Lesson video

Hello there.

My name is Mrs. Dhami.

Thank you for joining me for your design and technology lesson today.

Now, the big question for today is how can we join timbers? Now, there are an absolute variety of different options that we can choose.

So today we're gonna explore these so that you can choose the right one for the right application.

So hard hats on.

Let's get cracking.

Our outcome for today is we will be able to explain various mechanical and chemical methods to join different materials.

We have three different keywords today.

Mechanical fixings, which are parts that hold materials together using force.

Chemical joining, which is when we use adhesives or heat to bond materials through a chemical reaction.

And lastly, component, which is a ready-made part used across different products to make manufacturing easier.

We have two learning cycles to our lesson today.

We're gonna start off with mechanical fixings and then move on to chemical joining.

So let's get cracking with mechanical fixings.

Mechanical fixings are a way of holding materials together using physical means, such as fasteners or shaped joints.

Mechanical fixings use force or shape to hold materials in place, are common in timber construction and product assembly and can be permanent or sometimes can be removable.

Time for our first check-in.

Which of the following is a mechanical fixing? Is it A, PVA adhesive, B, epoxy resin, C, screw, or D, contact adhesive? Have a think.

Come back to me when you've made your decision.

Well done if you got C.

A screw is a type of mechanical fixing.

Nails are driven into timber to hold pieces together.

The compressive forces of timber fibers push back against the nail, creating friction to help hold the nail in place.

Nails come in different lengths and some have features like ridges or twists to further enhance grip.

Take a little look at the picture on the right.

You can clearly identify the twists and the ridges in that picture.

So where do we use them? We use them in lightweight or temporary joins.

Benefit: they are fast to insert with a hammer.

However, limitations, they may loosen over time or with movement.

So if that product is going to come in contact with a lot of vibration, it might not be the most suitable choice.

There are different types of nails.

Different types suit different tasks.

Let's take a little look.

We have the round wire nails, which are used for general purpose.

We then have lost head nails.

Now, these tend to be used when we do not want to see the head and we need it to be hidden, such as a floorboard.

And then we have panel pins.

Panel pins are for thin timber sheets and moldings.

For example, hardboard backing of furniture Screws are mechanical fixings that grip the wood, making joints stronger and more secure than nails.

Now, screws have threads and you can clearly see that in the picture on the right.

Now, threads are basically spiral ridges that run along the shaft, which help to grip the wood fibers.

Screws come in many different lengths and can also be self-tapping.

Now if they are self-tapping, this basically means that they have a really, really sharp thread which cut into the material as it's directly driven in.

So where do we use screws? They tend to be used in frame construction.

Benefit, they provide a strong hold, but they're also removable.

Limitation is that they may require a pre-drilled hole, like a pilot hole.

Sometimes screws require a pilot hole, as we've just said.

This is a small hole that is pre-drilled before a full sized hole, which acts as a guide.

You can see the pilot hole in the picture on the right.

Depending on the type of screw, a countersunk hole may be needed.

Take a little look on the right-hand side on the second picture down.

Basically a countersunk hole is a conical-shaped recess that is drilled into a material that accommodates the head of a screw to provide a flush finish.

And you can see this in the third picture.

A flush finish basically means that the head of the screw does not stick out.

You can't see it above the material because it's flush with the surface.

Understanding the parts of a screw make differentiating the different types easier.

So let's take a closer look.

At the top, we have the head of the screw.

We then have the main body, which we call the shank.

Now, around that shank is where the thread wraps around.

And then finally, we have the sharp tip.

Now, countersunk heads sit flush with a surface, as we've just said on the previous slide.

Whereas you can get round head screws which sit above the surface.

And this is often used for decoration 'cause sometimes a round head to a screw does look quite nice.

Now, there are different drive types.

Now, what I mean by drive type is the shape of the slot in the screw's head.

So we have the Phillips, which is like a cross.

We have the slotted, which is a straight line across.

We have the pozi, which is a bit more like a star.

And then we have the hex, which is clearly said in its name, in a hexagon shape.

Thread types and shank diameters can differ depending on the material type and the thickness.

Time for a quick check-in.

Why are screws often stronger than nails? Is it A, they are longer, B, they are glued in, C, they have a thread that grips the wood or D, they are wider? Have a little think.

Come back to me when you've made your decision Well done if you got C.

Screws are often stronger than nails because they have a thread that grips the wood.

Nuts and bolts are mechanical fixings used to securely join timber parts, especially in frames or large structures.

They are removable and allow for strong, reusable connections.

Nuts and bolts are used with washers to prevent damage to the timber and can be tightened and removed easily.

Take a little look at the picture on the right.

