Introduction: DIY Balisong / Butterfly Knife Trainer + Bottle Opener

About: My name is Lenno. I'm an undergraduate engineering student studying MSE. My hobbies range from the art of flipping to music, to all sorts of stuff.

Want a hobby more flashy than pen spinning, but one that also hones your dexterity? Search no more! The art of flipping is a great way to get your fingers in shape.

"But I don't have a balisong / butterfly knife!"

Well then this instructable is for you! You can make your own custom trainer! (Or just order one. That works too.)


8/10 - if you need to waterjet the parts yourself

5/10 - if you know what you're doing

4/10 - if you get someone else to waterjet the parts (Skip to step 9!)

DISCLAIMER: Laws differ by countries and states/provinces/etc. Please check if balisongs / butterfly knives are legal in your country and area.

I am not responsible for any legal action incurred.

Even though a trainer is not a weapon, you may get questionable looks and such due to the connotations of the real thing.

Step 1: Access to Tools and Materials


Waterjet Cutter (and .dxf template)


Drill Press (3/16" drill bit) / Hand drill

Arbor Press

OPTIONAL: Belt Sander

(Clamp, Vice grip)

(Safety Goggles)


Aluminium Sheet Metal, 1/8 in thick (minimum about 6" x 4.5")

~1"x 1/8 in Pin Stock (for two ~1/2" pins, I used brass)

4x 3/16 in OD Round Standoff, 1/2" length (or somewhat longer)

4x 3/16 in ID Washers - Teflon or Phosphor Bronze

8x Screws for standoffs - 1/8 in length (my standoffs were 4-40 size)

2x 3/16 in ID Spacers / Washers

OPTIONAL, RECCOMENDED: Loctite 242 Blue Threadlocker

Step 2: Preparing to Waterjet - 1: Import and Clean

(Numbers correlate to pictures)

#1: Open the .dxf file on OMAX Layout.

This opens the import settings.

Select 'Generation IV', and follow the import settings as shown.

Click 'OK'. The file will be imported to OMAX Layout.

#2: Click on the 'Clean' icon at the top right.

This opens the cleaning settings.

#3: Select the cleanup settings shown and click 'Start'.

Once cleanup is finished, it will display the results.

#4: Click 'OK'.

#5: Repeat Steps #2 -> #4 until no gaps are closed.

Step 3: Preparing to Waterjet - 2: Set Quality and Path

#1: Click on 'Quality' at the bottom left bar.

Right click on '3', and select 'All'.

This is the default quality for general-purpose cuts.

#2: Right click on 'Lead i/o' and select 'Autopath (Advanced/Configure)'.

#3: Click 'Go!'.

Note the Starting Corner (bottom left), and External and Internal direction offsets

NOTE: If the waterjet is not pathing correctly (kerf on wrong side of cuts), UNDO the pathing and select the other direction offset.

(The last picture is me repeating the pathing after I rearranged the parts to fit onto my aluminium sheet, which was very long and thin)

Step 4: Preparing to Waterjet - 3: Scaling and Tabs

#1: Select a round hole in a handle. Click 'Size'.

#2: Double check the size. The hole should be 0.1875 in (3/16) for both width and height. If not, enter those numbers and click 'OK'.

#3: Use the shortcut 'Ctrl + T' to create tabs.

This prevents parts from sinking into the waterjet machine.

#4: Autopath again to include the tabs in the path.
(follow #2 and #3 on 'Preparing to Waterjet - 2: Set Quality and Path')

Step 5: Preparing to Waterjet - 4: Final Pathing and Export

#1: Right click 'Path' at the top right and click 'Automatically Generate'.

#2: Click the end of the green line at the bottom left corner of the template.

#3: Check that the kerf is on the correct side of the parts. Click 'Save' to continue.

If the kerf is NOT on the correct side, go back to 'Preparing to Waterjet - 2: Set Quality and Path' and select the other direction offset.

#4: Right click 'Path' at the top right and click 'Open ORD path in Make'.

