Dead Space: Schofield Tools 211-V Plasma Cutter

"Congratulations on your purchase of a Schofield Tools 211-V Directed Energy Plasma Cutter! The 211-V combines power and reliability in a portable form factor, allowing for one-handed operation.

The Plasma Cutter delivers a cohesive pulse-stream, or "bolt", of ionized plasma when fired. It is capable of firing bolts vertically (primary firing mode) and horizontally (secondary firing mode). The Plasma Cutter is very accurate, utilizing three blue lasers to indicate the desired cutting plane.

On impact with the target, bolt cohesion fails frontward first, penetrating the target with a focused jet of superheated matter. This causes intense localized shear effects as well as a tunnelling thermal expansion. When used upon brittle, frozen rocks riddled with faults, it can split them open in one or two shots in skilled hands. Against pliable targets, however, impact will cause minimal damage and thermal expansion will not so much cut as stress the area around the impact site, sometimes requiring several consecutive hits with the non-upgraded tool. Still, when presented with a less than effective alternative against dense organic matter, the 211-V Plasma Cutter retains its utility."

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I've probably spent hundreds of hours on this - I originally made it for a costume in 2014 but it was a very rough design and some of the moving parts were unreliable. THE MARKER COMPELS ME TO DO BETTER. This year I've decided to revive it, clean it up, make it more durable, and add some extra features.

The Plasma Cutter features a rotating front blade capable of mounting either three lasers, or for a more cosplay-safe version, three LEDs. The LEDs take up considerably less space which enabled me to design a mechanism to extend the 'fins' on the front of the cutter, making it more game-accurate. The actual movement of the fins in-game can only be described as 'physics defying' as they move through parts of the model, but extending the fins in real life still looks totally cool! The vast majority of the design is my own, but I borrowed and modified the grip from this Seburo M5, and this Rack and pinion.

I had (and still have) minimal 3D modelling skills so I used the Tinkercad platform to design all my parts. I aimed to design the parts so that they could be printed without any support material to reduce complexity, though there are a couple of parts that will require minimal amounts. With the addition of some electronics, glue, spray paint and a few nuts and bolts, the result was... well, awesome!

Just a heads-up: you'll need some soldering equipment and a little bit of soldering skill to complete the electronics build.

At some point I'll work out how to actually make it fire bolts of superheated plasma and make a killing in the extra-terrestrial mining market.

NOTE: I've made some minor design tweaks since I took the photos for the build guide, so you may find a couple of parts look a little different to the photos. The instructions remain the same though!

Step 1: Reference Material and 3D Design

I fired up Dead Space and made sure I got a few screenshots of the Plasma Cutter in each configuration (vertical/horizontal and stowed/deployed). This also let me get a sense of it's scale relative to Isaac, and get a feel for the colour scheme. I kept the screenshots handy so I could scroll through them at my leisure as I designed each part, and if I needed to see how something moved I could just jump back into the game. I also performed a few reload or two to determine which part was the magazine.

Design was definitely the longest part of the process, as it would sometimes involve printing a part only to discover that something was slightly misaligned or I hadn't taken something into account, which would mean a redesign and reprint. I didn't work on it every day, but it took at least 3 months to get everything done.

The first one I made worked to a degree, but the rotating mechanism wasn't very good and tended to come loose from the servo. There was also a lot of fettling and trimming to get everything to fit nicely, so I didn't want to release it to the world in that state. I came back to it a couple of weeks ago and have tidied it up and made the rotator much more solid, plus added extending front fins to make it more game accurate! It's a good opportunity to tidy up the costume and add a few extra details, so I'll probably be wearing it again this Halloween...

Step 2: Materials

I tried to use M3 nuts and bolts throughout, but there are a few M2's for the small parts like microswitches and the trigger. You'll also need some M6 rod and nuts for the bottom bar. A full list of the non-3D-printed parts I needed to complete the project follows. Most of the parts can be picked up on ebay cheaply.

