Travel on Shinkansen with non-reserved seats

Can I buy shinkansen tickets for unreserved seats at vending machines or must I buy them at the manned ticket counter?
Are there 'Sold-out' situations for such tickets, that is, will I be able to buy such tickets on popular routes where many people opt not to reserve seats? They do allow standing in unreserved seat cars, don't they?
Is there a fixed time for travel with such tickets? If I find myself at the end of the queue and unlikely to get a seat, and there are regular trains, can I just wait for the next train instead? Thanks.

yes you can buy ticket at vending machines

yes you can stand if all seats in non reserved cars are full

yes you can take another train

Thanks hakata14.

Just to add one point to above (correct) answers.

Not all Shinkansen (or other reservation trains) do have a non reserved car. If you do not have a reservation you cannot board a reserved car even if there are free seats.

Enjoy your trip to Japan!

Noted, thanks , LikeBike.

When will you travel?
What Shinkansen line do you plan to use?

In the Shinkansen trains listed below, all the seats require reservation; when the seats in a specific train are fully reserved, standing tickets may be issued.
: Hayabusa trains and Hayate trains
on the Tohoku Shinkansen and the Hokkaido Shinkansen.
: Komachi trains
on the Tohoku Shinkansen and the (so-called) Akita Shinkansen.
: Kagayaki trains on the Hokuriku Shinkansen.

Trains on the Hokkaido Shinkansen and the Tohoku Shinkansen's Morioka -- Shin-Aomori part are either Hayabusa or Hayate trains, where reservation is mandatory to use a seat.
On the other Shinkansen lines and the other part of the Tohoku Shinkansen,
there are trains made up of also some cars where seats are, without reservation, secured on a first-come, first-served basis.

They do allow standing in unreserved seat cars, don't they?

When all the non-reserved seats are used by other passengers, you basically can stand or sit on the floor of the car, as long as you find your space.

Can I buy Shinkansen tickets for unreserved seats at vending machines or must I buy them at the manned ticket counter?

At some ticket-vending machines, Shinkansen tickets are sold for that day only.
When you hope to buy Shinkansen tickets before the boarding date, I recommended you visit a JR ticket office or travel service center.

At ticket offices of JR stations,
Shinkansen tickets for rides without seat reservation are,
according to the written JR rules, not sold before the boarding date;
however, practically it seems that they in many cases go on sale in advance at the same time as reserved-seat tickets do.

Shinkansen reserved-seat tickets go on sale at 10 o'clock (Japan Standard Time) on the day one month prior to the boarding date;
in a case where a day of the same number as the boarding date does not exist in the previous calendar month, they go on sale on the 1st day of the boarding month.

Trains on the Hokkaido Shinkansen and the Tohoku Shinkansen's Morioka -- Shin-Aomori part are either Hayabusa or Hayate trains, where reservation is mandatory to use a seat.

In fact, if you travel only on those sections where no non-reserved seats are available, you can buy a "special limited express ticket" ( 特定特急券), which lets you use any vacant seat as if it were a non-reserved seat (in particular, such tickets do not include a seat reservation fee).

I found that one out completely randomly when I went to book a limited express ticket from Morioka to Tazawako (because I had missed the morning local train). Weirdly, eki-net never mentions them.

The comment by Firas gradually reminds me of this exceptional rule....; I forgot about it when I posted my previous response.

if you travel only on those sections where no non-reserved seats are available, you can buy a "special limited express ticket"

Unlike standing tickets, these special tickets may be issued (also) when the seats are not fully reserved.

@Firas

Weirdly, eki-net never mentions them.

This rule is a part of the written JR rules, but it seems not mentioned in the monthly JR timetable magazine published by Kotsu Shimbunsha, which is the source of the explanations about the ticket rules on the JR websites.

Thanks very much for the detailed explanations, omotenashi & firas. I'll be using the shinkansens between Hiroshima, Shin Osaka, Himeji and Okayama. I believe all the shinkansens covering this area have unreserved cars. So I'm planning to just go for the unreserved seats.

Still, the info you have provided will be good reference for my future trips. That bit about the special limited express ticket is interesting too. Is the price of these tickets anywhere close to what we would have to pay for the reserved seat? Do you have to buy this before you board or can we pay a top-up fee when we are already on board? Unless they allow this, I can't see what the advantage is for the rail companies to sell this special ticket. They might as well insist that we pay the reserved seat price if we want to take that particular train.

This rule is a part of the written JR rules, but it seems not mentioned in the monthly JR timetable magazine published by Kotsu Shimbunsha

Yes, it is, at least the large format ones that cost around 1100 yen. It is explained at least in the timetable section.

Let me add the following line between the lines "... to use a seat. " and "On the other Shinkansen lines... Shinkansen," in my response sent at 2018/3/10 16:26:
Likewise, trains on the Akita Shinkansen are all Komachi trains.