This model is ready to take off!
I've been using mold-making in my studio practice for the past six months and have loved it! I made a mold using a Boeing 747 replica that I had bought from a hobby store but I didn't like how small it was. My molds were too fragile. Then I realized that I can make a bigger model using a 3-axis CNC router. I thought it turned out so well that I would share the experience!
First, I would like to give the artist, 3dregenerator, credit for rendering the Boeing 747 model and posting it as a free file on the link below. I've included the files of parts that I cut apart using Netfabb Basic (a free program that is often used for preparing files for 3D printing).
Posted by 3dregenerator, 2011.
WHAT YOU NEED:
-- Wood glue
-- Pipe Clamps
-- Wooden dowel 0.25” or 0.375” thickness
-- Wood screws (1”, 1.25”, and 2.5”, also depends on thickness of your material)
-- 1/8" drill bits for pilots holes
-- 0.5” down spiral end mill carbide router bit (at least 2.5" cutting depth)
-- 0.5” ballnose carbide router bit
-- 0.25” or 0.375” down spiral carbide end mill (depending on your dowel thickness)
-- Orbital Sander Sandpaper & Sheet Sandpaper (100 grit, 180 grit, 240 grit)
-- Nitrile gloves
-- 5-Minute Epoxy
-- Respirator mask with organic fumes canisters/ventilation booth
-- Polyurethane Finish
-- Rag/Fine Bristle Brush/Foam Brush
-- 400/600 Grit Sheet Sandpaper
-- Miter Saw*
-- Table Saw
-- Hand Drill & Driver
-- 3-axis PRS Standard Shopbot CNC router
-- Orbital Sander
*Use these tools if you're choosing to glue up solid wood and not use plywood.
Netfabb Basic [free!]
Vcarve Pro 8
This Instructable has specific directions on how to use Vcarve Pro 8 and a Shopbot CNC Router. If you do not have access to one or both of these programs you can easily exchange them with other CAM software and other CNC routers with at least a 2' x 4' bed with at least a 8" Z-height capacity (or you can slice up your model into thinner layers). One should also note that I purposefully carve into my sacrificial bed. If this is a problem for you—whether you have a vacuum table or morally cannot think of purposefully marring your work surface—you can use a dummy-sacrificial board!
Step 1: Prepare Your Material
I wanted to experiment with solid wood (rather than plywood, although I did an Appleply version that was pretty neat!). I chose to try a lower priced softwood and went with blue pine--$3/board ft and still pretty! If you’re using plywood, cut the material closer to the size of your parts so you can easily flip and register your material. Also keep in mind that you can save your CNC machining time--as well as your bits’ lives--by preparing your material to be as close to the final thickness as possible.
-- I used 2 x [2" x 6" x 10'] boards of blue pine.
-- Glue up two sticks at 40" lengths one on top of the other for the fuselage.
-- For the large wings and the top back wing, glue up a 22" x 24" board (our drum sander has a 23" width parameter. If you have access to a drum sander or a planer that can handle wider, I would recommend adding 6" or so). I also recommend not adding too much to this second glue-up to keep flipping and registering 2" thick blanks manageable.
-- Make an 11" x 11" glue up for the two small back wings. Plane it down to 0.5" thick. Resawing this piece beforehand would be ideal.
Step 2: Prepare Your Table & Registration
I have already sliced the individual airplane pieces (the fuselage and wings) apart for this Instructable and included my working files for Vcarve Pro 8. In particular, I cut the wings from the fuselage so I could cut the fuselage in one double-sided file.
In Vcarve Pro 8, open 01_Fuselage_Left.vc and design your registration holes. My registration holes are provided to give an idea of how I did it but test out your registration holes with your dowel on some scrap plywood beforehand. Scale your holes to the width of your dowel with an appropriate offset. I made mine by centering the left-most registration hole at an inch or two from the leftmost edge by programming the center of the circle to X, 3, Y, 3, whatever seems best. Then, I highlighted the registration hole and the material boundary, copied it, and mirrored it horizontally.
You'll be zeroing on the top of the material for both sides of the fuselage and you also want to zero on top of your sacrificial board to pocket the registration holes. Get your bit ready--I used a 0.375" bit because my dowel was a little wider. Cut your holes on the table.
I like to make a dummy fence to start with. Using a scrap piece of plywood, design a 2" thick fence with a dog-boned corner at the "new" home position. I do this because I can't guarantee that my material's width is exactly as I program it and when I flip it to carve the other side It may hit my existing fence on my sacrificial bed.
Now secure your material with the method you feel most comfortable with. I decided that the best way for me secure my board to the table was to screw through the bottom of the plenum into the bottom of my board. I drilled from the top to get it right in the right spot and screwed from the bottom using self-drilling screws to avoid tear-out on my material.
