Gemara

Beraisa: One may not fix or sharpen a spit.

Beraisa: One may not split a reed to make it a spit to roast salted food.

28a - Mishnah: One may not sharpen a knife on Yom Tov. One may rub it against another knife.

Rav Huna: It is forbidden only with a sharpener made of stone, but a wooden sharpener is permitted.

Four versions of Shmuel's opinion are given. They argue about rubbing a knife against a stone to remove grease and sharpening using a wooden sharpener.

Rav Chisda: Our Tana forbids sharpening. It is unlike R. Yehudah:

Beraisa: The only difference between Shabbos and Yom Tov is preparation of food;

R. Yehudah permits Machshirim.

28b: The first Tana expounds "Hu" (Ochel Nefesh is permitted), but not Machshirim;

R. Yehudah expounds "Lachem" - all your needs are permitted.

The first Tana expounds "Lachem" to forbid Meleches Ochel Nefesh for Nochrim or dogs.

R. Yehudah expounds "Hu" to forbid Machshirim that could have been done before Yom Tov. "Lachem" permits those that could not.

28a - Rava (to Rav Chisda): I heard in your name that the Halachah follows R. Yehudah.

Rav Chisda: May it be His will that such great teachings be said in my name!

Rava and Rabah rubbed knives against the mouth of a barrel and a millstone to sharpen them. They told their Talmidim that this was to remove grease. They hold that the Halachah follows R. Yehudah, but Ein Morin Ken (we do not publicly expound this).

Rav Yosef: If a knife dulled (but was not dented), one may sharpen it on Yom Tov. This is only if it cuts when pressed hard. If not, it is forbidden.

Rav Chisda or Rav Yosef: R. Yehudah and Chachamim argue about fixing a dented knife or a spit that was Nirtzam, and sweeping out an oven (if plaster fell from the walls).

Shmuel: If a spit was Nirtzaf (bent), one may not fix it.

Objection: This is obvious!

Answer: The Chidush is, even if he could straighten it with his hand, it is forbidden.

Rishonim

Rif and Rosh (3:10 and 4:17): It was taught in the name of Rav Chisda that the Halachah follows R. Yehudah. Rava and Rabah rubbed knives against the mouth of a barrel and a millstone. They did not admit that this was to sharpen. They hold that the Halachah follows R. Yehudah, but Ein Morin Ken. R. Yehudah and Chachamim argue about fixing a dented knife or a Nirtzam spit, and sweeping out an oven. One may not fix a bent spit, even if he could straighten it with his hand. One may not sharpen a spit. One may not split a reed to make it a spit to roast salted food.

Rosh (ibid.): The Rif permits sharpening only against the mouth of a barrel or a millstone. Really, one may sharpen it against a sharpener for the Halachah follows R. Yehudah, but Ein Morin Ken. One may not fix a bent spit, even by hand, for it can be used bent.

Beis Yosef (OC 509 DH Aval): R. Yehudah permits fixing a spit that is Nirtzam. The Rosh must explain that this means broken, and it is unusable.

Ba'al ha'Ma'or: If a knife was dented, it should have been fixed before Yom Tov, so it is forbidden on Yom Tov. If it is too dull to cut even with pressure, one may not sharpen it. Rashi says that it is too much exertion. It seems to me that in this case it is not a Keli, and R. Yehudah agrees that one may not make a Keli (Mishnah, 32a). A Beraisa (34a) forbids fixing a spit. Rashi says that this is unlike R. Yehudah; alternatively it broke and could have been fixed before Yom Tov. I say that fixing a wooden spit or a severely bent metal spit is making a Keli, and even R. Yehudah forbids. R. Yehudah permits fixing a spit that is Nirtzam, i.e. slightly bent.

Ran (19b DH v'Ein Metaknin). The Beraisa refers to making a new spit (not fixing a spit).

Ran (DH Kol): Even though Ein Morin Ken, the Rif brings the Pesak like R. Yehudah in the name of Rav Chisda because regarding some Machshirin, Morin Ken, such as sweeping out an oven.

Ran (DH Omar): Even R. Yehudah forbids sharpening with a stone sharpener, for this is making a Keli. Even though he permits proper Melachos for Machshirin, we are not more lenient than for Ochel Nefesh. Regarding Ochel Nefesh we do not permit Melachos normally done at once for a long time, be this mid'Oraisa or mid'Rabanan.

