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AR Lower--from wood!
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  dcorb

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Posted: October 11 2008 at 10:10am | IP Logged Quote dcorb

I am thinking of making a laminated grip stick with an AR15 fcg for one my tube gun builds.
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  Desert Doc

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Posted: October 28 2008 at 1:12am | IP Logged Quote Desert Doc

A denser wood with much tighter grain is really necessary for something like this to really work. My first thought was Iron Wood from Africa. The silicon content is so high that it tends to wear out saw blades and drill bit quickly. Working with it is very similar to working with metal.

Another, probably even better idea would epoxy impregnated aircraft grade plywood with metal reinforcements in critical stress areas. The plastisizing of the ply with epoxy would be very close to the strength and density of the Cav Arms style lower.
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  gundoctor

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Posted: October 28 2008 at 1:52am | IP Logged Quote gundoctor

I like the brainstorming going on about "exotic" materials for construction.  Reminds me of John Dillinger escaping from jail with a pistol made from a bar of soap.   A firearm doesn't have to fire (at all or too many times) to be highly effective.

I think a bamboo laminate might be very strong.

one also might salvage exotic materials from discarded things like skis, aircraft parts, helmets  .....?  who knows.    What about kevlar--plenty of sources for that.  Kevlar fabric and epoxy placed in a mold and pressed with a 12 ton press?   The aluminum inserts in critical areas?

quite possibly a very strong laminate might be paper (or fabric) and the proper glue.  The old paper belt pulleys used years ago are pretty dang tough

 I have seen some carbon fiber scrap sheets somewhere that were about 1/8" thick but I can't put my finger on it yet.  I think it would look great laminated with aluminum.

Even if some of these ideas don't work for receivers they might make a great way to build up or mold stocks etc.

I have had a Winchester model 59 shotgun for over 30 years.   A very thin steel liner wrapped in fiberglass for a barrel.
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  orions_hammer

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Posted: October 28 2008 at 3:02am | IP Logged Quote orions_hammer

Doc, plywood is a darn good idea.  I haven't been able to get epoxy to soak into wood very effectively, though--but the vacuum-bag trick might help!  I've also tried MDF, which is a really fine-grained fiberboard--it mills nicely, and it's about twice as strong as pine, but it still splits apart too easily.  I also tried coating both wood and MDF in polyurethane, which soaks in beautifully, but sadly polyurethane doesn't add much strength.

(Modem folks beware: many images coming below!)

But I really do like how a fairly soft plastic like HDPE machines on a mill, so...



Spiral bits for a scrollsaw sure are awesome--you can cut in any direction!

Step two was to "weld" the above slices of cutting board into one solid block.  I used a hot air gun, which just barely had enough heat output to keep the whole surface liquid.  Hot HDPE gets really sticky, so once both sides of a weld are hot, be sure it's lined up before you squish the surfaces together!



I'm not super happy with this welding technique--I got the edges basically fused properly, but as I discovered large sections inside there aren't fully fused, and HDPE warps badly due to its high thermal expansion coefficient.  It'd be better to start with one solid 1.5" thick block of plastic, or to heat the sections in an oven broiler and then fuse in a nice level aligned jig.  Ah well, at least it's one piece now!

I pasted my template on, ready to mill the top deck flat.  "High helix" aluminum end mills work very nicely on plastic, scraping off weird blue chips at a ridiculously high feed rate!


Ready to drill the buffer tube hole.  Little did I know, I'm actually following the wrong line in my template while drilling this hole, so it's going in the wrong place!  (D'oh!  I've cleaned up my template substantially after this screwup...)



I usually start with a 3/8" pointer to find the center of the hole, then lock down the mill table so nothing moves in the horizontal plane.  I then open up the hole enough to fit a boring bar with a 1/2" end mill, switch to the boring head, and work outwards to 1.130".  Then I can drop in the huge buffer tube tap, and tap out the threads.  The only tricky part here is that my (crappy!) weld failed, visible as a thin white line above, and the laminations came apart a bit--hence the clamps during tapping.

