In the process of building the 'modular Pinball', I realized that I needed an easy way to propel the fairly heavy ball (metal, 27mm, 80g) into the playfield.
I could have used some complicated mechanism, involving servos and gears...Instead I decided to make the plunger similar to the ones used in early pinball machines, including just a metal rod, a spring and some sort of retainer for the spring.
So I got to work with the metal lathe and started shaving of some material. I ended up with the rod having a diameter of 8.3mm about 10cm into the material and drilled a 3mm hole to screw in a m3 screw with a large washer.(to retain the spring you need a washer larger in diameter than the spring). Unfortunatly the metal lathe had to be removed from the workshop before I had the chance to cut in the m3 thread, so I tried to cut the thread with a bolt and some WD40 - and it worked! (a lot of screws lost their life in this process)
Then I designed a mount for the rod and spring in openScad. For me it was important to accomodate for the 10° of gradient in the playfield, so the surface where the spring would be pressed against to, had to be at an angle as well. Due to some angles in my design, I could'n print the mount in one piece, so i had split it in two. (Printed on a Dremel without supportmaterial) You can find the file below.
What materials you need:
- 12mm x 18cm aluminium rod
- M3 x 15mm screw
- M3x d=15mm washer
- Spring(D=9mm(outer diameter),d= 1.3mm (springwire))
- PLA filament for the 3d printer
What tools you need:
- metal lathe (oh yes exactly, I have one in every room...)
- pointy bit to decrease diameter
- 3mm drill
- dremel with a cutting disc
Step 1: Reduce the Diameter of the Aluminum Rod
Before you start using the lathe please note: No rings, no gloves, no wide t-shirts and always always wear protective glasses!
If you secured the workpiece into the lathe you can start to shave of material. To accomodate the spring I chose, I had to reduce the diameter from 12 mm to 8.3 mm about 10cm into the rod. To get a better surface you should do the 'cut' in one go, without removing the cutting tool. Unlike I did. If you want an even better and smoother surface, you can grab a piece of sandpaper and sand the workpiece with the lathe running. But be careful.
Step 2: Drill and Thread a Hole
To drill a hole into the rod, it is best to do it on the lathe. Assuming you already have the rod in the headstock, you are now going to put a 3mm drill bit into the tailstock. Then you bring the tailstock to the already turning rod and drill the hole. While you are at it you should cut the M3 thread into the hole with the thread cutter. I had to discover that the lathe I was using had to be moved out of the shop. Now you can put a large washer over the screw, insert the rod into the mount(Shoot Kopie.svg)and secure the spring for good.
Although it did work to cut the thread by screwing a couple of screws in and out until they were destroyed, I would't recommend it.
Step 3: Attach Assembly to the Pinball
Now it's just a matter of attaching your PlungR to the front wall of the pinball. For that you need to drill 5 holes, four 3mm holes to attach the assembly and one 3cm hole to make room for the overhang of the mount.