Bending PMMA (Plexiglas)

We are a group of 3 students of the second year Industrial Design (Kortrijk, Belgium).

We got an assignment for building a machine with which we could bend PMMA, also known as plexiglas.

We chose to experiment with the concept of using several tubes, through which the plexiglass is led for bending.

We did a lot of research to invent and construct a good machine, using a principle that does not yet exist in this application.

Good luck to everyone who wants to rebuilt our machine himself!

A lot of components are necessary to make this machine

- 6 MDF plates (6mm thick)
- 1 (oven) heating element + metal box
- 1 oven thermostat + button
- 1 ceramic plate (hot plate) (if not found: use a galvanized metal plate)
- isolation material
- plug + electrical wire
- 20 bolts, M6*30 + 20 square nuts, M6 + 20 washers (inner diameter 4.3mm, outer diameter 12mm)
- 8 bolts M3*14 + 20 washers M3
- 1 wing nut M5 + 1 bolt M5*30
- 3 tubes
- 4 hot rolled steel shafts, diameter 12mm
- 1 steel shaft, diameter 8mm
- machine keys
- spacers
- 8 ball-bearings (outer diameter 26mm, inner diameter 10mm, thickness 8mm)
- 4 nails, diameter 3mm length min. 30mm
- 4 compression springs
- coupler for 2 tubes
- compressor connector + metal lashing strap
- PUR (plastic) tube, 1.5 meters long, inner diameter 9mm outer diameter 12mm
- 1 timing belt (Optibelt, XL 80)
- toothpicks + wood glue + clamps
- Loctite 640

For the machine, we need 3 tubes made of stainless steel with an outer diameter of 40mm and an inner diameter of 38mm. We bought our tubes at MCB (other companies can serve as well, as long as they sell the same tubes). The tubes are sold in ends of 6m. We cut one tube in 3 pieces, each with a length of 444mm. For this, we use a hacksaw.

For the 4 shafts, we need hot rolled steel tubes, diameter 12mm. They can also be bought at MCB (or others companies) into pieces of 6 meters. We need 4 different lenghts;

- shaft 1: 548mm
- shaft 2: 480mm
- shaft 3: 530mm
- shaft 4: 504mm

The shafts need to be turned of from diameter 12mm to 10mm at some places. For this, we need a lathe.

Look at the pictures to see how every shaft needs to be turned of.

Pay attention!
The turning of needs to be executed very accurately!

Next is milling the grooves for the machine keys. An end mill, diameter 4mm is used.

The first picture shows where the grooves need to be milled on the different shafts (blue indications).

Picture 2 indicates that the depth of the grooves needs to be 2.5mm, the width is 4mm.

Pay attention!
It is important, especially for shaft 4, that the grooves on one side of the shaft are milled in the same line as the grooves on the other side of the shaft. Otherwise, it will be impossible to set the tubes in the right position to bend (one side of the tube will be set higher than the other side).

At the ends of every shaft, a threaded hole needs to be made. This can be done by hand tapping or by using a lathe, but the easiest and fastest way is machine tapping.

The holes need to be M3, with a depth of 15mm (thread depth 14mm)

In the end, when every component is set on the machine, there will be bolts with washers turned into these threaded holes to hold every component on a shaft together.

After the plexiglass left the adjustable (third) tube, it needs to be cooled.
We chose to cool it with compressed air (blows strongly and is rather cold).

There are 2 tubes needed for the cooling system. We use tubes with an outer diameter of 10mm, inner diameter 8mm (again, bought at MCB).

The tubes are both cut off at a length of 542mm with an hacksaw.

Next, the holes where the compressed air comes out need to be bored.

In total, there need to be 45 holes with a diameter of 1.2mm. The first hole needs to be bored 40mm from the end of the tube. Between every hole is a space of 10.5mm.

