Weaponeer.net
Welcome Guest
Not a member yet? Register Now! or Login
0 member and 34 guests currently online.
Search Forums:
Site Partners

This site is Gunny Approved

 


Site Login
Username

Password

Auto Login
Add me to the active users list


Forgot password | Register

Online Users
Total Users Online: 34

We have 0 member(s), 4 spiders, 34 guest(s), and 0 anonymous users online.

Members Online:
None.


[ View Full List ]
[Based on the last 10 minutes]

The most online was 215 and occured on March 28 2013 at 11:38am.
We had 5 members, 203 guests, 0 anonymouse users, and 7 bots online at the same time.
Todays Visitors (68):

AR Lower--from wood!
Weaponeer Forums : Home Build Projects

Posted in Home Build Projects
Members Viewing Topic: None

Post New TopicPost Reply
Prev Topic :: Next Topic
Author Message
  midmichigun

Avatar
CPT
CPT

Joined: March 01 2008
Location: United States
Posts: 1921
Posted: December 08 2008 at 1:25am | IP Logged Quote midmichigun

orions hammer

I like that modular magwell idea alot. Slick. Modular designs are the future.

Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View midmichigun's Profile Search for other posts by midmichigun
 
  orions_hammer

SM
SM

Joined: February 14 2008
Posts: 423
Posted: March 14 2009 at 7:19pm | IP Logged Quote orions_hammer

(Copied here from dcorb's MAC build thread, and expanded.)

I've been working on "the ARK", an AR lower that use AK fire control parts, since AR lower kits currently range from expensive to unobtainable, yet 922(r) means imported AK fire control parts are still plentiful and very cheap or free.  Here's the top and side plans for this AR/AK hybrid lower.  It's drawn with AR upper mounting pin holes and magazine well, AK fire control group and pistol grip, and a PPSh magazine adapter.  I can now mill out a complete wood prototype lower in about two hours, and they seem to work quite nicely; but I'm still working on a compatible pistol upper!


I've decided the right way to mill an AR lower is mostly with one machine setup:
  • Clamp the raw billet facing up.
  • Face off the whole top of the billet, where the upper will attach.
  • Glue on a template to the freshly-milled top face.
  • Use a spot drill to locate the corners of the magazine well.
  • Use a long drill to drill through the corners of the magazine well.
  • Use a long mill to chop out the trigger slot (BEFORE you mill away that part of the template with the fire control group pocket!)
  • Mill out the fire control group pocket and magazine well.
  • Test fit the fire control group and magazine, open up where needed.
  • Mill out the upper mounting slots.  Test fit the upper right there on the mill.
  • NOW unclamp the lower, and do the finish milling (all the holes, the pistol grip, magazine release, buffer tube hole) on the other sides of the lower.
The advantage of doing all these in one setup is you don't have to swear at your dial indicator for half an hour just to get the lower reciever aligned properly before each step--it's already clamped in exactly right.

Milling the fire control group pocket, after facing off the top of the receiver:


Here I'm drilling the fire control group holes from my billet of hickory:


Here's an ordinary imported AK FCG group sitting inside the milled FCG well.  It works!


Here's the same lower, viewed from the side, with Romanian bakelite pistol grip attached:


You notice I've got no buffer tube tower on my pistol lower.  This is basically just paranoia on my part--since the rules on "constructive possession of a Short Barreled Rifle" seem very fuzzy to me, I've decided I want to make an NFA violation physically impossible with my parts.  This means there shouldn't be any way to attach a buttstock to a pistol lower; hence no buffer tube hole.  My pistol uppers will contain their own recoil spring, and extend over the buffer tube area of the lower, making it physically impossible to attach one of my pistol uppers to a rifle lower.

Here's where I am with the pistol upper, bent up from a chunk of steel sheet.  The upper blank is too long to fit on a 8.5x11" template, so I had to use legal size 8.5x14" paper!  Here's the first two easy bends, made in my little bending brake.  The little tabs will fit down into the lower receiver, and take 1/4" pins:


Here's three bends:


I made the fourth bend over a 1.25" steel square mandrel, also the stock for making the bolt.  I now realize I should have wrapped a few layers of tape around the mandrel, so the bolt would have a little bit more clearance to slide freely--right now, the 1.25" bolt is a tight fit!


