Convert 3x9 Cannondale F700 to 1x10 and keep Shimano Deore XT Cranks

i did a similar upgrade on my old mtb, no my commuter.

if you find a chainring, you can install it on the old XT cranks, i had used 1x SLX cranks so I took them.

no front shifter is required for 1x

you need new shifter, derailleur and cassette

if you have brake/shifter combination you also need new brake levers.

for me it was an easy install

My friend asked me the same thing a couple of months ago. Here was my answer:

Option1 : you keep your shifter and derailleur

1 chainring (narrow -wide) probably a 32t, pay attention to the bolt patterns, there are many standards
https://www.amazon.com/s?k=narrow+wide+chainring+104+bcd&sprefix=narrow…
it can be as cheap as $10
https://www.amazon.com/DJC-Chainring-104BCD-Aluminum-Lightweight/dp/B09…

then you need a wide-range cassette. If you want to keep your shifter and derailleur, stick with 10 speed.
something like https://www.amazon.com/Cassette-11-40T-Mountain-Bicycle-Shimano/dp/B07C…
an 11-40 is reasonable with your derailleur but if you want more range then your derailleur will be a limitation . the biggest gap between small and big cog, the harder it is for your derailleur to shift, your derailleur might be  supposed to get 36t, but if you maxed out or use a longer B screw ()https://www.wolftoothcomponents.com/products/25-mm-b-screw or https://www.amazon.com/Wolf-Tooth-Components-25mm-B-Screw/dp/B00LMY7BA0…) , you can easily go to 40 to 42 teeth

If you still need to reach a bigger gear, you might need a derailleur hanger extension ($10)
https://www.amazon.com/s?k=derailleut+link&crid=V5BKC120PMQZ&sprefix=de…
(I don’t think it’s required for a 40t)

Option2:
You can also get a groupset from ltwoo: it’s a Chinese knockoff that is supposed to be decent:
for $90 you can get everything you need

Option3:
If you want to spend more you can get a full 1x groupset (cassette, shifter, derailleur, chain) from Microshift  or Shimano for $130-$200.
Deore or SLX are really good but microchip is also supposed to be reliable
https://www.ebay.com/itm/374566344345?hash=item5735e4d699:g:MtgAAOSwE2t…

https://www.ebay.com/itm/234915408343?hash=item36b20ca9d7:g:yJQAAOSwLAx…
(with these kits you will need the chainring)

Note: if your chain is worn, it won’t play well with new cassette and chainring..

( just make sure you are getting a cassette for an HG hub (aka shimano standard) , not XD(new sram 12 speed standard) or microspline (new shimano 12 speed standard)..

For your chainring selection, you can find calculator to find the ratio/range you need. it mostly depends on which cassette you can get away with and if you'd rather get more top speed or climbing gear. Something like a 32x40 ot 42t used to be the norm but now people crawl on a 30x52t (which I feel is way too small for most trails)