breaker bar designs

[rmsg0040]

Hey guys, I got a new proto breaker bar 5469 today. Was looking at it and realized the design is different than other breaker bars that I have seen.

Is any one design better than the other, I know with the proto bar if it breaks you wouldn't be able to repair it.

Here are 4 different styles that I know of:

This picture is of a ratchet, but you get the idea.

Screw that goes through square drive:



Screw through design:



Have a koken bar that is pinned but 2 pieces which is repairable:



Proto bar is pinned but unlike 2 pieces with the koken bar, numbers 1 and 2 in top picture is 1 solid piece:

 

[zkling]

No, they are just different ways to accomplish the same task. The larger head is cheaper to manufacture.

The screw on the ratchet head is completely different. It allows for adjustment in head flex drag or "flop". Not really a concern on a breaker bark and a solid pin is going to give more shear resistance than on that is threaded, hence the different selection for different applications. The weak point is still the transition between the head and the square dive stud.

 

[rmsg0040]

So is a pinned design technically stronger than a screw design?

To me, a screw design looks as if the ears will break first whereas the pinned style the square drive will shear off?

Could you elaborate on "hence the different selection for different applications"

Thanks

 

[zkling]

Yes

Between a pin and a threaded fastener of the same diameter and same material; a solid pin will take a higher load before failing. The sharp threads not only reduce the effective diameter, but act as stress risers. Think of pulling on a piece of paper, now pull on a piece of paper with a V cut in the edge. Which one tears first?

The flex head ratchet is threaded as it is not intended for high torque a breaker bar is asked to endure. Also with time and user preference slop can form causing the ratchet head to flop around. A user can tighten or loosen the screw to change that slop as desired. With a breaker bar, where high torque is expected and head slop isn't really a factor, a solid pin is a better design selection.

The usual failure of a breaker bar or any drive mechanism is between the square drive stud and the head. The sharp to slightly radius ed shoulder is another stress riser.

Edit, if you are talking about the pin and the drive head (parts 1 and 2), they are two separate pieces. They may share the same black oxide finish, but they are indeed two pieces. Otherwise assembly and manufacturing would not be possible.

 

[rmsg0040]

On the proto breaker bar, I was assuming it was one piece, but the way you explained it makes sense.

I always looked at a breaker bar as just as a breaker bar but I learned something new today

I appreciate the info,

Thanks

 

[Wakefield]

The modern Snap on bars and I believe SK have threaded axle bolts. (in 1/2"drive) If I remember right a Snap On dealer explained that the bolt is to be kept tight,not used loose to induce more flop.The shoulder of the bolt snugs up against the inside of the ear that has threads. The axle should be long enough. The flop (stiction) is controlled by a spring washer between the drivepiece and one of the ears-I think the drivepiece has a countersink or recess on its side where covered out of sight by one of the ears.
Wright may still use the traditional steel pin which may be a press fit through the drivepiece to keep it from falling out.
There was an extensive thread on here a couple years ago about the handle fitted into a head with ears style vs. the handle having fork of two ears with the drivepiece between. Fork on the handle seems a little more compact.

If I remember right when I took my Williams apart (it is similar to the shorter Snap On) the nonthreaded section of the axle bolt that fits through the drivepiece is fatter than most of the pins in the pinned ones.
My Craftsman looks stronger than a Snap On one but the consensus here seems to be that it isn't!

 

[impactsocket]

Which breaker bar design is the strongest design?

 

[Wakefield]

Which breaker bar design is the strongest design?

I believe (remembering Mr. Holeshot) that either design can be made strong but the limiting part is the square drive cross section,it can only be so much (the 1/2" square or 3/4" square on 3/4" drive,that's why 3/4" stuff is much stronger the rest of the bar can be made stronger but is usually made as compact as possible so might not be any stronger than the square drive

I believe it has been mentioned about ears breaking off on some of them.
An old Mac with the head fork over the handle design is said to have been very strong
A new type of Snap On that is 36" long(still talking 1/2" drive) has that forked head over the handle design and is designed so that the drive square can be replaced,I think it (drivesquare bit) is supposed to fail before the rest of the tool therefor sacrificing itself if the tool is overloaded.

