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.