This is likely to be the last of the big weapons for a while. I am running out of scrap to make them with!
This was simply an exercise to try and build a non-functional (but rotating) minigun prop for a stills shoot. It basically uses up all my remaining odds and ends of PVC pipe.
The methods and materials I have used are simply because that is what I had in the workshop. I didn't want to spend any money on this project if possible.
YouTube video of the gun spinning can be found
Step 1: The Barrels
Without a doubt the defining feature of the minigun is the six barrel Gatling arrangement. I sourced as many images of the variants of minigun in existence as well as few imaginary ones. I also found some diagrams and drawings.
The main components of my barrels are lengths of PVC tubing used for plumbing and cable trunking. Unfortunately none of them were long enough individually to match the correct barrels so there are 6 lengths of 20mm tubing, and then 6 lengths of 15mm tubing to form the barrels. The central shaft is made from a length of 25mm conduit.
I began by cutting and cleaning up the pipes. I laid out the cleaned up sections and checked they were all the same length.
Next comes the barrel spacers. I used two card templates and carefully drew and marked up the spacers. These were then cut out and I looked around for two plastic tubs of similar diameter. I poured resin into the tubs to a depth of about 1/4" or 6mm and left them to cure.
Step 2: Spacer Assemblies
Once I had the two cured resin 'pucks' I glued the templates to them, gave them a coat of resin to protect them, then carefully drilled out the holes and cleaned them up.
These two spacers then formed the masters to cast the rest. I needed three of the smaller and three of the larger sizes to complete the barrels.
Step 3: Barrel Assembly
Starting with one of the smaller pucks, I placed the 25mm central spar into place, carefully made sure it was perpendicular and glued the spacer on to the end.
Using three of the 15mm sections to ensure alignment, I slid the second of the smaller pucks onto the central shaft and glued it into place. I then fitted all 6 of the 15mm sections into the spacers and glued them all in. The final spacer was then glued to the tops of the 15mm sections.
The process was repeated for the upper barrels making sure to align the two sets of pipes so that they looked like continuous barrels. I used two of the larger spacers at the top of the 20mm sections for rigidity. Then the whole assembly was set aside to dry.
Step 4: Main Body
I agonised for some time about electrifying this gun and making the barrels spin. I thought of using a car starter motor and mounting the barrels directly, or using a smaller motor and a drive system..
The problems with this are the fact that the barrels would need some kind of bearings fitted, or some sort of belting or gearing arrangements. I searched the workshop to see what I had left over.
I had plenty of resin and fibre mat, some old skate bearings and a blown 14V cordless drill. There was a 12V motor from an old printer, but no drive belts at all. I decided to give it a go and worry about the final drive later.
The main body is a piece of 4" / 160mm soil pipe, you can buy end caps to fit this stuff but I didn't have any so I used an off-cut to cast the ends in resin. Again I made a card template with the centre marked on it for drilling later. I didn't bother to make a mould, I just made two ends using the off cut as a mould of the pipe. These were then drilled out and sanded with a centre hole to a diameter of 27mm to give 1mm clearance all round the barrel shaft. The ends will be secured with self tapping screws once everything has been tested.
Next comes the fiddly bit. Each end needs three skate bearings to hold the barrel shaft and allow free rotation. The barrel diameter is 25mm, and the bearings were 22mm diameter. In theory this gives a distance of 33.5mm from the centre of the shaft to the centre of each bearing. If I had used my brain I could have marked all of this onto the card template, but I didn't, so used a bit of measuring, a bit of best guess and a bit of pot luck and marked the bearing centres. Fingers crossed eh?
I painted the outer faces of the end caps in black to save time and effort later. The whole thing was then assembled and tested for free running. It worked fine, so the final step in building the main body is to drill through the body into the end caps and add three self tappers for each end. I recessed the front end by an inch to allow for the drive assembly and put a retaining ring on the end of the barrel shaft to stop it from dropping out.
In this way the assembly can be stripped down for servicing, maintenance and adjustments.
Step 5: The Motor Mount and Pistol Grip
I decided that the easiest way to construct the pistol grip was to cut up the old cordless drill with the Dremel. I marked out the section I wanted, dismantled the drill and reassembled the shell. I then cut through it with the Dremel and cleaned off the edges.
