Kelim, Chapter Sixteen, Mishnah One
1) A wooden vessel that was broken into two parts becomes clean, except for a folding table, a dish with compartments for [different kinds of] food, and a householder’s footstool.
2) Rabbi Judah says: a double dish and a Babylonian drinking vessel are subject to the same law.
3) When do wooden vessels begin to be susceptible to impurity?
4) A bed and a cot, after they are sanded with fishskin.
a) If the owner determined not to sand them over they are susceptible to impurity.
b) Rabbi Meir says: a bed becomes susceptible to impurity as soon as three rows of meshes have been knitted in it.
Section one: Generally, if a wooden vessel is broken into two parts it becomes clean if it was previously impure. So too, the two parts are no longer susceptible to impurity. The exceptions are wooden vessels whose pieces can still be used when the original vessel is cut into two. All of the vessels listed here can be used even when broken into two parts.
Section two: The mishnah now asks the question that it has asked with regard to vessels made of other types of material (earthenware and metal)when is the manufacture of the vessel completed such that the vessel can become impure?
For a bed and a cot to be susceptible, the wood frame must have been sanded.
However, if the owner decided to use them without sanding them, then they are susceptible even without sanding.
Beds were made by tying ropes under the frame and then tightening them to form a support (hence the phrasesleep tight!). The ropes ran the length and the breadth of the bed. According to Rabbi Meir, as soon as three rows are made in each direction, the bed is usable and is susceptible to impurity.