HDPE sure works beautifully.  There's a tiny bit of hair on the corners, but it's definitely a precise substance to mill!

On to the trigger finger hole:


I ended up setting up a shop vac to deal with the hairy blue plastic shards going everywhere--they're soft, but lighter and fly a lot farther than metal chip, and they seem to electrostatically cling to everything in sight (think shopping bag fragments!).

Now that the main exterior profiling is complete, ready for the interior templates.  It turns out that Elmer's glue doesn't stick at all to HDPE, but Plumber's GOOP actually sticks paper to HDPE pretty well, but can eventually be peeled off cleanly.  I *love* using templates for machining, because it means I don't have to measure anything; I just set the vertical depth stop based on the side profile, and then mill out a pocket based on the top outline:


I usually do a FCG hole starting with a long 1/4" mill to get the trigger hole.  I always make this hole too short and too narrow to start with, so go outside the lines a bit!  Then I use a 3/8" mill (above) to clean out the narrow area around the safety switch, and finally a 1/2" mill to do the rear upper mounting pocket and main FCG pocket.

Then it's on to the magazine well.  I began with the usual ray-vin 1/8" holes in the corners, but rather than slowly step up a series of drills down the centerline, this time I just plunged out the magwell outside with a 3/8" end mill.  It's literally like five minutes work in plastic, and the narrower end mill leaves a little island of uncut material that falls out of the middle of the magwell. 


The narrower endmill lets you get a lot closer to the corners, so it only took a tiny amount of hand filing to fit the magazine proper.  Rather than carefully remove all the chips between test fittings, I just wrapped the magazine in a plastic bag--this protects the magazine, and adds a little clearance for drop-free function!


Here's where I realized my big mistake--the buffer tube hole should be just exactly lined up on the bolt, not 1/8" lower than the bolt!


So, I just cut the back end off and re-welded it!


Sadly, it's a lot trickier to place the hole to within 10 thousandths when you're squishing hot sticky HDPE, so I had to cut off and re-weld again:


I thought I was pretty darn close, so I just drilled the rest of the holes.  The trigger, sear, and hammer all fit fine on the first try, just like with the Pine ABORTION! 


And again, there wasn't clearance for a factory magazine latch, so I recycled the longer ghetto magazine latch from the ABORTION:


HDPE's strong enough to drill and tap well, so I even did the pistol grip screw, and buffer tube retainer hole, the milspec way:


Ta dah!  Tactical tupperware at its finest!  And unlike the wood model, nothing broke off during assembly either!


Only one tiny problem: the bolt doesn't cycle, because the welded-and-re-welded buffer tube hole isn't lined up with the upper mounting pins.  Solution?  Weld on a blank plate, and mill and tap it fresh and concentric:



During finishing I popped another one of the crappy lamination welds on the magwell, so I re-welded it and put in some 1/8" brass rivets just to hold it together better.  Note to self: build next billet receiver from... one billet, not a set of laminations.


My magwell was a bit tight, and thanks to some post-weld warping the bolt no longer ran over the magazine lips properly, hanging up as shown below.  Filing out the magazine well just a tad on the proper side, to let the magazine jiggle out of the way of the bolt, cured this problem.


I even put in the buffer spring retainer hole, which works nicely:


I fired off a few rounds yesterday, and dang it, the bolt wedged itself up way back in the buffer tube again, like a misaligned buffer tube!  It's a bit stiff when inside, but it really siezes up in the (0 deg F) cold.  I think the problem is that plastic contracts a lot more than metal, so I need to add a bit of expansion room around the upper mounting area for it to function properly.  Also, in a warm inside room, the pistol grip feels a tad mushy--HDPE is pretty flexible (low elastic modulus), despite its toughness (high tensile modulus).

But overall, I'm really happy with this version!  HDPE mills like a dream--they actually make practice "milling wax" from some variant of HDPE.   It seems to be plenty tough enough for actual use, unlike wood--except along my crappy welds, nothing has broken off yet. 

