Thicknessing Reclaimed Oak Slats
A school workshop has a thicknesser with 3 mm snipe on the outfeed end. A student must machine 24 reclaimed oak slats, each 350 mm long × 60 mm wide, from 25 mm rough stock to 19 mm finished. The manual states a minimum stock length of 300 mm and a maximum depth of cut of 2 mm per pass. One board contains a hidden 3 mm steel staple and some grit; another is bowed by 4 mm over its length. Dust extraction is a 1 kW shop vacuum connected to the machine's 100 mm port by a 50 mm hose. The class has 40 minutes of machine time and one operator. The thicknesser blades were changed two weeks ago and have since machined 40 m of particleboard. The student plans to cut all slats to 350 mm first, then take one 6 mm pass because the machine has a 2 mm scale marked on the side.
1. Prepare a machining plan: stock length, jointing, number of passes and depth of cut. Show your reasoning.
Read the worked answer
Stock length: cut at 420 mm, not 350 mm. The extra 35 mm at each end allows the snipe and any end checks to be trimmed after machining. Although 350 mm is above the manual's 300 mm minimum, short stock is more likely to snipe. Sequence:
- Inspect and joint one face flat. The 4 mm bow must be removed on the jointer or with a planer sled; a thicknesser copies the bow.
- Plane the second face and one edge, then rip to 60 mm.
- Thickness to 19 mm. Total removal = 25 - 19 = 6 mm. With a 2 mm maximum, use four passes: 2.0, 2.0, 1.5, 0.5 mm. The final 0.5 mm is a clean-up pass.
- Trim 35 mm from each end and check thickness. Support: use a carrier board or backer for the short slats and support the outfeed.
2. Identify the hazards in the reclaimed timber and the extraction set-up, and state the controls you would apply before machining.
Read the worked answer
Staple and grit: pass every board over a metal detector or inspect closely; remove the staple with pliers and brush off grit. A hidden staple will chip the blades and may be thrown. The blades have already cut 40 m of particleboard, which dulls them; check for nicks and rotate or replace before oak. Bow: joint first; do not rely on the thicknesser. Extraction: a 50 mm hose on a 100 mm port restricts air flow. Chips will build up, causing snipe, burning and blocked cuts. Use a 100 mm hose or a proper adaptor, check the bag/filter, and stop if chips stop moving. Short stock: 350 mm is close to the minimum; use a push stick and never put hands under the cutterhead. Wear eye, hearing and dust protection.
3. Estimate whether the 40-minute slot is realistic, and state what you would change.
Read the worked answer
24 slats × 4 passes = 96 passes. At about 8-10 s per pass including handling, that is 13-16 minutes of pure machining, plus inspection and trimming. Forty minutes is realistic only with two people: one feeding and one stacking, with extraction working. With one operator, allow 50-60 minutes. Do not reduce the number of passes to save time; a 6 mm pass is three times the maximum and will stall, snipe or damage the machine. If time is fixed, machine fewer slats and complete the rest later.