General Processes - Spray Painting on Wood Surface

General Processes

Pre-Check

• Check if your workpiece is best painted before or after jointing. If you get that wrong, the process of spray painting for the subsequent layers will become a nightmare.
• Ensure that the surfaces for spray painting is well finished (sanding), dry and and cleaned of wood dust.
• Note surfaces or edges that will be covered or out of sight, you need not spray paint those areas.
• If you have to drill holes or cut a rebate joint somewhere in your workpiece, get it done before spray painting.

Step 1: Part 1 of 2 Preparation for Location and Supports

• Locate a well-ventilated designated area suitable for spray painting.
• Prepare a few waste blocks of wood to support and elevate your project. A turntable will be perfect.
• The turntable or the blocks of wood will also enable you to turn your project around during spray painting without touching your project.

Step 2: Part 2 of 2 Preparation for Spray Can

• Shake the can for two full minutes once you hear the mixing ball begin to rattle.
• Before you start spaying on your workpiece, it is a good practice to spray first on a piece of scrap material. to make sure the paint is coming out in the way it is meant to.

Step 3: Spray Painting

• Maintaing a distance of about 300mm from the spray nozzle to the project.
• Select a starting point on one end and spraying across your project in one sweeping motion.
• Do not hold down the spray button continuously, when you are at the end of the first pass release the spray button.
• Always be mindful and maintain a constant distance from the item being painted.
• Overlap each pass by about a third to keep paint finish even and consistent.
• Continue in this fashion until entire project has one coat of paint.
• Allow paint to dry for the recommended amount of time before adding a second coat.

Repeat Step 3 if necessary.

Tips:
Apply each coat of paint in thin coats to avoid runs or drips.

Note:
Unlike lacquring on on wood, there is usually no need to sand the surface before applying the next coat.

General Processes - Jointing Multiple Layers with Multiple Dowels

Example using a Typical Photo Frame Project:

You want to join a piece of clear acrylic to a wood with 4 dowels to make a photo frame. So that the clear acrylic cover can be removed to add or change photos. You want to place one dowel in each corner. How do you install the dowels and make sure all the holes are aligned?

Note: This section assumes that the student is able to prepare and get ready the wood and acrylic material for the next stage. It also assumes that the student is able to mark out both wood and acrylic proficiently.

Step 1: (Marking Out)

• Use double-sided tape to tape the acrylic sheet to the wood.
• Avoid taping where the holes will be drilled.
• Mark out the positions for each of the 4 holes with an 'x'.

Step 2: (Preparation to drill)

• By now you should have worked out the length of each dowels based on the thickness of your wood and acrylic.
• If the diameter of each of your dowels is 6mm, the get ready a 6mm diameter drill bit.
• Install the drill bit to the drilling machine.
• Get ready 4 dowels that is already cut to length.

How to get the length of each dowels?

• 2/3 the thickness of the wood + thickness of acrylic sheet + how much you want the dowel to protrude out of the acrylic sheet.

Tips:

• If you are unsure if your dowels will be tight fit on your photo frame, test using waste acrylic and wood. (see step 1 for preparation)

Step 3: (Drilling Procedure)

• Secure your combined work piece (see step 1) on the drilling machine with an F-Clamp.
• Set the drill bit to the required depth.
• (To drill a through hole, see 'tips' just below this step)
• Drill the first hole and install a dowel.
• Drill the second hole diagonal to the first hole and install a second dowel.
• Repeat the process until all holes are drilled.

To appreciate why you need to do the above, mark out and try drilling four holes individually on an acrylic sheet and wood one after the other. Put them together and try putting in the second dowel. How's that?

Tips:

• If you plan to drill through the holes, i.e. you want to expose the dowels on the other end of your photo frame, you need to place a piece of waste wood below your workpiece. Drill through your workpiece into the waste wood.
• This is to minimize splitting (on the wood part) at the other end of the drilled hole.

To appreciate why you need to do the above, try clamp a waste wood suspended on a machine vice without a waste wood below. Drill through. You will know what I mean.

