SpudFiles

No shame to KillGorrila, but his 'rifled' barrels were short of any standards. The setup was essentially a broom stick with (I believe two) nail tips extruding, spun by hand along the course of the barrel. This producing a small impression in width, depth, and of a inconsistent rate. Not to mention, he lives in Australia, just far enough for a jacked shipping rate.

The dog stake rate of twist is to steep, so I do not see how it could be effectively implemented. Nor have it the length.

I often speculated by thumbing threw Joels pictures how in the F he rifled his barrels. For a while there I also believed that he may have modified his lathe to a incredibly fast feed rate, and attached the barrel to the carriage somehow. The second picture on this <a>page</a> is what I believe made this temporary conclusion. The AL bar to me appeared to be a custom cutting head of some sort, but it in reality is a support to distance the pipe from the chuck, while still securing it to cut the muzzle knife. (by feeding the tool post on the compound slide at a angle)

In all truth though I think the highest feed rate a un-modded carriage feed is capable of is 8TPI. (not trying to be overly definitive, because I know there is a lot of lathe manufactures, and I am sure those types of things may vary) To get a for instance 1:36 twist rate, your carriage feed is going to need, and be .0277...TPI Sure some custom gears could achieve that, but now you have a speeding carriage. Then you will need and slow your chuck RPM down to like 30RPM. I feel like I have already beaten the point, not to mention that the length abilities of you lathe no where near the required.

Demon, this is one of those discussions that has never came to a satisfactory conclusion. So I would promote any discussion on this subject, as well as it is done in a well-behaved manner. Searching will only turn up more broomstick, with nails in the end discussions.

Just a little eye-candy, the following 3 renderings were made for another member, the system is overly tedious, and prone to failure. Anyways, here they are:

<img src="http://www.spudfiles.com/uploader/uploadFiles/009.PNG">
<img src="http://www.spudfiles.com/uploader/uploadFiles/010.PNG">
<img src="http://www.spudfiles.com/uploader/uploadFiles/011.PNG">

Next is a idea I had on cutting rifilings that I rendered. (Note the cutting head pictured cutting surfaces are points, which would create a "V" groove. In reality those would be replaced for cutters to produce 'lands') The cutting head would be fixed, while the pipe is rotated. The system would then use a series of rotating cylinders at symmetrically opposing direction. (Hopefully that makes sense in conjunction with the renderings) The cylinder exteriors being of a neoprene surface to 'grip'. From there the rate of twist would be controlled by the degree in which the rotating cylinders were positioned. Below are some theoretical renderings of the design:

<img src="http://www.spudfiles.com/uploader/uploadFiles/013.PNG">
<img src="http://www.spudfiles.com/uploader/uploadFiles/014.PNG">
<img src="http://www.spudfiles.com/uploader/uploadFiles/015.PNG">

Jrrdw, mentioned a another system I tossed about on IM services, and forum wide chats. I in a lack of time do not have the time to explain, or make any illustrations to accompany the idea. So I will be sure to post it in a follow up post.

hmm
i was at my machine shop yesterday making random robot parts on my lathe and i think it would be very hard to do. my .22 hornet has i turn per 20", so 200 RPM would be high. I did figure out that i could rifle small aluminum bits, but its difficult and takes forever. I might make a custom airsoft pistol if im really bored next week.

i think it might be possible to build something out of old sander parts for the drive. Maybe use the second idea would work, if timed properly. The real challenge would be timing the feed/rotation wheels.

another idea i has to get PVC sheet, use a hot piece of iron to make grooves, then wrap it around a pipe with an outer diameter equivalent to the desired ID of your barrel. Only problem is, there might be a great danger of rupture if hot gasses got into the seam left form the folding.

ill think of more ideas, but i might not post for a bit since i have a huge battle bots tourney next week (i have 48 hrs to finish the damn thing)

thanks for the suggestions though!!!