Step 3: Fuselage Body
Double-sided carving is such a joy!
The first thing you want to do on your fuselage file is to carve the registration marks on top. Then you can dive right in. Some programming things I like to stick to are: leave a 0.1" machining tolerance on the roughing pass and give your roughing and finishing passes 0.125" boundary parameters. If you're using a harder wood, then maybe kick it back to 0.07" or less for the machining tolerance to save your bit's life. Programming the machining tolerance saves from the roughing bit taking too much material off before the finishing pass and often leaves chatter. Keeping a machining boundary with deep models like this one is important to prevent your bit trying to dive 4" on the sides.
After carving your roughing and finishing passes, run a profile pass at a depth of 2" with a long 0.5" down-spiral endmill. Since the material is so thick, this is important to do so you can carve all of the way through and make un-tabbing your model easier.
Next, take the material off of the bed and flip it horizontally (so that the top of the airplane is still up and the nose is pointing away from your home position). Take off the dummy fence and register the material using 1" bits of your dowel in the registration holes.
After running the roughing and finishing passes using the 02_Fuselage_Right.vc file, program tabs and use your long 0.5" down-spiral endmill to cut out the last 2" deep profile pass.
Step 4: Wings!
The next set of files are the large wings [03_Big_Wings_Left_Top, 04_Big_Wings_Right_Bottom, 06_Big_Wings_Left_Bottom, 07_Big_Wings_Right_Top] and the dorsal fin [05_DorsalFin_Top_Left, 08_DorsalFin_Top_Right].
This is where making sure you have your files perfectly mirrored and toolpaths properly labeled is very important. Vcarve Pro 8 only allows for one 3D model per file. Since I wanted to carve three files for one blank, I needed three files per side. It gets a little repetitive running the roughing and finishing passes while keeping three or more different model files in mind.
Just like the fuselage file, plan out where you want the registration holes. I used the left registration hole from the fuselage file and reflected it horizontally in Vcarve to get the new one using the new material boundary. After cutting the new registration hole(s) into the bed, secure the dummy fence and secure your material. Be sure to zero on top of the material for this side of machining.
-- Cut your new registration holes on top of the material
-- Running the roughing and finishing passes (Left Wing top, Right Wing Bottom, Dorsal Fin Top)
-- Flip the material (and open new files, flipping the vectors lines) and be sure to program your tool paths to zero on the bed surface.
-- Run the roughing and finishing passes. (Left Wing Bottom, Right Wing Top, Dorsal Fin Bottom).
-- Mark the tabs in your file and run the final profile pass.
-- Take the board off the table and cut out tabs using a jig-saw or band-saw.
Step 5: Stabilizer Wings
Here we go again!
You'll need the files for the stabilizer wings [09_StabilizerWing_Left_Bottom, 10_StabilizerWing_Right_Bottom, 11_StabilizerWing_Left_Top, 12_StabilizerWing_Right_Top].
-- Figure out where your registration marks lie and cut them into the bed.
-- Secure your material and zero on top of the material.
-- Run the roughing and finishing passes and flip the material.
-- Zero on the table and run the final rough and finishing passes.
-- Mark the tabs on your file in Vcarve and run the final profile pass.
-- Cut out the tabs with a jig-saw or band-saw.
Whew! You should be a pro at double-sided carving (if you weren't already). Lots of registering, flipping, tool path generating, and patience. Next is another way to test patience: finishing.
Step 6: Finishing
Now it's time to get this bad boy sanded, epoxied and finished!
For the rough edges I used 80 grit orbital sand paper. Per usual, I worked my way up to 240 grit--using a rasp to clean up the epoxy smudges. The big wings will look nice with the flat edges they have already but I preferred to bring them to the belt sander and set the angle of the plate to 7 degrees. I did this by cutting a scrap piece of wood and ripping a 7 degree angle down one side. Using my quick jig, I adjusted the resting plate to 7 degrees. Make sure the the angle is making the wing bend upward!
-- Fill in holes and tear out. I chose to fill in small holes with 5 minute epoxy because I didn't have any filler that would match blue pine. I also think that it just looks sharper. Sand this down to smooth.
-- Sand the wings and the fuselage to a nice finish, attach the wings one at a time using 5-minute epoxy. This may be crude, but I found just holding the wings in place firmly for the five minutes and then holding them in place with a wedge, they were stable and strong.
-- After attaching the wings, file and sand off any epoxy that dripped out and put 3-5 coats of a polyurethane finish, buffing in between layers with 400 grit sandpaper.
Hope you found this Instructable helpful and fun! You're cleared for take off!