TKSnake's 3D Printed DLT-19 Build

[TKSnake[TK]]

For a long time now I've wanted a DLT-19. I've been looking at buying one but don't have the scratch for a prefab blaster at present. But due to the pandemic, I have time, a 3D printer, and filament.

 

After some minor searching on FISD I came across two previous build threads here and here. The Sketchfab files have been updated by the creator a bit, and included threaded screw-together parts for easier break-down and potentially part replacement should the need arise.

 

The Printer

 

The first tool of my trade was the Ender-3 Pro. I got this during the holidays and started with small prints and then larger ones, adding upgrade parts, the usual stuff, until I've come to a point where I'm comfortable enough with the slicer program (I use Ultimaker Cura) and the printer to attempt something if this scale.

 

Firstly was how to print it. After reading the other build threads, this seemed like the best advice for a good mix of durability and weight:

 

I created a new DLT-19 printing profile in Cura with the following parameters:

• Layer thickness: .2mm
• Wall thickness: 4
• Infill: 30% grid
• Plate adhesion: brim (no need to lose a 10 or 20 hour print because of lifting, especially on sharp corners)
• Supports: variable - some parts only need supports for parts touching the build plate, while others will need supports everywhere (perhaps with support blockers)

 

Other Tools

Other tools I'm using for this build:

• Hobby knife
• Miniature files
• Sanding block
• Quick-release C-clamps
• Quick-release bar clamp (for gluing the larger assemblies and barrel parts together)
• CA Glue (for basic adhesion)
• Epoxy (for structural/ load-bearing adhesion)
• Ruler
• Digital callipers (for measuring pats to within fractions of a millimeter)

 

The Build

 

Buttstock

 

After a quick failed start wherein I needed to get my print bed more sufficiently leveled and locked down, I started with something easy, the buttstock. It is in three parts; left, right, and a front cetner section. I started with the right section.

 

  

 

You can see the walls and infill on the first photo, then the finished right part on the right photo.

 

After successfully printing the right, I printed the left and center pieces,

 

 

 

Once they were finished, I did some minor deburring and sanding, and fitted them together. Even without adhesive, they fit together like one piece.

 

 

So far, so good. Next, I'll be starting on the receiver and grip. More to come soon.

Edited August 3, 2020 by TKSnake
Added list of tools

[TKSnake[TK]]

Receiver, Pt 1

 

After printing out the stock and a few other parts, I was starting to run low on filament. It was too close to call, and I didn't want to leave a print running overnight if I wasn't there to pause the print and change filament, so I paused it overnight. Before I did, I made sure to pause the print right at a new Z-axes increment (horizontal slice) in case something happened.

 

 

And something did happen. When I tried to resume the print the next morning, the printer went to the last point on the print... and simply did nothing.

 

Not about to lose hours of printing and filament, I decided to alter the gcode directly until I found the z position at 14.8, and start the print from there.

 

 

This almost worked. the rest if the print printed out, but 1) a bunch o f filament extruded at first due to a bit of gcode I forgot to to remove and 2) the print was offset lengthwise by about 2mm.

 

  

 

STILL not about to lose hours of printing and filament, I came up with an idea that actually worked pretty well. Because of the big pause in the print combined with the glob of extruded filament, for better or worse the to pieces of the print were very easy to split from each other. After removing the supports (to ensure they didn't get cemented to the pieces, I sanded the edges smooth with a sanding block and used CA glue and clamps to cement them together.

 

 

 

 

The final product is very usable, and should only need some plastic putty and sanding to finish before painting and installation.

 

 

 

I was right to worry though as there wasn't much left on the spool once this part was printed.

 

 

I printed out some monir items and then finally changed to new filament that ended up being matte black instead of gloss. It won't matter since everything is getting painted anyhow, but if the paint scratches off, I think I actually prefer the matte black. Look how nice this charging handle came out, for instance.

 

 

I finished printing out all the smaller pieces of the receiver and started working on the main receiver pieces. There will be a lot of supports for these since they're hollow (so I can fit electronics in later.

 

 

 

More to come once the receiver pieces are finished and I get into assembly.

Edited August 3, 2020 by TKSnake

[TKSnake[TK]]

Receiver, Pt 2: Reinforcing a Poor Design

 

Late replay as I've been pretty heavily invested in this build, but I'll make new posts in the context of when the photos were taken. Also going to update the original post to include tools I've been using.

 

I decided to build the hollow receiver; eventually I might add electronics, and it would be terribly easy to hide most everything in a hollow receiver.

 

Printing the receiver parts required a lot of supports. I was apprehensive at first, but with the matte black PLPA, they popped out without issue.

 

 

The hollow receiver is printed in four quadrants. I started with the rear quadrants to ensure parts would match up. Test fitting the stock was very satisfying.

 

 

 

Eventually I was able to print all the parts out without too much effort. For all receiver parts, they were printed with the seam down and outside up, so that supports marks would be on the inside of the pieces. 