Sometimes the solution is so simple that it isn't obvious. A flat drive shaft with a twist like a twist drill bit can be pushed through a slot so the tool rotates as it goes in. With several passes several sets of parallel passes can be made.

actually, if you could figure out how to get/make the tools, thats a legitimate idea

tomthebomb137 wrote:actually, if you could figure out how to get/make the tools, thats a legitimate idea

Twisting the flat iron bar is easy. Put a flat iron bar in a pipe so the ends stick out about an inch. Clamp one end of the bar in a bench vise. Using an adjustable open end wrench, twist the rod in the pipe. It's the same technique used for wrought iron work.

Making the cutting head is another project.

There is a repllica of an old design here. Fairly simple.

http://www.orro.net/lukens/

i learn so much more here than i ever do at school

anyone got a CNC/milling machine?

Look at Hubb's barrel guide..it mentions PVC rifiling directly.

Unless done properly, riflings will have little or negative effect. If you are using potatoes, then forget it. Too inconsistent.

Rather than wasting time with rifling if you can't do it well, why not build stabilized projectiles?

The rifling pitch will depend mostly on the diameter length ratio, muzzle velocity will also take part, but in the range of spudgun speeds alot less.

200RPM is nothing in firearm standards, I've shot potato bits out of 1:16 and 1:8 inch barrels with no destructive effect on the potato.

The barrels do actually stabilise the projectile over quite a range and greatly improve accuracy just through stopping the tumbling.
The potato bits tend to corkscrew after a certain distance, probably down to unadequate twist rate...

I dont believe the Greenhill formula is good for homemade airguns with hard projectiles, but the slower rate it gives might be best for spuds.

I rifle my barrels using a specialy made tool or a modified reamer tool of the right diameter, but then it tends to be hard to get the required twist rate.
For big PVC pipes it might jsut be easier to make the tool. And PVC should be much easier to rifle.
So sort of what Techincian suggested.

@ mr nickname

something like this maybe??

Yep Fore

Dart projectiles or projectiles with a forward center of gravity are the way to go (foster slugs etc).

In all honesty, there would be absolutely no point in building a machine that is described to rifle a barrel. If one were to begin selling rifled pvc like Joel did back in the day, then yeah, but for one barrel; not worth it.

tomthebomb137 wrote:actually, if you could figure out how to get/make the tools, thats a legitimate idea

That's not a "legitimate" idea... It's how rifling is done in firearms. Or close enough, anyways (ie, it's how it was done in the old days.).

al-xg wrote:...but in the range of spudgun speeds a lot less.

Actually, at these speeds, MORE.

The best version of the Greenhill formula is 3.5 * SQRT(Velocity) * D^2/ L *SQRT (Density/10.9)
Feet/Second, inches and Grams per CC for units. Output is "Inches per turn".

Or, if you prefer metric:
1.92 * SQRT (Velocity * Density) * D^2 / L
Velocity is in m/s, density in grams per cc. Dimensions are in either cm or metres (as long as you're consistent), and output will be in whatever units those dimensions were per turn.

The fact that it's the SQRT of velocity means that the twist rates change more at lower velocities than at higher ones.
Also, the less dense projectiles demand faster twist rates as well.

Try feeding in a spud for HEAL, and you get a twist rate of 1 turn in 8.3 inches - which is a spin speed of 48,000 rpm.
I wouldn't gamble on a potato holding together at those speeds. Indeed, the surface of the spud would be under forces of tens of thousands of G - more than I'd bet on it surviving.

As I don't have any figures for the yield strength of potato*, I can't tell you whether it would survive in given conditions, so I'd just cut back on twist rates a lot - the forces on a projectile are inversely proportional to the twist rate.
So - 3 times the length of twist means the forces are 9 times less.

It might harm accuracy over an "ideal rate" - but if your projectiles aren't holding together, you're screwed either way.

*If anyone does have one, get back to me.