After I started designing this I discovered self-tapping screws for plastic that are excellent for printed parts where you don't want to mess about with fitting a nut somewhere! I've used them pretty extensively, but the slots for the nuts are still there on the parts.

3D printing filament. Sliced with 20% infill, 2 perimeters and 0.2mm layers, Simplify 3D estimates 484g of PLA, so well under a 1kg spool. If you don't have access to a printer try 3DHubs.
22x M3x20 cap head bolts black OR 4x M3x20 cap head and 18x M3x16 self-tapping plastic screws (e3d-online)
2x M3x10 cap head bolts black
2x M3x5 cap head bolts black
26x M3 nuts (or 8 if using self-tapping screws)
3x M2x20 screws
1x standard low-profile servo
1x micro servo (extending version only)
1x 20kohm resistor (extending version only)
1x Arduino Nano (without pre-soldered pins)
1x sub-mini push switch (Maplin)
1x sub-mini microswitch (Maplin)
1x XT60 connector pair
2x servo connector pairs (1 if building standard version)
2x JST connector pairs
some multi-core wire in various colours (at least red, black and white)
1x 3A adjustable voltage regulator
Laser version: 3x green laser pen (£2-3 each on ebay) - Blue lasers aren't cheap or small yet!
LED version: 3x bright blue LEDs
LED version: 3x resistors (value depends on the LED you use - see below)
1x spring max 5mm in diameter and about 25mm long - try an old ball-point pen
1x M6x250 threaded rod
1x M6 standard nut
3x M6 flanged nut (you can get away with 3 more standard nuts, the flanged ones just look nicer)
1x Cyanoacrylate (aka super glue) - bonds PLA well but not tested with ABS.
1x battery, 2S 7.4V about 50x30x15 in size to fit inside the magazine. You can get more than one if you want and have multiple magazines!

You'll need some spray paint and related supplies too. I got most of mine from Halfords as it's nearby, and automotive paint tends to be tougher and more long-lasting than others.

2x large cans plastic filler primer
Sandpaper, around 220-240 grit
1x can chrome
1x can grey (use reference screenshots to choose your shade)
1x can brown/gold (use reference screenshots to choose your shade)
1x can black
1x can lacquer
1x roll masking tape
1x pot mustard (for creating weathering effects)

LED Resistors:

We'll be using a 5V supply (Vs), so to work out what resistance (R) you need for the LEDs you need to know some specs about the LED: forward voltage (Vf) and operating current (I).

(Vs - Vf) / I = R

So, if we have 3.3V LEDs with an operating current of 20mA (0.02A):

(5 - 3.3) / 0.02 = 85ohms

85ohms doesn't sound like a widely available value, but this isn't an exact science. As long as you use a value pretty close to whatever value the equation gives you, your LEDs will still last for years.

Step 3: Printed Parts

Brace yourself. Depending on your printer you're probably looking at 40+ hours of printing here! Plenty of time to play through the Dead Space games while you wait...

All the printed parts are in the attached zip file, but they are also available on Thingiverse:

Dead Space 211-V Plasma Cutter

You'll need to decide which version you want to make before you print!

If you want the standard blade with no extending fins and the ability to fit lasers (but you can still fit LEDs if you wish), then print the following:

plasma_cutter_blade_standard.stl
plasma_cutter_fin_panel_top_l_standard.stl
plasma_cutter_fin_panel_top_r_standard.stl
plasma_cutter_fin_panel_bot_l_standard.stl
plasma_cutter_fin_panel_bot_r_standard.stl

If you want the extending blade with fins that move, but is limited to fitting LEDs only, then print the extending fin panels, extending blade, and the rack and pinion parts:

plasma_cutter_blade_extending.stl
plasma_cutter_fin_panel_top_l_extending.stl
plasma_cutter_fin_panel_top_r_extending.stl
plasma_cutter_fin_panel_bot_l_extending.stl
plasma_cutter_fin_panel_bot_r_extending.stl
plasma_cutter_blade_extending_rack.stl (x2)
plasma_cutter_blade_extending_pinion.stl

Laser version:

plasma_cutter_blade_front_laser.stl

LED version:

plasma_cutter_blade_front_led.stl

Print everything else that isn't in the above lists. Each STL file only needs to be printed once, apart from the rack in the extending version which needs to be printed twice. The largest part is the handgrip and main body, so it's probably wise to check that it fits in your printer's build volume before you print anything else. It will fit into a 200x200x200 build volume if you turn it 45 degrees.

