What is a jack plane?
What it's used for
A general purpose plane
A jack plane is a general-purpose bench plane.
It can take over from where the scrub plane leaves off, being used for shaving off smaller amounts of wood to reduce a piece to the desired size (known as ‘sizing’) and for initial smoothing.
It is longer than the smoothing plane, so is better suited to taking off the high points along the length of the wood rather than following any undulations, giving a straighter edge.
In preparing wood, the jack plane is used after the scrub plane and before the fore plane, jointer plane and smoothing plane.
How it got its name
Its name is related to the saying "jack of all trades", as jack planes can be made to perform some of the work of smoothing, fore and jointer planes, especially on smaller pieces of work.
Angle of the iron
There are standard and low angle metal versions of the jack plane, with irons pitched at 45 degrees bevel down and 12 degrees bevel up respectively.
Wooden jack planes usually have their irons pitched at 45 degrees.
How big is it?
Jack planes are usually between 292mm (11½") and 380mm (15”) long.
The width of a jack plane's iron (which, as with all bench planes, is just 10mm (3/8") or so narrower than the plane's body) can be 44.5mm (1¾"), 50mm (2") or 60mm ( 2 3/8") wide.
Shape of the cutting edge
The jack is often used as multi-purpose plane, so its iron's cutting edge is often honed straight with rounded corners. This makes it suitable for jointing work (flattening the edges of boards that are to be joined together) and smoothing. The rounded corners will prevent "tracks" being left in surfaces that are wider than the the iron.
Metal versions of the jack plane made by Stanley were allocated Stanley model numbers which are still often used today when cataloguing, advertising and ordering planes.
Jack planes made to the Stanley/Bailey design are the No. 5, No. 5¼ and No. 5½. The 5¼ is slightly smaller than the No. 5 and the 5½ is the biggest, at 380mm (15") long, with a 60mm (2 3/8") wide iron.