I was considering making version 2 in UHMW, but I managed to find some little pieces locally, and I don't like how they mill--UHMW is way more stringy and chattery to mill, and it actually feels floppier than HDPE (low elastic modulus).  I ended up ordering Grainger item 1ZBK9, which is 1 square foot of 1.5" thick ABS plastic.  It's $70, but that should be enough for at least five more receivers!  I can now crank out a receiver in about two evenings (assuming I don't screw up!), most of which is time spent lining up and clamping the work.

Here's the final firing version, together with its "parent" cutting board and "brother" giant bag o' chips.


Grizzly mini-mill: $600.
Victor buffer tap and end mills: $100.
Building an AR-15 from a cutting board: priceless!
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  weaponeer

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Posted: October 28 2008 at 4:21am | IP Logged Quote weaponeer

I love the AR lower builds!

ever consider using Version two as a mold for a possible version three?

They make some really easy to mix plastics now (lots of info on youtube) they may allow you to just Pour you next receiver..

example: http://www.youtube.com/watch?v=ng6do9yj7co

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  Inabadhood

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Posted: October 28 2008 at 10:03am | IP Logged Quote Inabadhood

WOW!  Great, and IMPRESSIVE progress, Orions_Hammer!!! 

GREAT!!!

Also, thanks for the great link, Weaponeer!  That's pretty interesting stuff! 

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  Darkmeat

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Posted: October 28 2008 at 3:32pm | IP Logged Quote Darkmeat

I'm drooling over that plastic one. It seems almost like it's what should have been on an AR in the beginning, instead of aluminum!
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  Darkmeat

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Posted: October 28 2008 at 3:51pm | IP Logged Quote Darkmeat

I'm drooling over that plastic one. It seems almost like it's what should have been on an AR in the beginning, instead of aluminum!
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  orions_hammer

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Posted: October 29 2008 at 4:33am | IP Logged Quote orions_hammer

I've confirmed the cycling problem is indeed cold-related--with the receiver at room temperature, the bolt carrier moves freely; with the receiver at 0 deg F outside temperature, the bolt carrier binds and then jams up almost solid near the back of its travel.

Now I've just got to figure out how to modify the receiver geometry to work in either warm or cold--I think I just need a little more clearance around the upper mounting pins...
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  padkychas

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Posted: November 02 2008 at 12:00am | IP Logged Quote padkychas

I think if you use a good cabinet grade hard wood plywood that is 1/4" thick,  it would work for what you are doing. I think that it could be put together in layers with metal in week spots. and you could push epoxy into the wood with a used pressure cooker pot and put air pressure on it to push the epoxy into the wood (keep the PSI under the max or the pressure cooker can fly apart), and hold until it is cured.
The buffer tube could be cut with a ball end mill or a round router,  from the side on each side of the plywood before it is epoxied together so the cut would be good to go.
have you seen a KT ordnance 1911 80% receiver? it is machined in 2 sides, the inside is cut out first and it is brazed together, this makes the inside cuts easy and then it is finished on the outside. if you cut all the open inside space first by using a saw and then epoxy together the layers, you would not to need to do much milling work. 
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  orions_hammer

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Posted: November 02 2008 at 1:27am | IP Logged Quote orions_hammer

Tons of good ideas so far, guys!   Keep 'em coming!

Lamination is definitely a powerful technique--a stack of simple shapes can make a very complicated part. The tricky part about lamination is keeping the dang slices stuck together, so you'd really need to get a good adhesive setup.  The AR-15 lower receiver only has a couple of high-stress areas, though: the front mounting ears, and the buffer tube.  Clear unreinforced wood breaks in both places.  HDPE seems plenty strong on the mounting ears, but it's pretty marginal at the buffer tube.  One big old backstrap of metal (take your pick) on the buffer tube might pretty much fix the thing. 

I posted a YouTube video of a test firing.  I filmed in the dark, so you can see the muzzle flash, laser aiming device, and sparks from the glowing embers I was shooting!




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  orions_hammer

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Posted: November 02 2008 at 1:31am | IP Logged Quote orions_hammer

Here's the rifle's configuration for the above video.  The little forward-mounted laser aiming device works great in the dark.  The 6-24 scope is totally useless in the dark, but I was too lazy to umount it.  Burning off half a mag for no reason, like in the video, is sure fun!