Here's a mockup of how the freshly-bent upper, hickory prototype lower, and PPSh 43 magazine will fit together.  I *really* need to chop down at least a few PPSh 43 magazines to a more reasonable size, like 15-20 rounds!


My plan at this point is to use another CZ-52 barrel and bolted-on aluminum trunnions, just like my blowbAK pistol.  I'm still trying to figure out how exactly to machine the magazine well adaptor, probably from two mating pieces of HDPE.  I also bought a 45acp barrel and some Thompson mags, for a 45 version, but the 45 barrel geometry is a lot more complicated, and I'm having a hard time figuring out how to machine the forward trunnion for that version.
Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View orions_hammer's Profile Search for other posts by orions_hammer
 
  midmichigun

Avatar
CPT
CPT

Joined: March 01 2008
Location: United States
Posts: 1921
Posted: March 14 2009 at 11:24pm | IP Logged Quote midmichigun

o-hammer,

I was wondering what you have been doing... good to see ya posting some more ideas.

I like the ARK concept. I was just batting some of that idea round. I have been purchasing alot of AK FCG's... just because of adaptability and cost. Just like ya said.

I am getting ready to burn out a few conventional AR lowers... what drill bits are you using for the mag corners?

And as a special favor... when you are further along, would you be willing to post a dimensional dwg of your lower? You are doing some tremendous work there!

As far as 922r... please make sure you are using AMERICAN WALNUT... you never know about some of the other woods out there. God forbid you get some Canadian pine or Brazilian teakwood.  I also beg you... don't use bamboo.

Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View midmichigun's Profile Search for other posts by midmichigun
 
  orions_hammer

SM
SM

Joined: February 14 2008
Posts: 423
Posted: March 15 2009 at 12:38am | IP Logged Quote orions_hammer

Luckily, it's a pistol build, so 922(r) does not apply!

I usually drill out the magwell corners with 1/8" bits, then use a long 3/8" or 1/2" end mill on the rest of the receiver.  I bought some extra long 2 flute high-helix aluminum end mills for aluminum, and have been using them for wood and plastic with excellent results on my Grizzly mini-mill.

The definitive walkthrough and reference for fabricating AR lowers, from setup to anodizing, is Ray Vin's online PDF "book".  He sorta assumes you've got a digital read out (DRO) mill though; without this you'll be stuck with calipers and templates (like me!).

As far as blueprints, I started with the "D Snider" prepared dimensioned AR15 blueprints, available in PDF or DXF format at biggerhammer.  (I don't provide a link there because annoyingly, the same AR page links to plans for an oh-so-illegal drop-in auto sear or "DIAS", which nobody with an AR and a mill should ever even look at.  Seriously.)  I use the awesome free drawing program Inkscape to design and edit my templates.

Here's a PDF template of my AR/AK lower, wearing a matching Tokarev upper:
     2009-03-15_002834_upper4.pdf

It's a life-size PDF, ready for printing and gluing.  I don't have any actual dimensions (e.g., 1.037"+-0.003") because I normally mill straight from the template.  This seems to work nicely with any chunk of wood or plastic a bit over 1.6" thick and 9" by 2.2".
Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View orions_hammer's Profile Search for other posts by orions_hammer
 
  dcorb

Avatar
BG
BG

Joined: November 28 2004
Location: United States
Posts: 10168
Posted: March 15 2009 at 8:07am | IP Logged Quote dcorb

This is looking good !

I am seeing all sorts of ideas I may borrow from this project.

Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View dcorb's Profile Search for other posts by dcorb
 
  midmichigun

Avatar
CPT
CPT

Joined: March 01 2008
Location: United States
Posts: 1921
Posted: March 15 2009 at 1:43pm | IP Logged Quote midmichigun

O-Hammer,

Thanks a bunch. Great minds think alike! Keep chugging along with your ideas. I will post more later... currently fighting with the wife!

Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View midmichigun's Profile Search for other posts by midmichigun
 
  orions_hammer

SM
SM

Joined: February 14 2008
Posts: 423
Posted: March 21 2009 at 4:20am | IP Logged Quote orions_hammer

In designing my upper's trunnions, I started thinking...

In a blowback gun, a huge fraction of the recoil energy ends up in the slide.  Because pistols aren't long enough for the recoil spring alone to have any chance of stopping the slide, the slide ends up dumping its momentum into some part of the frame. 

