CabinBike™ enclosed motorcycle by Fred Nelson Fabrication
Vacuum forming machine
We use this 2 x 2 machine to make "wheel pockets" for the landing gear on our CabinBike among other things.
We started with a cheap 'experimental' wood machine that eventually evolved into our commercial duty Vac Mach #3 (shown here).
If you want to experiment you can build a simple wood machine for a few dollars with free instructions (below). But, if you really want to produce some NICE parts or use the machine commercially you'll need a nice steel machine like our Vac Mach #3. We don't sell the completed machine however plans and instructions are available in the member's area.
If you purchased the dxf files for our vacuum machine, study the pages below before moving on to the assembly instructions page in the members area (ypur Pit Pass level membership is included with purchase of the dxf files).
Vacuum Machine demonstration and explanation
Thermal plastic vacuum forming heater box
A 24 inch square tray is too big for most conventional kitchen ovens or small powder coating ovens. To build an "oven" to heat our thermal plastic, we started with a 1300 watt quartz room heater from Walmart. A simple 4 square foot oven for .090 polystyrene amazingly only requires the components from one of these.
We removed the plastic housing, controls, and tip-over switch from the room heater then installed the heater components into a fabricated metal box** that will act as the base for our reflector box. I just wired it directly to the plug but you could and should install an off-on switch.
**for CAD drawings and CNC files see the members area.
The reflector box is simply made of 1/8 inch plywood or MDF and lined with heavy duty common kitchen foil. The box is smaller at one end than the other. The smaller end of the reflector box fits and sits atop the quartz heater. The other end is larger and matches up with the material holder. I used a very light weight aluminum angle stock on the corners.... light 1 x 1 x 10 angle for suspended ceilings (i.e. Home Depot). I think it was about 5 bucks. The sides are just under 24 inches tall (so we can maximize the common 4 x 8 material size (i.e. wood paneling). I drilled a few small holes and installed common hardware to hold it all together.
Here we can see the quartz heater in the bottom of our oven. We were very successful pulling a 24 x 24 .090 polystyrene sheet over a fairly large and deep mold after 8 minutes of heating. That may even be more time than needed. I noticed you need to wait for the plastic to warp, then re-tighten, then sag, then outgas (smells like plastic), then give it about a minute more.
Here we can see a pretty 'deep' pull we did to form a wheel pocket. Obviously the heater worked well enough to heat up the .090 white polystyrene to the proper temp and the table pulled hard enough to perfectly form this rather tall part (pretty tall for a 2ft x 2 ft table).
Vacuum table and heater explained.
If you are building a table from our kit, now go to the instructions page in the members area.
Evolution of our vacuum forming machine:
As part of the learning process, I first made a simple thermal vacuum forming machine that I saw on-line.
I started by making a low profile sealed MDF box for the bottom. Peg board with support bridges make up the top. I used the peg board 'rough side' up.
I sealed the top made of peg board to the bottom made of 24 x 24 1/2 inch thick MDF board and sides made of 1 x 2 MDF strips.. I glued, nailed, and sealed everything together.
The lid (material holder) is 24 x 24, 1/2 inch and 1/4 inch MDF sandwiched together with an opening cut out. Hardware holds the 2 halves together. Countersink the hardware on the bottom side. Use the opening in the top as a guide to make a primary gasket from PVC or rubber sheet (shower/tub liner).
Silicone the PVC sheet gasket to the rough side of the pegboard. Insure complete coverage for a good seal. Install secondary rubber weather striping.
Shop vac installed into the vacuum box side. First we tried a shop vacuum alone for a single stage system .
When I decided it wasn't 'pulling' hard enough I added a "second stage". I added a hose fitting into the vacuum box side. This port connects to a tank and vacuum pump.
Everything worked 'ok' but it just couldn't pull hard enough or hold a vacuum so I made some more modifications.
Thermal vacuum forming table version 2
3/4 inch thick MDF with a port for the vacuum manifold is used for the bottom. 3/4 inch thick MDF scraps are used as bridges between the bottom and the platen (this set up has enough vacuum to warp the 3/4 MDF platen without support).
I added a quality pressure gauge to the box via a new manifold so I could monitor the actual vacuum in the box. The larger gauge monitors the amount of vacuum in the storage tank.
Well, I was still having trouble getting 100% seal and I decided I was going to keep chasing the problem plus 'clean-up' that exterior plumbing. Before I was done I ended up rebuilding the entire table resulting in design #3. I found that with ANY MDF board or wood for the exterior construction (outside the seals), you just can't pull and hold full vacuum (MDF is ok for the platen which is inside the seals). Wood was cheap and great to experiment with, but, for commercial quality production I just had to get rid of all the wood on the exterior.
Thermal vacuum forming table #3
I scraped the existing plumbing for our #2 design and simplified it. I also added a valve. Now, there are 3 valves. One valve to close off the pump, one for the vacuum cleaner, and one for the table top (plenum). A separate gauge added to the platen indicates actual vacuum at the platen.
I was having trouble keeping a good seal on the MDF where the vacuum cleaner attached. Some simple plumbing pipes and a rubber seal finally solved that problem for good.
"Floor flange" opening on the bottom of the steel plenum.
The only MDF part remaining is the raised platen, but, since it's inside the seal I'll leave it for now. It seems to work fine.
I made a new steel top frame (material holder) and ran a bunch of tests using a sheet of plastic bag. I can pull full vacuum* and it will hold until I decide to release it. I can release the vacuum by opening the valve to the vacuum cleaner and letting the system bleed of backwards through the shop vac.
*The term "full vacuum' refers to the maximum vacuum I should be able to get at a given altitude and pressure based on my particular vacuum pump's specifications.
Now that I have refined and tested design, parts, plans and CNC files are available in the members area and in our online store. Next, I'll build a 4 x 4 table for some of the bigger parts and eventually a 4 x 8 table for the entire body.
Vacuum Machine Plans and instructions
FREE to "Pit Pass" password holders
FREE to "Mechanics Credentials" password holders
CabinBike.com by Fred Nelson Fabrication 2012 - present. All rights reserved.