Author Topic: Derailleur hanger alignment tool  (Read 3078 times)

LittleWheelsandBig

  • Whimsy Rider
Re: Derailleur hanger alignment tool
« Reply #25 on: July 12, 2020, 11:54:36 pm »
I prefer my 1st edition Shimano hanger tool, complete with little ruler. It was much nicer than the previous Campag tool and the others I’ve tried recently.
http://velobase.com/ViewTool.aspx?ID=200131aa-6578-40ad-bbaa-ea3f3f559cf3 but doesn’t show the supplied SS ruler and the chromed centring tool designed to screw onto a bare freewheel hub (in place of checking against a wheel).

Part of the reason I like 8sp is the greater tolerance of misalignment and wear. I’ve seen too many folk having shifting problems from trivial causes partway through a 1200.

If 0.5 degree is the difference between working and not, you are asking for trouble. Should I realign the gear hanger when swapping between Shimano and Campag mechs? Don’t be silly.
Wheel meet again, don't know where, don't know when...

Re: Derailleur hanger alignment tool
« Reply #26 on: July 13, 2020, 01:04:32 am »

If 0.5 degrees is the difference between working and not, you are asking for trouble. Should I realign the gear hanger when swapping between Shimano and Campag mechs? Don’t be silly.

good
better
best

IME campag mechs usually work well at the shimano settings too, i.e. the range of settings that is OK certainly overlaps. However plenty of bikes have gear hangers that are imperfectly aligned, and/or flex more than half a degree (differently) every time the QR is done up. But then again plenty of bikes have gears that don't work quite as well as they should do, too.

In reality you should probably realign the hanger so that the mech works as well as it can do; in the case of many used mechs (and some new ones) this means adjusting it to suit, which may be outside any manufacturer's specifications.

cheers

Re: Derailleur hanger alignment tool
« Reply #27 on: July 13, 2020, 10:18:28 am »

If 0.5 degrees is the difference between working and not, you are asking for trouble. Should I realign the gear hanger when swapping between Shimano and Campag mechs? Don’t be silly.

good
better
best

IME campag mechs usually work well at the shimano settings too, i.e. the range of settings that is OK certainly overlaps. However plenty of bikes have gear hangers that are imperfectly aligned, and/or flex more than half a degree (differently) every time the QR is done up. But then again plenty of bikes have gears that don't work quite as well as they should do, too.

In reality you should probably realign the hanger so that the mech works as well as it can do; in the case of many used mechs (and some new ones) this means adjusting it to suit, which may be outside any manufacturer's specifications.

cheers

And this is probably and iterative process;)

lW&B - yes, positive that the hanger twisted rather than the mech. I was more surprised that the road link stayed straight. However, a moments thought illustrates that the moment results in more force at the hanger than anywhere else in the chain.

LittleWheelsandBig

  • Whimsy Rider
Re: Derailleur hanger alignment tool
« Reply #28 on: July 13, 2020, 12:00:07 pm »
Given that plasticly deforming aluminium takes away from its fatigue life, repeatedly realigning a replaceable aluminium hanger to compensate for derailleur wear is not a good idea. Work hardening is a real thing. When I was a bike mechanic, the rule of thumb was that realigning a crashed aluminium hanger once would probably be fine but doing it more often risked failure down the road.
Wheel meet again, don't know where, don't know when...

SoreTween

  • Most of me survived the Pennine Bridleway.
Re: Derailleur hanger alignment tool
« Reply #29 on: July 13, 2020, 12:33:27 pm »
Thanks Brucey :thumbsup:

The cyclus tool works well, precision is easily achieved.  Hardest part is getting the wheel absolutely straight in the frame this being a nutted axle.  Flipping thing wanders as the nuts are tightened.
2020 targets: None
There is only one infinite resource in this universe; human stupidity.

LittleWheelsandBig

  • Whimsy Rider
Re: Derailleur hanger alignment tool
« Reply #30 on: July 13, 2020, 12:40:47 pm »
Are the dropouts parallel and undamaged? The wheel wandering when tightening axle nuts is usually the result of uneven contact between axle nuts and dropouts.
Wheel meet again, don't know where, don't know when...

