an anchor point for the gear reduction (like locking an orbital ring to a stationary piece of the part) I don't know how you'd get more torque into a fastener than your body's putting into a wrench even if you move the handle 100 degrees for every ten of output... :confused:
 
I have a BS in ME.

Sounds painful! Seriously, I think you have been thinking yourself into confusion, or alternatively, confused me.

the user will have to apply the same amount of torque to achieve equilibrium.

Why would you want to achieve equilibrium? The sole purpose of a wrench is to move something. That means acceleration at some point and thus not force equilibrium. If the situation is static then forces would have to be equal like you say, but what would be the use of that?

I don't know how you'd get more torque into a fastener than your body's putting into a wrench even if you move the handle 100 degrees for every ten of output... :confused:

Of course you wont get more force actually into the wrench than you yourself are exerting. But if the ratio of movement is 10 to 1 then you will get out 10 times the input force just over a smaller movement. That also goes for rotation and torque. (Wrenches basically is the added benefit of a long arm - which also just provides a lever/ gearing through larger movement by having a larger radius. And if internal gears can add to the movement difference the difference in torque will follow).

I guess this either helps, or digs you a deeper hole. :) (Been there!)
 
If you are refering to the McMaster "Universal Torque Multipliers" you will see from the spec table that it has a reaction arm. It is the reaction arm that is shown in the picture.

Phil
 
The 'handle' on that 'ratchet' is the reaction lever. You plug another ratchet, or torque wrench, into this one and somehow block the lever from rotating the opposite direction.

that would explain it then!

In re the previous post control surfaces help greatly simplify visualizing problems and "equilibrium" is useful to figure out the math for when input forces equal output forces to detemine minimum load to prevail. Phone won't let me line by line respond right now but thanks!

K

and ps the bs in me was very painful!
 
The torque multiplier is just an epicyclic gearbox.

Put a full turn in, and you get an xth of a turn out, but with x times the torque (actually a bit less, due to friction).

As has been said, the rotation of the gearbox has to be prevented by a reaction bar.

The principle is exactly analogous to a lever, which only works in conjunction with a pivot to provide the reaction.
 
I've used them. There's planetary gearing where the planet is connected to a, say, 3/4" drive square for the socket and the sun gear is driven by a square driving recess where you connect the ratchet, torque wrench, whatever. The ring gear is integral with the outer housing and the socket for the reaction bar. The ratio is selected for easy calculation of torque multiplication. I seem to recall 3 to 1 but don't quote me. It's been 30 years.

This is a young man's tool. If you have a passle of fasteners requiring manual tensioning the guys on it better be husky.

I like the newer hydraulic fastener tensioner equipment I saw at a tool show a couple of years ago. It uses the neighboring fastener to restrain the reaction arm. The thing had a compact little pump and some skinny hoses, and a stout looking short storke cylinder that had only a little over-travel past the next click on the ratchet. I like it but it's for weenies.

I used slugging wrenches back in the day when I was working propeller shafting on aircraft carriers. The nuts were 4 1/4" across the flats as I recall and after a little conditioning, I swung a 24 lb short handled hammer one-handed to strike the wrench with. Work that job and you didn't need a coat even in cold weather and 45 degree F pouring rain felt cool and refreshing. My wrists still get sore when the weather changes.

Anyway torque multipliers are not intended to be used with impact wrenches but i've seen a few yo-yos do it.
 
The above posters are correct about a reaction arm. You input 1/4 the torque, the reaction arm inputs the other 3/4 (for a 4:1).

I have a couple of the things. The one that gets used the most is a Proto (probably made by 4X Corp), 1/2 in, 3/4 out. It is a mechanical 4:1, but by torque it is 3.03:1. The other is a little larger, 1" in and 2 1/2" out. I don't even like to carry it.
 
The torque multiplier is just an epicyclic gearbox.

Put a full turn in, and you get an xth of a turn out, but with x times the torque (actually a bit less, due to friction).

As has been said, the rotation of the gearbox has to be prevented by a reaction bar.

The principle is exactly analogous to a lever, which only works in conjunction with a pivot to provide the reaction.

I actually (with a team since it was a whole apparatus we were designing) designed an epicyclic gearbox at school senior year. It had to be really flat in our impelementation and have an absurdly high reduction due to the motor we picked to drive it.

the lever analogy is a good one!

see next reply
 
Yes, they work and they work well. As noted it is a planetary type gear setup. It's a funky feeling to pull on a handle with about 100lbs of force and see it break a nut loose that your best impact wrench wouldn't budge.
 