Whilst doing all this I realised that the 12V printer motor was exactly the same diameter and had the same locating holes as the drill motor which was knackered. The printer motor was around 10mm longer than the original, but where i had cut back the drill body this didn't matter. Using the original drill mount and fittings I installed the new motor and soldered some long leads to it. This should be able to make the motor mount if I am careful in fitting it to the main body.
You can see the old burnt out motor with it's gear attached in the very top of the first picture.
I will re-use the original drill trigger and electrical contacts for the minigun, and hopefully mount the battery pack into the feeder to hide it. That way I should (in theory) be able to recharge the batteries using the drill charger with some Heath Robinson adaptations.
I set the pistol grip aside for later.
One problem is the fact that the motor mount has been so butchered that it has nearly an entire side missing. I found an old stout cardboard tube of about the same diameter, and cut out a section big enough to fit the mount. This was coated in three coats of resin to strengthen it and then hot melted into place. This will be filled and sanded back and the whole thing painted to match.
To make the mounting yokes, I constructed a simple jig from an off cut of the cardboard tube, and off cut of the body pipe and two pieces of wood. These were tack sealed to my resin board using plasticine (nu-clay?) and then resin was poured into the mould. I made two of these yokes, cleaned them up with the Dremel and then glued them to the body.
I made a small aluminium extension for the motor shaft, then glued the motor mount to the body yokes. I did a quick test using a rubber band as the drive belt and it all worked well. I will need to find an old Hoover belt for the final assembly.
Step 6: The Feeder
My original plan was to find some 3" plastic drainpipe for the feeder. I was going to strip down the cordless drill battery pack into individual cells and then re-arrange them n the 3" pipe.
However, I couldn't find any 3" pipe, and as luck would have it, the original battery pack in it's plastic cover was a nice fit inside the 4" downpipe I had used for the body. I decided to use that instead, and although it's really too big a diameter to be accurate I thought I could disguise this later with some embellishments.
I decided to try and mount the battery pack as far back as I could relative to the body to try and balance the weight of the barrels and motor at the front.
I cut a section of pipe roughly half the length of the body, lined it up on the bench and tacked it on with 6 blobs of hot-melt. Then I used the off cut rings of scrap pipe left over from cutting out the feeder to make a mould and cast a set of small yokes. These were glued in place and then the joints were run over with hot melt to seal and strengthen it all.
I then cast two end plates, drilling one in the centre to allow the wiring to pass through. Leads were soldered to the battery pack, then taped up in electrical tape to try and stop moisture from getting to them. the battery pack was glued in with hot melt and the end caps fitted. These end caps will have cosmetic additions at a later stage. I used some old panel sockets and plugs for the wiring end and added an end plate with a chassis fitting I found in the spares box. This will allow the battery pack to connect to the trigger, or the charger by simply swapping the plug over.
The wiring end was secured with three self tapping screws to allow access if required.
I found a bottle top from a washing detergent bottle and trimmed to for a good push fit over the end of the motor housing.
Step 7: The Front Handle and Frame
This is probably the most difficult part of this build. The front handle is fixed to a frame that then runs down the body to the rear grip and trigger. The frame is fitted to the body and has to take all the weight slung beneath it. My main concern is the front handle arrangement since it will effectively just be glued to the main body.
I used up all the remaining fittings I had for the cable trunking, two corner joints, two 'T' joints and a few off-cuts of 20mm pipe. I also had a piece of lightweight aluminium angle, and four ABS plastic feet from an old cupboard. Not much to go on.
I glued the four feet together to form two cylinders. They had a hole running through them where they were originally screwed to the base of the cupboard. I found a couple of long nuts and bolts that would fit. So I then filled the two corner joints with resin and let it set. I then drilled through the joints so that the bolts of the two cylinders would slide through.
Next I used one of the cylinders and three off-cuts of the 160mm pipe to form a yoke mould and cast two yokes for the cylinders using the same method as before. These will have to take the entire weight of the gun when carried. I made them 25mm thick to give as big an area for the glue as possible. These were glued to the ends of the feet.
