The Sawmill operator can be found along the southern wall of the Varrock Lumber Yard on members servers, at the icon on the minimap. He can turn four kinds of logs into planks (see sawmill), and also runs a Construction Supplies shop selling bolts of cloth, three kinds of nails, and saws. He will not accept noted logs, except indirectly through house servants.
Members can obtain planks by taking logs to the sawmill operator. Right-click on this NPC, and there will be a "Buy planks" option. Players can then choose to make regular planks from regular logs, oak planks from oak logs, teak planks from teak logs, or mahogany planks from mahogany logs, for a price.
The fastest way to make planks using the Sawmill involves the Lumberyard teleport. The teleport will take the player directly to the sawmill. An amulet of glory or a ring of dueling can then be used to bank.
The second fastest way to make planks using the Sawmill involves the Balloon transport system. Start at Castle Wars and use the balloon to travel to the location northeast of Varrock, which is close to the Sawmill. One willow log is required to make this journey. The balloon has a weight restriction (under 40 kg), so some players may only be able to carry 19 oak logs per round; however, wearing Weight-reducing equipment can allow the maximum of 26 oak logs to be brought. After making the planks, use a worn ring of dueling to teleport back to Castle Wars.
Another way to do this is to fly from Castle Wars to the lumberyard and chop down the oak logs there. Once the planks are made, teleport back to Castle Wars. This eliminates the weight restrictions for balloon travel, though it is a bit longer than taking logs from your bank. It is possible to make over 1500 planks per hour using this method.
The third fastest way to make planks using the Sawmill involves the Gnome Glider system. Use a ring of dueling to teleport to the Duel Arena, run southwest and take the glider to the Grand Tree. From there, take the Glider (run north into and its up at the top of the Grand tree) to Lemanto-Andra, which is south-east of the Digsite in Varrock. Run north from there, until you reach the first gate on your left (marked by a red line on your minimap) to the Sawmill and make the planks. Then use a ring of dueling to teleport to Castle Wars to bank.
The fourth fastest way to make planks using the Sawmill involves teleporting to Varrock. Run from Varrock to the Sawmill and make planks, then teleport to Varrock using the spell or a tablet, and run to east Varrock bank to bank.
A variation on these methods that would add woodcutting experience and increase profit per plank at the expense of time would involve cutting oak logs from the Oak Trees west of the Balloon.
Butlers can take oak logs to the Sawmill to create oak planks. They take the Sawmill fee with them. One way to use this is to carry noted oak logs, then ask the Butler to unnote them, then ask for the unnoted logs to be taken to the Sawmill. The planks received can then be used to train construction immediately, or can be sent to the bank using the Butler for profit.
Another variation is to go outside your house, cut oak logs, go inside your house, have the oaks sent to the sawmill, and use them to train construction.