20% infill and 2 perimeters is enough for a sturdy but lightweight build.

Dead_Space_211-V_Plasma_Cutter.zip
Download

Step 4: Electronics

The principle of operation is as close to the game as I could get it without actually being able to fire bolts of superheated plasma:

Pull trigger, fins extend and LEDs/lasers activate.
If the rotate button is pressed while the trigger is pulled, then the front blade rotates 90 degrees.
When the trigger is released, the fins retract and the LEDs/lasers switch off.
The fins will retract if the blade is in either of its orientations.
Pressing the rotate button with the fins retracted does nothing (the fins will hit the main body if they rotate while retracted).
If you're not building the extending version (i.e. rotate only) then the rotate button will work regardless of the trigger state.

The Plasma Cutter is controlled by an Arduino Nano as they're cheap and very capable for their small size. The whole thing is powered by a 7.4V LiPo battery that is regulated down to 5V. A SPDT microswitch in the trigger passes 5V to the LED's/laser when the trigger is pulled. The trigger state is read by the Nano to determine wether to extend or retract the fins. A push button above the trigger is also monitored by the Nano to determine if the blade should be rotated. A standard low-profile servo controls the blade rotation and a micro servo controls the extending fins, both of which are controlled by PWM outputs on the Nano.

When the plasma cutter is powered up (i.e. when the magazine is inserted) it will run through a setup sequence that puts the blade vertical and the fins retracted, no matter what positions they were in to start with, so it always starts from a known point.

I used prototyping breadboard to test out my electronics and develop the Arduino code to control the servos. It's a relatively simple program thanks to the in-built Servo library. To upload it to your Nano:

Extending version: Download and unzip the plasmacutter_full.zip file and go into the created folder.
Standard version: Download and unzip the plasmacutter_rotate_only.zip file and go into the created folder.
Open the plasmacutter_x.ino file in the Arduino IDE
Use the 'Tools' menu to select the correct board (Nano), processor (328) and the COM port your Nano is on
Upload!

Later on you'll need to fine tune some variables in the code so that your servos have the correct amount of travel to rotate the blade by 90 degrees and extend/retract the fins properly. This is covered in a step during the assembly.

Step 5: Assembly: Glued Parts

There are a few parts that need to be glued, namely the rear pod, the magazine, magazine housing with iron sights, and the fins and panels. If you're making the standard (i.e. non-extending) blade version then you can glue that together now too.

Note that if you paint these before gluing them then you're just bonding the outer layer of paint instead of the plastic itself, so it will break much more easily.

1. Rear Pod

Glue the rear_detail_1 and rear_detail_2 pieces onto the rear pod. You might need to trim rear_detail_2 and the hole it fits into with a sharp knife to get a good fit.
Glue the rear_bar piece into the front of the pod. Use the 6mm rod as a placeholder to make sure you glue it straight.

2. Magazine

Glue the magazine_detail piece onto the back of the magazine.

3. Mag Housing

Glue the iron_sights piece onto the mag_housing, making sure it's engaged properly in the groove. Try to keep the flaps either side level with the ground.

4. Fins and panels

Glue the fins onto the panels. This can be done now for both the extending and standard versions. Try to keep them as square as possible while gluing - see image.

5. Standard Blade

Glue the fins and panels on to the sides of the blade. Make sure the panels are at least 55mm apart so that the fins will clear the other parts of the model when the blade rotates.