#5: Select 'Aluminium 6061' and adjust the thickness to '0.13' inches. Tool offset should not be changed. Click 'OK'.

#6: Congratulations! You should end up with something resembling this screenshot.

Step 6: Waterjet Cutting - 1: Securing and Calibrating

#1: Secure the aluminium using clamps, weights, whatever necessary to prevent it from moving.

#2: Calibrate the x and y axis of the waterjet. Flip the cup upwards. Move the nozzle to the bottom left corner of the sheet metal.

Do this using the arrow keys.

#3: Zero the User Home and Path Start.

Do this by clicking the two 'Zero' buttons. This will set the green numbers to 0 (not shown in picture).

#4: Calibrate the z axis of the waterjet.

a) Lower the nozzle using 'Page Down'.

b) Check the distance using the spacer.

c) Repeat a) and b) until the spacer does not fit under the nozzle.

d) Raise the nozzle using 'Page Up' until the spacer fits without friction.

Note: Do NOT lower the nozzle while the spacer is under the nozzle. Damage to the expensive nozzle may occur. Alternate between lowering and checking.

#5: Zero the z height.

Do this by clicking the '00' button as shown.

#6: Check z height on other areas.

a) Raise the nozzle using 'Page Up'.

b) Right click on 'Begin Machining', and select 'Go to spot on path'.

This will bring up a window.

c) Click to another spot to check.

The machine will move to the spot.

Note: Be careful not to run the nozzle into anything. Damage to the expensive nozzle may occur.

d) Repeat step #4 at this new spot.

e) Zero the z height ONLY IF the new spot is higher than other spots (z height > 0)

f) Repeat a) to e) for other areas.

I recommend checking corners. In the case of a long strip, I recommend checking the middle as well.

Step 7: Waterjet Part 2: Cutting!

#1: Raise the nozzle. Click 'Go Home'.

This will move the nozzle to wherever was set as 0 in both x and y.

#2: Click the arrow at the z height.

This will move the nozzle to wherever was set as 0 in z height.

#3: Flip the cup down. Failure to do so may cause high pressure abrasive and water to splatter everywhere.

#4: Click 'begin machining'.

A menu may pop up asking to square the nozzle. Doing this is typically not necessary.

Click 'Start'

The machine will start cutting.

Step 8: Waterjet Part 3: Removing

Once the waterjet is finished, close the machining window.

#1: Raise the nozzle and move it aside.

The finished part can be seen and inspected for defects.

#2: Remove the clamps and weights. Clean off the residual abrasive.

#3: Remove the parts from the sheet metal. Recycle scrap metal!

Step 9: Machining Part 1: Removing Tabs

#1 - #2: Using a file or a belt sander, file/sand off the tabs.

#3 - #4: Repeat for the other handles and the blade.

Step 10: Machining Part 2: Smoothing Sides and Corners

#1 - #2: File the side of the handle to smooth the side of the handle.

Notice the change from a rough to a shiny surface.

#3: File the semicircle corner closest to the hinge.

Repeat #1 - #3 for all sides of all handles and all semicircle corners.

#4: File the back and tang portions of the blade.

#5: File the tip of the blade.

Step 11: Machining Part 3: Rounding Edges

#1: Clamptwo handle parts together, making sure the semicircle notches match.

#2: File the edges until rounded.

#3: Turn the handles upside down. File the remaining edges of the handle until round.

#4: Repeat with the other two handles.

Step 12: Machining Part 4: Widening Holes

The holes on the parts are not precise, and must be widened to freely swing.

#1: Clamptwo handles as shown in the drill press.

#2: Align the drill press to the hole (using a 3/16 in drill bit). Drill the holes.

#3: Repeat #1 - #2 for the other two handles, and the blade portion.

#4 - #5: Using an arbor press, press a #10 size bolt through the hole.

#6: Turn the piece upside down and press the bolt out.

#7: Deburr the hole.

#8: Check that the round standoff fits easily in the hole. If not, repeat #4-6 until it swings easily.

