A 3D printed PSG-1 style furnature set for your CETME

I didn't use a punny title for this post because I'm an attention whore and a descriptive title will pop up better in Google searches.  This post is going to be all about the 3D printed stock set that I designed for my CETME based PSG-None project.  I'm going to assume that if you're here you know how to print and finish parts so I won't go into detail on that, but it's still going to be a long post(see my previous post on how to make your prints look like not prints HERE).  Also keep in mind that these are not identical to actual PSG-1 parts, they are just a close approximation.  The few necessary HK G3 parts(primarily the recoil assembly) are easy to get and fairly cheap as surplus.  It was actually cheaper to buy a used recoil assembly with a green surplus stock than it was to buy the recoil assembly alone.  This will also help with your 922r parts count too, as long as you print these in the US.

We'll start at the back and work our way forward.  The buttstock is made to work with a standard G3 recoil assembly, G3 recoil buffer, and wood stock G3 sling hardware.  I got surplus wood stock sling hardware kit from RTG.  It was much rustier that the pic, but was also cheap, so I cleaned up the parts and cold blued them.  I cut the pin tubes in half using a jewelers saw because the kerf is only .015" wide and wouldn't remove much material.  I used JB Weld to bond the hardware into the stock

The comb on the stock is adjustable.  The comb has a big tab on the bottom and the stock has a matching slot to keep things in alignment.  It's not spring loaded like a real PSG-1, but it doesn't really need to be.  It attaches and adjusts with a single 1/4" screw.  In this pic you can also see the two 1/2" holes in the back of the stock for some 1/2" hardwood dowels.  Superglue works best for gluing the dowels in place.  On the print, you'll probably have to chase the holes with a 1/2" drill bit for the dowels to fit.

I took some liberties with the buttpad and decided to attach it with screws instead of the spring clips found on real HKs.  The holes are sized for 10-24 countersunk screws.  It is also non-adjustable.  It's printed in Ninjaflex TPU flexible filament to help absorb some of the recoil.  The recoil assembly attaching holes are also sized for 10-24 screws, and it is made to also use the large screw that goes into the buffer from the back side.  Here's how it looks all together(I haven't decided how I want to finish the cheekrest yet, so it's still a raw print, and I need to replace the cheekrest bolt with a button head 1/4-20).

Next up is the pistol grip. The palm rest is adjustable for both height and angle.  You can see how I printed the textured part HERE.  It will probably take a little fitting to work with your trigger housing as CETME's aren't exactly known for their precision tolerances, and I've never tried it on a G3 lower.  The palm rest hole is sized for a 10-24 socket head screw, through on the left side, and threading into the right side.

The next piece isn't part of the stock, but it is printed so I'll include it with this set.  The real PSG-1 uses an expensive Hensoldt scope with a rubber bellows.  I am using a cheap scope, and it didn't look right without the bellows, so I made one.  It will fit on any scope with a 39mm diameter rear eyepiece.  It MUST be printed in TPU flexible material, otherwise you'll break your face when it recoils.  The file is made to print in Vase mode with 0 top/bottom layers so it's only 1 wall thick.  Any thicker than that and it will be too rigid.  It's also got a separate base piece that should be set to non-vase and 100% infill to be used with Cura's Per-Model settings, similar to how the fuzzy skinned grip above was set up.  If you want to be clever and not use the Per-Model method, you can sink the model so that the base flange below the bed, then use 10-15 brim lines on the print to get a similar, all be it thinner, result.

The last piece is the handguard.  The stock and grip will for with either HK or CETME rifles, but the handguard is CETME specific because they use different cocking tubes. This will also work with CETMEs that have the triple frame installed on the barrel if you want the MSG-90 look, or you just don't want to semi-permanently modify your pre-built rifle.  The handguard won't sit as far back on the receiver and may have a bit more wiggle in it, but it will still work. This thing is long enough that it gets printed in 3 pieces.  This handguard makes the barrel free floating(unless you have a triple frame installed).  The pieces of the handguard have holes in them for 1/4" hardwood dowel to align things and hold them together.  Like the stock, superglue is the best adhesive to use here.  Because I have a tendency to shoot until my gun is very hot, I bent up some aluminum sheetmetal to wrap around the inside and act as a heatshield so I don't accidentally melt my stock.  The handguard attaches to the cocking tube with a 1/4" countersunk screw, and an expanding wellnut wrapped in electrical tape inserted into the cocking tube.  It's not a great solution and I'll probably come up with something better in the future, I just haven't gotten that far yet.  If all else fails, a standard 1/4" nut can be JB Welded into the end of the cocking tube.