Step 6: Assembly: Servo Mount

Glue (or use self-tapping plastic screws) the rear fin onto the servo mount. You might also get away with using M3x20 bolts to tap the holes.
Use either self-tappers or M3x20's and 4 nuts to attach the servo to the mount. The wire should come out towards the bottom of the plasma cutter.

Step 7: Assembly: Top Plate

Solder about 40mm of wire onto the XT60 (make sure the polarity is correct)
Put the XT60 into the slot in the top plate, ensuring the back of the XT60's plastic shell is flush with the back of the slot.Use a 3mm drill bit to make a mark in both sides of the XT60 by hand
Remove the XT60 and continue using the drill bit on the marks you've made. You can use an electric drill but be careful not to go deeper than about 1mm or you'll expose the contacts inside.
Put the XT60 back in the slot, and use 2 nuts and 2 M3x10 bolts to clamp down into the holes you made in the previous step. This will stop the XT60 moving when inserting or removing the magazine.
Flip the top plate over and solder the wires onto your 5V regulator, and check the polarity is correct.
I used an adjustable regulator that I had lying around already. To adjust it I connected a 2S battery and turned the potentiometer until I got 5V on the output pins.
Solder a female JST onto the output pins. Keep the wires relatively short.
You will hopefully be able to tuck the regulator up into the top plate to keep it out of the way, leaving only the JST connector poking out.

Step 8: Assembly: Blade

Trim down the servo horn so it fits nicely in the slot on the back of the blade. Try to ensure that the hole in the centre of the horn lines up with the overall centre of the blade and sits flat in the slot. Glue it in place, ensuring the teeth that engage with the servo are on the outside of the part.
If building the extending blade, pass your micro servo lead through the blade and then through the off-centre hole in the main body. For both blade types, pass a female JST with 160mm of cable through the same hole.
Slot the servo mount into the back of the main body, while ensuring that all the cables pass up the side of the servo and out the top without being trapped. The servo mount fits in easiest if you latch the bottom in first, then push the top into place. It's not quite as easy as I'd like, but it pops in relatively nicely. Now is a good time to shorten and re-terminate the servo leads. This can be done with pliers, but is much easier with a servo pin crimp tool.
Pass the JST connector through the blade, then screw the horn onto the rotator servo. Don't worry about what position the servo is in just yet, this just keeps everything from falling apart while you put it together.
Extending blade only: Screw the micro servo into the blade, ensuring the wires come out towards the top of the plasma cutter.
Extending blade only: Slot the extending racks into place. You may need to carefully flex the sides a little to pop them in.
Extending blade only: Attach the fin plates to the racks using either self-tappers or M3x20 bolts and nuts.
Extending blade only: With the racks at the ends of their travel, ease the pinion onto the micro servo. You'll need to flex the sides a little to get the herringbone teeth to engage with both racks. If the pinion won't fit onto the servo, very carefully enlarge the hole. You want this to be a tight fit so it won't slip during use, so don't overdo it. Again, don't worry about servo alignment just yet.

