Spare parts rant

StewartR

StewartR

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Stewart
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If there's one thing I hate about the equipment that I handle most days, it's the hood locking mechanisms on big telephoto lenses. All the manufacturers basically use the same device, which is one of the worst examples of engineering "design" I've ever come across. It's fiddly, easy to break, and not very good at doing its job at the best of times. As one of my friends put it, it's as if the designers said "this will do for the moment for the prototype, we'll concentrate on the glass for now and come back and do this bit properly later", and then they got distracted by a cat video or something and never came back to finish the job.

But the worst aspect is the prices of these stupid little things. We used to be able to buy replacement locking knob mechanisms for the lens hoods of Canon super-telephoto lenses, and they cost about £60 each. But for the Mk II hood designs, Canon have moved away from supplying the locking knob assembly as a complete unit, and instead we have to buy replacements for specific parts. Anyone care to guess what a complete set of these 7 spare parts (i.e. a complete locking knob assembly) would cost?

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Quite believe it. Many years ago, the place I worked used a Philips X-ray spectrometer. This used four 1/4 inch phosphor-bronze leaf springs to hold the sample in place. In 1982(ish) these cost £400 each. It was a case of pay-up or junk the spectrometer.
 
Is it the same component that fails each time?

GC
 
Hmm... part YB2-5313 - a disk of double sided tape to hold the cap on for £7.50? Ridiculous? Well, I hope it offers true value for money when it comes to stickiness, as the plastic cap (YB2-3356) it's holding on apparently costs £37.02! Then there's £126.06 for a plastic knob? If Canon are paying the wholesale cost to necessitate those retail prices I think they perhaps need to review their production and/or materials procurement processes?
 
I wonder if the components are common across different hoods?

If so and you are having to replace them frequently and bearing in mind this is an accessory.......find a local precision engineering firm and see of they might duplicate suitable alternatives. Your quantity requirements might keep the unit price more manageable???

PS I am sure this duplication is questionable but if the parts are "common forms", then is it???
 
Box Brownie said:
find a local precision engineering firm and see of they might duplicate suitable alternatives.
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Local model making club/society? (I mean "real", live steam type models!) Pretty sure there are a couple of model makers on the forums.
 
Box Brownie said:
I wonder if the components are common across different hoods?

If so and you are having to replace them frequently and bearing in mind this is an accessory.......find a local precision engineering firm and see of they might duplicate suitable alternatives. Your quantity requirements might keep the unit price more manageable???

PS I am sure this duplication is questionable but if the parts are "common forms", then is it???
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I went to a local precision engineering firm for that sort of repair in the 1980s. Later I started making replacement hoods out of plastic containers painted with blackboard paint.

Nowadays I use a LensCoat TravelHood. It can't get broken by baggage hurlers and doesn't break if you bang it against something. Some of the more recent hoods are so fragile they'll break if someone sneezes when stood within 6 feetof the hood.
 
I would think you could adapt one of these type of fixings, cut the thread to size and glue a small knob on it cost would be under £5 .
Just a thought.

Rob.
 

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GyRob said:
I would think you could adapt one of these type of fixings, cut the thread to size and glue a small knob on it cost would be under £5 .
Just a thought.

Rob.
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That sort of repair wouldn't bother me or a lot of others for our own lenses, but when like Stewart you are running a professional hire service people want a proper repair not something cobbled together. If it's the same bit that keeps breaking then a visit to a local machining company is in order or as Nod said a serious model maker if there is one in your area.
 
Of cause it want's to look right that's why I said one of these type as an example :)

Rob.
Edit just checked and no this wont work
 
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£126 for a plastic knob - quite reasonable. Wonder what the mark-up is on that....
 
cymruchris said:
£126 for a plastic knob - quite reasonable. Wonder what the mark-up is on that....
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The cost of 20 parts would fund an Asian injection moulding tool then a UK trade moulder would could knock them out for less than a tenner, even with low run set-up costs!

Parts would look identical to the OEM item but could be tuned to reduce failures (stress raising notches removed etc).

GC
 
Big Andy said:
That sort of repair wouldn't bother me or a lot of others for our own lenses, but when like Stewart you are running a professional hire service people want a proper repair not something cobbled together. If it's the same bit that keeps breaking then a visit to a local machining company is in order or as Nod said a serious model maker if there is one in your area.
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If it's rental stock the cost is covered by the renters insurance.
 
Big Andy said:
But if you can keep your overheads down you will be more competitive or have a higher profit margin than others in the same game. I'm sure Stewart will have worked that out for himself though. ;)
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It shouldn't affect overheads, the person who rented the item and broke it is responsible for the repair.
 
gcgraphs said:
Is it the same component that fails each time?
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Not quite. There are several failure modes.

1. By far the most common failure is when you try to turn the knob too far whilst removing the hood. This causes the threaded shaft to retract into the threaded hole slightly, and that puts pressure on the circlip. The circlip can easily pop off, and since it's only about 2mm across it can easily be lost. That's not a total disaster if you see it happen, because the wedge is held in place when the hood is tightened against the lens, either in the normal orientation for use or the reversed orientation for storage. So if you see the circlip go, you can avoid losing the wedge by just being careful when attaching and removing the hood. But if you don't see the circlip go, you can easily lose the wedge too, and there's no workaround for that.

2. Over time, the business end of the threaded shaft tends to get worn. So the circlip doesn't fit so snugly on it, and that means that the circlip is more prone to popping off as described above.

3. Over time, repeated tightening and loosening can cause the wedge - and specifically the narrow bit of the wedge which the shaft passes through - to become distorted. I don't think we've yet seen one suffer failure through metal fatigue at that point, but I think it's a definite possibility if they last long enough without being lost.

4. Not exactly a failure, but the white plastic knob is actually a black plastic knob that's painted white. It's in a very exposed position so it picks up a lot of wear and the black substrate starts showing through.
 
Darth M said:
If it's rental stock the cost is covered by the renters insurance.
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Darth M said:
It shouldn't affect overheads, the person who rented the item and broke it is responsible for the repair.
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Not as simple as that.
  1. Our insurance policy has an excess of £180, so in effect it doesn't cover losses of small components.
  2. Most problems aren't single-incident failures which can be pinned unambiguously on a specific customer.
  3. It's not good customer service to demand payment for small components which might be lost through no particular fault of the customer. It really is surprisingly easy to pop the circlip off, and personally I don't think ts reasonable to hold the customer responsible if that happens. It's just "one of those things" that has to be managed.
 
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