Boring on a round element is difficult. It's for that reason that we made a little flattening on the tube by scouring it with sandpaper (fine grain) of a file. By doing this, the bore will have more grip on the tube and won't break easily.

Of course, you need to use a drill press (not a simple drill; you can't control how deep you drill with a simple drill).
Before you start to drill, indicate on the tube where the holes need to be bored.
Try to get all the holes (as good as possible) on one line.

Next, we need something to close one end of every cooling tube (so the air doesn't come out there, but leaves through the bored holes). A little piece of a shaft (+- 15mm long), diameter 8, could be used for this.

The pieces of the shaft need to be glued into the tubes. Use Loctite (metal glue) for this.

These components need to dry some hours before using them (let them dry 24 hours to be sure it's sufficiently cured). Note that the glue must not come out of the tube!

At last, we fix the coupler for the compressed air on the cooling tubes.

We need 4 components: the connector for the compressor, a small metal lashing-strap (that fits the PUR-tube), the coupler and some plastic (PUR) tube (+- 1.5 meters long), inner diameter 9mm.

2 pieces (some 70mm each) of plastic tube are cut off. They are pushed (with force) over the ends of the 2 tubes that are NOT closed by the piece of shaft. The plastic tubes are then clicked into the coupler (in the 2 entries above each other).

A long piece of the plastic tube (at least 1.5 metres) is clicked into the third entry of the coupler. On the other end of the plastic tube, a connector for a compressor is attached with the metal lashing-strap.

Another element in the machine is the ceramic plate. A plate like used in the prototype can be bought new (but that's very expensive), second hand or can be recycled (from a waste disposal or thrift shop).

kapaza.be http://www.kapaza.be/nl/keuken-en-huishoudelektro?q=keramische+plaat
2dehands.be http://www.2dehands.be/elektronische-apparatuur/keukenapparatuur/2/keramische%20plaat/

Mostly, the ceramic plate is still attached to the whole cooker, so it has to be detached.

The plate needs to be 440mm width and 468mm long. So, when detached from the cooker, the plate has to be cut in the right size. To do this: use a glass knife. The sharp edges of the plate can be smoothened with sandpaper (coarse grain).

Pay attention:
This material is very fragile!

** If it's really impossible to find a ceramic plate, you can also use a galvanized metal plate with the same dimensions.

Next thing needed is the heating element, 1500W, 220V.

Some links to sites where you can buy them:

http://onderdelen.electrolux.be/product/3157954003/Bovenste+grillverwarmingselement+1500W
http://www.europart.nl/onderdelen+koken/atag/oven-magnetron/verwarmingselement/90658160/

The heating element needs to be placed in a metal case, and around that case comes isolation (later in this instructions) to make sure the heating element can't touch anything (wood, cabling,...) and to prevent the wood from warming up too much.

You can recycle a case, make one by yourself (by welding metal plates) or buy something that exists.

To control the warmth of the heating element, an oven thermostat is needed.

You can buy them new or second hand, on internet or in a shop.

http://www.ebay.com/bhp/oven-thermostat

http://www.ebay.com/itm/Oven-Thermostat-for-General-Electric-Hotpoint-WB20K10008-WB20K10023-/131349017751

Now comes an important step: lasercutting the components for the machine.

The components need to be lasered out of plates MDF, 6mm thick.

Make sure that the lasercutter you're using has a big accurancy (max. 0.05mm deviation compared to the drawed dimensions). If the accurancy is less, it's possible that the components don't fit well in the machine and so don't fulfill their function (well).

Some of the lasered parts need to be glued together (2 of the same parts for extra strength, or 2 parts that form 1 entirety).

For the following 5 steps, you need the lasered components, wood glue, toothpicks and clamps.

Pictures:
There are 2 parts lasered (see lasercut plans) of each of the components shown in the pictures. So the 2 of every part need to be glued together.