Step 9: Assembly: Main Body

Solder about 150mm of wire onto the two Normally Open (NO) contacts on the microswitch. I used red wire to indicate this is the main path for the LEDs/lasers. If building the extending blade, solder an additional 150mm cable onto the Normally Closed (NC) contact - this will be used to sense the trigger state. Also bend a few mm of the microswitch lever up 90 degrees - this will come into play when the trigger is installed.
Solder one end of the NO wires (doesn't matter which) onto the positive lead that runs down into the blade, and cover with heatshrink. Pass the microswitch through the hole in the centre of the main body.
Extending blade: Crimp up two sets of servo pins with about 40mm of wire, and solder both positives and both negatives together. Leave the signal wires loose. Standard blade: only 1 set of pins is required. The pins can be crimped with pliers, but it is much easier done with a proper servo pin crimp tool.
Add a male JST with 40mm of wire. Also add and extra positive and negative wire pair about 30mm long. Solder together all the negative connections, i.e. the -ve servo pins, the lead running into the blade, the JST and the extra wire. Then solder all the positive connections together, i.e. the other NO wire, the +ve servo pins, and the extra wire. This can be a tricky business with so many wires, so it takes either a practised hand or some 'helping hands' hardware to keep them all together while soldering. Cover with heatshrink (as an alternative I used liquid electrical tape).
Extending blade only: We need a 20kohm pull-down resistor for the trigger switch. Solder it between GND and D3 on the nano, leaving some resistor leg exposed on the D3 side for further soldering.
Solder the trigger sensor wire onto the resistor leg attached to D3. Also solder the 30mm wire pair to Vin and GND on the other side of the Nano (check polarity!)
Extending blade: Solder the two servo signal pins onto D9 and D10. Standard blade: Solder to D9 only
Slot the microswitch down into the trigger well.
Use 2x M2x20 screws to secure the microswitch in place. You may need to jiggle the microswitch around a bit to get the screws to line up with the holes.
Solder two wires about 100mm in length onto your push button, then insert it into the side of the main body. Secure it using the supplied nut.
Solder one side of the push button to GND on the Nano. I used the resistor leg that is already connected to GND. Solder the other side onto D2.

Step 10: Assembly: Trigger

This is fiddly! Be prepared for frustration. Take your spring and insert it into the hole in the back of the trigger. slide the trigger up into the trigger well, and use a small screwdriver or similar to push the spring onto the part of the microswitch lever you turned 90 degrees earlier.
Line up the holes for the screw, then screw it partially down with an M2x20. Test the trigger; there should be some movement before you hear a 'click' as the switch is pressed. When you release it, the trigger should move back out and the switch should disengage. If the switch is permanently engaged, remove the trigger, cut a couple of mm off the spring, and try again. Repeat until you're happy that the trigger action is nice and reliable, then tighten the screw fully.

Step 11: Servo Configuration

This is an important step!

Now you have the trigger and push button installed, connect up the two servos (rotator to pin 9, extender to pin 10). Upload the code to the Nano if you haven't already done so. Connect the top plate and main body using the JSTs. Leave the top plate off while testing in case you need to change some variables on the Nano.

If you're using the extending blade, unscrew the pinion, then unscrew the micro servo so you can remove the blade - don't pull it too far off or you might damage the cables. Connect a 2S battery to the XT60 on the top plate. The servos should run through a short routine that would normally put the blade vertical and fins retracted.

Now reattach the blade to the rotator servo. If it won't sit vertically because of the alignment of the teeth on the servo, change the rotupper variable by 5 and reupload the code to the Nano. If it's still not quite right, adjust it by small amounts as necessary and reupload until you get it to sit vertically, then screw it down onto the servo.

Hold the trigger and push the rotator button. The blade should rotate by 90 degrees. If it overshoots, increase the rotlower variable by small amounts and reupload. If it undershoots, decrease the variable. Repeat until you get 90 degrees of movement.

If you're using the extending blade, pull and hold the trigger and then disconnect the battery. Reattach the micro servo, then manually slide the fins to their outermost position and keep them there while you reattach the pinion. Reconnect the battery and wait for the blade to turn vertical and the fins to retract. If the fins are at the lowest point of their travel and the servo is humming as if its struggling then you need to decrease the extupper variable and reupload until the fins stop just shy of the end of their travel.

You probably won't need to change the extlower variable (it's 0 by default) but the option is there.

Congratulations! Your servos are now configured for the proper amount of travel.

Step 12: Assembly: Fitting Top Plate, Mag Housing, Arch and Bottom Plate

Tuck the Nano down into the main body, leaving only the JST hanging out. Insert 4 M3x20 bolts through the holes on the underside of the main body.
If you're not using self-tappers, put M3 nuts into the slots at the front of the main body. Connect the JSTs on the main body and top plate, and pass the M3 bolts through the holes. Screw the front down using 2 M3x20's or self-tappers.
Insert 4 M3 nuts into the slots in the magazine housing. Clip the housing in at the front first, just above the XT60. It may take some persuasion to pop it into place. Once it's in position screw the 4 M3 bolts up into the nuts to tighten it all together.
Glue the front arch and bottom plate pieces into position as shown.

