What is "Toch ha'Chatzer"?
Rashi (citing R. Yehudah, Zevachim 59a): It is like the simple meaning. The floor of the Azarah received Kedushas Mizbe'ach; Haktarah (burning offerings to Hashem) is permitted on the floor. (He was Mekadesh the floor, for even Shlomo's Mizbe'ach was too small for the Korbanos.)
Rashi (citing R. Yosi, Zevachim 59a): He fixed the stone Mizbe'ach in the Chatzer (attached it to the ground).
What is "Mizbe'ach ha'Nechoshes"?
Rashi (citing R. Yehudah, Zevachim 59a): It is the stone Mizbe'ach that Shlomo made in place of the copper Mizbe'ach [of the Mishkan].
Rashi (citing R. Yosi, Zevachim 59b): It is Moshe's copper Mizbe'ach.
Why was the Mizbe'ach too small for the Olah, Minchah and Chelev of the Shelamim?
Rashi (citing R. Yehudah, Zevachim 59a): It is because he offered so much (verse 63, even though the verse refers to Shlomo's Mizbe'ach). 1
Rashi (citing R. Yosi, Zevachim 59b): The Ma'arachah (area folr the fire) on Moshe's Mizbe'ach was only one square Amah, and Shlomo offered on it 1,000 Olos (3:4) [in one day]. The Ma'arachah of Shlomo's Mizbe'ach was 24 by 24 2 , 576 times bigger. Surely it sufficed to burn these Korbanos 3 ! Moshe's Mizbe'ach was too small for them. 4
Radak: Even though verse 63 taught only the number of Shelamim, of which only the Eimurim are offered, we can say that there were also many Olos, so it was too small for all of them. Ya'avetz (59b) - the number includes also the Olos, like our verse says "Asah Sham Es ha'Olah v'Es ha'Minchah v'Es Chelvei ha'Shelamim."
Malbim: Midos 3:1 says that the entire Mizbe'ach was 28 by 28. (We deduct one Amah each for the Yesod, Sovev, Keren and walkway, on each of two sides, so) only 20 by 20 remained for the Ma'arachah! (Also Divrei ha'Yamim II, 4:1 says that Shlomo's Mizbe'ach was 20 by 20. We cannot say that the Ma'arachah was bigger than this! - PF)
Refer to 8:64:3:1*. Radak - R. Yehudah disagrees; he holds that the Ma'arachah of Moshe's Mizbe'ach was five by five Amos (59b). Also, perhaps the 1000 Olos were not offered in one day, rather, before he returned from Giv'on to Yerushalayim!
Radak: Divrei ha'Yamim II, 7:7 explicitly says "Mizbe'ach ha'Nechoshes Asher Asah Shlomo" was too small! It is difficult to explain 'the Mizbach Shlomo made in place of Moshe's, for Moshe's was too small.' Malbim - R. Yosi must say that 'Mizbe'ach ha'Nechoshes Asher Asah Shlomo" means that he fixed Moshe's Mizbe'ach to the ground.
