Jul 30, 2012
The CNC 1911 I’ve been working on currently looks like this …
… which is pretty much how it looked four months ago. It still needs a fair bit of machining in order to get all the parts to fit. The problem is what little time I have for hobbies has been taking up by other things. First I decided to paint my basement, and before that got finished, I discovered my car had a head gasket leak.
Unfortunately, because of the type of engine, its age, and high mileage, it makes more sense to do an engine swap or full rebuild than to just replace the head gaskets. The main problem is that the engine has paper seals at the bottom of the cylinder liners, and there is a good change they will break when you remove the cylinder heads, which you may not know until you put everything back together and run the engine. If they break, to replace them, you have to pull the engine and remove the pistons. If you’re going that far you might as well do a full rebuild.
Feb 15, 2012
UPDATE (From Sebastian): If you choose to make a lower from Delrin, you’re safest using Food Grade Delrin, which is highly x-ray detectable. While I believe ordinary Delrin should be dense enough to be detectable by the modern equipment used for airport screening, it is unlawful to make a firearm, the major component (which includes the receiver) does not show its true shape on the types of x-ray equipment commonly used for airport screening. Be careful about the types of plastic you choose. Jason did not mention this in the original post, but I am updating now as a warning. You are responsible for compliance with federal law.
After finishing the aluminum bolt together lower, I went back to trying to make a single piece lower out of Delrin.
The process described below is my third attempt. In the first two I had alignment problems which made the right and left sides not quite match up and gave an egg shape to some of the holes.
I also switched from PyCAM to Deskproto. While the people working on PyCAM have done a nice job so far, it needs more work. For the kind of things I do its just barely useable. Deskproto has all the things that drive me nuts in PyCAM fixed, and while its commercial, the cost, especially for a hobby license, is quite reasonable (less than an AR-15 parts kit) and it doesn’t use any nasty DRM, so after you’ve purchased it you don’t have to get permission from the mother ship to reinstall it or install it on a different computer.
In Deskproto, I added support bridges to the model that run through the buffer tube hole and magazine well.
This way I could use the outside edges of the Delrin block for holding down the part while machining the left and right sides, but don’t need to do extra machining steps later to remove the supports.
Update: Here is the 3d model of the lower (originally from www.cncguns.com) and the Deskproto project I used to generate the tool paths.
I used an inexpensive Chinese import band saw to cut the block of Delrin down to an appropriate size….
Jan 19, 2012
To finish up the AR-15 pistol I milled on my CNC machine, I decided to try Alodine and then Duracoat instead of anodizing. I wanted a process I could do myself, and while I probably could have managed anodizing at home, the process seemed more complicated than I wanted to get into right now, nor do I have a good place to set things up. Buckets of acid wired to a high current power supply aren’t a good things to have lying around with small children in the house.
The basic process is to coat the parts with Alumiprep (a phosphoric acid based etcher/cleaner), wait a few minutes, rise with water, coat with Alodine, wait a few more minutes, rinse with water, let dry, and then airbrush on Duracoat.
The first attempt at applying Duracoat didn’t go so well. After I was done I noticed a few tiny areas around some bolt holes that I missed. I decided to just mix up a little Duracoat in a cup and do some touch ups with a brush. This turned out to be a bad idea for two reasons. One, Duracoat doesn’t look the same when its brushed on. The instructions do say only to airbush it, but I though that for such a small area (1mm so square) it wouldn’t matter. But it does. Two, Durocoat dissolves plastic cups. After I was done when I picked up the cup the bottom fell out and I ended up with paint all over my work table. Luckily Duracoat wipes off pretty easily if you get it before it dries.
Then when I went to assemble the gun, even though I waited the recommended 24 hours for the paint to dry, it chipped off in a few places. Argh! So I airbrushed on a few more coats..
…and then put the parts in the oven at 120 degrees for a hour to speed dry it. This time there was no chipping and no funky spots from the brush touch ups.
Dec 23, 2011
In the comments of my last post, Grego pointed out firearmfiles.com where there are CAD files for a multi-part AR-15 lower where all the parts fit nicely in the working area of a Taig mill. It also doesn’t require any special jigs or the crazy long, thin drill bit for making the hole for the bolt catch pin. Since I wouldn’t need to make any jigs or buy any drill bits to finish that version, I figured I’d try it before continuing on with the normal one-piece lower. I went straight to aluminium since I had a slab the right thickness.
Starting to mill the left half of the lower out of a slab of aluminium.
After the end of the roughing pass, where you can see some pretty crappy edges because I was making cuts that were too aggressive for the Taig.
After a couple of contouring passes to give it the right shape.
After the finishing pass.