Step 13: Assembly: Rear Pod

Slot the M6 nut into the back of the pre-glued pod. Put an M6 flanged nut about half way up the rod (so it sits between the rear pod and the bar that sticks out) then screw the rod down through the rear pod until it engages with the nut.
Tighten the flanged nut up against the front of the pod, then screw another flanged nut on at the end.
Pass the rod through the hole in the main body and fit a flanged nut the other side. Tighten up both nuts so the rear pod is level and cannot move.

Step 14: Assembly: Magazine

Put the female XT60 into the slot in the magazine. Use the same process as you did with the top plate, i.e. line it up with the back of the slot, then make 1mm holes in the XT60's sides with a 3mm drill bit.
Solder the XT60 onto your battery (in my case a ZIPPY 2S 500mah). Secure the XT60 in place using 2 nuts and 2 M3x5 bolts. The battery may sit nice and tight up against the discharge lead (make sure its not so tight as to be damaging), but if not some double sided tape should keep it secure. Keep the balance lead accessible if you wish to charge it with a balance charger.

Step 15: Assembly: LED Front Plate

Take your 3 LEDs and solder a resistor (value depends on the LED) to the positive side of each one. Cut the legs down to a manageable size and bend them over.
Slot the LEDs into their holes and place a male JST connector at one end. Cut enough lengths of wire so that you can wire all 3 LEDs in parallel. You'll want to keep the wiring down to a bare minimum so that it fits in front of the extender servo. Make sure you connect the positive feed from the JST to the correct side of the resistor for each LED!
Take your LEDs back out and solder them up in parallel with the JST using the wires you just sized up. Use heat shrink or liquid electrical tape to cover any exposed contacts. Once done, slot the LEDs back into their holes.
Connect the male JST to the female JST in the plasma cutter's blade. It doesn't matter if you route it over the top or the bottom of the racks in the extending version, there should be enough room to accommodate the wires when the fins are fully extended. Use self-tappers or 2 nuts and 2 M3x20 bolts to secure the plate onto the blade at either end. It should clip on nicely in the middle (this also helps prevent the blade flexing and letting the racks slip under heavy load). Depending on how well calibrated your printer is you may need to file the edges of the plate a little to get a decent fit.

Step 16: Assembly: Laser Front Plate

This step requires you to dismantle the laser pens to extract the laser itself to be mounted into the blade. Usual safety rules apply: don't look straight into the lasers, and don't point the lasers at people, animals, planes or anything else daft. Steps 1 to 6 need to be repeated for each of the three lasers.

Remove the front cover, being sure not to damage the optics underneath. It should pull out towards the front with some persuasion from a pair of pliers.
We need to remove the outer body. These laser pens seem to be constructed using a very tight compression fit., so I found using a rotary tool with a cutting blade made this much easier. Use eye protection! Make sure you don't cut too deeply; it doesn't matter if you mark the outside of the optics barrel, but avoid cutting right through it. WARNING: the body can get quite hot when you cut it with a rotary tool, give it a minute to cool after cutting!
Use a tool to open up the outer body enough for the laser to slide out. Remove any plastic covers or foam spacers that may be present.
So far I've come across two designs when ordering these cheap pens. One has a thin barrel for the focussing lens, and the other a fat barrel. The fat barrel type needs to have the driver board carefully bent over by 90 degrees in order to fit inside the blade. There are 3 legs joining it to the laser emitter; ensure the single leg is on the outside of the 90 degree bend. The thin barrel type doesn't have the room to bend the board over, but it can fit further down the laser mount so space in the blade isn't as much of an issue.
Desolder the battery spring from the end of the driver board.
Bridge the legs on the push button to bypass it. A short piece of wire should do the trick.
Slot the lasers into the printed laser plate by a small amount. Use them as a guide to cut enough wires to connect them in parallel to a male JST connector.
Solder the wires on. There are 3 legs joining the driver board to the laser emitter. You need to carefully solder the positive wire to the leg that is on it's own on one side.
The negative wire should be soldered to the end of the board where the battery spring used to be.
Once you've soldered the male JST on, push the lasers down into the plate. They'll be a tight fit, so they might need a little persuasion. If you're using the 'thin barrel' type where you can't bend the board over, you need to push the middle one quite far down (you can push the other two further down too if you like) so that it clears the servo mount in the middle of the blade.
If you're using M3 hardware, put nuts into the slots in the blade. Connect up the JSTs, then clip the plate into the front of the blade. Screw down with self-tappers or M3x20's. Depending on how well calibrated your printer is you may need to file the sides of the plate a little to get a good fit. Connect up a battery and (safely!) test your lasers!

