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PostPosted: Wed Mar 14, 2012 7:48 pm 
retrobike rider
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Not too hot on these frames but is that where the mech hanger tag should be ?

though by the sound of it, the frames not upside down and just the start of the bend on the top half of the frame.

They're not exactly thin light frame.


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PostPosted: Wed Mar 14, 2012 7:59 pm 
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poweredbypies - Well they are not unknown for doing bike frames so they should know what blast media to use.

FluffyChicken - it's above the front mech. It's right where the seatpost would bottom out if it wasn't tightened enough.

Do you think it's beyond repair?


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PostPosted: Wed Mar 14, 2012 8:03 pm 
Old School Grand Master

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I thought that's the place where they tended to rust through or crack (usually from rusting weakening the tube).

The roughness in the photos looks as though they have been too aggressive. I've had Alu frames blasted smooth, and they are much softer metal.

However, the result is the same - looks as though it's a goner. You could get a new seat tube welded in - but that's a big costly job on a welded frame.


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 Post subject: Frame photo
PostPosted: Wed Mar 14, 2012 8:31 pm 
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Better picture of frame, anybody any further comments on if they think it's repairable? This is my first restoration and I would hate to think I'm going to have to scrap the frame, but I accept it might just be screwed.
You Alpinestars fans should thank me, I might just have made your bikes that little bit rarer :oops:


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 Post subject: Too aggressive
PostPosted: Wed Mar 14, 2012 8:35 pm 
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Close up of top tube, do you think they've been too harsh with the media?


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 Post subject:
PostPosted: Wed Mar 14, 2012 8:37 pm 
BoTM Winner / Gold Trader
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There are a few factor besides media/grit to take into account. distance, nozzle dia., and air pressure come into play as well. Having said that, As soon as I saw the pic I thought sand, and a heavy grit at high pressure, to boot. As an experiment, I went out back to the scrap bin we share with the HVAC place next door and grabbed a piece of gas pipe. It is very soft steel. I brought it in and had at it mercilessly with M16 (medium) glass beads at a fairly high pressure. This is the result.

Image

I've stripped the paint off forks and the anodizing off numerous Al bike parts. It would take me a good minute working the same spot on an Al-Mega frame, let alone a Cro-Mega to do that to the surface of the tubes with the proper media, let alone put a hole in it. It barely touches a pair of P2s.


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 Post subject:
PostPosted: Wed Mar 14, 2012 8:40 pm 
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Blimey,
I might just have to out this lot as a warning. Looks like they messed up.


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PostPosted: Wed Mar 14, 2012 8:54 pm 
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Johnboy wrote:
Blimey,
I might just have to out this lot as a warning. Looks like they messed up.


No, you shouldn't. There was already something wrong with the frame and it doesn't have a damn thing to do with the shot blasting. Is the media/method they used a bit too aggressive? Probably, but there may have been a reason. Was the previous finish paint or powdercoat? Sometimes using less abrasive media can take forever if the finish is difficult to remove, should they spend hours on your frame and charge you for the extra time? I doubt you would be happy with that either. Is it a shop that does bicycles regularly? That makes a huge difference, but they usually charge more because it is more detailed than just stripping a hunk of cast iron. If you went to the cheapest place that you could find, you probably got what you paid for.

You are not suddenly an expert because you've read 10 responses on Retrobike. Publicly badmouthing someone's business is not something to be taken lightly.


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 Post subject:
PostPosted: Wed Mar 14, 2012 9:04 pm 
Old School Hero
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I totally agree that something went very wrong. The surface of the frame looks it has been hit by very sharp blasting media (e.g. aluminium oxide). Indeed nozzle diameter and blasting pressure/speed has a high influence on the effect.

At work (Aerospace) we clean and remove paint of aircraft parts with plastic media. This does not damage the surface (e.g. metal hardness, coating, etc...) and leaves a clean surface. This works on aluminium, steel and titanium.

Never seen any damage like this before and you must check how they did the job.


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 Post subject:
PostPosted: Wed Mar 14, 2012 9:12 pm 
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shogun700 wrote:
Johnboy wrote:
Blimey,
I might just have to out this lot as a warning. Looks like they messed up.


No, you shouldn't. There was already something wrong with the frame and it doesn't have a damn thing to do with the shot blasting. Is the media/method they used a bit too aggressive? Probably, but there may have been a reason. Was the previous finish paint or powdercoat? Sometimes using less abrasive media can take forever if the finish is difficult to remove, should they spend hours on your frame and charge you for the extra time? I doubt you would be happy with that either. Is it a shop that does bicycles regularly? That makes a huge difference, but they usually charge more because it is more detailed than just stripping a hunk of cast iron. If you went to the cheapest place that you could find, you probably got what you paid for.

You are not suddenly an expert because you've read 10 responses on Retrobike. Publicly badmouthing someone's business is not something to be taken lightly.


I agree with you, there was an underlying problem with the frame, I suspect it was probably weakened by the seatpost. So perhaps they did me a favour by revealing something that would have come back to bite me.

I went to a company that has been recommended on this site, cost was not a factor in my choice.

I didn't mean the 'outing comment' seriously, which is why I haven't done it. But I do think if they have made an error in the way they blasted the frame, i.e with too much force (what's your opinion of the close up photos?), then someone who takes their treasured frame to them should be aware of it, what is the consensus on that?
You are also right to say I am not an expert, which was the point of the post, there are people here who can advise me, and that's what I asked for.


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