Delrin Dustcover

[CPTBeaker]

Recently several industrious folks have been working on a do-it-yourself dust cover for the 15-22. Forum member PainterlyShotgroup first realized this basic design (Thanks for the inspiration!). Here is my approach. I fabricated the cover from a piece of Delrin plastic. I'll attempt to detail my particular approach below.

I'm a hobbyist woodworker so my approach uses woodworking tools. This would be a pretty easy project for someone with a milling machine, which would open up the project to other materials like aluminum and mass production (hint, hint Tacticool22 ).

Note: I have no plans to make any more of these for sale. I would have to sell these for $400 ea to equal my time spent vs. a couple of hours OT at my job. The best I can do is this 'how to'.

Here is a video of the completed project, mounted to my 15-22.
Video

View when closed:

View when open:

 

[CPTBeaker]

Basic Part Fabrication:

I used a black plastic called Delrin Available Here. I chose this material because it's machinable, would not require painting when finished, and pretty much matches the receiver material in appearance. You could use any plastic that can be machined (ex. cut, drilled, sanded) or any metal (if you have the correct tools). I started out with a 2" x 1.5" x 6" block.

Tip: If you work at a factory or have a friend that does, most have machine shops with loads of scraps. Ask if you can get a piece.

Making the Cover

Step 1: Using a table saw, make the 1st cut as below.

Step 2: Using a table saw, make the 2nd cut to remove piece.

Step 3: Using a table saw, split the block, leaving the rough dust cover shape on the right.

Step 4: - Using a belt sander (recommended), block sander, or file, round the pin body.

Step 5: - Using a drill press (recommended) or hand drill, drill the pin hole - I used a 1/8" drill.

Step 5: Using a band saw (recommended) or hack saw, remove the center of the pin body to make room for the spring. Using a band saw or belt sander (recommended), round the corners of the cover as desired.

Making the Pin Boss

Step 1: Using a table saw (miter gauge), nibble out the 1st cut as below.

Step 2: Using a table saw, make the second cut.

Step 3: Using a belt sander or files, round off the bosses.

Step 4: - Using a drill press (recommended) or hand drill, drill the pin holes - I used a 1/8" drill.

Shape, sand, and polish the parts as desired after this.

Here is how the two parts look when placed together.

 

[CPTBeaker]

Next Step - Assembling the Parts

Additional parts needed:
- one 1/8" steel rod about 4" long (I got mine at the local Ace Hardware store)
- one retaining ring - 1/8" inside diameter Link
- one spring - 1/8" inside diameter (I got mine at the local Ace Hardware store)
- one strong magnet (I got a Neodymium magnet at the local Ace Hardware store)
- one roll of exterior 3M tape (I got mine at the local Ace Hardware store)

Step 1: Cut the spring to length using a pair of wire snips.

Step 2: Form the spring ends using a small pair of needle nose pliers. Note the orientation of the 'tails'.

]

Step 3: Clip the retaining ring using the cutting edge on a pair of needle nose pliers. This allows the ring to sit low enough on the boss so all of the holes align so you can put the pin in. Note: The retaining clip is directional and when a rod is inserted, it cannot be pulled out backwards. The CAD image of the retaining clip does not show how the ring is directional. The tabs are bent slightly inward so when a pin is inserted into the ring, the 'teeth' grab the pin when it is pulled backwards.

Step 4: Notch the end of the cover, making a space for the retaining ring by using a flat file. This provides a space between the boss and the dust cover for the retaining ring. Without this space, the cover binds up and won't flip smoothly.

Step 5: Notch the cover for the first spring leg using a small triangular, flat, or round file. This provides a space to capture the spring leg that applies the downward pressure on the cover to flip it open when released.

Step 6: Notch the boss for the other end of the spring leg using a small triangular, flat, or round file. (Note: This notch is on the top of the boss as it would be mounted on the receiver.)

Step 7: Assemble

View from the other side. (Note: after assembly is complete, trim the spring legs down as short as possible)

or attach using screws:

1 - using a #43 bit, drill two holes in the boss and countersink the holes with a larger bit.
2 - using a #43 bit, drill two holes in the receiver using the boss as a guide.
3 - tap all 4 holes using a 4-40NC tap.

I used two 1/4" 4-40NC screws.

Note: I recommend using a new tap & drill to ensure the holes and threads are crisp.

 

[CPTBeaker]

Updated the magnet...

I replaced it with a much smaller magnet and put the magnet in a block. The other magnet was too big and 'loud'.

 

[tacticool22]

Very, Very nice.

 

[Brett248Vista]

Your time must be worth much more than mine

Oh well guess I will have to fire up the table saw! You did a phenomenal job on this, and great documentation as well! Thanks for sharing!

 

[industrialfish]

While that looks absolutely fantastic, I still question the point of having a dust cover that only works when the bolt is closed.

Also particulates that get on that magnet may scratch the bolt, and/or fall into the chamber as they are pulled off by the bolt sliding across the magnet.

 

[Brett248Vista]

While that looks absolutely fantastic, I still question the point of having a dust cover that only works when the bolt is closed.

Also particulates that get on that magnet may scratch the bolt, and/or fall into the chamber as they are pulled off by the bolt sliding across the magnet.

