Vacuum forming tool construction, materials and technique.

[Gearup]

I promised earlier to prove an update on the vacuum canopy forming adventure. Here I have constructed a vacuum platen platen and material carrier that are used with a household vacuum cleaner and an inexpensive hot plate. Flat material is essential. The process is really very simple, but drilling lots of holes takes the most time. Once the platen is built, different carriers can be built to accommodate up to 10" square material. I have it setup for a 4" square working size. BTW, the 10" square of unsupported space has to hold about 350 lbs of force: thinner material for the top and bottom plates is not recommended.

***First was the building of the platen. ***
One of the things I've noticed on web projects is the various platens seem to have a lot of internal volume. In fact, the internal volume of the platen should be kept to a minimum. Having a large volume takes longer to evacuate with the vacuum source and this added time allows the plastic to cool before the sheet is fully formed.  Therefore the construction of the platen is designed as a 3-piece sandwich with minimum volume.

To construct the platen I started with two pieces of ¾" smooth faced plywood 12" square.  On one of the pieces, I marked out a 9" square centered in the panel. I then divided the square into a ½" grid. Making a ½"graph paper created using https://www.blocklayer.com/graph-papereng.aspx makes this task easier and more accurate.

Then I drilled 1/8" holes at each intersection of the grid lines (324 holes !). The easiest way is to use a drill press with a fence. This helps you to make straight and parallel rows by moving the fence over ½" after completing each row. It can be done with only a hand drill but it may take a bit longer.

On the second ¾" panel, a hole, sized for the vacuum cleaner nozzle end is drilled at the center. It can be drilled with the appropriate sized drill bit, hole saw or scroll saw. It should be a snug fit to the nozzle but if it is too large, duct tape around the nozzle will with provide a good vacuum seal.

Next a ¾" thick block of plywood or solid wood, sized at least 1" bigger on a side than the vacuum nozzle diameter, is drilled with the same sized hole for the nozzle as used before. Align the two holes and glue and screw the block to the outside face of the bottom plate. Ensure that the block is parallel to the edges of the base as it will be used to clamp the platen in position with the hose connected below.

The center spacer was made from four pieces of 1" x 12"x ¼" plywood. Solid wood strips would be just as good. Cut two pieces 12" long and glue them flat to the inside face of the bottom plate flush to the edges opposite from each other. Take the remaining two pieces and mark them for length between the installed spacers (10" in a perfect world). You want a nice tight fit with no gaps at the corners. If you get a gap, seal it with caulking, glue or wood putty.

Now you should have a bottom plate assembly with a vacuum nozzle connector on the bottom face and a ¼" high x 1" wide flat lip around the inside face. When you are satisfied with the bottom assembly, glue and screw or finish nail the drilled top plate to the lip, clamping it tight to make sure it is flat and airtight.

The main vacuum box platen is now complete. It should be flat and smooth on the top drilled surface.

***Next is the carrier construction.***
The two parts are made from 6" squares of 3/8" plywood. Flat and smooth faces are important, so birch plywood or smooth plywood is required.

Cut a 1/8" deep x ¼" wide rabbet around the perimeter of the each piece on one face using a router, table saw or hand plane. Even a handsaw and chisel will work. Now use masking tape around the edges to hold them together to work them as a pair. Draw a 4" square centered on the face. Cut the 4" square out with a scroll saw, jigsaw or a coping saw.

While they are still matched face-to-face and secured with the tape, drill a 1/8" hole at each corner ¼" in from each edge. Insert 1/8" dowels in each hole to act as locating pins for the plates during use. Glue the dowels to ONE plate only and cut them off flush on the rabbet side.

***Hot plate heat deflector and carrier support.***
Experimentation with the hot plate showed that the direct radiant heat from the burner and trying to hold the carrier at the correct height usually ended up with un predictable heating of the plastic.