Now, use a band saw to cut off the excess aluminium block, flip the part over, and start roughing the other side.
The four completed parts of the lower and the bolts that hold them together.
The finish is funky on the inside of one of the halves because, due to software issues, I was having trouble getting accurate Z positioning. I managed to fix the problem for the other parts.
The assembled lower.
With the fire control parts installed.
And, finally, the completed firearm.
That’s everything except the bolt catch. Since the bolt catch is held on by a press in roll pin, I’m going to leave that off until the lower is painted, rather than have to press it out again to do the painting. My plan is to treat with Alodine and then spray on Duracoat. I think that should work out pretty well, and it is easier than anodizing.
I modified the design a bit from the original. My version is thinner (though still not as thin as a standard AR lower), and instead of using a custom extended selector switch, I cut a recess so that a standard selector switch would fit.
Now that that’s done, I’m going to try to finish the one piece Delrin lower. But first, I think I need to make some sort of enclosure for the mill to keep the chips from getting all over the place. When working on parts that big, it makes a hell of a mess. Normally, when I use the mill for work, I’m just working with small Delrin parts, making cutouts in aluminium sheets, or etching small printing circuit boards.
Nov 17, 2011
The following is a post by my friend Jason, who is not a regular contributor, but has posted in the past on our 3D magazine printing project. I thought this would be an interesting addition, and a demonstration of how technology is making gun control a virtual impossibility. Below is his post.
I’ve been meaning to try this for a while now (using the AR-15 lower receiver solid model from http://www.cncguns.com/downloads.html), but I wanted to do it using all open source software, and was having trouble finding something that could generate tool paths from the AR-15 model. PyCAM seemed to be the best bet, but whenever I tried it on very complex model it would very quickly use up all the memory (8GB of ram plus 8GB of swap) and bring the computer to a screeching halt.
I recently had a project at work where I needed to make a much simpler part, and not wanting to go back to using BobCAD under Windows, I gave HeeksCAD and PyCAM a try. It worked out pretty well, and in the process I discovered and fixed a memory leak in PyCAM
PyCAM is still horribly inefficient in its memory usage, but with the memory leak fixed and a new computer with 16GB of ram I was finally able to generate decent toolpaths for the AR-15 lower.
So now I’m all set to give this a try, but I can’t find the block of aluminum I had intended to use. But I did have a block of Delrin left over from an earlier project, and Delrin should be strong enough to handle a .22 cal upper. So I’m trying to make a delrin lower first for use with a .22 cal upper, and if that works I’ll order some aluminum and make another lower for use with a .223 upper.
Note that I’m not an expert in material properties (nor a machinist) so don’t take the above statements to mean that its safe to fire an AR-15 made of Delrin. Do at your own risk.
The original block of Delrin.
After a first pass rough cut with a 0.25″ diameter end mill.
After a second pass using a 0.125″ end mill and a much smaller grid size.
After a finishing pass with a 0.125″ ball nose mill.
Now things are going to get a little complicated. I’m going to have to make some sort of jig to hold the part in place while I machine the other side.
Mar 10, 2011
My goal was to try to come up with a design where if you had one of these low cost ABS printers, you could just download the file, print the parts, superglue them together, add the spring, and you’d have a working 32 round magazine.
Right now I’m at the point where you can download the file, print the parts, superglue them together, sand like crazy, add the spring, and you would have a somewhat finicky 20 to 25 round magazine.
The problem I’m having is a combination of ABS being a bit too flexible and software issues with tool path generation. The walls of the magazine needs to be at least a couple millimeters thick and solid in order to prevent excessive flexing. The tool path generating software (Skeinforge) doesn’t deal well with thin solid walls whose thickness is some uneven multiple of the print head width. For example, if the wall thickness is 3.5 times that of the print width, it will generate one pass along the outer surface of the wall, one pass along the inner surface, and then one more interior pass against either the outside or inside surface. But that leaves the remaining 0.5 of the wall thickness unfilled, and you end up with a hollow very flexible wall. What it really should be doing is a zig-zag like pass over the wall interior. I can trick Skeinforge into filling in the walls completely by lying to it about print head width, but the wall surfaces end up off a bit and then I have issues with the magazine fitting in the mag well or the rounds fitting in the magazine. So I’ve been tweaking the wall thickness and print head size setting in order to try to get Skeinforge to do what I want.
The right solution is probably to modify Skeinforge so that it will generate the correct tool paths from the correct model, rather than adjusting the model to try to make up for Skeinforge’s deficiencies.
Other than the flexing issue ABS seems to be strong enough. I have one magazine I printed which can hold the full 32 rounds and feeds fine, but it bulges so much when fully loaded that it won’t fit in the mag well. The one magazine rupture I had was due entirely to a mistake in the cad file that caused the printer not to correctly bond the insert pieces (where one section of the mag body fits into another) to the rest of the part.