If the slide is stopped by the part of the frame directly over your hand, the slide's impulse will tend to rotate the gun, which is muzzle flip.  But it seems like if the slide was stopped far out in front of the frame, the slide's impulse would mostly be directed straight backwards, giving less muzzle flip but more of a hand-pounding.

Do y'all think this an important effect in real life?


Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View orions_hammer's Profile Search for other posts by orions_hammer
 
  orions_hammer

SM
SM

Joined: February 14 2008
Posts: 423
Posted: April 01 2009 at 3:50am | IP Logged Quote orions_hammer

Over the weekend, I fabricated the front trunnion.  It began life as a 1.25x0.75x1" chunk of aluminum, drilled and then bored out to 0.464". 


I also milled out a little clearance in front, which I was planning on using for a recoil spring, but I don't quite have enough room there, so I'm going to put the recoil spring on top of the barrel.


The CZ-52 barrel is 0.465" outside diameter, so it's an interference fit.  I chilled the barrel in the freezer, heated the trunnion up with a torch and then pounded the barrel down through it--the barrel seems to really solidly stay on there!


The trunnion is designed to slide into the sheet metal upper I bent above.  To hold the trunnion in place, I clamped, drilled, and tapped it for four short 1/4" screws:



The barrel's actually a little shorter than I'd planned, but I kinda like the look of the recessed muzzle:


The bolt began life as a rusty chunk of 1.25" square steel:


I used my harbor freight 4" angle grinder (mine hasn't burned out yet like dcorb's!) to face off the sides and round down the corners until the bolt slides nicely in my upper:


The next step was to drill the firing pin hole, using a long 9/64" aircraft drill bit.  The bit wandered a little (maybe 1/8" over the 2.5" bolt), but the only critical location is the location of the firing pin on the bolt face, which I marked with a transfer punch first.


I need a spring to keep the firing pin pulled back off the bolt face (it'll hang up the round sliding up the bolt face, unless you want to fab a lower lip on the bolt).  I also need some sort of firing pin retaining device.  Solution?  The firing pin spring doubles as a firing pin retainer, and lives inside a 5/16" hole in the back of the bolt, held down by a small chunk of threaded rod with a hole in it:




The firing pin's just a chunk of 1/8" drill rod.  I'll harden both ends if the geometry turns out OK.  It needs a tiny 1/64" hole to hold the firing pin spring:


Here's the spring, wound from 0.025" music wire. 


Here's the underside of the upper, showing the bolt, back of the firing pin, and firing pin retaining screw.  The firing pin spring buried in there seems to work nicely!


Here's the bolt's breech face shot from down the barrel, showing the firing pin.  It's pretty darn close to being exactly on center!


The next step is to mill out the bottom of the bolt so it will clear the magazine's feed lips.  I used permanent marker, the poor man's Dychem marking fluid, to mark out the area to mill away:


I started with my only carbide tooling, a 3/8" 4-flute end mill.  The initial slot was really slow, but then I could shave off a more reasonable cut in each subsequent pass:




I switched to a longer 1/4" end mill to dig out the area around the magazine lips.  The cut is rectangular instead of half-round like factory bolts, but I don't think the outside of the bolt is under any serious stress, and there's a huge amount of metal left behind the breech face anyway.


Here's the finished bolt.  I don't think I've ever made so many steel chips in one milling setup!  I need to check how it'll ride against the hammer; the back "bump" has to be high enough to push the hammer down enough to engage the disconnector.


To do:
  • Drill the upper mounting pin holes in the upper.
  • Single-shot test fire!
  • Fabricate a magazine well block for the PPSh magazine.
  • Test feed, tune magazine position and feed ramp (I need to make some 7.62x25 snap caps for this!)
  • Figure out a recoil spring, extractor, and ejector setup.  I still haven't decided whether to dump the recoil energy into the front or back trunnion.
  • Semiauto test fire!
Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View orions_hammer's Profile Search for other posts by orions_hammer
 
  dcorb

Avatar
BG
BG

Joined: November 28 2004
Location: United States
Posts: 10168
Posted: April 01 2009 at 9:59am | IP Logged Quote dcorb

Great progress!

I could not live without my angle grinder so I picked up yesterday. On sale for $19.99. I think the screwes on the head came lose so it added ply to the gears. I will keep the screws tight on the new one.

Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View dcorb's Profile Search for other posts by dcorb
 
  weaponeer

Avatar
Admin Group
Admin Group

Joined: July 16 2005
Location: United States
Posts: 25293
Posted: April 01 2009 at 11:45am | IP Logged Quote weaponeer

I agree great progress
Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb


__________________
Weaponeer.net survives on donations made each Month by the membership. if we don't get enough donations, our hosting provider turns off the website, and only turns it back on after the hosting fee's have been paid. Please... every donation counts
  Status: Offline
View weaponeer's Profile Search for other posts by weaponeer Visit weaponeer's Homepage
 
  midmichigun

Avatar
CPT
CPT

Joined: March 01 2008
Location: United States
Posts: 1921
Posted: April 01 2009 at 11:58am | IP Logged Quote midmichigun

o-Hammer!

You are an artisan, craftsman and scholar! I just got a huge chuck of metal for free. Its around 2" square stock probably 18inches long. I was thinking about how to turn it into a bolt.... now I see!

I like your upper that you posted. I was debating about using a square tube for a similar purpose. I bought a Tommy Gun wood stock and now MUST make a gun for it! Isn't that strange how we sometimes build around a single component? And then later discard it when finishing the build?

Anyways, I am seriously impressed by your progress. You now have me torn between NEXT building a sten or suomi or a whatchamacallit!

I will mull over your contemplations on forces derived from the recoil impulse. There is something I want to add... let me have my brain wander around for a few.

Good posts!

Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View midmichigun's Profile Search for other posts by midmichigun
 
  orions_hammer

SM
SM

Joined: February 14 2008
Posts: 423
Posted: April 01 2009 at 2:18pm | IP Logged Quote orions_hammer

On thinking about it, I don't think the horizontal position of slide/frame impact affects muzzle flip after all.  You're trying to minimize the torque caused by the slide's forces on the frame.  Torque is calculated as the cross product of the lever arm vector (impact position) and force vector (along the slide's velocity): T = L x F.  So moving the slide impact point by a vector I changes the lever arm, which changes the torque to:
    T = (L+I) x F
which because cross product distributes over addition is:
    T = L x F + I x F

The new factor there is I x F.  The slide's moving straight back, so F is horizontal.  The cross product of parallel vectors is zero, so if we move the slide/frame impact point I horizontally, I x F is zero, so the torque stays the same.

However, if we move the slide/frame impact point vertically, that changes the torque a lot (I x F is biggest when I is perpendicular to F).  The bottom line is muzzle flip in blowback pistols is mostly a function of the height of the slide/frame impact point, which should be as low as possible.  In breech-locked pistols,  muzzle flip is mostly a function of the height of the bore axis, which I think is pretty well known.
Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View orions_hammer's Profile Search for other posts by orions_hammer
 
  midmichigun

Avatar
CPT
CPT

Joined: March 01 2008
Location: United States
Posts: 1921
Posted: April 01 2009 at 4:48pm | IP Logged Quote midmichigun

O- hammer,

Sounds like you have technical training.

Due to your discourse, this is why I am suprised at some attemps at blowback pistols. It looks like some designers went for MAXIMUM muzzle flip! That being said, a few well placed engineering equations eliminates ALOT of guesswork.

Right now I am birthing an AK in the garage and came in for something hot (its cold outside.. .with enough humidity to make it seem very cold). Anyway, I will follow your thread as it progresses.

Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View midmichigun's Profile Search for other posts by midmichigun
 
  orions_hammer

SM
SM

Joined: February 14 2008
Posts: 423
Posted: April 13 2009 at 2:02pm | IP Logged Quote orions_hammer

Work's been killing me, so progress has been slow.  I welded up a little rear trunnion / bolt stop, which looked a lot nicer before welding:


I welded a similar 0.5x0.5x0.420" solid block to the thin sheet metal on the front mounting pin:


I then used my hickory pistol lower as a drill jig to drill out my front and back mounting pin holes:


As you can see, the hickory lower split right at the front mounting pin hole--the same place as the pine ABORTION!  The problem this time was a tiny 0.010" lip of steel sticking out maybe 1/32" after drilling; because the lower is a tight fit, something had to give to pull the upper off.  Turns out 0.010" of mild steel is stronger than 0.250" of solid hickory!


On the plus side, the small amount of missing wood above doesn't seem to cause any problems (there's still plenty of wood left), and the lower and upper hold together tightly!

