1. Home
  2. ⏣ General Metalworking
  3. design descisions for internal tube expander

design descisions for internal tube expander

I'm thinking of making a tool to be slid up inside a bicycle frame down tube that would expand and push out dents from the inside.

I have been thinking about two different inter-acting problems.

  1. how to manipulate the tool - so far the best solution is to have it have one part a curved shoe with two bowden cables attached; both cables go in from one side of the BB shell if the dent is on the side, and one from each side if the dent is top/bottom. The cables outers should be stiff enough the push/pull and twist it. Each cable will go out to a handlebar (what else?) with two stout brake-levers mounted.

  1. how to expand and contract the other part of the tool - I am not sure if contracting it will be a problem but want a positive method anyway, don't want the bloody thing left up there; not sure I can trust a spring. I can't decide whether to use a toggle, or a screw at 90 degrees to the long axis of the tube. The tube wall will be at most 1.5mm thick, often less, dents might be as much as 5mm deep.

A toggle might be tricky to fit inside a tube, so I'm leaning toward a screw with a ratcheting cross-lever operated by the two bowden cables. That'd be a bit of a bother as I think the ratcheting will be insert - place - push - remove - advance ratchet - repeat. A toggle might allow all the push to be done at one go, but getting positive contraction is not a simple as with a screw - and as well I am not sure the cable would take the strain needed to push the dent out. Toggle mechanical advantage is best at the angle most constrained by tube diameter, there is probably less than an inch to work inside.

I also thought about a screw-operated pair of wedges - but the manipulation arm would have to be able to take torque as well, yet be flexible enough to bend through the 90 degrees of the bb shell/tube joint. A pair of wedges could be operated by cables, but again would the advantage be sufficient given the limit of the cable.

Reply to
charliebrown
Loading thread data ...

I'm thinking of making a tool to be slid up inside a bicycle frame down tube that would expand and push out dents from the inside. ================================ Shotgun barrel dent remover:

formatting link

Reply to
Jim Wilkins
<snip>

You might want to consider hydraulics too. Like a miniature jack/expander that could slip inside. It could have its own spring return. Maybe design for the high pressure hose to both fit and allow you to move it around inside the tube...

Reply to
Leon Fisk
<snip>

You might want to consider hydraulics too. Like a miniature jack/expander that could slip inside. It could have its own spring return. Maybe design for the high pressure hose to both fit and allow you to move it around inside the tube...

Leon Fisk Grand Rapids MI

=====================

Grease gun hose and copper-nickel brake line are thin, flexible tubes that hold high pressure and connect with pipe threads. I'd start by finding a small enough hydraulic piston seal and designing the cylinder around it. Maybe a gas strut could be modified.

Reply to
Jim Wilkins

Instead of a press, why not use an internal hammer? Just get a heavy rod, set it into the tube, and slam the whole frame down onto a sturdy table; the rod's inertia will hammer the dent out.

Another popular solution is to force a large hardened BB through the tube.

Reply to
whit3rd
<snip>

You might want to consider hydraulics too. Like a miniature jack/expander that could slip inside. It could have its own spring return. Maybe design for the high pressure hose to both fit and allow you to move it around inside the tube...

Leon Fisk Grand Rapids MI

=====================

Grease gun hose and copper-nickel brake line are thin, flexible tubes that hold high pressure and connect with pipe threads. I'd start by finding a small enough hydraulic piston seal and designing the cylinder around it. Maybe a gas strut could be modified.

===================================================== A similar idea:

formatting link
Notice that he modified parts on his metal lathe. The job may not be possible without one.

Reply to
Jim Wilkins

That's a nice article. Both the failures and solutions to what he was trying to do :)

I'd hazard a guess that if I was to poke around in the Patent database I'd find some interesting items that pertain to this subject. Seeing how Charlie Brown hasn't been back to comment I don't think it's worth my time. I'm not that interested in making such an item ;-)

Reply to
Leon Fisk

That's a nice article. Both the failures and solutions to what he was trying to do :)

I'd hazard a guess that if I was to poke around in the Patent database I'd find some interesting items that pertain to this subject. Seeing how Charlie Brown hasn't been back to comment I don't think it's worth my time. I'm not that interested in making such an item ;-)

Leon Fisk Grand Rapids MI

=====================================

I am, mildly, to tighten the excessively loose fit of the slip joints in the chain link fence top rail I use for my antenna mast. The exhaust pipe tool might work if I can find it. Also I acquired a collapsed tube-framed tarp garage that could be rearranged into a smaller snow blower shelter if I could swage the tube ends to join them. I re-roofed it twice for the owner by attaching a new tarp to PT wood strips screwed to the tubes.

Reply to
Jim Wilkins

Don't know whether this is going to help, but this:

formatting link
is how they get dents out of brass musical instrument tubes. Of course you'd have to scale up the sturdiness of the tools and use a hammer on the outside, but it ought to work.

Reply to
rangerssuck

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.