 

 

For the rear site, If I had to print this again, I't probably do 100% infill. The bottom ring is thin and fragile near where it connects to the rest of the piece, and I had to glue it back onto the main body after it cracked during test fitting. It should be strong enough now but I still think it may break in the future.

 

I did some preliminary fitting of the top cover to the receiver parts. It required sanding down part of the rear lip so that the door could come down far enough to close over the rear receiver.

 

   

 

So far the build parts have been clean and crisp. However, the one thing that bothers me about this kit is the lack of connector parts. For example, although the left and right sides fo the receiver have connection and alignment tabs, there's no such luxury between the front and rear right parts. For one of the most vulnerable joints in the build, where the weight of the butt stock and barrel assembly will be centered, there's nothing but a simple butt joint, the weakest of all mechanical connections.

 

 

Finding some parts on thingiverse (later I would build custom parts with MS 3D Builder) I created some reinforcement shims the help keep the pieces together.

 

 

 

 

Between these, using epoxy, and perhaps even spare hardware fasteners like shallow screws, I'm hoping this will be enough to keep the thing from possibly breaking in half during a troop.

 

More to come soon as I have done a lot more since this.

 

Edited August 3, 2020 by TKSnake

[TKSnake[TK]]

Barrel: Overcoming More Poor Design Issues

 

Waiting to get to the electronics shop to get the switch for the receiver's trigger assembly, I started focusing on printing and assembling barrel parts. The barrel consists of an inner and outer barrel, along with miscellaneous parts for front & rear braces, front site, and the end pieces for the muzzle.

 

The main issue with these parts, like with the receiver, is that, besides some small male and female tabs, there's very little in the way of strong joints on these parts - they're all butt jointed together without any overlap or increase in surface area to make strong adhesion.

 

 

Taking what I did with the receiver, I used MS 3D builder to slice up some barrel parts and make small connector pieces that would fit inside the barrel pieces, like pipe joints in plumbing, but inside the pipes instead of outside so they'd be hidden from casual view. This took some trial and error, but eventually I found some pieces for the inner and outer barrels that would be close enough but not snug, so I could easily CA glue them in place, and then epoxy two or more pieces together.

 

 

For the inner barrel pieces, I printed these horizontally since their cross section would not offer a lot of surface area for printing vertically, even with brims. Thankfully, they also didn't require inside supports, making them super easy to print, with only the brim and a slight flat section to remove.

 

I also decided to print these pieces in gunmetal instead of black. Ultimately, these pieces will be inside the outer barrel and not very visible, so I plan to only lightly sand, polish , and paint them in matte clear coat to preserve the PLA's actual color. Some of the muzzle pieces will also be painted in gunmetal but will have some paint and weathering added so they don't stick out too much.

 

 

The inner barrel had 5 pieces number from front (muzzle side) to rear (receiver side). The outer barrel also has 5 pieces but numbered 1, 2a, 2b, 3, and 4, for no apparent reason.

 

The outer barrel pieces were harder. I printed all but one vertically. Outer Barrel 1 was particularly tricky because it has holes near the very end of the print. I printed the pieces from last to first, starting with piece 4 (with the screw post) to 1. Pieces 1 through 2b I printed vertically, as seen here with the inner barrel counterparts.

 

 

Piece 2a was high and popped off the print bed during printing (below, center). I ultimately printed this horizontally after running a small test print for feasibility, and although structurally sound, will require a lot of post work to remove print lines and support leftovers.

 

 

I had the worst time with Outer Barrel 1 (which I'll show in another post). After about 5 attempts and a lot of filament, I discovered on Cura (my slicer) that I could uncheck the "print brim on outside only" to also print the brim inside the hollow part of the piece, and increase surface area to successfully print it vertically. Of course, I ran out of filament after printing about 95% of the piece, so instead of reprinting it again, I used 3D Builder to slice of the missing part, print it separately, and glue it to the end.

 

One of the reasons I ran out of filament is because, for Outer Barrel 3, both ends are the same and aren't keyed to any particular direction, so if you don't check the Sketchfab image, you can easily glue it backwards, which is what I did, and the holes aren't in the correct position. Here's what that looked like:

 

 

Unfortunately, I didn't realize this until after the pieces were permanently bonded with epoxy. Because sawing them would change their length, which needs to match up precisely with the inner barrels, my only recourse was to redo 15 hours of printing. Again, I was caught off guard by bad design.

 

So.... while I reprinted those pieces, I used the bar clamp on the inner barrel pieces. Inner barrel pieces are easier since they are keyed in one direction and easier to  ensure they don't get messed up. The reinforcement inserts were placed with CA glue, and then the pieces were epoxied together for extra strength.

 

 

Once I had the outer barrel piece printed (AGAIN), I was able to use the bar clamp to get them in the CORRECT order and epoxy them together, shown below. Note how the holes from Piece 3 (the bigger diameter piece on the left) are right up against piece 2b.

 

Also note: piece 2a NEEDS to have the holes oriented on the bottom so the tripod holder can be mounted correctly. Mounting the tripod holder first can help you keep track of proper orientation (Piece 4's flat part on far left is the top of the barrel). After piece 2a but before piece 1 is the AA mount. Piece 1 will be added with corresponding muzzle piece later.

