In part one of this series on making your own homemade scaffolding tower I discussed the research and design aspects of building the tower. In part two I perform a few quick calculations to prove the platform will be strong enough and put together a parts list for the material purchase.
Calculations
Having worked with wood for about 20 years I was sure that my design was strong enough but I thought it wouldn’t hurt to do some calculations to make sure. The biggest unknown for me was the platform as I’d never really made a span before so decided to calculate for that. I figured it was approximately the same as the floor of a house so I used the same calculations an architect or engineer would. First though a few definitions:
- Joist spacing is the centre to centre distance of the joists (typically 400 or 450 mm centres).
- Span is the clear span between supports.
- Dead load is the joists, floor and screws.
- Imposed load is the person and any tools or materials.
Standard Floor Loading
Imposed loads should not exceed 1.5kN/m^2 for a regular floor (figures from BS6399-1, Current version is probably BS EN 1991-1-1:2002).
1 N = 1 kgm/s^2
Gravity (a) = 9.81 m/s^2
Since: F=ma
1500 = m * 9.81
m = 1500 / 9.81 = 152.9 kg
In other words 153kg evenly distributed over every square meter of floor.
The table below shows maximum spans (in meters) for C16 graded timber with the given centre spacing (columns)
| Timber | 400mm | 450mm | 600mm |
| 47 x 97 | 1.92 | 1.82 | 1.46 |
| 47 x 122 | 2.55 | 2.45 | 2.09 |
| 47 x 147 | 3.06 | 2.95 | 2.61 |
| 47 x 170 | 3.53 | 3.4 | 2.99 |
| 47 x 195 | 4.04 | 3.89 | 3.39 |
| 47 x 220 | 4.55 | 4.35 | 3.79 |
Designed Platform
- Width: 840mm
- Length: 1800mm
- Joists: 47×100 C16 on 450mm centres
- Span: 1500mm
The designed platform has a surface area of 1.5m^2 which gives a maximum loading of 1.5*152.9 = 229.3kg evenly distributed and assuming exactly the conditions given in the table. My platform however has a span of just 1500mm, significantly less than the maximum allowable span for C16 timber of 1820mm. Additionally I’ve assumed a centre spacing of 450mm which is true for the two centre beams but not the beams to either side which are more like 300mm centres. I’ll also be screwing down a single sheet of 18mm ply over the platform which is much stronger than floorboards. All things considered I would be happy saying the maximum safe load is 300kg, more than enough for me and my tools.
Material Purchase
From the design I put together a list of parts and I then mapped that onto timber that I could actually buy. I shopped around online for the best price and got the whole lot delivered for £225. The tables below show the parts list and the timber I bought.
CLS Parts List
| Part | Thickness | Width | Length | Quantity | Total Length |
| Kickboard Long Support | 50 | 50 | 100 | 4 | 400 |
| Ladder Leg | 50 | 50 | 1200 | 4 | 4800 |
| Ladder Rung | 50 | 50 | 250 | 8 | 2000 |
| Long Rail Stiffener | 50 | 50 | 1700 | 2 | 3400 |
| Platform Stop | 50 | 50 | 840 | 2 | 1680 |
| Rail Support Block Small | 50 | 50 | 100 | 4 | 400 |
| Rail Upright | 50 | 50 | 1200 | 4 | 4800 |
| Cross Brace | 47 | 100 | 2400 | 4 | 9600 |
| Noggin (Short) | 47 | 100 | 126 | 4 | 504 |
| Noggin | 47 | 100 | 400 | 3 | 1200 |
| Platform Joist | 47 | 100 | 1800 | 4 | 7200 |
| Rail Support Full | 47 | 100 | 846 | 2 | 1692 |
| Rung | 47 | 100 | 940 | 14 | 13160 |
| Leg | 47 | 150 | 2340 | 4 | 9360 |
| Stretcher | 47 | 150 | 1800 | 4 | 7200 |
| Rail Long Stretcher | 25 | 101 | 1800 | 2 | 3600 |
| Rail Long Mid Stretcher | 25 | 200 | 1800 | 2 | 3600 |
CLS Timber
| Timber Size | Total Length | Bought Length | Price | Cost |
| 50×50 | 17.5 | 20 | £1.26 | £25.20 |
| 47×100 | 33.4 | 40 | £2.11 | £84.48 |
| 47×150 | 16.6 | 20 | £3.17 | £63.36 |
| 25×100 | 3.6 | 4 | £1.56 | £6.24 |
| 25×200 | 3.6 | 4 | £3.24 | £12.96 |
| Total | £192.24 |
Ply Parts List
All parts can be cut from a single sheet of 18mm ply costing £33.12.
| Part | Thickness | Width | Length | Quantity |
| Platform Bed | 18 | 840 | 1800 | 1 |
| Cross Brace Gusset | 18 | 225 | 240 | 2 |
| Hatch Bed | 18 | 440 | 440 | 1 |
| Kickboard Long | 18 | 150 | 1600 | 2 |
| Kickboard Short | 18 | 195 | 840 | 2 |
| Rail Short Stretcher | 18 | 100 | 840 | 2 |
| Rail Support Plate | 18 | 100 | 151 | 4 |
Other Parts
| Part | Notes | Quantity |
| M10 x100 Bolts | Main frame, guard rail | 32 |
| M10 Washers | Use thick repair washers | 64 |
| M10 Nylock Nuts | 24 | |
| M10 Wing Nuts | Guard rail | 8 |
| M6 x 70 Bolts | Guard rail, platform locks | 20 |
| M6 Washers | 32 | |
| M6 Wing Nuts | 20 | |
| M5 x 50 Bolts | Castor attachment | 16 |
| M5 Washers | 16 | |
| M5 Nylock Nuts | 16 | |
| 4 x 50 Wood Screws | Platform | 30 |
| 4.5 x 70 Wood Screws | Rails | 64 |
| 6 x 150 Wood Screws | 32 | |
| Exterior Wood Glue | 1000 ml | 1 |
| Heavy Duty Castor | 60kg or greater | 4 |
| Bottle Jack | 1 Ton or greater | 1 |
On to part three where I start the construction.