Step 4: (Finishing)

• Split both the clear acrylic cover and the wood for finishing separately.
• Finish both the clear acrylic cover and the wood respectively with your desired finish.

The end.

General Processes - Working with Acrylic

General Processes:

Pre-Check

Make sure all parts given to you are 'square'. That means the edges are 90 degress to each other before you start marking out.

Marking Out (After you got your freshly cut acrylic sheets)

1) Mark out all parts with lines for sawing, or trimming, or bending with a pencil and mark the centres of curves (radius) and holes to be drilled with an 'x'. Mark out all the positions for screws and/nails nails.

Tips:

• Do not tear the protective paper away from the acrylic yet. The paper surface is for you to draw and mark out.
• If you plan to have screws to join acrylic to wood, work out the correct length, type of head, and the diamter & depth of the pilot holes to drill on the acrylic. Generally if you want the surface to be 'flushed', use a Countersunk Head Screw. If you do not mind the screw head popping out of the surface, use a Round Head Screw.
• Make sure that you do not screw too close to the edge of the acylic. At least 10 - 15 mm away from the edge is a good guide. But that will depend on your application.
• For bending, the marking-out lines should be 'dashed-lines'.
• For circles or radiuses, the marking-out lines should be 'centre-lines' cutting through the centre (or 'x').

Drilling

2) Drill all the holes first.

Tips:

• If dowels are required, make sure you check that the diameter of the dowels matches the diameter of the drill bit. To check if the fit nicely, try it on a piece of waste acrylic.
• If you require a flat hole, use a Forstner Bit instead of a Drill Bit.
• If you require a large hole and not even the Forstner Bit can create it, consider using a Hole Saw instead.

Sawing & Trimming

3) Saw / Trim curves using the Scroll Saw (concave or convex curves) or a Hacksaw (for long straight cuts). For external curves, the Circular Sanding Machine may be used.

Edge Finishing (Part 1 of 3: Filing)

4) File the edges with the correct files. (see 'Important' just below).

Tips:

• Holes cut out with a drill bit or a hole saw need not be filed extensively. The curved surface are already perfect as it is. If need to, file lightly to get rid of the burrs, or use a Wet & Dry paper instead.
• Always use the right file for your work. Generally a Half-Round file for curve edges, and a Flat File for straight edges and for rounding off corners.
• The objective of filing is to take away large scratches from the edges from saw cuts. So make sure at the end of your filing, inspect the edges for remaining deep scratches.
• Round the edges for aesthetics. It usually works.

Dry Assembly (to test if parts fit)

5) Dry fit all your parts, check that they are OK. If not ok, modify or re-do. Tips: Don't join them with Chlorofoam yet!

Tips:

• Important!: If bending is required, make sure you complete your finishing process first.

Edge Finishing (Part 2 of 3: Wet & Dry Paper)

6) Prepare acrylic edges for polishing using the Wet & Dry Paper.

• IMPORTANT: If you are joining edges, you MUST NOT sand the edges to be joined! It will not fit after that.

Edge Finishing (Part 3 of 3: Polishing with the Buffing Machine)

7) Finish the edges of the acrylic on a Buffing Machine till shine.

Jointing (also see 'Bending & Forming')

8) Acrylic to Acrylic: Butt-join acrylic parts using Chlorofoam. Use tapes to sequre the parts if necessary.

Note:

• Make sure the edges for jointing is straight, not filed, and not polished.

Others:

• Acrylic to Wood: Jointing using Wood Screws, or Bolts and Nuts, etc.
• Acrylic to Metal: Machine screws or Rivets, or Bolts and Nuts, etc.

Bending & Forming (also see 'Jointing')

9) Bending acrylic on the Strip Heater: For straight bends.

Tips:

• Plan the steps before hand how you want to bend your acrylic.
• Use a piece of paper to rehearse if you are unsure.
• Use formers (of various bending angles) to help you achieve accurate angles while bending.
• If there is no formers available, design and make them before bending.

10) Forming acrylic can be done using the Oven, the Vacuum Former, or the Blow Moulding machine.

