Rolling out a dent, need tube blocks

[jkilpatrick]

Hi. I'm about to try rolling a very mild dent out of a frames down tube, a la http://chuck.kichline.com/bikes/Framedents/default.htm

Anyway, can anyone recommend a place in the UK where I can find tube blocks similar to the one he refers to on the web page? Paragon Machine Works tube blocks are fairly cheap to be fair, but ordering from California and shipping to the UK makes the cost a bit hefty in my opinion. There must be something similar available in a good machinists supply shop here?

Cheers,
John

[Mick F]

Having watched body-shop workers in garages removing dents in cars, I'd have thought the easiest way to get a dent out of bike tube would be to use the same technique.

Drill a small hole and insert the puller.
Pull out the dent, and fill the hole with filler.

[gaz]

It might be worth an e-mail to Ceeway: http://ceeway.com/index.html

Nothing similar in their tools list but they do say:

If there's something you need that you think we should have, please contact us (tab above). Maybe we actually already do, or we can easily get it for you.

[breakwellmz]

28mm?

I would have a go with one of these and/or the straight ones you use in conjunction with them.-

http://www.ebay.co.uk/itm/HILMOR-28MM-P ... 1188227899

You can hire a tube bender for bugger all.

[Brucey]

if you have a moderate dent then you normally don't need to roll it out or indeed any tube blocks either.

The trick is to use a bench vice (with smooth jaws and radiused ends) to squeeze the tube sideways. It can take many squeezes but the tube can come to within ~0.5mm of where it is meant to be, at which point filler-primer is enough to render a perfect job.

Describing how and where to squeeze is difficult, but basically you are trying to reverse the crease, if there is one. Squeezing alternately so that each end of the crease is against the jaw seems to work OK. I have fixed quite a few frames this way, normally working on thinner walled top tubes.

If you want to practice on something, to see how best to squeeze, you can make tubes from paper (use sellotape on the seam), 'dent' them and then squeeze with your fingers. You will soon see how best to reverse a crease.

If the dent is very small (say smaller than half the tube diameter) then it won't come out like that, not very well, anyway. In this case use the alternate method below, or just fill the dent.

Small dents in steel tubes are rarely structurally problematic unless they are close to a brazed or welded part of the tube. I would not recommend drilling holes in dents; this is a double whammy and is asking for trouble.

On a down tube you can insert steel balls (or better still round slugs with radiused ends) of increasing size from the BB and use those to push dents out. When the slug is jammed beneath the dent, tapping with a soft hammer (whilst supporting the other side of the tube on a sandbag or similar) will push the dent out and free the slug. You should not worry unduly about getting a slug stuck in the tube; provided it is undersize you can always find a way to tap it or squeeze it so that it comes free. Because the tube is always slightly springy you don't need the final slug to be any larger than ~0.5mm undersize in order to get the tube very nearly perfect. If you attach a length of steel cable to a slug you will be able to gauge where the slug is in the tube (if you mark the cable first) plus you will always be able to pull it out again without too much difficulty.

Cheers

[123malford]

I think this seller was advertising some a few weeks back. Scroll down the page and he has a mobile number. http://www.ebay.co.uk/itm/Vintage-PAIR- ... 2ecf79eb4b

[123malford]

It might be that it is these I'm thinking of. http://www.ebay.co.uk/itm/BICYCLE-TUBE- ... 3f32e6a2ca

[jkilpatrick]

Thanks. That's exactly what I am after! Cheers all.

[Mick F]

........... I would not recommend drilling holes in dents; this is a double whammy and is asking for trouble.

Not arguing, and no experience and am willing to be educated ..........

What's wrong with a dent in a tube being drilled and pulled out?
The tube walls are thin and not very "structural" mid way along. If the integrity of the tube is fine when it has a dent, why not drill a small hole into it and pull the dent out?

Conversely, why not leave the dent where it is?

[drossall]

I had no idea this was possible. After a bit of Googling:

You can get Bicycle Research blocks from Ison Distribution or Billy's, but they are more expensive.

18 Bikes mention other Paragon products. You could try them to see whether they can order through their channels?

I'd be interested to hear how you get on.

[jkilpatrick]

Regarding drilling the hole, maybe its a bad idea due to fatigue? Having seen some failures which were apparently related to stress raisors on the tubes (downtube shifter bosses or at the tip of very pointly lugs) its would seem that even if you were successful in pulling out the dent, you wouldn't want the hole unless you properly brazed it closed.

If only the dent was in the right place for a bottle boss!

[Brucey]

........... I would not recommend drilling holes in dents; this is a double whammy and is asking for trouble.

Not arguing, and no experience and am willing to be educated ..........

What's wrong with a dent in a tube being drilled and pulled out?
The tube walls are thin and not very "structural" mid way along. If the integrity of the tube is fine when it has a dent, why not drill a small hole into it and pull the dent out?

Conversely, why not leave the dent where it is?

Actually leaving the dent alone isn't a terrible idea. And yes, the stresses away from the tube ends are usually not that bad. But there is a mess of residual stresses around a dent; that, and the way the service stresses are distributed means that cracks may form later in or near the dented region.

In an infinite flat plate drilling a hole of any size generates a stress concentration factor of '3'. However drilling a hole in a region of a finite tube with (possibly) higher than normal stresses already obviously has a worse effect. Certainly filling the hole with braze afterwards would be a good idea.

However I have an additional concern which is related to what happens as you pull the dent out. If you try this on the rolled up paper model I suggested earlier, you may find that something horrid happens near the hole; in this case simply reversing the stress that created the dent mightn't be the best way of getting rid of it.

BTW I think the tube blocks reverse a crease in pretty much the same way as the method I suggested using the vice, it is just that they do it in a more controlled (less sphincter twitching) fashion....

cheers

[jkilpatrick]

OK. After some searching around on the internet, I found a few folk that have used an approach using wooden tube blocks, and it looks really useful. I expect most home handy-people could do this themselves. Here is the link: http://forums.mtbr.com/vintage-retro-cl ... 25354.html

About halfway down the page are some really good pictures of a top tube dent removal with excellent results. I think I''ll give this a shot before resorting to anything more complicated. Anyway, many thanks to all who contributed to this thread. Enjoyed the discussion and comments so far.

[mrjemm]

A much better option-

http://sheldonbrown.com/dent-removal.html

If the guru's gang endorse it, it must be good...

[Mick F]

I have a small dent in the top tube about half way along. It's been there years, and happened as a result of Bike falling over.
I cannot get Sheldon's thingy into my top tube because it's blanked off at either end.

Dent?
Who cares?
I certainly don't.