 

[Adam.C]

Between a pin and a threaded fastener of the same diameter and same material; a solid pin will take a higher load before failing. The sharp threads not only reduce the effective diameter, but act as stress risers.

All dead on except you missed one detail. The screws are never threaded in the area of max stress. They are only ever threaded at the very end where there is essentially no bending stress.

The flex head ratchet is threaded as it is not intended for high torque a breaker bar is asked to endure.

Full agreement, no quibbles except:
The handle and pin portion of a Snap On ratchet and breaker are identical. What limits the ratchet capacity as a breaker is the ratchet mechanism itself.

For the SHLF80A, (long flex head ratchet) the std 1/2" dual 80 ratchet mechansim is rated at a max torque of 750ft lbs. Note that this portion of the ratchet is covered under warranty and only about $10 if you are not the original owner. I'm not sure what the failure mode is- whether its the teeth (I assume so) or the 1/2" drive shearing off.

Also with time and user preference slop can form causing the ratchet head to flop around. A user can tighten or loosen the screw to change that slop as desired. With a breaker bar, where high torque is expected and head slop isn't really a factor, a solid pin is a better design selection. .

Except: The clevis ears may spread under load. That increases the "unsupported (i.e. exposed) length" of the screw or pin, increasing it's bending stress. A screw can easily react the tendancy for the ears to spread. A screw design is a better/stronger one, especially if you keep the flex firm. Note that the Snap On breakers (SN24C, SHBB24) use screws.

Last, I think we are all well aware that foreign manufacturers do a good job of copying US designs. But they don't always do a good job of copying materials, processes, tolerances etc.

A good breaker is one with roughly the Snap On design ( a large screw, a firm spring). It also needs to have high quality steel, careful heat treatment, and manufacturing processes which are inspected by an independant minded and empowered inspector. The clearnace between the screw or pin and clevis holes is critical.

There are all sorts of tools I am happy to buy from China or other countries. A breaker bar isn't one of them. Brand new SN24 is about $120.

 

[Westly]

I've wondered about this. I think the stiffer the bar the better. My 1/2 Craftsman has scallops in the shaft that reduce the metal and probably the stiffness. Stiffness would be especially important if you were going to hit it with a hammer, so the bar wouldn't just absorb the blows.

 

[owenst7]

scallops in the shaft that reduce the metal and probably the stiffness. Stiffness would be especially important

I thought those were put there to increase feel?

 

[rockinacummins]

I never really paid attention to a breaker bar that much... But now that you brought it up I know I'm gonna inspect every one that I encounter from now on. Don't forget the sliding head type breaker bar! (or t-bar, whatever you call it)

 

[inzanoqiaw]

The sharp threads not only reduce the effective diameter, but act as stress risers.

 

[theknurl]

breaker bars are a waste of time for serious stuff......

the Model 750 Swench Wrench

manufactured by Curtiss-Wright, yes, the aircraft engine people

go to the Heavy Equipment Forums.....and look around

the BIG Swench Wrench is 7,000lbft of torque

the are FAA certifiable as torque wrenches on aircraft

I have 2;
a 1/2" Model 500 1/2" drive its 9 1/2" long with 500lbft of torque
and a Model 750 3/4" drive with 800lbft

last weekend my neighbor broke 2 wheel studs on his Dodge truck......is 1/2" Snap On air impact wouldn't pull the new studs in

he laughed to whole time using the Swench Wrench......."damn, I need one of these......No Tom, I have 2, you won't need it very often.....but when you do...."

 

[n8n]

I need one of those... But so spensive!

Sent from my Nexus 7 using Tapatalk

 

[Olafur]

Seen many bars of this design with the square drive twisted off flush to head. Never seen a joint like this broken.





This type either twists the square or the ears brake off the handle.



Either way, both types are limited by the strength of the square drive it self. Put in stronger joint and you are not much better off since the square is the limiting factor. For 1/2" drive the limit seems to be in the neighborhood of 700 lbs/ft. -> http://image.snapon.com/international/pdf/sf80_slf80_shlf80_sx80_npa.pdf