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Old 09-21-2012, 08:27 PM   #1
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DIY Vacuum Former Q's


I want to build a DIY vacuum former

The plastics I'll be using will be styrene, PETG, ABS, & perhaps acrylic. Each of these plastics have a melting temp of around 325 degrees Fahrenheit, therefore my goal is to create an oven that'll reach 400 degrees Fahrenheit.

This is where I am at on this project:

Oven needs to be electric. I am not sure how many watts I can draw w/ out popping a circuit, so this needs to be taken into consideration.

Heating element. What to use? Microwave, oven, hot plates, etc. Infrared? Any ideas would be awesome!

*I want to build the vacuum former as a whole; oven included.

Dumb Question: What is used as a connection between heating elements & thermostats? Do thermostats use a probe or a basic thermometer?

Thermostat. I need something to control temp w/ right. How do these work? Relays?

How difficult would it be to control the temperature using my computer? Do they have thermostats that operate via USB? I'd imagine they have software you can download.

I've also seen a lot of people use Arduino Boards as thermostats. This may be something to look into.



Any advice would be great!


Last edited by 05LGT; 09-21-2012 at 08:30 PM.
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Old 09-21-2012, 09:14 PM   #2
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DIY Vacuum Former Q's


I think you should repost to "electrical" forum.

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Old 09-22-2012, 09:40 AM   #3
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DIY Vacuum Former Q's


Did the designer ever build one or was this just a mental exercise? Or maybe he wants someone else to test it? Fabricating the housing out of wood sounds exciting, I think it would be a matter of when, not it, it self destructs.

If it were me, I would buy a used pizza oven, they are sizable and built for 500 degrees or more. Then you wouldn't have to cobble together all the bits to make it work, i.e., electric element(s), thermostat and wiring.

You'd need one with only a top burner, maybe they all are, I don't know. But then you could open up the bottom or drill it. You would also need a vacuum source and lines that can handle the temperature. One other consideration is bracing the vacuum base plate, the plan designer doesn't show one (which makes me think it's just an exercise) but enough vacuum to do the job will pull the surface down. I've built two screen printing tables, first one had to come back apart for reinforcement. A few strategically placed angle iron inserts would work. I used wood dowels but printed at room temperature.

If you decide to do it, post up some photos. BTW, I wouldn't think acrylic would work well as it's fairly brittle. Polycarbonate would probably do well and would take some abuse. I don't know what your ultimate goal is though.
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Old 09-22-2012, 03:28 PM   #4
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DIY Vacuum Former Q's


Quote:
Originally Posted by 05LGT View Post
I want to build a DIY vacuum former

The plastics I'll be using will be styrene, PETG, ABS, & perhaps acrylic. Each of these plastics have a melting temp of around 325 degrees Fahrenheit, therefore my goal is to create an oven that'll reach 400 degrees Fahrenheit.

This is where I am at on this project:

Oven needs to be electric. I am not sure how many watts I can draw w/ out popping a circuit, so this needs to be taken into consideration.

Heating element. What to use? Microwave, oven, hot plates, etc. Infrared? Any ideas would be awesome!

*I want to build the vacuum former as a whole; oven included.

Dumb Question: What is used as a connection between heating elements & thermostats? Do thermostats use a probe or a basic thermometer?

Thermostat. I need something to control temp w/ right. How do these work? Relays?

How difficult would it be to control the temperature using my computer? Do they have thermostats that operate via USB? I'd imagine they have software you can download.

I've also seen a lot of people use Arduino Boards as thermostats. This may be something to look into.
You almost certainly want a PID (proportional-integral-differential) temperature controller. These are self-contained microcontroller-based temperature control units. You connect a thermocouple to the controller to measure temperature, and use a solid-state relay to interface between the controller and the heating elements. This is the only good way to establish and maintain a precise temperature in a system like this. With a fast response thermocouple attached to the surface of the plastic you are heating, you'll be able to very rapidly raise the temperature to the correct working value, and automatically hold it there within a range of about 2 degrees. Google search for PID temperature control and you'll find plenty of information on how to use them. Lots of Chinese sellers on ebay offer them very cheap.
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Old 09-22-2012, 04:25 PM   #5
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http://www.ebay.com/itm/Digital-PID-Temperature-controller-25A-SSR-K-thermocouple-thermostat-/271062881914?pt=LH_DefaultDomain_0&hash=item3f1c9b 567a

Dumb Question: Do these come in both AC & DC (input). This needs to be ran off an ordinary home outlet. Some PID's I've seen are ran off of DC batteries.
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Old 09-22-2012, 06:03 PM   #6
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Quote:
Originally Posted by 05LGT View Post
http://www.ebay.com/itm/Digital-PID-Temperature-controller-25A-SSR-K-thermocouple-thermostat-/271062881914?pt=LH_DefaultDomain_0&hash=item3f1c9b 567a

Dumb Question: Do these come in both AC & DC (input). This needs to be ran off an ordinary home outlet. Some PID's I've seen are ran off of DC batteries.
Yes, they are available with a wide variety of input voltages. Most are for universal line power, 100-240VAC 50-60Hz. Others are 12VDC or 24VDC, and a few are for high voltage DC (rectified line power). The ebay listing you posted doesn't seem to say what the input is, but I would bet on universal line voltage.
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Old 09-22-2012, 06:09 PM   #7
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If you use that thermocouple, be careful to avoid temperature overshoot. That thermocouple probably has a much longer thermal time constant than the plastic you are heating. That means the plastic temperature can spike higher than the thermocouple's temperature for some time until the thermocouple catches up. This can be solved by either using a smaller thermocouple (a small bare junction in contact with your plastic would be best), or by manually adjusting the PID parameters for a more gradual approach to the setpoint. Increasing the proportional bandwidth and differential coefficient would do it, at the cost of longer heating time and less precise temperature stability.
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Old 09-23-2012, 06:02 AM   #8
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DIY Vacuum Former Q's


You need air flow.

Unless you are using a specific type of material that will accept the heat radiation from specific sources, you will have to use hot air.

Microwave only works if the target material will heat up when radiated by microwaves.

Infrared is a bit more forgiving.....

My advice....build an oven with electic heaters....the KW of the heaters will depend on how fast you want to heat up and the mass of the material you are trying to 'warm up'. You need a fan to circulate the air so that it flows across the part to be formed.

You need a temp controller such as a Watlow or Honeywell to controll the heaters to get to the target temp. Once you are at the target temp, you 'punch' the vacuum on the part.....if all is right, the material is hot enough and the vacuump pulls it down.

A little advice from someone who works in the composites industry (making airplane parts)....if your parts are any bigger than about 12"x12"....you are in over your head....unless you toss some serious $$ at it.
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Old 09-23-2012, 03:28 PM   #9
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The video doesn't make it clear, but when you are heating the plastic, you literally watch it to know when it's ready. When you put your plastic in the oven, you wait for it to "wave." After it waves, it will "flatten" out. As soon as it flattens, that's when you take the plastic out.

I've been doing this in my oven for the past few days. At 325 degrees F, it really only takes 8-11 seconds until it "waves." It takes about 3-4 seconds to "flatten" out.

The plastic is only in the oven for about 20 seconds, if that. I leave my oven door open as well. It's really a watching & waiting game.


You're right though. I wonder if the plastic is going to heat up evenly w/ heating elements only. I'd probably have to raise my plastic way above the heating elements for this to work. Meh, but even then, I stll don't think it'll heat up evenly. Maybe hot air is the way to go.


Last edited by 05LGT; 09-23-2012 at 03:40 PM.
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