#9: Repeat for other handles and the blade portion.

Step 13: Machining Part 5: Creating Pins and Press Fitting

#1: Shear about 1/2" of pin stock for a pin. Repeat for two pins.

#2 - #3: Sand/File the ends of the pins into a bit of a taper.

Use a clamp (file) or a vice grip (belt sander) to hold the pin.

#4 - #5: Press the pin into the small holes in the blade portion.

#6, #7: Repeat for the other pin.

Step 14: Tuning - Adjusting Standoffs

#1: Partially assemble a hinge.

a) Push a standoff through a handle

b) Put a washer on the standoff

c) Put the blade portion on the standoff

d) Put another washer on the standoff

e) Put a handle on the standoff.

#2: Measure the thickness of the stack.

I got 0.4325 in. Yours may differ.

#3 - #4: Sand/File the standoff. Measure frequently!

#5 - #6: Using a countersink drill bit, countersink the sanded/filed end of the standoff (just a little, no need to drill press).

Note: It might be hard to see the countersink, but it makes a difference in how far the screw will go.

Step 15: Assembly - Part 1: Hinges

#1: Gather components

#2: Take two matching handles. Make sure their notches align and their rounded edgesface outwards.

#3: Flip the top handle over. The rounded edges should be against the table.

Color around the hole with a pencil. This (graphite) is the lubricant.

#4: Put a standoff through the handle.

#5: Put a washer on the standoff.

#6: Take the blade portion. Color around the holes.

#7: Flip the blade portion over. Color around the holes.

#8: Check that the notch aligns with the pin.

#9: Put the blade portion onto the standoff.

#10: Put another washer on the standoff.

#11: Flip the handle and put it on the standoff.

#12: Screw in the standoffs on both sides to hold the hinge together.

OPTIONAL, RECOMMENDED: Apply Loctite 242 Blue Threadlocker to the threads of the screws before screwing them in.

#13: Repeat for the other side.

Step 16: Assembly - Part 2: Handles

#1: Spread the handles out.

#2: Insert standoffs into the lower handles

#3: Put your spacer(s) on the handle. They should be around ~3/16 in thick overall.

#4: Put the upper handles on the standoffs.

#5: Screw in both sides to hold the handles together.

Congratulations! You have just assembled your very own balisong / butterfly knife trainer!

Step 17: Troubleshooting

Possible Issues:

#1: Handles are 'sticky' when in completely-open / completely-closed position
This is most often caused by a press-fit pin that isn't straight.
To fix this problem, find the handle that is sticky and find which side it's having issues.

The area where the pin is getting caught will be shiny.
File down the shiny part by a little bit. If the problem isn't with the pin, there won't be a shiny spot.

Test and see if it has been resolved. If there's improvement, decide if you want to continue to file the handle or not.

#2: Handles are 'sticky' while swinging.
This is most often caused by pressure on the hinge. There can be three causes.

a) There is no / not enough lubricant, or there's stuff in the hinge.
Unscrew the hinge. Wipe off any dirt or debris found in the hinge.
Color the hinge again with pencil for lubricant and reassemble it.

b) The holes are not widened enough in the handle and/or the blade portion.
Unscrew the hinge.
Try rotating the standoff in the handle by itself, the blade portion by itself, and the other handle.
Use an arbor press and a #10 size bolt to widen the hole that is tight.
Reassemble the hinge.

c) The standoff was ground too short.
Test by trying swing the handles with loosened screws. It should swing fine with loosened screws. See Step 3: Machining - 6: Tuning.
You will need to create two more standoffs of correct length.

#3: Screws are loosening by themselves!
Apply threadlocker to the screws.
Only use red threadlocker if you want it to be permanent. Blue threadlocker works, and I personally recommend purple threadlocker if available (low-strength). Epoxy works as well but I would not recommend it.

Step 18: Fin

If you've made it this far, you've assembled your trainer. Now you can get to the art of flipping!

I have indicated the safe handle and the bite handle.