SpudFiles

That would have to be one badass current supply to heat up a metal rod filling a pvc pipe.


Can't help thinking you'd find it easier being a bit more specific in heat application.

Off the top of my head, I'm thinking of a melting head drawn through the pipe.

The pipe isn't metal, localised melting would be easier than cutting. The head would require a heating system - could even be electrical or even gas (no I don't mean petrol) powered if you were feeling adventurous - and a groove forming face (or several) which transfers the heat to the plastic.

Keep the speed to a level that allows sufficient melting to accept the shape of the mould but no so much as to collapse the pipe through its own weight.

We could keep the metal head hot using liquid sodium molten by a plutonium fission reactor...


This is getting way out of hand and far too complex.

Are we making Rube Goldberg machines or are we trying to find a practical manner in which todo this?

john bunsenburner wrote:I think it is easyer to inster a piece of pipe with a positive form of the rifeling on it into the heated and expanded pipe, once said pipe cools the rifeling will be engraved and the mold should be able to come out with a bit of turnining.

Your idea is to heat the entire pipe and use a cold form to create the rifling.

Mine is to heat just the form and through that the section of pipe currently being rifled, then move it along to rifle sections at a time.

Hardly out of hand. Whatever you had in mind to heat an entire length of pipe is almost certainly possible to use for heating an internal mould.

Well both ideas are Goldberg then, lets stick to nails in a cork...

Hubb wrote:Okay, to clear up the "how", here is what I was thinking.

Insert a metal rod into the pipe. The rod (or pipe, whatever) should be nearly equal to the inside diameter as the PVC. It should also leave a little bit of PVC overhang on both sides. Wires connect to the rod and a current is passed through it.

Now, this rod serves two purposes at the moment. (1) It heats the pipe at a constant rate, which is a rate that can also be controlled fairly easily if need be, and (2) it will allow the PVC to maintain it's internal diameter during the entire process.

That still wouldn't work, the rod would get hotter on cathode end.

Zach1188 wrote:

Hubb wrote:Okay, to clear up the "how", here is what I was thinking.

Insert a metal rod into the pipe. The rod (or pipe, whatever) should be nearly equal to the inside diameter as the PVC. It should also leave a little bit of PVC overhang on both sides. Wires connect to the rod and a current is passed through it.

Now, this rod serves two purposes at the moment. (1) It heats the pipe at a constant rate, which is a rate that can also be controlled fairly easily if need be, and (2) it will allow the PVC to maintain it's internal diameter during the entire process.

That still wouldn't work, the rod would get hotter on cathode end.

Why would one end be hotter than the other? And if it is powered by AC then there isn't a "cathode" end.

Pumping current through a conductive rod (or pipe) will heat the rod (or pipe) equally along it's length.

One (of several) challenges with this approach is the power supply. It'll take a heck of a lot of current, as in electric oven type current levels. But the rod (or pipe) doesn't have sufficient resistance, unlike the heating element in an oven. If you were to connect the rod to a typical 15A 120VAC wall outlet all that'll happen is you will trip the breaker. The pipe won't heat up. To get the pipe to heat you would end up heating the wiring in the walls to much higher temps than the pipe since the wall wiring has a much lower cross sectional area and therefore higher resistance. The circuit breaker is specifically designed to keep the wiring in the wall from heating up. Indeed, that is all a home circuit breaker is designed to do.

So, you would need a current limited power supply that'll supply at least a couple killowatts.

So, you would need a current limited power supply that'll supply at least a couple killowatts.

Such as a low powered welder.....

no an arc welder increases voltage to allow it to arc
what you need is current but less voltage having less voltage will limit the curret (because the electrons have less energy to flow but more quantity) the obvious way to do this is to use a transformer this will pump the current up and decrease the voltage to less than a volt, this is all about resistance relative to voltage, since we have no special heating coil alloy with high resistance to use as a heating element we must increase the current and decrease the voltage to use a basic cast iron pipe as a heating element

Not sure if this has been mentioned, but you could try taking a soft steel rod and wrapping it in a spiral around a pipe smaller than the pipe you plan to rifle. The finished rod should resemble a spring.

For strength, you can secure this rod to the pipe which you bent it around. Grind a cutting tip onto the end of the rod and add a few at points along the rod. More than one cutting tip is necessary.

Take the whole thing and "thread" it into your intended barrel. It should cut grooves similar to the way a tap would.

It may help to devise something that would center the cutting tool in your barrel instead of attempting to center it yourself when threading it.

iknowmy3tables wrote:no an arc welder increases voltage to allow it to arc
what you need is current but less voltage having less voltage will limit the curret (because the electrons have less energy to flow but more quantity) the obvious way to do this is to use a transformer this will pump the current up and decrease the voltage to less than a volt, this is all about resistance relative to voltage, since we have no special heating coil alloy with high resistance to use as a heating element we must increase the current and decrease the voltage to use a basic cast iron pipe as a heating element

Most common arc welders use a step down transformer to lower the voltage, not raise it. This is why you have to scratch an arc. Once the arc is struck the high current provides a low resistance ionized current path. This low voltage is how a welder can output 150 Amps on a 50 amp outlet. The arc voltage when welding is typically 20-30 volts and up to about 70 volts open circuit.

Higher current at much lower voltage can be found in a spot welder or electric pipe thawer. If you work with transformers and care to custom wind your own secondary a microwave oven transformer can easily be rewound into a resistance heating ballasted power supply for heating the cutting head wires or rods. A proper impedance match can provide the full 800+ watts into the cutting head rods. I have some surplus microwave transformers and may tackle this later. 150 Amps at 5 volts or 300 amps at 2.5 volts would work nicely and is within the power range of a modified microwave oven transformer. Normal 12 AWG house wire can be used for the cutting elements in the head.

I'll keep you posted with a full how to if I do try it. I'll work out the new turns ratio later.

Yeah, from what I've heard from good sources,
Only a fraction of the barrel length needs to be rifled for rifling to work the same. (?)
The rifling should be on the breech end though.
A plastic cup shape or wadding behind the shot would be needed to prevent leaking through where the rifle grooves are cut also though.
Seems Worth testing out.

BTW, interesting info on welders...I was watching a MIG one time and wondering how the capacitors charged so fast...course they don't use capacitors...wonder what the electric usage was like in the old factory that laid off 3/4's of us the day after I got married...My thoughts on labor unions have 180'd since BTW...