Thanks a lot you guys. I had to remove a 2" NPT plug off of a very large air receiver tank that was put on with a lot of liquid pipe dope in addition to apparently being powdercoated in place on the tank (seriously why did they do this? i don't want to get a freaking torch on the finish and it really wasn't necessary for it to be nearly this stuck/tight etc).

I was using a 2' long crescent wrench (square drive on the plugs so no socket/impact wrench was going to fit right out of the drawer), plus I avoid impact wrenches until I'm in a bad way or I feel like they're the right tool, and I couldn't budge the damn thing. I got a small sledge to try to break it loose by tapping (and then really hitting) the handle of the 2' crescent with no luck, but with lots and lots of noise even though I kept the slop very very low and preloaded by hand. FWIW I didn't damage the head or the wrench in this process except to break off the powdercoat on the plug (which isn't needed) where the wrench flats were touching it.

Anyway no matter how hard I went (using my judgment on when is the time to give up) 0 degrees of rotation. So I soaked it with penetrating lube for a couple of hours, still no rotation even with the sledge/driving hammer. I was almost considering using the high bay crane to pull on the wrench (our facilities safety guy would have loved that but I wasn't really advertising what I was doing...) until I finally found a cheater tube that would fit around the handle of the big wrench (we don't keep a lot of material stock so this was a big find since our aluminum tube that was big enough didn't seem like it was worth potentially damaging) and it took a 6' piece of tubing and all of my weight and a great deal of effort to move it. Took several removings of the wrench for clearance to move the cheater around before it could be taken off with just the 2' wrench. Never had something stuck that bad but it got me thinking about how to gently/constantly apply torque (i.e. not with an impact) (and why I was thinking of using the crane if all else failed) when truly defeated by a truly stuck fastener.

Anyway so all that I or our expert machinist knew about those multipliers was from seeing small pictures in weekly catalogs and I have forever wondered, for the reasons cited above, how they could work at all if they were just a socket wrench-style thing. Torque is funny that way but I wasn't able to explain it well to our machinist why I fundamentally didn't get how it was possible, like perpetual motion, but the additional wrench (reaction torque to drive it) is exactly what I meant by "something you fix in place to prevent rotation." Torque isn't like a lot of things and this particular product has always made me wonder. The ads I had seen just showed a "3/4" drive torque multiplier" saying things like "increase your torque 4x" without really showing in the catalog that you even needed another wrench. Seemed to violate the laws of physics but I thought I must be missing something because they wouldn't be selling them in legit tool catalogs if they didn't do anything, especially for the price...

Altogether that seems like the most sensible method for a fixed rotational point, that is, using the included arm more like a breaker bar and the socket like a second wrench on the other side but I had always thought that even a 400:1 epicyclic gearbox doesn't do anything for you since your reaction torque doesn't care about rate... Totally explained by fixing the tool's handle and using a second device to create rotation.

Anyway thanks a lot! I could have looked this up more thoroughly but I wanted to post it since I think the principle is important to understand and I wanted to share. I almost went to an engineering only questions forum but I've missed PM badly and I have learned way way way more here than I ever had from any other tech forum. You should hear me at work "well I learned on the macinist forum..." mostly tricks from old-timers like Forrest et al... I have 1000++ machining hours (direct time running mostly manual machines) and I am as much an engineer as I am a machinist. But still so much to learn.

PS in designing the epicyclic(planetary) gearbox I was able to come up with a perfect way of understanding why such high reductions can be possible with this type of gearbox if anyone is interested just ask. Might be obvious to others how they work but if you have good tolerances (i.e. you can put in 90 tooth gears custom fit as easily as 91 tooth gears) you can achieve truly incredible gear reductions for size. PM or reply if you want my quick way to think about it.
 
Yes, they work and they work well. As noted it is a planetary type gear setup. It's a funky feeling to pull on a handle with about 100lbs of force and see it break a nut loose that your best impact wrench wouldn't budge.

I'm guessing this 2" NPT plug (square drive so no impact without tools we don't have) took 900+ lbf-ft to prevail on, and even then it didn't just break free - it took a lot of sustained torque to move it enough to get off with normal tools. I'm guessing somehow the powdercoat cured the liquid dope compound they sealed it with but my supervisor came down and was giving me a hard time until he couldn't budge it at all under any circumstances.
 