With lower and upper pinned together (with two simple 1/4" cold rolled pins), I checked the bolt travel, and ended up having to file off a little bit of metal so the bolt will clear the fire control group, in particular the little hook sear sticking up from the AK trigger.  I also took off a little metal over the hammer.  If the bolt hangs down too low, the hammer will hang up on it, and the bolt will jam up; if it doesn't hang low enough, the hammer might not get pushed down far enough to reach the disconnector, resulting in hammer follow (and possibly a slamfire!).  I also managed to not take any photos of the tuned-in bolt!

I made a little sheet metal jig to help me figure out how to build the magazine well block.  Lining up the magazine well has always been the Achilles' heel of my semi-auto builds, so I wanted the ability to easily adjust the position of the magazine until the thing feeds nicely *before* I build the permanent block.  So I cut a little chunk of sheet metal that fits tightly into the magazine well, and then clamped the magazine to that:


I eventually put on another clamp to keep the magazine from rotating in the magwell:


With the jig in place, I carefully tuned the magazine location for reliable feed:




Bottleneck rounds sure feed nicely!  Just for paranoia's sake, I ended up making a little feed ramp wrapped around the chamber, seen above.  More details on that to come.

Finally, with the magazine in exactly the right place, clamped to the jig, in turn sitting in a known location in the magazine well, I carefully bent the top tab and removed the jig + magazine, and traced the correct location of the magazine in the well:


Now the hope is that I can build a little magazine block from this paper pattern, drop it in the magazine well, and it'll feed reliably.  We'll see!


Finally, I noticed this FN FNC full-auto carbine.  $7,100 is way more than I ever want to spend on any gun, but it's sure a cool AR-ish design, and the ugly welds and straight-sided billet lower looks a lot like the guns I've been building lately!
Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View orions_hammer's Profile Search for other posts by orions_hammer
 
  midmichigun

Avatar
CPT
CPT

Joined: March 01 2008
Location: United States
Posts: 1921
Posted: April 13 2009 at 6:04pm | IP Logged Quote midmichigun

O-Hammer,

Looks like you are making ALOT of progress.

Don't worry about the look of your welds and the intermediate stages... what counts is the end result. We are all just enjoying your fabrication process. And I do look forward to the end result!

Keep going!

Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View midmichigun's Profile Search for other posts by midmichigun
 
  orions_hammer

SM
SM

Joined: February 14 2008
Posts: 423
Posted: May 12 2009 at 1:00am | IP Logged Quote orions_hammer

This project isn't dead yet!  I milled out a little channel in the bolt face for the extractor to ride in:


I also cut out a little chunk of steel for the extractor itself:


It seems to work OK, here holding one of my orange-painted dummy rounds (recycled bullet epoxied into spent shell casing).


I also fabricated a little magazine well block, using the template I determined above, glued onto a chunk of my favorite blue HDPE cutting board:


There's almost no "meat" to clamp onto, but polyethyelene mills so easily the block didn't slip out of the vice:


I'm really happy with how securely the magazine block holds the magazine in place!


I actually milled out the magazine latch clearance into the receiver and magazine well block at the same time.  The magazine is just there to keep the magwell block in the right spot for cutting (no magazines were harmed during the making of this slot).


Here's how the magazine catch works: it sticks up through the magazine well block (also holding the mag block in place!), and holds up the back end of the magazine.  The close end in this picture is threaded for a little #10-32 rod, which runs through the receiver to a typical AR-style magazine release button.


Here's a view from above, showing my lumpy machining on the magazine well block (I gotta work on my clamping), and the mag latch:


I also milled the lower receiver's sides down a little, because 1.6" wide is just too fat!


Here's where we are.  The magazine now latches securely in place, and the hickory receiver is now a svelte 1.3" wide.


I'm trying to keep myself from test firing it until I've got the recoil spring sorted out, along with a decent charging handle, so I can save my ammo for a full-up test.  I'm not sure I can wait, though!

