dwmckee

I have considered buying a couple of really top bike frames over the past several years with dents in them, convinced that I could build a tool that could be slipped inside the frame and force the dent out, leaving me with a great frame for not a lot of money. I have drawn up my CAD plans for the tool and have access to a machine shop but have not yet done the machining. My question is, does such a tool (or technique) already exist and would there be a market for such a tool among frame builders?

BTW, I understand that there are limits to what reasonably and safely can be repaired.

How often do you see someone bring in a dented frame for repair?

Thanks,

Don

unterhausen

The only commonly available tool are tube blocks for rolling dents out.
top tubes are the most commonly dented tube, and there is usually very poor access to the inside. I am thinking that it's unlikely that they can be fixed from the inside.

Scooper

Yep; tube blocks are your best bet.

HERE's how to do it.

HonestOne

You could try contacting a local "Paintless Dent Removal" company for cars and see if they may have some ideas.
- Aaron

BenCooper

Pushing them out from the inside would be very tricky on anything other than the seat tube. Tube blocks can be surprisingly effective - or of course you can just fill the dent with brass or car body filler.

Blue Belly

So long as the tube is perfectly round, it could be pretty easily done from the inside. I came up with a tool to do it but didn't end up making it. I've used the blocks & they'll get you close. They'll also ruin the paint. At that point you use filler & paint over it, never to be seen again.

ftwelder

On two of my vintage lugged bikes that had badly dented top tubes, I was able to machine bungs/plugs that sealed the top tube. I then pressurized them with 50 psi of shop air and fluxed then heated the tubes at the dent. It worked well.

The tubes were dented to a depth about 1/3 of the diameter.

dwmckee

Thanks guys. The frame blocks can be rough on the paint so I started working on a way to do it from the inside. I thought the pressureized tube idea is really cool, but it has some limitations too.

I figure if a surgeon can take out half of my lung through a 3/4 inch slit between my ribs, I should be able to come up with something that can pop a dent out of a frame from the inside. I planned out a very small hydraulic cylinder with special end fittings that can be driven by a tiny high pressure hydraulic line. It can be snaked even into a top tube and if you can get it aligned with the dent (probably not so easy, I admit) I should be able to apply up to 2,000 pounds of force. Maybe could couple it with frame blocks on the outside so even the last millimeter or two of a dent could be squeezed out with no further damage to the paint. This could probably be used with oval, tapered and other shaped tubes as well within limits of course.

Number400

I have used water and a long cold night outside to remove dents from exhaust headers. A little trickier with a bike frame but I am betting it could be done. Don't come running to me when it's splits-ville

ksisler

DWMCKEE; Just such a tool did exist at one time. It had a pump that looked like a grease gun, a long tough looking hose with measurement marks on it, and an inflatable ballon like thing about 3" long. Saw it in use several times circa 1972 though 1974. Bear was using a die grinder to increase the size of the vent hole in the headtube so the thing could be pushed down into the top or down tube. But once in place a few pumps would pop the dent out. A few too many pumps would split the top tube (in the one example I saw that went South). Haven't seen one since. Should show up in old Mel Pinto catalogs if those still exist.

For seat or head tube dents, a expanding tail pipe tool can do it. Those are still easy to find at most autoparts stores. Here is pointer to Amazon set of three sizes for under $16 delivered. Need long 3/8" extensions to get it down the ST to where you have the dent.

https://www.amazon.com/AMPRO-T75822-S...lpipe+expander

BTW: Yes tube blocks are very likely a better answer. MSC industrial has them amongst other

/K

fietsbob

thing is, a dent includes stretching the metal , as well as perhaps some oval-izing the outside .
the frame block can only take out the out of round.

Michael Angelo 

I use these with good success.

https://www.bicycletool.com/frameblock1.aspx

ricklp

Thanks for the ideas, both here and elsewhere. I got a ding out of the top tube of a pretty interesting frame.

I started with water in the tube and a seat post in the seat tube and and an inflated air tire tube rolled up in the head tube to keep the water in. let it freeze for 3-4 hours, looked away, then looked back and it was mostly out.

Then I ordered a tube block and now it is almost good enough to skip filler. It will likely get away with only spot putty.

reddog3

fietsbob's comment on "stretching" points to the problem. Any dent (deformation) does indeed stretch the metal. You ain't gonna get it out successfully unless you have access enough that you can "shrink" the metal in the area around the joint. It's possible on the seat tube where you have room for a mandrel (dolly) of sorts so you can hammer from the outside. Any other tube- forget it. Franks idea has merit, and if you know what you're doing you can use the heat to shrink the metal. Stretching thins the material at some point, and unless you know what your doing... displacing the material is difficult, and nearly impossible on small diameter tubes.

Best solution- fill it!