1/2 scale AR-15

[MachIVshooter]

If you sell it is it going to be half price?

Half of what a decked out Stoner SR25 cost, maybe. lol.

In all seriousness, by the time I'm done, I'll have probably invested >200 hours and dropped at least $500 on materials and new/replacement tooling.

The good news is I did score a barrel. It's a used .17-222 tube, but I won it for $50 shipped on fleabay. Now I just have to decide if I'm buying a $75 PTG reamer or reprofiling one of the 50 or so reamers I got in a lot a couple months back. Even if I do buy the new reamer, I'll still come out well ahead of the alternative $225 option for a chambered Clark barrel.

Of course, I'm still waiting on a reply from ATF FTB, and that's likely at least a month away yet, so there's not a huge rush to finish out the last half dozen parts.

I should have the 5/16-40 tap and die for the barrel and flash hider later this week, though. Perfect scale would, of course, be 1/4-56, but I don't want to trim it down that far. With a .172" bore, there would be less than 0.025" thickness, and that's getting a little thin for comfort, even with a rimfire. 5/16-40 will leave about 0.055".

You're not even a machinist by trade

Nope. Mechanic since age 16. Did carpentry for a year and a half before that, but it wasn't my calling, and I never liked having to travel to new destinations all the time for work.

It is a natural progression, I think. Going from fixing mechanical things to making mechanical things isn't exactly a quantum leap. The relationships between mechanical parts have always just made sense to me, and though I lack a formal education beyond 9th grade, I have never had trouble understanding and applying practical math-algebra, geometry and trig.

Also always liked metals, despite my father having been a woodworker and custom cabinet maker. And my fascination with guns, though nurtured by him, far exceeded his own. He died when I was 11, though, and mom & stepdad were antis. Solution? Build one! My first gun was a muzzle loader made from a pellet gun barrel, some cap gun parts and an aluminum frame. I was lucky to survive that one, being as I used smokeless power in it, and bullets were a bit heavy, swaged down from .22 LR pills (the powder was from the .22 LR cartridges). Metallurgy and pressures I just didn't have a solid grasp on at 11/12 years old. Eventually the brazed in nipple blew out of it; the hammer deflected it away from me, but I acquired a healthy dose of fear, and decided to move into cartridge firing guns. Next one was all steel (thanks, metal shop class!), and fired .22 LR from a hinged barrel made of 1/2" hexagonal steel stock. Crude trigger mechanism held back the equally crude striker, but it did work. That one landed me in jail a couple years later; I was lucky to have only been charged with minor in possession of a handgun, since it was a smooth bore pistol. I guess they figured a 13-15 year old kid probably wasn't familiar with NFA laws (I wasn't). Fortunately it was a deferred adjudication, and I did stop building guns until I came of age.

Anyhow, since I didn't manage to kill myself or lose my gun rights with my adolescent ventures, I am lucky enough today to have the equipment and the knowledge/resources to get it done right!

 

[barnbwt]

"It's a used .17-222 tube, but I won it for $50 shipped on fleabay."
Aw, dude; Green Mountain has 21" .17 blanks for 40$ .

You might also look at simply making a D-reamer yourself from cartridge specs. That method tends to work very well for the little rimfire rounds (the reamer gets a little loosey-goosey if you push it hard doing a bigger cartridge, though). A few inches of 1/4" rod, some MAPP gas, and quenching oil --worth a shot, at least

"Trent's Postulation #2; the greater the gift we have in that "one thing", the worse we are at everything else."
I excel at wasting time!

TCB

 

[MachIVshooter]

Aw, dude; Green Mountain has 21" .17 blanks for 40$

Eh, six of one, a half dozen of the other. Same amount of work to chamber them. I didn't see that sale, just the $88 tag on the .17 HMR barrels they've always had in stock. Be less material to remove on this used one anyway, since the final diameter for most of my barrel is going to be .380".

You might also look at simply making a D-reamer yourself from cartridge specs. That method tends to work very well for the little rimfire rounds (the reamer gets a little loosey-goosey if you push it hard doing a bigger cartridge, though). A few inches of 1/4" rod, some MAPP gas, and quenching oil --worth a shot, at least

Definitely one way. Reprofiling a twist drill would work, too. But since I have a pile of 5, 6 and 8 flute HSS reamers anyway, might as well use the tool that will do the best job. And if it doesn't work, all I lose is an inch of barrel stock and a reamer I have duplicates of.

 

[WestKentucky]

End of story...I'm buying equipment before more guns. Truly inspiring...and I already have a collection of guns that need minor work. It may pay itself off in the long run...but I doubt it.