The small holes (diameter 2mm) are made to make a good positioning of the 2 elements (related to each other). A piece of a toothpick (that also has diameter 2mm) needs to be stung in the holes when you glue 2 elements together. Always check if the components are truly good positioned (holes on holes, hubs on hubs,...)

When the parts are positioned well, you have to shut in the components by using the clamps. Make sure you have a lot of clamps. If you don't, you will have to wait a long time before you can remove one clamp from a component and use it to glue another component.

Follow these steps for every component that's glued.

There are 4 parts of the gear (picture 1). The same action as described in the previous step needs to be done, only you do it 2 times (so the result is 2 gears, each one double layered).

And of the second part, the centering component, exist 12 elements. They need to be glued per 2 together (in order to become 6 of the two-layered parts).

There are 4 parts of each of the drawings above. You have to make 2 parts with them.

First, glue 2 times 2 of the squares together.
Then, glue 2 times 2 of the L-formed parts together.
Last, glue 2 times one square (that actually exists of 2 squares) on the L-formed part (consisting also of 2 elements).

What you need to become is shown in the third picture.

Every part that must be formed with these components, consists of 1 component of the 2 shown in the pictures.

As there are 4 of each of the 2 components, you need to obtain 4 parts (each one consisting of 1 element of both drawings).

These are the plates that form the bottom of the machine. Good positioning and a strong bonding is extremely important (otherwise the bottom will never be able to carry the weight of the entire machine).

The parts shown in the first 2 pictures are glued together (thin straight sides glued together)

Then, the 2 next parts are glued together. After that, they are glued on the first 2 plates. The cutting line of the last 2 plates (horizontal line, like in the picture) need to be glued in an angle of 90° on the cutting line of the first 2 plates (vertical line). The result needs to be like the last picture.

Pay attention!
Make sure that the plates are glued together in the right way. You can check if it's good by looking at the cutouts, but also at the holes for the bolts and nuts.

In 2 of the 4 holders (that where glued in the previous steps), there need to be made 2 drilling holes.

The holes need to be bored at 10mm from the edge of the biggest part (see picture). Make sure the center of the hole is in the middle of the component!

Drill with a drill press and use a bore, diameter 3mm. The holes need to be +- 6mm deep.
Make sure the component is shut in very well!

We will need 4 nails, diameter 3mm to serve as shafts. The compression springs will be places over/around these nails.

The heads of the nails need to be cut off. In total, the nails should have a length of +- 28 up to 30mm.

Use a hacksaw to shorten the nails.

Next to be done is fixing the handgrip into the lever.

The handgrip consists of a shaft, 50mm long (can be longer if preferred), diameter 8mm. Again, you can buy them at a company like MCB, or maybe in a do-it-yourself shop.

Use Tec 7 or Trans 7 (transparent) for glueing the handgrip in the lever. This is a type of glue that can be used to glue almost every surface on another one.

When the holders (4 rectangle-formed and 2 L-formed components) have sufficiently dried, it's time to add the ball-bearings. In every hole, there needs to be placed a bearing (8 in total). Use your forces to push them into the holes (if you don't succeed, use a hammer).

Make sure the bearing fits concentric in the holes!

When all of the previous steps are done, and every glued component is dry, it's time to assemble all the components to make the machine.

As you will see, it's like making a puzzle, only a bit more difficult. So make sure you follow the instructions conscientiously!

For the first roller, you need: the shaft length 548mm, 1 tube, 2 centering components, 2 machine keys length 8mm, 4 spacers, 2 rectangle-formed holders WITHOUT boring holes (with the ball-bearings already assembled in them)

1. Place one machine key in a groove of 8mm long (it doesn't matter what side of the shaft)
2. Slide 1 centering component over the shaft, until it's placed over the machine key and it touches the 12mm diameter-part of the shaft
3. Slide the tube over the shaft and fix it over the centering component (use a hammer to clamp)
4. Slide the other centering component over the other side of the shaft and fix it also in the tube. Make sure the hub (gap in the centering component) goes over the machine key!
5. Add a spacer on each side
6. Slide a rectangle-formed holder over each side of the shaft (it has to touch the spacers)
7. Add again a spacer on each side

The rest will be assembled later.