At the top, we have the bolt.

We then have that washer, which helps to stop the timber becoming damaged.

And then at the bottom, you can see the nut which joins it all together.

So where do we use them? We tend to use them in frame construction.

Benefit: they provide a strong hold and are removable.

Limitation is that they require correct size drilled hole, but also it requires access to both sides too.

Knock-down fittings are components used to assemble and disassemble products, especially flat-pack furniture.

So this slide and the next slide, if you have ever put together some flat-pack furniture, I think you will be able to relate quite well to this.

So a component is one of our keywords today.

A component is a ready-made part used across different products to make manufacturing easier.

The components used for knock-down fittings are usually standardized, which make it easier for manufacturers to buy in but also for consumers to replace.

Now, I'm thinking of a rather large branded shop that you may or may not have been to that sell flat-pack furniture because they also at the.

It's normally towards the exit, they have this big display where actually if you need another knock-down fitting or perhaps a part is missing from your pack, you can go and help yourself to that part.

So it makes it really easy to replace those if they're broken or if they are missing.

You know what you need.

You know what you need to get.

So where do we use knock-down fittings? We tend to use them in flat-pack furniture.

Benefit: the ease of assembly, disassembly, but also reassembly too.

Limitation is they may weaken over time through continued use.

There are many, many different types of knock-down fittings.

So let's explore a few of them together.

Let's start with cam lock fittings.

Now, cam lock fittings are made of two parts, a cam lock and a connecting dowel.

Take a second and just have a quick look at the diagram.

Notice the connecting dowel and notice the cam lock.

Brilliant.

So the dowel is inserted into one panel and we can see that on the left-hand side and the cam lock, which is a disc, is inserted into the adjacent panel.

Then if you turn the head of that cam, so you turn that round, that locks the dowel in place.

You can normally turn that round with a screwdriver.

Let's take a little look at confirmat screws.

Now, these are ideal for manufactured boards because of their large thread that grips very, very well.

Now, they require an Allen key to install.

Now, an Allen key is an example of a piece of standard tooling.

Normally in a flat-pack you would get one of those with the flat-pack.

However, let's say it's missing, it's a standard tooling which most people have somewhere in their home that they might be able to get their hands on and might be able to use instead.

Next step are block connectors.

Now, block connectors, you can see that's the dark gray bit in our picture, they are used to hold timber panels at a 90-degree angle.

They are secured using screws from both sides.

Take a little look at the direction of the screws.

We've got two going into the panel on the left and then we've got one going into the panel on the top.

So it holds them at a 90-degree angle.

Next up are barrel nuts and bolts.

Take a little look at the bolt.

Now take a little look at the barrel nut next to it.

And note, if you look very carefully at the inside of that hole on the barrel nut, you will see that it is threaded, okay? So barrel nuts and bolts are used for load-bearing joints, like bed frames.

A bolt goes through one panel and threads into the barrel nut housed inside the other one.

Okay, so that thread joins them together.

Time for a check-in.

I would like you to match the image of the knock-down fitting to its label.

So all the pictures you can see on the right-hand side with numbers and the labels on the left-hand side.

So for labels, we have A, a block connector, B, cam lock, C, barrel nut, and bolt, and lastly D, confirmat screw.

Have a think, do some matching.

Come back to me when you've got some ideas.

Well done with all of your efforts on that.

Let's see if your matching matches mine.

So for A, we match that to image two.

That's the block connector to image two.

For B, the cam lock, we match that to image four.

For C, the barrel nut and bolt, we match that to image one.

And lastly D, the confirmat screw, we match that to image three.

Well done with all of your hard work.

Joinery methods use shaped wood pieces to hold parts together, ideally without extra components.

Joinery is a type of mechanical fixing in the sense of that they are shaped to interlock with one another.

Timber joints are cut into the timber either by hand or machine and can be made to look decorative too.

So where do we use them? We tend to your use joinery methods with furniture.

Benefit is that there are many types that can be very strong.

Limitations though, they require skill and specialist equipment.

So let's explore a few over the next few slides.

There are many different types of timber joints.

We have butt joints, which are simple to make as they are two pieces of wood butted against each other.

They are, however, quite weak but can be reinforced with nails or screws.

They are common in basic frames.

We then have comb joints.

Now, comb joints have interlocking fingers that increase the surface area for adhesive and improve strength.

They are commonly used for box construction.

We then have mortise and tenon joints.

Now, mortise and tenon joints are very strong and used in structural frames, like tables and chairs.

We make a little stall at our school and we use a mortise and tenon joint in that.

The students love it because we get to use the mortiser.