Also, I visited a gun show wearing my blue HDPE AR lower from a single-point sling on my chest.  I got a lot of stares and questions, and had several interesting discussions with fellow machinists and gun nuts.  One licensed seller was convinced that I needed a federal firearm manufacturer's license to make these--c'mon man, read the FAQ!  Nobody was selling bare AR uppers, though, so I guess I gotta keep making them myself!
Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View orions_hammer's Profile Search for other posts by orions_hammer
 
  orions_hammer

SM
SM

Joined: February 14 2008
Posts: 423
Posted: May 17 2009 at 12:56am | IP Logged Quote orions_hammer

I've got the recoil spring riding on top of the barrel in this design.  I always have a hard time figuring out where to put the recoil spring--the AK trigger group doesn't leave much room at all behind the bolt, and I'm trying to keep the barrel as low as possible (to fight muzzle flip).  So that leaves around the barrel, on top, or to either side.  For the correct bolt mass of a little over one pound, I've got a lot of space on top of the bolt, here showing the bolt sitting in front of the barrel and aluminum front trunnion:


So I welded on a little strap of 1/8" by 0.400" steel, to hook onto the recoil spring in front.  Here the bolt is upside down and post-weld slow cooling on a firebrick, buried in chunks of charcoal both to stop rust and to try to get a little carbon into the steel.  I'm really liking oxy-acetylene gas welding, though I'm still pretty bad at it, especially on a peice like this where one side is big (and cold), and the other side is tiny (and hence gets way too hot).


I then wound my first and best looking of about four recoil springs:


That's a little recoil spring guide rod that runs over the barrel. 

Here's the whole bolt-barrel-spring assembly, which I've learned I need to put together *before* sliding it down into the upper receiver!


The return spring seems to work fairly nicely, although I'm still having a hard time finding the happy medium between a stiff uncockable bolt, and a too-weak return spring where the bolt hangs up on the AK fire control group.  I've had this problem with my "real" AKs too though!

I tried a couple of things to fight this, from smoothing out the back of the bolt (I think I milled away a little too much metal to leave a nice smooth ramp), to smoothing the hammer's surface.  I even added a little block to the AK hammer so the disconnector/triggersear hammer travel distance isn't so ridiculously huge: this little block took it from 1/4" down to a 1/32" or so.


While I was at it, I hardened my firing pin, and tempered it to a light blue.  The firing pin is made from drill rod, which is hardenable carbon steel, but it ships in soft annealed normalized state, so even dry-firing caused the soft firing pin to begin to mushroom where it's hit in the back.  I hardened it by heating to orange hot (the "critical temperature"; a magnet no longer sticks to the metal) and quenching in water, which leaves the part very hard but brittle.  I then tempered with a propane torch in air until the part hit blue, which is a springy but still hard temper:


This stopped the pin from getting battered (too soft), and it hasn't broken (too hard/brittle), so I think I've basically figured out hardening steel!  On thinking about it, I probably should have held the firing pin from the striker end during tempering, since the plier jaws keep the metal under them a little cooler, hence harder, which I want on the end not the middle.

Other odds and ends... I'm a lot happier test-firing with a safety, so I milled out a little safety from 1/4" rod, and welded a little lever on the end.


The safety slides down through the receiver, and holds the back end of the AK trigger down.  Here's the hole where the safety fits.  You can just see the AK trigger's back end sticking up.


You rotate the safety lever down to let the trigger group move, and rotate it back (just like an AR) for fire.  Also, I just realized the safety is actually reversible for left-handed operation, by just sticking it in the hole from the other side!  I eventually aught to drill a little plunger hole in the receiver and file some flats on the safety pin for a positive "click" into place (AR style).  But it seems strong enough to stop the trigger even when just friction-fit in the hole:


Here's the safety installed, along with all the other parts in this build!


Here's the crucial bolt-barrel-spring assembly, disassembled:


And assembled.  The little triangular slot in the upper is for an ambitious non-reciprocating charging handle that just didn't work out, so I cut a big wide opening in the top for an M3 greasegun-style finger hole!


ARK lower and Tokarev upper fully assembled.  I really like the way the pistol balances, although weighing 4lb unloaded, it's definitely a man's gun!


Here we are, strapped to the remote test jig and ready for test fire!


Rounds seem to feed beautifully:


The firing pin is hitting off-center a little bit, but I get a bang every time I pull the trigger!  Extraction is fine, as a blowback action uses chamber pressure to push the bolt back, but ejection is very spotty.  My idea on ejection was to use the firing pin as an ejector, Hi-Point style, when the bolt+round hit the rear trunnion, but apparently this doesn't work dynamically, because I get at least 15% stovepipes and other ejection failures.  Does the PPSh 43 have a fixed ejector pin?


