@Hawaii-5-0 

Try to seach for "Chromebook access smd share" with Google Search.

It doesn't actually matter that your storage device is connected to your router via USB. The client won't be able to notice.

Theoretically you should be able to connect to the Seagate disk by opening the "Network File Share for Chrome OS" App and in the "Share Path" field type something like "\\192.168.0.1\g" or "smb://192.168.0.1/g". (Of course if you have changed your router's LAN IP address from the default to another one, then you have to use that IP address)

@woozle , I have done all this and more it seems.. i've tried every possible variation of  your suggested IP addresses but nothing works. I'm sure it's something stupid, but i've googled , youtubed this problem to death and everyone says to do the same thing and that it hsould just work, but it doesn't. frustrating. 

@Hawaii-5-0 

I just made myself an installation of Chromium OS (which is similar to the Chrome OS on a Chromebook) and connected an external USB HDD to my AX50.

Surprisingly to me, the "Network File Share for Chrome OS" App indeed failed to mount the AX50's network share, no matter what I tried.

My other Linux-based devices with file shares (like my Synology NAS) were mounted without any problem, though.

So, is there is some weird incompatibility between the "Network File Share for Chrome OS" App and the Archer AX50 ?

Here is another way that does work, however:

Install the App "File System for Windows" and then enter the IP address of your AX50 and "g" as the share's name like in the attached picture. Click "Mount" and a couple of seconds later it should say that it has mounted successully. Then the network share will show up in the Files App.

@Kevin_Z 

After some more testing it turns out that being unable to mount a network share using the native built-in support for SMB file shares in Chromium OS is not solely an Archer AX50 problem.

I have another router with USB port that is running OpenWRT and thus allows me to freely control the SMB protocol level using the "server max protocol" parameter of "smb.conf".

What I found is that Chromium OS can natively (without the before-mentioned third-party App) mount the file share if the protocol level is SMB3_11, SMB3_02, SMB3_00 or SMB2_10, but mounting fails if protocol level is set to SMB2_02 or lower.

Now, the AX50 with the latest firmware is running Samba Version 3.6.25, whose maximum supported protocol level is SMB2_02 and hence mounting an USB disk connected to the AX50 in Chromium OS without a third-party App does not work.

Samba Version 4.x has been available for about 8 years and does support higher SMB protocol levels, but that would require the router manufacturer to integrate it in their firmware.

@Hawaii-5-0 @All 

I am not able to find "Network File Share for Chrome OS" anywhere. it is a 404 error.

I have tried "Add file share" but it just gives "Error mounting share"

Please suggest

@KunalD 

If the Chrome web store gives you a 404 error, then this could be a temporary issue. Maybe try again later.

You could also try the other app called "File System for Windows".

@Hawaii-5-0 

It seems like Google might have gotten rid of the app--two months later and still 404 error, and no one seems to be mentioning if it's been removed.  Pity since being able to access network drives is an important value added for barebones devices like chromebook.  :/  Apparently, my network drives (I have two) and my desktop are all recognized by VLC Player (Which apparently has the ability to stream from DLNA media servers).  But nothing shows up on chromebooks smb file share.  File system for windows can detect one of the two drives (WD Mypassport wireless) but not the HDD connected to TP Link Router via USB.  Seems typical of the way Google is run nowadays--getting rid of functionalities that people like and appreciate in order to force them to use Google's own increasingly intrusive (and even abusive) services.  :(  

PS.  It appears that using the IP address of the device (in case of the HDD, same address as the router itself) seems to work!