I then bolted the corners to the ends of the cylinders. I took the two 'T' joints and cut one side off each, placed a bit of 20mm pipe between them to form the handle. I then cut two short stumps of 20mm and filled them with resin. Once this had set i glued them into the joints to give a solid mass that could take a self tapping screw.
The angle was cut to length then drilled to take the ends of the mounts and the ends of the handle. The entire assembly was offered up to the main body and the yolks swung round to fit correctly. They were then glued into place with cyanoacrylate and a fillet of hot-melt run round the joints. The handle was dis-assembled and a bit of hot-melt applied to each joint then it was all screwed back together.
With the front handle and mounting plate in place it was time to look at the front to back brace assembly and the rear grip.
Step 8: Body Brace and Rear Grip
I began by sketching out how I wanted it to fit together. On the original gun the frame bolts to the rear of the body, but I didn't think that mine would be strong enough in that configuration. Instead I decided that I would construct the 'Y' frame as a non load bearing part, then make a yoke that could be glued and screwed to the upper rear of the body. The 'Y' frame would then be screwed onto the yoke from above. I would make the 'L' shaped bracket for the rear grip from two rectangular sections. These would be glued and screwed together, then screwed and glued to the end of the yoke and 'Y' Frame assemblies. I thought that this would be strong enough to support the weapon.
I started by creating the three rectangular boxes for the rear parts (one drops below the grip plate and will be used to hold the main body end cap). These were cut from high density card 1.5mm thick and glued together with general purpose glue. Once set they were filled with resin and fibre matt and allowed to cure.
I used the same process to create the 'Y' frame running mine right to the edges of the front angle iron, again a deviation for the original. Once I had the main cardboard structure created I did a test fitting. Once mounted this will be held with small self tapping screws at the front.
Step 9: Putting It All Together
With the addition of the yoke at the back of the body, it is now time to assemble everything. Some of the wiring can only be done with the grip wires passed through the base plate so assembly order had to be worked out to fit.
Basically the blocks are screwed and glued together.
The 'Y' frame, back plates and grip are designed to be a single unit that can be removed to allow access to the rest of the gun. Two self tapping screws at the rear hold the frame to the rear yoke, and two at the front secure it to the angle frame. Once these were in place the gun begins to take on a more realistic look.
The grip was both glued and bolted into place and everything was tested to make sure it was secured.
The motor wiring needs to be tidied up, and I wanted some kind of plug arrangement so that the entire Y frame and grip can be removed from the gun. I am also waiting for a better drive belt at this stage since the neoprene drive belt keeps slipping.
The electrics were tested and work correctly, so the top of the grip can be made.
At this stage the weapon is mechanically and electrically complete.
All that is left now is detailing, some cosmetic additions and painting.
Step 10: Details and Additions
Due to the dry-brush painting system I like to use, raised details will help to enhance the final look of the weapon. First I had to help to 'tone down' the look of the feeder. I made up a face plate from two end caps (a bottle top and card tube end). these were hot-melted together and three short screws were added for detail.
Next I made up the feeder motor tube from a piece of 40mm drainage pipe, two strips of card and two plastic bottle tops. these were super-glued and hot-melted together then glued to a circle of card and four plastic nuts were added. Both these assemblies were then hot-melted into place.
A card top cover was added to the pistol grip, a better shape will be added later. Panels were added to the main body from cereal packet card super glued into place. these will simply add some surface relief detail and break up the smooth body surface a bit.
Various small screws and bolts were also glued on for effect.
Step 11: Painting and Finishing
Next I gave the main body a dry brush coat of natural steel hobby acrylic, followed by a lighter dry brush coat of silver.
I also dry brushed certain areas with a little bronze.
Next I gave some of the shadow areas a gentle airbrushing with dark brown and black to bring up the highlights.
Finally I added some dirt and dust marks with artist pastel chalks ground up on some wet and dry paper. Some brush work to mark areas of peeling paint and the weapon is done.
I gave it a quick spray with cheap 'max hold' hairspray to seal the pastels then set it aside for another two days to completely cure.
It just needs a carry strap, the back pack and ammunition belt to make it totally finished.