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Pillow bearing massive failure

Overland

Hot Rolled
Joined
Nov 19, 2017
Location
Greenville, SC
Scott,
Interesting idea that I was considering last night.
My interpretation of the idea was cut the feet off the cast iron bearing housing, then turn it round to be used as a bushing inside the new steel housing.
Are we saying the same thing ?
Bob
 

Peter S

Diamond
Joined
May 6, 2002
Location
Auckland, New Zealand
My interpretation of the idea was cut the feet off the cast iron bearing housing, then turn it round to be used as a bushing inside the new steel housing.
Bob,
See post #37, you can buy the cartridge ready-made if it helps.

Here's a page from the NTN USA website showing a 2 1/2" size with set screw lock.

You can buy them as a unit (housing and bearing) or housing only. Also in a larger series.

NTN Cartridge type.jpg


FWIW, I was interested to see they also sell steel pillow blocks and flange mount types. Made from steel plate, not cast steel. See page 5 for strength comparison:

 
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BT Fabrication

Stainless
Joined
Nov 3, 2019
simple problems need simple soloutions.
take solid steel bar, somewhere around 2' have it reach both pivots.
cut 3 pieces of tubing close to bar on id.
weld one to ramp. weld other 2 onto the pivot areas. done. grease till it flows everywhere. no need for bearings when its only teeter tottering.
 

michiganbuck

Diamond
Joined
Jun 28, 2012
Location
Mt Clemens, Michigan 48035
I think best would two pieces of steel for each pillow block
1. 4x4 x1" (So making a 3/4" wall thickness to 2 1/2" shaft)
2. 1 x1 x 8"
Welded together to make the basic shape
The 4x4x1 would have a 2 1/2" + a few thow for grease, + counterbores for seals + top corners rounded.
The 1 x 1 x 8 would be the PB base welded to, and have the bolt holes, top corners rounded.
Oh, and a grease zerk someplace.

Overkill for fancy would include a brass bushing bearing inside.
Likely cost $100each but would be way strong to available stuff.

Steel 4x4 x1 $30. Each
1x1x8" $23 each
 
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blcksmth

Cast Iron
Joined
Nov 17, 2006
Location
Bowling Green, Ohio
I'm not an engineer. This teeter-totter weighs 2000 pounds and the pivot is 26" above the ground. My simple mind says that is 1000 pounds each side of the pivot. The vehicle drives onto the low side. The far side is now close to 35 inches above ground- I'm guessing. The vehicle drives across the pivot point as the platform reverses high and low ends. The end going down now hits a solid stop. There is nothing to stop the end going up. How fast in inches per second is the back end rising when the front end hits the stop? Not counting the vehicle, you have 1000 pounds leaving the ground at some fairly rapid rate when the front end suddenly stops. The only thing there to stop the rising 1000 pounds, plus the vehicle which is also rising, is the 1/4 inch upper shell of the bearing. Some how I don't think this is going to end well.

Bob
WB8NQW
 

Scottl

Diamond
Joined
Nov 3, 2013
Location
Eastern Massachusetts, USA
Scott,
Interesting idea that I was considering last night.
My interpretation of the idea was cut the feet off the cast iron bearing housing, then turn it round to be used as a bushing inside the new steel housing.
Are we saying the same thing ?
Bob
Yes, that is exactly what I was proposing, the geometry of the cast iron spherical bore inside a sturdy steel housing.
 

Nagol

Aluminum
Joined
May 21, 2020
Did it break right away or just after a bit of abuse? What about just adding another on on the inside of each rail. If it didn't break right away surely twice as strong would do it. Should be easier to engineer as well. Could mount a plate with some heavy gusseting on the post side to accommodate the extra bearing.
 

michiganbuck

Diamond
Joined
Jun 28, 2012
Location
Mt Clemens, Michigan 48035
I think that with one shaft the hard slam was aided by some twist and angle issues so magnifying the force enough to break the bearing's construction/thickness.

And both cast iron and cast steel are prone to break with a shock force.
With the bearing taken out just think how easy one could break the shell with a hefty hammer.
 

