Fast heat Heating Panels kit build. The kits are great. Everything you need is in the box (except tools) and you don’t have to know how many feet of wire at what wrap gives you the right resistance to make each one 1200 watts. And then how far to stretch it to make it fit and still keep the edges warm so there are no hot spots. All those calculations are worked out for you. That said they are still kits and have to be very carefully assembled so as not to break the ceramic fiber board or kink the wire. There are many hours in this project and this step is one that takes longer than it looks.
One note about the heating panels. This is the heart of the machine. If this doesn’t work well you do not get good performance out of you vacuum former. The TK560 forum goes on and on about this topic. It all comes down to this. A vacuum form machine is an oven. A big oven. In fact by the time I have both zones of mine working it is twice as much power (in amps and watts) as a kitchen oven. A very good source said (see link below) that you need to heat the plastic from room temperature to forming temperature (about 350-400 F) in about one minute to keep the plastic pliable. Heat too slow and you change the plastic elasticity. This is like baking 15 minute rolls in one minute. It takes a lot of heat. This my second try to build a machine. The first I abandoned for lack of heating power. 110v is just not enough to do the job. The kits are not cheap but the price is fair for the work and research that has gone in. Heating is king in this game and Doug has it worked out.
For more, read down around page 16 of the document linked here from one of the commercial heating element suppliers which talks about Estimating Power Requirements. It works out to just under 11 watt/in2. That’s watts per square inch. So, if you have a 2′ x 2′ machine that’s 24 x 24 x 11 or 6336 watts a minute needed.
The Platen. This is one of the key ways that you get a really good vacuum form. To produce a good high definition product from a vacuum form you need high pressure. Or really very low pressure. About 25″ hg. You can’t get that from a vacuum cleaner. They only get about 6″. So you need tanks and you need to pull the vacuum from underneath allowing the normal atmosphere pressure to press down on the hot plastic, forming it into the details of your mold. The Platen makes that possible. By keeping the volume of the Platen down you reduce loss during the process. So these two sheets of aluminum with a very small gap and 450 holes do that.
Here is where you need LOTS of time and a good drill press doesn’t hurt. Clearing the burs by hand was the toughest part of this job. Building this one 2 x 2 platen took most a weekend and every night for a week. I still need to build the 2×3 and a 2×4. If anyone knows of a better way to make 600 – 900 holes without burs, let me know.
There are lots of photos of this step. I think the photos tell the story and I don’t have much to add. Take your time, don’t rush.
Not having a welder, I decided that the Lifting Arms and mechanisms could be made from wood. In these shots you will see that using a stick of conduit as a pivot rod I recreated the complex lifting arms and sliders from oak. I’m sure steel is a better choice, it would last longer, have less play and might be more secure. But I used what I had and I like the more steampunk look the oak arms give it. If it does ever need to be redone I’ll consider the cost of the welding again.
The sliders ( which are hard to see in the photos) go between the vertical supports and guide the lift frame from it’s lower position to the upper position. They are small pieces but they take a lot to get right. The lift arms bolt to them from the out side and the lift frame bolts to them on the inside. The sides have little contact pads top and bottom out of nylon so they slide on the rails smoothly. To help I tapered the ends as well so they hang on the deck to the heating frame.
The nice part of this design is that when you get everything worked out it “locks”. When in the up position the frame holds itself. You don’t have to hold the bar up while the plastic heats. This is very nice. You can step back, make one final check on the vacuum tanks and get ready.
This was one of the more tricky parts to work out. Had I just gone with the given design and paid to weld it up it might have cost more but been simpler. It took me about two weekends to get it right. Correcting lengths and angels till the “Lock” worked just right.