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  elmacgyver0

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Posted: November 10 2008 at 7:18am | IP Logged Quote elmacgyver0

Epoxy can be thinned with denatured alcohol, perhaps it would soak into wood better then?
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  Darkmeat

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Posted: November 21 2008 at 5:41pm | IP Logged Quote Darkmeat

Orion, do you know where I could find a template like what you used?
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  orions_hammer

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Posted: November 23 2008 at 11:33pm | IP Logged Quote orions_hammer

Sure!  Here's my template.  It began life as the biggerhammer DXF (originally from D Snider), but I've edited the heck out of it in the free drawing program Inkscape.


The following is a PDF version of the same template (and probably a better one for printing):
2008-11-23_233015_receiver_template_7_simplified.pdf

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  tr6guns

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Posted: November 24 2008 at 8:10am | IP Logged Quote tr6guns

This would be easier   http://www.biggerhammer.net/ar15/cad/  
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  Darkmeat

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Posted: November 25 2008 at 11:36pm | IP Logged Quote Darkmeat

Thanks, both of you!
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  mikey_mick

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Posted: December 03 2008 at 12:44pm | IP Logged Quote mikey_mick

Ok. I have been reading through this forum and I like the idea of making a receiver out of wood.  It would be easier for most people to complete a wood build because most people dont have the tools required to complete a metal build. Also, wood is easier to work with. 

I like this idea a lot and I think I'm going to construct the lower on my tube gun build with wood.  This would be much easier to do than the ar15 build because I could extend the parts of the receiver (what are those parts called?) down where the pins would hold the lower and upper together.  The pin holes on the ar upper are obviously too short  to allow a sturdy lower built from wood because the holes on the lower are too close to the top of the receiver.

I'm probably being Captain Obvious on some of these statements but I just thought I would add my two cents worth.

Anyway... Somebody else on this forum suggested making small metal parts to extend into the wood receiver on the ar15 build. I think this would be a good idea. I actually have some ideas on that that I plan to draw out and post here but I'm at the library so I cant do that right now.  I'm sure people are looking at me and thinking "why is that phycho looking at guns in the library?".  : )

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  Uraijit

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Posted: December 05 2008 at 3:05pm | IP Logged Quote Uraijit

You can get it in black!

http://cgi.ebay.com/HD-Polyethylene-Sheet-2-x-13-x-34-Black- HDPE_W0QQitemZ110291722623QQcmdZViewItemQQptZBI_Plastics_Equ ipment?hash=item110291722623&_trksid=p3286.c0.m14&_t rkparms=72%3A1205|66%3A2|65%3A12|39%3A1|240%3A1318|301%3A0|2 93%3A2|294%3A50
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  orions_hammer

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Posted: December 08 2008 at 12:19am | IP Logged Quote orions_hammer

Good suggestions guys, thanks!  I wanted my first lower to work with stock uppers, but if you were building your own upper you could definitely adjust the mounting pin dimensions to be a lot more wood-friendly.  A properly designed and finished wood lower made from decent wood should last the life of the gun, just like a gun's stock.  Wood prototypes really are a nice trick--it seems Samuel Colt also whittled wood prototype parts for his famous revolver.

And I actually already bought a 1.5x12x12" chunk of black HDPE from Grainger.  The price per square foot on that ebay auction is substantially lower, but shipping to Alaska almost doubles the price (!); while Grainger will ship to their local store for free.

My billet of black HDPE looks nice and solid, and aesthetically a black lower looks a lot better with a black upper.  It turns out AR lowers actually "stack" into an 8" wide by 1.5" thick by 2.75" high per receiver format--so you can get maybe five lowers from one square foot block of material! 

I've got to finish some AK builds first, but after they're done (and AK's are so quick!) I'm definitely going to mill out a few more AR lowers--I want at least one in black and tan each for rifle and pistol. I'm also trying to figure out how to do a modular magazine well, like this $500 version.  I've reprioritized my semiauto builds much higher due to the election, but it's still tough to find spare time!
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