Axle stands.

I'd have said any standard mild steel rod of the diameter normally found on axle stands would stand ordinary working loads forever.

Have you ever tried shearing mild steel of that size with a hammer and chisel?

I was taught always to place a wheel under the sill for this very reason.

When I was an apprentice 45 years ago I foolishly worked under a MK 9 Jaguar which had the rear wheels off and only on a trolley jack. It was during the dinner hour and I was alone in the workshop when I realised the jack had gradually come down and I was trapped. Fortunately somebody hear me yelling and I was saved. I always took greater care after that;-) pete

Horrifying! That's why I never trust 'em alone, I always have some back-up - an additional scissor jack, blocks of wood, spare tyre, even bricks!

I'll never forget my mentor, when I was an apprentice mechanic, telling me the tale of a four-poster ramp which collapsed, somehow, on some poor guy, killing him instantly.

I'll also never forget *nearly* walking backwards off a four-poster whilst it was 7 foot in the air - I'd been topping up the brake fluid as my mentor and another apprentice bled the brakes - it took so long I forgot where I was!

Steve.

So was I. You ex REME as well? Mike.

Obviously crap steel. They should take quite a bend, before showing any signs of cracking. What dia is it, 10mm? Even a MS rod that diameter should last forever on an axle stand. I suspect yours are made of very poor quality high tensile steel, or from flawed rod. Mike.

Also sprach "Dave Plowman (News)" :-

I usually use the shank of a really thick screwdriver, having lost the pins yonks ago. Though I prefer ramps mostly.

They should but shouldn't need to as Dave eluded to earlier in this thread, they shouldn't be able to bend very much as they should be in shear?

Chris, how good a fit are the upright parts of the stands with the bases?

Assuming the pins have been put *right through* the stands and the sliding parts are a good fit within the base then even 1/4" dia rod will hold a lot?

Just interested ...

All the best ..

T i m

I was replying to the comment the OP made, about his pins cracking I wasn't suggesting they are subject to bending in service, but that pins made from decent material should not crack _even_ if they are bent, let alone shear. Mike.

: They should but shouldn't need to as Dave eluded to earlier in this : thread, they shouldn't be able to bend very much as they should be in : shear?

The situation in an axle stand pin is the same as in a "four point bend test" - between the inner walls you have, effectively zero shear and constant bending moment.

Quick calculation: Normal car. One tonne. 250kg each corner. 2.5kN.

1.25kN each side of the pin. Gap between tubes 2mm. Bending moment 5Nm.

Yield strength of mild steel: 240MPa (direct), 140MPa shear.

Area required for shear 1.25kN/140Mpa = 8.9 * 10^-6 m^2. Circle diameter 3.4mm

Elastic section modulus required for mending = 2.5Nm/240MPa = 2.08 *

10^-8 m^3. Circle diameter 4.73mm.

So in that case - and I'm quite surprised - it's the bending that's critical.

Good news: I've done it for yield strength. Ultimate is higher, and using a suitably treated steel will up it even more.

Bad news: These are fairly high stresses, axles stands get rusty, and I would beware of cracking, particularly stress corrosion cracking..

Memo to self: Check axles stand pins!

Ian

erm, yea, wot he said....

Regards. Mark.(AKA, Mr.Nice.)

I've stopped using my axle stands of that design for that reason.. never had a pin snap, but i don't trust that little bit of metal to hold the 3.2 tons of weight it's holding when i use them on my van, even tho they are rated for 3.5 tons.

i now always use my sealy axle stands.. of the snap on design with a ratchet type pawl that holds the stand up, the ones where you just slide the stand under the vehicle, and lift the centre piece untill it's at the right hight, the pawl clicks and locks automaticaly,

it's quite a hefty bot of metal, and designed so the weight of the vehicle forces the ratchet and pawl to lock together tighter,

They are more expensive than the usual axle stands.. but a hell of a lot nicer to use, and you feel more secure under there... mind i've always put the wheel under, left the jack in place and so on just in case.

Think of acro props and the load they take using the same principle. With a pin little bigger than a decent axle stand. And they are subjected to impact loads when being tightened.

Of course I'm sure you can buy rubbish axle stands - like anything else.

Also sprach "Dave Plowman (News)" :-

Also, beware of the cheap ones which give the max load as a pair, not indidually - which is dangerously sneaky if you ask me.

Strange you should say that.....yes.

My eldest son too. He was a welder and got out when he realised he was only moving up if others moved up or out. He now runs a building redevelopment company and doesn't need the welding qualifications the army failed to put him up for. pete

Good reminder to us all. Incidentally-never, but never crawl under a Citroen (or any other with self levelling suspension) without first blocking up the body. DaveK.

Having had chance now to put them under a scope it would appear both have failed in the same way. The pins have a "button" at one end so you cannot push them all the way though, and this goes through a single hole in the outer, through one of three sets of holes in the inner and out the other side.

The button obviously lines up the pin the same each time it put in, and there is a drilled hole and chain to keep them captive, which rotates the pin the same way. End result is that the pin is in the same position each time it's used.

The one that failed totally has what looks like a fatigue crack that's propogated two thirds of the way through the pin (it's about 3/8" btw) and then it's failed entirely. The other side shows a sort of wiped surface ie, polished free of oxide which then failed as the inner pushed down.

The other pin has the same crack which opened up when loaded and broke with a good hit from a hammer. The rest of the pin seemed un good shape - I managed to bend it 45deg with a pipe and vice before giving up breaking it.

Idea's why these cracks developed? They are right on the load points where the pin bears down on the outer pipe.

Usually I do but since I wasn't taking the wheel off I left the trolley jack there pumped up. Bloody glad I did!