Introduction: +Bow - Homemade Spring-Powered Nerf Rifle

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Specifications
Length: 36 inches
Weight: 2lb
Plunger load: 18-32lb
Spring load maximum: 38lb
Optimal Barrel Length: 12 inches

Performance
Plunger rod has three notches affording different load rates which gives the user different range options.

Distances averaged
28lb Pull: 140 feet
22lb Pull: 110 feet
16lb Pull: 80 feet

Individual results will be dependent upon too many factors to list so take these only at face value.

Tools REQUIRED for following this guide
+ Scrollsaw
+ PowerDrill or Drillpress
+ Mitre Box & Mitre Saw or a power tool useful for cutting plastic rod or tube (such as a table saw, circular saw, or band saw)
+ #6-32 Tapping Bit
+ Screwdriver
+ Hobby Knife (to clean the edges of the sheets once cut)
+ Scissors

No other tools expressly needed. All tools listed are not easily substitutable and I don't recommend attempting to make this gun with anything other than a scrollsaw due to the size of the parts you will be making.

Part List
Download: plusbow_partlist.txt
Note: You will also need some full sheet label paper, electrical tape, and some spray silicone lubricant.

All items available through Mcmaster Carr

Simply search for the part #s listed. Total cost of supplies listed is around $80 plus shipping. You will have enough excess of most materials to make atleast 2 or 3 more guns.

Be warned. This guide has 37 steps. Not because the project is extremely complicated, but because I'm going to go into a good deal of detail on each step.

Step 1: Step One

Download the cuttings template sheets: plusbow_templates.doc (100kb)

Print them on full sheet label paper. If you ran out of color ink (like I did) make sure to use a colored pencil to mark the holes with the size you will need to drill them to.

Step 2: Step Two

Cut out all of the templates from the full sheet.

Set aside the labels indicated in the picture because you won't be applying them right away.

They will have to be applied to the opposite ends of the 13.25 x .5" length piece of 1/4" thickness polycarbonate that will become the plunger rod. You can cut this out now or later using a scroll saw or table saw after marking the dimensions.

Step 3: Step Three

Apply the cutting templates to the indicated thicknesses of polycarbonate sheet.

You can group them fairly close together to minimize excess, but keep enough of a gap to allow the blade of the scroll saw to cut inbetween the parts.

Step 4: Step Four

Cut the labeling sheets into smaller more manageable sections using a scroll saw or band saw.

Wait to cut out all of the small parts until later. This will make drilling holes in the smaller pieces much easier and safer.

Step 5: Step Five

Using a drill press or power drill follow the color legend you printed or wrote on the labels to drill out all of the holes to the required sizes.

Also make sure to drill 5/32" diameter pilot holes in the center of the areas you will have cut out. Such as the pass-through holes in the frame pieces and catch plate, The slide tracks in the trigger and catch plate, the trigger wells in the sides of the grip, the center of the priming handle, and the optional decorative "+" signs on the body sides

Step 6: Step Six

Use a scroll saw or band saw to make all of the external cuts needed to free and shape all of the parts out of the sheet.

Step 7: Step Seven

Use a scroll saw to make all of the internal cut outs. Start by feeding the blade through the pilot hole you drilled in Step Five then retensioning the blade.

Step 8: Step Eight

Now all of your plastic sheet parts are cut out.

Step 9: Step Nine

Using the side plates that they will eventually screw into as a guide, mark the edges of both sides of the frame pieces as shown.

Step 10: Step Ten

Using a 7/64" bit in a drillpress or power drill drill to a depth of around 1/2 of an inch. Then tap the holes with a UNC #6-32 tapping bit.

Step 11: Step Eleven

Using a mitre saw with box, table saw, table saw, or circular saw cut a 7/16" length section off of the 1" diameter plastic rod.

Using the 1/8" thickness plunger rod piece as a template (as centered as you can get it), mark the two holes as shown.

Using a 5/32" bit in a drill press or power drill drill through at the marked points.

Step 12: Step Twelve

Using a mitre saw with box, table saw, table saw, or circular saw cut two 11-1/4" length sections and one 12" length section off of the 1/2" diameter plastic rod.

Mark the center of both ends of the rods.

Using a 7/64" bit in a drillpress or power drill drill to a depth of around 1/2 of an inch. Then tap the holes with a UNC #6-32 tapping bit.

Step 13: Step Thirteen

Remove the cutting templates and protective film from the plastic sheet parts.
The catch plate will need its lower edge beveled and the corners of the stub at the top beveled to accept a spring. To see more detail on this part see Step Seventeen and Step Eighteen.

Step 14: Step Fourteen

Deburr the edges of all of the sheets using a hobby knife To quickly remove the burrs simply orient the blade perpendicular against the edges of the sheet and run it along them. Any trouble spots and be cleaned with the hobby knife by manually cutting away the burrs.
Further smoothing can be done with sandpaper if desired. I would recommend doing so on the grip.

Step 15: Step Fifteen

Using the 1/8" thickness plunger rod part as a template, mare the front edge of the plunger rod.

Using the front piece of the adapter bracket, do the same on the front edge of the side pieces for the adapter bracket.

Using a 7/64" bit in a drillpress or power drill drill to a depth of around 1/2 of an inch. Then tap the holes with a UNC #6-32 tapping bit.

Step 16: Step Sixteen

Squeeze two Dash 316 O-Rings onto the 7/16" section of 1" diameter plastic rod. Sandwich it inbetween the 1/8" and 1/4" thickness plunger head pieces and bolt them onto the end of the plunger rod using 1" length screws.