So, how's it look with everything assembled?  Not too bad.  A lot of little tweaks left to do, but it's mostly done at this point.  I still have to find or make a shorter 5rd mag for it(they are available, but spending $25 on a 5rd mag when surplus 20rd's are only $5 just grates against my cheapness).  I'm going to get some lower scope rings for it too, these tall ones are just what came with the scope and I just don't like them.  I still need to paint it obviously and that may take a while because it's too cold in the garage to paint, and the air compressor hose won't reach to the basement.  I haven't decided exactly which paint I'm going to use yet either, I think I might try something new.

Basic print settings:

Buttstock, grip pieces, and handguard:  7 walls and 15% Gyroid infill, Textured grip section Per-Model settings of 1 wall, 0 top/bottom layers, and Fuzzy Skin turned on.

Buttpad: I used Ninjaflex TPU with 4 walls and 15% infill. 

Scope bellows: TPU, vase mode, 0 top/bottom layers, Base flange Per-Model setting with Vase off and 100% infill.

Thingiverse link, finally:

https://www.thingiverse.com/thing:4787497

The cocking tube

You get some words this time and only one picture(because I forgot to take any more).  Long story short, after pinning the barrel I got the cocking tube installed on my PSG-None.  Properly setting the cocking tube gap is essential for proper operation of the rifle, so I did it very carefully.  Needless to say there are some great tutorials on this out there(Holescreek's is probably the best), so I won't bore you with all the steps and no pictures.  I used an aluminum mandrel as a backer for my welds, and only had the slightest bit of burn through on my welds, causing some drag on my cocking piece.  To clean it up, I used the tool shown below, a 1/2" wood dowel, some sticky backed 80 grit sandpaper, and my drill. 

Catchy...CETME mag catchy.

I actually had a heck of a time installing the mag catch on my PSG-None.  The tutorials I'd been following didn't even mention it, and searching for "CETME Mag catch" yielded tons of posts on how to install a paddle mag release, but virtually nothing on the mag catch it's self.  Since the PSG-1 doesn't use the paddle release found on standard G3s and CETMEs, I don't need to either, and that saves us a bit of work.

The biggest problem is that I didn't realize that none of the mag release holes in the receiver flat were finished, and I couldn't see how it was supposed to work.  You don't know what you don't know I suppose.  Once I did realize that everything needed to be opened up, I set about doing it.  First was to drill the holes for the mag catch shaft.  The left side gets drilled to .238" with  "B" drill, and the right side gets drilled to 5/16".  With the shaft holes the right size, I could see where the arm that catches the mag needed to be. I used it as a guide to scribe some lines, then carefully dremeled the window open.  I left it a little undersized so that I could finish it with a file.  If you make this window too big, your mags won't lock in solidly.

I also couldn't find any good pictures of how all the parts were supposed to fit together, or any explanation of what I did or didn't need because I wasn't using a paddle release.  So here's the order and orientation the parts go in.  Mag catch-spring-pivot bushing-release button(with the pin holding the button on).

Then I couldn't find any good pics of how everything was supposed to look installed either, again because everyone out there was posting about paddle release installation.  So here's how it should look with all the parts installed.  It's tricky getting the spring in place, and it will want to go flying if you slip.  I found it easiest to use a punch to get the bushing and spring aligned in the receiver, then slide the mag catch in.   

Actually getting the mags to fit into the receiver took some work too.  CETMEs and HKs use a nose in, rock back style mag lock like an AK, just slamming it in like an AR doesn't really work.  The front of the mag catches on a little lip on the bottom of the trunion, all the receiver sheetmetal does is keep it from wobbling.  The RTG flat I'm using has just slightly too much radius on the front corners of the magwell so the mags didn't want to fit.  The sheetmetal is very soft so I used a block of wood and plastic hammer to massage the magwell opening until mags fit.  I also had to very slightly shorten the bottom of the magwell to match my mag catch height.  

