Take a ball point pen and dismantle it (
Fig 11a, Fig 11b):
Fig 11a: Dismantle a pen
|
Fig 11b: Ink cartridge to be cut
|
Cut a piece of the ink free tube to about 2mm less than the height of the tin cans you cut earlier.
This is to hold the displacer bushing in place. Place the tube on the brass rod (
Fig 12a), then put the tin can with
the holes drilled in it on top of that (
Fig 12b). Put the bushing on there too, making sure that it goes through the tin can:
Fig 12a: Plastic spacer from the pen |
 Fig12b: Tin can fitted to the jig
|
Step 4: Make the template
[Diagram for the template will be here soon]
Use the tin can to draw the curves of the template (Fig 13a). When it's done, cut it out (Fig 13b).
Fig 13a: Marking the curves
|
Fig 13b: Template cut out
|
Step 5: Cut the displacer cylinder plastic to size.
Take a 2 litre plastic bottle (
Fig 14a), cut the top and bottom off and then cut it straight down it's length (
Fig 14b). There's usually
lines left from the manufacturing process that you can follow.
Fig 14a: A 2 litre plastic bottle
|
Fig 14b: Cut the ends off
|
Now tape your template to the cut plastic (
Fig 15a), and cut around it(
Fig 15b).
Fig 15a: Tape the template down
|
Fig 15b: Cut around the template
|
It should look like this when it's cut out (
Fig 16a). You also need a small piece about 15x50mm for the seam(
Fig 16b).
Fig 16a: Cut plastic
|

Fig 16b: Spacer piece
|
Tape the seam of the plastic together on the inside of the cylinder (Fig
17a,
17b):
When it's done, is should be a snug fit around the third tin (
Fig 18):
Leave it on there for the next step.
Fig 18: Plastic cylinder fitted to the tin can
|
Step 6: Epoxy time!
Gather all of your parts together, here's what you need (
Fig 19) :
- Top tin on the jig, with bushing fitted
- A bottle lid
- Sellotape
- The plastic displacer cylinder
- The small piece of plastic for the seam
Fig 19: Parts ready for gluing
|
Epoxy around the displacer bushing first (
Fig 20a). From this point onwards, whenever you get the epoxy out, add a bit extra to around the displacer bushing to strengthen it.
Epoxy the bottle lid next to the bushing(
Fig 20b), there isn't much room, but there should be a few mm either side.
Keep an eye on it as the epoxy is setting as it might slide out of position
Fig 20a: Epoxy around the bushing
|
Fig 20b: epoxy the lid down
|
Epoxy the extra piece for the seam in place(
Fig 20c). Tape over it to keep it in place whilst the epoxy sets(
Fig 20d)
Fig 20c: Apply epoxy to the seam
|
Fig 20d: Fit the seam piece and tape over it
|
Step 7: Make the diaphragm
Take two bottle caps and drill holes in the centre of each one (
Fig 21a) to match the bolt size you have (M4 , 5 or 6).
Then cut around the sides (
Fig 21b):

Fig 21a: Drill two bottle caps
|
Fig 21b: Cut around the sides
|
Until you have two plastic washers that look like
Fig 21c.
Place one of the washers on the bolt (
Fig 21d).
Fig 21c: Finished washers
|
Fig 21d: Fit one of the washers to the bolt
|
Take a balloon and cut the neck off (
Fig 22a). Then pierce a hole through the approximate centre (
Fig 22b).

Fig 22a: Cut the neck off a balloon
|
Fig 22b : Pierce a hole in the balloon
|
Thread the bolt and plastic washer though (
Fig 22c), and stretch the balloon over a bottle cap (
Fig 22d).
Add the next washer and tighten it up as much as possible (
Fig 22d).
Fig 22c: Thread the bolt through the balloon
|

Fig 22d : Stretch the balloon out and tighten the bolt
|
Remove the balloon and tighten the bolt properly (
Fig 22e).
Fig 22e: Fully tighten the bolt
|
Continued on page 2
Back to top