That's the only time an AR dust cover is closed, when the bolt is closed. As soon as you rack the charging handle and pull the bolt back, it pushes the dust cover open. Yes I'm sure you could then manually close the dust cover with the bolt pulled back, but why?

 

[bulldozerd8t]

Nice job CPTBeaker looks like a lot of work. Guess I'll have to wait tell somebody makes these and sells them. I operate bulldozers, big bulldozers not little plastic peices. ha ha

 

[Foxtrot]

I'd just like to mention that I thought you did a good job on this. I'd also like to mention that you should have actually filed a patent on it too.

I know it doesn't seem like much, but i've a little bad experience with things like this. I like to design and build my own suppressors. In 1999 I had designed and built a suppressor for use with a 9mm handgun I had at the time. It was a great suppressor, lab measured at 40db reduction with regular off the shelf ammo, a little first round pop but so muted as to be ignored and I could have probably refined it a little more and gotten rid of that, and all you really heard was the metal parts of the gun from any angle. I told a guy at a dealer I had dealt with several times at gun shows over the years about it in general conversation, he seemed interested in wanting to build his own as he had the same handgun. I gave him a copy of the design plans. He turns around and patents the plans, and today his company has made more than a few million selling one of the top of the line suppressors based on that design to the commercial consumer and government markets. I made nothing off it. Its also the reason I don't post pictures of my weapons with suppressors on them so as not to give away clues to another design. Once its in the public domain, its fair game for anyone to rip off and patent.

Ya never know when something like this could make a buck for you. I'm sure there are more then just in this forum that have been wanting a dust cover for their rifle.

A little refinement (the magnet is OK but need firmer more perm attachment and could be smaller - and a better attachment to the weapon other than tape - i'd look into adhesives if I were you if your really going to stick with a no mechanical attachment system) , and you could sell these for about $10.00 each minimum. There are places that will fabricate these for you in thousand piece production runs for probably less than $3.00 per unit.

 

[VooDuuChild]

Well done sir....and I totally understand not wanting to hand-mass-produce those buggers. Way too much time involved for negative profits for time worked (as materials are cheap).

It's also really spendy to get a patent done, and for something this cheap, that is designed to fit one rifle (and not one that's been out for years with a hundred thousand of them floating around), well, that doesn't look like it'd pay either.

Still, excellent, quality work you've done that does not look hand made in the slightest. Vurry Nice.

 

[51reva]

Excellent job; considering the tooling you had to work with. Congrats!!

 

[CPTBeaker]

Still, excellent, quality work you've done that does not look hand made in the slightest. Vurry Nice.

Thanks!

My first priority was to try and make it look as factory as possible. I wouldn't want to put it on my rifle if it looked like a 'homemade' job. I got close enough to please myself. I would have preferred to make the pieces on a milling machine to ensure everything is exactly square, parallel, etc.

The only thing I'm not happy about is the magnet. I will find a solution that fits better with the appearance.

 

[CPTBeaker]

particulates that get on that magnet may scratch the bolt, and/or fall into the chamber as they are pulled off by the bolt sliding across the magnet.

The magnet does not touch the bolt. It's about 1/8" or so away from it.

The magnet is very strong.

 

[TwistedCreations]

Wow, very nice work.. I didn't read every detail yet, but when cutting the delrin, did you use more of a ripping blade or a fine tooth blade?

If using a smaller blade(more teeth count), do you run across the problem of melting the delrin more than cutting?



Off topic - what rail covers are those?

 

[CPTBeaker]

Wow, very nice work.. I didn't read every detail yet, but when cutting the delrin, did you use more of a ripping blade or a fine tooth blade?

If using a smaller blade(more teeth count), do you run across the problem of melting the delrin more than cutting?



Off topic - what rail covers are those?

Thanks!

I used a plain old combination blade. If you've ever worked with a very hard hardwood like Beech or Rock Maple, this stuff behaves about the same. I didn't have any melting problems while cutting. It's important to go slowly. This stuff is really hard.

I did most of the sizing with my table mounted belt/disk sander. The Delrin does have a tendency to melt if you try to sand it too quickly or for too long. Again, going slowly is the key.

Since these parts are small, make the rough pieces well over-sized, then sand them down to final size and shape.

Ref. the rail covers, they are Magpul covers. MAGPUL : AR-15/M16 ACCESSORY RAIL COVER - World's Largest Supplier of Firearm Accessories, Gun Parts and Gunsmithing Tools - BROWNELLS

 

[Brett248Vista]

Here's a tip for doing the radii on the pieces, you could use a router table with half round bits to do the radii. All precautions you would adhere to while using the table saw would apply to the router table!

 

[CPTBeaker]

Here's a tip for doing the radii on the pieces, you could use a router table with half round bits to do the radii. All precautions you would adhere to while using the table saw would apply to the router table!

Only trouble is...these parts are pretty small.

I'd personally prefer to use a Dremel with a roundover router bit.

They make an attachment for a Dremel so you can use it as a router.

http://www.stewmac.com/shop/Tools/Special_tools_for_Routing/Precision_Router_Bases/Precision_Router_Base.html

 

[boltman]

Great add-on for the 15-22 !!

 

[Shooting Padre]

This set up is really a pleasure to look at. Nice job. Thanks for taking the time to post such explicit directions.