Now, if you don't have one of those at your school, it's a little bit like a pillar drill.

But rather than drilling a round hole, it drills a square hole.

It's great, you tend to go halfway through, turn it round and go halfway through again.

Well, a little bit more than halfway to make that mortise joint there.

And then we tend to cut the tenon joint by hand.

They can be strengthened further with adhesive and pins.

We then have half-lap joints.

Now, half-lap joints have overlapping sections reduced to half the timber's thickness, which you can clearly see in that picture there.

They're commonly used for frames.

We then move on to miter joints.

Now miter joints connect two angled ends, usually at 45 degrees, to form a corner.

They hide the end grain of the timber and are often used in picture frames.

So next time you're at home, take a little look at some of the pictures on your walls 'cause you're very, very likely to find a miter joint on one of those.

Now, to calculate a miter joint, you divide the total angle between the two joining pieces by two to get the correct cutting angle for each piece.

And you can see that with the purple line above.

We've got the 90-degree angle divided by two with the purple line into 45 and 45.

And then with the 60-degree one, the purple line goes through, dividing it into 30 and 30.

We then have dowel joints.

Now, dowel joints use fluted dowels to align and hold pieces together securely.

Take a little look at the little image.

You can see those two dowels sticking through one piece of wood into the next.

The ridges on the fluted dowels improve grip because they increase the surface area, there is more for that adhesive to stick on to.

Time for a quick check-in.

You are making a regular pentagonal frame.

Oh, that was a mouthful.

You're making a regular pentagonal frame from five equal wooden pieces.

What angle should you cut each miter joint? Have a think.

Think back to the example I shared on a few slides ago and then come back to me when you've made your decision.

Well done if you got A, with 54 degrees.

A regular pentagon has interior angles of 108 degrees.

So for a miter joint, you divide 108 by two, which gives us 54 degrees per piece.

Onto task A, part one, describe the difference between a nail and a screw when joining timber.

Part two, name one type of knock-down fitting and explain its purpose.

Part three, explain why a mortise and tenon joint is stronger than a butt joint.

And lastly, state one advantage of using bolts and nuts in timber construction.

Good luck.

Have a go.

Use your wonderful knowledge and come back to me when you've got some lovely answers.

Part one, I asked you to describe the difference between a nail and a screw when joining timber.

You might have said a nail is smooth and is hammered into timber quickly, but it doesn't grip as well.

A screw has a thread that grips into the wood fibers, making the joints stronger and easier to remove if needed.

Part two, name one type of knock-down fitting and explain its purpose.

You might have chosen a cam lock fitting.

So a cam lock fitting is a knock-down fitting used in flat-pack furniture.

It allows the product to be taken apart and reassembled without damaging the timber.

Part three, explain why a mortise and tenon joint is stronger than a butt joint.

You might have said a mortise and tenon joint interlocks and has a larger contact area for gluing, which makes it stronger and more resistant to movement than a simple butt joint.

Part four, state one advantage of using nuts and bolts in timber construction.

You might have said nuts and bolts create strong, removable joints that can be tightened or adjusted, which is useful for large or load-bearing timber structures.

Well done with all of your hard work on these questions.

On to learning cycle two, chemical joining.

Chemical joining is the process of bonding materials using substances, otherwise known as adhesives, that create a chemical reaction to hold parts together.

Chemical joining is often invisible, but not all the time, and used for clean finishes.

It is dependent on the material compatibility and it is not easily reversible.

Time for a check-in.

What makes chemical joining different from mechanical fixings? A, it's always weaker.

B, it uses force, C, it requires bolts or D, it involves a chemical reaction to bond materials.

Have a think.

Come back to me when you've got an answer.

Well done if you got D.

Chemical joining is different from mechanical fixings because it involves a chemical reaction to bond the materials together.

PVA stands for polyvinyl acetate.

Now PVA, I am sure you have come across it before, probably during primary school was your first experience of it.

It's that glue and I bet many of you have put it onto your hands, waited for it to dry and peeled it off.

I know you all far too well.

So PVA has a wide range of applications for timber-based materials like papers and boards, but many different types of wood too.

PVA adhesive chemically joins by soaking into porous materials like wood or paper and forming a strong bond as the water evaporates, leaving behind a flexible plastic film that holds the surfaces together.

So where do we use it? We use it with joining timber-based materials but also papers and boards.

Benefit is it is non-toxic.

That's why you were allowed to use it in primary school.

And it dries clear.

Limitation though, it is not waterproof unless it has been modified.

Polyurethane adhesive forms a very strong waterproof bond and is used in both indoor and outdoor timber products.