I've used them. There's planetary gearing where the planet is connected to a, say, 3/4" drive square for the socket and the sun gear is driven by a square driving recess where you connect the ratchet, torque wrench, whatever. The ring gear is integral with the outer housing and the socket for the reaction bar. The ratio is selected for easy calculation of torque multiplication. I seem to recall 3 to 1 but don't quote me. It's been 30 years.

This is a young man's tool. If you have a passle of fasteners requiring manual tensioning the guys on it better be husky.

I like the newer hydraulic fastener tensioner equipment I saw at a tool show a couple of years ago. It uses the neighboring fastener to restrain the reaction arm. The thing had a compact little pump and some skinny hoses, and a stout looking short storke cylinder that had only a little over-travel past the next click on the ratchet. I like it but it's for weenies.

I used slugging wrenches back in the day when I was working propeller shafting on aircraft carriers. The nuts were 4 1/4" across the flats as I recall and after a little conditioning, I swung a 24 lb short handled hammer one-handed to strike the wrench with. Work that job and you didn't need a coat even in cold weather and 45 degree F pouring rain felt cool and refreshing. My wrists still get sore when the weather changes.

Anyway torque multipliers are not intended to be used with impact wrenches but i've seen a few yo-yos do it.

Thanks Forrest - I always like it when you drop in. Hydraulic pressure/hydrostatic pressure (any gas) is incredible and still hard to believe how strong it can be for sizes involved. But I agree that this type of device is best avoided (weenies) but when you've got a fastener like this where it's not even clear if it was tack welded in place for all the headway I was able to make...

Also I'm sure the main reason not to put an impact on one of these is that even if they have hardened gears inside it's a good way to chew the crap out of the internals of a $300+ tool.

Glad to hear you hit a wrench with a sledge/"driving" hammer - I've never had to go that far before a few days ago but as a basis for this: ~3/4" is a pretty big fastener for whatever I've ever had to deal with.
 
Yes, they work and they work well. As noted it is a planetary type gear setup. It's a funky feeling to pull on a handle with about 100lbs of force and see it break a nut loose that your best impact wrench wouldn't budge.

If I get a minute today I'm going to do the math on it and see if the reaction force on the static handle of the tool is the same as the applied torque or not. Just my own curiosity and just in thinking about it quickly it's not obvious if it is or not...
 
I have an MSE in ME which did not hurt near as much as the BSE; at least it was over faster.

I have watched mechanics using big multipliers on truck parts many times. The rear axle pinion nut and transmission output yoke nut require hundreds of pound-feet to tighten to spec and are pretty hard to remove, too. A huge long-handled torque wrench or ratchet is not practical to use while you are on a creeper under a truck. So the answer is to use a shorter/smaller torque wrench and a multiplier. Even if the unit was attached to an assembly stand, the multiplier was used if our biggest torque wrench was too small.

Larry
 
If I get a minute today I'm going to do the math on it and see if the reaction force on the static handle of the tool is the same as the applied torque or not. Just my own curiosity and just in thinking about it quickly it's not obvious if it is or not...

The reaction force is the difference. Example: w/ 4:1 ratio, if torque wrench is 100lbft, reaction arm is 300lbft, bolt sees 400lbft.
 
If you're only got one or two bolts to do, torque multipliers are OK. Try putting flanges on both sides of a 24" CL 2500 valve. There are 16, 3 1/2" studs on each side that get torqued somewhere north of 10K ft-lbs. Then you've got to take them off.

Here's what we use http://www.hytorc.com/

First thing that we say when somebody says they've got an ME degree.... I'll talk slower. If they say they've got an ME degree from Iowa, we say.... Let me draw you a picture. All of the ME's end up out on the production floor at one time or another when they find out we can't built what they drew on their CAD system.
JR
 
I've never had any luck getting large NPT fittings out of air tanks - they always seem stuck permanently in place. There have been times when I truly thought I would twist the fitting out of the tank before the threads gave way. So I stopped.
 
Harbor Freight has 33:1 torque multipliers for $20. or less on sale. :D

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93645

And not only that, awhile back I talked someone into buying one and he took at least one pic of the inside and made a widget. (This was in conjunction with the FIRST Robotics competition for high school kids, so cheap stuff has a place.)

http://www.chiefdelphi.com/forums/showthread.php?t=49073

http://www.chiefdelphi.com/forums/showthread.php?t=49064

And the design might have been lifted from something like this:

http://www.plumettaz.ch/en/products/personnel_lifting/tq/tranquart.aspx
 








 
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