sure... but I do wonder if (in this case) MPI is going to be the best way of finding cracks? If the material isn't very ductile, there are residual stresses that are forcing the crack closed during the inspection, and the relative permeability of the steel (at the surface) is low anyway, the leakage flux at the crack (which is what you are trying to find) might be very small indeed. This isn't my specialist field, but I do wonder if some other technique (eg eddy current testing) might be more sensitive? -just a thought.
BTW I feel I should mention that whilst I can't say for sure how long it took for cracks to grow in the broken forks that I have seen, in every case the cracks in steel parts had started to corrode near the initiation point, in such a way that it might indicate 'months' (rather than a much shorter period of time) between when the crack started and when the part failed . By contrast the relatively rapid progression of the crack past a certain point means that there is rarely any corrosion on the main part of the crack face.
cheers
Fork column failure on thread less forks.
Re: Fork column failure on thread less forks.
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Re: Fork column failure on thread less forks.
by how much would a fork steerer have to be made thicker to be significantly more resistant to everyday type fatigue?
are all threadless steerers standardised around the same thickness? or is it 'anything goes'?
are all threadless steerers standardised around the same thickness? or is it 'anything goes'?
Re: Fork column failure on thread less forks.
mig wrote:by how much would a fork steerer have to be made thicker to be significantly more resistant to everyday type fatigue?
are all threadless steerers standardised around the same thickness? or is it 'anything goes'?
For a 1 1/8th they have to be the same thickness (or pretty close) ....
Internally - because of the standard outer diameter of the star nut
Externally - because of the inside diameter of their respective stem and bearings.
There would be some leeway regarding tapered steerers - but that would add more weight - negating one of the benefits of a tapered steerer
Re: Fork column failure on thread less forks.
!" steel steerers are almost invariably made butted ( in fact I wouldn't ride one that wasn't)
1-1/8" steel steerers are sometimes butted, sometimes not. I think that they ought to be butted if they are welded or brazed.
1-1/8" aluminium steerers are often butted (again I wouldn't ride one that wasn't a decent thickness at the base)
Some road bike forks come with an aluminium A-head steerer that is thin-walled at the top. This is a bad idea; such steerers tend to break if they are used by 'handlebar wrestler' types.
Obviously threaded forks must have a 1/16" steerer wall thickness at the top, else the quill won't go in. By the time the thread is cut, the wall thickness is around 0.8mm, and if the die doesn't run quite true, the cut can be lopsided so that the wall thickness is even less on one side.
Above, a failure in the threaded section was described; this is rare (when the quill is below the threaded section as it should be) but there are circumstances which can increase the chances of this happening. In particular if the headset has a low contact angle in the bearings and/or a high preload, every bump in the road will create a large tension load in the steerer which may eventually break it. I have an idea that if the upper set race is slightly cocked, this may also increase the tension load generated as the fork tracks the road irrgularities.
cheers
1-1/8" steel steerers are sometimes butted, sometimes not. I think that they ought to be butted if they are welded or brazed.
1-1/8" aluminium steerers are often butted (again I wouldn't ride one that wasn't a decent thickness at the base)
Some road bike forks come with an aluminium A-head steerer that is thin-walled at the top. This is a bad idea; such steerers tend to break if they are used by 'handlebar wrestler' types.
Obviously threaded forks must have a 1/16" steerer wall thickness at the top, else the quill won't go in. By the time the thread is cut, the wall thickness is around 0.8mm, and if the die doesn't run quite true, the cut can be lopsided so that the wall thickness is even less on one side.
Above, a failure in the threaded section was described; this is rare (when the quill is below the threaded section as it should be) but there are circumstances which can increase the chances of this happening. In particular if the headset has a low contact angle in the bearings and/or a high preload, every bump in the road will create a large tension load in the steerer which may eventually break it. I have an idea that if the upper set race is slightly cocked, this may also increase the tension load generated as the fork tracks the road irrgularities.
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Re: Fork column failure on thread less forks.
Nothing to stop the alu steerer being butted at the fork crown, but that wouldn't address the risk of cracking up near the stem.Threevok wrote:mig wrote:by how much would a fork steerer have to be made thicker to be significantly more resistant to everyday type fatigue?
are all threadless steerers standardised around the same thickness? or is it 'anything goes'?
For a 1 1/8th they have to be the same thickness (or pretty close) ....
Internally - because of the standard outer diameter of the star nut
Externally - because of the inside diameter of their respective stem and bearings.
There would be some leeway regarding tapered steerers - but that would add more weight - negating one of the benefits of a tapered steerer
I've never compared the internal diameter of an alu and steel steerer. I'd expect steel to be thinner wall thickness, but how much difference does that make to inserting the star nut in either steerer type?
Re: Fork column failure on thread less forks.
well, you often need a different size star nut with an Al steerer vs a steel one....
cheers
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Re: Fork column failure on thread less forks.
To answer both - as far as I know - there are only two sizes of star nut 1/1 8 and 1/5 - the latter used for tapered forks. I have only ever used 1/1 8, both on steel and alloy. The tools to insert them are standard sized too.
As for butting further down the fork - i'm sure this is done on some forks already. I had a set of Mozo Vibe R forks that had an internal diameter at the base of the steerer, that was far narrower than any RS forks I have owned. This was probably down to the way the were attached to the crown though, rather than any safety factor.
To go back to my original point though - either solution is a total waste of time. If the fork is going to fail due to stress, the point between the upper and lower bearings is the last place it will happen - even if the entire fork was one solid piece.