Garwood

Diamond
Joined
Oct 10, 2009
Location
Oregon
This is some dumpster fire engineering.

The designer really did not even consider the vehicle wheelbase and just arbitrarily picked 20 feet? I guess it's better to be lucky than good, but that's a pretty serious oversight that kinda goes along with the rest of the project.

As for the fix, NO, you don't any spherical internal bullshit. This thing is not anything precise. It needs a dumb, simple, common sense fix.

1) take a tape measure to old bearing.
2) go to rem pile.
3) find something round that has or can have a 2-5/8" hole drilled in it.
4) find something flat that will stack with the round thing to achieve the correct center height.
5) do some drilling/boring for the 2-5/8 holes and the mounting bolt holes.
6) weld them together.
7) bolt in place of old bearings. Use antiseize or grease.

If you stick with same design, adding a hydraulic cylinder/reservoir style damper would be a good move. I can't see cheap auto shocks worked very good.
 

Overland

Hot Rolled
Joined
Nov 19, 2017
Location
Greenville, SC
I'm not an engineer. This teeter-totter weighs 2000 pounds and the pivot is 26" above the ground. My simple mind says that is 1000 pounds each side of the pivot. The vehicle drives onto the low side. The far side is now close to 35 inches above ground- I'm guessing. The vehicle drives across the pivot point as the platform reverses high and low ends. The end going down now hits a solid stop. There is nothing to stop the end going up. How fast in inches per second is the back end rising when the front end hits the stop? Not counting the vehicle, you have 1000 pounds leaving the ground at some fairly rapid rate when the front end suddenly stops. The only thing there to stop the rising 1000 pounds, plus the vehicle which is also rising, is the 1/4 inch upper shell of the bearing. Some how I don't think this is going to end well.

Bob
WB8NQW
It didn't.
 

michiganbuck

Diamond
Joined
Jun 28, 2012
Location
Mt Clemens, Michigan 48035
Seems to me, that if it broke I would want it twice as strong.
The thickness of the existing wall is about 3/8 to 7/16 Of cast so I would go with 3/4" steel.
And keep it as simple as possible.
I dont see anything on the market that would be as strong as the homemade 4x4 x1 that I fudged up.

Yes, the strong pivot would put the breaking point somewhere else on the apparatus.
 

Overland

Hot Rolled
Joined
Nov 19, 2017
Location
Greenville, SC
Bob,
See post #37, you can buy the cartridge ready-made if it helps.

Here's a page from the NTN USA website showing a 2 1/2" size with set screw lock.

You can buy them as a unit (housing and bearing) or housing only. Also in a larger series.

View attachment 371184


FWIW, I was interested to see they also sell steel pillow blocks and flange mount types. Made from steel plate, not cast steel. See page 5 for strength comparison:

Peter,
Thanks for taking the time to do this research.
Seems an interesting alternative, but I can't see a supplier for this style in the US.
I've gone ahead and ordered pieces of plate cut to shape of the bearings to make new, very simple blocks.
Bob
 

Overland

Hot Rolled
Joined
Nov 19, 2017
Location
Greenville, SC
This is some dumpster fire engineering.

The designer really did not even consider the vehicle wheelbase and just arbitrarily picked 20 feet? I guess it's better to be lucky than good, but that's a pretty serious oversight that kinda goes along with the rest of the project.

As for the fix, NO, you don't any spherical internal bullshit. This thing is not anything precise. It needs a dumb, simple, common sense fix.

1) take a tape measure to old bearing.
2) go to rem pile.
3) find something round that has or can have a 2-5/8" hole drilled in it.
4) find something flat that will stack with the round thing to achieve the correct center height.
5) do some drilling/boring for the 2-5/8 holes and the mounting bolt holes.
6) weld them together.
7) bolt in place of old bearings. Use antiseize or grease.

If you stick with same design, adding a hydraulic cylinder/reservoir style damper would be a good move. I can't see cheap auto shocks worked very good.
Lighten up Garwood !

My son, not the designer, said 20 feet.
I accepted it at face value, than another friend was wondering about wheelbase. Turns out the vehicles in question are fine.
 

Overland

Hot Rolled
Joined
Nov 19, 2017
Location
Greenville, SC
Seems to me, that if it broke I would want it twice as strong.
The thickness of the existing wall is about 3/8 to 7/16 Of cast so I would go with 3/4" steel.
And keep it as simple as possible.
I dont see anything on the market that would be as strong as the homemade 4x4 x1 that I fudged up.

Yes, the strong pivot would put the breaking point somewhere else on the apparatus.
Yes, we're going big, and your point about moving the weak link is fair.
We'll also put some serious effort into absorbing the energy on the bump.
Thanks
Bob
 

michiganbuck

Diamond
Joined
Jun 28, 2012
Location
Mt Clemens, Michigan 48035
Everything that is subject to stress is subject to a test to failure and then make it better up to the needed whatever. Engineering is the starting endeavor and testing is the proof of the design. In this project, the welds or even the construction material may be next to fail.

I should go over to China and start a heavy-duty pillow block bearing of my simple design. With shipping advantages, nobody in the USA could touch my prices.
 
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Overland

Hot Rolled
Joined
Nov 19, 2017
Location
Greenville, SC
Buck,
We've ordered some 2" plate in the profile of the pillow block.
We'll then clean up the base, bolt holes and spotface then bore a big hole in the middle.
Blanks are $85 each.
Oh well.
 

Overland

Hot Rolled
Joined
Nov 19, 2017
Location
Greenville, SC
Got the blanks from the steel shop today, Watkins Bros, Cowpens, SC.
Excellent job.
Skimmed the bottom off, and cleaned out the bore.
Just need to drill mounting holes, and they'll be good to go.
Bob
 

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Strostkovy

Stainless
Joined
Oct 29, 2017
Did not have a chance to read the whole thread yet, but the angular momentum can for sure cause a lifting force. But there is other possible abuse here. It's not impossible to side load the teeter totter, which gives considerable leverage and can shove the bearings into the seat, which can promote a crack. I don't know how long after the failure the picture was taken, but if it was recent and the failure was that rusty, then this was a slow crack progression to failure.

If I were to design this myself I'd have use a 4 bolt flange bearing with a 2" diameter pin, but that's just me.

Tie rod ends are also pretty good alternatives to bearings in some cases
 

cyanidekid

Titanium
Joined
Jun 4, 2016
Location
Brooklyn NYC
surprised nobody mentioned weight transfer, a super well known braking effect.

if the operator brakes as the teeter happens, the rear is unloaded and "weight" is transferred quite significantly forward (this is not actually transferring weight obviously, what you have is a combination of the center of gravity being higher than the point of resistance of the forward inertia, creating a lever arm, I think. if I got that wrong, please correct IF you can explain that better!),
the rear of the platform is unloaded right as the front hits the stops, and it is still traveling up. obviously you would need some forward velocity but I think it would be human nature to hit the brakes just as the teeter happens, and with reaction time and mechanical delays, it could time the unloading perfectly to maximize shock load in the up direction.

as to the original "design" I too have some questions about the engineering..? from the photo it looks like the stub axles are particularly flexibly mounted (although someone else posted that they were subsequently welded to something at the inside end?) and cobbled up with bar and pipe. I hope the bar isn't high carbon, or its going to break at that weld. better to have it sticking out of a snug fitting block of 1" min. thick steel, with the weld on the backside only, putting the HAZ outside the highly stressed area.

Junkyard ( excuse me,recycling center!) trailer parts are actually designed and engineered for this function, made of decent quality steel, and are pennies on the dollar, why not use them?

an "I" beam which is actually a "W section" usually, (12 X 22 is a W section) is particularly bad at resisting torsional load, so particularly unsuited as an axle, although at the speed of rotation here probably not really a factor.

as to the retrofit, I see no particular reason to recreate the original form of the pillow block. I'd probably bore it out of rectangle bar on the lathe and bandsaw it to a simple form, but I don't know what your shop has for a vertical bandsaw. looks like it will hold, if you have some actual support for those little stub axles. good luck and keep us updated!
 








 
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