The basics: First, a vacuum is created in a closed chamber. Next, heated plastic is pushed down onto a mold. Lastly, a valve is opened and the vacuum pulls the hot plastic tightly over the mold. Once the plastic has cooled the new part can be removed.
We originally designed this this 400 sq. in. two stage vacuum machine to make the “wheel pockets” for the landing gear on our CabinBike. Since then it has become a ‘must have’ tool around the shop.
In a two stage system, the first stage (here, a Shop Vac) makes the initial ‘pull’ to create a good seal and begin forming. Then a second stage (Vacuum Tank) is quickly opened to pull very hard and finish the pull.
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 heater then installed the components into a fabricated metal stand that will act as the base for our reflector box.
The reflector box is made of one piece of 4 x 8ft. 1/8 inch paneling and lined with heavy duty common kitchen foil. The box is smaller at one end. The small end of the reflector box sits on top of the quartz heater assembly.
I used light weight 1 x 1 angle for the corners (suspended ceiling metal from Home Depot). The sides are just under 24 inches tall (so we can maximize the 4 x 8ft. material.) The larger end matches up with the material holder.
Here we can see the quartz heater in the bottom of our oven. A piece of .090 polystyrene needs to heat for about 8 minutes. Wait for the plastic to warp, re-tighten, sag, then outgas (smells like plastic). Then give it about a minute more.
Here we can see a fairly deep eight inch tall ‘pull’ on an .090 inch thick polystyrene part (this is a rather tall part for a 24 inch by 24 inch table).
THE MACHINE FACE. The face mounts all of the control valves, gauges, and switches.
THE PLUMBING. The vacuum tank (with gauge) leads to valves that control the flange and vacuum pump. The flange has it’s own gauge and a valve to the shop vac. Vacuum out the tank with valves to the flange and shop vac both closed.
PLUMBING SCEMATIC. This shows the 2 stage system. To operate, first build up vacuum in the tank. Next, turn on the shop vac and load the part. As soon as you have a good seal, quickly ‘dump’ the tank before the plastic cools.
The plenum flange is made of some simple plumbing pipes and a hand made rubber seal. Once we put the top on, then we can install the connection to the flange.
The plenum flange assembly consists of a steel ‘floor flange’ from Home Depot, a threaded PVC elbow, and a rubber seal. Countersink the holes on top of the plenum.
This part is called the ‘PLATEN”. The platen is made of 1/2 inch thick MDF. Drill holes every inch. The holes are .20 inch diameter.
You can use a piece of peg board as a quick guide to drill the holes. Spray the plenum with paint or primer to seal the edges and areas with out holes.
MATERIAL HOLDING FRAME: Top view of the top and bottom frame assembled.
Bottom view of the frames.
Corner detail of the top side of the bottom section of the frame.
Corner detail of the top section of the frame (seen from the below).
Corner detail top section (seen from the top).
Top and bottom frame ready for a piece of plastic to be sandwiched in between.
Common spring clips hold the top and bottom half of the frame together.
Top frame (side view) with the plastic material in place.
Bottom frame detail.
Top frame detail.
THE PLENUM. This is a steel plate with a hole in the center. A threaded floor flange (plumbing) is attached to the bottom side.
The plenum is made of 11 gauge steel. TIP: Counter sink all the holes on top so that all of the hardware is perfectly flush.
A small piece of wire mesh helps distribute air under the platen. Foam weather striping helps make a seal against the material frame.
MAIN BOX. This is 14 gage steel. Cut with Plasma, laser, or water jet. The cutting lines along the folds make this super simple to bend up by hand with no special tools. It basically holds the plumbing, gauges, and valves and supports the plenum. .
Vacuum Machine Base. 14 ga steel.
11 gage parts layout. Requires one 48 x 48 inch piece of material. Platen and material frame faces.
14 gage layout. Requires one 60 x 48 inch piece of material. Machine base, face, heater box, and frame handles.
BASIC PARTS LIST.
Harbor Freight:
air tank, vacuum pump, vacuum gauge (large).
eBay:
vacuum gauge (small).
Home Depot:
Ball valve (3), 1 inch Floor flange, 1/2 inch MDF, 1 x 1 inch x 1/8 angle, hoses, PVC, fittings, wall switch box, light switches, wire mesh, weather striping.