Rambam (Hilchos Yom Tov 1:8): On Yom Tov we may knead, bake, be Shochet and cook, for these are better when done the same day. Also Machshirin that are not as good if done the previous day, such as grinding spices, are permitted.

Hagahos Maimoniyos (5): This is like R. Yehudah. Sefer ha'Terumos permits Libun (to make a Keli glowing hot to Kasher it) on Yom Tov, provided that he uses it to cook immediately afterwards. This is only if Libun Kal (mild) suffices, e.g. to enable a dairy Keli to be used for meat or vice-versa. If it absorbed Isur, total Libun is required, and it is evident that this is done to Kasher.

Rambam (4:8): We do not break earthenware in order to roast over it. We do not split a reed to make it a spit to roast salted food. One may not fix a bent spit, even if he could straighten it with his hand.

Kesef Mishneh (9): The Rosh and Ran explain that the Rif rules like R. Yehudah, but Ein Morin Ken. The Ran says that the Rambam agrees.

Question (Ramach): Since the Halachah follows R. Yehudah, it should be permitted or break earthenware or fix a spit in order to roast!

Answer #1 (Kesef Mishneh 9): This is not needed for food. One can roast on a bent spit, or on the coals themselves.

Answer #2 (Magid Mishnah 8,9): The Rambam forbids even if the spit was ruined on Yom Tov, because he rules unlike R. Yehudah. The Sugya (28b) is like Chachamim, and also several Stam Mishnayos.

Question: Why does the Gemara say that it is obviously forbidden to straighten a bent spit? Rav Chisda rules like R. Yehudah! (This suggests like Rashi, that all forbid because a bent spit can be used!)

Answer (Lechem Mishneh): If Shmuel forbids because the Halachah follows Chachamim, he should have said so explicitly. The Gemara assumes that he discussed a spit for a Chidush.

Questions: If the Halachah follows Chachamim, why may one sharpen a knife on a barrel top or millstone? Why does the Rambam permit to sweep out an oven if one cannot bake without this?

Answers (Kesef Mishneh, for the Magid Mishnah): Chachamim agree about this, for it is a Melachah only with the sharpening stone. Also, the knife could cut as it was. The Tana'im argue about a spit that is Nirtzam, i.e. totally bent and needs Tikun. Shmuel decrees to forbid a spit that is Nirtzaf, i.e. slightly bent, lest one fix one that is totally bent. Rav Chisda teaches that the Tana'im argue about sweeping out an oven when it is difficult to bake without sweeping it. All permit when it is essential, for it is not a real Melachah. Chachamim decree lest one do real Melachah, but not when it will inhibit Simchas Yom Tov. We can say all this for the Rambam, but the Rif surely rules like R. Yehudah, for he brings Rav Chisda who rules like him!

Poskim

Shulchan Aruch (OC 509:1): One may not fix a bent spit, even if he could straighten it with his hand.

Taz (1): In some cases the Halachah does not follow R. Yehudah.

Rema: This is if he can roast on it while it is bent. If not, or if it broke on Yom Tov one may fix it, but Ein Morin Ken in public, lest people fix one that broke before Yom Tov. The same applies to all Machshirin that could not be done before Yom Tov.

Gra (DH v'Ein): Above (495:1) the Shulchan Aruch permitted Machshirei Ochel Nefesh that could not have been done before Yom Tov and did not say Ein Morin Ken. This is because the Rambam (1:8) permits Machshirin without stipulating that Ein Morin Ken, and the Rif cites Rav Chisda who rules like R. Yehudah.

Magen Avraham (2): If it broke before Yom Tov but one did not know or did not have time to fix it, it is permitted. If one forgot, it is forbidden.

Mishnah Berurah (3): Even if one can roast only with difficulty, Tikun is considered excess exertion.

Mishnah Berurah (6): If it is unusable one should be stringent, like those who forbid absolute Tikun of a Keli. If one can borrow, all forbid fixing it.

Mishnah Berurah (5): Some say that if it broke on Yom Tov Rishon one may not fix it on Yom Tov Sheni, for perhaps Yom Tov Rishon was Chol. Others disagree.

Mishnah Berurah (7): One may sharpen it a bit to enable sticking it through meat. One may not sharpen it on a sharpener, just like one may not sharpen a knife.

Shulchan Aruch (2): If a spit is too long, one may not cut it or burn it.

Beis Yosef (DH Kosav ha'Mordechai): Avi ha'Ezri forbids to cut a spit that is too long. Even though one may cut a wick into two using fire (if its ends are in lamps), there it looks like he lights two lamps.