Re: Derailleur hanger alignment tool
« Reply #31 on: July 13, 2020, 06:14:39 pm »
Given that plasticly deforming aluminium takes away from its fatigue life, repeatedly realigning a replaceable aluminium hanger to compensate for derailleur wear is not a good idea. Work hardening is a real thing. When I was a bike mechanic, the rule of thumb was that realigning a crashed aluminium hanger once would probably be fine but doing it more often risked failure down the road.

this is a very sensible precaution. However I note that in the last couple of decades, the range and quality of ductile aluminium casting alloys has improved somewhat. I therefore fancy my chances of straightening a bent replaceable hanger a bit more these days.

In general terms a ductile material will plastically deform (and it may work-harden) up to a point and then you are on 'a slippery slope' to failure.



The curve above is from tensile testing but something similar may be seen in bending too.

So when you are straightening something, if the force required to move it is still increasing, you probably have a way to go yet. However if it isn't or it is actually starting to decrease, then you are in the poop and the part is well on the way to failure.

A really ductile material will withstand several tens of percent elongation to failure; this might correspond with straightening a bent hanger a couple of times (depending on how bad the bend was and how ductile the alloy is) or resetting a gear hanger (by a much smaller amount) about a dozen times or so.

cheers

LittleWheelsandBig

  • Whimsy Rider
Re: Derailleur hanger alignment tool
« Reply #32 on: July 13, 2020, 07:11:57 pm »
All true Brucey but the residual fatigue life of aluminium is what I am talking about. To cold-set an item means taking it past the yield stress. That significantly drops the number of additional low stress cycles the item can sustain in future. High stresses mean few cycles before fracture. Tensile tests explain the response to a single stress event. Fatigue tests explain the response to repeated stress cycles.

There are lots of instances of derailleur hangers broken while riding (that destructively drags the derailleur over the cassette) after an unremarkable gear change. Possibly a complicated combination of overstress, crack initiation and propagation, fatigue and corrosion but minimising potential factors (e.g. repeatedly cold-setting aluminium) seems like a good idea.
Wheel meet again, don't know where, don't know when...

Re: Derailleur hanger alignment tool
« Reply #33 on: July 13, 2020, 07:55:23 pm »
one way of representing the likelihood of fatigue failure is on a diagram like this one;



The mean stresses in the part are low (mostly residual stresses after straightening) and the applied cyclic stresses are also low.  In practice this means that for a hanger to break in use, it (more or less) has to be cracked when it is put back into service.  So as if it needs to be said, if you have straightened a hanger, you should check it for cracks before using it again.

Like spokes, once there is a crack, nothing will save the part from eventual failure. Without there being cracks present, normal service stresses are unlikely to cause the part to fail; were  it otherwise, you would see failures in undamaged gear hangers more often than you do.

cheers

Re: Derailleur hanger alignment tool
« Reply #34 on: July 14, 2020, 08:57:24 am »
Apologies if I’ve missed someone mentioning this further up and I’ve missed it.
It is, in my experience, vital to fit a wheel as tightly as you would to ride the bike before checking/adjusting the hanger.  When you put a wheel in and tighten the quick release you’ll often see the angle of the hanger change a little.

Re: Derailleur hanger alignment tool
« Reply #35 on: July 20, 2020, 07:26:02 pm »
You could always make your own like this:
https://www.youtube.com/watch?v=KIzd0xdkowM

Re: Derailleur hanger alignment tool
« Reply #36 on: July 21, 2020, 11:15:00 am »
I did a very bent one on my Cinder Cone with a long steel rule, some calipers and a lot of eyeballing.  It was skewed (you can check this relative to the RH BB shell face) as well as bent inwards.  Those old steel built-in hangers take a fair bit of welly to realign.
And Darkness and Decay and the Coronavirus held illimitable dominion over all.