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Author Topic: Vacuum forming  (Read 440 times)
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g_kandylakis
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« on: June 21, 2020, 05:55:57 AM »

Hi George

Can you share any details on your vacuum molding jig etc.  I'm currently overthinking the same thing and getting no where.  I bought a 1.5kw heater to 'do the needfuls' re heating the plastic.

Sorry to hijack thread ... maybe start another  Smiley

Nice model.

Cheers

Mike

So, here is a new thread on vacuum molding / forming... Others may join in with info and suggestions.

My setup is nothing spectacular, mainly a wooden box built from plans in Model Builder magazine. Unfortunately, I do not have the article with me at the moment, but maybe someone else does.

A similar box is well detailed in this site:
http://www.ratomodeling.com/articles/vacform1/vacform1.html

I use the kitchen oven for heating and the vacuum cleaner for the vacuum...

It is important to settle for the size you need, depending on the part sizes you expect to make. Too small and you cannot make bigger parts. Too big and you waste a lot of material when doing small parts.

You can always make more than one box, for different sizes.

I 'll post some pictures of mine later...

George
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TimWescott
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« Reply #1 on: June 21, 2020, 01:08:56 PM »

Two more thoughts: 

First, there's a slew of "how to vacuum form" videos on YouTube.  I don't know how good they are, because I haven't tried any, but they all look slick.

Second, If all you want is one canopy in "RC-ish" sizes, Nick Zirolli is alive and well and will custom-make a canopy from your plug.  I did this for a scale project I'm working on (1/6 scale profile Ercoupe for control line).  Nick's canopy faithfully reproduces just about every ding and dent and wow and other sorts of screwup in my plug, so I have to call it a good deal (and I'll make a better plug next time!).  It was something reasonable to me for two canopies ($20 overall, or $20 each -- my memory is dim on that).
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piecost
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« Reply #2 on: June 21, 2020, 03:03:41 PM »

I appreciate poeple sharing techniques. So I will share my limited experience. I broke the vacuum formed cowl on my Aerographics camel. So I built a round vacuum box. I employed a plastic party plate bulldog clipped to a wooden embroidery hoop and a thin sheet of MDF with a hole a few mm wider than the cowl plug. I heated the plate with a hot air gun and plunged it over the form held in a vice. There was no need for the vacuum box!

The plate size matched the embroidery hoop perfectly in the rim of the plate and with the bulldog clips and MDF held the plastic firm.

The plastic party plates seem to form much easier than the random pieces of clear plastic used for canopies. Plus they come in varied colours.

I used a blue foam plug sealed.with aliphatic glue. I needed a layer of cling film as a release. The form was rather rough and i must make a more accurate and smooth one to use on the model.
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g_kandylakis
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« Reply #3 on: June 24, 2020, 02:14:53 PM »

 Here are some pictures of my vacuum forming box...

Made of MDF, glued and varnished to seal it completely.

The half plastic part is for when I need to make smaller parts, helps to save on material. You need to glue the two well together...
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g_kandylakis
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« Reply #4 on: June 24, 2020, 02:15:52 PM »

frame...
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g_kandylakis
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« Reply #5 on: June 24, 2020, 02:16:24 PM »

...
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ZK-AUD
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« Reply #6 on: June 24, 2020, 04:34:47 PM »

A bed of nails George - How you must suffer for your art! Grin
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USch
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« Reply #7 on: June 25, 2020, 03:36:18 PM »

Just to add my experience to the discussion about thermoforming on the kitchen table.

Thermoforming is normally a quite simple industrial process but has some points which need attention. Most thermoplastic materials can be deep-drawn over a mould or into a negative mould. But some plastics have a very narrow temperature range within the sheet can be deformed and stretched. A typical example is polycarbonate (PC), an other wise excellent material but hard to form if the temperature is not "just right".

One of the easiest to work plastics is polystyrene (PS) with a large temperature band and easy to find in thin thicknesses like plates, glasses and the like. It is also easy to evaluate as it will melt touching it with thinner like acetone. The same applies to a parent plastic, ABS (Acronitrile – Butadiene – Styrene), more resilient and flexible thanks to the butadiene (sort of rubber). But unfortunately not available  transparent.

Second point is SPEED. The thin sheets we use have very little thermal inertia and cool down immediately either during the transport from the heating station or at the first contact with the mould. As for the transport you can only be aware to heat the sheet near to the forming mould.

You can do a lot during the forming process to speed up the forming. Try to have a good seal between the plastic sheet and the perforated box top. I use foam strips as used as windows seals. Try to keep the  void volume as small as possible. As most of us use the vacuum cleaner which is not a champion of air removal try at least to have little air to  extract. If you look at my box bellow you will notice it is quite voluminous, the reason is that the hole for the cleaner hose has a certain diameter. To remove the void volume inside the box I placed a foam block to fill about 90% of the space. Don't be afraid about reducing the space, the air will always find his way out  Smiley

Prepare more than one frame to fix the plastic on it. I have one which covers the space of a normal A4 sheet of paper and a second one for an A5 sheet. If I use the small one I cover the outside holes with tape and put foam tape to form a gasket around the frame. To simplify and speed up the preparing I spill the plastic to the plywood frames rather than use clamps. So the plastic with his perfect surface acts well to seal the volume to be extracted. You may also continuing to heat the sheet with a hot air gun during the actual forming, sometimes this allow to draw the corners down.

Urs
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alfakilo
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« Reply #8 on: July 03, 2020, 09:03:06 AM »

Here in the US, crafts stores such as Michaels or Hobby Lobby have a selection of wood boxes that work well for vacuforming.
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TheLurker
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« Reply #9 on: July 03, 2020, 09:20:47 AM »

Quote from: alfakilo
....crafts stores ...a selection of wood boxes that work well for vacuforming.
Now that's an idea that appeals to my inner, lazy, skinflint.  Thank you for that.
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