Dented top tube; DIY repair

[fenmanctc]

Any mileage in completely removing paint from the area of the dent and using epoxy resin adhesive, i.e. Araldite Standard, as a filler. This stuff is aircraft-grade strong, can be filed to a profile on setting and takes paint well. I've used it on smaller damaged areas than Brucey's example, and it worked.

[alexnharvey]

Pure epoxy will generally be harder to use to fill (aka less 'featherable'), be more likely to run and sag and be harder to sand than products designed for filling, whether they're based on epoxy or other resins. However, if it's all you have on hand then it will work ok to fill a small chip, pit or dent, especially if this allows you to seal the surface promptly.
The strength is irrelevant, it's not going to reinforce the tube in any way and so a filler which is easier to work with but less strong is more suitable.

All the other caveats about filling dents outlined by Brucey on the first page are worth bearing in mind, especially whether any metal around the dent has been forced proud of the surface. Here you would need 'negative filler'.

[bgnukem]

Any mileage in completely removing paint from the area of the dent and using epoxy resin adhesive, i.e. Araldite Standard, as a filler. This stuff is aircraft-grade strong, can be filed to a profile on setting and takes paint well. I've used it on smaller damaged areas than Brucey's example, and it worked.

According to a reference I found, the elastic modulus of epoxy resin with no filler is around 4GPa (Gigapascals) whereas the elastic modulus of steel is around 200-210GPa.

If any stress (load) is applied to the tube, producing a strain (elongation), then the load will disproportionately act in the tube rather than the resin as the tube is so much stiffer than the resin, so load transfer to the resin will be very small, and so it does not really strengthen the tube, it just acts as a very hard filler material.

[Jamesh]

How about chemical metal fillers??

Cheers James

[rjb]

Those aluminium welding rods which keep popping up as adverts on my tablet may be another solution. I wouldn't trust them for safety critical use.

[alexnharvey]

How about chemical metal fillers??

Cheers James

These are resins filled with metal powders. You can add all sorts of powders to epoxy and other resins. Some will be loadbearing (wood/glass fibres), most will be thickening, some are also very light and easy to sand (microballoons). Steel filled epoxy would be hard. Good for some uses (filling a wrongly drilled hole in a metal surface) but probably not for dent filling on a tube I reckon.

[Brucey]

Those aluminium welding rods which keep popping up as adverts on my tablet may be another solution....

not for steel!

[Brucey]

Any mileage in completely removing paint from the area of the dent and using epoxy resin adhesive, i.e. Araldite Standard, as a filler. This stuff is aircraft-grade strong, can be filed to a profile on setting and takes paint well. I've used it on smaller damaged areas than Brucey's example, and it worked.

According to a reference I found, the elastic modulus of epoxy resin with no filler is around 4GPa (Gigapascals) whereas the elastic modulus of steel is around 200-210GPa.

If any stress (load) is applied to the tube, producing a strain (elongation), then the load will disproportionately act in the tube rather than the resin as the tube is so much stiffer than the resin, so load transfer to the resin will be very small, and so it does not really strengthen the tube, it just acts as a very hard filler material.

this is exactly the case, (hence my comments upthread). It takes rather a lot of glass or carbon to make the added material stiff enough that it is going to usefully share the load with the steel beneath.

Most things that you might slap on a steel tube are a palliative for the mind, not so much of real structural benefit.

cheers