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From: AMuzi <am@yellowjersey.org>
Newsgroups: rec.bicycles.tech
Subject: Re: Machine Shop
Date: Tue, 4 Mar 2025 23:50:54 -0600
Organization: Yellow Jersey, Ltd.
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On 3/4/2025 10:04 PM, Frank Krygowski wrote:
> On 3/4/2025 3:06 PM, AMuzi wrote:
>> On 3/4/2025 11:03 AM, Frank Krygowski wrote:
>>> On 3/4/2025 12:44 AM, AMuzi wrote:
>>>>
>>>> For a typical dent, this Waterford for example:
>>>> http://www.yellowjersey.org/wfd12a.jpg
>>>>
>>>> the tube is rolled to reform the greater part of the 
>>>> deformation:
>>>>
>>>> http://www.yellowjersey.org/wfd12b.jpg
>>>>
>>>> then the remaining low spots are filled with polyester 
>>>> bondo or with metal (brass, silver, lead. I use lead):
>>>>
>>>> http://www.yellowjersey.org/wfd12c.jpg
>>>>
>>>> and finished:
>>>>
>>>> http://www.yellowjersey.org/wfd12e.jpg
>>>
>>> Could you explain what's meant by "the tube is rolled"? 
>>> As I said earlier, I'd thought the first step would be 
>>> pushing a mandrel through (if the dent was in the 
>>> seatpost) to partially push out the dent. Of course, that 
>>> wouldn't work except on a seat tube, and I suppose would 
>>> still require filling. Are you skipping that step entirely?
>>>
>>> BTW, my antique BMW has a slight dent in the top of the 
>>> gas tank, apparently from something falling onto it. I've 
>>> heard of "paintless dent repair" for car bodies and 
>>> wondered about it, but never looked deeply into it. I 
>>> gather that some skilled body workers can do pretty well 
>>> at pushing dents back out from the underside.
>>>
>>
>> Can't generally fit anything inside a bicycle frame tube 
>> in any reasonable time. Taking a frame apart is more than 
>> a magnitude of labor greater than the cost of a tube. Once 
>> apart, you'd just replace it rather than repair.
>>
>> Here's one set of steel blocks for rolling dents.
>>
>> http://www.yellowjersey.org/photosfromthepast/den24a.jpg
> 
> So how exactly are the blocks used? Are the blocks tightened 
> in place and rotated around the tube?
> 
>>
>> I have various diameters. On oval tube of course there are 
>> limited options. I generally don't take those jobs except 
>> where the dent is minimal:
>>
>> https://www.yellowjersey.org/photosfromthepast/denw25a.jpg
> 
> It occurred to me after posting that forcing a mandrel 
> inside the tube might cause some of the metal around the 
> dent to bulge outward. I can see why you wouldn't want that 
> to happen.
> 
Hold lower block in a vise. Lay tube in the block, add 
plenty of gear oil, place top half of block on the tube, 
tighten the bolts gradually while working the tube back and 
forth between the two block halves. Once bolts are fully 
tightened, remove tube, clean and fill remainder of dent.

-- 
Andrew Muzi
am@yellowjersey.org
Open every day since 1 April, 1971