 

[200Apples]

.
Well, Mach, I'm still impressed...

I spent some of my early middle age, four years, in fact, learning to drive then racing 1/10 scale electric on-road. Never whittled up any parts, though.

I'm just glad to have made your acquaintance, here. Well done, sir.

 

[MachIVshooter]

I'm buying equipment before more guns.

You will never regret it. Not once in my life have I thought to myself "I should have spent that money on (insert item) instead of a tool". Can't say the same is true for anything else...........including guns.

It may pay itself off in the long run...but I doubt it.

It just might. I've salvaged some rather expensive assemblies by making a part that is not available for sale on its own. For example, a cylinder head on a 4.7L SOHC V8 in a Grand Cherokee; the boss for the timing chain guide had snapped off, which is part of the casting. I was able to carve out a mounting surface and fabricate a steel block to replace the broken off cast piece. I also saved a Subaru 2.0L turbo engine block that a shadetree hack had hopelessly damaged by machining a threaded insert to repair a hole that was well beyond heli-coil/time-sert repair. About a month ago, I had a Kia Sorento in here that had a completely seized U-joint, and the replacement was dealer only and 3 days out. I was able to find in-stock joints with the correct cap OD and a much smaller ID, and then machine the damaged joint cross to accept the caps so the single mom could make her 80 mile daily commute to work.

I was also able to get my Remington model 51 up and running again, despite total unavailability of a correct extractor. Just a small piece of music wire and a couple hours of my time.

Those are just a few examples. Having equipment gives you options that are not available to the masses.

 

[jlr1962]

Really cool stuff. A childhood friends father make some of his own HO trains, and made an entire countryside that was suspended from their garage ceiling on pulleys. He was a career machinist/machine shop owner.

Thanks for sharing.

 

[Dangerous Dan]

Talk about Thinking out of the Box ... You are one sharp cookie My Hat is off for You Sir Amazing Work DD

 

[SleazyRider]

… Having equipment gives you options that are not available to the masses.

These words should be enshrined in a granite block somewhere, or at the very least in Bartlett's Book of Great Quotations.

 

[Zach S]

Having equipment gives you options that are not available to the masses.

Very true. While I have done some machining, I have spent most of my time in sheetmetal fabrication. Learning how to program the punch and set up the press brake was definitely a smart move. The addition of the laser added possibilities, and with the software that came with it, all I had to do was draw up the .dxf. I couldn't count how many parts I've made on my lunchbreak. Some of them were even for me. While my current employer doesn't pay near as well, it is much more laid back.

I have thought about a china freight mini mill and lathe, or a smithy, but haven't bothered due to the machines I have access to at work. Now, being in a more laid back environment, I have a few more resources available, and quick side work/lunchbox parts can be worked in between production jobs.

 

[CapnMac]

Mechanic, machinist, experienced with r/c?
You will not want to check out any of the 1/6 scale armor "kits" (which often are only 80-90% finished parts).

A 2:1 scale AR is an interesting idea, if probably impractical. If only for finding an 11x90mm round (.416 rigby might suffice, one supposes). The being near 2 meters overall, and a ±600mm LOP could be inconvenient, though.

So, perhaps, a half-scale Barrett, in oh, .25-06?

 

[MachIVshooter]

Mechanic, machinist, experienced with r/c?
You will not want to check out any of the 1/6 scale armor "kits" (which often are only 80-90% finished parts).

Oh, I've seen them. Never really got into scale stuff, though: more about performance. 1/10 scale and 1/8 scale off-road is where it's at for me, with a few odd projects thrown in, like this highly modified RC10GT that we clocked at 92 MPH:



I was shooting for a nitro speed record, fell 32 MPH short of that (although I kinda doubt there has been a faster 1/10 nitro stadium truck built). Next step is twin engines.

A 2:1 scale AR is an interesting idea, if probably impractical. If only for finding an 11x90mm round (.416 rigby might suffice, one supposes). The being near 2 meters overall, and a ±600mm LOP could be inconvenient, though.

So, perhaps, a half-scale Barrett, in oh, .25-06?

I mull such ideas over, but honestly, this may be my only scale build for awhile. It's an awful lot of work for something totally impractical, and some of the challenges are really aggravating - specifically the springs with this one. I have made the hammer spring a half dozen times now, and though it has a pretty good snap with my current 0.020" music wire spring, it's still not enough to ignite the primer. I'll get it sorted eventually, but that kind of hang-up is really frustrating. I did contact spring makers about it, but the cost is far too high-over $300 for 2 springs.

I think it may come down to redesigning the firing pin to have a much smaller striking surface, which also means keeping it in a specific orientation.