Apr 25, 2007
I discovered Calico is still in business. They managed to survive the hi-cap magazine ban. So I gave them a call.
While they have never heard of the exact failure mode I had, they said that with the older bolt design (which my gun has), they have seen a few rare cases of the gun firing out of battery as the bolt is closing. As Armed Canadian pointed out the bolt was damaged when the shell ruptured. For around $100 they’ll repair the bolt and upgrade it to the current design. If I ship them the whole gun they’ll clear the barrel, inspect everything, and test fire it.
The people in charge of the gun club where the accident occurred are interested in what happened, so I’m going to do a little show and tell there (any maybe give them my eyeglass lens to stick up on the bulletin board), and then I’ll probably ship the gun off to Calico.
Apr 23, 2007
Yesterday I was shooting my Calico M950.
This is a 9mm pistol with a 100 round helical magazine that feeds from the top.
I had a round that failed to go off when I pulled the trigger. I waited a minute to make sure it wasn’t a hang fire, cleared the round from the gun, set it aside, and finshed shooting the contents of the magazine.
I removed the magazine from the gun, made sure it was empty, locked to bolt back (it doesn’t lock automatically) and made sure the breech was empty.
So now I had this one bad round left. I could see the dimple on the primer from the firing pin, so it was struck. The round otherwise looked normal. I figured I might as well see if I can get it to fire (this was probably bad move #1).
I dropped the round into the breech, released the bolt, and without inserting the magazine (this was bad move #2), aimed, and fired.
There was an exceptionally bright flash from the top of the gun. My first though was…
You know, it’s probably not a good idea to fire this particular gun without the magazine inserted.
Then I felt something strike me in the face. My next thought was….
Yes, its definitely not a good idea to fire this gun without the magazine inserted.
At this point I’m thinking that the shell, instead of ejecting downward, ejected upward though where the magazine feeds and hit me in the face. This shouldn’t happen though. The ejector pin is part of the bolt assembly, and should function even without the magazine.
I set the gun down, and reach up to check my face for damage. My next though was…
Wow. Thats a awful lot of blood.
I don’t however, feel any major damage. So where is all the blood, now all over my shirt and all over the floor, coming from? Teeth! Check teeth!. Ah, good, all my teeth are intact. The inside of my upper lip does feel a little strange though. So, ok, shell ejects backwards, hits my upper lip, pushing it into my teeth, tearing the inside. Not fun, but I’ll live. I get a handkerchief from my dad (who was standing next to me), and use it to stop myself from bleeding all over everything. My dad doesn’t see anything on my face that makes him want to dial 911, and the bleeding quickly slows to something that isn’t scary. Ok. Time to pack up, head home, and get cleaned up.
I pick up the M900, and go to open the bolt to make sure the gun is empty before putting it away in the case. Hmmm. The bolt is jammed closed. And then I notice something metallic on the inside of my upper lip. I discover what seems to be a tiny piece of shell casing that has obviously gone through the front of my upper lip and out the back. And there is a large chip knocked out of the front of my glasses.
So the gun somehow sprayed shrapnel at me. I decide I better go to the ER and get an x-ray to make sure there aren’t any metal bits somewhere scary that I haven’t noticed. So we pack up the guns, hop in the car, and go.
On the way there I call my wife. “First, before I say anything else, I’m ok, so don’t worry. I’m going to be home a little late…….”
At the ER its determined that all the wounds are tiny and don’t require any bandaging or stitches, and that there is one metal fragment stuck in my right cheek and one just at the top of the left eye socket. Most of the blood came from the one small hole that went all the way through my upper lip.
I always wear glasses, so I don’t normally think about the need to wear safety glasses while shooting, but it should be noted here that had I not been wearing glasses, I would have lost my right eye.
So now I need to go see a plastic surgeon to decide if the fragments should be removed.
I got home that evening, and did an ‘autopsy’ on the gun. With the bolt removed you can see where the shrapnel came from.
The shell never ejected. Instead the primer and top of the shell blew out.
The bullet is lodged in the barrel, about an inch down from the breech. So it looks like the gun fired without the bolt all the way closed, and without the magazine inserted there was a fairly direct path from the exploding shell casing to my face.
Whats strange is that bolt is designed so that this can’t happen. There are a set of rollers on the bolt. With the rollers retracted, the firing pin can’t reach the shell.
Only with the rollers extended will the firing pin hit the primer.
and there is only space for them to extend like that when the bolt is fully closed.
So at this point I’m not sure what went wrong or how to make the gun safe to fire again.