Tips:

• Plan the steps before hand how you want to form your acrylic.
• Use formers to help you achieve accurate shapes and forms while bending.
• If there is no formers available, design and make them before bending.

What if your project has both Jointing and Bending and/or Forming?

• You have to plan the sequence well on which to complete first before the other.

Additional Notes

• You will notice that finishing your acrylic edges is put before jointing, bending or forming.
• The reason is because once you join, bend or form, it is more difficult to file and polish.
• If in doubt... alway ask.

General Processes - Working with Wood

General Processes:

Pre-Check

Make sure all parts given to you are 'square'. That means the edges are 90 degress to each other before you start marking out.

Marking Out (After you got your raw materials)
1) Mark out all parts with lines for sawing and trimming with a marking knife, mark the centres of curves (radius) and holes to be drilled with an 'x'. Mark out all the positions for screws and/nails nails.

Tips:

• If you have screws or nails in your joints, work out the correct length, type of head, and the diamter & depth of the pilot holes to drill. Also make sure that you do not screw or nail too close to the edge of the wood.

Drilling
2) Drill all the holes first.

Tips:

• If dowels are required, make sure you check that the diameter of the dowels matches the diameter of the drill bit. To check if the fit nicely, try it on a piece of waste wood.
• If you require a flat hole, use a Forstner Bit instead of a Drill Bit.
• If you require a large hole and not even the Forstner Bit can create it, consider using a Hole Saw instead.

Sawing
3) Trim (concave or convex) curves using Scroll Saw (if wood is thin) or Tenon saw (for straight cut). For external curves, the Circular Sanding Machine may be used.

Dry Assembly (to test if parts fit)
4) Dry fit all your parts, check that they are OK. If not ok, modify or re-do.

Tips:

• Don't join them with PVA and nails yet or screws yet!

Finishing (Part 1 of 2: Sanding Preparation)
5) Sand surfaces and edges smooth using Glass Paper (aka sand paper).

IMPORTANT:

• If you are joining edges, you MUST NOT sand the edges to be joined! It will not fit after that.

Tips:

• Round the edges for aesthetics. It usually works.

6) Join parts using PVA and and Panel Pins or Screws.

Note:

• When using screws no PVA glue is required. Because one of the reasons for using screws instead of nails is so that the parts can be taken apart later on.
• If you use nails (and PVA glue), then you are prepared for a permanent joint.

Finishing (Part 2 of 2: Spray Paint or Lacquer)
7) Finish as desired (spray paint or lacquer).

Tips:

• Always spray paint at least 300mm away from the object.
• Test spray in thin air before applying your coat. This procedure is used to get rid of blogged droplets.
• Lacquer on a clear sunny day instead of a rainy and humid day.
• Use spray lacquer to achieve even coat on surface.
• When using brush for lacquer, always ensure thin coat for every layer of coat.
• Allow coats (spray paint, spray lacquer or brush lacquer) to dry completely in cool and dry places before applying the next coat.
• Drying time varies with types of coats. Generally up to 2 hours is required to ensure surface is completely dry.
• Sanding is required for the first 3 coats of lacquer. But use very old and used glass paper.
• For really glossy surfaces, up to 10 coats of lacquer is needed.
• Use the drying time in between lacquer to update your journal or complete the other parts of your project.

Special Note:

• Sometimes it is necessary to join (step 6) first before sanding (step 5).
• Sometimes it is necessary to join all parts (step 6) before the applying the finishing coat (step 7).
• It all depends on the nature of the project.

If in doubt... alway ask.

How to draw Oblique to 1-Point Perspective & Isometric to 2-Point Perspective Drawing Made Easy

D&T Coursework Attendance for Week1 & 2 June 2011

Dear D&T students,

Your attendance is required on the above mentioned dates to catch up with your work.

I noticed there are some of you whose prototype is almost complete. Catch me ASAP and I will assess your work and decide if I can excuse you for the rest of the week. But you will work from home on the necessaries and I will take a look at your work the next day after your extra lessons in the morning.

Note: Please inform your parents about the requirement to be present for Week 2 too. Some of your parents claimed that they did not know about this.

Regards

Mr Daniel Lim