 

[barnbwt]

"A 2:1 scale AR is an interesting idea"
There was a guy doing a 50cal AK like this a while back...

"1/2 scale Barrett"
That's basically the inspiration for my recoil operated 223. Copying the actual Barrett would make the gun much harder to craft, but I seek to emulate its operation with simpler parts.

TCB

 

[MachIVshooter]

Got my new capacitors, found a little time to tinker. Made the front sight, and a faux barrel so that I can keep fitting parts while I wait on my letter. I do have my .17 barrel now, but still need to make or buy a chamber reamer before profiling it.

Anywho, the sight still needs pin holes, sling swivel and drilled/tapped for sight post, but is basically done. 'Bout a 6 hour project there:

 

[OldBrownDog]

I've been following this thread since it started. Very neat. Your skills are impressive!

And the rifle looks great!

 

[Catshooter]

Sweet.

Are you going to anodize it black? Or pink?


Cat

 

[Sheepdog1968]

Cool. Are you going to make a half scale bayonet as well?

 

[MachIVshooter]

Are you going to anodize it black? Or pink?

Definitely not pink. lol.

Not sure if I'll anodize or coat. Anodizing is ideal, but will not cover some of the tiny blemishes as well as gunkote or ceracoat. This thing has received a few nicks here and there as a result of being handled so much in an unfriendly environment for parts fitting.

Are you going to make a half scale bayonet as well?

Can't think of a good reason not to.

 

[shotgunjoel]

Ooh, the bayonet will be cool. You could finish out the actual barrel, minus chopping it down. It'd look really weird, but it'd be progress.

 

[1911 guy]

I'm a machinist by trade, have done manual mills, drill, lathe and broach work for over 20 years. Color me impressed.

Many folks don't realize that the smaller a workpiece is, the harder it generally is to make.

 

[Zach S]

Lol. I learned that the hard way.

 

[clearcut]

I just read all 221 posts what a cool thread,I love your work!! Thanks!
CC

 

[1911 guy]

MachIVshooter, I may have the answer why your 1hp machine is taking out your power supply while the 3hp isn't.

It takes approximately 1 horsepower to remove 1 cubic inch of mild steel per minute. Using faster speed because of both smaller tooling and higher surface feet per minute because you're working with a lot of aluminum, it'll be pretty easy to exceed the demand for the one horsepower the machine is capable of supplying. The 3hp machine, on the other hand, isn't approaching its limit yet and therefore doesn't overdraw the power supply. Just a thought.

One approach I use when running smaller, less powerful machines, is to be very conservative with feed and speed. For aluminum, I run about 180 SFM with high speed tools and about 500 SFM with carbide and don't exceed .004" per spindle rev with tools under 1/4" diameter, not over .006" for tools over 1/4" and less than 1". This, of course, will vary a little depending on whether you're using 2 or 4 flute end mills.

The other school of thought is to run feeds and speeds balls to the wall, but take very shallow cuts, usually not more that .050". I prefer to use the previous method, conservative feed and speed, but removing most of the stock with only .020" or so left for finish.

I read that you were "figuring out" feeds and speeds. Forgive me if I'm talking down to you, but I'm trying to help someone who obviously has a knack and some skill on mills.

Figure your speed using the following formula:
3.82*SFM/dia.=RPM
3.82 (actually 3.8197XXX) is 12 inches in a foot divided by Pi because we want to turn a linear measurement (foot) into something usable in a circular tool. SFM is desired surface feet per minute. Dia is the diameter of the item being rotated, whether it be the endmill or drill or the actual workpiece in a lathe.
Example, a 3/8" HSS endmill in 4150 steel: 3.82*50/.375= 509.333. Run your spindle at 510 RPM.

Feed is expressed in IPM or inches per minute. RPM*T*C/L=IPM
RPM is spindle speed, T is cutting teeth or flutes, C/L is desired chip load per flute. Using the same example as above, we'll say the 3/8" endmill is a 2 flute HSS (high speed steel) cutting the standard .187" depth.
510*2*.0015"=1.53 IPM

 

[1911 guy]

Did a little math and i think I'm right. You're probably using 4 flute carbide endmills. 1/4" endmill at 500 SFM would be 7640 RPM. 7640*4*.0015" is 45.84 IPM. Max normal depth would be .125" and that's 1.4325 cubic inches a minute (45.84*.25*.187), almost 50 more horsepower requirement than your machine is rated for. Aluminum does machine much easier than steel (aprox 3X), but you also lose more horsepower to the spindle the faster it's turning.

 

[Rubber_Duck]

Just checking back in on this thread. Still impressed.