If you can imaging clamping one end of a 2ft pipe between two sets of blocks in a vice, with 8 inches between the two set of blocks, then bending the pipe - where do you think it's going to bend ? The part between the blocks ?
The only reason for failure (for steel) at that point would be due to corrosion. As such - regular checking would be the only safeguard. I cant think of excuse for this to happen to an alloy steerer though, unless someone's been using something stupid with chemicals.
As for butting further down the fork - i'm sure this is done on some forks already. I had a set of Mozo Vibe R forks that had an internal diameter at the base of the steerer, that was far narrower than any RS forks I have owned. This was probably down to the way the were attached to the crown though, rather than any safety factor.
To go back to my original point though - either solution is a total waste of time. If the fork is going to fail due to stress, the point between the upper and lower bearings is the last place it will happen - even if the entire fork was one solid piece.
If you can imaging clamping one end of a 2ft pipe between two sets of blocks in a vice, with 8 inches between the two set of blocks, then bending the pipe - where do you think it's going to bend ? The part between the blocks ?
The only reason for failure (for steel) at that point would be due to corrosion. As such - regular checking would be the only safeguard. I cant think of excuse for this to happen to an alloy steerer though, unless someone's been using something stupid with chemicals.
Re: Fork column failure on thread less forks.
^ sorry, your idea that the steerer is somehow 'clamped by the headset' is not correct; in point of fact the steerer articulates in bending about the headset bearings, and this movement can contribute significantly to the feel of the fork. Steerers see very large loads and unless they are engineered properly, they break. The idea that they are somehow unassailable is nowhere near the truth....
You can get a very good idea of the relative (average) stresses involved by looking at a bike that has had a frontal prang; the parts can yield in the fork blades, in the steerer, or the frame itself, very occasionally all three at once. Bent (steel) steerers are commonplace; I have even seen a (good quality) steerer bend due to over-enthusiastic application of the brakes.....
The same (relative) stresses exist in normal use, and they can eventually fatigue the steerer if it has any stress concentrations in it, even if it isn't 'the weakest link' in a frontal prang.
Forgive me for restating the obvious, but if there is one tube you really don't want to break on a bike, the steerer is it.
cheers
You can get a very good idea of the relative (average) stresses involved by looking at a bike that has had a frontal prang; the parts can yield in the fork blades, in the steerer, or the frame itself, very occasionally all three at once. Bent (steel) steerers are commonplace; I have even seen a (good quality) steerer bend due to over-enthusiastic application of the brakes.....
The same (relative) stresses exist in normal use, and they can eventually fatigue the steerer if it has any stress concentrations in it, even if it isn't 'the weakest link' in a frontal prang.
Forgive me for restating the obvious, but if there is one tube you really don't want to break on a bike, the steerer is it.
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Re: Fork column failure on thread less forks.
Brucey wrote:^ sorry, your idea that the steerer is somehow 'clamped by the headset' is not correct;
That was just an example, They could just as easily been held loosely, or between 4 pegs in a jig - the result would be the same.
Re: Fork column failure on thread less forks.
Threevok wrote:Brucey wrote:^ sorry, your idea that the steerer is somehow 'clamped by the headset' is not correct;
That was just an example, They could just as easily been held loosely, or between 4 pegs in a jig - the result would be the same.
Fork designs do vary, but the peak loadings are always around the crown, and plenty of forks use highly stressed steerers that are wont to fail as I have described.
Suggestion; try googling 'bent steerer' if you want so see what I mean.
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Re: Fork column failure on thread less forks.
CREPELLO wrote:
I've never compared the internal diameter of an alu and steel steerer. I'd expect steel to be thinner wall thickness, but how much difference does that make to inserting the star nut in either steerer type?
Alu steerers are significant thicker.
I own a 1/18" Monoq fork which I had to use with a 1"starnut because the 11/8" one didn't fit. Wallthickness > 3 mm
Re: Fork column failure on thread less forks.
Brucey wrote:Fork designs do vary, but the peak loadings are always around the crown
Precisely what I was saying
Re: Fork column failure on thread less forks.
Keezx wrote:CREPELLO wrote:
I've never compared the internal diameter of an alu and steel steerer. I'd expect steel to be thinner wall thickness, but how much difference does that make to inserting the star nut in either steerer type?
Alu steerers are significant thicker.
I own a 1/18" Monoq fork which I had to use with a 1"starnut because the 11/8" one didn't fit. Wallthickness > 3 mm
There probably are exceptions, I just measured my SIDs and they are a little more than 3mm. I got a 1 1/8 star nut in there OK, with the tool I used.
Strangely, the inside diameter at the crown on the SIDs, is wider than at the top. The steerer seems to get thicker toward the crown (as you would expect for an alloy) but then there's a lip that extends diameter - inside the crown. I suspect it's the way it's attached to the carbon crown, that requires this.
Re: Fork column failure on thread less forks.
Might have something to do with the way many carbon forks with metal steers are built.
The steerer tube is pressed over or pressed in the crown part, i've never seen a steerer and crown in one piece of metal.
The steerer tube is pressed over or pressed in the crown part, i've never seen a steerer and crown in one piece of metal.
Re: Fork column failure on thread less forks.
Threevok wrote:Brucey wrote:Fork designs do vary, but the peak loadings are always around the crown
Precisely what I was saying
-which can mean that the highest stresses (in relation to yield) are in that part of the steerer just above the crown.....
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~