Step 17: Step Seventeen

Assemble the center frame piece and catch plate together as shown using washers and 1" length screws.

Attach the 12" length section of 1/2" diameter rod to the center frame piece using a 3/8" length screw. Mark on it where the centerline of the catch plate is.

Remove the 12" rod and using a 7/64" bit in a drillpress or power drill drill through where marked. Then tap the hole with a UNC #6-32 tapping bit.

Attach the 12" length rod to the rear frame piece again using a 3/8" length screw. Install a set screw into the newly tapped hole by hand.

Step 18: Step Eighteen

Install a 1" length spring (one with a load between one and ten pounds) onto the catch plate and the set screw.

Step 19: Step Nineteen

Attach the 11-1/4" length sections of 1/2" diamter rod to both the rear frame piece and the butt stock using 3/8" length screws.

Step 20: Step Twenty

Slide the 12" length rod through the 1/2" hole in the rear frame piece and then bolt it to the butt stock using 3/8" length screws.

Step 21: Step Twenty One

Attach the side plates to the center and rear frame pieces using 3/8" length screws.

Use one of the grip pieces as a template to mark the edges on both sides of the rear frame piece where shown.

Using a 7/64" bit in a drillpress or power drill drill where marked to a depth of around 1/2 of an inch. Then tap the hole with a UNC #6-32 tapping bit.

Step 22: Step Twenty Two

Attach the front plates to the side plates using two 1/4" length screws, four 3/8" length screws, and two 1-1/2" standoffs. Wrap and tie a rubber band onto the standoff where shown.

Step 23: Step Twenty Three

Place the plunger cross where shown inbetween the 1" screws protruding from the front of the center frame piece.

Step 24: Step Twenty Four

Assuming you order exactly one foot of the 1-3/8" ID polycarbonate tube it should already be at the length you need. If not then use a mitre saw with box, table saw, band saw, or circular saw to cut a 12" length section from the longer tube.

Slide the 12" length plunger tube onto the plunger cross and push it down to meet the top of the 1-1/2" standoffs.

Step 25: Step Twenty Five

Mark where shown.

Using a 5/32" bit in a drillpress or power drill drill where marked on both sides.

Step 26: Step Twenty Six

Insert the hex bushing adapter into the end of the plunger tube and mark it as shown as well.

You don't want to drill the holes in the hex bushing too far forward or it will prevent you from installing a barrel.

Using a 5/32" bit in a drillpress or power drill drill where marked on both sides of the hex bushing.

Step 27: Step Twenty Seven

Wrap the hex bushing in 3 or 4 layers of electrical tape then use a hobby knife or ice pick to poke through the drill holes in its sides.

Push it into the end of the plunger tube and line up all the holes. Lightly hammer then hand screw the bolt all of the way through and affix it on the other side using a lock nut.

Step 28: Step Twenty Eight

Remove the new plunger tube assembly from the rest of the gun as shown.

Step 29: Step Twenty Nine

Clean out the inside of the plunger tube then spray a generous amount of silicone lubricant into it.

ONLY USE SILICONE LUBRICANT WITH PLASTICS. It's the only lubricant that won't eat away or degrade the material.

Install the plunger rod and spring in the plunger tube. Work the plunger rod back and forth in the plunger tube a few times to get the o-rings lubricated.

Step 30: Step Thirty

While depressing the catch plate by hand, slide the plunger rod through the plunger cross, center frame piece, catch plate, and rear frame piece.

Reattach the plunger tube assembly to the rest of the gun, starting with the 1/4" length screws.
Attach the priming handle to the exposed end of the plunger rod.

You can make and attach either one or two of these depending on your preferences. Other handle options are possible, but the other methods I've tried weren't as comfortable as this one.

Step 31: Step Thirty One

Use one of the grip pieces as a template for marking the 3/4" thickness polyethylene foam sheet. How much padding extends away from the grip is up to you, but 1/4" to 1/2" is plenty.

Make sure to mark the two holes as well.

Step 32: Step Thirty Two

Finish marking like so and the foam shouldn't interrupt the trigger.

Use a hobby knife or ice pick to stab out the holes. Use a band saw, hobby knife, scroll saw, or scissors to cut out the foam piece.

Step 33: Step Thirty Three

Follow the photograph labels for attaching the hardware to one of the grip pieces.

Step 34: Step Thirty Four

Slide the foam grip core onto the standoffs. Slide the trigger piece onto the 1-1/4" length screws and add another 1/4" length spacer. Install a 3/8" length screw in one side of the trigger.

Step 35: Step Thirty Five

Add a 3/8" spacer to the opposite grip piece. Put a washer and a lock nut on the end of both 1-1/4" length screws, but only tighten them enough for them to lock or the trigger won't slide.

Step 36: Step Thirty Six

Attach the front of the grip to the side pieces using 3/8" screws as shown. Hook the loose end of the rubber band onto the 3/8" screw you installed on one side of the trigger.

Hinge the grip into place over the rear frame piece and attach it to both the rear frame piece and side pieces using four 3/8" screws.

Step 37: Step Thirty Seven

Add your preferred barrel, and your gun is now complete. The process has taken anywhere from 6 to 12 hours from start to finish depending on the tools you were using.

Final Notes:
+ This gun is extremely durable, but in the rare event something does break it's not at all difficult toreplace any of the parts.
+ This gun doens't involve any glue. Hot, cold, or otherwise. So it should be able to take heat, cold, or humidity without any problems.
+ The rubber band on the trigger isn't a vital part and the gun will still function if it were to break. It's only there to improve the feel of the trigger and could just as well be replaced with a short/weak extension spring. I didn't have any on hand.