 

For assembly with epoxy, the bar clamp is indispensable and keeps the right amount of pressure on the pieces until the epoxy sets, and makes it easy to make sure the assembly is very straight (super important for barrels). Between this, the extra reinforcement parts between the barrel parts, and using 4 wall prints and 30% infill, I'm hoping for something stronger than the average PLA prop.

 

 

Finally, I printed out the last of the inner barrel pieces and reinforcement parts. There's a muzzle piece between piece 2 and piece 1 which I also printed out in gunmetal.

 

 

I'll finish up the barrel more after I get more printed. Until then...

 

[gmrhodes13[Staff]]

I find that with a lot of 3D parts not having the strength. A fellow member who printed a few DLT19's ended up hollowing the barrel in places and using a clear acrylic tube inside just to help with strength, but wasn't cheap.

[TKSnake[TK]]

1 hour ago, gmrhodes13 said:

I find that with a lot of 3D parts not having the strength. A fellow member who printed a few DLT19's ended up hollowing the barrel in places and using a clear acrylic tube inside just to help with strength, but wasn't cheap.

It's certainly worth future consideration, although one might have to worry about dirt and grime building up on the clear parts over time. I've also had to tear parts apart and glue them together due to bad layer lines, probably due to some extruder clogging. Overall, the epoxy joints seem to be stronger than layer lines.

 

One thing I kept in mind was the "grain" of the print. most of the outer barrel was printed vertically, and the inner barrels printed horizontally, in order to "cross the grains" and further increase strength in the barrel especially. Overall, I'm considering doing a light resin coat on the outside before sanding, priming, and painting. Epoxy's an option but I would have to whip up a lot of small batches and apply it as evenly as possible to avoid pooling, which might be tricky and sticky. I'm currently researching spray-on solutions as I finish initial building.

[TKSnake[TK]]

Barrel pt 2 and Receiver Assembly

 

I finished printing out all the barrel parts and tripod parts. At this point, the only pieces left to print are the t-tracks.

 

I finished glueing the inner and outer barrel assemblies up to the muzzle parts, except for Muzzle pt 5 that goes on the ned of the outer barrel. The other muzzle parts were glued together. In the image below, the muzzle is placed on the inner barrel but not glued, so that I can paint and finish the assemblies separately.

 

 

The reason why I couldn't cut the outer barrel when it was mis-assembled is apparent when the inner barrel is inserted. They need to match perfectly at the muzzle so both assemblies connect there.

 

 

For the receiver, I installed some shallow screws on the structural reinforcements I added, after drilling pilot holes, for additional strength and to help keep parts aligned during epoxy gluing.  After using CA glue to add some structure for the electronic trigger switch (discussed next), there was nothing left to do but epoxy the front and rear right receiver pieces together.

 

 

One the right side had cured for an hour or so, I dry fit and clamped the left receiver pieces to the right receiver assembly to ensure that there was no bowing an that the left pieces would be able to be bonded without issue.

 

 

I finally obtained the fast action switch I want to install in case I decide to install electronics later. I wanted to mount it on the mounting arm on the right front receiver part, but I had to highly modify it to make way for the electrical contacts. After that, the arm was flimsy, so I printed some custom supports using MS 3D Builder to make some simple shapes to CA glue into place before major assembly. Once those were dry I bonded the right receiver pieces together as previously described. Then, I CA glued the switch into pace after adding lead wires for future use.

 

 

 

Once the right had cured more, I commenced to epoxy the left front and rear receiver together, insert shallow screws in the reinforcement, and then immediately exofy that sub-assembly to the rest of the receiver.

 

 

 

I had to use all my clamps for the latter.

 

Notice that the left rear piece is missing the grip. For future electronics installation, I decided to make the left grip removable in order to install a USB battery or other components, since getting into the hollow grip without a removable panel would have been extremely difficult with everything glued together. I fastened a mini rocker switch into the panel to turn any future electronics on or off. I could have mounted it elsewhere but it was an easy instal that required little modification of the model.

 

 

The additional blocks in the right receiver's handle are for mounting screws for the panel. The reinforcement on the other part of the left rear receiver also doubles screw mounts for the top of the grip panel. When the panel is mounted, it looks like it a natural part of the piece.

 

 

Finally, the tripod legs are two parts each, but like the barrel parts, only connected together with weak, tiny tabs. I created some scaled-down sections based on the same legs, printed them, and inserted them in the hollow section of the legs to act as reinforcement.

 

 

While I glued the left receiver to the right, I used the extra epoxy to glue the tripod legs together, and the front sight to the muzzle. Then I laid everything out on the garage floor.

 

 

I do need to finish assembling the receiver top door, but other than that, I'm going to wait until I get the spray resin I purchased so I can start finishing assembly. The idea is to sand and apply a coat of spray resin to smooth the parts and also add additional strength before fine sanding, priming, painting, drybrushing, and a matte finish.

 

More to come...