Nap training

Have any of you had luck nap training? Let me explain my situation... My 10 month old son is sleep trained and does so well at night. He takes 2 naps a day and falls asleep great on his own in his crib but only sleeps 30-40 minutes and begins crying the moment he wakes up. He will not fall back asleep if I leave him alone. How can I get him to take longer naps??? He sleeps 1:15 if he is held for naptime! I feel like he's over tired but the bugger won't sleep and I'm done holding him during naps!