how is the inside profile of quad rail free floats typically machined?

I don't have one so I can't get a real close look, but from pictures it seems like the inside has lots of relatively square corners. Are these typically edm'ed, or do they come as extrusions with the internal profile already done (and then the outside is just machined), etc?

EDM would be cost prohibitive. The ones that I've taken a close look at were extruded and then machined.

From what iv seen they are extruded at the shape they are finished and they just mill each rail slot and cooling slots ect. They come out of the extruder basically the same shape as if you were to look at one from the end just without the finish milling of the slots and the mounting set up.

They are made from extrusions usually. It wouldn't be cost effective to machine that whole SOB out from a single piece of a billet.

Here are some pics of the extrusions used to make the spikes tactical rails:

Were those cut to length on a Wilton cold saw?

I don't know the specifics on how they were cut or machined from the extrusions.
Those pics were posted in the spikes tactical industry section by member heatseakins in a thread about the new spikes rails made by seekins precision: http://www.ar15.com/forums/topic.html?b=2&f=282&t=195178

So do they start out with an aluminum tube first to run threw the extrusion dies?

Nope, the molten aluminum is squirted through a custom die at the mill...kinda of like those old play-doh factories from when we were kids. It comes out in long sticks where it cools and they cut it to a specific size for shipping. Then they are shipped to the manufacturer for finish machining.

lol wilton manual on the rack

I've never been in an extrusion plant but I'd bet that it sounds a lot like this.

I don't suppose it would be possible to get a raw extrusion somewhere? I don't think I could put in a big enough order to have my own made

Do they finish machine the picatinny interfaces, or are those just left at the tolerances of extrusion? ETA I don't mean the slots, I mean the 45deg angles.

The pic rail is machined after extrusion. I don't think they could hold the tolerance required without machining.
You could try to find thick walled aluminum tubing to make your own rail.

If your good with a tig welder I bet you could machine up an aluminum tube, weld some machined rails on it and have a good looking rail.

Hah, I'm not a good TIG welder. I thought about practicing up for something like this though, I have someone who said they would be willing to sit down and bring me up to speed. However, I know next to nothing about how the weld would affect the aluminum heat treat, and how that may or may not compromise its strength. Would something like 6061-T6 lose it's heat treat condition, and could it be brought back to T6?

Right now I'm just playing around with ideas. I thought maybe I could do something like the omega rail, and make it a two piece. I also considered just using a thick walled tube as guncrank mentioned, and milling the rails on it (I have some already that would work well) but I'm a little concerned about how much it would weigh.

I could go the easier route and just make it round (with small rail sections), but I want a quad rail so I can put grip covers on it. I don't like how quickly bare aluminum forends become too hot to touch.

Thanks for all the input.

sure you can get raw extrusion...you design the die and order a batch of material... the catch is..the dies typically run $2500+ and they have a minimum of extrusion you need to order..ie no less than 1000 lbs of material etc.

maybe one of the places that machines the rails would sell you a pre-machined extrusion section?

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