Does anyone have a design requirement for how stable (i.e. tip resistant) a toolbox or other piece of relatively tall shop equipment should be?
Some googling shows that there are two (voluntary) tests that furniture manufacturers use (ASTM F2057-19). The first is that you be able to open all the drawers and the furniture doesn’t tip, and the other is that a 50 lb load applied to the front of any drawer doesn’t cause the toolbox to tip over. These seem potentially insufficient for toolboxes given the different loadings (presumably toolboxes have a much higher weight loaded with tools and so 50 lbs isn’t much), and the fact that you don’t anchor toolboxes to the walls like you do furniture (and the 50 lb drawer case is for a child climbing on the drawers, which hopefully should not happen to a toolbox).
I measured my 44" Harbor Freight US General Toolbox w/ top, and assuming a uniform weight distribution got a fore/aft tipping angle of about 20°. I am not sure how accurate my uniform weight assumption is though (obviously in a dynamic tip scenario I’d expect tools to exacerbate the problem).
I figured maybe someone on here does this in real life and knows what the pros do, or has pondered this in more depth than I have. Is it just one of those “if it looks like a typical toolbox it’s good”?
Funny, I’ve been thinking about this too. I don’t know if there’s one overall stability criteria. I can think of a couple that might apply, of increasing stringency:
I had to design a manual forklift a few years ago at work, so I know that the ANSI B56.10 standard requires those devices pass a Tilting Platform test at up to 10% grade (~6 degrees).
It also requires that devices withstand a horizontal load of 15% of the device capacity (would be something like 300 lbf side load on a 2000lbf capacity cart - equivalent to somewhere between a 5 and 10 degree tilt table test depending on where the CG is compared to the side load.)
Similarly the IEC60601 standard requires that medical equipment carts pass a 10 degree tilt table test. There are a couple of other applicable tests in this standard too.
The nuclear plants which contract my company consider any unsecured equipment with a CG height to base width ratio greater than 1:1 (the equivalent of a 26 degree tilt table test) to be vulnerable to tipping over in an earthquake.
Where do FRC Pit Carts fit in this spectrum? I have no idea - but the middle criteria (10 degree tilt table test, or even a little steeper) seems reasonable to me.
I’ve been thinking about this as well, and top of mind for me is the ramp angle into and out of our trailer. This is the place more than any other I’ve seen teams get into real safety issues. I think I would want to measure that angle and then add in the possibility of a further inclined unloading dock area like we encountered last year.
This seems potentially problematic for a standard, as many rolling toolchests now feature interlocks that prevent opening more than one drawer at a time.
Sounds like the perfect opportunity to introduce a real-world example of engineering mitigation strategies. The tool chest would tip over if everything were open at once. How do you solve the problem? Widen the wheel base? Limit the number of drawer that can open? Limit how far the drawers can open? Anchor it to the wall?
Even so, we can take the proposed test and still apply a modified version of it - open all of the drawers that can be opened simultaneously.
As others have noted, 10% seems a minimum standard and 20% fairly robust.
Another thing is to inspect these things from time to time, especially if there has been some sort of impact. One session a week or so after a demo where there had been some issue getting the tall
(54"?) toolbox off (or was it on) the trailer, one of the front casters collapsed while a heavy drawer was open, sending the unit on top of one of the students. Fortunately, several other students and I were nearby. We managed to slow the fall enough for him to get out of the way. It turned out that one of the casters had lost three of its four mounting bolts, and was able to swivel towards the center. We re-built it using larger casters and nylock nuts on all the bolts, and soon afterwards relegated the tall unit to remain at the shop, purchasing a workbench-style box for travel.
There is no way our loaded tool box stays upright if all the drawers are opened together. We know this from experience. It stays locked closed while in transit.
The toolboxes at work have mechanical interlocks to ensure that only one drawer can be opened at a time. Those tool boxes are also over $4k each, empty.
I’ve seen it in checks notes everything more expensive than Harbor Freight.
It is inconsistent, even between different product lines of one brand at a similar price, one set may have it and the other does not. I can’t see any consistent pattern, other than being absent from the absolute cheapest offerings. Even very high end boxes may not have it, though this seems to be because it’s a feature that can be individually selected/added.
Making things more complicated, the draw lockout can sometimes be be disabled by removing a drawer and flipping a dedicated latch or some other mechanism.
Yikes, that is a scary scenario. Glad no one was hurt and you acquired a safer toolbox.
That said, are larger casters actually more tip resistant? If the caster angle was constant with varying wheel size then larger wheels could put the points of contact with the ground further inside the cabinet while you are moving it around, right? Based on a quick survey of the caster wheels in my house, it looks like the dimensional caster trail does increase with caster wheel diameter.
bigger wheels will go over bumps much smoother which in turn reduces the damage a caster sustains, larger casters make the wheel base minutely smaller but they’re much less likely to fail in the manor described because a crack in a sidewalk won’t shake the bolts off.
Sure, more completely it is is that vibration benefit worth the extra tipping susceptibility? Obviously the toolbox maker didn’t think so – they elected to use 5" wheels (typically) instead of 1" wheels or 10" wheels. But the people on this forum probably move their cabinets more frequently and on rougher surfaces than most.
And for the extreme case geetwo describes, not sure larger wheels would have fully mitigated the problem. They thought so too having retired that toolbox from travel.
A factor going in your favor is that you tend to load the toolboxes along their long axis which keep the COG well inside the wheelbase.
Our team always had two concerns:
the raw weight / momentum of the tool box to get it up the ramp
Making sure it didn’t high-center going from the ramp to the trailer resulting in an awkward and potentially unsafe situation to get it in or out
Toolboxes fall into that set of things that people tend to load by volume; with a lot of your typical hand tools being actual chunks of steel, it’s pretty easy to get incredibly heavy.
It’s easier than we think to get too heavy to move safely and/or too heavy for the trailer (or trailer floor). My old Scout Troop at one point had a trailer that was close to 2.5X overloaded (3000# trailer with close to 6500# of stuff in it). We’re lucky the safety margin went our way…
Probably not, but we had to change or relocate the wheels because some of the screw holes had stretched (particularly on the caster that came loose), and we opted for slightly larger ones because they handle bumps better.