Polyurethane adhesive chemically joins by reacting with moisture in the air or materials to create a strong expanding foam bond that adheres to a wide range of surfaces.

And you can see that foam in the diagram there.

So where do we use it? We tend to use it with bonding timbers, polymers or metals.

Benefit: it's very strong, it's also waterproof.

So it's a waterproof bond on many different materials.

Limitation is it often expands while curing, which can squeeze out.

Let's go back to that diagram.

You can see the two pieces of timber.

You can see the polyurethane adhesive in the middle and you can see it's dried and expanded up and out.

It can, however, be sanded afterwards to give yourself a nice flat finish.

Time for a quick check-in.

Why is polyurethane adhesive used for outdoor timber? Is it A, it looks like wood, B, it washes off easily, C, it expands and is waterproof or D, it dries instantly.

Have a think.

Come back to me when you've made your decision.

Well done if you got C.

Polyurethane adhesive is used for outdoor timber because it expands and is waterproof.

Contact adhesive is used when two surfaces are coated separately, allowed to dry slightly and then pressed together to create an instant bond.

Contact adhesive is used on large flat surfaces, such as veneers and laminates, with little need for clamping.

So where do we use them? We use them with bonding laminates or veneers.

Benefit is it's an instant bond and clamping is not always necessary.

Limitations: they are difficult to reposition once joined.

You've gotta get the right location when you are putting them together.

Contact adhesive is often used between veneer sheets when making plywood.

Epoxy resin chemically joins by mixing two parts, a resin and a hardener, which chemically react to form a very strong and rigid bond.

Epoxy resin though has a long curing time in comparison to other adhesives.

What I mean by curing time, it's the setting time.

However, it is waterproof and it is chemically resistant.

So where do we use it? We tend to use it to bond dissimilar materials where other adhesives will not work.

Benefit: it's very reliable, it is water and chemical resistant.

But the limitation is this: it requires precise mixing.

Now, as I've put in this little bit of writing on the right-hand side, I've put epoxy resin is often sold in a double syringe to dispense the resin and hardener evenly.

So basically you push that orange part and out comes the resin and the hardener at exactly the same point and at exactly the same measurement too.

The other limitation, as I mentioned before, is it takes a long curing time.

So a long time for it to dry.

Another check-in.

Which adhesive forms an instant bond after being applied to both surfaces and allowed to dry slightly? Is it A, contact adhesive, B, polyurethane adhesive, C, epoxy resin or D, PVA? Have a think.

Come back to me when you've made your decision.

Well done if you got A.

Contact adhesive forms an instant bond after being applied to both surfaces and allowed to dry slightly.

It's often used with veneers.

Different adhesives suit different applications depending on strength, setting time and the environment.

Considerations include material type.

Is it a softwood, a hardwood, a composite? And what is it being joined to? Strength required.

Is it a big bed or is it a bedside cabinet? What is the use of that product? Two, is it going to be used indoor or outdoor? And the drying or curing time.

How quickly do you need that adhesive to set.

Onto task B, part one, I'd like you to compare the use of PVA and contact adhesive when joining timber.

Give one advantage of each.

Part two, a designer is creating an outdoor bench from hardwood.

Explain why polyurethane adhesive may be more suitable than PVA for this project.

And lastly, explain why epoxy resin is often used in high-strength timber applications.

Good luck, apply all of your wonderful knowledge and come back to me when you've got some wonderful answers.

Part one, I asked you to compare the use of PVA and contact adhesive when joining timber, giving one advantage of each.

You might have said PVA is good for joining porous timber because it soaks into the surface and creates a strong, long-lasting bond, especially when clamped.

On the other hand, contact adhesive is ideal for large, flat surfaces like laminates and gives an instant bond without the need for clamping.

Part two, a designer is creating an outdoor bench from hardwood.

Explain why polyurethane adhesive may be more suitable than PVA for this project.

You might have said polyurethane adhesive is waterproof and can withstand outdoor conditions while PVA is not water resistant.

It also expands slightly as it cures, helping to fill small gaps in the timber for a stronger bond.

And lastly, part three, I asked you to explain why epoxy resin is often used in high-strength timber applications.

You might have said epoxy resin forms a very strong, durable bond that can handle heavy loads and stress, making it ideal for structural timber joints.

Well done with all of your hard work in this lesson.

Well done, folks.

So this brings us to the end of our lesson today.

Let's summarize what we have found out.

Materials can be joined using mechanical fixings or components.

Materials can be joined using substances that create chemical bonds between surfaces.

Well done with all of your hard work today.

I hope you have enjoyed the lesson and I look forward to seeing you in another lesson soon.

Take good care.

Bye, bye, bye.