NOTE: These lasers are designed to run on 3 volts (2 AA batteries). We're running them at 5 volts. There is what looks like a voltage regulator on the driver board, but I don't know what voltage it's rated up to. To be on the safe side I'd recommend operating the lasers in short bursts, though I've used mine for quite a while now and I've not had one burn out on me yet.

Step 17: Assembly: Complete!

This is it. You've built it, you've configured it, and you've probably poured hours of printing time and a few curse words into it. Now it's time to go pretend the cat is a necromorph! (Seriously though don't point it at any animals, ESPECIALLY not the laser version!). But we're not done yet...

Remember that time you thought you were safe on the shuttle, tearing away from the infested colony at high speed? CreepyNicole appears on the seat next to you and goes for the jugular.

Now begins the arduous task of painting it...

Step 18: Painting

Painting will require some disassembly. You'll want to remove the top plate, take the blade off the front, remove the extending fins and racks if present, pop the servo mount out, and remove the rear pod from the bottom. You'll also need to take the trigger off. Use masking tape to cover any electronics and the XT60 connectors while painting.

I've seen good things about XTC-3D. Using it might save you some time rather than repeating steps 1 and 2 below using plastic filler primer and sandpaper, but I've yet to try it

Coat the parts in filler primer. Try to apply an even coat, and don't let it build up too thickly or you'll have trouble when parts are a close fit e.g. magazine and magazine housing. Wait for the coat to dry before the next step.
Sand the filler coat down until you start seeing the plastic underneath. The layers should start becoming less visible. Repeat steps 1 and 2 until the part is smooth enough that you're happy with the finish. Usually 3 or 4 coats will do it, but it depends on how smooth you want it.
Apply an undercoat of chrome, and wait for it to fully dry.
Use mustard to create areas where you want the part to appear worn, as if the original finish has come off over time. Battling necromorphs tends to do that.
Apply your top coat over the chrome and mustard. I chose a dark grey. Wait for it to dry.
Using some damp kitchen towel or similar, wipe off the areas with mustard to leave the chrome exposed again.
Lightly apply some black spray paint if you like to give the part some tone and make it look a bit 'dirtier'.
Apply a coat of lacquer to protect the part. Done!

I wanted the front parts of the plasma cutter (blade, fins etc) to look like they had been on the business end of some mining/necromorph dismembering so before I started painting I used a small file to create lots of scrapes and gouges. I then ran mustard up the gouges during painting to make it more convincing, and used black spray paint on the front of the fins. I think it came out rather well!

For a finishing touch I found some rubber mat and cut it to shape to fit on either side of the handgrip. It adds some grip and looks good at the same time.

Step 19: Remember to Dismember!

Thanks for reading my first Instructable! It turned out WAY longer than I thought it would, but I'm quite pleased with it. I hope you find it useful! If you've followed my guide and built one be sure to share it, either here or on the Thingiverse page.

Credit to my girlfriend who put up with all the hours I spent on this labour of love (and to AprilStorm and theodleif for the Seburo grip and rack and pinion parts respectively, re-used under their Creative Commons licenses)

Don't forget, aim for the limbs to inflict maximum damage on those pesky necromorphs!