Working on creating a new pinball machine with the Halifax Makerspace, we realized we needed a ramp or two. Ramps add an exciting 3D aspect to a pinball machine. We also wanted a raised playfield, so ramps were a necessity.
After some research, it seemed there were a number of ways to make ramps, with the best candidates being sheet metal, laser-cut acrylic or vacuum forming. Having no skills and few tools to do metal work, and with a busted tube on our laser cutter, I decided to try vacuum forming. This also had the advantage of allowing complex curves that are difficult to get from sheet metal or acrylic.
Most of the instructions I could find relied on having a ramp to copy, which is great if you're restoring a pinball machine, but not helpful if you're making a new one. So this is my method for making a ramp from scratch.
Though this specifically deals with pinball ramps, you could use the same or similar techniques for any number of modelling projects.
Step 1: Determine Your Ramp Footprint and Limiting Features
Imagine the "shadow" of your completed ramp, and where it lands on the board. Draw this in with pencil, if you're real-world-inclined, or model it in your CAD program of choice. We drew ours in pencil on the actual playfield, then copied it approximately onto paper, making sure to get the left and right openings exact, and, on the larger ramp, indicating where it passed over the smaller ramp. I made note of the height it needed to be at that point. If your ramp needs to go under, over or around other things make sure to note these. Be sure you'll have room on the playfield for mounting hardware. Cut out your paper footprint.
Step 2: Making the Rough Form: Bottom
Using your paper footprint as a rough guide, cut some plywood, chipboard or similar to act as a base for your rough form. Cut it large enough to accomodate supports all around. I used 5/8" chipboard.
Transfer your start and end points of the footprint to the base, as well as any limiting features. In my case, the only limiting feature was that the ramp had to be elevated at least 1 3/4" at a certain point to miss hitting another ramp. So I cut a 1 7/8" piece of scrap and hot glued it at that point. I cut another piece at the upper end of the ramp at the height I wanted the bottom of my ramp to be, and hot glued it. Make sure you can extend your start and end points 1/4" or more. You'll make your ramp slightly longer than needed to make cutting it easier later.
Add support blocks as needed to support the bottom of your rough form. I found three supports sufficient for my approximately 10" long ramp: the base acts as a support for the start of the ramp, the 1 7/8" block and the block at the top of the ramp. I wanted my ramp bottom to be slightly angled, so I hot glued a thin wedge to the top of my middle block.
Cut a very rough strip of flexible plastic to act as the base of the rough form. I used .03 styrene sheet, available from plastics suppliers. Use your paper footprint as a rough guide, but know that you'll have to make it a little longer. Mark the fixed points (left and right of the openings, etc.), then use a french curve or flexible plastic straight edge to mark nice curves. Ensure the inside and outside are either parallel, or taper nicely if desired. Cut your form bottom out and hot glue to your supports. Ensure the start and end are flat against the base/support for a smooth transition. You don't want your pinball to jump when it hits the ramp.
Step 3: Making the Rough Form: Sides
The sides are a bit tricky, but we are making a rough form, so we can be forgiving of errors.
You'll need to add some supports to hold the sides of the rough form. Choose some points to place them. You'll need one at each end. The number you'll need in the middle will depend on the flexibility of your plastic, and the length and curviness of your ramp. I used six in total for my long ramp. Number each support point, with one side being "A" and the other "B".
We're going to vacuum form our ramp, which means we need the sides to taper. If the sides are parallel, it will be very difficult to remove the vacuum formed plastic from the mold. After some research, I choose 7 degrees as the ideal taper.
For each support point, cut a thin strip of wood that's the height of the bottom of the rough form at that point, plus the height of the ramp. I used 3/8 plywood. Number these as you go along and mark where the bottom of the rough form meets it. Sand or cut a 7 degree taper from the mark to the top. I set my chop saw to 7 degrees and cut a test board, then used the test board to mark my supports. Then I used a disk sander to sand to the mark. These pieces are too small to safely use a chop saw to cut them. Hot glue the supports in place.