For the second roller, you need: the shaft length 480mm, 1 tube, 2 centering components, 2 machine keys length 8mm, 4 spacers, 2 rectangle-formed holders WITH boring holes (with the ball-bearings already assembled in them), 4 nails, 4 compression springs

1. Place one machine key in a groove of 8mm long (it doesn't matter what side of the shaft)
2. Slide 1 centering component over the shaft, until it's placed over the machine key and it touches the 12mm diameter part of the shaft
3. Slide the tube over the shaft and fix it over the centering component (use a hammer to clamp)
4. Slide the other centering component over the other side of the shaft and fix it also in the tube. Make sure the hub (gap in the centering component) goes over the machine key!
5. Add a spacer on each side
6. Slide a rectangle-formed holder over each side of the shaft (it has to touch the spacers)
7. Add again a spacer on each side
8. Put the nails in the 4 holes in the holders
9. Slide a spring over every nail

For the third roller, you need: the shaft length 530mm, 1 tube, 2 centering components, 2 machine keys length 8mm, 6 spacers

1. Place one machine key in a groove of 8mm long (it doesn't matter what side of the shaft)
2. Slide 1 centering component over the shaft, until it's placed over the machine key and it touches the 12mm diameter part of the shaft
3. Slide the tube over the shaft and fix it over the centering component (use a hammer to clamp)
4. Slide the other centering component over the other side of the shaft and fix it also in the tube. Make sure the hub (gap in the centering component) goes over the machine key!
5. Add 3 spacers on each side

1. Put the bottom plate in front of you in the same way as shown on the picture (gaps on top, cutting line horizontal, largest piece of the upper plate close to you)
2. Place the 2 front and 2 back plates (plates with gaps on the inner side of the machine, see pictures)
3. 1 side can be closed, so place the 2 side plates of the right side on the bottom plate and click the crenel-formed cut-aways of the front and back plates into the gaps on the side plate.

1. Take the third roller and put the SHORTEST end of the shaft in the bean-like gap of the RIGHT side plates.
2. Grab the left side plate (the inner plate, the one with tha gaps in it) and put the plate in the housing, while you slide the other side of the shaft through the bean-like gap in this plate. When the roller is set between the side plates, you can add the outer left side plate.

1. Now the housing is completed, it's time to fix the plates together with bolts, nuts and washers.
You need 16 bolts M6x30, 16 square nuts M6 and 16 washers inner diameter 6.4, outer diameter 12mm.

Look at the picture to see what's need to be done. The steps are the same for every cut-away in the whole housing.

First, put a square nut in the rectangular gap.
Slide a washer over the bolt you're gonna use
After that, stab the bolt (with the washer) through the hole, made in the plate you want to attach to another plate
When the bolt touches the nut, start to screw the bolt in the nut.
Make sure the the nut is sufficiently tightened (but also not too hard)

1. Assemble roller 1 in the machine: the rectangular holders can be slid into the housing.
Pay attention! The LONGEST end of the shaft has te be on the LEFT side of the machine! (so the same side as the longest end of shaft 3)

2. Assemble the adjustability: the L-formed holders have to be fixed on the shafts. Slide the 2 holders over the shafts as shown in the picture. You may have to use some force to get them in the right position. The right position is: the bearings pushed against the spacers, and the bottom of the holder has to rest on the housing.

After doing this, add one more spacer on the left side (longest end of the shaft) of both rollers.
The right side of the shaft ends in the bearing (so no more components can be attached there).

3. Assemble roller 2: the rectangular holders (with the nails and springs already assembled) have to be slid into the housing.

Place the cover or 'roof' plate over the nails. Check if the springs really touch the plate!