The brass looks fine, although it's amazing it's even firing hitting that far off the center of the primer.  I think I can fix this by adjusting my front trunnion mounting screws.


Trust in the system's basic safety thus esablished, I fired the gun offhand a few times.  Recoil is almost nothing compared to my CZ-52; the big round AK grip and heavy overall weight make 7.62x25 a lot more comfortable to fire!  The round actually sounds a little different too, with more of a shotgun-like bass thud than the smaller pistol's "snap".  I'll have to compare the two side-by-side once the new pistol is running right.

Sadly, it only took about fifteen rounds for my hickory lower receiver to crack, right where the recoil-absorbing rear trunnion bolts in.  Bummer.


I've filled the crack with epoxy temporarily, which is drying now, but a long-term solution is either to mill a new lower from a tougher material, or else use a lower-punishment rear trunnion design like a big stiff spring.  It ticks me off, because I carefully secured a 1/8" thick recoil buffer of Sorbethane rubber in front of the rear trunnion to help absorb impact, but wood still let me down.  I'm about done trying wood lowers if they break this easily!  
Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View orions_hammer's Profile Search for other posts by orions_hammer
 
  orions_hammer

SM
SM

Joined: February 14 2008
Posts: 423
Posted: June 14 2009 at 4:03am | IP Logged Quote orions_hammer

I bought a little Casio EX-FC100 camera which shoots slow motion video at 210fps, 420fps, or 1000fps, and filmed my blue "AR from a cutting board" firing in slow-motion, showing the empty shells lazily floating away.  Annoyingly, the blue AR is having cycling problems in hot weather due to the plastic receiver expanding too far for the FCG to quite work right.  It works fine between -40F and room temperature, but on a warm day in the hot sun after firing a few rounds, the trigger won't fully reset after each shot.  I've got a design fix, but I'll need to mill out a new lower for it...

I've also got my Tokarev pistol pretty close to working again.  I repaired the cracked wood lower with epoxy, and am working on a new spring-based rear trunnion that should absorb recoil energy better. 

Speaking of slow motion and absorbing recoil energy, I've been playing with the new freakishly strong neodymium magnets and their eddy current effects.  Any moving magnet induces an electrical "eddy" current to flow in any good conductor (copper is better than aluminum is better than steel), and the Lenz force from this current opposes the magnet's motion, causing weird slow-motion movement in gravity.  The stronger the magnet, and the faster the magnet moves, the bigger the Lenz force.  This could make a good self-adjusting recoil buffer for a semi-auto gun: just attach a few magnets to the bolt, and when you fire beefy rounds, the (fast-moving) slide should automatically dump velocity as eddy current (e.g., in an aluminum frame); yet wimpy practice loads wouldn't lose much precious energy.
Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View orions_hammer's Profile Search for other posts by orions_hammer
 
  weaponeer

Avatar
Admin Group
Admin Group

Joined: July 16 2005
Location: United States
Posts: 25293
Posted: June 14 2009 at 11:53am | IP Logged Quote weaponeer

great progress on the build!

I love the slow motion videos...  great for testing to see what is going on.

Now the Neodymium buffer idea is a great idea...!

Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb


__________________
Weaponeer.net survives on donations made each Month by the membership. if we don't get enough donations, our hosting provider turns off the website, and only turns it back on after the hosting fee's have been paid. Please... every donation counts
  Status: Offline
View weaponeer's Profile Search for other posts by weaponeer Visit weaponeer's Homepage
 
  chapaev

MSG
MSG

Joined: March 26 2007
Posts: 211
Posted: June 14 2009 at 1:57pm | IP Logged Quote chapaev

hehe, nice idea about the Eddy currents, but akin to the rail gun - once you actually do the numbers it won't work practically
Agree Disagree Funny Informative Polite/Nice/Friendly Useful Optimistic Artistic Late Bad Spelling Bad Reading Dumb
  Status: Offline
View chapaev's Profile Search for other posts by chapaev
 
<< Prev Topic Home Build Projects Next Topic >>

<< Prev Page of 6 Next >>
  Post ReplyPost New Topic
Printable version Printable version

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot delete your posts in this forum
You cannot edit your posts in this forum
You cannot create polls in this forum
You cannot vote in polls in this forum
Forum Jump


This page was generated in 7.4683 seconds.