Next, rough cut some thin plastic for the side. Put it in place along the supports, as close to the bottom as you can. Scribe a line, following the contour of the form bottom. Cut this out, test and modify as necessary to get close. You can safely have up to a 1/8" gap. Once you're happy with it, copy the contour to make the sides as tall as you want. Cut this out and hot glue it to the supports. Fill any large gaps with hot glue and strips of plastic on the outside of the form.
Repeat for the other side. Add more plastic to the start and end of the form, and your rough form is complete.
Step 4: Casting the Mold
With your rough form complete, you're ready to cast the mold. I chose Bondo for this, as I had it on hand, I am familiar with it, it cures quickly, and it's viscous enough that it won't run out of the form.
Spray your rough form with a non-stick cooking spray to make releasing it easier. Mix up a bunch of Bondo according to the directions. You want enough to coat your rough form at least 1/4" to 1/2" thick. If you have a small ramp, you can likely mix enough to fill it all at once. Otherwise, you'll have to do several rounds of Bondo. Do this outside. Bondo stinks. Don't use the Bondo that has fiberglass strands in it for the first coat, as it doesn't really sand smooth. Work quickly. You won't get a good finish if you're still messing with it as it sets up.
Once your first coat has set (about a half hour), you can add more and more until you fill the mold. Make the top as level as possible. I added a bunch of small dice-sized pieces of wood before my second coat, in order to save on Bondo. I tried styrofoam in my first ramp, but regretted it. You don't want your filler to be compressible, as it will compress when vacuum forming if the Bondo walls are thin. It took me three rounds of Bondo to fill my mold. I alternated through Bondo, Bondo Hair and Bondo Gold, as they were what I had on hand.
Wait for it to set, then break apart your form to release your mold. Sand it as smooth as possible, rounding the corners of what will be the bottom of the ramp. Sand the top of the ramp flat, and leave the corners sharp there. A one inch belt sander and spindle sander really help. Use a respirator and dust collection. You'll likely have to fill some holes with more Bondo, and sand it again. Repeat until you're happy with the surface.
Step 5: Adding the Lip
Next, we need a lip as an attachment point for our mounting hardware and to strengthen our ramp. Since you've sanded the top of the mold smooth, you can hot glue thin plastic strips along the edges. Make these wider than you want the final lip to be. It should come out maybe 3/4" from the ramp. You'll use a Dremel tool or similar to cut the lips to width after the final vacuum forming.
Apply a bit of Bondo to the underside of the strips. Use your finger to make it nicely rounded. Sharp corners will crack later. Add a layer of Bondo at least 1/2" thick to the upper side, to strengthen the thin plastic strip for vacuum forming.
Push and prod the lip everywhere. If it flexes, add more Bondo to the backside.
Give your mold a final sand with 220 grit sandpaper. Any imperfections will show in the final product. You don't have to sand the top.
Step 6: Vacuum Forming the Ramp
This is the most rewarding part. I will leave making a vacuum former up to you, but know that it's easy, and there are lots of 'ibles on it, like this one. My rig is just a box with little holes and one big hole for my shop vac. There's foam on top to make a seal. I chose to build it to accept 16x16" pieces of plastic because 1) that's close to the limit of my kitchen oven and 2) I can get 18 pieces from a single 8x4' sheet of plastic with no waste.
Before vacuum forming, clean your plastic and mold. The process will pick up even small bits of dust. I sprayed my form with a silicone lubricant and wiped it off, so act as a mould release.
The plastic I used was clear .06 PETG. It came in an 8x4' sheet from Sabic. You need a plastic that is pliable when hot, but strong at room temperature. PETG will eventually yellow with UV exposure, but we should get many years out of it before that happens.
I set my oven to 400 on broil (meaning the top burner only), and put in my plastic with wood frame resting on wood boxes at the corners. I left the door cracked open. You don't want the plastic to touch metal. When it sagged 3" or so, after a minute or two, I pulled it out, put it over the former and turned on my shop vac. I left the vacuum on while the plastic cooled, then cut out my new ramp with a Dremel and cutting disk.
See a video of the vacuum forming process.
Clean up the edges with a utility knife and sanding. Clearly label and store your mold for future use.
Enjoy your new pinball ramp!