Grab your last 4 bolts, square nuts and washers (all of them M6) and fasten the roof plate to the side plates.

1. Place 1 machine key of 8mm length in shaft 3 and the machine key length 28mm in shaft 1.

2. Slide the gears over the machine keys.
As you can see: shaft 3 is fully assembled.

3. Next component that has to be assembled is, of course, a spacer. As there is a machine key on the shaft, you can't use a metal spacer you bought at the shop. That's why there's a spacer with a hub.

4. Last component that's needed on the roller is the lever.

5. And to finish these rollers: put the timing belt over the gears. Make sure it fits them well!

For this step, you need shaft 4 (504mm long), 2 machine keys length 8mm and the 2 adjustment blocks.

1. Push shaft 4 through the holes in the side plates (see picture).
2. Place the machine keys in both grooves.
3. Attach the adjustment blocks: the cilindrical one has to be attached on the left side of the machine, the one with the groove in it must be attached on the right side (where there's also a groove in the side plate).
If necessary, use a hammer to make them clips.

4. Now it's time to add the bolt and nut that will fasten the adjustment block with the groove on a choosen place.
Push the bolt through the groove from the inner side of the side plate to the outer side.
On the outer side, the nut can be screwed on the bolt. We used a 'vijfsterknop' for the nut, literally a 'five star button' (see picture). These nuts are easier to tighten.

To finish the rollers, there's one thing that's need to be done.

Take the 8 bolts M3*14 and the 8 washers (inner diameter 4.3mm, outer diameter 12mm).

Slide a washer over each bolt, and screw the bolt in the threaded holes at the end of each shaft.

Now, it's impossible for the components on the shaft to slide of.

Needed:

- electrical cable, 2*1.5+1.5, 2 metres long
- heating element
- plug
- oven thermostat
- soldering iron + solder wire

There's no switch needed: the oven thermostat serves as the switch.

1. Place the heating element in the metal case. Put the end of it through the hole in the case and click the clamp (with the wiring) on it (on the outside of the case).

2. Assemble the eye-bolt in the middle of the metal case.

3. Fill the whole case of the machine with a thin layer of isolation material (glass wool).

4. Place the case with the heating element in the machine. Place the front side of the metal case against the front plate of the housing.

1. Put the sensor (long metal pin) of the oven thermostat through the hole in the case, and through the eye of the eye-bolt. Fasten it with a nut.

2. Push the oven thermostat through the hole in the back plate of the housing (green circle on picture). Tighten the 2 screws M4*8 in through the back plate, in the case of the thermostat (red circles).

3. Insert the button on the pin of the oven thermostat.

1. The cable is pushed trough the hole in the left side plate.

2. The plug is set on the cable.
Pay attention: the plug can't be set on it until the cable is pushed through the side plate!

3. Place the ceramic plate on top of the machinecase.
Pay attention: there are grooves in the side plates (see picture) where the ceramic plate needs to be slided in. Do this carefully: the ceramic plate is very fragile!
It's almost impossible to remove the plate again, without breaking it, so be careful.

The last thing that needs to be done, is pushing the cooling element (already prepared in steps 8-9-10) through the holes in the L-formed holder.

Now the machine is finished. You can start to test!

Note:

- the plexiglass needs to be heated on a temperature of +- 130°C. Set the button on this temperature.
this means that the ceramic plate is very hot; make sure you don't burn yourself!

- the compressed air is needed: without, you will not be able to cool the plexiglass enough
this means you won't be able to create the bend radius that you set on the adjustment block

- make sure you turn the lever slowly
if you turn to fast, the plexiglass won't be able to cool enough when it leaves the roller system

We also designed a lamp, made of wood and plexiglass. Have a look at this too!

https://www.instructables.com/id/Simple-minimalistic-design-lamp/

And if you want to see our design process, take a look at our blog!

http://ontwerptools22014iogroep5.blogspot.be/ (language: Dutch)