I had a piece of 1/8" steel plate in the shop that I cut to 6" square with an angle grinder.  I drilled a 1/4" hole at each corner 5/8" in from the edge. Cut four 1/4-20 all thread rod pieces 1-1/2" long and shape a point at one end (optional, flat is ok). Use a nut on either side of the deflector plate to secure the posts in place to act as supports for the carrier. The bottom of the posts will help prevent the deflector from sliding across the electric hot plate burner. Come to think of it, this would also work with a camp stove, but I have not tried it.

That's it: the rig is done. Next will be material prep, buck making and finally forming a part.

[Gearup]

Photos Platen and carrier construction

[Gearup]

Here is a plan for the vacuum forming rig. I reviewed the first post to have the dimensions line up together with the drawing.

Materials
(2) 3/4 x 12 x 12 plywood
(2) 1/4 x 1 x 12 wood spacer strips
(2) 1/4 x 1 x 10 wood spacer strips ( to fit)
(2) 3/8 x 6 x 6 plywood carrier halves
(1) 3/4 x 4 x 4 (approximately sized to fit the vacuum hose with good edge distance from hole)
(4) 1/8 dowel pegs cut to fit
(4) medium sized binder clips
(1) 1/8" x 6 x 6 steel plate deflector ( or what ever you have for thickness) An option here is also to use an old steel frying pan ( not the good one as you're going to drill holes in it)
(4) 1-1/2 1/4-20 all thread rod (equivalent length bolts or machine screws would also work. Just make sure the nuts fit)
(8 ) 1/4-20 nuts ( or sized to fit bolts as noted above)

(1) Heat source. I used a small single burner hot plate with a simple coil style element. Cheap on amazon or you may find one cheaper at a second hand store.
https://www.amazon.com/IMUSA-GAU-80305-Electric-Single-Burner/dp/B01KQ9CTIU/ref=sr_1_5?crid=2UHTSHWZCVGMJ&keywords=single+hot+plate&qid=1638518252&sprefix=single+hot%2Caps%2C227&sr=8-5

Fraser

[Gearup]

Here are the pictures of the various components completed and ready to use.

The green tape is used to define the vacuum area for the size of carrier opening (4 x 4) and contain the vacuum to that area.
Disregard the 2 locating blocks taped to the platen. They aren't really required and were removed later.
Fraser

[Gearup]

Material used for clear vacuum forming:
Clear PET plastic 10" plates......
Super cheap, try to get thinner plates with the PET recycling label. The centre flat section should be without molded or raised marks in the centre. The rim can be any design as it will not be used. I bought mine from a party supply store. Sometimes you can find them at dollar stores.

https://www.partycity.ca/en/pdp/plastic-dinner-plates-10-in-20-pk-8420021p.html#srp

The bottom of the plate should fit a 6 inch diameter circle. Cut the rim away and you have a 6 inch disk ready to vacuum form.

I started using scissors only and the most difficult part of the cut is to get through the rim to the flat part and then cut around the bottom. If you let the scissor completely close, it tends to break or crack the plastic at the tip, so take only short cuts and don't close the scissors completely.

Then I found a faster way. I cut a plywood template disk to fit the diameter of the bottom flat part. Using a sharpie I marked around the disk to provide a guide line. Next I took the plate to my small belt sander and while supporting the rim on the table, I rolled the plate while sanding away the radius of the rim to the bottom marking. Short arcs of about 2 inches at a time with a light touch thinned the plastic and usually cut through the plastic. After a full turn, you end up with the rim attached loosely to the bottom with a thinned ragged plastic edge.

It is a lot easier to separate the rim from the bottom and trim with scissors to the line without fighting the rim.

You end up with a pile of 6 inch disks in under 10 minutes.

Next is the forming of the buck.

[Gearup]

Forming the buck. Yup, that's the term for the form (shape) that you are going to use for the part you are vacuum forming.