Because 5rd PSG-1 magazines are expensive and this project is not, for now I'm using standard G3 20rd mags because by golly are they cheap, probably the cheapest surplus mags on the market at the moment.  I'll probably try to cut one down at some point, just to see if I can.  I got some from RTG, and some from Apex.  RTG's "Very Good" mags ranged from little wear so some wear(the worst one shown below), Apex's "Very Good" mags look basically brand new, hardly even showing any shelf wear. Everything I've ever gotten from Apex has been better than advertised(and they're not even paying me to say that!)  This isn't the best pic because it looks like the mag isn't seated fully, but it is.  This particular mag is a little bent(not unexpected for being a 50 year old aluminum military mag, and I didn't want to scratch my nice ones while trying to size the magwell ).

 

Making your 3D prints look like...not prints

On all the other printed guns I've made, namely my SCR style bolt action AR, my half printed STI style 1911, and my VZ-61, I shamelessly left the 3D prints looking like 3D prints.  After all, that was the point, to make printed guns.  My PSG-None project is different though.  It's intended to be a "stand back and squint" clone of an HK PSG-1.  I'm using printed parts for all the furniture, but I don't want them to look like obviously printed parts.  

Since I have a variety of parts, I'm going to use a variety of techniques to finish them.  All my parts are printed in black so that if/when they get scratched or dinged up, they will scratch to black and it won't be visible.  If you print in bright orange and then paint it black, when scratched the bright orange will show through and be super obvious.

The first and most basic method is to just sand down your parts so that there are no more layer lines.  For this to work, your part has to be printed in the color you want, or you'll have to prime and paint after sanding.  I prefer just printing in color.  I always use wetsanding for plastics.  Dry sanding is fine for rough 80-120 grit paper, but any finer than that, and the sanding dust can melt from the friction and gum up your sandpaper.  For the palm rest on my PSG-none, I knocked it down with 80 grit dry, then wetsanded 320 and 600 grit(because that's what I had handy), then finished with a Mr. Clean Magic Eraser which is equivalent to 3,000 grit sandpaper.  There are still a few scratches showing because I'm lazy.  Since PLA is largely immune to most solvents, once dry I wiped it down with my preferred gun oil to "wet" the surface and make it a little darker.

The next method is very simple and kind of like magic.  I wanted to make some parts look like HK's textured molded plastic.  Normally this would be almost impossible to replicate, but I know of a product made just for that.  SEM 39853 Texture Coating is a spray on automotive product primarily aimed at auto repair stuff like textured plastic bumpers, dashboards, etc.  It's made specifically for plastics and bonds very well to PLA.  The first step is to knock down the high spots with 80 grit sandpaper, that's it.  If your print is clean, you don't even need to do that much, Texture Coating hides layer lines great.  

Next, spray on the SEM Texture Coating.  You can make a wide variety of textures from very fine to very rough, depending on how heavy you spray, and from what distance.  Once dry, it can be topped with paint of your choice.  My preference is SEM Colorcoat.  It's also an automotive oriented product and is made specifically for plastics, fabrics, and vinyl, and is very durable while still being flexible(if that's what you need).  It's durable enough that the steering wheel of my daily driver was painted SEM grey 7? years ago, and it hasn't worn off yet.

The last method I'm going to show is the hardest to do, and I am not very good at it.  I want to make the grip handle look like wood.  Some people are simply amazing at this technique, I...am not.  We'll be using artist's oil paints for it because they blend very well.  I started out with a base coat of brown spraypaint.  Once that was dry, I covered the textured part of my grip with a thin black wash to darken up the low spots in the texture.

Next is where the magic is supposed to happen, but again, I'm me.  Artists oils are basically just pigment suspended in Linseed oil, so they're not that much different from what you'd use on a wood stock.  A cheap set of oils is $13 at Hobby Lobby, and if you use their weekly 40% off coupon(downloadable on your phone straight from their website), you can get a set for $8.  Using a combination of Burnt Umber, Burnt Sienna, and Yellow Ochre, the idea is to basically paint on the woodgrain.  As I said, I am not good at this.  This was only my second attempt, and I'm colorblind, so that's a big help...  Since I suck at this game, my method was to basically just put on streaks of color and blend them out so it looked less uniform.  My brush strokes go the same direction as my print layer lines to help hide the print lines without having to sand them down.  The paint it's self isn't super durable so after a month or two(or more, raw Linseed oil takes forever to dry), it can be top coated with an oil based polyurethane for durability.  I'm not really satisfied with how this turned out, but I guess it will do(and the sharp streaks on the bottom will be covered by the palm rest shown above). 

