This Instructible will show how to fabricate the parts to make a 6 1/2 foot tall dome that is rigid enough to support approximately 50lbs from the apex.
Step 1: Tools and Materials
3/8" drill bit
1/4" drill bit
olfa snap off knife and extra blades
2 disposable paint brushes
3/4" square, 1/16" thick wall extruded aluminum
3/8" thick rubber sheet (8568K536 - $51.07/ linear foot x 36" wide)
26x 2 1/2" long 1/4" lag bolts
260x 1 1/2" long 1/4" lag bolts
26x wide 1/4" washers
26x 1/4" wing-nuts
red and blue paint
Step 2: Dimensions and Templates
- 35x struts 47" long (red)
- 30x struts 41 1/2" long (blue)
- 20x 6way hubs blanks
- 12x 5way hub blanks
- 20x 4way hub blanks
- 130 wooden pegs 3-4" long
- The aluminum for the red and blue struts can be obtained online at McMaser Carr, or at an aluminum wholesaler at about half the cost. Look for places that sell "extruded aluminum" and also check to see if they'll cut it to length for you. If not, you can cut them on the chop saw.
- Rip wood for the inserts so they slip into the struts easily, and then cut them about 3 inches long. Paint and sand them before assembly so they will appear cleaner, like a plastic insert, not just a painted end of a stick. When you do glue in the inserts, use 5 minute epoxy, and just dab a bit on each side of the insert before sticking it in the strut. If they are tight, you can push them in against a wall, or if very tight, just throw the strut at the floor, like a spear to jam the insert in. I tried to avoid hammering them in because the struts seemed like they were bending.
- Drill the holes in the struts on the drill press using a good machinists vice clamped down to the table. I just put some tape with a mark on it to show me where to put the first hole, and then slid the strut to the edge of the vice for the other one. Make sure the far end of the strut is supported so the holes don't start getting more and more angled. Be very careful when drilling the holes, they are a bit bigger than the bolts, but if they are too far apart it won't fit, and will be garbage, or if they are not centered correctly, they look really bad.
- Sand and de-burr all the metal parts to get rid of anything that might hurt the kids.
- The rubber sheet material for the hubs and caps can be obtained at McMaster Carr. It is "shore A 80 neoprene" (shore A 80 refers to the hardness, and neoprene is the kind of rubber) Cut the rubber only with a utility knife, or snap off OLFA blade - If you cut too much rubber with the power tools, It Will Set Off The Fire Alarm. Cutting with a knife works best if you bend open the cut as you go so there is less blade friction. Have plenty of extra blades handy.
- Make templates for drilling the hub and cap holes out of at least 1/2 inch plywood and use a clamp to hold the template down,. Make sure you use a sacrificial board underneath, because the rubber really pulls the drill down when it's through.
- It's much easier and nicer looking to paint the bolts for the hubs before they are assembled.
- Getting the bolts into the rubber is the most arduous part of the process. Sometime you will need to get them started by twisting them in with a pair of vice-grips. You can also simply push them in with your thumbs, but that really starts to hurt after about 5. I've had some success with positioning the hole over a gap in the table and hammering the bolts in that way. Without the gap, the rubber bounces too much, and never goes in. You can also experiment with the size of the holes, as drilling a 1/4 inch hole through rubber never produces a 1/4 inch hole.
Step 3: Assembly Instructions
Now begin working on the first row of 10x red and 10x blue struts. Once all the bolts on a given hub have been used, you can secure them by attaching the appropriate hub cover with a washer and wingnut. Make sure you have plenty of spares on hand as they get lost very easily and make a very attractive souvenir :P
Connect their tips with 5 and 6way hubs and add 10 blue struts, making a ring to top off the first row. Now add the 10x red and 5x blue struts to fill up the remaining bolts. Add the caps to secure this level and now you should have 15x struts poking/ dangling in the air.
At this point you can either assemble the top of the dome in place or raise it into position already assembled. You may need a short step ladder to get to the top - I'm 6'3" and had my head poking through the dome when I constructed it.
Once it's all up, double check the hubs and caps. Give it a few sturdy shakes around the perimeter to make sure it's not going to fall apart before you try hanging anything from the center.
I never did any destructive testing, but I have a feeling the rubber will deform and invert areas of the dome before anything else comes loose or breaks. I'd recommend a maximum weight of 50 pounds, but you can experiment and if you feel it's safe, ask one of the kids to hang from the center. You could even consider replacing the center bolt of one of the 5way hubs with an eye-bolt to make hanging a test load or small child easier.
Tear down can be pretty fast once you've gotten a little practice. Just start at the top and start pulling apart hubs. chuck the hubs into a pile and lay the struts out according to length. The aluminum can be loud if you bang it against one another, so just drop them lightly onto a carpeted floor.
The whole kit should be able to be packed into a couple of 5 gallon buckets, but you will probably need a cart to push the whole thing around the aluminum weighs more than 50 pounds.
The dome kit PDF I've included at the end is an overall manual of how to reproduce this kit.