Module 1 of 2 · 40 minutes
Timber, fixings and getting it accurate
By the end of this module you will be able to
- Choose timber by grade, moisture content and treatment for the job
- Select the right fixing, and explain why the wrong one fails
- Mark and cut accurately enough that joints close
- Work safely with dust, blades and vibration
Amara Why do my skirting joints open up a few months after I fit them?
Nadia Because the timber was wetter than the room when you fixed it, and it has been drying and shrinking ever since. That single fact explains most carpentry complaints in a house.
Amara Doors sticking in winter too?
Nadia Same mechanism in reverse. Wood takes up and gives off moisture until it balances with its surroundings, and it moves far more across the grain than along it. Doors bind in a damp winter and swing free in a dry summer.
Amara So what do I do?
Nadia Bring the timber into the room it is going to live in and leave it there for days. Not hours, days. It is free, it needs no skill, and it prevents the commonest callback in domestic carpentry.
Amara Right, fixings. I use screws for everything.
Nadia Which is fine until it is not. Screws hold by thread engagement, so what matters is how much thread is in the receiving piece. At least two thirds of the screw length, minimum.
Amara And nails?
Nadia Better in shear and where things move, which is why structural work is nailed rather than screwed. Screws win on withdrawal and on being removable. Different jobs.
Amara What about into brick? Mine always spin loose.
Nadia Then it is the hole, not the plug, and it is almost always dust. A plug needs a clean hole, exactly the right diameter, drilled deeper than the plug, with the dust blown or vacuumed out.
Amara I have never once cleaned a hole out.
Nadia Almost nobody has, and it is exactly why fixings spin. The plug is sitting on a bed of dust instead of gripping brick.
Amara Plasterboard?
Nadia Ordinary plugs are useless in it. Spring toggle or a metal self drill anchor. And for anything genuinely heavy, find the stud and fix into that. A television on plasterboard fixings alone will come off the wall, usually at three in the morning.
Amara Let us talk accuracy. Some people just seem to have the knack.
Nadia It is not a knack, it is four habits. Measure from one datum, never cumulatively.
Amara Why does that matter?
Nadia Because marking each piece off the last one accumulates every tiny error. Do that ten times and the last piece is out by three or four millimetres and you have no idea where it went.
Amara Second habit?
Nadia Mark with a knife, not a pencil, where it matters. A knife line severs the fibres, so your saw or chisel has a shoulder to register against, and it is a fraction of the width of a pencil line.
Amara Third?
Nadia Decide which side of the line you are cutting and never vary. Half of all beginner inaccuracy is cutting on the line sometimes and beside it other times, so nothing is consistently anything.
Amara And fourth?
Nadia Cut it proud and trim to fit. Almost nothing can be made longer afterwards. A joint that closes because it was fitted rather than calculated is the difference between joinery and assembly.
Amara Last thing. Risks.
Nadia Wood dust is a carcinogen. Hardwood dust causes nasal and sinus cancer, and both hardwood and softwood cause occupational asthma.
Amara People sweep up sawdust with a brush constantly.
Nadia And that puts the finest and most dangerous fraction straight back into the air they are breathing. Class M vacuum, on tool extraction, work outdoors where you can. And be especially careful with MDF, because the dust is very fine and carries the resin binder with it.
The written material
Timber moves, and the whole trade follows from that
Wood takes up and gives off moisture until it reaches equilibrium with its surroundings, and as it does it shrinks and swells across the grain far more than along it. Almost every carpentry failure in a house, gaps opening in skirting, doors binding in winter and swinging free in summer, cupped floor boards, is that one fact.
Timber sold as kiln dried is typically around 12 to 16 per cent moisture content. Inside a heated house it will end up nearer 8 to 12. So bring timber into the room it will live in and let it acclimatise for several days before you fix it. Skipping that is why a floor laid on Saturday has gaps by Christmas.
Use treated timber anywhere it can get wet or touch masonry or ground: sole plates on a solid floor, anything outdoors, anything in a loft or cellar with moisture risk. And re treat every cut end, because the cut face is untreated timber you have just exposed.
Fixings, and the failure each one has
Screws hold in timber by thread engagement, so what matters is how much thread is in the receiving piece. A rule that works: at least two thirds of the screw length should be in the second piece. Pilot drill hardwood and anything near an end or an edge, or you will split it.
Nails hold by friction and are better than screws in shear and where movement is expected, which is why structural work is nailed. Screws are stronger in withdrawal and are removable.
Into masonry, the failure is nearly always the wrong hole. A plug needs a clean hole of exactly the right diameter, drilled deeper than the plug, with the dust blown or vacuumed out. Dust left in the hole is why a fixing spins and pulls out.
Into plasterboard with nothing behind it, ordinary plugs are useless. Use a spring toggle or a metal self drill anchor, and for anything heavy find the stud and fix into it. A television on plasterboard fixings alone comes off the wall.
- Two thirds of the screw in the receiving piece, minimum
- Pilot drill hardwood, and anything within about 50mm of an end
- Masonry: right diameter, deeper than the plug, dust removed
- Plasterboard: toggles or anchors, and find the stud for anything heavy
- Re treat every cut end of treated timber
Accuracy is a method, not a talent
Measure from one datum, not cumulatively. Marking each piece from the previous one accumulates every small error until the last one is out by several millimetres.
Mark with a knife rather than a pencil where it matters. A knife line severs the fibres, gives the saw or chisel a shoulder to register against, and is a fraction of the width of a pencil line.
Decide which side of the line you are cutting and stay consistent. Half the beginner's inaccuracy is cutting on the line sometimes and beside it others.
Cut proud and trim. Almost nothing can be made longer once it is cut, and a joint that closes because it was fitted rather than calculated is the difference between joinery and assembly.
The risks that accumulate quietly
Wood dust is a carcinogen. Hardwood dust causes cancer of the nose and sinuses, and both hardwood and softwood dust cause occupational asthma. Use on tool extraction, work outside where you can, and wear appropriate respiratory protection. Sweeping up with a brush puts the fine fraction back into the air; use a class M vacuum.
MDF deserves particular care because the dust is very fine and it contains resin binders.
Hand arm vibration from sanders, circular saws and SDS drills causes permanent nerve and vascular damage. Watch total trigger time, keep tools sharp because blunt tools take longer, and keep your hands warm.
Most serious injuries with a circular saw or a table saw are kickback. Never reach across the blade, use the riving knife and guard, and support the offcut so it cannot pinch the blade.
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