My main use is going to be making canopies and windshields for my models. There is an endless number of existing small objects that are used as bucks to make copies. One could even use a canopy from an existing plastic kit as a buck (they are usually quite thick and strong) Other parts can be carved to shape and molded to be used for use as casting molds such a wheels, wheel pants, cowlings, fairings. Well you get the idea...

For this project i came up with the shape I wanted for the canopy windshield and carved it from yellow cedar. It carves nicely, has no grain, smells nice and finishes super smooth. Any good carving wood should work including plaster, special foam and Femo clay etc can also be used. The vacuum forming process can pick up very fine detail from the buck.

The shape I made was a cone with an angular aft part that worked as a finger hold when working on the part later. When it is placed on the platen and vacuum formed the plastic sucks around the buck and makes it a bit harder to pop out. Ideally the buck should taper slightly on the sides a couple degrees and not have any curves or recesses on the sides to trap the part. Experimentation with the shape will show you what works best. Proper design of bucks for molding is a complete engineering subset in its own right. But what the heck, I'm only making canopies the size of my fingernails....

I have not tried too many shapes yet, but i think that you can make most of the parts fo these sized models with this set up.


Fraser

[lastvautour]

Very detail instructions. Thank you for the info.

Lou

[Gearup]

Making the vacuum formed part.
This is the fun part. From turning on the hot plate to the formed part is about 5 minutes. After that copies can be made about every 2 minutes.

Plug the vacuum hose to the outlet of the platen bottom and place the platen on a split surface to allow the hose to hang under the assembly. I use a workmate portable bench or two saw horses about 3 inches apart.

Here is something that is optional but will make a much better surface for the vacuum to act on the plastic. Take a piece of drywall sand paper, the type that is like a gritty screen or a piece of window screen material about 1/4 inch smaller on a side compared to the carrier opening. Place it on the platen over the vacuum area that is going to be used. Place the buck on top of it. This will allow for an even better distribution of the vacuum under the buck. It has the effect of acting like many hundreds of holes under the plastic during forming.

Place the hotplate heat deflector with the pins pointed upward on top of the hotplate and nearby your vacuum platen.  Turn on the hotplate to  medium and let the unit warm up. 

Take a disk of the PET plastic plate bottom and sandwich it between the two carriers. The dowel pins will help with aligning the two parts and keep them from shifting. Clamp with four binder clips to hold the carrier plates together. There is no gasket used or needed in the assembly of the carrier.  Also you may notice that the binder clip wire handles will hold the carrier above a flat surface by a small amount, sort of acting like springs. Don't worry as they will not interfere with the operation.


When the heat is stable after a few minutes, set the carrier on the hotplate deflector pins and start counting. Now is a good time to turn on your vacuum.

Observe the plastic plate. Initially it will appear to warp and ripple within about 10 seconds. Then the warpage will appear to smooth out. The plastic will start to sag down usually within 30-60 seconds. It doesn't have to sag very much because it is thin to start off with. If left too long, it may totally melt and form a hole or if it does get too hot, the plastic may turn milky and opaque. The heat deflector definite helps you control the heating better than trying to hold the carrier over the exposed burner.

You can use mitts to handle the carrier but because it is wood, it should not get too hot to handle. Once it has started to sag downward, pick up the carrier and quickly place it down and centred on the buck. The binder clip handles may touch the platen but the vacuum will suck it down tight to the surface.

How fast is the part formed? If the plastic is the right heat, it is almost instant! As soon as the carrier touches the surface....pop, it's done. Allow it to cool for a few seconds and turn off the vacuum.

There, now you have made a vacuum formed part! Now some work or look better than others, so practice is key. 

Remove the plastic from the carrier and remove the buck from the mold. Mark where you want to trim the part from the sheet and use sharp scissors to initially cut it free, then refine it again with scissors and sand paper.

I hope this encourages you to try vacuum forming. It's fun and those small formed parts will add  another dimension to your models.

Have fun
Fraser

[lastvautour]

Thank you for posting Fraser.

Lou