Textured grips with Cura's Fuzzy Skin

Back to my PSG-None project for a bit.  The real PSG-1 pistol grip has stippling textured onto parts of it.  I could come up with some sort of bumpy surface to replicate this in Solidworks, but the face count would skyrocket, and it would seriously drag down the speed of my whole system.  Solidworks hates high face counts. 

Fortunately, there's a very simple solution: Cura has a "Fuzzy Skin" option buried in it's settings.  What it does is generate the skin of the object with random jitters so that it ends up looking rough and fuzzy looking instead of nice and smooth.  But, I don't want my whole grip to have this fuzzy skin, I want to replicate the asymmetrical texturing of the PSG-1 grip.  There's a way around it with another seldom used Cura feature: Per model settings.  This lets you place several models on the print bed and use different settings for each one.  

Basically, we're telling the machine to print two parts in the same place, at the same time, but with different print settings.  One part is the normal grip and prints like anything else would.  The 2nd part is set to only print the outer layer, using the "Fuzzy Skin" option.  It works because the plastic from the normal part melts in with the overlapping plastic from the "fuzzy" part.

That's what we're going to do here, create two models, one of the complete grip, one of just the grip section that we want textured.  To make the fuzzy grip section I just copied the grip, then hacked away the parts I didn't want.  Here are the two parts in Solidworks:

Once that's done, both models are loaded into Cura.  We set the settings that we want to use, then merge the models so they print as one piece.  I'm not going to go over exactly how to use the Per Model settings here because there are some great Youtube how-to's that can do it faster and better.  The important thing is that on your fuzzy grip section model, turn on Fuzzy Skin, set it to 1 wall, and 0 top/bottom layers.  This will print a fuzzy skin outer wall on top of whatever your main model settings are set to.  When it's done printing, here's how it will look, textured where we want, smooth where we don't:

Llama XV progress

I'm now on V3 of my baby Llama frame.  Every iteration of this thing gets several changes and at this point my Solidworks feature tree is just a mess.  With V3, everything fits and the action hand cycles and resets like it should.  The problem now is that the safeties don't work.  It wouldn't be that big a deal, but the way it is now the thumb safety can slide up into the notch on the slide, locking the slide closed while still being able to fire.  If this happened, I think the force of the slide would blow the safeties off the back of the frame, and my hand would have a really bad day.  So back to the virtual drawing board to try to get the safeties to work.  Here's how it looks so far with everything assembled, standard 1911 magazine included for size reference:

Baby on board! A Llama XV miniture 1911 clone

I saw one of these at a gun show years ago, and didn't buy it because the guy wanted $450 for it, but I always thought it was really neat.  They haven't gone down in price since then either.  Then I found a frameless parts kit on Every Gun Part, and when they had their Cyber Monday 50% off  sale I didn't hesitate, and picked it up for $100.

It's a Llama XV, a Spanish copy of the 1911 in 22LR, but unlike most 1911-22's that are still full size, this one is scaled down considerably.  It's not just shorter like a Commander or Officer frame gun, the whole thing is uniformly scaled down in all directions.  All the internal frame parts look exactly like 1911 parts, but smaller.  Since it's a 22LR blowback pistol, the plan is to 3D print the frame for it.  Since it's a fixed barrel most of the recoil stress will be on the slide stop pin and barrel seat area and I think a printed part will be strong enough to handle it.  I took the CAD files I already have for 1911 frames, and scaled them down accordingly.  The Llama isn't a directly scaled copy, so there is going to be a lot of adjusting and reprinting to get everything to fit(particularly all the pin hole locations).  This is going to be a fill in when I don't have anything else going on project, so I don't know when it'll be done.

I spent a day measuring and adjusting my frame CAD file to be close, then test printed a frame to see how things fit.  It still needs a lot of tweaking to get everything to fit and work like it should.  When you look at it, it doesn't seem that small, but when you put it next to a full size 1911, you can see how tiny it really is.  It makes a standard 1911 look huge: