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Step Stool Safety

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Forum topic by John Smith posted 01-12-2018 10:23 PM 401 views 0 times favorited 12 replies Add to Favorites Watch
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John Smith

272 posts in 32 days


01-12-2018 10:23 PM

with all the recent posts and projects on and about step stools,
I don’t see anyone commenting on the possible “unsafe” designs.

it may take an engineer to apply the numbers, but, I know there
must be a formula or something to give guidance to step stool design.

this stems from an accident that my grandson experienced several years ago.
a good hearted grandfather with great intentions, gave a pre-school some
of his homemade stools with the top too big for the base and my grandson
fell and hit his head….. fortunately, he was not injured past a bump on his noggin.

now that I see all these project stools, I cringe at some of the unsafe designs and especially when
the builder says they made them in “shop class” ...... there has got to be a safety design factor
for the students to follow somewhere. (I searched OSHA and they don’t have anything).
- or – am I just imagining things and being overly cautious ???
[I am not out to implement a Nationwide Stool Safety program – but maybe just start a thought process
that can be passed from person to person, group to group and teacher to student].
any of you Number Crunchers out there ?

.


12 replies so far

View pontic's profile

pontic

539 posts in 478 days


#1 posted 01-12-2018 10:30 PM

Good points. Very practical advice.

-- Illigitimii non carburundum sum

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LesB

1440 posts in 3313 days


#2 posted 01-13-2018 12:36 AM

Hi John,

Here was a comment I made to one young fellows stool that had a flat bottom on the legs.

”I would point out one functional design problem. You made the legs flat on the bottom which is OK in most situations but if there is something that creates an uneven floor your stool will have a tendency to tip or rock and be unsteady. that is the reason some of the other stools had arches that created 4 contact points with the floor avoiding this rocker affect.
On the other hand if the ground is soft, like dirt, the flat bottom will be steadier even if it tilts a little.. Think of a ladder with 4 points of support on a soft surface. If one leg sinks in the whole thing tips but if there is a flat board between each pair of legs it is much more stable.
Functional design is an important part of wood working and other things in life.”

-- Les B, Oregon

View Richard Lee's profile

Richard Lee

75 posts in 645 days


#3 posted 01-13-2018 01:57 AM

All of my step and foot stools have the base as wide as the top.

View bigblockyeti's profile

bigblockyeti

4850 posts in 1590 days


#4 posted 01-13-2018 02:30 AM

I agree that it could be very dangerous to have a top larger than the perimeter of the base. It is better yet to have the base larger, it need not be tremendously larger, only ~5% or so greater than the length & width as right at the maximum points of the top could still allow a tip over with particularly acrobatic children.

View AlaskaGuy's profile

AlaskaGuy

3756 posts in 2179 days


#5 posted 01-13-2018 03:20 AM

I made this one a couple months ago. Pretty solid and not tipsy.

That being said, step stools aren’t for old people. DAMHIKT

-- Alaskan's for Global warming!

View clin's profile

clin

767 posts in 866 days


#6 posted 01-13-2018 05:49 AM

John, your drawing pretty much sums it up. If the top doesn’t go past the legs, then weight bearing straight down on the edge cannot tip the stool. Once you extend beyond that. Then you have to calculate the moments about the pivot point.

If the edge extended 2” past the base, and you applied 100 lbs of weight straight down, you have 100 lbs x 2” equals 200 lb-in for the moment. Moment is the proper term, but you’ll notice it is the same as a torque calculation.

Something else has to counter that moment, or it will tip. Worst case is there is no additional weight other than the stool itself. If the base were 10” wide, and we assume the stool is symmetric so the stools center of mass is in the middle, then the weight of the stool is 5” from the pivot point.

So if the stool weighed 10 lbs, it would supply 10 lbs x 5” = 50 lb-in of moment. This being less than the 200 lb-in and there is a net 150 lb-in that will rotate the stool.

It’s somewhat unlikely that all the weight would be on the edge. But a misstep is always possible. And of course, if you stand on the stool and lean forward, and then up against something, you can also apply lateral forces to the top. These create a moment equal to the applied force and the height of the stool. Even if you stand in the middle you can cause the stool to rotate.

I think most of us have done this. It won’t happen unless you lean up against something. But it’s easy to lean forward, but your weight on the shelf or whatever you are reaching, and you can feel the stool want to rotate out from under you.

-- Clin

View Roger's profile

Roger

20891 posts in 2674 days


#7 posted 01-13-2018 01:10 PM

Very good points.

-- Roger from KY. Work/Play/Travel Safe. Keep your dust collector fed. Kentuk55@yahoo.com

View John Smith's profile

John Smith

272 posts in 32 days


#8 posted 01-13-2018 01:11 PM

good info, Clin.

since LumberJocks is “Global” I was really hoping to reach shop teachers and students
from around the world to at least review the plans provided for their projects.
I remember in high school, we did have a “project book” that had plans with measurements
to make projects right from the book. (this is way before OSHA).

aaaahhhhhhh – I can still smell the freshly cut white pine and Resorcinol Glue complete with Formaldehyde.

designs something like this should be in pre-schools and where toddlers gather.
(should anyone get into the “donation” mood and make a few for the kids classrooms).


photo compliments of Etsy.com

.

View Rick's profile

Rick

8527 posts in 2902 days


#9 posted 01-13-2018 01:35 PM

Excellent Point John! I’d certainly do it that way. Stools can tend to be Dangerous even if they are built to the proper specs. IE: Extending your reach to far and therebye shifting the centre of balance off of what the stool is meant for.

I hope you accomplish this ” I was really hoping to reach shop teachers and students from around the world to at least review the plans provided for their projects.”

Rick

-- A Chip On The Shoulder Usually Indicates Wood Higher Up. (Rick, Ontario, Canada)

View AlaskaGuy's profile

AlaskaGuy

3756 posts in 2179 days


#10 posted 01-13-2018 06:07 PM

We don’t need no stinking engineers just some common sense would go a long ways

Where do these people come from?

-- Alaskan's for Global warming!

View Aj2's profile

Aj2

1222 posts in 1668 days


#11 posted 01-13-2018 07:17 PM

At least he has some there to tell his family how his back was broke.

This guy might as well have a safety rope around his neck.

-- Aj

View AlaskaGuy's profile

AlaskaGuy

3756 posts in 2179 days


#12 posted 01-13-2018 09:02 PM



At least he has some there to tell his family how his back was broke.

This guy might as well have a safety rope around his neck.

- Aj2


Amazing what some people do in a pinch.

-- Alaskan's for Global warming!

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